Isolated antibody or a fragment thereof, and methods for decreasing serum FGF23, for increasing the maximum renal threshold for phosphate reabsorption, for increasing serum inorganic phosphorus, for increasing the serum concentration of 1,25-dihydroxyvitamin D to treat a hypophosphatemic condition.

Abstract

The disclosure provides improved human FGF23-binding antibodies with increased affinity for human FGF23 as compared to burosumab, enabling reduced dosing frequency, improving convenience of therapy, and achieving higher efficacy compared to burosumab, without compromising safety.

Description

140 Isolated antibody or a fragment thereof, and methods for decreasing serum FGF23, for increasing the maximum renal threshold for phosphate reabsorption, for increasing serum inorganic phosphorus, for increasing the serum concentration of 1,25-dihydroxyvitamin D to treat a hypophosphatemic condition. Cross-reference to related applications.

[001] This application claims the benefit and priority of the Application U.S. Provisional Application No. 63 / 548,711, filed February 1, 2024, U.S. Provisional Application No. 63 / 514,180, filed July 18, 2023, and U.S. Provisional Application No. 63 / 489,458, filed March 10, 2023, the complete disclosures of which are incorporated herein by reference in their entirety for all purposes. REFERENCE TO A LISTING OF XML SEQUENCES

[002] This request contains a Sequence Listing that was sent electronically in XML format. The XML Sequence Listing is incorporated herein for reference. The XML file, created on February 28, 2024, is named UXB023-06WO_SL.xml and is 2,280,142 bytes in size. TECHNICAL FIELD OF DISSEMINATION

[003] This disclosure refers to human FGF23-binding antibodies with improved affinity and efficacy compared to burosumab. BACKGROUND

[004] Burosumab (i.e., burosumab-twza, marketed as CRYSVITA®) is a fibroblast growth factor 23 (FGF23) blocking antibody indicated for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients 6 months of age and older and for the treatment of adults and children 2 years of age and older with FGF23-related hypophosphatemia in osteomalacia-induced neuroleptic malignant syndrome. Petition 870250099897, dated 10 / 31 / 2025, p. 6 / 177 / 140 for tumor-specific immunoglobulin (TIO) when the tumor cannot be located or removed. Burosumab is a recombinant human monoclonal antibody of the IgG1K type. Burosumab consists of 4 polypeptide chains (2 identical heavy chains, 447 amino acids each and 2 identical light chains, 213 amino acids each) and has a molecular weight of 147 kDa. Burosumab specifically binds to FGF23 and blocks its interaction with the Klotho-FGF receptor complex.

[005] FGF23 is a natural cytokine involved in phosphate and vitamin D metabolism. Excessive levels of circulating FGF23 can lead to increased urinary phosphate excretion, reduced vitamin D synthesis, and subsequent hypophosphatemia, resulting in defective bone mineralization and impacts on other tissues, including muscles. Burosumab binds to FGF23 and inhibits its ability to bind to fibroblast growth factor receptor 1 (FGFR1) and the Klotho coreceptor. This inhibition restores tubular reabsorption of phosphate from the kidney and increases vitamin D production, which improves intestinal absorption of calcium and phosphate. These combined actions improve serum phosphorus levels and bone mineralization.

[006] Burosumab administration in pediatric patients is performed by subcutaneous injection every 2 weeks (Q2W), representing a significant treatment burden. Furthermore, both adult and pediatric patients must undergo high-volume burosumab injections, with a maximum of up to 3 ml administered in three separate 1 ml injections (see, for example, burosumab-twza prescribing information, available at www.accessdata.fda.gov / scripts / cder / daf / index.cfm). Consequently, there is a need for human FGF23-binding antibodies with improved affinity and efficacy compared to burosumab. SUMMARY

[007] Disclosure provides antibodies that bind to human FGF23 Petition 870250099897, dated 10 / 31 / 2025, page 7 / 177 / 140 enhanced with greater affinity for human FGF23 compared to burosumab, allowing for less frequent dosing, improving the convenience of therapy and achieving greater efficacy compared to burosumab, without compromising safety.

[008] This disclosure provides FGF23-binding antibodies designed to have improved affinity compared to burosumab by altering one or more amino acids in the heavy chain (SEQ ID NO: 1) and / or light chain (SEQ ID NO: 2) sequence(s) of burosumab. In some embodiments, the FGF23-binding antibodies are designed to have improved affinity compared to burosumab by altering one or more amino acids in the variable heavy chain region (VH, SEQ ID NO: 3) and / or variable light chain region (VL, SEQ ID NO: 4) sequence(s) of burosumab.

[009] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable region heavy chain (VH) amino acid sequence according to SEQ ID NO: 3, but comprising one or more amino acid changes relative to SEQ ID NO: 3, wherein one or more amino acid changes are selected from T30E, T30F, T30Q, T30S, T30Y, N31D, N31E, N31F, N31Q, N31R, N31Y, H32E, H32F, H32Q, H32S, H32T, I50D, I50E, I50F, I50S, I50T, I50Y, N52E, N52F, N52Q, N52Y, I54E, I54F, I54L, I54Q, I54S, I54T, I54V, I54Y, S55E, S55F, S55Q, S55T, S55Y, S59D, S59E, S59F, S59I, S59L, S59Q, S59T, S59V, S59Y, D99E, D99Q, D99Y, I100D, I100E, I100F, I100L, I100Q, I100V, I100Y, V101F, V101I, V101L, V101T, V101Y, D102E, D102F, D102I, D102L, D102Q, D102Y, A103D, A103E, A103F, A103Q, A103S, A103T and A103Y.

[0010] In some modalities, disclosure provides an antibody Petition 870250099897, dated 10 / 31 / 2025, p.8 / 177 / 140 isolated or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable light chain (VL) region amino acid sequence according to SEQ ID NO: 4, but comprising one or more amino acid changes relative to SEQ ID NO: 4, wherein one or more amino acid changes are selected from A25L, A25V, I29F, I29L, I29V, S30D, S30E, S30F, S30I, S30L, S30Q, S30T, S30V, S30Y, S31D, S31E, S31F, S31I, S31L, S31Q, S31T, S31V, S31Y, A32F, A32I, A32L, A32T, A32V, A32Y, V34F, V34I, V34L, V34Y, D50E, D50F, D50I, D50L, D50Q, D50R, D50S, D50T, D50V, A51F, A51I, A51L, A51S, A51T, A51V, S52D, S52E, S52F, S52Q, S52T, S52Y, S53D, S53E, S53F, S53I, S53L, S53Q, S53R, S53T, S53V, S53Y, Q90F, Q90Y, F91K, F91R, F91Y, N92D, N92E, N92F, N92Q, N92S, N92T, N92Y, D93E, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94D, Y94E, Y94F, Y94Q, Y94S and Y94T.

[0011] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a VH amino acid sequence according to SEQ ID NO: 3 and a VL amino acid sequence according to SEQ ID NO: 4, wherein the VH amino acid sequence comprises one or more amino acid alterations selected from T30E, T30F, T30Q, T30S, T30Y, N31D, N31E, N31F, N31Q, N31R, N31Y, H32E, H32F, H32Q, H32S, H32T, I50D, I50E, I50F, I50S, I50T, I50Y, N52E, N52F, N52Q, N52Y, I54E, I54F, I54L, I54Q, I54S, I54T, I54V, I54Y, S55E, S55F, S55Q, S55T, S55Y, S59D, S59E, S59F, S59I, S59L, S59Q, S59T, S59V, S59Y, D99E, D99Q, D99Y, I100D, I100E, I100F, I100L, I100Q, I100V, I100Y, V101F, V101I, V101L, V101T, V101Y, D102E, D102F, D102I, D102L, D102Q, D102Y, A103D, A103E, A103F, Petition 870250099897, dated 10 / 31 / 2025, page 9 / 177 / 140 A103Q, A103S, A103T and A103Y, and / or wherein the amino acid sequence of VL comprises one or more amino acid alterations selected from A25L, A25V, I29F, I29L, I29V, S30D, S30E, S30F, S30I, S30L, S30Q, S30T, S30V, S30Y, S31D, S31E, S31F, S31I, S31L, S31Q, S31T, S31V, S31Y, A32F, A32I, A32L, A32T, A32V, A32Y, V34F, V34I, V34L, V34Y, D50E, D50F, D50I, D50L, D50Q, D50R, D50S, D50T, D50V, A51F, A51I, A51L, A51S, A51T, A51V, S52D, S52E, S52F, S52Q, S52T, S52Y, S53D, S53E, S53F, S53I, S53L, S53Q, S53R, S53T, S53V, S53Y, Q90F, Q90Y, F91K, F91R, F91Y, N92D, N92E, N92F, N92Q, N92S, N92T, N92Y, D93E, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94D, Y94E, Y94F, Y94Q, Y94S and Y94T.

[0012] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises an amino acid sequence of the variable heavy chain (VH) region according to SEQ ID NO: 3 and a variable light chain (VL) region according to SEQ ID NO: 4, but comprising at least two amino acid changes in the VL, wherein the at least two VH and amino acid sequence changes are VH:N31F / VH:S59F, VL:D50F / VH:V101I, VL:N92E / VL:D93F, VH:N31E / VH:S59E, VH:S59T / VH:V101L, VL:N92D / VL:D93F, VL:Y94D / VH:S59D, VL:N92Y / VH:S59E, VL:S52E / VH:S59E. selected from VL:D50F / VL:S53E, VH:S59D / VH:V101I, VL:S31E / VL:S53E, VH:S57E / VH:S59D, VH:I54Y / VH:V101F, VH:N52F / VH:V101L, VL:Y94D / VH:S59E, VL:Y94E / VH:S59E, VL:S31E / VL:D50F, VL:S31F / VL:S52E, VL:S31F / VL:S53E, VL:S31F / VL:D50F, VH:N31E / VH:I54F, VH:N52F / VH:V101I, VL:S31F / VL:D50E, VL:N92F / VH:S59E, VL:S52D / VH:S59E and Petition 870250099897, dated 10 / 31 / 2025, page 10 / 177 / 140

[0013] Also provided here are FGF23-binding antibodies having one or more complementarity-determining regions (CDRs) unique to burosumab.

[0014] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a heavy chain complementarity-determining region 1 (HCDR1) according to an amino acid sequence selected from SEQ ID NO: 11 and SEQ ID NOs: 22-32.

[0015] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a heavy chain complementarity-determining region 2 (HCDR2) according to an amino acid sequence selected from SEQ ID NO: 12 and SEQ ID NOs: 33-65.

[0016] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a heavy chain complementarity-determining region 3 (HCDR3) according to an amino acid sequence selected from SEQ ID NO: 13 and SEQ ID NOs: 66-93.

[0017] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a light chain complementarity-determining region 1 (LCDR1) according to Petition 870250099897, dated 10 / 31 / 2025, page 11 / 177 / 140 with a selected amino acid sequence from SEQ ID NO: 14 and SEQ ID NOs: 94-126.

[0018] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a light chain complementarity-determining region 2 (LCDR2) according to an amino acid sequence selected from SEQ ID NO: 15 and SEQ ID NOs: 127-158.

[0019] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a light chain complementarity-determining region 3 (LCDR3) according to an amino acid sequence selected from SEQ ID NO: 16 and SEQ ID NOs: 159-185.

[0020] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises an HCDR1, an HCDR2, an HCDR3, an LCDR1, an LCDR2 and an LCDR3, wherein: HCDR1 comprises an amino acid sequence selected from SEQ ID NO: 11 and SEQ ID NOs: 22-32; HCDR2 comprises an amino acid sequence selected from SEQ ID NO: 12 and SEQ ID NOs: 33-65; HCDR3 comprises an amino acid sequence selected from SEQ ID NO: 13 and SEQ ID NOs: 66-93; LCDR1 comprises an amino acid sequence selected from SEQ ID NO: 14 and SEQ ID NOs: 94-126; LCDR2 comprises an amino acid sequence selected from SEQ ID NO: 15 and SEQ ID NOs: 127-158; and LCDR3 comprises a sequence of Petition 870250099897, dated 10 / 31 / 2025, p. 12 / 177 / 140 amino acids selected from SEQ ID NO: 16 and SEQ ID NOs: 159-185.

[0021] Also provided here are FGF23-binding antibodies with one or more unique variable region domains relative to burosumab.

[0022] For example, the isolated antibody or fragment thereof may comprise a variable heavy chain (VH) region and a variable light chain (VL) region, wherein the VH comprises an amino acid sequence with at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or wherein the VL comprises an amino acid sequence with at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[0023] The isolated antibody or fragment thereof may comprise a VH comprising an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the antibody or fragment thereof may comprise a VL comprising an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[0024] The isolated antibody or fragment thereof may comprise a VH comprising an amino acid sequence having at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the antibody or fragment thereof may comprise a VL comprising an amino acid sequence having at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[0025] The isolated antibody or a fragment thereof may Petition 870250099897, dated 10 / 31 / 2025, p. 13 / 177 / 140, comprise a VH and a VL, wherein the VH may comprise an amino acid sequence having at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL may comprise an amino acid sequence having at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[0026] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL may comprise an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[0027] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence having at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL may comprise an amino acid sequence having at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[0028] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the VL may comprise an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[0029] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186270, and the VL may comprise an amino acid sequence selected from Petition 870250099897, dated 10 / 31 / 2025, p. 14 / 177 / 140 SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[0030] In some respects, the present disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a VH amino acid sequence according to SEQ ID NO: 3 and a VL amino acid sequence according to SEQ ID NO: 4, wherein the VH amino acid sequence comprises one or more amino acid changes selected from I54F, I54Y, S59D, S59E, V101I and A103S compared to SEQ ID NO: 3.

[0031] In some respects, the present disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a VH amino acid sequence according to SEQ ID NO: 3 and a VL amino acid sequence according to SEQ ID NO: 4, wherein the VL amino acid sequence comprises one or more amino acid changes selected from S52D, S52E, N92F, N92Y, Y94D and Y94E compared to SEQ ID NO: 4.

[0032] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-027 (i.e., an antibody according to Antibody Structure ID Number UGX126).

[0033] Also provided is an isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or Petition 870250099897, dated 10 / 31 / 2025, page 15 / 177 / 140 fragment thereof comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-066 (i.e., an antibody according to Antibody Structure Identification Number UGX144).

[0034] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-067 (i.e., an antibody according to Antibody Structure Identification Number UGX145).

[0035] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-028 and a variable light chain (VL) region according to VL-001 (i.e., an antibody according to Antibody Structure Identification Number UGX156).

[0036] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-029 and a variable light chain (VL) region according to VL-001 (i.e., an antibody according to Antibody Structure Identification Number UGX157).

[0037] Also provided is an isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region. Petition 870250099897, dated 10 / 31 / 2025, page 16 / 177 / 140 according to VH-061 and a variable light chain (VL) region according to VL-001 (i.e., an antibody according to Antibody Structure Identification Number UGX175).

[0038] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-055 and a variable light chain (VL) region according to VL-001 (i.e., an antibody according to Antibody Structure Identification Number UGX182).

[0039] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-050 (i.e., an antibody according to Antibody Structure Identification Number UGX201).

[0040] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-054 (i.e., an antibody according to Antibody Structure Identification Number UGX202).

[0041] Also provided is an isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to Petition 870250099897, dated 10 / 31 / 2025, page 17 / 177 / 140 with VL-027 (i.e., an antibody according to the Antibody Structure Identification Number UGX203).

[0042] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-030 (i.e., an antibody according to Antibody Structure Identification Number UGX204).

[0043] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-066 (i.e., an antibody according to Antibody Structure Identification Number UGX205).

[0044] Also provided is an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-067 (i.e., an antibody according to Antibody Structure Identification Number UGX206).

[0045] In another aspect, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a heavy chain (HC) amino acid sequence according to SEQ ID NO: 1 and a light chain (LC) amino acid sequence according to SEQ ID NO: 2, wherein the antibody or Petition 870250099897, dated 10 / 31 / 2025, page. 18 / 177 / 140 fragment thereof comprises one or more amino acid changes of HC relative to SEQ ID NO: 1 and / or one or more amino acid changes of LC relative to SEQ ID NO: 2, wherein one or more amino acid changes of HC are selected from T28Y, T30F, T30K, N31D, N31E, N31F, N31Q, N31R, H32K, H32Y, Y33D, Y33L, Y33R, N52E, N52F, N52Q, N52R, N52Y, I54A, I54D, I54F, I54G, I54H, I54K, I54L, I54M, I54N, I54P, I54R, I54V, I54W, I54Y, S55E, S55F, S55I, S55Q, S55R, S55Y, S57E, S57F, S57R, S57Y, T58F, T58R, S59A, S59D, S59E, S59F, S59G, S59H, S59I, S59K, S59L, S59M, S59N, S59P, S59Q, S59R, S59T, S59V, S59W, S59Y, N60E, N60R, N60Y, A61F, A61R, A61Y, Q62L, Q62R, Q62Y, Q65E, Q65R, Q65Y, D99F, D99R, D99Y, I100D, I100E, I100F, I100Y, V101A, V101D, V101E, V101F, V101G, V101H, V101I, V101K, V101L, V101M, V101N, V101P, V101Q, V101R, V101S, V101W, D102E, D102F, D102K, D102R, D102Y, A103D, A103F, A103G, A103H, A103I, A103K, A103L, A103M,A103N, A103P, A103R, A103S, A103T, A103V, and A103W, and one or more LC amino acid alterations are selected from Q27F, Q27R, G28D, G28Q, G28R, G28Y, I29F, I29L, S30D, S30E, S30F, S30L, S30Q, S30R, S30Y, S31D, S31E, S31F, S31Q, S31Y, A32F, A32V, V34F, V34I, D50E, D50F, D50L, D50Q, D50R, D50S, D50T, D50V, D50Y, A51V, S52A, S52D, S52E, S52F, S52G, S52H, S52I, S52K, S52L, S52M, S52N, S52P, S52Q, S52R, S52V, S52W, S52Y, S53D, S53E, S53F, S53R, S53Y, L54E, L54Y, E55R, E55Y, S67E, S67R, S67Y, T69R, T69Y, F91E, F91R, F91Y, N92A, N92D, N92E, N92F, N92G, N92H, N92I, N92K, N92L, N92M, N92P, N92Q, N92R, N92S, N92T, N92V, N92W, N92Y, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94A, Y94D, Y94E, Y94F, Y94G, Y94H, Y94I, Y94K, Y94L, Y94M, Y94N, Y94P, Y94Q, Y94R, Y94S, Y94V and Y94W.

[0046] In another aspect, the disclosure provides an isolated antibody or a fragment thereof that binds specifically to a polypeptide of Petition 870250099897, dated 10 / 31 / 2025, page. 19 / 177 / 140 human fibroblast growth factor 23 (FGF23), wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region amino acid sequence according to SEQ ID NO: 3 and a variable light chain (VL) region amino acid sequence according to SEQ ID NO: 4, wherein the antibody or fragment thereof comprises one or more VH amino acid changes relative to SEQ ID NO: 3 and / or one or more VL amino acid changes relative to SEQ ID NO: 4, wherein one or more VH amino acid changes are selected from T28Y, T30F, T30K, N31D, N31E, N31F, N31Q, N31R, H32K, H32Y, Y33D, Y33L, Y33R, N52E, N52F, N52Q, N52R, N52Y, I54A, I54D, I54F, I54G, I54H, I54K, I54L, I54M, I54N, I54P, I54R, I54V, I54W, I54Y, S55E, S55F, S55I, S55Q, S55R, S55Y, S57E, S57F, S57R, S57Y, T58F, T58R, S59A, S59D, S59E, S59F, S59G, S59H, S59I, S59K, S59L, S59M, S59N, S59P, S59Q, S59R, S59T, S59V, S59W, S59Y,N60E, N60R, N60Y, A61F, A61R, A61Y, Q62L, Q62R, Q62Y, Q65E, Q65R, Q65Y, D99F, D99R, D99Y, I100D, I100E, I100F, I100Y, V101A, V101D, V101E, V101F, V101G, V101H, V101I, V101K, V101L, V101M, V101N, V101P, V101Q, V101R, V101S, V101W, D102E, D102F, D102K, D102R, D102Y, A103D, A103F, A103G, A103H, A103I, A103K, A103L, A103M, A103N, A103P, A103R, A103S, A103T, A103V, and A103W, and one or more VL amino acid alterations are selected from Q27F, Q27R, G28D, G28Q, G28R, G28Y, I29F, I29L, S30D, S30E, S30F, S30L, S30Q, S30R, S30Y, S31D, S31E, S31F, S31Q, S31Y, A32F, A32V, V34F, V34I, D50E, D50F, D50L, D50Q, D50R, D50S, D50T, D50V, D50Y, A51V, S52A, S52D, S52E, S52F, S52G, S52H, S52I, S52K, S52L, S52M, S52N, S52P, S52Q, S52R, S52V, S52W, S52Y, S53D, S53E, S53F, S53R, S53Y, L54E, L54Y, E55R, E55Y, S67E, S67R, S67Y, T69R, T69Y, F91E, F91R, F91Y, N92A, N92D, N92E, N92F, N92G, N92H, N92I, N92K, N92L, N92M, N92P, N92Q, N92R, N92S, N92T, N92V, N92W, N92Y, D93F, D93Q, D93R, D93S, D93T, D93Y, Petition 870250099897, dated 10 / 31 / 2025, page 20 / 177 / 140 Y94A, Y94D, Y94E, Y94F, Y94G, Y94H, Y94I, Y94K, Y94L, Y94M, Y94N, Y94P, Y94Q, Y94R, Y94S, Y94V and Y94W.

[0047] Also provided here are FGF23-binding antibodies or fragments thereof with increased affinity for human FGF23 compared to burosumab.

[0048] For example, the isolated antibody or fragment thereof may have a binding affinity to human FGF23 approximately 2 times to approximately 10 times greater compared to burosumab.

[0049] In some embodiments, the isolated antibody or fragment thereof has a binding affinity to human FGF23 (KD) between about 1x10'12M to about 7*10-12M.

[0050] In some embodiments, the isolated antibodies or fragments provided here are for use in a method to decrease serum FGF23 in a subject in need thereof.

[0051] In some embodiments, the isolated antibodies or fragments provided here are for use in a method to increase the maximum renal limit for phosphate reabsorption (TmP) in a subject in need thereof.

[0052] In some embodiments, the isolated antibodies or fragments provided here are for use in a method to increase serum inorganic phosphorus (Pi) in a subject in need thereof.

[0053] In some embodiments, the isolated antibodies or fragments provided herein are for use in a method for increasing the serum concentration of 1,25-dihydroxyvitamin D (1,25[OH]2D) in a subject in need thereof.

[0054] In some embodiments, the isolated antibodies or fragments provided herein are for use in a method for treating a hypophosphatemic condition in a subject in need thereof.

[0055] In some modalities, the subject is diagnosed with Petition 870250099897, dated 10 / 31 / 2025, page 21 / 177 / 140 X-linked hypophosphatemia (XLH) or tumor-induced osteomalacia (TIO).

[0056] Methods are also provided here for lowering serum FGF23 in a subject in need thereof, comprising administering an isolated antibody or fragment thereof described herein to the subject.

[0057] In another aspect, the disclosure provides methods for increasing the maximum renal limit for phosphate reabsorption (TmP) in a subject in need thereof, comprising administering an isolated antibody or fragment thereof described herein to the subject.

[0058] Methods are also provided for increasing serum inorganic phosphorus (Pi) in a subject in need thereof, comprising administering an isolated antibody or fragment thereof described herein to the subject.

[0059] Methods are also provided for increasing the serum concentration of 1,25-dihydroxyvitamin D (1,25[OH]2D) in a subject in need thereof, comprising administering an isolated antibody or fragment thereof described herein to the subject.

[0060] Methods are also provided for treating a hypophosphatemic condition in a subject in need thereof, comprising administering an isolated antibody or fragment thereof described herein to the subject.

[0061] In some modalities, the subject to be treated according to the methods described here is diagnosed with X-linked hypophosphatemia (XLH) or tumor-induced osteomalacia (TIO).

[0062] These and other aspects and features of the disclosure are described in the following sections of the application. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The objects, characteristics and advantages above and others of the systems and methods currently disclosed will become evident from Petition 870250099897, dated 10 / 31 / 2025, page 22 / 177 / 140, following description of preferred embodiments, as illustrated in the attached drawings. Elements with similar references identify common features in the corresponding drawings.

[0064] Figure 1 is a graph showing the percentage of deuteration measured by HDX-MS analysis of FGF23 in the presence of burosumab. Three boxed regions identify amino acid residues potentially involved in antibody binding, as evidenced by the increased protection against deuteration.

[0065] Figure 2 is a representation of protected region 1, protected region 2 and protected region 3, as defined here by HDXMS analysis superimposed on the 2P39 crystal structure of FGF23.

[0066] Figure 3 is a graph showing the percentage of deuteration measured in HDX-MS analysis of burosumab in the presence of FGF23. Six regions of low deuteration were identified, implicating amino acid residues involved in antigen binding.

[0067] Figure 4 shows statistics for collecting and refining crystallographic data for a Fab FGF23(R179Q):burosumab complex determined by molecular substitution methods using available structures (2P39.PDB and 2VEN.PDB).

[0068] Figure 5 shows two 3Â crystal structure molecules of the Fab hFGF23(R179Q):burosumab complex in the asymmetric unit. The two complex molecules are held together by the FGF23 dimer formed by residues known to be involved in FGFR1c binding.

[0069] Figure 6 is a ribbon model of the FGF23:Fab complex (only variable regions shown) with FGF23 epitope residues (C-alpha atoms) identified as colored purple spheres and FGF23-dimer / FGFR1c linking residues (C-alpha atoms) as colored cyan spheres, burosumab light chain paratope residues as colored green spheres and burosumab heavy chain paratope residues as Petition 870250099897, dated 10 / 31 / 2025, page 23 / 177 / 140 colored yellow spheres.

[0070] Figure 7 shows previously reported epitopes identified in relevant systems (Yamazaki et al. JBMR. 2008 and Kanhasut et al. Sci Report. 2022) mapped onto the FGF23:burosumab crystal structure to illustrate that these epitopes differ from the epitopes identified in the present study (Figure 6).

[0071] Figure 8 shows the FGF23:Fab complex in ribbon model (left) and surface models (right panels), with FGF23 and burosumab binding interfaces rotated in view and detailed amino acid positions superimposed as rod models (rightmost panels).

[0072] Figure 9 shows the FGF23 surface model interface with burosumab shown in the ribbon-stick model. Panel A shows the FGF23:Fab complex with the FGF23 portion rotated 90 degrees to display all burosumab residues in contact with FGF23 at the binding interface. Panel B shows the FGF23 surface model (top) with burosumab hydrogen bonding residues in the stick model (overlaid and bottom). Panel C and Panel D show closer views of the ionic interactions and aromatic stacking interactions at the FGF23:Fab interface, respectively. Black arrows indicate examples of burosumab residues targeted for rational structure-based design for affinity optimization.

[0073] Figure 10 illustrates relevant interface positions of the burosumab light chain and human FGF23 based on the crystal structure of the FGF23:Fab complex.

[0074] Figure 11 illustrates relevant interface positions of the burosumab heavy chain and human FGF23 based on the crystal structure of the FGF23:Fab complex.

[0075] Figure 12 shows a ribbon model of the FGF23:Fab complex, as shown in Figure 6 (leftmost column). Petition 870250099897, dated 10 / 31 / 2025, page 24 / 177 / 140, highlighting certain hypothesized amino acid substitutions to improve the affinity of variant antibodies compared to the parent burosumab. Burosumab light chain residues are shown in green and heavy chain residues in yellow. FGF23 residues are shown in purple. Stick model interfaces between burosumab and FGF23, focusing on selected paratope residues that, when modified alone or in combination, resulted in increased affinity for FGF23, as measured by SPR. Potential novel interactions formed by these modified residues with nearby FGF23 epitope residues are described in each box. DETAILED DESCRIPTION

[0076] This disclosure provides human FGF23-binding antibodies with higher affinity for human FGF23 compared to burosumab. The antibodies in this disclosure may allow for reduced dosing frequency, greater patient convenience and adherence, and improved potency compared to burosumab, while maintaining an acceptable toxicity and safety profile. To improve the affinity of burosumab for human FGF23, antibody variants have been rationally designed to have higher binding affinity for human FGF23 compared to burosumab. I. Definitions

[0077] Throughout this descriptive report, numerical intervals are provided for certain quantities. It should be understood that these intervals comprise endpoints and all subintervals contained therein, including every integer within and between a given interval. Thus, the interval “from 50 to 80” includes all possible intervals contained within it (e.g., 51-79, 52-78, 53-77, 54-76, 55-75, 60-70, etc.), as well as each individual integer from 50 to 80 (e.g., 50, 51, 52, 53, 54, etc.). When intervals are provided in the form of fractions, percentages, Petition 870250099897, dated 10 / 31 / 2025, page 25 / 177 / 140 decimals and similar, such intervals also include all possible subintervals and each individual fraction, percentage, decimal, etc. within and between the disclosed interval. For example, the interval “from 0.1 to 1.0” includes all possible intervals contained within it (e.g., 0.2 to 0.9, etc.) and each individual 1 / 10 decimal tenth of 0.1 to 1.0 (e.g., 0.1, 0.2, 0.3, 0.4, etc.). Furthermore, all values ​​within a given interval may be an endpoint for the interval covered by it (e.g., the interval 50-80 includes intervals with endpoints such as 55-80, 50-75, etc.).

[0078] The term “an” refers to one or more of these entities; for example, “an androgen receptor modulator” refers to one or more androgen receptor modulators or to at least one androgen receptor modulator. Thus, the terms an, one or more, and at least one are used interchangeably in this document. Furthermore, the reference to “an inhibitor” by the indefinite article “an” does not exclude the possibility that more than one of the inhibitors is present, unless the context clearly requires that there be one and only one of the inhibitors.

[0079] The term “affinity” (or “binding affinity”) refers to the binding strength of a molecule or complex of molecules to a binding partner, such as a ligand, an epitope, or an antigen. Affinity can be expressed in terms of the dissociation constant (KD), which describes the rate of dissociation of a molecule or complex and its binding partner at equilibrium. KD can be expressed as a ratio between the association rate constant (kativa) and the dissociation rate constant (kinativa) of a ligand, or KD = kinativa / kativa. With respect to antibody / antigen binding affinities, the rate of formation of the antibody / antigen complex at equilibrium is equal to the rate of dissociation of the complex into the unbound antibody and the antigen, and the antibody affinity can be expressed as 1 / KD, so that lower KD values ​​reflect a higher affinity of the antibody for its target antigen. Petition 870250099897, dated 10 / 31 / 2025, p. 26 / 177 / 140 Methods for determining binding affinity are known and include, for example, enzyme-linked immunosorbent assay (ELISA) approaches and surface plasmon resonance (SPR)-based approaches.

[0080] The term “Antibody Structural Numbering System” or “ASN#” as used herein refers to a numbering scheme for the structural alignment and classification of complete antibody sequences and antibody-like structures. A description of the ASN# system is provided at www.just-evotecbiologics.com / white-papers-applicationnotes / coreab-sequence-classification / (last accessed July 5, 2023; incorporated herein by reference in its entirety). The ASN# system is based on and substantially identical to the Honegger numbering scheme, namely the “AHo” numbering scheme (see, for example, Honegger, Annemarie and Andreas PluÈckthun. Yet another numbering scheme for immunoglobulin variable domains: an automatic modeling and analysis tool. Journal of molecular biology 309.3 (2001): 657-670; incorporated here by reference in its entirety), which “numbers the variable domains of the immunoglobulin superfamily in a homogenized format...”based on structural alignments of the 3D structures of the variable regions of immunoglobulins covering the observed length variation” (Dondelinger, Mathieu, et al. Understanding the significance and implications of antibody numbering and antigen-binding surface / residue definition. Frontiers in immunology 9 (2018): 2278).

[0081] The verb “to include”, as used in this description and in the claims and their conjugations, is used in its non-limiting sense to mean that the items that follow the word are included, but items not specifically mentioned are not excluded.

[0082] The term “treat” or “treatment” refers to one or more of the following: attenuating, relieving, delaying, reducing, improving, or controlling at least one symptom of a condition in a subject. Treat can also mean Petition 870250099897, dated 10 / 31 / 2025, p. 27 / 177 / 140 one or more actions: interrupt, delay the onset (i.e., the period prior to the clinical manifestation of the condition) or reduce the risk of developing or worsening a condition.

[0083] The term “subject” may refer to a human being, non-human primate, mammal, rat, mouse, cow, horse, pig, sheep, goat, dog, cat, and the like. The subject may be suspected of having or be at risk of having a hypophosphatemic condition, such as XLH or TIO, or may be diagnosed with a hypophosphatemic condition, such as XLH or TIO.

[0084] This disclosure includes information that may be useful for understanding the subject matter currently disclosed. It is not an admission that any of the information provided in this document is prior art or relevant to the inventions currently claimed, or that any publication specifically or implicitly referenced is prior art. II. Overview

[0085] Burosumab therapy effectively improves the clinical symptoms of hypophosphatemia. Several clinical trials have established burosumab as a safe and effective therapy for adults and children with X-linked hypophosphatemia (XLH) (Schindeler et al. Clinical evidence for the benefits of burosumab therapy for X-linked hypophosphatemia (XLH) and other conditions in adults and children. Frontiers in Endocrinology 11 (2020): 338.). Additional studies have confirmed the safe and effective treatment of tumor-induced osteomalacia (TIO) with burosumab (Jan de Beur, et al. Burosumab for the treatment of tumor-induced osteomalacia. Journal of Bone and Mineral Research 36.4 (2021): 627-635.).

[0086] However, treatment with burosumab only returns serum phosphorus levels to 3.3 mg / dL after 64 weeks, which is close to the lower limit of 3.2 mg / dL of normal levels observed in populations. Petition 870250099897, dated 10 / 31 / 2025, page 28 / 177 / 140 healthy individuals (see, for example, Section 12, Figure 1 and Figure 2 of the Singapore Health Sciences Authority's Summary Risk-Benefit Assessment Report in conjunction with a New Medicinal Product Application for Crysvita, available at www.hsa.gov.sg / docs / default-source / hprgtpb / summary-reports / crysvita_summary-report_2021.pdf). Furthermore, treatment with burosumab requires subcutaneous injection every 2 weeks (Q2W) in pediatric patients, and both adult and pediatric patients must receive high volumes of burosumab injection, with a maximum of up to 3 ml administered in three separate 1 ml injections, representing a significant treatment burden for patients.

[0087] Therefore, the present description provides human FGF23-binding antibodies with improved binding affinity to human FGF23 compared to burosumab. The improved binding affinity of burosumab is considered to increase antibody potency, reduce the amount of bioavailable FGF23 in serum, and allow for reductions in dosage amounts and / or dosing frequency, thus decreasing the treatment burden for patients requiring human FGF23-binding antibody therapy, without significantly affecting the safety profile of the therapy.

[0088] Burosumab is believed to bind to intact human FGF23 with high affinity. However, different assays to measure the affinity of burosumab using different source materials have yielded different values. For example, the European Medicines Agency's Assessment Report for Crysvita states: “In a competitive binding study, Biacore [burosumab] demonstrated binding with similar binding affinity (KD~10-11 M) to human, cynomolgus monkey and rabbit FGF23” (see Assessment Report: Crysvita, 14 December 2017 (EMA / 148319 / 2018), available at www.ema.europa.eu / en / documents / assessment-report / crysvita-epar-public- Petition 870250099897, dated 10 / 31 / 2025, p. 29 / 177 / 140 assessment-report_en.pdf). Studies by the present inventors used a surface plasmon resonance (SPR) approach to determine the affinity of burosumab using recombinant human FGF23 (R179Q) from HEK293S cell supernatant and burosumab manufactured using CHO cells and found an estimated binding affinity (KD) on the order of approximately U10-11a 3*10-11 (data not shown). Yamazaki et al. They reported an affinity of 4.7*10-11 for FN1, a mouse anti-FGF23 monoclonal antibody described by the authors as binding to human FGF23 in a manner similar to burosumab (Yamazaki, Yuji, et al. AntiFGF23 neutralizing antibodies show the physiological role and structural features of FGF23. Journal of Bone and Mineral Research 23.9 (2008): 1509-1518.). Another group used ELISA to determine the affinity of burosumab using recombinant human FGF23 expressed in E.Coli and burosumab expressed in HEK293 cells and found an estimated binding affinity of approximately 0.5*10-9 or 0.77*10-9 (Kanhasut, et al. “Prediction of the structural interface between fibroblast growth factor 23 and burosumab using alanine scanning and molecular docking”. May 16, 2022, PREPRINT (Version 1) available on Research Square [doi.org / 10.21203 / rs.3.rs-1630525 / v1]). The disparate results of studies evaluating the affinity of burosumab highlight the need for a comprehensive study of the binding kinetics of this monoclonal antibody to human FGF23.

[0089] Kanhasut et al. further investigated approaches to improve the binding affinity of burosumab to FGF23. Using alanine scan and molecular docking data to model the interaction between a homology-modeled burosumab and an FGF23 crystal structure, the authors identified four amino acid alterations in the variable domain of the burosumab light chain (VL) that were predicted to increase interactions with the epitope: A32S, S52D, S67Y, and T69D (scheme of Petition 870250099897, dated 10 / 31 / 2025, page 30 / 177 / 140 (Kabat numbering). Based on the original alanine scan data, the authors also questioned a fifth alteration, V97A (Kabat numbering scheme) in the variable domain of the heavy chain (VH). This study provided data supporting an approximate 3-fold increase in FGF23 binding affinity of Kd=0.21x10⁹ in a burosumab variant antibody with amino acid alterations VH:V97A (i.e., V101A by the linear numbering scheme) and VL:A32S (i.e., A32S by both Kabat and linear numbering schemes).

[0090] The study by Kanhasut et al., however, has several shortcomings that call into question the validity and biological significance of its conclusions. For example, Kanhasut et al. employed FGF23 expressed in E. coli cells, meaning that the antigenic protein was not glycosylated in a form similar to that which would be found in a mammalian cell-based system. Furthermore, for the determination of Kd, Kanhasut et al. used an ELISA titration approach, which is recognized as highly variable and not the most precise assay for affinity measurement. Inconsistencies in the Kd of burosumab reported in Kanhasut et al. belie the high degree of variability in the assay and call into question the ultimate precision and significance of the study. Finally, the structural evaluation of the burosumab:FGF23 complex described here suggests that the epitope residues identified by Kanhasut et al. do not agree with the epitope residues identified in the crystal structure.In fact, the present inventors conducted a surface plasmon resonance analysis of the amino acid substitutions VH:V97A and VL:A32S (i.e., heavy chain V101A and light chain A32S according to the linear numbering scheme, respectively) and demonstrated that these changes impair rather than improve the affinity of burosumab (data not shown).

[0091] These and other studies reveal that a more definitive investigation of the binding kinetics of burosumab, including the determination of Petition 870250099897, dated 10 / 31 / 2025, page 31 / 177 / 140 The Kd of burosumab binding to human FGF23 and precise epitope mapping are needed, along with novel approaches to improve burosumab binding affinity. It is important to emphasize that when designing antibodies with improved binding affinity compared to burosumab, it is essential to adjust the affinity to human FGF23 so that potency is improved without compromising safety. For example, increasing affinity too much may result in reductions in serum FGF23 concentrations in individuals, leading to unsafe serum phosphorus levels and symptoms of hyperphosphatemia. Conversely, very small improvements in affinity may not provide clinical benefit compared to burosumab treatment. Consequently, rationally designed anti-human FGF23 antibodies with adjusted binding affinity are needed to increase potency without leading to unsafe serum phosphorus levels or clinical symptoms of hyperphosphatemia.

[0092] This disclosure provides rationally engineered human FGF23-binding antibodies with higher affinity to human FGF23 compared to burosumab.The rational design of the human FGF23-binding antibodies described herein may involve, for example, crystallographic analysis of the burosumab-human FGF23 interaction and / or in silico modeling involving any of the following: conformational sampling using molecular dynamics and selection of a set of target conformational states representing docking templates; generation of a homology model of the leader antibody(ies) and energy minimization by selecting likely conformational states; guided molecular docking of leader antibody templates to the FGF23 structure (e.g., epitope selected based on HDX data); paratope and epitope determinations based on docking results; evaluation and classification of antigen-antibody binding interactions (e.g., 1st layer paratope:epitope and 2nd layer); comparison with recently published results describing the... Petition 870250099897, dated 10 / 31 / 2025, page 32 / 177 / 140 burosumab:FGF23 binding (Kanhasut et al., Nature (2022) 12:14754); assessment of any additional changes needed (e.g., stability, development capability); and / or assessment of post-translational modifications and associated remediations. From these studies, single or multiple amino acid changes can be introduced into the burosumab main sequence and analyzed for binding properties. Variant antibody designs can be screened to identify burosumab variants with improved binding properties.

[0093] Thus, the present disclosure provides human FGF23-binding antibodies with higher affinity for human FGF23 compared to burosumab, allowing for less frequent dosing, greater convenience and patient adherence, and better potency compared to burosumab, while maintaining an acceptable toxicity and safety profile.

[0094] To improve the affinity of burosumab for human FGF23, antibody variants were designed to have a higher binding affinity for human FGF23 compared to burosumab.

[0095] These and other aspects of disclosure antibodies and their uses are described in more detail below. III. Compositions

[0096] The compositions of the present disclosure comprise one or more antibodies or antigen-binding fragments that bind to human FGF23. In some embodiments, the human FGF23-binding antibodies are variants of burosumab engineered to have improved affinity (i.e., engineered human FGF23-binding antibodies).

[0097] In some embodiments, the engineered human FGF23-binding antibodies provided herein may be administered to individuals for use in reducing serum FGF23 in those individuals.

[0098] In some embodiments, the engineered human FGF23-binding antibodies provided herein may be administered to individuals Petition 870250099897, dated 10 / 31 / 2025, page 33 / 177 / 140 for use in increasing the maximum renal threshold for phosphate reabsorption (TmP) in individuals.

[0099] In some embodiments, the engineered human FGF23-binding antibodies provided herein may be administered to individuals for use in increasing serum inorganic phosphorus (Pi) in individuals.

[00100] In some embodiments, the engineered human FGF23-binding antibodies provided herein may be administered to individuals for use in increasing serum concentrations of 1,25-dihydroxyvitamin D (1,25[OH]2D) in individuals.

[00101] In some embodiments, the human FGF23-binding antibodies designed here are useful in the treatment of hypophosphatemic conditions in individuals, including XLH or osteomalacia, such as tumor-induced osteomalacia (TIO).

[00102] In some embodiments, the engineered human FGF23-binding antibodies provided here have a higher affinity for human FGF23 compared to burosumab.

[00103] In some embodiments, the binding affinity of the antibodies provided here to human FGF23 is increased relative to burosumab by decreasing the Kd of the antibodies to between approximately 1*10-12 and approximately 7*10-12.

[00104] In some embodiments, the binding affinity of the antibodies provided herein to human FGF23 is increased from about 2-fold to about 10-fold compared to burosumab. For example, the binding affinity of the antibodies provided herein to human FGF23 may be increased by about 2-fold, about 2.5-fold, about 3-fold, about 3.5-fold, about 4-fold, about 4.5-fold, about 5-fold, about 5.5-fold, about 6-fold, about 6.5-fold, about 7-fold, about 7.5-fold, about 8-fold, about 8.5-fold, about 9-fold, about 9.5-fold, or about 10-fold compared to burosumab. Petition 870250099897, dated 10 / 31 / 2025, p. 34 / 177 / 140

[00105] In some embodiments, the increased binding affinity of the antibodies provided here to human FGF23 relative to burosumab results in a decrease in free FGF23 in subjects compared to the decrease observed with burosumab treatment in subjects. Free FGF23 refers to bioavailable FGF23. Binding of FGF23 by the antibodies provided here may reduce the amount of free FGF23 in subjects by at least about 5% or at least about 10% compared to burosumab.

[00106] The engineered human FGF23-binding antibodies described herein may have one or more amino acid substitutions compared to the burosumab amino acid sequence. For example, the engineered FGF23-binding antibodies described herein may comprise one or more amino acid substitutions in the heavy chain sequence relative to the burosumab heavy chain sequence (SEQ ID NO: 1). The engineered FGF23-binding antibodies described herein may comprise one or more amino acid substitutions in the light chain sequence relative to the burosumab light chain sequence (SEQ ID NO: 2). The engineered FGF23-binding antibodies described herein may comprise one or more amino acid substitutions in the heavy chain sequence relative to the burosumab heavy chain sequence (SEQ ID NO: 1) and one or more amino acid substitutions in the light chain sequence relative to the burosumab light chain sequence (SEQ ID NO: 2).

[00107] The human FGF23-binding antibodies designed herein may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid substitutions compared to the amino acid sequence of burosumab. For example, the FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 substitutions. Petition 870250099897, dated 10 / 31 / 2025, page 35 / 177 / 140 of amino acids in the heavy chain sequence relative to the burosumab heavy chain sequence (SEQ ID NO: 1). The FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid substitutions in the light chain sequence relative to the burosumab light chain sequence (SEQ ID NO: 2). The FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid substitutions in the heavy chain sequence relative to the burosumab heavy chain sequence (SEQ ID NO: 1) and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid substitutions in the light chain sequence relative to the burosumab light chain sequence (SEQ ID NO: 2).

[00108] The human FGF23-binding antibodies designed herein may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid deletions compared to the burosumab amino acid sequence. For example, the FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid deletions in the heavy chain sequence relative to the burosumab heavy chain sequence (SEQ ID NO: 1). The FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid deletions in the light chain sequence relative to the burosumab light chain sequence (SEQ ID NO: 2).The FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more of 20 amino acid deletions in the heavy chain sequence relative to the burosumab heavy chain sequence (SEQ ID NO: 1) and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. Petition 870250099897, dated 10 / 31 / 2025, page 36 / 177 / 140 more than 20 amino acid deletions in the light chain sequence compared to the burosumab light chain sequence (SEQ ID NO: 2).

[00109] The human FGF23-binding antibodies designed herein may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid insertions compared to the burosumab amino acid sequence. For example, the FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid insertions in the heavy chain sequence relative to the burosumab heavy chain sequence (SEQ ID NO: 1). The FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid insertions in the light chain sequence relative to the burosumab light chain sequence (SEQ ID NO: 2).The FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid insertions in the heavy chain sequence relative to the burosumab heavy chain sequence (SEQ ID NO: 1) and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid insertions in the light chain sequence relative to the burosumab light chain sequence (SEQ ID NO: 2).

[00110] The human FGF23-binding antibodies designed herein may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid alterations compared to the burosumab amino acid sequence, wherein the alterations comprise a combination of substitutions, deletions and / or insertions relative to the burosumab amino acid sequence. For example, the FGF23-binding antibodies designed and described herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid changes in the heavy chain sequence in Petition 870250099897, dated 10 / 31 / 2025, page 37 / 177 / 140, relating to the burosumab heavy chain sequence (SEQ ID NO: 1), where the changes comprise a combination of substitutions, deletions and / or insertions in relation to the burosumab heavy chain sequence (SEQ ID NO: 1). The FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid sequence alterations in the light chain relative to the burosumab light chain sequence (SEQ ID NO: 2), wherein the alterations comprise a combination of substitutions, deletions and / or insertions relative to the burosumab light chain sequence (SEQ ID NO: 2).The FGF23-binding antibodies designed herein may comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid sequence alterations in the heavy chain relative to the burosumab heavy chain sequence (SEQ ID NO: 1) and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 amino acid sequence alterations in the light chain relative to the burosumab light chain sequence (SEQ ID NO: 2), wherein the alterations comprise a combination of substitutions, deletions and / or Insertions relating to the heavy chain and light chain sequences of burosumab (SEQ ID NO: 1 and SEQ ID NO: 2, respectively).

[00111] In some embodiments, the engineered human FGF23-binding antibodies described herein comprise one or more amino acid substitutions, deletions, and / or insertions (collectively, “alterations”) with respect to the amino acid sequence of the burosumab heavy chain sequence and / or burosumab light chain sequence, wherein one or more amino acid alterations affect one or more burosumab paratop residues and / or one or more residues neighboring a burosumab paratop residue. Examples of burosumab paratop regions and paratop residues are provided in Table 4 herein. Burosumab residues neighboring a burosumab paratop residue may include residues within 1, Petition 870250099897, dated 10 / 31 / 2025, page 38 / 177 / 140 within 2, within 3, within 4, within 5, within 6, within 7, within 8, within 9 or within 10 amino acid residues of a burosumab paratopo residue.

[00112] In some embodiments, the human FGF23-binding antibodies designed herein comprise one or more amino acid changes in the variable region of the light chain provided in Table 13.

[00113] In some embodiments, the human FGF23-binding antibodies designed herein comprise one or more amino acid changes in the variable region of the heavy chain provided in Table 14.

[00114] In some embodiments, the human FGF23-binding antibodies designed and described herein comprise two amino acid changes in accordance with those provided in Table 15.

[00115] In some embodiments, a designed human FGF23-binding antibody provided here is one of UGX101 to UGX196 described in Table 16 and Table 17.

[00116] Amino acid alterations of certain engineered FGF23-binding antibodies

[00117] The FGF23-binding antibodies designed herein may comprise one or more amino acid changes in the variable region of the heavy chain (VH) relative to SEQ ID NO: 3, wherein one or more amino acid changes are selected from T30E, T30F, T30Q, T30S, T30Y, N31D, N31E, N31F, N31Q, N31R, N31Y, H32E, H32F, H32Q, H32S, H32T, I50D, I50E, I50F, I50S, I50T, I50Y, N52E, N52F, N52Q, N52Y, I54E, I54F, I54L, I54Q, I54S, I54T, I54V, I54Y, S55E, S55F, S55Q, S55T, S55Y, S59D, S59E, S59F, S59I, S59L, S59Q, S59T, S59V, S59Y, D99E, D99Q, D99Y, I100D, I100E, I100F, I100L, I100Q, I100V, I100Y, V101F, V101I, V101L, V101T, V101Y, D102E, D102F, D102I, D102L, D102Q, D102Y, A103D, A103E, A103F, A103Q, A103S, A103T and A103Y.

[00118] The FGF23-binding antibodies designed and described herein Petition 870250099897, dated 10 / 31 / 2025, page. 39 / 177 / 140 may comprise one or more amino acid changes in the variable region of the light chain (VL) relative to SEQ ID NO: 4, wherein one or more amino acid changes are selected from A25L, A25V, I29F, I29L, I29V, S30D, S30E, S30F, S30I, S30L, S30Q, S30T, S30V, S30Y, S31D, S31E, S31F, S31I, S31L, S31Q, S31T, S31V, S31Y, A32F, A32I, A32L, A32T, A32V, A32Y, V34F, V34I, V34L, V34Y, D50E, D50F, D50I, D50L, D50Q, D50R, D50S, D50T, D50V, A51F, A51I, A51L, A51S, A51T, A51V, S52D, S52E, S52F, S52Q, S52T, S52Y, S53D, S53E, S53F, S53I, S53L, S53Q, S53R, S53T, S53V, S53Y, Q90F, Q90Y, F91K, F91R, F91Y, N92D, N92E, N92F, N92Q, N92S, N92T, N92Y, D93E, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94D, Y94E, Y94F, Y94Q, Y94S and Y94T.

[00119] The FGF23-binding antibodies designed herein may comprise one or more amino acid changes in the variable region of the heavy chain (VH) and in the variable region of the light chain (VL), relative to SEQ ID NO: 3 and SEQ ID NO: 4, respectively, wherein one or more amino acid changes in the VH are selected from T30E, T30F, T30Q, T30S, T30Y, N31D, N31E, N31F, N31Q, N31R, N31Y, H32E, H32F, H32Q, H32S, H32T, I50D, I50E, I50F, I50S, I50T, I50Y, N52E, N52F, N52Q, N52Y, I54E, I54F, I54L, I54Q, I54S, I54T, I54V, I54Y, S55E, S55F, S55Q, S55T, S55Y, S59D, S59E, S59F, S59I, S59L, S59Q, S59T, S59V, S59Y, D99E, D99Q, D99Y, I100D, I100E, I100F, I100L, I100Q, I100V, I100Y, V101F, V101I, V101L, V101T, V101Y, D102E, D102F, D102I, D102L, D102Q, D102Y, A103D, A103E, A103F, A103Q, A103S, A103T and A103Y, and where one or more amino acid changes in VL are selected from A25L, A25V, I29F, I29L, I29V, S30D, S30E, S30F, S30I, S30L, S30Q, S30T, S30V, S30Y, S31D, S31E,S31F, S31I, S31L, S31Q, S31T, S31V, S31Y, A32F, A32I, A32L, A32T, A32V, A32Y, V34F, V34I, V34L, V34Y, D50E, D50F, D50I, D50L, D50Q, D50R, D50S, D50T, D50V, A51F, A51I, A51L, A51S, A51T, A51V, S52D, S52E, S52F, S52Q, Petition 870250099897, dated 10 / 31 / 2025, page 40 / 177 / 140 S52T, S52Y, S53D, S53E, S53F, S53I, S53L, S53Q, S53R, S53T, S53V, S53Y, Q90F, Q90Y, F91K, F91R, F91Y, N92D, N92E, N92F, N92Q, N92S, N92T, N92Y, D93E, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94D, Y94E, Y94F, Y94Q, Y94S and Y94T.

[00120] The FGF23-binding antibodies designed and described herein may comprise at least two amino acid changes in the variable region of the heavy chain (VH) relative to SEQ ID NO: 3, in the variable region of the light chain (VL) relative to SEQ ID NO: 4, or in the VH relative to SEQ ID NO: 3 and in the VL relative to SEQ ID NO: 4, wherein the at least two amino acid changes are selected from VL:S31E / VL:D50F, VL:S31F / VL:S52E, VL:S31F / VL:S53E, VL:S31F / VL:D50F, VH:N31E / VH:I54F, VH:N52F / VH:V101I, VL:S31F / VL:D50E, VL:N92F / VH:S59E, VH:N31F / VH:S59F, VL:D50F / VH:V101I, VL:N92E / VL:D93F, VH:N31E / VH:S59E, VH:S59T / VH:V101L, VL:N92D / VL:D93F, VL:Y94D / VH:S59D, VL:N92Y / VH:S59E, VL:D50F / VL:S53E, VH:S59D / VH:V101I, VL:S31E / VL:S53E, VH:S57E / VH:S59D, VH:I54Y / VH:V101F, VH:N52F / VH:V101L, VL:Y94D / VH:S59E, VL:Y94E / VH:S59E, VL:S52D / VH:S59E e VL:S52E / VH:S59E.

[00121] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a VH amino acid sequence according to SEQ ID NO: 3 and a VL amino acid sequence according to SEQ ID NO: 4, wherein the VH amino acid sequence comprises one or more amino acid changes selected from I54F, I54Y, S59D, S59E, V101I and A103S compared to SEQ ID NO: 3.

[00122] 21. An isolated antibody or a fragment thereof that is Petition 870250099897, dated 10 / 31 / 2025, page 41 / 177 / 140 specifically links to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a VH amino acid sequence according to SEQ ID NO: 3 and a VL amino acid sequence according to SEQ ID NO: 4, wherein the VL amino acid sequence comprises one or more amino acid changes selected from S52D, S52E, N92F, N92Y, Y94D and Y94E compared to SEQ ID NO: 4.

[00123] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-027 (UGX126).

[00124] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-066 (UGX144).

[00125] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-067 (UGX145).

[00126] In some modalities, FGF23 binding antibodies Petition 870250099897, dated 10 / 31 / 2025, page 42 / 177 / 140, the designs described herein may comprise an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-028 and a variable light chain (VL) region according to VL-001 (UGX156).

[00127] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-029 and a variable light chain (VL) region according to VL-001 (UGX157).

[00128] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-061 and a variable light chain (VL) region according to VL-001 (UGX175).

[00129] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-055 and a variable light chain (VL) region according to VL-001 (UGX182).

[00130] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a Petition 870250099897, dated 10 / 31 / 2025, page 43 / 177 / 140 fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-050 (UGX201).

[00131] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-054 (UGX202).

[00132] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-027 (UGX203).

[00133] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-030 (UGX204).

[00134] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that binds specifically to a factor polypeptide. Petition 870250099897, dated 10 / 31 / 2025, page 44 / 177 / 140 of human fibroblast growth factor 23 (FGF23), wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-066 (UGX205).

[00135] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-067 (UGX206).

[00136] In some embodiments, the FGF23-binding antibodies designed herein may comprise a single antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a heavy chain (HC) amino acid sequence according to SEQ ID NO: 1 and a light chain (LC) amino acid sequence according to SEQ ID NO: 2, wherein the antibody or fragment thereof comprises one or more HC amino acid changes relative to SEQ ID NO: 1 and / or one or more LC amino acid changes relative to SEQ ID NO: 2, wherein one or more HC amino acid changes are selected from T28Y, T30F, T30K, N31D, N31E, N31F, N31Q, N31R, H32K, H32Y, Y33D, Y33L, Y33R, N52E, N52F, N52Q, N52R, N52Y, I54A, I54D, I54F, I54G, I54H, I54K, I54L, I54M, I54N, I54P, I54R, I54V, I54W, I54Y, S55E, S55F, S55I, S55Q, S55R, S55Y, S57E, S57F, S57R, S57Y,T58F, T58R, S59A, S59D, S59E, S59F, S59G, S59H, S59I, S59K, S59L, S59M, S59N, S59P, S59Q, S59R, S59T, S59V, S59W, S59Y, N60E, N60R, N60Y, A61F, A61R, A61Y, Q62L, Q62R, Q62Y, Q65E, Q65R, Q65Y, D99F, D99R, D99Y, I100D, I100E, I100F, Petition 870250099897, dated 10 / 31 / 2025, page 45 / 177 / 140 I100Y, V101A, V101D, V101E, V101F, V101G, V101H, V101I, V101K, V101L, V101M, V101N, V101P, V101Q, V101R, V101S, V101W, D102E, D102F, D102K, D102R, D102Y, A103D, A103F, A103G, A103H, A103I, A103K, A103L, A103M, A103N, A103P, A103R, A103S, A103T, A103V and A103W, and one or more amino acid alterations of LC are selected from Q27F, Q27R, G28D, G28Q, G28R, G28Y, I29F, I29L, S30D, S30E, S30F, S30L, S30Q, S30R, S30Y, S31D, S31E, S31F, S31Q, S31Y, A32F, A32V, V34F, V34I, D50E, D50F, D50L, D50Q, D50R, D50S, D50T, D50V, D50Y, A51V, S52A, S52D, S52E, S52F, S52G, S52H, S52I, S52K, S52L, S52M, S52N, S52P, S52Q, S52R, S52V, S52W, S52Y, S53D, S53E, S53F, S53R, S53Y, L54E, L54Y, E55R, E55Y, S67E, S67R, S67Y, T69R, T69Y, F91E, F91R, F91Y, N92A, N92D, N92E, N92F, N92G, N92H, N92I, N92K, N92L, N92M, N92P, N92Q, N92R, N92S, N92T, N92V, N92W, N92Y, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94A, Y94D, Y94E, Y94F, Y94G, Y94H, Y94I, Y94K, Y94L, Y94M, Y94N, Y94P, Y94Q, Y94R, Y94S, Y94V and Y94W.

[00137] 36. An isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises an amino acid sequence of the variable region of the heavy chain (VH) according to SEQ ID NO: 3 and an amino acid sequence of the variable region of the light chain (VL) according to SEQ ID NO: 4, wherein the antibody or fragment thereof comprises one or more amino acid changes of the VH relative to SEQ ID NO: 3 and / or one or more amino acid changes of the VL relative to SEQ ID NO: 4, wherein one or more amino acid changes of the VH are selected from T28Y, T30F, T30K, N31D, N31E, N31F, N31Q, N31R, H32K, H32Y, Y33D, Y33L, Y33R, N52E, N52F, N52Q, N52R, N52Y, I54A, I54D, I54F, I54G, I54H, I54K, I54L, I54M, I54N, I54P, I54R, I54V, I54W, I54Y, S55E, S55F, S55I, Petition 870250099897, dated 10 / 31 / 2025, page 46 / 177 / 140 S55Q, S55R, S55Y, S57E, S57F, S57R, S57Y, T58F, T58R, S59A, S59D, S59E, S59F, S59G, S59H, S59I, S59K, S59L, S59M, S59N, S59P, S59Q, S59R, S59T, S59V, S59W, S59Y, N60E, N60R, N60Y, A61F, A61R, A61Y, Q62L, Q62R, Q62Y, Q65E, Q65R, Q65Y, D99F, D99R, D99Y, I100D, I100E, I100F, I100Y, V101A, V101D, V101E, V101F, V101G, V101H, V101I, V101K, V101L, V101M, V101N, V101P, V101Q, V101R, V101S, V101W, D102E, D102F, D102K, D102R, D102Y, A103D, A103F, A103G, A103H, A103I, A103K, A103L, A103M, A103N, A103P, A103R, A103S, A103T, A103V and A103W, and one or more amino acid changes of VL are selected from Q27F, Q27R, G28D, G28Q, G28R, G28Y, I29F, I29L, S30D, S30E, S30F, S30L, S30Q, S30R, S30Y, S31D, S31E, S31F, S31Q, S31Y, A32F, A32V, V34F, V34I, D50E, D50F, D50L, D50Q, D50R, D50S, D50T, D50V, D50Y, A51V, S52A, S52D, S52E, S52F, S52G, S52H, S52I, S52K, S52L, S52M, S52N, S52P, S52Q, S52R, S52V, S52W, S52Y, S53D, S53E, S53F, S53R, S53Y, L54E, L54Y, E55R, E55Y, S67E, S67R, S67Y, T69R, T69Y, F91E,F91R, F91Y, N92A, N92D, N92E, N92F, N92G, N92H, N92I, N92K, N92L, N92M, N92P, N92Q, N92R, N92S, N92T, N92V, N92W, N92Y, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94A, Y94D, Y94E, Y94F, Y94G, Y94H, Y94I, Y94K, Y94L, Y94M, Y94N, Y94P, Y94Q, Y94R, Y94S, Y94V and Y94W.

[00138] Complementarity-determining regions of certain FGF23-binding antibodies designed

[00139] Burosumab has complementarity-determining regions (CDRs) defined as follows: CDR1 heavy chain with amino acid sequence NHYMH (SEQ ID NO: 11), referred to herein as HCDR1-001; CDR2 heavy chain with amino acid sequence IINPISGSTSNAQKFQG (SEQ ID NO: 12), referred to herein as HCDR2-001; CDR3 heavy chain with amino acid sequence DIVDAFDF (SEQ ID NO: 13), referred to herein as HCDR3-001; CDR1 of Petition 870250099897, dated 10 / 31 / 2025, p. 47 / 177 / 140 light chain with amino acid sequence RASQGISSALV (SEQ ID NO: 14), referred to herein as LCDR1-001; CDR1 light chain with amino acid sequence DASSLES (SEQ ID NO: 15), referred to herein as LCDR2-001; and CDR1 light chain with amino acid sequence QQFNDYFT (SEQ ID NO: 16), referred to herein as LCDR3-001.

[00140] The FGF23-binding antibodies designed herein may comprise one or more unique complementarity-determining regions (CDRs) relative to those of burosumab. That is, the designed FGF23-binding antibodies may have one or more amino acid changes relative to SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15 and / or SEQ ID NO: 16.

[00141] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a heavy chain complementarity-determining region 1 (HCDR1) according to an amino acid sequence selected from SEQ ID NO: 11 and SEQ ID NOs: 22-32.

[00142] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a heavy chain complementarity-determining region 2 (HCDR2) according to an amino acid sequence selected from SEQ ID NO: 12 and SEQ ID NOs: 33-65.

[00143] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a region Petition 870250099897, dated 10 / 31 / 2025, page 48 / 177 / 140 heavy chain complementarity determinant 3 (HCDR3) according to an amino acid sequence selected from SEQ ID NO: 13 and SEQ ID NOs: 66-93.

[00144] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a light chain complementarity-determining region 1 (LCDR1) according to an amino acid sequence selected from SEQ ID NO: 14 and SEQ ID NOs: 94-126.

[00145] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a light chain complementarity-determining region 2 (LCDR2) according to an amino acid sequence selected from SEQ ID NO: 15 and SEQ ID NOs: 127-158.

[00146] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises a light chain complementarity-determining region 3 (LCDR3) according to an amino acid sequence selected from SEQ ID NO: 16 and SEQ ID NOs: 159-185.

[00147] In some embodiments, the disclosure provides an isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises an HCDR1, an HCDR2, an HCDR3, an LCDR1, an LCDR2 and an LCDR3, wherein: a Petition 870250099897, dated 10 / 31 / 2025, page 49 / 177 / 140 HCDR1 comprises an amino acid sequence selected from SEQ ID NO: 11 and SEQ ID NOs: 22-32; HCDR2 comprises an amino acid sequence selected from SEQ ID NO: 12 and SEQ ID NOs: 33-65; HCDR3 comprises an amino acid sequence selected from SEQ ID NO: 13 and SEQ ID NOs: 66-93; LCDR1 comprises an amino acid sequence selected from SEQ ID NO: 14 and SEQ ID NOs: 94-126; LCDR2 comprises an amino acid sequence selected from SEQ ID NO: 15 and SEQ ID NOs: 127-158; and LCDR3 comprises an amino acid sequence selected from SEQ ID NO: 16 and SEQ ID NOs: 159-185.

[00148] Variable regions of certain FGF23-binding antibodies designed

[00149] Burosumab has a variable heavy chain (VH) region and a variable light chain (VL) region as follows: VH of amino acid sequence SEQ ID NO: 3, referred to herein as VH-001 and VL of amino acid sequence SEQ ID NO: 4, referred to herein as VL-001.

[00150] The FGF23-binding antibodies described herein may have one or more unique variable region domains relative to burosumab. That is, the FGF23-binding antibodies may have one or more amino acid changes relative to the VH and / or VL sequence of burosumab.

[00151] For example, the isolated antibody or fragment thereof may comprise a variable heavy chain (VH) region and a variable light chain (VL) region, wherein the VH comprises an amino acid sequence with at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or wherein the VL comprises an amino acid sequence with at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[00152] The isolated antibody or a fragment thereof may Petition 870250099897, dated 10 / 31 / 2025, page 50 / 177 / 140, comprise a VH comprising an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the antibody or fragment thereof may comprise a VL comprising an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[00153] The isolated antibody or fragment thereof may comprise a VH comprising an amino acid sequence having at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the antibody or fragment thereof may comprise a VL comprising an amino acid sequence having at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[00154] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence having at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL may comprise an amino acid sequence having at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[00155] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL may comprise an amino acid sequence having at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368. Petition 870250099897, dated 10 / 31 / 2025, p. 51 / 177 / 140

[00156] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence having at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL may comprise an amino acid sequence having at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[00157] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the VL may comprise an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[00158] The isolated antibody or fragment thereof may comprise a VH and a VL, wherein the VH may comprise an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL may comprise an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

[00159] Certain FGF23-binding antibodies designed with double amino acid modifications

[00160] The FGF23-binding antibodies described herein may have one or more amino acid changes relative to the native amino acid sequence of burosumab. For example, FGF23-binding antibodies may have at least two amino acid changes relative to burosumab. In some embodiments, FGF23-binding antibodies have: one amino acid change in the variable region of the heavy chain relative to burosumab and one amino acid change relative to the variable region of the light chain relative to burosumab; two amino acid changes relative to the variable region of the heavy chain relative to burosumab; or two amino acid changes relative to the variable region. Petition 870250099897, dated 10 / 31 / 2025, page 52 / 177 / 140 regarding the light chain in relation to burosumab.

[00161] For example, in some embodiments, the disclosure provides an isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof comprises an amino acid sequence of the variable heavy chain (VH) region according to SEQ ID NO: 3 and a variable light chain (VL) region according to SEQ ID NO: 4, but comprising at least two amino acid changes in the VH and amino acid sequences are VH:N31F / VH:S59F, VL:D50F / VH:V101I, VL:N92E / VL:D93F, VH:N31E / VH:S59E, VH:S59T / VH:V101L, VL:N92D / VL:D93F, VL:Y94D / VH:S59D, VL:N92Y / VH:S59E, VL:S52E / VH:S59E. Main Sequences VL, in which at least two changes are selected from VL:D50F / VL:S53E, VH:S59D / VH:V101I, VL:S31E / VL:S53E, VH:S57E / VH:S59D, VH:I54Y / VH:V101F, VH:N52F / VH:V101L, VL:Y94D / VH:S59E, VL:Y94E / VH:S59E, VL:S31E / VL:D50F, VL:S31F / VL:S52E, VL:S31F / VL:S53E, VL:S31F / VL:D50F, VH:N31E / VH:I54F, VH:N52F / VH:V101I, VL:S31F / VL:D50E, VL:N92F / VH:S59E, VL:S52D / VH:S59E and

[00162] The FGF23-binding antibodies designed herein may comprise a leader sequence at the N-terminal of the light chain and / or the N-terminal of the heavy chain. In some embodiments, the leader sequence is a self-cleaving leader sequence. In some embodiments, the leader sequence facilitates the expression, trafficking, stability, secretion, and / or purification of the heavy chain and / or light chain when expressed in a cell. In some embodiments, the leader sequence is a secretory signal to enhance the extracellular trafficking of the heavy chain and / or light chain.

[00163] In certain modalities, antibodies that bind to FGF23 Petition 870250099897, dated 10 / 31 / 2025, page 53 / 177 / 140, the designs described herein may comprise a leader sequence at the N-terminal of the heavy chain, wherein the leader sequence comprises the amino acid sequence MKWVTFISLLFLFSSAYS (SEQ ID NO: 369).

[00164] In certain embodiments, the FGF23-binding antibodies designed herein may comprise a leader sequence at the N-terminal of the light chain, wherein the leader sequence comprises the amino acid sequence MVSSAQFLGLLLLCFQGTRC (SEQ ID NO: 370). C-terminal lysine clipping

[00165] The burosumab heavy chain has a C-terminal lysine residue. C-terminal lysine residues of antibody heavy chains are known to be frequently cleaved during bioproduction by carboxypeptidases present in cell culture or cell culture media. This phenomenon can give rise to varying amounts of process-related charge variants and non-homogeneous antibody preparations, thus complicating efforts to manufacture homogeneous, safe, and effective batches of antibodies (see, for example, Faid et al., Eur J Pharm Sci., 2021 Apr 1:159:105730). Consequently, in some embodiments, the antibody variants described herein are modified to remove the C-terminal lysine residue from the heavy chain.That is, any heavy chain antibody sequence provided herein, including the parental burosumab heavy chain sequence (SEQ ID NO: 1), can be further modified to remove the C-terminal lysine residue (SEQ ID NO: 371). Thus, all variant heavy chain variable region (VH) sequences described in this application are contemplated for incorporation into full-length heavy chain sequences with or without the C-terminal lysine residue. IV. Pharmaceutical Formulations

[00166] The human FGF23-binding antibodies described herein can be supplied in pharmaceutical formulations. One formulation Petition 870250099897, dated 10 / 31 / 2025, page 54 / 177 / 140: Pharmaceuticals may be capable of local or systemic administration. In certain aspects, administration may be by any route, including intravenous, subcutaneous, pulmonary, intramuscular, intraperitoneal, dermal, oral, inhalation, or nasal administration.

[00167] A pharmaceutical formulation of this disclosure may include carriers, diluents, or excipients, as known in the art. Examples of pharmaceutical formulations and methods are described, for example, in Remington's Pharmaceutical Sciences, Mack Publishing Co. (AR Gennaro ed. 1985) and Remington, The Science and Practice of Pharmacy, 21st edition (2005).

[00168] Examples of excipients for a pharmaceutical formulation include antioxidants, suspending agents, dispersing agents, preservatives, buffering agents, tonicity agents, and surfactants.

[00169] In certain embodiments, the pharmaceutical formulations of this disclosure are solutions for subcutaneous injection comprising a human FGF23-binding antibody provided herein and one or more pharmaceutically acceptable excipients selected from L-histidine, D-sorbitol E420, Polysorbate 80, L-methionine, hydrochloric acid (for pH adjustment) and / or water. V. Management Methods

[00170] Burosumab is indicated for subcutaneous use only. In pediatric XLH patients 6 months of age or older, the initial dose regimen is 1 mg / kg of body weight, rounded to the nearest 1 mg, administered every two weeks (Q2W) for patients weighing less than 10 kg. For XLH patients 6 months of age or older and weighing 10 kg or more, the initial dose regimen is 0.8 mg / kg of body weight, rounded to the nearest 10 mg, administered every two weeks (Q2W). The minimum starting dose is 10 mg up to a maximum dose of 90 mg. The dose may be increased up to approximately 2 mg / kg (maximum 90 mg), administered at Petition 870250099897, dated 10 / 31 / 2025, page 55 / 177 / 140 every two weeks (Q2W) to achieve normal serum phosphorus. In adult patients with XLH, the dosage regimen is 1 mg / kg of body weight rounded to the nearest 10 mg up to a maximum dose of 90 mg administered every four weeks (Q4W). In pediatric patients with TIO aged 2 years or older, the initial dose is 0.4 mg / kg of body weight rounded to the nearest 10 mg every 2 weeks (Q2W). The dose may be increased up to 2 mg / kg, not exceeding 180 mg, administered every two weeks (Q2W). In adult patients with TIO, the initial dose is 0.5 mg / kg every four weeks (Q4W). The dose may be increased up to 2 mg / kg, not exceeding 180 mg, administered every two weeks (Q2W).

[00171] The antibodies in this disclosure can be administered in accordance with the indicated uses of burosumab.

[00172] In some embodiments, the antibodies or their pharmaceutical formulations of this disclosure may be administered at a therapeutically effective dose. A therapeutically effective dose may be an amount of an agent or formulation that is sufficient to cause a therapeutic effect in a subject to whom the therapeutically effective dose has been administered.

[00173] Therapeutically effective doses of human FGF23-binding antibodies provided herein, or pharmaceutical formulations thereof, decrease serum FGF23 in individuals; increase the maximum renal threshold for phosphate reabsorption (TmP) in individuals; increase serum inorganic phosphorus (Pi) in individuals; increase serum concentration of 1,25-dihydroxyvitamin D (1,25[OH]2D) in individuals; and / or are useful for treating hypophosphatemic conditions in individuals, including XLH or osteomalacia.

[00174] A therapeutically effective dose may be administered in one or more separate administrations and by different routes. As will be appreciated in the technique, a therapeutically effective dose or quantity Petition 870250099897, dated 10 / 31 / 2025, page 56 / 177 / 140. Therapeutically effective is largely determined based on the total amount of the therapeutic agent contained in the pharmaceutical formulation. Generally, a therapeutically effective amount is sufficient to achieve a significant benefit for the subject (e.g., to treat, modulate, cure, prevent, and / or improve conditions related to hypophosphatemia). For example, a therapeutically effective amount may be an amount sufficient to achieve a desired therapeutic and / or prophylactic effect. Generally, the amount of a therapeutic agent (e.g., disseminating antibodies or functionally active fragments thereof) administered to a subject in need thereof will depend on the subject's characteristics. These characteristics include the subject's condition, disease severity, general health, age, sex, and body weight.A person with average skill in the technique will be able to quickly determine the appropriate doses depending on these and other related factors. Furthermore, both objective and subjective assays can optionally be employed to identify ideal dosage ranges.

[00175] The methods provided herein contemplate single and multiple administrations of a therapeutically effective amount of the human FGF23-binding antibodies and their pharmaceutical formulations described herein. Pharmaceutical formulations comprising human FGF23-binding antibodies may be administered at regular intervals depending on the nature, severity, and extent of the subject's condition (e.g., the severity of a subject's disease state and associated symptoms of hypophosphatemia). In some embodiments, a therapeutically effective amount of the human FGF23-binding antibodies and their pharmaceutical formulations of this disclosure may be administered periodically at regular intervals (e.g., once a year, once every six months, once every four months, once every three months, once every two months, once a month), once every 4 months, once every six months, once every four months, once every three months, once every two months, once a month, once every four months, once every four months, once a month, once every four months, once every four months, once a month, once every four months, once every six months, once every four months, once a month, once every four months, once every six months, once every four months, once a month, once every four months, once every six months, once every four months, once a month, once every four months, once every six months, once every four months, once a month, once every four months, once every six months, once every six months, once every three months, once every three months, once a month, once every four months, once every three months, once every three months, once every three months, once every three months, once a month, once every four months, once every four months, once a month, once every four months, once every six ... three months, once every three months, once every three months, once every three months, once every three months, once a month, once every four months, once every three months, once every three months, Petition 870250099897, dated 10 / 31 / 2025, p. 57 / 177 / 140 weeks, once every 3 weeks, once every two weeks, weekly, daily, twice a day, three times a day, four times a day, five times a day, six times a day, or continuously. For example, a therapeutically effective amount of the human FGF23-binding antibodies and their pharmaceutical formulations of this disclosure may be administered weekly, once every two weeks, or monthly.

[00176] The administration of a therapeutically effective amount of human FGF23-binding antibodies or formulations thereof provided herein may comprise administration to the subject of between about 0.1 milligrams of antibody per kilogram (mg / kg) of the subject's body weight and about 100 mg / kg of the subject's body weight, between about 0.1 mg / kg and about 50 mg / kg, between about 0.1 mg / kg and about 20 mg / kg, between about 0.1 mg / kg and about 10 mg / kg, between about 0.1 mg / kg and about 1 mg / kg, about 0.1 mg / kg, about 0.2 mg / kg, about 0.3 mg / kg, about 0.4 mg / kg, about 0.5 mg / kg, about 0.6 mg / kg, about 0.7 mg / kg, about 0.8 mg / kg, about 0.9 mg / kg, about 1 mg / kg, about 1.1 mg / kg, about 1.2 mg / kg, about 1.3 mg / kg, about 1.4 mg / kg, about 1.5 mg / kg, about 1.6 mg / kg, about 1.7 mg / kg, about 1.8 mg / kg, about 1.9 mg / kg, about 2 mg / kg, about 2.1 mg / kg, about 2.2 mg / kg, about 2.3 mg / kg, about 2.4 mg / kg, about 2,5 mg / kg, about 2.6 mg / kg, about 2.7 mg / kg, about 2.8 mg / kg, about 2.9 mg / kg, about 3 mg / kg, about 3.1 mg / kg, about 3.2 mg / kg, about 3.3 mg / kg, about 3.4 mg / kg, about 3.5 mg / kg, about 3.6 mg / kg, about 3.7 mg / kg, about 3.8 mg / kg, about 3.9 mg / kg, about 4 mg / kg, about 4.1 mg / kg, about 4.2 mg / kg, about 4.3 mg / kg, about 4.4 mg / kg, about 4.5 mg / kg, about 4.6 mg / kg, about 4.7 mg / kg, about 4.8 mg / kg, about 4.9 mg / kg or about 5 mg / kg. In some modalities, the administration of a therapeutically effective amount of FGF23-binding antibodies, Petition 870250099897, dated 10 / 31 / 2025, page 58 / 177 / 140 human or its formulations provided herein may comprise the administration of less than 4 mg / kg, less than 3 mg / kg, less than 2 mg / kg or less than 1 mg / kg to the subject.

[00177] Throughout the description, where compositions are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that, additionally, there are compositions of this disclosure that consist essentially of, or consist of, the components mentioned, and that there are processes and methods according to this disclosure that consist essentially of, or consist of, the steps mentioned.

[00178] In the application, when an element or component is said to be included and / or selected from a list of cited elements or components, it will be understood that the element or component may be any of the cited elements or components, or the element or component may be selected from a group consisting of two or more of the cited elements or components.

[00179] Furthermore, it should be understood that elements and / or features of a composition or method described herein may be combined in various ways without departing from the spirit and scope of the present disclosure, whether explicitly or implicitly. For example, when reference is made to a specific compound, that compound may be used in various embodiments of compositions of the present disclosure and / or in methods of the present disclosure, unless the context indicates otherwise. In other words, in this application, the embodiments have been described and illustrated in a way that allows for a clear and concise application to be written and drawn, but it is intended and will be appreciated that the embodiments may be combined or separated in various ways without departing from the present teachings and disclosure(s). For example, it will be appreciated that all the Petition 870250099897, dated 10 / 31 / 2025, p. 59 / 177 / 140. The features described and depicted herein may be applicable to all aspects of the disclosure(s) described and depicted herein. All features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature that serves the same, equivalent, or similar purpose.

[00180] The expression “at least one of” shall be understood to include each of the objects mentioned after the expression and the various combinations of two or more of the objects mentioned, unless the context and usage indicate otherwise. The expression “and / or” in connection with three or more objects mentioned shall be understood to have the same meaning, unless the context indicates otherwise.

[00181] The use of the term “include”, “includes”, “including”, “have”, “has”, “having”, “contain”, “contains” or “containing”, including their grammatical equivalents, will generally be understood as open and non-limiting, for example, not excluding additional elements or steps not mentioned, unless specifically stated or otherwise understood from the context.

[00182] The use of any and all examples, or illustrative language herein, for example, “as an example,” “such as,” “for instance,” “e.g.,” or “including,” is intended only to better illustrate the present disclosure and does not represent a limitation on the scope of the disclosure unless claimed. No language in the descriptive report shall be construed as indicating any unclaimed element as essential to the practice of the subject matter of this disclosure.

[00183] It is understood that this disclosure is not limited to the specific methodology, protocols, materials, and reagents described, as these may vary. It should also be understood that the terminology used here is intended to describe only specific modalities and is not intended to limit them. Petition 870250099897, dated 10 / 31 / 2025, p. 60 / 177 / 140, the scope of this disclosure, which will be covered by the attached claims.

[00184] All publications, patents and patent applications, including any drawings, sequences and appendices mentioned therein throughout this description, are incorporated by reference in their entirety for all purposes, to the same extent as if each individual publication, patent or patent application, drawing, sequence or appendix were specifically and individually indicated to be incorporated by reference in its entirety for all purposes. EXAMPLES

[00185] The disclosure, now described in general terms, will be more easily understood by reference to the following examples included for the purpose of illustrating certain aspects and modalities of this disclosure, without limiting the disclosure. Example 1. Antibody Structural Numbering System (ASN#)

[00186] Several numbering schemes are used to describe antibody amino acid sequences, including linear numbering, Kabat numbering, Chothia numbering, and antibody structural numbering systems (ASN#). The antibody residues described here are presented according to the ASN# system and / or the linear numbering system. To facilitate conversion between these numbering schemes, Table 1 shows the amino acid sequence of the parent burosumab light chain with linear, Kabat, and ASN# systems, and Table 2 shows the amino acid sequence of the parent burosumab heavy chain with linear, Kabat, and ASN# systems. In Table 1 and Table 2, the “Residue” columns show the amino acid residue of the burosumab light chain sequence of SEQ ID NO: 2 and the burosumab heavy chain sequence of SEQ ID NO: 1, respectively. In the “Kabat #” columns, the designation “L” refers to the light chain and the designation “H” refers to the heavy chain. In the columns “ASN #”, “KV” Petition 870250099897, dated 10 / 31 / 2025, p. 61 / 177 / 140 refers to the variable region of the light chain, “KCnst-Ig” refers to the constant region of the light chain, “HV” refers to the variable region of the heavy chain, “HCnst-Ig” refers to the constant region of the heavy chain, “Fc-N” refers to the CH2 region of Fc, “Fc-C” refers to the CH3 region of Fc, “HCnst-Po” refers to residues potentially attributable to the constant region of the heavy chain, and “Hinge” refers to residues of the hinge region. Table 1. Conversion table for the numbering scheme of the amino acid sequence of the burosumab light chain. Linear Waste # Kabat # ASN # Linear Waste # Kabat # ASN # A 1 L1 KV:1 F 95 L96 KV:2 T 96 L97 KV:138 Q 3 L3 KV:3 F 97 L98 KV:139 L 4 L4 KV:4 G 98 L99 KV:140 T 5 L5 KV:5 P 99 L100 KV:141 Q 6 L6 KV:6 G 100 L101 KV:142 S 7 L7 KV:7 T 101 L102 KV:143 P 8 L8 KV:8 K 102 L103 KV:144 S 9 L9 KV:9 V 103 L104 KV:145 S 10 L10 KV:10 D 104 L105 KV:146 L 11 L11 KV:11 I 105 L106 KV:147 S 12 L12 KV:12 K 106 L107 KV:148 A 13 L13 KV:13 R 107 L108 KV:149 S 14 L14 KV:14 - 107.1 KCnst-Ig: 1 V 15 L15 KV:15 T 108 L109 KCnst-Ig:2 G 16 L16 KV:16 V 109 L110 KCnst-Ig:3 D 17 L17 KV:17 A 110 L111 KCnst-Ig:4 R 18 L18 KV:18 A 111 L112 KCnst-Ig:5 V 19 L19 KV:19 P 112 L113 KCnst-Ig:6 T 20 L20 KV:20 S 113 L114 KCnst-Ig:7 I 21 L21 KV:21 V 114 L115 KCnst-Ig:8 T 22 L22 KV:22 F 115 L116 KCnst-Ig:9 C 23 L23 KV:23 I 116 L117 KCnst-Ig:10 R 24 L24 KV:24 F 117 L118 KCnst-Ig:11 A 25 L25 KV:25 P 118 L119 KCnst-Ig:12 S 26 L26 KV:26 P 119 L120 KCnst-Ig:13 - 26.1 KV:27 S 120 L121 KCnst-Ig:14 - 26.1.2 KV:28 D 121 L122 KCnst-Ig:15, Petition 870250099897, dated 10 / 31 / 2025, p. 62 / 177 / 140 Q 27 L27 KV:29 E 122 L123 KCnst-Ig:16 G 28 L28 KV:30 - 122.1 KCnst-Ig:17 I 29 L29 KV:31 - 122.2 KCnst-Ig:18 S 30 L30 KV:32 Q 123 L124 KCnst-Ig:19 S 31 L31 KV:33 L 124 L125 KCnst-Ig:20 - 31.1 KV:34 - 124.1 KCnst-Ig:21 - 31.2 KV:35 - 124.2 KCnst-Ig:22 - 31.3 KV:36 K 125 L126 KCnst-Ig:23 - 31.4 KV:37 S 126 L127 KCnst-Ig:24 - 31.5 KV:38 G 127 L128 KCnst-Ig:25 - 31.6 KV:39 T 128 L129 KCnst-Ig:26 A 32 L32 KV:40 A 129 L130 KCnst-Ig:27 L 33 L33 KV:41 S 130 L131 KCnst-Ig:28 V 34 L34 KV:42 V 131 L132 KCnst-Ig:29 W 35 L35 KV:43 V 132 L133 KCnst-Ig:30 Y 36 L36 KV:44 C 133 L134 KCnst-Ig:31 Q 37 L37 KV:45 L 134 L135 KCnst-Ig:32 Q 38 L38 KV:46 L 135 L136 KCnst-Ig:33 K 39 L39 KV:47 N 136 L137 KCnst-Ig:34 P 40 L40 KV:48 N 137 L138 KCnst-Ig:35 G 41 L41 KV:49 F 138 L139 KCnst-Ig:36 K 42 L42 KV:50 Y 139 L140 KCnst-Ig:37 A 43 L43 KV:51 P 140 L141 KCnst-Ig:38 P 44 L44 KV:52 - 140.1 KCnst-Ig:39 K 45 L45 KV:53 - 140,2 KCnst-Ig:40 L 46 L46 KV:54 R 141 L142 KCnst-Ig:41 L 47 L47 KV:55 E 142 L143 KCnst-Ig:42 I 48 L48 KV:56 A 143 L144 KCnst-Ig:43 Y 49 L49 KV:57 K 144 L145 KCnst-Ig:44 D 50 L50 KV:58 V 145 L146 KCnst-Ig:45 - 50.1 KV:59 Q 146 L147 KCnst-Ig:46 - 50.2 KV:60 W 147 L148 KCnst-Ig:47 - 50.3 KV:61 - 147.1 KCnst-Ig:48 - 50.4 KV:62 K 148 L149 KCnst-Ig:49 - 50.5 KV:63 V 149 L150 KCnst-Ig:50 - 50.6 KV:64 D 150 L151 KCnst-Ig:51 - 50.7 KV:65 N 151 L152 KCnst-Ig:52 - 50.8 KV:66 A 152 L153 KCnst-Ig:53 A 51 L51 KV:67 L 153 L154 KCnst-Ig:54 S 52 L52 KV:68 Q 154 L155 KCnst-Ig:55 Petição 870250099897, on October 31, 2025, pág. 63 / 177 / 140 S 53 L53 KV:69 S 155 L156 KCnst-Ig:56 L 54 L54 KV:70 G 156 L157 KCnst-Ig:57 E 55 L55 KV:71 N 157 L158 KCnst-Ig:58 S 56 L56 KV:72 S 158 L159 KCnst-Ig:59 G 57 L57 KV:73 Q 159 L160 KCnst-Ig:60 V 58 L58 KV:74 E 160 L161 KCnst-Ig:61 P 59 L59 KV:75 S 161 L162 KCnst-Ig:62 S 60 L60 KV:76 V 162 L163 KCnst-Ig:63 R 61 L61 KV:77 T 163 L164 KCnst-Ig:64 F 62 L62 KV:78 E 164 L165 KCnst-Ig:65 S 63 L63 KV:79 Q 165 L166 KCnst-Ig:66 G 64 L64 KV:80 D 166 L167 KCnst-Ig:67 S 65 L65 KV:81 - 166.1 KCnst-Ig:68 G 66 L66 KV:82 - 166.2 KCnst-Ig:69 S 67 L67 KV:83 - 166.3 KCnst-Ig:70 G 68 L68 KV:84 - 166.4 KCnst-Ig:71 - 68.1 KV:85 S 167 L168 KCnst-Ig:72 - 68,2 KV:86 K 168 L169 KCnst-Ig:73 T 69 L69 KV:87 D 169 L170 KCnst-Ig:74 ​​D 70 L70 KV:88 S 170 L171 KCnst-Ig:75 F 71 L71 KV:89 T 171 L172 KCnst-Ig:76 T 72 L72 KV:90 Y 172 L173 KCnst-Ig:77 L 73 L73 KV:91 S 173 L174 KCnst-Ig:78 T 74 L74 KV:92 L 174 L175 KCnst-Ig:79 I 75 L75 KV:93 S 175 L176 KCnst-Ig:80 S 76 L76 KV:94 S 176 L177 KCnst-Ig:81 S 77 L77 KV:95 T 177 L178 KCnst-Ig:82 L 78 L78 KV:96 L 178 L179 KCnst-Ig:83 Q 79 L79 KV:97 T 179 L180 KCnst-Ig:84 P 80 L80 KV:98 L 180 L181 KCnst-Ig:85 E 81 L81 KV:99 S 181 L182 KCnst-Ig:86 D 82 L82 KV:100 K 182 L183 KCnst-Ig:87 F 83 L83 KV:101 A 183 L184 KCnst-Ig:88 A 84 L84 KV:102 D 184 L185 KCnst-Ig:89 T 85 L85 KV:103 Y 185 L186 KCnst-Ig:90 Y 86 L86 KV:104 - 185,1 KCnst-Ig:91 Y 87 L87 KV:105 E 186 L187 KCnst-Ig:92 C 88 L88 KV:106 K 187 L188 KCnst-Ig:93 Q 89 L89 KV:107 H 188 L189 KCnst-Ig:94 Q 90 L90 KV:108 K 189 L190 KCnst-Ig:95, Petição 870250099897, on October 31, 2025, pág. 64 / 177 / 140 F 91 L91 KV:109 V 190 L191 KCnst-Ig:96 N 92 L92 KV:110 - 190.1 KCnst-Ig:97 - 92.1 KV:111 - 190.2 KCnst-Ig:98 - 92.2 KV:112 Y 191 L192 KCnst-Ig:99 - 92.3 KV:113 A 192 L193 KCnstIg:100 - 92.4 KV:114 C 193 L194 KCnstIg:101 - 92.5 KV:115 E 194 L195 KCnstIg:102 - 92.6 KV:116 V 195 L196 KCnstIg:103 - 92.7 KV:117 T 196 L197 KCnstIg:104 - 92.8 KV:118 H 197 L198 KCnstIg:105 - 92.9 KV:119 Q 198 L199 KCnstIg:106 - 92.10 KV:120 G 199 L200 KCnstIg:107 - 92.11 KV:121 L 200 L201 KCnstIg:108 - 92.12 KV:122 S 201 L202 KCnstIg:109 - 92.13 KV:123 - 201.1 KCnstIg:110 - 92.14 KV:124 S 202 L203 KCnstIg:111 - 92.15 KV:125 P 203 L204 KCnstIg:112 - 92.16 KV:126 V 204 L205 KCnstIg:113 - 92.17 KV:127 T 205 L206 KCnstIg:114 - 92.18 KV:128 K 206 L207 KCnstIg:115 - 92.19 KV:129 S 207 L208 KCnstIg:116 - 92.20 KV:130 F 208 L209 KCnstIg:117 - 92.21 KV:131 N 209 L210 KCnstIg:118 - 92.22 KV:132 R 210 L211 KCnstIg:119 - 92.23 KV:133 G 211 L212 KCnstIg:120 - 92.24 KV:134 E 212 L213 KCnstIg:121 Petition 870250099897, dated 10 / 31 / 2025, p. 65 / 177 / 140 D 93 L93 KV:135 C 213 L214 KCnstIg:122 Y 94 L94 KV:136 - 213.1 KCnstIg:123 Table 2. Conversion table for the numbering scheme of the amino acid sequence of the burosumab heavy chain. Linear Residue # Kabat # ASN # Linear Residuo # Kabat # ASN # Q 1 H1 HV:1 T 225 H238 Hinge: 112 V 2 H2 HV:2 C 226 H239 Hinge: 113 Q 3 H3 HV:3 P 227 H2 40 HV: 14 Lça HV:4 P 228 H241 Hinge: 115 V 5 H5 HV:5 C 229 H242 Hinge: 116 Q 6 H6 HV:6 P 230 H243 Hinge: 117 S 7 H7 HV:7 A 231 H244 Hinge: 1183 HV: 283 HV: 127 H244 H245 Hinge: 119 G 8 H8 HV:9 E 233 H246 Hinge: 120 A 9 H9 HV:10 L 234 H247 Hinge:121 E 10 H10 HV:11 L 235 H248 Hinge: 122 V 12 HV: 121 H21 HV: Hinge:123 K 12 H12 HV:13 - 236.1 Fc-N:1 K 13 H13 HV:14 - 236.2 Fc-N:2 P 14 H14 HV:15 - 236.3 Fc-N:3 G 15 H15 HV:16 - 236.4 Fc-N: 16 A Hc: HV:17 G 237 H250 Fc-N:5 S 17 H17 HV:18 P 238 H251 Fc-N:6 V 18 H18 HV:19 S 239 H252 Fc-N:7 K 19 H19 HV:20 V 240 H253 Fc-N: 28 HV:20 HV:2 H254 Fc-N:9 S 21 H21 HV:22 L 242 H255 Fc-N:10 C 22 H22 HV:23 F 243 H256 Fc-N:11 K 23 H23 HV:24 P 244 H257 Fc-N:12 A 24: H24 HV:25 H25 HV Fc-N:13 S 25 H25 HV:26 - 245,1 Fc-N:14 G 26 H26 HV:27 K 246 H259 Fc-N:15 - 26,1 HV:28 P 247 H260 Fc-N:16 Y 27 H27 HV:29 K 248 H261 Fc-N:17 T 28 H28 HV:30 - 248,1 Fc-N:18 F 29 H29 HV:31 D 249 H262 Fc-N:19 T 30 H30 HV:32 T 250 H263 Fc-N:20 N 31 H31 HV:33 L 251 H264 Fc-N:21, Petição 870250099897, de 31 / 10 / 2025, pág. 66 / 177 / 140 - 31,1 HV:34 M 252 H265 Fc-N:22 - 31,2 HV:35 I 253 H266 Fc-N:23 - 31,3 HV:36 S 254 H267 Fc-N:24 - 31,4 HV:37 R 255 H268 Fc-N:25 - 31,5 HV:38 T 256 H269 Fc-N:26 H 32 H32 HV:39 P 257 H270 Fc-N:27 Y 33 H33 HV:40 E 258 H271 Fc-N:28 M 34 H34 HV:41 V 259 H272 Fc-N:29 H 35 H35 HV:42 T 260 H273 Fc-N:30 W 36 H36 HV:43 C 261 H274 Fc-N:31 V 37 H37 HV:44 V 262 H275 Fc-N:32 R 38 H38 HV:45 V 263 H276 Fc-N:33 Q 39 H39 HV:46 V 264 H277 Fc-N:34 A 40 H40 HV:47 D 265 H278 Fc-N:35 P 41 H41 HV:48 V 266 H279 Fc-N:36 G 42 H42 HV:49 S 267 H280 Fc-N:37 Q 43 H43 HV:50 H 268 H281 Fc-N:38 G 44 H44 HV:51 E 269 H282 Fc-N:39 L 45 H45 HV:52 D 270 H283 Fc-N:40 E 46 H46 HV:53 P 271 H284 Fc-N:41 W 47 H47 HV:54 E 272 H285 Fc-N:42 M 48 H48 HV:55 V 273 H286 Fc-N:43 G 49 H49 HV:56 K 274 H287 Fc-N:44 I 50 H50 HV:57 F 275 H288 Fc-N:45 I 51 H51 HV:58 N 276 H289 Fc-N:46 N 52 H52 HV:59 W 277 H290 Fc-N:47 P 53 H52A HV:60 - 277,1 Fc-N:48 - 53,1 HV:61 Y 278 H291 Fc-N:49 - 53,2 HV:62 V 279 H292 Fc-N:50 - 53,3 HV:63 D 280 H295 Fc-N:51 I 54 H53 HV:64 G 281 H296 Fc-N:52 S 55 H54 HV:65 V 282 H299 Fc-N:53 G 56 H55 HV:66 E 283 H300 Fc-N:54 S 57 H56 HV:67 - 283,1 Fc-N:55 T 58 H57 HV:68 - 283,2 Fc-N:56 S 59 H58 HV:69 V 284 H301 Fc-N:57 N 60 H59 HV:70 H 285 H302 Fc-N:58 A 61 H60 HV:71 N 286 H303 Fc-N:59 Q 62 H61 HV:72 A 287 H304 Fc-N:60 K 63 H62 HV:73 K 288 H305 Fc-N:61, Petição 870250099897, de 31 / 10 / 2025, pág. 67 / 177 / 140 F 64 H63 HV:74 T 289 H306 Fc-N:62 Q 65 H64 HV:75 K 290 H307 Fc-N:63 G 66 H65 HV:76 P 291 H308 Fc-N:64 R 67 H66 HV:77 R 292 H309 Fc-N:65 V 68 H67 HV:78 E 293 H310 Fc-N:66 T 69 H68 HV:79 E 294 H311 Fc-N:67 M 70 H69 HV:80 Q 295 H312 Fc-N:68 T 71 H70 HV:81 - 295,1 Fc-N:69 R 72 H71 HV:82 - 295,2 Fc-N:70 D 73 H72 HV:83 - 295,3 Fc-N:71 T 74 H73 HV:84 - 295,4 Fc-N:72 S 75 H74 HV:85 Y 296 H313 Fc-N:73 T 76 H75 HV:86 N 297 H314 Fc-N:74 S 77 H76 HV:87 S 298 H317 Fc-N:75 T 78 H77 HV:88 T 299 H318 Fc-N:76 V 79 H78 HV:89 Y 300 H319 Fc-N:77 Y 80 H79 HV:90 R 301 H320 Fc-N:78 M 81 H80 HV:91 V 302 H321 Fc-N:79 E 82 H81 HV:92 V 303 H322 Fc-N:80 L 83 H82 HV:93 S 304 H323 Fc-N:81 S 84 H82A HV:94 V 305 H324 Fc-N:82 S 85 H82B HV:95 L 306 H325 Fc-N:83 L 86 H82C HV:96 T 307 H326 Fc-N:84 R 87 H83 HV:97 V 308 H327 Fc-N:85 S 88 H84 HV:98 L 309 H328 Fc-N:86 E 89 H85 HV:99 H 310 H329 Fc-N:87 D 90 H86 HV:100 Q 311 H330 Fc-N:88 T 91 H87 HV:101 D 312 H331 Fc-N:89 A 92 H88 HV:102 W 313 H332 Fc-N:90 V 93 H89 HV:103 - 313,1 Fc-N:91 Y 94 H90 HV:104 L 314 H333 Fc-N:92 Y 95 H91 HV:105 N 315 H334 Fc-N:93 C 96 H92 HV:106 G 316 H335 Fc-N:94 A 97 H93 HV:107 K 317 H336 Fc-N:95 R 98 H94 HV:108 E 318 H337 Fc-N:96 D 99 H95 HV:109 - 318,1 Fc-N:97 I 100 H96 HV:110 - 318,2 Fc-N:98 V 101 H97 HV:111 Y 319 H338 Fc-N:99 - 101,1 HV:112 K 320 H339 Fc-N:100 - 101,2 HV:113 C 321 H340 Fc-N:101, Petition 870250099897, dated 10 / 31 / 2025, p. 68 / 177 / 140 - 101,3 HV:114 K 322 H341 Fc-N:102 - 101,4 HV:115 V 323 H342 Fc-N:103 - 101,5 HV:116 S 324 H343 Fc-N:104 - 101,6 HV:117 N 325 H344 Fc-N:105 - 101,7 HV:118 K 326 H345 Fc-N:106 - 101,8 HV:119 A 327 H346 Fc-N:107 - 101,9 HV:120 L 328 H347 Fc-N:108 - 101,10 HV:121 P 329 H348 Fc-N:109 - 101,11 HV:122 - 329,1 Fc-N:110 - 101,12 HV:123 - 329,2 Fc-N:111 - 101,13 HV:124 A 330 H349 Fc-N:112 - 101,14 HV:125 P 331 H350 Fc-N:113 - 101,15 HV:126 I 332 H351 Fc-N:114 - 101,16 HV:127 E 333 H352 Fc-N:115 - 101,17 HV:128 K 334 H353 Fc-N:116 - 101,18 HV:129 T 335 H354 Fc-N:117 - 101,19 HV:130 I 336 H355 Fc-N:118 - 101,20 HV:131 S 337 H357 Fc-N:119 - 101,21 HV:132 K 338 H358 Fc-N:120 - 101,22 HV:133 A 339 H359 Fc-N:121 D 102 H98 HV:134 K 340 H360 Fc-N:122 A 103 H99 HV:135 G 341 H361 Fc-N:123 F 104 H100 HV:136 - 341,1 Fc-C:1 D 105 H101 HV:137 Q 342 H363 Fc-C:2 F 106 H102 HV:138 P 343 H364 Fc-C:3 W 107 H103 HV:139 R 344 H365 Fc-C:4 G 108 H104 HV:140 E 345 H366 Fc-C:5 Q 109 H105 HV:141 P 346 H367 Fc-C:6 G 110 H106 HV:142 Q 347 H368 Fc-C:7 T 111 H107 HV:143 V 348 H369 Fc-C:8 M 112 H108 HV:144 Y 349 H370 Fc-C:9 V 113 H109 HV:145 T 350 H371 Fc-C:10 T 114 H110 HV:146 L 351 H372 Fc-C:11 V 115 H111 HV:147 P 352 H373 Fc-C:12 S 116 H112 HV:148 P 353 H374 Fc-C:13 S 117 H113 HV:149 - 353,1 Fc-C:14 - 117,1 HCnst-Ig: 1 S 354 H375 Fc-C:15 - 117,2 HCnst-Ig:2 R 355 H376 Fc-C:16 A 118 H114 HCnst-Ig:3 D 356 H377 Fc-C:17 S 119 H115 HCnst-Ig:4 - 356,1 Fc-C:18, Petição 870250099897, de 31 / 10 / 2025, pág. 69 / 177 / 140 T 120 H116 HCnst-Ig:5 E 357 H378 Fc-C:19 K 121 H117 HCnst-Ig:6 L 358 H381 Fc-C:20 G 122 H118 HCnst-Ig:7 - 358.1 Fc-C:21 P 123 H119 HCnst-Ig:8 - 358.2 Fc-C:22 S 124 H120 HCnst-Ig:9 T ​​359 H382 Fc-C:23 V 125 H121 HCnst-Ig:10 K 360 H383 Fc-C:24 F 126 H122 HCnst-Ig:11 N 361 H384 Fc-C:25 P 127 H123 HCnst-Ig:12 Q 362 H385 Fc-C:26 L 128 H124 HCnst-Ig:13 V 363 H386 Fc-C:27 A 129 H125 HCnst-Ig:14 S 364 H387 Fc-C:28 P 130 H126 HCnst-Ig:15 L 365 H388 Fc-C:29 - 130.1 HCnst-Ig:16 T 366 H389 Fc-C:30 S 131 H127 HCnst-Ig:17 C 367 H390 Fc-C:31 - 131.1 HCnst-Ig:18 L 368 H391 Fc-C:32 S 132 H128 HCnst-Ig:19 V 369 H392 Fc-C:33 K 133 H129 HCnst-Ig:20 K 370 H393 Fc-C:34 S 134 H130 HCnst-Ig:21 G 371 H394 Fc-C:35 T 135 H133 HCnst-Ig:22 F 372 H395 Fc-C:36 S 136 H134 HCnst-Ig:23 Y 373 H396 Fc-C:37 G 137 H135 HCnst-Ig:24 P 374 H397 Fc-C:38 G 138 H136 HCnst-Ig:25 - 374,1 Fc-C:39 T 139 H137 HCnst-Ig:26 - 374,2 Fc-C:40 A 140 H138 HCnst-Ig:27 S 375 H398 Fc-C:41 A 141 H139 HCnst-Ig:28 D 376 H399 Fc-C:42 L 142 H140 HCnst-Ig:29 I 377 H400 Fc-C:43 G 143 H141 HCnst-Ig:30 A 378 H401 Fc-C:44 C 144 H142 HCnst-Ig:31 V 379 H402 Fc-C:45 L 145 H143 HCnst-Ig:32 E 380 H405 Fc-C:46 V 146 H144 HCnst-Ig:33 W 381 H406 Fc-C:47 K 147 H145 HCnst-Ig:34 - 381.1 Fc-C:48 D 148 H146 HCnst-Ig:35 E 382 H407 Fc-C:49 Y 149 H147 HCnst-Ig:36 S 383 H408 Fc-C:50 F 150 H148 HCnst-Ig:37 N 384 H410 Fc-C:51 P 151 H149 HCnst-Ig:38 G 385 H411 Fc-C:52 - 151.1 HCnst-Ig:39 Q 386 H414 Fc-C:53 - 151.2 HCnst-Ig:40 P 387 H415 Fc-C:54 E 152 H150 HCnst-Ig:41 - 387.1 Fc-C:55 P 153 H151 HCnst-Ig:42 - 387.2 Fc-C:56 V 154 H152 HCnst-Ig:43 E 388 H416 Fc-C:57 T 155 H153 HCnst-Ig:44 N 389 H417 Fc-C:58, Petition 870250099897, de 31 / 10 / 2025, pag. 70 / 177 / 140 V 156 H154 HCnst-Ig:45 N 390 H418 Fc-C:59 S 157 H156 HCnst-Ig:46 Y 391 H419 Fc-C:60 W 158 H157 HCnst-Ig:47 K 392 H420 Fc-C:61 - 158.1 HCnst-Ig:48 T 393 H421 Fc-C:62 N 159 H162 HCnst-Ig:49 T 394 H422 Fc-C:63 S 160 H163 HCnst-Ig:50 P 395 H423 Fc-C:64 G 161 H164 HCnst-Ig:51 P 396 H424 Fc-C:65 A 162 H165 HCnst-Ig:52 V 397 H425 Fc-C:66 L 163 H166 HCnst-Ig:53 L 398 H426 Fc-C:67 T 164 H167 HCnst-Ig:54 D 399 H427 Fc-C:68 S 165 H168 HCnst-Ig:55 - 399.1 Fc-C:69 G 166 H169 HCnst-Ig:56 - 399.2 Fc-C:70 V 167 H171 HCnst-Ig:57 - 399.3 Fc-C:71 H 168 H172 HCnst-Ig:58 - 399.4 Fc-C:72 T 169 H173 HCnst-Ig:59 S 400 H428 Fc-C:73 - 169.1 HCnst-Ig:60 D 401 H430 Fc-C:74 - 169.2 HCnst-Ig:61 G 402 H433 Fc-C:75 - 169.3 H174 HCnst-Ig:62 S 403 H434 Fc-C:76 F 170 H175 HCnst-Ig:63 F 404 H435 Fc-C:77 P 171 H176 HCnst-Ig:64 F 405 H436 Fc-C:78 A 172 H177 HCnst-Ig:65 L 406 H437 Fc-C:79 V 173 H178 HCnst-Ig:66 Y 407 H438 Fc-C:80 L 174 H179 HCnst-Ig:67 S 408 H439 Fc-C:81 Q 175 HCnst-Ig:68 K 409 H440 Fc-C:82 - 175,1 HCnst-Ig:69 L 410 H441 Fc-C:83 - 175.2 HCnst-Ig:70 T 411 H442 Fc-C:84 - 175.3 HCnst-Ig:71 V 412 H443 Fc-C:85 - 175.4 HCnst-Ig:72 D 413 H444 Fc-C:86 S 176 H180 HCnst-Ig:73 K 414 H445 Fc-C:87 S 177 H182 HCnst-Ig:74 ​​S 415 H446 Fc-C:88 G 178 H183 HCnst-Ig:75 R 416 H447 Fc-C:89 L 179 H184 HCnst-Ig:76 W 417 H448 Fc-C:90 Y 180 H185 HCnst-Ig:77 - 417.1 Fc-C:91 S 181 H186 HCnst-Ig:78 Q 418 H449 Fc-C:92 L 182 H187 HCnst-Ig:79 Q 419 H450 Fc-C:93 S 183 H188 HCnst-Ig:80 G 420 H451 Fc-C:94 S 184 H189 HCnst-Ig:81 N 421 H452 Fc-C:95 V 185 H190 HCnst-Ig:82 V 422 H453 Fc-C:96 V 186 H191 HCnst-Ig:83 - 422.1 Fc-C:97 T 187 H192 HCnst-Ig:84 - 422.2 Fc-C:98, Petition 870250099897, de 31 / 10 / 2025, pag. 71 / 177 / 140 V 188 H193 HCnst-Ig:85 F 423 H454 Fc-C:99 P 189 H194 HCnst-Ig:86 S 424 H455 Fc-C:100 S 190 H195 HCnst-Ig:87 C 425 H456 Fc-C:101 S 191 H196 HCnst-Ig:88 S 426 H457 Fc-C:102 S 192 H197 HCnst-Ig:89 V 427 H458 Fc-C:103 L 193 H198 HCnst-Ig:90 M 428 H459 Fc-C:104 - 193.1 HCnst-Ig:91 H 429 H460 Fc-C:105 G 194 H199 HCnst-Ig:92 E 430 H461 Fc-C:106 T 195 H200 HCnst-Ig:93 A 431 H462 Fc-C:107 Q 196 H203 HCnst-Ig:94 L 432 H463 Fc-C:108 T 197 H205 HCnst-Ig:95 H 433 H464 Fc-C:109 - 197.1 HCnst-Ig:96 - 433.1 Fc-C:110 - 197.2 HCnst-Ig:97 - 433.2 Fc-C:111 - 197.3 HCnst-Ig:98 N 434 H465 Fc-C:112 Y 198 H206 HCnst-Ig:99 H 435 H466 Fc-C:113 I 199 H207 HCnst-Ig:100 Y 436 H467 Fc-C:114 C 200 H208 HCnst-Ig:101 T 437 H468 Fc-C:115 N 201 H209 HCnst-Ig:102 - 437,1 Fc-C:116 V 202 H210 HCnst-Ig:103 Q 438 H469 Fc-C:117 N 203 H211 HCnst-Ig:104 K 439 H470 Fc-C:118 H 204 H212 HCnst-Ig:105 S 440 H471 Fc-C:119 K 205 H213 HCnst-Ig:106 L 441 H472 Fc-C:120 P 206 H214 HCnst-Ig:107 S 442 H473 Fc-C:121 S 207 H215 HCnst-Ig:108 L 443 H474 Fc-C:122 N 208 H216 HCnst-Ig:109 S 444 H475 Fc-C:123 - 208.1 HCnst-Ig:110 P 445 H476 HCnst-Po:1 - 208.2 HCnst-Ig:111 G 446 H477 HCnst-Po:2 T 209 H217 HCnst-Ig:112 K 447 H478 HCnst-Po:3 K 210 H218 HCnst-Ig:113 - 447.1 HCnst-Po:4 V 211 H219 HCnst-Ig:114 - 447.2 HCnst-Po:5 D 212 H220 HCnst-Ig:115 - 447.3 HCnst-Po:6 K 213 H221 HCnst-Ig:116 - 447.4 HCnst-Po:7 - 213.1 HCnst-Ig:117 - 447.5 HCnst-Po:8 K 214 H222 HCnst-Ig:118 - 447.6 HCnst-Po:9 V 215 H223 HCnst-Ig:119 - 447.7 HCnst-Po:10 - 215.1 HCnst-Ig:120 - 447.8 HCnst-Po:11 - 215.2 HCnst-Ig:121 - 447.9 HCnst-Po:12 - 215.3 HCnst-Ig:122 - 447.10 HCnst-Po:13 - 215.4 HCnst-Ig:123 - 447.11 HCnst-Po:14 - 215.5 Dobradiça: 1 - 447.12 HCnst-Mon:15, Petition 870250099897, dated 10 / 31 / 2025, p. 72 / 177 / 140 - 215.6 Hinge:2 - 447.13 HCnst-Po:16 - 215.7 Hinge:3 - 447.14 HCnst-Po:17 - 215.8 Hinge:4 - 447.15 HCnst-Po:18 - 215.9 Hinge: 5 - 447.16 HCnst-Po:19 - 215.10 Hinge: 6 - 447.17 HCnst-Po:20 - 215.11 Hinge:7 - 447.18 HCnst-Po:21 - 215.12 Hinge:8 - 447.19 HCnst-Po:22 - 215.13 Hinge:9 - 447.20 HCnst-Po:23 - 215.14 Hinge: 10 - 447.21 HCnst-Po:24 - 215.15 Hinge: 11 - 447.22 HCnst-Po:25 - 215.16 Hinge: 12 - 447.23 HCnst-Po:26 - 215.17 Hinge:13 - 447.24 HCnst-Po:27 - 215.18 Hinge: 14 - 447.25 HCnst-Po:28 - 215.19 Hinge: 15 - 447.26 HCnst-Po:29 - 215.20 Hinge: 16 - 447.27 HCnst-Po:30 - 215.21 Hinge: 17 - 447.28 HCnst-Po:31 - 215.22 Hinge:18 - 447.29 HCnst-Po:32 - 215.23 Hinge:19 - 447.30 HCnst-Po:33 - 215.24 Hinge: 20 - 447.31 HCnst-Po:34 - 215.25 Hinge:21 - 447.32 HCnst-Po:35 - 215.26 Hinge: 22 - 447.33 HCnst-Po:36 - 215.27 Hinge:23 - 447.34 HCnst-Po:37 - 215.28 Hinge: 24 - 447.35 HCnst-Po:38 - 215,29 Hinge: 25 - 447.36 HCnst-Po:39 - 215.30 Hinge: 26 - 447.37 HCnst-Po:40 - 215.31 Hinge:27 - 447.38 HCnst-Po:41 - 215.32 Hinge: 28 - 447.39 HCnst-Po:42 - 215.33 Hinge:29 - 447.40 HCnst-Po:43 - 215.34 Hinge:30 - 447.41 HCnst-Po:44 - 215.35 Hinge:31 - 447.42 HCnst-Po:45 - 215.36 Hinge:32 - 447.43 HCnst-Po:46 - 215.37 Hinge:33 - 447.44 HCnst-Po:47 - 215.38 Hinge:34 - 447.45 HCnst-Po:48 - 215.39 Hinge:35 - 447.46 HCnst-Po:49 - 215.40 Hinge:36 - 447.47 HCnst-Po:50 - 215.41 Hinge:37 - 447.48 HCnst-Po:51 - 215.42 Hinge:38 - 447.49 HCnst-Po:52 - 215.43 Hinge:39 - 447.50 HCnst-Po:53 - 215.44 Hinge: 40 - 447.51 HCnst-Po: 54 - 215.45 Hinge: 41 - 447.52 HCnst-Po: 55, Petition 870250099897, dated 10 / 31 / 2025, page 73 / 177 / 140 - 215.46 Hinge:42 - 447.53 HCnst-Po:56 - 215.47 Hinge:43 - 447.54 HCnst-Po:57 - 215.48 Hinge:44 - 447.55 HCnst-Po:58 - 215.49 Hinge:45 - 447.56 HCnst-Po:59 - 215.50 Hinge:46 - 447.57 HCnst-Po:60 - 215.51 Hinge:47 - 447.58 HCnst-Po:61 - 215.52 Hinge:48 - 447.59 HCnst-Po:62 - 215.53 Hinge:49 - 447.60 HCnst-Po:63 - 215.54 Hinge: 50 - 447.61 HCnst-Po:64 - 215.55 Hinge: 51 - 447.62 HCnst-Po:65 - 215.56 Hinge: 52 - 447.63 HCnst-Po:66 - 215.57 Hinge: 53 - 447.64 HCnst-Po:67 - 215.58 Hinge: 54 - 447.65 HCnst-Po:68 - 215.59 Hinge: 55 - 447.66 HCnst-Po:69 - 215.60 Hinge: 56 - 447.67 HCnst-Po:70 - 215.61 Hinge: 57 - 447.68 HCnst-Po:71 - 215.62 Hinge: 58 - 447.69 HCnst-Po:72 - 215.63 Hinge: 59 - 447.70 HCnst-Po:73 - 215.64 Hinge: 60 - 447.71 HCnst-Po:74 - 215.65 Hinge:61 - 447.72 HCnst-Po:75 - 215.66 Hinge:62 - 447.73 HCnst-Po:76 - 215.67 Hinge:63 - 447.74 HCnst-Po:77 - 215.68 Hinge: 64 - 44775 HCnst-Po:78 - 215.69 Hinge: 65 - 447.76 HCnst-Po:79 - 215.70 Hinge:66 - 447.77 HCnst-Po:80 - 215.71 Hinge:67 - 447.78 HCnst-Po:81 - 215.72 Hinge:68 - 447.79 HCnst-Po:82 - 215.73 Hinge:69 - 447.80 HCnst-Po:83 - 215.74 Hinge:70 - 447.81 HCnst-Po:84 - 215.75 Hinge:71 - 447.82 HCnst-Po:85 - 215.76 Hinge: 72 - 447.83 HCnst-Po: 86 - 215.77 Hinge: 73 - 447.84 HCnst-Po: 87 - 215.78 Hinge: 74 - 447.85 HCnst-Po: 88 - 215.79 Hinge: 75 - 447.86 HCnst-Po: 89 - 215.80 Hinge: 76 - 447.87 HCnst-Po: 90 - 215.81 Hinge: 77 - 447.88 HCnst-Po: 91 - 215.82 Hinge: 78 - 447.89 HCnst-Po: 92 - 215.83 Hinge: 79 - 447.90 HCnst-Po:93 - 215.84 Hinge:80 - 447.91 HCnst-Po:94 - 215.85 Hinge:81 - 447.92 HCnst-Po:95, Petition 870250099897, dated 10 / 31 / 2025, page 74 / 177 / 140 - 215.86 Hinge:82 - 447.93 HCnst-Po:96 - 215.87 Hinge:83 - 447.94 HCnst-Po:97 - 215.88 Hinge:84 - 447.95 HCnst-Po:98 - 215.89 Hinge:85 - 447.96 HCnst-Po:99 - 215.90 Hinge:86 - 447.97 HCnst-Po:100 - 215.91 Hinge:87 - 447.98 HCnst-Po:101 - 215.92 Hinge:88 - 447.99 HCnst-Po:102 - 215.93 Hinge:89 - 447,100 HCnst-Po:103 - 215,94 Hinge:90 - 447,101 HCnst-Po:104 - 215,95 Hinge:91 - 447,102 HCnst-Po:105 - 215,96 Hinge:92 - 447,103 HCnst-Po:106 - 215,97 Hinge:93 - 447,104 HCnst-Po:107 - 215,98 Hinge:94 - 447,105 HCnst-Po:108 - 215,99 Hinge:95 - 447,106 HCnst-Po:109 E 216 H226 Hinge:96 - 447,107 HCnst-Po:110 P 217 H227 Hinge:97 - 447,108 HCnst-Po:111 K 218 H228 Hinge:98 - 447,109 HCnst-Po:112 S 219 H232 Hinge:99 - 447,110 HCnst-Po:113 - 219,1 Hinge: 100 - 447,111 HCnst-Po:114 - 219,2 Hinge:101 - 447,112 HCnst-Po:115 - 219,3 Hinge: 102 - 447,113 HCnst-Po:116 - 219,4 Hinge:103 - 447,114 HConst-Po:117 - 219,5 Hinge: 104 - 447,115 HCnst-Po:118 - 219,6 Hinge:105 - 447,116 HCnst-Po:119 - 219,7 Hinge: 106 - 447,117 HCnst-Po:120 C 220 H233 Hinge: 107 - 447,118 HCnst-Po:121 D 221 H234 Hinge:108 - 447,119 HCnst-Po:122 K 222 H235 Hinge:109 - 447,120 HCnst-Po:123 T 223 H236 Hinge: 110 H 224 H237 Hinge: 111, Example 2: Mapping of human burosumab-FGF23 epitopes

[00187] Hydrogen-deuterium exchange mass spectrometry (HDX-MS) measures the solvent exchange rate, that is, the phenomenon by which atoms that make up the solvent with a heavier hydrogen isotope are exchanged for protein atoms within the amide bonds of the main structure. This approach allows determining the solvent absorption by proteins by exposing the proteins to a deuterated solvent for a period of time. Petition 870250099897, dated 10 / 31 / 2025, page 75 / 177 / 140, defined, extinguishing the solvent exchange reaction and then measuring the increase in protein mass by mass spectrometry. Typically, a ligand binding event results in a localized reduction in deuteration uptake at the ligand interaction site, allowing approximate mapping of regions involved, for example, in antibody / target epitope and paratope interactions.

[00188] In an attempt to map burosumab epitopes to human FGF23, HDX-MS was performed using FGF23 (R179Q) produced in HEK293S cells. Burosumab was produced in CHO cells (while FGF23-binding antibodies designed in later examples were expressed in HEK293S cells). Antigen-antibody complexes were formed by combining burosumab and FGF23 (R179Q) in solution and then diluted 1:10 in ice-cold deuterated assay buffer for 60 seconds, 600 seconds, 1800 seconds, or 3600 seconds. Briefly, the HDX-MS assay used PBS at pH 7.4 as assay buffer. Extinguishing buffer with 1 M glycine, 4 M guanidine HCl, and 400 mM TCEP at pH 2.5 was used. 100 pmol were injected in duplicate in a 1:1 ratio of assay buffer to quenching buffer. The antigen concentration during labeling was 1.5 μM and the antibody concentration during labeling was 1 μM.The deuteration reaction was quenched using a 1:1 addition of quenching buffer (pH 2.5), and the solution was subsequently loaded onto a liquid chromatography (LC) column for in-column proteolytic digestion, followed by LC separation and mass spectrometry.

[00189] The HDX-MS results are shown in Figure 1. The geometric y-axis shows the % deuteration (% D), that is, the peptide length-normalized difference in deuteration between unbound FGF23 and antibody-bound FGF23. Values ​​less than zero (0) reflect decreased deuteration, i.e., protection against the deuteration reaction by antibody-antigen binding. Values ​​greater than zero (0) reflect Petition 870250099897, dated 10 / 31 / 2025, page 76 / 177 / 140 increased deuteration, i.e., exposure to the deuteration reaction. The geometric x-axis shows FGF23 amino acid residues 1-251. The colored horizontal bars represent the deuterium labeling time point for each identified peptide (black = 60 s, blue = 600 s, orange = 1800 s, magenta = 3600 s). The C-terminal region of FGF23 is not represented due to lack of sequence coverage for the region comprising approximately amino acid residues 158 to 251. Endogenous glycosylation in this region of the protein is believed to prevent accurate measurement of deuterium exchange in the present assay. Repeated samples after enzymatic deglycosylation of FGF23 support this hypothesis (data not shown).Overall, three regions of strong protection (red boxes) were identified where the % of deuteration was low and / or the labeling time points were relatively short (protected region 1, protected region 2, and protected region 3). Protected region 1 (Y43 to Y70) had the weakest protection of the three strong protection regions. Protected region 2 (A80 to R92) had stronger protection than protected region 1. Protected region 3 (L135 to F157) had the strongest protection of the three.

[00190] Based on HDX-MS data, protected regions 1-3 in FGF23 were hypothesized to be involved in antibody binding or to be protected due to conformational change in the presence of antibodies.

[00191] These three protected regions were mapped to an FGF23 (R179Q) crystal structure (the “2P39” structure; see Goetz et al. “Molecular insights into the klotho-dependent, endocrine mode of action of fibroblast growth factor 19 subfamily members” Mol Cell Biol (2007) 27 p.3417-28) to visualize regions with probable antibody binding interaction. Figure 2 shows the 23P9 crystal structure of FGF23 with protected regions defined according to the HDX-MS analysis results: amino acids ~43 to ~70 (protected region 1) in purple, amino acids ~80 to ~92 Petition 870250099897, dated 10 / 31 / 2025, page 77 / 177 / 140 (protected region 2) in green and amino acids ~135 to ~157 (protected region 3) in red.

[00192] In summary, HDX-MS identified three FGF23 (R179Q) regions that are protected in the presence of burosumab, shown in Table 3: Table 3. Protected regions of FGF23 by HDX-MS FGF23 (R179Q) Amino acid position (relative to SEQ ID NO: 17 or 18) Amino acid sequence Amino acid sequence SEQ ID NO Protected region 1 43-70 YTATARNSYHLQIHKNGHVDGAPHQTIY 19 Protected region 2 80-92 AGFVVITGVMSRR 20 Protected region 3 135-157 LVSLGRAKRAFLPGMNPPPYSQF 21

[00193] HDX-MS data suggest that the strongest protected regions (2 and 3) represent a possible burosumab epitope in the vicinity of FGF23 residues 82 to 90 and 136 to 140 (R179Q). In protected region 3, residues L135, V136, S137, L138, G139, R140 and A141 represent the strongest protected area and therefore may be among the most important residues involved in the FGF23-burosumab interaction.

[00194] Comparing these findings with previous efforts to map burosumab epitopes in human FGF23, it was observed that protected region 1 encompasses residues of FN1 epitope 1 and FN1 epitope 2 identified by Yamazaki et al. Anti-FGF23 neutralizing antibodies show the physiological role and structural features of FGF23. Journal of Bone and Mineral Research 23.9 (2008): 1509-1518. However, FN1 epitope 3 and FN1 epitope 4 lie outside protected regions 1, protected region 2, and protected region 3 identified in the present study, suggesting that the FN1 antibody previously characterized by Yamazaki et al. recognizes a different face in FGF23 compared to burosumab. Furthermore, Kanhasut et al. In 2022, epitopes were identified that broadly correspond to those previously described by Yamazaki et al., demonstrating Petition 870250099897, dated 10 / 31 / 2025, page 78 / 177 / 140 further highlights the importance of the present comprehensive study in which the hFGF23:burosumab binding surface was definitively defined by crystallographic analyses and supported by HDX-MS. Example 3: Human FGF23-burosumab paratope mapping

[00195] Burosumab paratope residues / regions for human FGF23 binding were interrogated using HDX-MS in a manner similar to the FGF23 epitope mapping described in Example 2. FGF23 (R179Q) was produced in HEK293S cells. Burosumab was produced in CHO cells (while FGF23-binding antibodies designed in later examples were expressed in HEK293S cells). Antigen-antibody complexes were formed by combining burosumab and FGF23 (R179Q) in solution and then diluting 1:10 in ice-cold deuterated assay buffer for 60 seconds, 600 seconds, 1800 seconds, or 3600 seconds. The deuteration reaction was quenched using a 1:1 addition of quenching buffer (pH 2.5), and the solution was subsequently loaded onto a liquid chromatography (LC) column for in-column proteolytic digestion, followed by LC separation and mass spectrometry.

[00196] In summary, the HDX-MS assay used PBS at pH 7.4 as the assay buffer. A quenching buffer with 1 M glycine, 4 M guanidine HCl, and 400 mM TCEP at pH 2.5 was used. 100 pmol were injected in duplicate at a 1:1 ratio of assay buffer to quenching buffer. Labeling (deuteration) was performed for 15 seconds, 60 seconds, 600 seconds, and 3600 seconds. The antigen concentration during labeling was 1.5 μM and the antibody concentration during labeling was 1 μM.

[00197] The HDX-MS results are shown in Figure 3. The geometric y-axis shows the % deuteration (% D), that is, the peptide length-normalized difference in deuteration between the unbound antibody and the antibody bound to FGF23. Values ​​less than 0 reflect Petition 870250099897, dated 10 / 31 / 2025, page 79 / 177 / 140 decrease in deuteration, i.e., protection against the deuteration reaction by antibody-antigen binding. Values ​​greater than 0 reflect increased deuteration, i.e., exposure to the deuteration reaction. The x-axis shows the amino acid residues of burosumab (light chain on the left and heavy chain on the right, separated by a vertical bar). The colored horizontal bars represent the deuterium labeling time point for each identified peptide (black = 15 s, blue = 60 s, orange = 600 s, magenta = 3600 s).

[00198] Burosumab antibody protection was observed and considered to represent conformational protection of the protected regions against deuteration and / or antigen binding (FGF23). In particular, the following regions in the burosumab light and heavy chain sequences shown in Table 4 were identified as exhibiting reduced deuteration by HDX-MS. Table 4. Burosumab Paratope Positions by HDX-MS Burosumab Amino acid position (relative to SEQ ID NO: 1) Amino acid sequence Amino acid sequence SEQ ID NO Heavy chain paratope region 1 24-35 ASGYTFTNHYMH 5 Heavy chain paratope region 2 49-69 GIINPISGSTSNAQKFQGRVT 6 Heavy chain paratope region 3 148-163 DYFPEPVTVSWNSGAL 7 Burosumab Amino acid position (relative to SEQ ID NO: 2) Amino acid sequence Amino acid sequence SEQ ID NO Light chain paratope region 1 23-33 CRASQGISSAL 8 Light chain paratope region 2 50-70 DASSLESGVPSRFSGSGSGTD 9 Light chain paratope region 3 103-122 VDIKRTVAAPSVFIFPPSDE 10

[00199] Among them, region 1 of the heavy chain paratop of burosumab (SEQ ID NO: 5) and region 1 of the light chain paratop (SEQ ID NO: 8) were considered to be involved in antigen binding. Petition 870250099897, dated 10 / 31 / 2025, page 80 / 177 / 140 Example 4: Molecular fit to assess the burosumab-FGF23 interaction

[00200] Protein-protein fit was used to predict the three-dimensional structure of the burosumab-FGF23 complex and to identify antibody-antigen interaction surfaces and residues involved in binding. Even without a crystal structure of the Fab-antigen complex, computational fit was used to gain insights into the interaction of the burosumab Fab fragment and FGF23 structures.

[00201] A crystal structure of FGF23 in complex with sucrose octasulfate is available (“2P39”; see Goetz et al. “Molecular insights into the klotho-dependent, endocrine mode of action of fibroblast growth factor 19 subfamily members” Mol Cell Biol (2007) 27 p.3417-28, incorporated here by reference). In addition, a crystal structure of the ternary complex FGF23-FGFR1c-aKlotho is also available (“5W21”; see Chen et al. “alpha-Klotho is a non-enzymatic molecular scaffold for FGF23 hormone signaling” (2018) Nature 553: 461-466, incorporated here by reference). These available crystal structures were used to perform molecular docking studies of human FGF23 with the known crystal structure of burosumab Fab (“7VEN”; Heo, YS “Structure of burosumab Fab” DOI: 10.2210 / pdb7ven / pdb; released September 14, 2022, incorporated herein by reference).The 2P39 FGF23 crystal structure and the 7VEN burosumab crystal structure were used for fitting studies here.

[00202] In summary, protein-protein docking was performed using the FFT-based search algorithm implemented in Molecular Operating Environment “MOE” (2022.02). After molecule preparation (i.e., minimization, geometry, protonation, encapsulation), all docking studies were initially performed with antibody and antigen molecules treated as rigid bodies. Conformational sampling of individual loops in the FGF23 antigen that are expected to be more flexible was Petition 870250099897, dated 10 / 31 / 2025, page 81 / 177 / 140, performed using LowModeMD and regular MD. The models were first rendered in a coarse-grained (CG) residue-based representation, in which each residue is composed of one to three spheres of bonded atoms, following the scheme proposed by Basdevant et al (doi: 10.1021 / jp0727190). The CG representation includes the following energy components: van der Waals, electrostatic, and solvation via the Generalized Born Volume Integral (GB / VI) formalism.

[00203] In the docking process, the antibody was considered as the ligand and the FGF23 antigen as the receptor. The system was biased on the paratope side to consider the burosumab CDRs defined by Kabat as the main interaction sites; that is, heavy and light chain CDR1, CDR2, and CDR3 with sequences established at SEQ ID NO: 11, SEQ ID NO: 12, and SEQ ID NO: 13 (HCDR1, HCDR2, and HCDR3, respectively) and SEQ ID NO: 14, SEQ ID NO: 15, and SEQ ID NO: 16 (LCDR1, LCDR2, and LCDR3, respectively). In other words, the restricted ligand sites were fixed to the burosumab CDRs, while the epitopes were considered as a whole (i.e., unbiased) or specifically selected based on HDX data. The potential of the hydrophobic patch was utilized throughout the search and refinement process. For pose selection, the threshold for maintaining a pose as valid was set to 10000 for pre-positioning, 1000 for positioning, and 100 for refinement.

[00204] For fitting purposes, epitopes were selected based on empirical HDX-MS data (Example 2 and Example 3 here) in combination with (i) comparative analysis of interspecies reactivity studies using burosumab and FGF23 from different species, (ii) kinetic studies using sandwich SPR analysis of different mutational variants of burosumab (Yamazaki et al., 2008), and / or (iii) patch analysis to assess the alignment of hydrophobic and polar surfaces of FGF23 and burosumab. Petition 870250099897, dated 10 / 31 / 2025, page 82 / 177 / 140, which impact linking interactions.

[00205] With regard to the comparative analysis of burosumab binding between different species, it was observed that burosumab exhibits “high binding affinity similar (Kd 10-11 mol / l) to human, cynomolgus monkey and rabbit FGF23 (Study r-12-0326)” and cross-reactivity “with recombinant forms of monkey and human FGF23, but not mouse FGF23 (Study r-13-0026) and with plasma FGF23 from humans and monkeys, but not from dogs or rats (Study r-13-0027)” (See the Centre for Drug Evaluation and Research, Application Number 761068Orig1s000, Application for Multidisciplinary Review License for Biologics 761068, available at www.accessdata.fda.gov / drugsatfda_docs / nda / 2018 / 761068Orig1s000Multidi sciplineR.pdf).Thus, FGF23 amino acid sequences from humans, cynomolgus monkeys, rabbits, dogs, and rats were aligned and overlaid with HDX-MS data to identify potential residues or epitope regions consistent between cross-reacting burosumab species, but not necessarily consistent with non-cross-reacting species.

[00206] The results of these various analyses were used to guide different biasing conditions in five separate docking studies (all based on FFT and all biased toward the antigen side) to generate diversity of poses and antigen-antibody contacts: Search #1: Impartial

[00207] Research #2: biased using each HDX protected region 1, protected region 2, or protected region 3 considered separately

[00208] Research #3: biased using all HDX protected regions (1, 2, and 3) together

[00209] Research #4: biased using epitopes described in Yamazaki et al., 2008

[00210] Research #5: biased using a shared epitope Petition 870250099897, dated 10 / 31 / 2025, pp. 83 / 177 / 140 between the protected regions of HDX 1, 2 and 3 and Yamazaki et al., 2008

[00211] Each research run resulted in five different clusters, all of which were examined in more detail for validation against energetic and empirical data (e.g., mutational data). The main requirement for a pose to be considered a valid match was approximately 30% to 40% correlation with available HDX data, i.e., at least about 30% to about 40% (based on contacts within a 4.5 Angstrom sphere) of the total number of residues in the three epitopes suggested by HDX had to engage in at least one contact with any residue of the burosumab CDRs. Unbiased matching resulted in clusters with low overall correlation with HDX data and mouse antibody-bound epitopes found by Yamazaki et al. (doi:10.1359 / JBMR.080417).Biased runs were more successful in this regard, with the best match (i.e., highest correlation with HDX data) resulting from a biased run on the antigen side with the reported mouse Ab epitope in Yamazaki et al. (i.e., Search #4). Two poses were selected as leads based on the criteria defined above: FGF23:AbPose-1 (1st-preferred.moe) and FGF23:Ab-Pose-2 (2nd-preferred.moe). Several additional poses from dockings 3, 4, and 5 were subsequently evaluated.

[00212] Valid poses of all dockings were examined to identify common paratopes. The information was combined with learnings from epitope and paratopes mapping studies described in Example 2 and Example 3. Overall, 18 burosumab heavy chain residues and 18 burosumab light chain residues were identified as potential common paratopes. The energetics of antigen-antibody contacts at these poses were evaluated for all poses. A summary of the modeling and docking runs is provided in Table 5. Petition 870250099897, dated 10 / 31 / 2025, page 84 / 177 / 140 Table 5. Summary of modeling and fitting operations. Fitting Protocol (MOE) Conformational Search Epitope Bias Exit Poses Average % Epitope Coverage Used in Mutational Scans Unbiased No No Selection Involves Protected Region 2 or 3 30~50 Biased No Only protected region 1 Involves protected region 1 60~75 Biased No Only protected region 2 Involves protected region 2 60~75 Biased LowModeMD Only protected region 3 Involves protected region 3 60~75 Biased No Protected regions 2 and 3 combined Involves protected regions 2 and 3 ~50 Biased LowModeMD Protected regions 1+2+3 Involves all protected regions 20~30 YES Biased LowModeMD Mu Ab Involves all protected regions 20~30 YES Biased LowModeMD Protected regions 1+2+3+Mu Ab Involves all protected regions 20-30 YES Example 5. Predictive mutagenesis of burosumab based on molecular fit, HDX-MS protection mapping, and comparative mutation analysis.

[00213] Mutational variants of burosumab were engineered using predictive mutagenesis performed at common burosumab interaction positions in 5 mean clusters. Common paratope positions (18 burosumab VH residues and 18 burosumab VL residues) were targets of predictive mutagenesis, taking into account valid poses from all docking searches that involved at least about 60% of HDX epitope residues. Mutational positions and variants were assessed based on energy calculations and MM-based mutations and rotameric (extended) optimization within 4.5 angstroms of a mutation site.

[00214] The initial 1X scan using predictive mutagenesis resulted Petition 870250099897, dated 10 / 31 / 2025, page 85 / 177 / 140, concerning 520 FGF23-binding antibody designs, each comprising a single amino acid alteration relative to the burosumab light chain (SEQ ID NO: 2) or the burosumab heavy chain (SEQ ID NO: 1). All 520 mutational variants were evaluated and screened according to the following criteria: dAffinity (ΔΔΘ (kcal / mol)) between -4.5 kcal / mol and 0.4 kcal / mol; dStability (ΔΔS (kcal / mol)) less than 3.0 kcal / mol; and redundant positions were re-evaluated based on dSASA (difference in solvent-accessible surface area) as an indicator of gain or loss of buried surface area after mutation introduction. ΔΔΘ is a metric for predicting how a single point mutation will affect protein stability. It is a measure of the energy change between the folded and unfolded states and the change in folding ΔΘ when a point mutation is present.This metric is used as a predictor to determine if a point mutation will be favorable in terms of protein stability. The more negative the value, the more stable the protein. Values ​​of ΔΔΘ > 0.5 suggest that a mutation would be destabilizing; values ​​of 0.5 > ΔΔΘ > -0.5 suggest that the changes should be considered neutral or nearly neutral; and ΔΔΘ < -0.5 suggest that the mutation would lead to a more stable protein. ΔΔS, on the other hand, is a measure of the vibrational entropy difference. A positive value indicates greater flexibility, while a negative value indicates a more rigid protein. It is used to predict how a mutation will alter the protein's entropy. The water-accessible surface area (“VdW SA”), the water-accessible surface area of ​​the protein's hydrophobic atoms (“Hydrophobic SA”), and the water-accessible surface area of ​​the protein's hydrophilic atoms (“Hydropophilic SA”) were also calculated.Table 6 provides a summary of the complete 1X scan predictive mutagenesis results for burosumab light chain positions, and Table 7 provides a summary of the complete 1X scan predictive mutagenesis results for burosumab heavy chain positions. Petition 870250099897, dated 10 / 31 / 2025, page 86 / 177 / 140 burosumabe.

[00215] From the complete 1X scan results, 96 mutational variants were selected for further evaluation based on the screening criteria described above to select predicted affinity enhancements with minimal negative impacts on predicted stability or solvation. These 96 mutational variants are referred to here as the burosumab variant or FGF23-binding antibody designed “design panel 1”. Table 8 provides a summary of the 1X scan predictive mutagenesis results for burosumab light chain positions selected for design panel 1, and Table 9 provides a summary of the 1X scan predictive mutagenesis results for burosumab heavy chain positions selected for design panel 1. Table 6. Results of predictive mutagenesis from a complete 1X scan of the burosumab light chain. LC mutation (relative to SEQ ID NO: 2) AAG (kcal / mol) AAS (kcal / mol) SA VdW (Â2) SA hydrophobic (Â2) SA hydrophilic (Â2) G30A -1.08 -0.37 -63.95 0.33 -61.95 G30C 0.12 0.13 -39.47 1.83 -39.84 G30D 1.90 0.98 -66.97 -12.15 -51.79 G30E 0.79 1.37 -51.29 23.50 -83.41 G30F 2.29 0.23 52.36 40.51 9.03 G30G 0.00 0.00 0.00 0.00 0.00 G30H 4.44 1.47 -26.20 3.15 -29.23 G30I 3.09 -0.19 -12.10 5.94 -16.62 G30K 1.64 1.12 7.07 -12.95 11.50 G30L 2.81 1.76 -34.42 50.57 -91.40 G30M 2.15 1.00 -70.00 12.67 -84.98 G30N 0.33 0.52 -66.45 -21.05 -44.73 G30P -0.88 0.23 -83.92 -20.74 -71.30 G30Q 2.33 1.21 -29.03 -9.02 -18.24 G30R -1.55 0.54 68.26 22.89 45.58 G30S -0.56 0.30 -46.30 7.83 -53.98 G30T -3.88 -0.30 -57.13 -5.29 -51.15 G30V 1.20 0.13 -57.42 -16.26 -41.77 G30W 2.87 0.76 13.94 39.40 -29.14 Petition 870250099897, dated 10 / 31 / 2025, p. 87 / 177 / 140 G30Y 1,24 0,63 -20,15 1,31 -14,59 I31A 0,06 3,21 -5,87 -13,07 6,42 I31C -0,09 2,31 0,87 -0,85 1,73 I31D -0,04 3,61 -10,07 -16,86 8,48 I31E -1,08 2,17 -6,42 -11,39 6,18 I31F -0,39 1,50 -1,00 0,00 3,00 I31G -1,71 3,86 -1,37 -8,42 7,08 I31H -0,40 1,80 -2,97 -0,96 0,00 I31I 0,00 0,00 0,00 0,00 0,00 I31K -0,96 2,85 0,00 -0,81 1,68 I31L -1,65 0,85 -2,03 0,87 -2,03 I31M -1,01 1,29 -0,83 -2,94 4,97 I31N -1,59 2,43 1,39 -0,06 2,67 I31P -0,26 2,92 -3,59 -10,87 10,62 I31Q -1,00 2,08 -1,40 -2,25 2,03 I31R -0,52 2,68 -4,48 -2,34 -2,45 I31S -0,49 3,45 -10,23 -14,00 4,69 I31T -1,27 2,90 4,88 -1,15 6,87 I31V -0,28 2,24 -1,85 -2,59 1,61 I31W 2,17 5,12 -10,09 -3,42 -4,34 I31Y 2,76 2,53 -6,15 -6,61 3,03 Q29A 3,58 1,21 8,36 16,36 -11,58 Q29C 1,31 1,06 10,76 13,01 -12,00 Q29D 1,19 1,62 -0,45 -0,49 -2,31 Q29E 2,31 1,41 1,79 14,42 -16,97 Q29F -2,13 0,79 5,77 78,62 -66,50 Q29G 4,08 1,94 28,49 24,75 1,76 Q29H -2,04 0,80 -4,70 3,37 -15,47 Q29I 0,67 0,41 4,66 48,06 -38,55 Q29K -1,10 0,68 -5,52 24,69 -26,92 Q29L -0.46 -0.01 -10.49 21.41 -36.24 Q29M -0.94 0.48 -12.24 46.42 -52.52 Q29N -1.91 0.69 2.51 6.49 -8.07 Q29P 6.13 2.91 -6.95 52.50 -33.64 Q29Q 0.00 0.00 0.00 0.00 0.00 Q29R -1.95 0.90 16.97 -12.44 33.58 Q29S 2.14 1.39 9.74 12.69 0.26 Q29T 1.56 0.99 7.72 7.81 0.26 Q29V 1.17 0.43 8.79 31.73 -21.59 Q29W -3.73 0.60 13.78 86.64 -73.10, Petition 870250099897, dated 10 / 31 / 2025, page 88 / 177 / 140 Q29Y -1,06 0,87 15,15 30,63 -16,45 S26A 1,22 0,24 19,75 11,17 13,17 S26C -0,26 0,31 1,85 -23,46 0,59 S26D 2,08 0,80 -19,24 -19,39 -7,40 S26E 2,54 0,14 -79,86 -34,05 -52,03 S26F 1,30 0,37 82,49 98,00 -15,18 S26G -0,30 0,66 -11,94 -17,30 -3,57 S26H 1,12 1,13 40,54 -11,65 29,49 S26I -0,48 -0,32 14,88 30,28 -11,87 S26K 1,28 0,90 2,27 -4,62 10,95 S26L -0,63 0,13 62,63 79,30 -12,14 S26M 1,37 0,16 21,44 18,30 5,84 S26N -0,49 0,92 21,55 -29,43 43,81 S26P 0,24 1,09 -7,97 9,25 -23,82 S26Q -0,49 0,45 20,00 -25,33 40,32 S26R 1,83 0,11 23,69 -5,99 29,98 S26S 0,00 0,00 0,00 0,00 0,00 S26T 1,32 0,59 19,80 32,21 -10,00 S26V 1,20 -0,06 37,12 33,29 4,36 S26W 1,14 0,66 54,57 77,14 -19,85 S26Y 1,28 0,46 92,65 54,87 38,20 S32A 2,49 0,43 -4,77 11,84 -10,00 S32C -0,03 0,29 -6,61 -0,67 -7,54 S32D -2,66 0,44 -9,12 -1,80 0,03 S32E -0,80 0,12 -5,77 -39,70 34,24 S32F -4,69 -0,56 -3,27 -13,45 14,81 S32G 4,69 1,32 14,29 21,55 -5,77 S32H -6,44 0,20 -20,75 -14,86 -7,11 S32I -2,25 -1,07 -42,54 -7,75 -27,30 S32K 1,07 0,60 -14.15 -36.86 28.89 S32L -4.17 -1.11 -18.80 4.45 -15.84 S32M -3.15 -0.78 -25.54 -4.30 -13.99 S32N -2.94 0.57 10.54 1.42 10.66 S32P 1.18 0.63 -11.06 2.69 -11.04 S32Q 0.11 0.79 -23.04 -60.57 35.10 S32R -1.79 -0.62 -9.67 -43.08 35.07 S32S 0.00 0.00 0.00 0.00 0.00 S32T -0.85 0.02 -11.88 2.31 -8.79 S32V -0.42 -0.60 -18.06 2.26 -17.52 S32W -6.27 -0.45 -18.02 -23.70 8.10, Petition 870250099897, dated 10 / 31 / 2025, page 89 / 177 / 140 S32Y -5.79 -0.37 0.57 -37.64 40.23 S33A 0.42 1.04 -19.60 3.17 -23.86 S33C -1.78 0.70 -30.85 15.97 -44.48 S33D -1.23 1.44 -33.47 14.96 -44.59 S33E -3.97 0.61 -58.52 -14.16 -40.81 S33F -1.23 0.62 -60.92 22.56 -75.92 S33G 0.12 1.65 -27.32 7.55 -30.28 S33H -4.61 0.61 -47.58 14.15 -53.65 S33I -2.49 -0.10 -64.49 -16.97 -49.90 S33K -4.60 0.52 16.06 8.18 3.00 S33L -4.30 -0.51 -53.17 -10.39 -36.81 S33M -5.46 -0.23 -54.79 -7.60 -41.30 S33N -6.15 0.42 -42.16 3.36 -41.24 S33P 1.64 0.69 -35.76 7.61 -36.38 S33Q -2.86 0.58 -49.64 -11.74 -29.14 S33R -4.65 -0.09 3.22 -18.33 15.86 S33S 0.00 0.00 0.00 0.00 0.00 S33T -1.88 0.39 -44.64 2.43 -33.14 S33V -1.11 0.12 -59.36 -11.72 -49.40 S33W -6.76 0.88 -45.79 27.60 -73.54 S33Y -4.14 -0.36 -72.63 1.47 -67.33 S83A 0.22 0.92 -6.72 38.16 -42.08 S83C 0.29 1.10 4.76 -10.56 -46.40 S83D -1.30 1.16 -2.26 -3.69 -1.50 S83E -0.17 1.82 16.44 -2.49 18.89 S83F 0.02 1.30 70.68 128.97 -53.32 S83G -0.42 1.04 -20.68 -21.10 -6.99 S83H 0.89 1.69 12.07 -18.61 -5.30 S83I -0.46 0,39 -3.21 52.92 -47.57 S83K 0.29 1.84 82.80 61.47 25.24 S83L -0.30 0.82 32.04 86.55 -49.87 S83M -0.31 1.58 70.71 123.15 -46.29 S83N 0.08 1.30 -4.21 -28.74 29.15 S83P 0.45 1.96 20.25 62.78 -39.59 S83Q 0.35 1.53 12.03 8.05 6.29 S83R 0.58 0.90 44.01 18.56 26.23 S83S 0.00 0.00 0.00 0.00 0.00 S83T -0.10 0.75 17.37 29.78 -11.74 S83V -0.26 0.55 -2.82 53.07 -49.37 S83W 0.78 1.29 57.36 116.69 -52.42, Petition 870250099897, dated 10 / 31 / 2025, page 90 / 177 / 140 S83Y 0.46 0.97 42.34 47.97 3.36 T87A -0.64 1.14 -18.97 22.19 -30.86 T87C -2.50 1.18 -8.75 33.33 -61.14 T87D 0.20 1.27 -4.04 7.63 -4.53 T87E 2.35 0.76 26.67 -30.54 45.87 T87F -2.28 0.53 -13.05 87.51 -99.87 T87G 0.99 1.69 -23.87 17.34 -45.19 T87H -2.75 1.18 -25.21 -10.02 -48.75 T87I -1.18 0.21 -36.31 33.07 -74.65 T87K -3.26 -0.18 -3.48 14.78 -24.84 T87L 3.89 0.27 8.67 16.55 -13.64 T87M -2.76 0.12 -28.64 28.49 -63.56 T87N -0.24 1.16 -11.62 11.93 -23.03 T87P -2.12 1.57 -28.90 42.05 -68.33 T87Q -4.00 -0.27 -56.56 9.56 -63.09 T87R 0.49 0.25 T87W -1.79 1.03 1.07 60.34 -58.28 T87Y 2.45 0.53 41.40 -1.95 35.47 Table 7. Results of predictive mutagenesis from a complete 1X scan of the burosumab heavy chain. HC mutation (relative to SEQ ID NO: 1) ΔΔG (kcal / mol) ΔΔS (kcal / mol) SA VdW (Â2) SA hydrophobic (Â2) SA hydrophilic (Â2) A71A 0.00 0.00 0.00 0.00 0.00 A71C -0.24 0.48 -0.72 -21.39 4.27 A71D 0.32 1.06 16.06 -42.98 46.54 A71E 0.29 0.61 4.60 -36.43 31.29 A71F -0.44 -0.62 -9.45 -48.46 30.05 A71G -0.20 1.33 10.48 -1.56 7.41 A71H -0.28 0.77 -18.70 -81.39 32.28 A71I -0.14 -0.84 -16.55 -54.35 34.35 A71K 0.90 -0.27 -2.30 -22.30 19.74 A71L -0.44 -0.71 12.87 -33.80 38.27 A71M 0.01 0.01 -24.22 -7.29 -13.59 A71N -0.40 0.64 22.26 -37.11 55.88 A71P -0.01 0.86 4.30 -0.17 3.35 A71Q 0.11 0.45 -13.00 -15.99 4.53 Petition 870250099897, dated 10 / 31 / 2025, p. 91 / 177 / 140 A71R -0,11 -0,47 -43,20 -25,75 -8,14 A71S -0,40 0,68 1,48 -10,95 7,87 A71T -0,25 0,40 -1,24 -6,85 3,63 A71V -0,23 -0,11 2,42 -26,12 28,84 A71W -0,25 -0,71 -8,16 -37,88 21,91 A71Y -0,29 -0,44 -4,12 -78,46 72,85 D109A 1,09 1,31 -6,11 -3,48 3,78 D109C 0,23 1,10 -3,63 -1,53 3,78 D109D 0,00 0,00 0,00 0,00 0,00 D109E 0,99 2,47 -2,85 -3,60 17,65 D109F -0,74 1,95 -22,60 -14,06 18,55 D109G 0,63 2,02 -0,29 -0,63 9,28 D109H 0,79 1,80 -3,52 -2,19 8,31 D109I 0,33 0,16 -11,67 -10,77 6,63 D109K 0,24 2,07 -8,01 0,94 6,55 D109L 0,32 0,20 -12,39 -12,27 6,63 D109M -0,34 0,67 -6,76 -1,29 7,15 D109N -0,22 0,69 -1,90 -1,94 8,80 D109P 0,52 1,51 0,44 -0,89 6,74 D109Q 0,74 1,17 -9,52 -4,71 3,29 D109R 2,29 0,82 -9,27 -5,93 8,72 D109S 0,56 0,86 0,06 -1,02 9,28 D109T 0,36 1,09 6,75 -0,48 10,97 D109V 0,37 0,38 -6,17 -10,64 9,77 D109W 0,25 1,59 -6,48 -9,44 6,56 D109Y 0,34 1,16 -3,95 -4,89 4,04 D134A 1,13 0,94 -0,89 -5,78 1,36 D134C 0,53 1,32 -1,26 -16,26 10,62 D134D 0,00 0,00 0,00 0,00 0,00 D134E -0,58 0,33 34,00 -29.02 64.96 D134F -5.28 -1.09 -1.49 -58.64 44.83 D134G 1.64 1.76 19.43 6.80 7.11 D134H -1.77 1.49 -2.56 -25.84 -11.33 D134I -1.23 -1.15 -9.23 6.61 -13.56 D134K -0.95 0.39 3.94 -34.20 41.75 D134L -1.39 -1.00 -11.79 1.86 -9.58 D134M -1.49 0.72 -1.36 15.35 -16.27 D134N -1.06 0.42 -7.80 -11.52 3.02 D134P 1.46 0.81 1.82 3.11 -1.06 D134Q -0.56 0.73 26.93 -38.77 66.46, Petition 870250099897, dated 10 / 31 / 2025, page 92 / 177 / 140 D134R -3.70 -0.60 6.07 -30.65 42.00 D134S 1.08 1.60 -6.50 -14.68 1.74 D134T -0.07 0.61 -1.67 2.87 -4.67 D134V -0.55 0.08 -10.96 -7.73 -5.71 D134W -4.83 0.33 8.34 -2.89 7.63 D134Y -5.18 -0.94 -0.38 -60.19 45.38 H39A 0.16 1.33 33.62 52.56 -16.66 H39C 0.16 0.81 22.54 -1.36 27.45 H39D 0.09 1.81 35.80 22.22 4.93 H39E -0.11 1.76 5.07 12.65 -6.02 H39F -0.19 0.26 56.90 71.52 -23.28 H39G 0.12 2.13 21.20 36.22 -16.44 H39H 0.00 0.00 0.00 0.00 0.00 H39I 0.12 -0.53 2.41 13.42 -14.45 H39K 0.14 1.26 4.30 18.00 -10.81 H39L 0.15 0.33 14.36 61.64 -49.58 H39M -0.20 0.87 15.03 59.67 -50.37 H39N 0.30 1.22 41.04 25.61 8.48 H39P -0.04 1.16 26.21 -15.45 42.03 H39Q 0.12 0.76 -12.43 13.28 -25.82 H39R -0.06 0.29 23.54 -1.64 22.15 H39S 0.09 1.46 15.65 -4.91 22.49 H39T 0.10 0.67 -1.67 -2.52 -0.55 H39V 0.02 0.03 -5.04 -2.30 0.92 H39W 0.04 0.28 28.21 33.64 -4.07 H39Y -0.21 0.30 49.59 33.74 11.43 I110A 0.03 2.52 3.86 -22.74 29.99 I110C -0.11 1.91 7.13 -17.14 23.77 I110D -1.11 4.20 15.76 -56.14 86.19 I110E -0.08 2,61 -4.10 -56.28 65.04 I110F -0.35 0.96 -23.99 -25.37 5.99 I110G 0.66 2.84 24.81 -20.46 54.01 I110H -0.86 1.80 -25.00 -45.31 22.01 I110I 0.00 0.00 0.00 0.00 0.00 I110K -0.04 0.92 -14.89 -10.14 26.38 I110L -0.75 0.74 -20.88 -25.94 3.67 I110M -0.97 1.38 -10.18 -13.53 11.87 I110N -0.10 2.04 9.43 -12.38 31.55 I110P 0.49 2.68 -15.84 -33.85 35.29 I110Q -1.22 1.59 -21.18 -62.41 63.88, Petition 870250099897, dated 10 / 31 / 2025, page 93 / 177 / 140 I110R -0.24 1.42 5.96 -48.18 53.29 I110S -0.94 2.52 -2.78 -33.44 45.29 I110T -0.20 1.50 9.40 -31.40 44.59 I110V 0.22 1.91 -7.61 -14.51 5.64 I110W -3.68 1.40 14.00 -3.39 24.52 I110Y -2.98 1.93 29.93 -8.17 51.25 N33A -0.02 0.77 -30.82 35.02 -58.06 N33C 0.00 0.57 -8.55 8.36 -49.97 N33D -0.09 0.57 20.42 51.48 -32.54 N33E -0.10 0.63 -1.03 -3.95 0.01 N33F -0.05 1.38 61.03 141.95 -90.36 N33G -0.02 1.18 -35.33 23.42 -49.87 N33H -0.04 1.18 0.77 11.38 -55.78 N33I -0.14 0.21 4.21 49.75 -54.51 N33K 0.04 1.38 40.21 32.19 -7.94 N33L -0.01 0.18 3.27 65.34 -59.41 N33M 0.01 0.94 33.57 84.15 -52.32 N33N 0.00 0.00 0.00 0.00 0.00 N33P -0.05 1.12 -23.46 41.13 -61.32 N33Q 0.01 0.64 18.36 -8.17 22.72 N33R 0.12 1.04 62.06 -4.16 62.99 N33S -0.03 0.82 7.00 55.14 -51.31 N33T -0.08 0.58 -24.68 36.49 -70.86 N33V -0.09 0.13 5.70 36.04 -29.54 N33W -0.02 1.33 62.07 108.12 -62.31 N33Y -0.03 1.38 107.14 106.68 2.14 N59A 2.81 1.04 0.98 -5.70 12.78 N59C 2.02 0.54 11.73 1.94 15.38 N59D 0.44 0.47 -4.01 -0.83 1.73 N59E 410 0.31 -3.26 -10.48 16.92 N59F 3.42 -0.20 -11.66 -28.85 28.57 N59G 3.64 2.22 -20.06 -26.07 17.71 N59H 3.09 0.76 -7.82 -16.99 13.51 N59I 5.73 0.61 -24.09 -28.10 14.52 N59K 2.76 1.02 20.05 2.57 26.74 N59L 5.05 -0.32 -4.36 -27.22 32.89 N59M 1.75 0.40 -9.34 -30.05 29.49 N59N 0.00 0.00 0.00 0.00 0.00 N59P 3.64 2.10 -17.39 -8.28 1.58 N59Q 4.08 0.98 -9.24 -33.40 30.19, Petition 870250099897, dated 10 / 31 / 2025, page 94 / 177 / 140 N59R 5,05 1,24 77,11 -71,11 147,91 N59S 1,49 1,09 2,34 -4,04 12,33 N59T 3,18 1,08 3,67 -5,68 17,74 N59V 3,51 0,32 -1,53 -16,96 17,42 N59W 1,71 0,31 -17,88 -29,79 20,45 N59Y 2,22 -0,02 -17,18 -42,37 32,60 N70A -0,10 1,03 -2,51 3,31 -7,39 N70C -0,08 0,76 3,57 3,39 -10,23 N70D 0,08 1,06 -4,61 -6,87 9,88 N70E 0,02 0,92 -11,30 -9,93 -0,76 N70F -0,37 -0,34 -14,89 41,70 -67,38 N70G -0,16 1,80 16,02 16,98 -1,18 N70H -0,59 0,64 -19,03 17,89 -47,66 N70I -0,19 -0,17 -22,82 -1,75 -22,68 N70K -0,79 0,46 -12,35 -33,00 14,18 N70L -0,09 0,20 -20,21 2,14 -16,58 N70M -0,12 0,31 -17,79 20,53 -40,15 N70N 0,00 0,00 0,00 0,00 0,00 N70P -0,12 1,10 -38,08 -11,79 -26,89 N70Q 0,10 0,61 -9,05 -6,74 3,05 N70R -0,82 -0,13 -30,02 -43,49 12,01 N70S -0,09 1,27 -26,89 -13,88 -8,22 N70T -0,01 0,95 -24,39 -5,99 -17,68 N70V -0,02 0,09 -25,15 -5,26 -14,47 N70W 0,00 -0,79 -19,19 17,58 -41,18 N70Y -0,59 -0,26 -13,76 3,60 -18,76 Q72A 0,81 1,11 43,69 69,49 -29,12 Q72C 0,26 1,01 1,45 11,33 -42,15 Q72D 0,22 1,28 9,09 1,52 -1,98 Q72E 1.86 0.94 12.44 18.24 -12.71 Q72F 0.73 0.19 12.64 46.68 -43.84 Q72G 0.84 1.31 36.98 56.63 -27.59 Q72H -0.13 0.85 -19.50 -13.97 -19.77 Q72I 0.67 0.09 18.98 53.40 -38.11 Q72K -0.57 1.00 -7.25 17.06 -26.61 Q72L 0.44 -0.06 -8.56 27.95 -38.60 Q72M 0.05 0.37 -4.86 20.97 -34.50 Q72N 1.36 1.19 -7.97 -19.87 3.40 Q72P 0.78 1.02 27.69 50.65 -30.55 Q72Q 0.00 0.00 0.00 0.00 0.00, Petition 870250099897, dated 10 / 31 / 2025, page 95 / 177 / 140 Q72R -1.50 -0.07 -42.84 0.77 -48.40 Q72S 0.81 1.26 36.22 33.43 -0.29 Q72T 0.83 0.83 21.49 22.57 -4.67 Q72V 0.84 0.39 16.87 47.51 -36.60 Q72W 0.81 0.62 21.38 63.16 -47.99 Q72Y 0.81 0.01 4.42 27.35 -25.52 Q75A 0.67 1.25 10.50 46.35 -37.75 Q75C 0.89 1.02 0.03 16.79 -42.18 Q75D 0.93 1.56 12.95 16.57 -2.77 Q75E 0.27 1.12 4.40 23.65 -16.61 Q75F 0.16 0.06 -44.15 7.99 -56.72 Q75G 0.71 1.44 -6.84 15.41 -29.12 Q75H 0.49 0.83 -40.66 -4.81 -44.63 Q75I 0.50 0.37 -13.64 34.56 -49.02 Q75K -0.01 1.31 -51.15 -22.59 -35.80 Q75L 0.36 0.27 -9.89 34.92 -47.72 Q75M -0.08 0.09 -13.78 36.04 -48.31 Q75N 0.99 1.18 3.23 6.29 -1.86 Q75P 0.68 1.60 23.11 76.20 -48.18 Q75Q 0.00 0.00 0.00 0.00 0.00 Q75R -1.13 0.02 -60.61 -27.51 -32.47 Q75S 0.67 1.38 14.56 21.14 -7.46 Q75T -0.06 0.97 5.14 46.41 -41.22 Q75V 0.69 0.74 7.10 54.24 -48.08 Q75W -1.42 -0.54 -37.32 -5.77 -32.09 Q75Y 0.35 0.32 -31.53 3.48 -45.08 S65A -0.12 0.53 13.08 23.81 -9.53 S65C -4.12 -0.13 -8.32 -23.34 -7.17 S65D -4.17 0.26 2.28 -6.78 8.01 S65E -1.10 0,39 -2.60 -0.24 -4.82 S65F -4.44 -1.01 3.16 20.91 -16.75 S65G 2.62 1.27 9.93 -18.07 18.74 S65H -5.02 0.05 -3.22 -29.17 17.09 S65I -2.78 -1.04 15.97 14.52 -2.59 S65K 3.80 1.97 89.30 36.14 50.78 S65L 0.34 0.20 51.12 43.52 10.62 S65M -3.92 -1.15 -17.54 -9.74 -12.34 S65N -1.48 0.48 3.19 -19.58 24.87 S65P -5.04 0.17 -1.09 24.81 -31.29 S65Q -2.39 0.09 4.90 -37.41 42.36, Petition 870250099897, dated 10 / 31 / 2025, page 96 / 177 / 140 S65R 2.04 2.07 108.27 -10.53 112.57 S65S 0.00 0.00 0.00 0.00 0.00 S65T -4.54 0.04 0.58 15.66 -25.65 S65V -2.04 -0.87 59.01 17.96 28.42 S65W -6.13 -0.30 30.56 54.00 -18.70 S65Y -0.49 0.49 131.42 57.12 65.45 S67A 2.92 0.61 19.59 -6.66 24.04 S67C 1.46 0.49 64.67 -1.73 36.81 S67D -2.53 -0.28 26.94 4.50 17.83 S67E 0.08 -0.45 26.27 13.43 7.14 S67F -1.50 -0.50 106.56 43.44 49.84 S67G 3.79 1.40 42.47 0.89 35.01 S67H -1.22 -0.33 83.94 -7.51 82.67 S67I 4.55 -0.82 26.00 -7.76 21.19 S67K -0.36 0.35 78.41 -4.44 67.49 S67L -0.58 -1.05 81.94 14.21 57.62 S67M -1.84 -0.62 36.69 -10.26 39.68 S67N -0.03 0.31 45.11 -8.29 45.32 S67P 3.15 1.14 17.80 -15.72 32.07 S67Q -3.56 -0.14 0.39 -11.02 5.48 S67R -4.48 -0.10 -22.51 -34.67 2.34 S67S 0.00 0.00 0.00 0.00 0.00 S67T 0.10 0.09 20.02 -0.42 14.33 S67V 5,45 -0.20 6.78 -9.75 13.56 S67W -0.22 0.41 108.15 70.33 34.17 S67Y -2.41 -0.40 12.16 -6.81 8.35 S69A 0.32 0.24 7.58 0.23 6.83 S69C 0.34 0.59 4.35 -24.72 -1.95 S69D -0.38 0.79 -1.82 -8.07 12.29 S69E 0.57 0.86 -3647 -30.01 -0.83 S69F -2.00 -1.23 -70.46 -5.67 -58.52 S69G 2.51 0.93 4.56 -5.99 7.06 S69H -2.51 0.15 -18.70 -33.09 4.06 S69I 0.25 -0.50 -25.49 4.41 -27.92 S69K -0.58 0.03 -64.03 -25.62 -36.75 S69L 0.50 -0.54 -33.67 -18.55 -18.57 S69M -0.89 -0.13 -56.36 -20.97 -26.61 S69N -0.53 0.79 3.79 -31.49 39.29 S69P -0.06 0.75 1.88 0.61 2.65 S69Q -0.34 0.48 -15.74 -20.27 5.48, Petition 870250099897, dated 10 / 31 / 2025, page 97 / 177 / 140 S69R -0.77 0.06 -59.67 -4.42 -45.82 S69S 0.00 0.00 0.00 0.00 0.00 S69T 0.07 0.15 1.64 -9.94 19.53 S69V 0.38 -0.26 13.93 12.39 -5.67 S69W 2.16 -1.49 -46.54 -47.78 12.09 S69Y -1.47 -1.26 -67.28 -19.66 -37.97 T30A 0.00 0.61 -11.74 11.77 -24.87 T30C 0.00 0.71 -8.14 -14.15 -37.98 T30D -0.02 1.30 -2.98 -12.93 3.72 T30E -0.01 1.23 15.27 -8.84 18.91 T30F 0.00 1.13 46.05 98.24 -54.98 T30G 0.00 0.76 -18.68 -13.38 -4.36 T30H 0.00 1.68 18.63 -10.90 -3.27 T30I 0.00 0.49 39.16 82.28 -43.13 T30K 0.00 1.18 28.72 45.67 -21.13 T30L 0,00 0,35 29,04 78.75 -49.35 T30M 0.00 0.82 25.87 70.83 -47.96 T30N 0.01 1.10 16.14 -17.42 24.76 T30P 0.00 1.22 5.32 39.38 -33.98 T30Q 0.00 0.85 18.27 -11.79 28.08 T30R 0.00 0.76 22.62 18.79 -4.70 T30S 0.00 0.86 -4.91 -3.81 -1.05 T30T 0.00 0.00 0.00 0.00 0.00 T30V 0,00 0,45 17.71 58.37 -41.21 T30W -0.01 1.48 114.88 123.88 -9.38 T30Y 0.00 1.47 116.20 94.79 18.90 T32A 0.19 0.38 -6.18 -37.56 20.12 T32C 0.20 0.40 -11.53 -50.81 20.13 T32D 0.12 0.78 14.57 -24.89 33.84 T32E 0.16 093 26.17 -38.13 59.09 T32F 0.13 -0.15 28.84 25.65 0.78 T32G 0.19 1.08 -1.36 -36.58 24.21 T32H 0.07 0.74 10.44 -17.33 10.59 T32I 0.11 -0.25 -15.44 -27.53 3.90 T32K 0.37 0.61 -26.14 -49.64 20.11 T32L 0.10 -0.10 25.37 17.42 2.58 T32M 0.14 0.28 31.60 -11.72 44.26 T32N 0.16 0.51 -17.14 -67.87 45.79 T32P 0.29 -0.72 -19.41 -77.33 50.21 T32Q 0.31 0.31 -19.90 -72.23 41.94, Petition 870250099897, dated 10 / 31 / 2025, page 98 / 177 / 140 T32R 0,18 0,72 63,76 -22,60 80,26 T32S 0,20 0,53 -16,27 -47,27 24,69 T32T 0,00 0,00 0,00 0,00 0,00 T32V 0,13 -0,21 -16,86 -32,39 11,90 T32W 0,16 0,22 37,36 36,07 3,94 T32Y 0,07 -0,13 27,88 4,80 15,38 T68A -0,18 0,57 -1,00 -13,74 13,13 T68C -0,69 0,70 -0,05 -41,46 0,84 T68D -0,22 1,72 -4,80 -54,49 44,08 T68E -0,30 0,81 -8,59 -30,67 12,93 T68F 0,45 -0,74 -8,40 -1,89 -6,36 T68G -1,16 1,00 -1,72 -42,39 37,06 T68H -0,33 1,13 3,11 -59,32 30,18 T68I 0,31 -0,19 -20,19 -6,23 -13,07 T68K -0,12 1,35 27,97 -6,20 38,22 T68L 0,29 -0,01 -18,31 -25,44 8,66 T68M -0,59 0,24 -5,95 5,21 -14,50 T68N -0,69 0,88 -10,74 -45,81 36,93 T68P 0,18 1,61 4,02 8,35 -9,56 T68Q -0,39 0,86 1,34 -42,99 45,85 T68R -1,44 1,39 21,36 -20,24 30,08 T68S -0,31 0,79 7,63 -35,17 42,84 T68T 0,00 0,00 0,00 0,00 0,00 T68V 0,46 0,08 -10,52 -8,51 -0,07 T68W 0,47 -0,45 -6,62 23,33 -28,66 T68Y 0,16 -0,57 -9,52 -2,27 -5,81 V111A 3,33 2,33 -18,99 -31,37 15,52 V111C 1,74 2,65 -5,84 -0,77 -4,05 V111D 4,78 2,90 -2,37 0,06 2,36 V111E 5,59 3,19 -13.41 -1.95 -9.26 V111F 1.40 2.91 -21.61 -18.60 -3.79 V111G 5.03 2.67 3.57 -1.87 5.25 V111H 1.11 1.35 8.97 14.37 -2.44 V111I 2.10 1.18 23.09 -26.50 46.90 V111K -0.12 1.41 -3.09 0.53 -5.32 V111L 2.81 0.89 -0.93 0.46 2.65 V111M 0.87 1.80 -10.16 -2.62 -5.17 V111N 1.05 2.83 -0.92 0.77 -1.10 V111P 1.01 1.72 -0.59 0.25 1.46 V111Q 0.83 2.23 -10.49 -3.02 -5.92, Petition 870250099897, dated 10 / 31 / 2025, page 99 / 177 / 140 V111R -1.55 1.47 -9.66 -2.37 -6.33 V111S 2.86 2.08 3.15 4.38 -0.72 V111T 3.45 1.54 13.58 -31.54 48.63 V111V 0.00 0.00 0.00 0.00 0.00 V111W -0.88 2.30 -36.42 -27.02 -7.00 V111Y 1.01 2.62 -38.71 -34.80 0.84 Y40A 1.39 1.09 17.94 12.69 -3.82 Y40C 0.57 1.07 8.41 3.72 -4.83 Y40D -2.54 1.59 25.93 10.84 6.17 Y40E -1.15 1.24 15.75 6.86 -0.69 Y40F -0.27 0.03 3.07 4.87 -4.15 Y40G 1.36 2.08 32.33 20.21 -5.50 Y40H -0.79 0.87 -3.02 -4.37 -3.48 Y40I -2.73 -0.32 19.63 12.59 3.12 Y40K -1.63 0.63 -3.55 -1.51 -2.20 Y40L -3.11 -0.43 14.84 7.13 1.10 Y40M -1.14 -0.19 20.57 10.21 -1.65 Y40N 0.38 1.01 4.80 -0.24 6.22 Y40P -1.54 1.35 18.71 9.01 -0.62 Y40Q -0.63 0.78 15.18 8.32 -3.20 Y40R -3.05 -0.29 2.89 4.69 -6.25 Y40S -0.94 1.21 26.63 14.15 2.19 Y40T -3.15 0.33 20.04 6.19 12.18 Y40V -1.94 0.02 15.85 11.13 2.19 Y40W -2.56 -0.51 -1.33 4.76 -3.41 Y40Y 0.00 0.00 0.00 0.00 0.00 Table 8. Panel 1 of the burosumab light chain diagram. Mutation (ASN#) (relative to SEQ ID NO: 2) AAG (kcal / mol) AAS (kcal / mol) G30A -1.1 -0.4 G30P -0.9 0.2 G30S -0.6 0.3 I31E -1.1 2.2 I31K -1.0 2.8 I31M -1.0 1.3 I31Q -1.0 2.1 I31R -0.5 2.7 I31S -0.5 3.5 I31T -1.3 2.9 Q29K -1.1 0.7 Petition 870250099897, dated 10 / 31 / 2025, pages 100 / 177 / 140 Q29M -0.9 0.5 Q29Y -1.1 0.9 S26I -0.5 -0.3 S26L -0.6 0.1 S26N -0.5 0.9 S26Q -0.5 0.5 S32D -2.6 0.4 S32F -4.7 -0.6 S32I -2.2 -1.1 S32L -4.2 -1.1 S32M -3.1 -0.8 S32R -1.8 -0.6 S32T -0.8 0.0 S32V -0.4 -0.6 S33D -1.2 1.4 S33F -1.2 0.6 S33L -4.3 -0.5 S33V -1.1 0.1 S83D -1.3 1.2 T87A -0.6 1.1 T87I -1.2 0.2 Table 9. Burosumab Heavy Chain Project Panel 1 Mutation (ASN#) (relative to SEQ ID NO: 1) AAG (kcal / mol) AAS (kcal / mol) A71F -0.4 -0.6 A71I -0.1 -0.8 A71L -0.4 -0.7 A71W -0.2 -0.7 D109F -0.7 2.0 D134E -0.6 0.3 D134F -5.3 -1.1 D134I -1.2 -1.1 D134K -1.0 0.4 D134L -1.4 -1.0 D134M -1.5 0.7 D134N -1.1 0.4 D134Q -0.6 0.7 D134R -3.7 -0.6 D134V -0.5 0.1 D134Y -5.2 -0.9 Petition 870250099897, dated 10 / 31 / 2025, p. 101 / 177 / 140 H39I 0.1 -0.5 I110D -1.1 4.2 I110H -0.9 1.8 I110L -0.7 0.7 I110M -1.0 1.4 I110Q -1.2 1.6 I110S -0.9 2.5 N70H -0.6 0.6 N70K -0.8 0.5 N70R -0.8 -0.1 N70W 0.0 -0.8 N70Y -0.6 -0.3 Q72K -0.6 1.0 Q72R -1.5 -0.1 Q75R -1.1 0.0 Q75W -1.4 -0.5 S65E -1.1 0.4 S65F -4.4 -1.0 S65I -2.8 -1.0 S65M -3.9 -1.2 S65N -1.5 0.5 S65V -2.0 -0.9 S65Y -0.5 0.5 S67F -1.5 -0.5 S67H -1.2 -0.3 S67I 4.6 -0.8 S67L -0.6 -1.1 S67M -1.8 -0.6 S69F -2.0 -1.2 S69I 0.2 -0.5 S69K -0.6 0.0 S69L 0.5 -0.5 S69M -0.9 -0.1 S69N -0.5 0.8 S69R -0.8 0.1 S69W -2.2 -1.5 S69Y -1.5 -1.3 T32P 0.3 -0.7 T68F 0.4 -0.7 T68G -1.2 1.0 Petition 870250099897, dated 10 / 31 / 2025, page 102 / 177 / 140 T68M -0.6 0.2 T68N -0.7 0.9 T68R -1.4 1.4 T68Y 0.2 -0.6 V111W -0.9 2.3 Y40E -1.2 1.2 Y40H -0.8 0.9 Y40M -1.1 -0.2 Y40Q -0.6 0.8 Y40S -0.9 1.2 Example 6. Rational design panel 1 of FGF23-binding antibody designed based on molecular docking studies.

[00216] Table 10 shows 96 FGF23-binding antibody designs designed from the 1X scan. Each variant is labeled with a sequential FGF23-binding antibody structure ID numbered from 001 to 096 and has an amino acid alteration relative to the parental burosumab heavy chain amino acid sequence (SEQ ID NO: 1) or the parental burosumab light chain amino acid sequence (SEQ ID NO: 2). No combined amino acid alterations relative to the parental sequences were included in design panel 1, and no variants were included with amino acid alterations in more than one light or heavy chain. In Table 10, all amino acid numbering is presented according to the ASN# system. Table 10. Design panel 1 of FGF23-binding antibodies designed FGF23-binding antibody structure ID - Light Chain Mutations (ASN#) (relative to SEQ ID NO: 2) FGF23-binding antibody structure ID - Heavy Chain Mutations (relative to SEQ ID NO: 1) UGX001 Q29F UGX044 T30Y UGX002 Q29R UGX045 T32K UGX003 G30D UGX046 H39K UGX004 G30Q UGX047 H39Y UGX005 G30R UGX048 Y40D UGX006 G30Y UGX049 Y40L UGX007 S32D UGX050 Y40R UGX008 S32F UGX051 N59E UGX009 S32R UGX052 N59Q Petition 870250099897, dated 10 / 31 / 2025, page 103 / 177 / 140 UGX010 S32Y UGX053 N59R UGX011 S33F UGX054 S65E UGX012 S33Y UGX055 S65F UGX013 D58E UGX056 S65I UGX014 D58Q UGX057 S65Q UGX015 D58R UGX058 S65R UGX016 D58Y UGX059 S65Y UGX017 S68E UGX060 S67E UGX018 S68Q UGX061 S67F UGX019 S68R UGX062 S67R UGX020 S68Y UGX063 S67Y UGX021 S69R UGX064 T68F UGX022 S69Y UGX065 T68R UGX023 L70E UGX066 S69F UGX024 L70Y UGX067 S69R UGX025 E71R UGX068 S69Y UGX026 E71Y UGX069 N70E UGX027 S83E UGX070 N70R UGX028 S83R UGX071 N70Y UGX029 S83Y UGX072 A71F UGX030 T87R UGX073 A71R UGX031 T87Y UGX074 A71Y UGX032 F109E UGX075 Q72L UGX033 F109R UGX076 Q72R UGX034 N110E UGX077 Q72Y UGX035 N110F UGX078 Q75E UGX036 N110Q UGX079 Q75R UGX037 N110R UGX080 Q75Y UGX038 N110Y UGX081 D109F UGX039 D135F UGX082 D109R UGX040 D135R UGX083 D109Y UGX041 D135Y UGX084 I110E UGX042 Y136E UGX085 I110F UGX043 Y136R UGX086 I110Y UGX087 V111E UGX088 V111F UGX089 V111L UGX090 V111Q UGX091 V111R UGX092 D134E Petition 870250099897, dated 10 / 31 / 2025, page 104 / 177 100 / 140 UGX093 D134F UGX094 D134K UGX095 D134R UGX096 D134Y Example 7. Structural evaluation of the burosumab-FGF23 interaction

[00217] To better characterize the human FGF23burosumab interaction, an X-ray crystallographic study was performed using fully glycosylated human FGF23 (R179Q) from the supernatant of HEK293S cells in complex with burosumab Fab fragments also expressed in HEK293S cells. Burosumab IgG heavy and light chains were digested with papain to separate Fc and Fab fragments, then with protein A to isolate approximately 50 kDa Fab fragments, according to routine methods (Pierce™ Fab Preparation Kit, Thermo Scientific™, cat n° 44985). The fully glycosylated human FGF23 (R179Q) and burosumab Fab fragments were incubated on ice for more than one hour (molar ratio of 1:0.8) and the stable complex was isolated by size exclusion chromatography (SEC) followed by SDS-PAGE assessment. The SEC fractions containing the complex were pooled, concentrated, and stored at -80 °C.

[00218] Briefly, crystallization assays were performed in 96-well vapor diffusion plates, mixing 200 nl of protein solution (4.5 mg / ml in 25 mM Hepes pH 7.5 and 150 mM NaCl) and 200 nl of well solution (0.2 M dibasic ammonium citrate and 20% (w / v) PEG 3350). Diffraction data were collected from a single crystal at the Advanced Photon Source (APS) synchrotron and processed using autoPROC (autoProc, XDS, POINTLESS, AIMLESS, CCP4 and STARANISO) (see Vonrhein C, Flensburg C, Keller P, Sharff A, Smart O, Paciorek W, Womack T, Bricogne G. Data processing and analysis with the autoPROC toolbox. Acta Crystallogr D Biol Crystallogr. April 2011; 67 (Pt 4): 293-302. [doi:10.1107 / S0907444911007773]). Petition 870250099897, dated 10 / 31 / 2025, pp. 105 / 177 101 / 140

[00219] The phase solution was obtained using Phaser (CCP4) (see J. Agirre et al. Acta. Cryst. D79, 449-461 (2023) “The CCP4 suite: integrative software for macromolecular crystallography”) [doi:10.1107 / S2059798323003595]) using FGF23 and burosumab (PDB IDs 2P32 and 7VEN) as models for molecular replacement. The refinement and construction of the model were performed with RECMAC, BUSTER, and COOT (see J. Agirre et al.; Bricogne G., Blanc E., Brandl M., Flensburg C., Keller P., Paciorek W., Roversi P, Sharff A., Smart OS, Vonrhein C., Womack TO (2017). Cambridge, UK: Global Phasing Ltd.; and Emsley P, Lohkamp B, Scott WG, Cowtan K. Features and development of Coot. Acta Crystallogr. D. Biol. Crystallogr. 2010; 66:486-501. [doi:10.1107 / S0907444910007493]).

[00220] Data collection and refinement statistics for the complex 3 Â structure solved by molecular substitution are provided in Figure 4.

[00221] Figure 5 shows the Fab hFGF23(R179Q):burosumab crystal structure with two antigen:Fab complexes linked by an FGF23:FGF23 dimer. It is worth noting that residues from the FGF23 dimerization interface are not present in the epitopes identified in the crystal structure, but some are involved in FGFR1c receptor binding. It was also observed that the binding of burosumab to FGF23 overlaps with the heparin sulfate binding residues previously reported (Goetz, Regina, et al. Molecular insights into the klothodependent, endocrine mode of action of fibroblast growth factor 19 subfamily members. Molecular and cellular biology 27.9 (2007): 3417-3428.). It is known that heparin sulfate is required for the dimerization of the FGF23:αKlotho:FGFR1c complex (Chen, G., Liu, Y., Goetz, R. et al. “α-Klotho is a non-enzymatic molecular scaffold for FGF23 hormone signalling”. Nature 553, 461-466 (2018).).The residues of the FGF23 dimerization interface in the current crystal structure correspond to those described earlier in the link. Petition 870250099897, dated 10 / 31 / 2025, pp. 106 / 177 102 / 140 of FGFRlc by Chen et al. 2018. These findings suggest that burosumab binding to FGF23 may additionally compete with or interfere in some way with receptor binding as well as dimerization.

[00222] Figure 6 is a ribbon model of the FGF23:Fab complex with FGF23 epitope residues identified as colored purple spheres and FGF23-dimer / FGFR1c linking residues as colored cyan spheres, burosumab light chain paratope residues as colored green spheres, and burosumab heavy chain paratope residues as colored yellow spheres. Identification of the epitope and paratope residues by crystallography allowed the rational design of variant burosumab molecules described in Example 6 herein.

[00223] Overall, the 3Å resolution crystallographic structure of the FGF23:burosumab complex provides information about the antigen:antibody interface, which is different from interfaces previously reported in related systems (e.g., FN1 antibody) or the predicted interface (Kanhasut et al. 2022) (compare the epitope residues – purple spheres – in Figure 6 versus Figure 7). Table 11 and Table 12 show the amino acid residues in the long and heavy chain sequences of human FGF23 (R179Q) and burosumab that are involved in the structural interface of the antibody-antigen complex.In Table 11: “Type” refers to the nature of the predicted interaction at the amino acid position(s) in question, “D” represents distance-based interactions, “H” represents hydrogen bonding-based interactions, and “I” represents ionic interactions; “Dist” refers to the distance in angstroms; “Freq” refers to the number of atom-atom contacts associated with the pair (main structure and side chain); and “Area” is given in square Angstroms and refers to the difference in surface area when changing the indicated amino acid. Petition 870250099897, dated 10 / 31 / 2025, pp. 107 / 177 103 / 140 Table 11. Crystal Structure - Con tatos da inl terface Ab:FGF23 Ab Chain Type Ab FGF23 Energy (kcal / mol) Distance (Â) Freq Area (Â2) DL Asn92 Thr46 1.14 4.02 6 13.7 DH L Asn92 Thr46 1.14 4.02 6 13.7 DH L Asn94 4.17 4.73 7.94 DH L Asp93 Ala47 -0.11 3.98 4 22.81 DL Asp93 Arg48 -0.73 3.79 8 18.04 DL Tyr94 Arg48 25.87 3.88 21 41.23 DL Phe95 Arg 48.3 38.3 L Asp99 Asn49 -1.27 4.02 10 14.17 DH Val101 Asn49 -0.28 3.96 4 12.04 DIH H Asp102 Arg140 -18.75 3.81 17 20.08 DH Ala103 Arg10.27 3.27 3.27 DH Asp105 Arg140 0.13 4.39 1 3.01 DL Asp50 Ala141 0.3 3.58 3 16.01 DH L Ser53 Ala141 -0.42 3.74 3 12.38 DH L Asp102 Ala141 -3.13 3.19 Ser Arg143 0.68 3.91 6 15.4 DIH L Asp50 Arg143 -10.44 3.69 15 29.33 DH L Ser52 Arg143 -1.18 3.9 5 26.38 DH L Ser30 Asn150 -1.243 DL Ser30 Pro151 -0.14 3.69 6 10.28 DL Ser30 Pro152 -0.07 3.78 6 10.01 DL Ser31 Pro152 -0.32 3.93 6 14.28 DL Ala32 Pro152 0.1 4.48 1 2.63 DH Asp 150 -250 3.77 2 7.6 DL Ala32 Pro153 0.47 4.13 2 11,57 DL Asn92 Pro153 1.02 4.04 5 23.2 DL Asp50 Tyr154 -1.11 3.84 12 22.08 DH Val101 Tyr154 -0.37 4.1 6 21.93 DH Asp102 Tyr102 541 1.83 1.88 DH Tyr33 Arg48 -0.26 3.86 4 19.34 DH Trp47 Arg48 -0.17 3.98 1 6.28 DH Ile50 Arg48 -0.45 3.95 4 16.24 DH H Ser59 Arg48 -0.93 3.345 DH Asn49 0.21 4.11 11 9.8 DH Ile50 Asn49 -0.46 4.26 3 6.76 DL Phe91 Asn49 -0.43 4.04 4 11.07 DL Phe95 Asn49 -0.6 4 6 13.540 DH Tyr 333, Ser -136 3.75 11 18.51, Petition 870250099897, of 31 / 10 / 2025, p. 108 / 177 104 / 140 DH H Asn31 Tyr51 -0.72 4.01 5 11.3 DH His32 Tyr51 -0.22 4.12 6 6.11 DH Tyr33 Tyr51 0.44 4.01 17 20.11 DH H Asp99 Tyr51 -1.91 3.8 12 17.81 DA H Val101 Tyr51 -0.84 4.17 14 38.24 DH Asn31 Gln54 0.14 4.35 2 7.88 DH Asn31 His56 0.07 4.43 1 5.83 DH H Asn31 Asp62 -2.72 3.79 3 18.27 DH Asn31 Gly63 -0.04 4.08 5 15.47 DH Thr30 Pro65 -0.51 3.87 4 9.73 DH Asn31 Pro65 -0.09 3.96 6 8.27 DH His32 Pro65 0.26 4.29 2 1.88 DH Tyr33 Pro65 0.31 4.19 11 15.76 DH H Asn52 Pro65 -1.87 3.95 9 26.25 DH Ile54 Pro65 -0.66 4.27 5 8.04 DH Ile54 His66 -0.48 4.04 6 21.23 DH Val101 Leu138 -0.94 3.85 8 23.59 DH Val101 Gly139 -0.11 4.11 4 5.8 DH Asp102 Gly139 -0.45 4.03 7 10.59 DL Leu46 Arg140 -0.32 4.3 2 5.34 DH Tyr49 Arg140 0.61 4.1 21 27.29 DIH L Glu55 Arg140 -11.85 3.54 6 21.48 DH Ile100 Arg140 -0.85 3.9 9 33.99 DL Tyr49 Ala141 0.85 4.09 5 9.53 DH Ser31 Tyr154 -0.15 3.74 2 3.82 DH Ala32 Tyr154 -0.25 4.1 8 13.34 Table 12. Main burosumab targets for antibody variant design. Burosumab Paratope AA Residue Type of interaction with FGF23 Variable region of the light chain I29 CAVITY Variable region of the light chain S30 DIRECT Variable region of the light chain S31 DIRECT Variable region of the light chain A32 DIRECT Variable region of the light chain V34 INDIRECT Variable region of the light chain D50 DIRECT Variable region of the light chain A51 DIRECT Variable region of the light chain S52 DIRECT Variable region of the light chain S53 DIRECT Variable region of the light chain F91 DIRECT Variable region of the light chain N92 DIRECT Petition 870250099897, dated 10 / 31 / 2025, pp. 109 / 177 105 / 140 Variable region of the light chain D93 INDIRECT Variable region of the light chain Y94 DIRECT Variable region of the heavy chain T30 INDIRECT Variable region of the heavy chain N31 DIRECT Variable region of the heavy chain N52 DIRECT Variable region of the heavy chain I54 DIRECT Variable region of the heavy chain S59 DIRECT Variable region of the heavy chain I100 DIRECT Variable region of the heavy chain V101 DIRECT Variable region of the heavy chain A103 DIRECT

[00224] As can be seen in Table 11 and Table 12, the amino acid residues found interacting between FGF23 and burosumab are within the protected region 1 and protected region 3 residues identified by HDX-MS (Example 2 above), validating these regions as important mediators of the FGF23-burosumab interaction. However, no residue within protected region 2 was found to be involved in the interaction. Regarding paratop residues, the interface residues within the burosumab heavy chain overlap with the HDX-MS data describing the paratop regions 1 and 2 of the heavy chain, but no interaction residue from the paratop region 3 of the heavy chain was observed (see Example 3 above).Similarly, the interface residues within the burosumab light chain overlap with the HDX-MS data describing region 1 and region 2 of the light chain paratop, but no interaction residues from region 3 of the light chain paratop were observed (see Example 3 above).

[00225] Based on the crystal structure, it was concluded that the HDX-MS data from Example 2 correctly identified the protected regions of the FGF23 molecule bound to burosumab; however, the crystal structure revealed that protected region 2 does not interact with burosumab. Instead, this region of FGF23 is likely protected by the conformational change of the FGF23 structure after burosumab binding (i.e., self-protection). Consequently, the in silico docking runs Petition 870250099897, dated 10 / 31 / 2025, pp. 110 / 177 106 / 140 (Example 4) biases in the HDX-MS data led to the selection of molecular poses that did not reflect the actual structure elucidated by crystallography. Even so, the molecular docking studies of Example 4 generated models that were structurally very similar to the final crystal structure (data not shown) — these models, however, were not initially considered due to the lack of involvement of protected region 2 residues.

[00226] The crystal structure revealed complementary charges and hydrophobic spots involved in the burosumab-FGF23 interaction. Figure 8 shows the FGF23:Fab complex in ribbon model (left) and surface models (right panels), with FGF23 and burosumab binding interfaces rotated in the view and detailed amino acid positions superimposed as stick models (rightmost panel). Positively charged surfaces are shown in blue, negative charges in red, leaving uncharged surfaces white. A positively charged region of FGF23 (R143 and R140) is seen in contact with negatively charged complementary residues of burosumab, and hydrophobic spots on the burosumab surface are seen in contact with uncharged and hydrophobic complementary residues of FGF23 (L138, Y51, and H66) (see insets in Figure 8 detailing the binding interface).

[00227] In particular, certain hydrogen bonding residues have been identified between burosumab and FGF23, which could be targeted to improve antibody binding affinity. Figure 9 shows the interface of the FGF23 surface model with burosumab shown in the ribbon-and-stick model. In the surface models depicted, positively charged surfaces are shown in blue, negatively charged surfaces in red, leaving uncharged surfaces white. Panel A shows the FGF23:Fab complex with the FGF23 portion rotated 90 degrees to display the binding interface with all burosumab residues in contact with Petition 870250099897, dated 10 / 31 / 2025, pp. 111 / 177 107 / 140 FGF23. Panel B shows the surface model of FGF23 (top) with positions of burosumab hydrogen-bonding residues in the stick model (overlaid and bottom). Panel C and Panel D show closer views of ionic interactions and aromatic stacking interactions at the FGF23:burosumab interface, respectively. In panel B, several selected burosumab residues are marked (black arrows) as hydrogen-bonding interaction sites that may be rational design targets across the FGF23 interface. Panel C focuses on the prominent ionic interactions with burosumab aspartate and glutamate residues in contact with FGF23 arginine residues (R143 and R140). Panel D focuses on a pi-stacking interaction at FGF23 residue Y51 interacting with burosumab valine and tyrosine residues.

[00228] In summary, the combination of HDX-MS (Example 2 and Example 3), in silico modeling (Example 4), and crystallography data (present Example 7) allowed the generation of a highly accurate and strongly predictive model of the FGF23:burosumab complex. All three lines of evidence were necessary to reliably identify burosumab residues that could be altered to change burosumab affinity. Together, these results elucidated burosumab residues that likely interact with human FGF23 (see Table 12), which could serve as candidate residues for amino acid alterations (deletions, additions, substitutions) for the rational design of burosumab variants with improved FGF23 affinity. Example 8. Predictive mutagenesis of burosumab based on crystal structure.

[00229] A list of candidate amino acid modifications for the variable heavy chain and variable light chain of burosumab was developed based on the crystal structure and interface contact residues described above in Example 7. Molecular mechanics-based tools were Petition 870250099897, dated 10 / 31 / 2025, page 112 / 177 108 / 140 were used to generate and optimize single (1X) and double (2X) amino acid modifications, focusing on 19 antigen-contact residue positions and 10 semi-distal residue positions (i.e., second-layer distance of approximately 6-8 angstroms). In summary, the crystal structure of the antibody complexed with human FGF23, refined to a 3 Å resolution, was used as a basis to generate the initial coordinates upon which molecular mechanics calculations were performed. The structure was evaluated for completeness, gaps were filled with corresponding residues, and terminals were capped. The resulting structure was subjected to protonation (pH 7) and energy minimization, as implemented in MOE 2022.02 (CCG), and the structural geometry was verified before in silico mutagenesis.

[00230] The antibody-FGF23 interface was analyzed and the relevant contacts were considered based on the distance between antibody and antigen residues. The positions of the residues on the antibody were selected and classified into three groups: close contacts (3~4 Å), second-layer contacts (up to 4.5 Å) and cavity / VdW interactions.

[00231] Three approaches were undertaken to improve affinity. First, variants were designed where a direct interaction was altered. Second, an indirect variant was designed to influence an already established direct interaction. And third, variants were designed that would fill an existing cavity. Emphasis was placed on hydrogen bonding interaction sites that could be modified by altering the interface burosumab residues to introduce ionic interactions or hydrophobic packing sites in aromatic pi-pi interactions, thus increasing affinity. For example, the S52 residue of the VL light chain of burosumab, which forms hydrogen bonding interactions with FGF23 Arg143, can be replaced by a large (Q, T) or negatively charged (D, E) hydrogen bonding (F, Y) stacking that can strengthen the Petition 870250099897, dated 10 / 31 / 2025, pp. 113 / 177 109 / 140 linkage / packing interactions. Similarly, a heavy chain residue Val101, which stacks with FGF23 Tyr51, can be replaced by a bulkier residue (F, I, L, Y) or with a hydrogen bonding property (T). Additional properties that were considered but not directly used for selections were: number of interactions per residue (connectivity), delta(SASA) and deltaG of interaction. Figure 10 and Figure 11 illustrate the relevant interface positions of the light chain and heavy chain of burosumab, respectively, along with details of each residue's interactions with its neighbors.

[00232] Each target position was initially scanned by 1X mutational screening with each mutation followed by rotameric optimization and refinement of the surrounding environment (4,5A). The resulting set of 420 variants was classified based on energetics and structural properties, and the main results (i.e., ΔG <0 and dSASA <0) were combined into 2X and 3X variants for further screening and classification. A final list of 96 variants (1X and 2X) was generated based on the structural analysis of each solution and used as a basis for creating a second list of expanded mutants to further explore the structural space around the interface of interest.

[00233] Initial 1X scanning using predictive mutagenesis resulted in 165 FGF23-binding antibody designs, each comprising a single amino acid alteration relative to the variable region of the burosumab light chain (SEQ ID NO: 4) or the variable region of the burosumab heavy chain (SEQ ID NO: 3). All mutational variants were evaluated and screened according to dAffinity (ΔΔG (kcal / mol)); dStability (ΔΔS (kcal / mol)) less than 3.0 kcal / mol; and dSASA (difference in solvent-accessible surface area) as an indicator of gain or loss of buried surface area after mutation introduction. ΔΔG is a metric to predict how a single-point mutation Petition 870250099897, dated 10 / 31 / 2025, pp. 114 / 177 110 / 140 (i.e., a change of 1 amino acid) will affect protein stability. It is a measure of the energy change between the folded and unfolded states and the change in folding ΔG when a point mutation is present. This metric is used as a predictor to determine if a point mutation will be favorable in terms of protein stability. The more negative the value, the more stable the protein. ΔG values ​​> 0.5 suggest that a mutation would be destabilizing; values ​​of 0.5 > ΔG > -0.5 suggest that the changes should be considered neutral or nearly neutral; and ΔG < -0.5 suggest that the mutation would lead to a more stable protein. ΔΔS, on the other hand, is a measure of the vibrational entropy difference. A positive value indicates greater flexibility, while a negative value indicates a more rigid protein. It is used to predict how changing a given amino acid will alter the protein's entropy.The water-accessible surface area (“VdW SA”) was also calculated. Table 13 provides a summary of the complete 1X scan predictive mutagenesis results for burosumab light chain positions, and Table 14 provides a summary of the complete 1X scan predictive mutagenesis results for burosumab heavy chain positions. Table 13. Results of predictive mutagenesis of Burosumab VL 1X Change in AA of VL (relative to SEQ ID NO: 4) AAG (kcal / mol) AAS (kcal / mol) SA VdW (Â2) A25L 0.04 0.76 21.9 A25V -0.04 -0.26 13.3 I29F 1.061050981 1.632365369 -28.147844 I29L -0.0728879 1.31929151 -46.247868 I29V 0.267352586 1.703597137 -16.464167 S30D -3.6718843 0.83782641 -22.677042 S30E -2.1534008 0.50762112 -29.107056 S30F -6.4906206 -0.0122742 -48.530941 S30I 2.286957776 0.549990944 22.1998 S30L -2.0238975 0.40896165 -44.38591 S30Q -5.4928488 0.42036524 -28.00009 S30T 0.648508526 0.928468736 21.659073 Petition 870250099897, dated 10 / 31 / 2025, pp. 115 / 177 111 / 140 S30V -0,093856649 0,305082747 20,52256 S30Y -5,1055876 0,32176219 -49,158344 S31D 3,56996088 0,63202685 -26,274542 S31E 1,94516954 0,28280798 -36,922615 S31F -2,5842167 -0,7461013 -54,371635 S31I 1,78221214 -0,612691345 10,200069 S31L -0,155463589 -0,263952687 11,979135 S31Q -1,7550465 0,55191751 -18,653433 S31T -1,062041542 0,082099018 1,1834005 S31V 1,667246701 -0,014243701 0,004099946 S31Y -2,7935664 -0,467704 -62,977528 A32F -1,09483682 -0,359228605 -21,611805 A32I 0,770987725 -0,23905564 -11,13908 A32L -1,67783134 -0,656360123 -9,6421356 A32T 0,502542557 0,410571808 0,085010208 A32V 1,83750345 0,406704427 -0,54136229 A32Y -1,232772705 -0,190198481 -15,123551 V34F 1,39938938 2,11635117 2,813026 V34I -0,0978386 0,83360469 -0,5620861 V34L -0,169944874 0,771558986 -0,26748687 V34Y 0,483978126 2,777714634 8,7362003 D50E -0,39974246 0,935434385 20,788279 D50F 0,247562478 0,341023073 18,485962 D50I 2,422160839 0,06896623 8,5886898 D50L 4,759496344 0,345141119 47,131916 D50Q -3,307256369 0.471066083 0.15281084 D50R 5.222100064 -0.239035501 -20.571472 D50S -1.345785356 1.05077198 29.196266 D50T -2.802816003 0.633723865 34.229179 D50V -1.24099163 0.574804443 22.772923 A51F -0.032679132 1.824740267 -3.2918215 A51I -0.341956382 0.844136509 1.9812078 A51L -0.435326019 0.219154085 0.025151623 A51S 0.590189424 1.108058478 -5.2083364 A51T 0.541854453 0.65930264 -4.8948936 A51V -0.874069958 0.174575554 1.8586986 S52D -0.4703946 1.30649565 9.6926641 S52E -0.3021981 1.31177809 11.95747 S52F -2.875389 -0.3494975 -10.131303 S52Q -0.143493129 0.884475034 25.364239, Petition 870250099897, dated 10 / 31 / 2025, pp. 116 / 177 112 / 140 S52T 0.128606217 0.530664437 1.207417 S52Y -3.133793831 -0.150231438 57.616718 S53D -4.9779845 0.37701257 12.876547 S53E -1.5124636 0.85673251 12.985263 S53F -4.4610498 0.13567548 -2.0610542 S53I -2.613199991 -1.08626583 0.62171143 S53L -1.16483418 -0.242817586 24.409243 S53Q -2.034307873 0.57250637 34.919781 S53R -0.9929227 0.2709468 -4.0244999 S53T -0.237225711 0.282621034 3.6471076 S53V -2.33446696 -0.812313395 -3.5696123 S53Y -5.0495748 -0.0684582 -6.7887955 Q90F -2.1 -0.03 -9.8 Q90Y -2.47 -0.07 -13.3 F91K -2.02 1.46 -1.37 F91R -2.5 0.69 -3.24 F91Y 0.073 1.13 -1.4 N92D -1.1543339 0.85687799 6.6619544 N92E 0.655305 0.92451717 -17.099483 N92F 0.14072043 -0.2581115 -6.1453514 N92Q 0.846794726 0.397366739 2.1917546 N92S 2.78115842 0.88155805 -3.7792108 N92T 4.790090325 0.834014183 -28.341656 N92Y -0.4386895 -0.121354 4.7035565 D93E -0.17027592 0.595523751 3.0977747 D93F 2.31451482 -0.969308461 -36.287567 D93Q -0.92803509 0.676351664 4.1740527 D93R 1.31 0.24 9.98 D93S 1.675917835 0389550331 -27.250326 D93T 3.624540183 -0.031258601 0.62384415 D93Y 0.167244776 -0.72587811 -0.26277241 Y94D 1.87364442 1.00868027 -18.932884 Y94E 2.30058187 1.24293306 -38.1619 Y94F 0.26675234 0.54350757 -12.910084 Y94Q 2.060892689 0.66556261 -48.488823 Y94S 2.79793208 1.1990931 -19.928265 Y94T 2.088321013 0.91544587 -44.222107, Petition 870250099897, dated 10 / 31 / 2025, pp. 117 / 177 113 / 140 Table 14. Results of VH 1X burosumab predictive mutagenesis. Change in AA of VH (relative to SEQ ID NO: 3) AAG (kcal / mol) AAS (kcal / mol) SA VdW (Â2) T30E 0.684137201 1.075241818 18.717197 T30F 0.18770538 0.83180798 15.709345 T30Q 0.329924618 0.977560421 18.959789 T30S 0.4350999 1.028327716 -1.8230846 T30Y 0.181118285 0.677831651 55.050991 N31D 2.965937522 0.843428248 8.5089788 N31E 3.141789251 0.790633166 4.7221541 N31F 1.505071443 0.156433609 -19.040478 N31Q -0.658144392 0.474920713 -5.7396598 N31R -0.505348545 -0.091904039 -18.215101 N31Y -1.320720057 0.171386205 76.718956 H32E 0.531400637 1.365501752 -37.351734 H32F -0.01862203 -0.408667274 -31.556114 H32Q -1.634162952 0.91749504 -27.375647 H32S 0.200916565 1.429533882 14.526258 H32T 0.082050769 0.718451694 -35.913139 I50D -3.728931574 3.567036759 19.925985 I50E -2.785319845 2.79166681 -0.059334006 I50F -7.869489552 0.861678876 -11.075091 I50S -3.535387748 3.347888483 19.529911 I50T -0.360198315 1.515972972 9.489028 I50Y -2.70969497 1.614834522 -11.143722 N52E 0.51388448 0.79113671 38,100883 N52F 5.20131785 0.51759159 -9.5689497 I54E 4.723370263 2.798599057 -13.66046 I54F 0.925662374 1.594214175 46.908218 I54L 2.609985936 1.638635049 6.9898171 I54Q 2.457363728 2.490175263 -26.007236 1.455407636 -6.6988673 I54Y 0.214285677 1.82058734 41.796417 S55E 0.420372588 0.92585963 29.211838 S55F -1.053741554 0.889186473 90.757767 S55Q -2.385053801 0.153300959 42.401405, Petition 870250099897, dated 10 / 31 / 2025, pp. 118 / 177 114 / 140 S55T -0,458709886 0,334143886 18,080853 S55Y -0,395620536 0,712916488 95,909492 S59D 0,86873275 0,93661783 11,031759 S59E 1,42930367 0,99314984 -0,1969754 S59F -2,4419416 -0,214348 -3,5550513 S59I -3,9262363 0,07231091 3,0604253 S59L -5,0521902 -0,0593502 11,594638 S59Q -4,7749639 0,34293134 -18,870623 S59T -4,596499 0,41333773 6,0870099 S59V -4,7103284 0,03496928 4,5306883 S59Y -1,6484989 0,52900749 47,218006 D99E -0,232029036 0,837742101 -10,336287 D99Q -0,515419631 1,354701357 -4,7501192 D99Y 2,55 -0,07 -3,24 I100D 3,863436116 3,059680528 14,038824 I100E 1,24916155 3,7849893 -6,1821141 I100F 1,413449602 1,211012567 -3,7273011 I100L 3,025129226 1,291439304 11,713667 I100Q 1,457092754 2,276656577 30,016344 I100V 4,501027071 1,853071862 37,992546 I100Y 1,196847279 1,623909144 50,271866 V101F 2,3716018 0,65795356 -68,693504 V101I -1,9797864 0,2883803 -12,589581 V101L -0,6986304 0,70348261 -6,3387203 V101T 0,332725095 1,418010059 -3,6793778 V101Y 0,70072691 0,683377056 -19,356924 D102E 7,977327323 0.609388647 -7.7275596 D102F 5.034696184 -0.615590492 -32.069496 D102I 3.502175813 -0.214283484 -16.338041 D102L 0.032551406 -0.396340168 -19.263794 D102Q 9.600856797 1.604072636 -6.4905972 D102Y 8.24642893 -0.280662341 -24.580505 A103D -2.96021076 2.462046405 -5.0743966 A103E -3.769332308 2.929902207 13.589715 A103F -2.123937787 0.593947072 -36.6259 A103Q -7.284866478 1.054712643 16.935923 A103S -3.532337047 0.779836492 -1.1532063 A103T 0.030754857 0.821138114 2.9620366 A103Y -3.31726254 0.09784497 -5.0800767 Petition 870250099897, dated 10 / 31 / 2025, pp. 119 / 177 115 / 140

[00234] 2X scanning using predictive mutagenesis for dual amino acid changes relative to the variable regions of the burosumab heavy and light chains resulted in 20 additional FGF23-binding antibody designs, each comprising two amino acid changes relative to the variable region of the burosumab light chain (SEQ ID NO: 4) and / or the variable region of the burosumab heavy chain (SEQ ID NO: 3). Table 15 provides a summary of the 2X scanning predictive mutagenesis results. Table 15. Results of predictive mutagenesis from the 2X burosumab scan_______________________________________________________ Alteração 1 de AA Alteração 2 de AA AAG (kcal / mol) AAS (kcal / mol) SA VdW (Â2) VL:S31E VL:D50F -4,9818861 -0,1303292 5,2358189 VH:N31F VH:S59F -4,1762399 -1,080179 -17,86721 VL:D50F VL:S53E -3,5323026 0,23339506 21,309801 VL:S31F VL:S52E -3,3569123 -0,3131565 -29,340513 VL:D50F VH:V101I -2,6177099 0,20896309 -0,251417 VH:S59D VH:V101I -2,3354685 0,43520707 -18,403811 VL:S31F VL:S53E -2,2152397 -0,0631116 -26,779749 VL:N92E VL:D93F -1,372372 -0,2463043 -26,993782 VL:S31E VL:S53E -0,366416 0,61385435 -2,1146641 VL:S31F VL:D50F -0,3102773 -1,383143 -38,363171 VH:N31E VH:S59E 0,46434414 1,54769119 11,696677 VH:S57E VH:S59D 0,95383059 1,34642839 33,086407 VH:N31E VH:I54F 1,17787603 1,53083549 23,253418 VH:S59T VH:V101L 1,93695757 0,72477322 -18,162439 VH:I54Y VH:V101F 2,69242757 1,60681199 -29,235994 VH:N52F VH:V101I 2,94986019 0,00652214 -24,637529 VL:N92D VL:D93F 2,9614789 -0,573638 -43,874622 VH:N52F VH:V101L 3,54531105 0,55270088 -54,158905 VL:S31F VL:D50E - - - VL:Y94D VH:S59D - - - Example 9. FGF23-binding antibody design panel 2 designed based on crystal structure.

[00235] Table 16 shows 76 antibody-binding designs to Petition 870250099897, dated 10 / 31 / 2025, pp. 120 / 177 116 / 140 FGF23 antibodies engineered from 1X scans as per Examples 7 and 8. Each variant is labeled with a sequential engineered FGF23-binding antibody structure ID numbered from 101 to 176 and has an amino acid alteration relative to the amino acid sequence of the variable region of the parental burosumab heavy chain (SEQ ID NO: 3) or the amino acid sequence of the variable region of the parental burosumab light chain (SEQ ID NO: 4). For clarity, each antibody represented by antibody structure ID numbers UGX101 to UGX176 has the heavy chain sequence (SEQ ID NO: 1) and the light chain sequence (SEQ ID NO: 2) of the parental burosumab, except for the indicated amino acid alteration relative to those sequences.

[00236] Table 17 shows 20 FGF23-binding antibody designs incorporating two amino acid changes (2X scan) as per Examples 7 and 8. Each variant is labeled with a sequential FGF23-binding Antibody Structure ID numbered 177 to 196 and has two amino acid changes relative to the amino acid sequence of the parental burosumab heavy chain variable region (SEQ ID NO: 3) and / or the amino acid sequence of the parental burosumab light chain variable region (SEQ ID NO: 4). For clarity, each antibody represented by antibody structure ID numbers UGX177 to UGX196 has the heavy chain sequence (SEQ ID NO: 1) and the light chain sequence (SEQ ID NO: 2) of the parental burosumab, except for the indicated amino acid changes relative to those sequences. Table 16. 1X2 design panel of FGF23-binding antibodies_______________________________________________________________ FGF23-binding antibody structure ID Designed VL AA alteration (relative to SEQ ID NO: 4) FGF23-binding antibody structure ID Designed VH AA alteration (relative to SEQ ID NO: 3) UGX101 I29F UGX148 T30F UGX102 I29L UGX149 N31D UGX103 S30D UGX150 N31E UGX104 S30E UGX151 N31F Petition 870250099897, dated 10 / 31 / 2025, pp. 121 / 177 117 / 140 UGX105 S30F UGX152 N31Q UGX106 S30L UGX153 N31R UGX107 S30Q UGX154 N52F UGX108 S30Y UGX155 N52Y UGX109 S31D UGX156 I54F UGX110 S31E UGX157 I54Y UGX111 S31F UGX158 S59D UGX112 S31Q ugx159 UGX163 S59Q UGX117 V34I UGX164 S59T UGX118 D50F UGX165 S59V ugx119 UGX123 D50T UGX170 V101F UGX124 D50V UGX171 V101I UGX125 A51V UGX172 V101L UGX126 S52D UGX173 A103D UGX127 S52E UGX174 A103F UGX128 S52F UGX175 A103S UGX129 S53D UGX176 A103T UGX130 S53E UGX131 S53F UGX132 S53R UGX133 S53Y UGX134 F91Y UGX135 N92D UGX136 N92E UGX137 N92F UGX138 N92S UGX139 N92Y UGX140 D93F UGX141 D93Q UGX142 D93S UGX143 D93T UGX144 Y94D Petition 870250099897, dated 10 / 31 / 2025, pp. 122 / 177 118 / 140 UGX145 Y94E UGX146 Y94F UGX147 Y94S Table 17. 2X2 design panel of engineered FGF23-binding antibodies. FGF23-binding antibody structure ID Designed VL AA change (relative to SEQ ID NO: 4) VH AA change (relative to SEQ ID NO: 3) UGX177 S31E, D50F UGX178 N31F, S59F UGX179 D50F, S53E UGX180 S31F, S52E UGX181 D50F V101I UGX182 S59D, V101I UGX183 S31F, S53E UGX184 N92E, D93F UGX185 S31E, S53E UGX186 S31F, D50F UGX187 N31E, S59E UGX188 S57E, S59D UGX189 N31E, I54F UGX190 S59T, V101L UGX191 I54Y, V101F UGX192 N52F, V101I UGX193 N92D, D93F UGX194 N52F, V101L UGX195 S31F, D50E UGX196 Y94D S59D Example 10. In vitro test of selected variants for increased affinity for FGF23

[00237] The FGF23-binding antibody designs from the 1X and 2X antibody design panels shown in Tables 16 and 17, respectively, along with additional antibody variants with 1 or 2 amino acid changes relative to burosumab, were evaluated for affinity by surface plasmon resonance (SPR).

[00238] 96 antibody variants were expressed on a small scale (3 ml) and screened by SPR analysis against human FGF23 (R179Q) in a Petition 870250099897, dated 10 / 31 / 2025, pp. 123 / 177 119 / 140 single concentration (100 nM). Experimental setup for SPR analysis: SPR device - 8K+; chip preparation - CM5 hIgG chip; channels - 1-8; immobilization concentration - 1.5 ug / ml; immobilization method - capture; flow rate - 5 pl / min; contact time - 60 s; running buffer - 1x HBS-EP+ pH 7.4; temperature - 20 °C; flow rate - 50 pl / min; association time - 270 s; dissociation time - 600 s; antigen - rhFGF23(R179Q); maximum concentration - 0.1 μM.

[00239] All antibody variants were classified by the kd turnoff rate or equilibrium dissociation constant kd. The main results with better affinity improvement compared to unmodified burosumab were confirmed with concentration-response curves (CRC). Experimental setup of the SPR analysis for CRC: SPR device - 8K+; chip preparation - CM5 hIgG chip; channels - 1-8; immobilization concentration - 1.5 ug / ml; immobilization method - capture; flow rate - 5 μl / min; contact time - 60 s; running buffer - 1x HBS-EP+ pH 7.4; temperature - 20 °C; flow rate - 50 μl / min; association time - 120 s; dissociation time - 1800 s; rhFGF23(R179Q) antigen; Maximum concentration - 0.1 μM, single-cycle kinetics in triplicate at 9 points.

[00240] The results of the SPR screening and CRC assessment are provided in Table 18, which shows Kd and the determination of the final kinetic parameters ka and kd, as well as the surface activity for selected variants of engineered antibodies. In Table 18, the column headings are abbreviated as follows: “AS ID” refers to “Antibody Structure ID”, a unique identifier for each antibody as defined herein; “AA Change(s)” refers to amino acid residue changes relative to the amino acid sequence of the parental burosumab heavy chain (“HC”) variable region (SEQ ID NO: 3) or the amino acid sequence of the parental light chain (“LC”) variable region. Petition 870250099897, dated 10 / 31 / 2025, pp. 124 / 177 120 / 140 of burosumab (SEQ ID NO: 4), or both; “CL” refers to the uptake level (RU); “Kd” refers to the equilibrium dissociation constant (M); “ka” refers to the association rate or constant (1 / Ms); “kd” refers to the dissociation rate or constant (1 / s); “Rmax” refers to the theoretical Rmax or calculated maximum observable signal (relative units); “SA” refers to the surface activity (%); and “Ratio” refers to the calculated ratio of the KD variant antibody / burosumab KD. Table 18. In vitro testing of selected antibody variants by SPR. ID AS Change(s) of AA CL Kd Ka kd RU SA Ratio UGX205 HC:S59E, LC:Y94D 152.7 4.07E-12 1.53E+07 6.25E-05 59.2 93.9 5 UGX201 HC:S59E, LC:N92F 79.6 5.17E-12 1.12E+07 5.81E-05 30.9 83.4 4 UGX144 LC:Y94D 168.5 5.77E-12 1.09E+07 6.31E-05 65.4 89.5 4 UGX157 HC:I54Y 184.1 7.58E-12 1.49E+07 1.13E-04 71.4 89.1 3 UGX202 HC:S59E, LC:N92Y 146.3 7.59E-12 1.29E+07 9.80E-05 56.7 91.6 3 UGX175 HC:A103S 188.5 7.72E-12 1.24E+07 9.61E-05 73.1 86.8 3 UGX206 HC:S59E, LC:Y94E 51.8 7.87E-12 6.25E+06 4.92E-05 20.1 107.6 3 UGX202 HC:S59E, LC:N92Y 2 UGX156 HC:I54F 111.5 1.05E-11 5.94E+06 6.25E-05 43.2 105.9 2 UGX206 HC:S59E, LC:Y94E 55.9 1.09E-11 7.69E+06 8.37E-05 21.7 85.9 2 UGX203 HC:S59E, LC:S52D 118.5 1.15E-11 1.26E+07 1.45E-04 45.9 81.4 2 UGX126 LC:S52D 145.0 1.24E-11 1.05E+07 1.30E-04 56.2 86.5 2 UGX145 LC:Y94E 120.6 1.33E-11 6.42E+06 8.52E-05 46.8 87.4 2 UGX204 HC:S59E, LC:S52E 120.2 1,33E-11 1.40E+07 1.86E-04 46.6 90.4 2 UGX160 HC:S59F 155.2 1.42E-11 6.15E+06 8.70E-05 60.2 94.5 1 UGX160 HC:S59F 143.0 1.47E-11 6.53E+06 9.61E-05 55.4 92.6 1 UGX139 LC:N92Y 137.0 1.64E-11 6.32E+06 1.04E-04 53.1 86.2 1 UGX127 LC:S52E 90.0 1.76E-11 6.93E+06 1.22E-04 34.9 85.0 1 UGX188 HC:S57E, HC:S59D 158.7 1.83E-11 1.39E+07 2.53E-04 61.5 95.8 1 UGX178 HC:N31F, HC:S59F 159.4 2.12E-11 6.33E+06 1.34E-04 61.8 85.6 1, Petition 870250099897, dated 10 / 31 / 2025, pp. 125 / 177 121 / 140 UGX166 HC:S59Y 176,8 2,24E-11 8,77E+06 1,96E-04 68,5 93,1 1 UGX159 HC:S59E 212,3 2,26E-11 9,91E+06 2,24E-04 82,3 93,0 1 UGX135 LC:N92D 101,3 2,35E-11 7,71E+06 1,81E-04 39,3 100,4 1 UGX140 LC:D93F 135,0 2,42E-11 2,63E+06 6,37E-05 52,3 103,1 1 UGX159 HC:S59E 163,3 2,51E-11 8,83E+06 2,22E-04 63,4 97,9 1 UGX151 HC:N31F 193,3 2,55E-11 8,32E+06 2,12E-04 74,9 90,3 1 UGX148 HC:T30F 157,8 2,72E-11 6,65E+06 1,81E-04 61,1 91,2 1 UGX137 LC:N92F 137,2 3,19E-11 5,04E+06 1,61E-04 53,2 86,5 1 UGX146 LC:Y94F 91,1 3,32E-11 5,14E+06 1,70E-04 35,3 89,9 1 UGX164 HC:S59T 201,0 3,36E-11 5,64E+06 1,90E-04 77,9 91,9 1 UGX130 LC:S53E 169,1 3,48E-11 1,03E+07 3,58E-04 65,5 88,4 1 UGX165 HC:S59V 159,4 3,63E-11 4,82E+06 1,75E-04 61,9 95,4 1 UGX131 LC:S53F 82,5 3,93E-11 6,78E+06 2,66E-04 31,9 95,7 1 UGX152 HC:N31Q 97,2 4,16E-11 6,29E+06 2,62E-04 37,7 91,2 0 UGX165 HC:S59V 166,7 4,48E-11 4,92E+06 2,20E-04 64,6 90,9 0 UGX117 LC:V34I 120,5 5,04E-11 3,35E+06 1,69E-04 46,7 86,9 0 UGX161 HC:S59I 236,6 6,10E-11 4,38E+06 2,67E-04 91,7 84,2 0 UGX117 LC:V34I 152,5 7,03E-11 2,90E+06 2,04E-04 59,1 94,6 0 UGX162 HC:S59L 174,5 9,86E-11 4,79E+06 4,72E-04 67,6 88,4 0 UGX153 HC:N31R 422,9 1,12E-10 2,87E+06 3,22E-04 164,0 83,7 0 UGX133 LC:S53Y 21,2 2,02E-10 3,63E+06 7,33E-04 8,2 84,8 0 UGX190 HC:S59T, HC:V101L 160,4 3,08E-09 3,35E+06 1,03E-02 62,2 92,7 0 UGX192 HC:N52F, HC:V101I 166,4 2,06E-08 1,15E+06 2,36E-02 64,5 82,3 0 UGX201 HC:S59E, LC:N92F 38,6 4,52E-12 8,08E+06 3,65E-05 14,9 99,0 5 UGX201 HC:S59E, LC:N92F 76,7 6,32E-12 9,99E+06 6,31E-05 29,7 85,3 3 UGX144 LC:Y94D 175,3 6,58E-12 1,07E+07 7,03E-05 68,0 89,8 3 UGX206 HC:S59E, LC:Y94E 91,1 6,62E-12 8,64E+06 5,72E-05 35,3 84,0 3 UGX202 HC:S59E, LC:N92Y 121,5 7,53E-12 1,18E+07 8,91E-05 47,1 91,7 3 UGX156 HC:I54F 196,5 9,24E-12 1,06E+07 9,77E-05 76,2 90,8 2 UGX203 HC:S59E, LC:S52D 102,3 1,13E-11 1,28E+07 1,45E-04 39,7 83,5 2 UGX203 HC:S59E, LC:S52D 61,5 1,24E-11 1,08E+07 1,34E-04 23,8 85,3 2 UGX145 LC:Y94E 129,2 1,38E-11 7,07E+06 9,74E-05 50,1 86,4 1 UGX204 HC:S59E, LC:S52E 107.9 1.40E-11 8.64E+06 1.21E-04 41.8 94.6 1 UGX160 HC:S59F 129.9 1.46E-11 6.16E+06 9.01E-05 50.4 93.2 1, Petition 870250099897, dated 10 / 31 / 2025, pp. 126 / 177 122 / 140 UGX204 HC:S59E, LC:S52E 105.0 1.83E-11 7.57E+06 1.38E-04 40.7 95.3 1 UGX140 LC:D93F 135.8 1.06E-10 2.27E+06 2.42E-04 52.6 74.0 0

[00241] These data show that the improved affinity in the engineered burosumab variants is likely due to the improved dissociation rate (inactive rate, or kd), while the association rate (active rate, or ka) remained very similar across all variants. These data also demonstrate at least 13 distinct engineered burosumab variants with a KD ratio greater than or equal to 2, meaning that these antibody variants have at least a 2-fold improvement (up to a 5-fold improvement) in affinity compared to burosumab. Antibodies that exhibited slower or similar elimination rates compared to burosumab were selected for further analysis using concentration-response curves (CRCs) to confirm kinetic parameters.

[00242] The results are given in Table 19, sorted according to the discount rate.In Table 19, the column headings are abbreviated as follows: “AS ID” refers to “Antibody Structure ID,” a unique identifier for each antibody as defined herein; “AA Alteration(s)” refers to amino acid residue alterations relative to the amino acid sequence of the variable heavy chain (“HC”) region of the parental burosumab (SEQ ID NO: 3) or the amino acid sequence of the variable light chain (“LC”) region of the parental burosumab (SEQ ID NO: 4), or both; “Kd” refers to the equilibrium dissociation constant (M); “ka” refers to the association rate or constant (1 / Ms); “kd” refers to the dissociation rate or constant (1 / s); “Rmax” refers to the theoretical Rmax or calculated maximum observable signal (relative units); “SA” refers to the surface activity (%); and “Ratio” refers to the calculated ratio of variant antibody KD / burosumab KD.For clarity, each antibody is represented by the antibody structure ID numbers UGX205, UGX201, UGX144, UGX157, UGX202,. Petition 870250099897, dated 10 / 31 / 2025, pp. 127 / 177 123 / 140 UGX175, UGX206, UGX182, UGX156, UGX203, UGX126, UGX145, and UGX204 in Table 19 have the heavy chain sequence (SEQ ID NO: 1) and the light chain sequence (SEQ ID NO: 2) of the parental burosumab, except for the amino acid changes indicated relative to those sequences. Table 19. Select antibody variants with a Kd ratio (calculated ratio of variant antibody Kd / burosumab Kd) greater than or equal to 2. ID AS Alteração( ões) de AA ID do VH ID do VL Kd ka kd RU SA Razão UGX205 HC:S59E, LC:Y94D VH031 VL066 4,07E-12 1,53E+07 6,25E-05 59,2 93,9 5 UGX201 HC:S59E, LC:N92F VH031 VL050 5,17E-12 1,12E+07 5,81E-05 30,9 83,4 4 UGX144 LC:Y94D VH001 VL066 5,77E-12 1,09E+07 6,31E-05 65,4 89,5 4 UGX157 HC:I54Y VH029 VL001 7,58E-12 1,49E+07 1,13E-04 71,4 89,1 3 UGX202 HC:S59E, LC:N92Y VH031 VL054 7,59E-12 1,29E+07 9,80E-05 56,7 91,6 3 UGX175 HC:A103S VH061 VL001 7,72E-12 1,24E+07 9,61E-05 73,1 86,8 3 UGX206 HC:S59E, LC:Y94E VH031 VL067 7,87E-12 6,25E+06 4,92E-05 20,1 107,6 3 UGX182 HC:S59D, HC:V101I VH055 VL001 9,47E-12 1,49E+07 1,41E-04 36,5 100,5 2 UGX156 HC:I54F VH028 VL- 001 1,05E-11 5,94E+06 6,25E-05 43,2 105,9 2 UGX203 HC:S59E, LC:S52D VH031 VL027 1,15E-11 1,26E+07 1,45E-04 45,9 81,4 2 UGX126 LC:S52D VH001 VL027 1,24E-11 1,05E+07 1,30E-04 56,2 86,5 2 UGX145 LC:Y94E VH001 VL067 1,33E-11 6,42E+06 8,52E-05 46,8 87,4 2 UGX204 HC:S59E, LC:S52E VH031 VL- 030 1,33E-11 1,40E+07 1,86E-04 46,6 90,4 2 Burosumab - VH001 VL- 001 2.08E-11 7.22E+06 1.57E-04 66.2 88.8 1,

[00243] SPR data suggest that several paratopo residues are acting through various mechanisms to support burosumab:FGF23 binding. In particular, amino acid substitutions S52D / E, N92F / Y, and Y94D / E following the light chain of the parental burosumab and I54F / Y, S59D / E, V101I, and A103S following the heavy chain of Petition 870250099897, dated 10 / 31 / 2025, pp. 128 / 177 124 / 140 parenteral burosumab significantly affect antibody affinity for FGF23, predominantly by decreasing the kd turn-off rate.

[00244] Without wishing to limit themselves to theory, the present inventors hypothesize that: Y94D / E light chain substitutions can form ionic interactions with the epitope residue Arg48; S59E heavy chain and Y94D / E light chain substitutions can work together to stabilize sandwich interactions with the epitope residue Arg48; N92F / Y light chain substitutions appear to strengthen hydrophobic packing interactions with epitope residues, such as Pro153, particularly with the S59E heavy chain substitution; the A103S heavy chain substitution likely introduces a hydrogen bond with a nearby epitope residue, including Arg140; S59E heavy chain and S52D / E light chain substitutions can form ionic interactions with epitope residues Arg48 and Arg143, respectively;The heavy chain substitution V101I likely promotes a stronger hydrophobic packing interaction with the epitope residues Tyr51, L138, and Tyr154; and heavy chain substitutions I54F / Y may promote stacking interaction with the epitope residue His66 (Figure 12). Example 11. Characterization of selected variant antibodies against cynoFGF23

[00245] The binding kinetics of 13 antibody variants shown in Table 19 were characterized against the cynomolgus macaque (Macaca fascicularis) FGF23 (R179Q) (i.e., “cynoFGF23”) (SEQ ID NO: 372). The antibody variants were expressed on a small scale (3 ml) and tracked by SPR analysis at a single concentration (100 nM). Experimental setup for SPR analysis for CRC: SPR device - 8K+; chip preparation - CM5 hIgG chip; channels - 1-8; immobilization concentration - 1.5 ug / ml; immobilization method - capture; flow rate - 5 pl / min; contact time - 60 s; running buffer - 1x HBS-EP+ pH 7.4; temperature - 20 Petition 870250099897, dated 10 / 31 / 2025, pp. 129 / 177 125 / 140 °C; flow rate - 50 μL / min; association time - 120 s; dissociation time - 1800 s; antigen - cynoFGF23(R179Q); maximum concentration 0.1 μM, single-cycle kinetics in triplicate at 9 points. The results are provided in Table 20, which shows Kd and the calculated antibody variant Kd / burosumab Kd ratio for each antibody variant against human FGF23 and cynoFGF23. Table 20. Characterization of selected antibody variants against cinoFGF23_____________________________________________________ Human FGF23 Cynomolgus monkey FGF23 ID AS Change in AA Kd (M) Kd Ratio Kd (M) Kd Ratio UGX205 S59E / Y94D 4.07E-12 5 2.57E-12 9 UGX201 S59E / N92F 5.17E-12 4 1.01E-11 2 UGX144 Y94D 5.77E-12 4 6.86E-12 3 UGX157 I54Y 7.58E-12 3 5.73E-12 4 UGX202 S59E / N92Y 7.59E-12 3 6.93E-12 3 UGX175 A103S 7.72E-12 3 6.17E-12 4 UGX206 S59E / Y94E 7.87E-12 3 7.16E-12 3 UGX182 S59D / V101I 9.47E-12 2 1.63E-11 1 UGX156 I54F 1.05E-11 2 4.15E-12 6 UGX203 S59E / S52D 1.15E-11 2 2.29E-11 1 UGX126 S52D 1.24E-11 2 1.03E-11 2 UGX145 Y94E 1.33E-11 2 1.29E-11 2 UGX204 S59E / S52E 1.33E-11 2 1.60E-11 1 UGX139 N92Y 1.64E-11 1 1.62E-11 1

[00246] The binding of selected antibody variants to cynoFGF23 was comparable to that observed with human FGF23. Example 12. Confirmation of HDX-MS epitope / paratope mapping by SPR analysis.

[00247] The HDXMS epitope and paratope mapping data, described in Examples 2 and 3, respectively, were re-evaluated in light of the SPR data described in Example 10 to confirm the effects of major residue changes within the protected HDX-MS regions. Petition 870250099897, dated 10 / 31 / 2025, pp. 130 / 177 126 / 140 Epitope mapping identified three putative epitopes (protected regions 1-3 in Table 3), and paratope mapping identified six regions potentially involved in antigen binding (see Table 4).

[00248] SPR data confirmed that burosumab light chain residues S52 in region 2 of the light chain paratop (see Table 4) and I54 and S59 in region 2 of the heavy chain paratop (see Table 4) are key residues within the HDX-MS protected regions of burosumab, suggesting that these residues are important mediators of burosumab binding to FGF23.

[00249] SPR data also confirmed that burosumab light chain residues S52, N92, and Y94 and burosumab heavy chain residues S59 and V101 are key residues that interact with protected regions 1-3 of FGF23 (Table 3).

[00250] Thus, of the 7 main burosumab residues determined by SPR (light chain S52, N92, Y94 and heavy chain I54, S59, V101 and A103) as replaceable to improve burosumab affinity, 6 of them were also identified by HDX-MS epitope / paratope mapping. This shows strong correlation and agreement between the results of the initial HDX-MS studies and the subsequent modeling based on crystal structure and antibody variant design. Example 13. In silico modeling of additional antibody variants based on SPR analysis.

[00251] Examples 10 to 12 identify and confirm at least 7 burosumab residues (light chain S52, N92, Y94 and heavy chain I54, S59, V101 and A103) that are replaceable to improve antibody affinity to FGF23. These key burosumab residues were subsequently evaluated by in silico modeling to identify additional antibody variants with equivalent or improved affinity compared to parental burosumab and / or variants identified in Table 18 and Table 19. Petition 870250099897, dated 10 / 31 / 2025, pp. 131 / 177 127 / 140

[00252] In summary, all 7 core residues of burosumab were interrogated using predictive mutagenesis by in silico modeling based on the Fab:FGF23 crystal structure of burosumab and SPR data. Specifically, antibody variants from Table 18 and Table 19 having a KD ratio (calculated antibody variant KD / burosumab KD ratio) greater than 2 (i.e., 3 or greater; UGX205, UGX201, UGX202, and UGX206) were analyzed using the Molecular Operating Environment “MOE” (2022.02) to define the structural determinants of binding (i.e., which single residues or residue pairs may be working synergistically to improve affinity). All possible combinations of amino acid changes in the 7 core residues of burosumab in these antibodies were computationally generated. Certain amino acid changes (by amino acid position) that were consistent with the initial empirical SPR data were then selected for further analysis.All combinations of amino acid variants predicted to improve affinity towards the parent burosumab from a structural / computational standpoint are shown in Table 21, where: “AS ID” refers to “Antibody Structure ID”, a unique identifier for each antibody as defined herein; “AA Change(s)” refers to amino acid residue changes relative to the amino acid sequence of the variable heavy chain (“HC”) region of the parent burosumab (SEQ ID NO: 3) or the amino acid sequence of the variable light chain (“LC”) region of the parent burosumab (SEQ ID NO: 4), or both; “ΔΔG” refers to the calculated dAffinity (kcal / mol); “ΔΔS” refers to the calculated dStability (kcal / mol); and “Rationale” refers to the main observations noted during the MOE assessment. Table 21. Structural computational evaluation of additional antibody variants______________________ ___________________________________ ID AS Change(s) of AA of LC Change(s) of AA of HC AAG AAS Justification UGX205 Y94D S59E 4.07 1.98 Petition 870250099897, dated 10 / 31 / 2025, pp. 132 / 177 128 / 140 UGX144 Y94D 2.35 1.07 UGX201 N92F S59E -5.8 1.87 In silico derived dAffinity energies consistent with SPR UGX157 I54Y 2.65 1.80 UGX175 A103S -0.09 0.23 In silico derived dAffinity energies consistent with SPR UGX206 Y94E S59E -1.82 3.43 In silico derived dAffinity energies consistent with SPR UGX202 N92Y S59E 1.34 0.24 UGX156 I54F 1.95 2.05 UGX182 S59D, V101I -0.49 0.56 In silico derived dAffinity energies Consistent with SPR: UGX203 S52D S59E 0.56 1.8 UGX126 S52D -0.50 1.28 In silico derived dAffinity energies consistent with SPR: UGX145 Y94E 2.58 1.05 UGX204 S52E S59E 0.53 1.8 UGX301 Y94D S59D 2.21 1.57 It is likely that S59D / E / Q will contact R48, which is also surrounded by Y94D, creating an electrostatic bridge. Provided the correct geometry can be achieved, these two interactions can significantly increase the affinity.UGX302 Y94D S59Q 1.88 1.08 UGX303 Y94E S59D 3.05 1.31 UGX304 Y94E S59Q -5.5 2.24 UGX305 Y94Q S59D 2.23 1.19 UGX306 Y94Q S59E -3.17 2.93 UGX307 Y94Q S59Q -3.81 2.75 UGX308 S59E, I54Y -1.82 2.24 I54Y likely comes into contact with nearby P65 and H66. S59E is likely to come into contact with nearby R48. These two interactions may increase the KD ratio and create an additive effect. UGX309 S59D, I54Y -3.2 2.27 UGX310 S59Q, I54Y 1.1 1.70 UGX311 Y94D I54Y 1.83 1.99 I54Y likely comes into contact with nearby P65 and H66. Y94D / E / Q is likely to come into contact with nearby R48. These two interactions may synergistically increase the KD ratio. UGX312 Y94E I54Y 3.30 2.04 UGX313 Y94Q I54Y 2.32 1.84 UGX314 N92Y S59D -5.05 1.38 S59D / E / Q likely comes into contact with nearby R48 and is the main driver of the affinity increase. An aromatic residue at the N92 position (i.e., F or Y) can further stabilize the R48 conformation by two possible mechanisms: 1.Pushing the A47 structure closer, which in turn may allow more space for R48 to form a stacking interaction with F95. 2. Sterilely preventing a potential return of R48. In any UGX315 N92Y S59Q 1.34 1.98 UGX316 N92F S59D -5.46 1.10 UGX317 N92F S59Q -5.75 1.33 UGX318 N92L S59D -2.07 1.10 UGX319 N92L S59E -1.17 1.87 UGX320 N92L S59Q -4.31 1.33 UGX321 N92I S59D -2.78 1.30 UGX322 N92I S59E -1.79 1.50. Petition 870250099897, dated 10 / 31 / 2025, pp. 133 / 177 129 / 140 UGX323 N92I S59Q -4.99 0.87 scenario, N92Y or F can interact with P153 near the antigen to complete the local interaction network. UGX324 N92T S59D 1.90 1.98 UGX325 N92T S59E 0.01 2.91 UGX326 N92T S59Q -2.64 1.93 UGX327 I54A 3.55 1.96 Consistent with existing experimental data provided here. UGX328 I54L 2.44 1.61 UGX329 I54V 2.53 1.52 UGX330 I54R 1.22 1.60 UGX331 I54D 4.31 2.76 UGX332 I54G 5.4 2.73 UGX333 I54H 3.57 2.54 UGX334 I54K 2.73 2.47 UGX335 I54M 1.53 1.09 UGX336 I54N 3.29 2.29 UGX337 I54P 6.25 2.50 UGX338 I54W 1.53 1.63 UGX339 S59A 0.56 0.42 Allows confirmation that S59 for acid is required to block R48. UGX340 S59R -1.23 0.51 UGX341 S59N -0.38 1.08 UGX342 S59G 0.74 0.82 UGX343 S59H -1.34 1.00 UGX344 S59K -0.36 1.23 UGX345 S59M -1.15 0.38 UGX346 S59P -2.83 0.55 UGX347 S59W -3.39 -0.53 UGX348 Y94A 3.18 1.07 Consistent with existing experimental data provided here.UGX349 Y94N 1.82 0.99 UGX350 Y94G 2.87 1.78 UGX351 Y94H 1.38 1.12 UGX352 Y94I 2.77 -0.18 UGX353 Y94L 2.91 0.14 UGX354 Y94K 6.05 1.56 UGX355 Y94M 3.22 1.71 UGX356 Y94P 1.32 1.03 UGX357 Y94W -1.52 0.90 UGX358 Y94V 1.67 0.31 UGX359 N92A 4.44 1.36 Consistent with existing experimental data provided here. UGX360 N92R 0.80 0.37 UGX361 N92G 5.24 2.08 UGX362 N92H -1.20 0.79. Petition 870250099897, dated 10 / 31 / 2025, pp. 134 / 177 130 / 140 UGX363 N92I 0.09 -0.51 UGX364 N92L -0.55 -0.68 UGX365 N92K 1.19 0.91 UGX366 N92M -1.51 0.20 UGX367 N92P 3.72 1.59 UGX368 N92W -1.16 0.45 UGX369 N92V 0.73 -0.11 UGX370 A103I -2.64 -0.19 Difficult to capture in silico, but may be beneficial for improving VH:VL interface stability with a positive effect on FGF23 binding and / or providing direct contact with nearby Arg140. Due to the potential for dual effects, it may also be beneficial to test with one of the additive combinations at position 103, in addition to a single mutation (see UGX418 to UGX423). UGX371 A103L 1.0 1.98 UGX372 A103R 5.39 -0.29 UGX373 A103N -0.27 0.58 UGX374 A103G 0.02 1.62 UGX375 A103H 2.93 0.09 UGX376 A103K 0.23 0.57 UGX377 A103M -0.14 0.56 UGX378 A103P -0.04 -0.12 UGX379 A103W 7.92 0.41 UGX380 A103V 0.8 0.84 UGX381 S52D S59Q -2.42 1.13 A shorter acidic residue in position 59 and / or 52 may be more compatible with contact residues in the epitope.UGX382 S52D S59D 0.03 1.77 UGX383 S52E S59Q -2.41 1.06 UGX384 S52E S59D 0.01 1.67 UGX385 S52Q S59E 0.42 1.48 UGX386 S52A -0.2 0.57 Consistent with existing experimental data provided here. UGX387 S52R -0.5 -0.32 UGX388 S52N -0.13 0.97 UGX389 S52G -0.01 0.84 UGX390 S52H -3.0 0.44 UGX391 S52I -0.57 -0.38 UGX392 S52L -0.91 -0.23 UGX393 S52K -1.7 0.21 UGX394 S52M -1.91 -0.10 UGX395 S52P 0.35 1.57 UGX396 S52W -3.18 -0.56 UGX397 S52V -0.21 -0.14 UGX398 S59E, V101I -1.0 0.40 Probably additive and improvement of KD > 3x. UGX399 S59D, V101L 0.81 1.06 UGX400 S59Q, V101I -6.8 0.33 UGX401 S59D, V101S 2.87 2.44 UGX402 S59E, V101S 2.46 2.21. Petition 870250099897, dated 10 / 31 / 2025, pp. 135 / 177 131 / 140 UGX403 V101A 4.38 1.97 Consistent with existing experimental data provided here. UGX404 V101R -3.47 0.31 UGX405 V101N 1.34 2.00 UGX406 V101D -0.69 2.50 UGX407 V101Q 0.55 1.46 UGX408 V101E -0.31 1.73 UGX409 V101G 6.56 2.84 UGX410 V101H -1.65 1.69 UGX411 V101K -3.46 0.91 UGX412 V101M -1.42 0.77 UGX413 V101P 1.70 1.95 UGX414 V101S 2.68 2.22 UGX415 V101W -2.91 0.13 UGX416 I54Y, A103S 3.00 1.80 Probably additive and KD improvement > 3x. UGX417 I54F, A103S 3.00 1.39 UGX418 Y94D A103S 0.46 0.24 UGX419 Y94E A103S -0.55 0.39 UGX420 N92F A103S -1.02 -0.72 UGX421 N92Y A103S 0.95 -0.10 UGX422 S52D A103S -1.76 1.29 UGX423 S52E A103S -0.7 1.24 UGX424 S59D, A103S -0.36 0.39 UGX425 S59E, A103S -0.23 0.53 UGX426 S59Q, A103S -3.10 -0.32 UGX427 N92Y I54Y 1.19 1.38 UGX428 N92F I54Y 1.00 1.00 UGX429 V101I, I54F -1.01 1.58 UGX430 V101I, I54Y -1.59 1.24

[00253] To summarize, mutational solutions of the main antibody variants (e.g., Table 19) were analyzed using structural computational methods, and a set of new variants was generated with designs predicted to have similar or superior affinity. Additional designs included several burosumab antibody variants predicted to have better affinity compared to the parent burosumab. Example 14. Data Summary

[00254] The studies described here sought to rationally design burosumab antibody variants with improved affinity for FGF23, Petition 870250099897, dated 10 / 31 / 2025, pp. 136 / 177 132 / 140 introducing one or more amino acid changes in the heavy chain amino acid sequence, in the light chain amino acid sequence, or in both the heavy chain and light chain amino acid sequences.

[00255] Amino acid residue changes were modeled based on contributions from epitope and paratope mapping studies (Examples 2 and 3), molecular docking and predictive mutagenesis studies (Example 4), structural analysis by crystallography (Example 7) and predictive mutagenesis based on resolved crystal structure (Example 8), refinement of antibody variant designs to identify the most promising antibody structural variants with 2-fold or greater improvements in affinity to human FGF23, and in vitro testing of variants selected by SPR analysis (Examples 9 and 10).

[00256] The studies reported here further characterized certain key antibody variants with respect to cynoFGF23 affinity (Example 11) and identified additional antibody variants through computational investigation of alternative amino acid substitutions at key residues identified as important for modulating burosumab-FGF23 binding (Example 13).

[00257] Table 22 lists unique burosumab antibody variants designed according to the studies described herein. In Table 22, each variant antibody is assigned a unique “AS ID” number. In addition, each antibody variant has one or more light chain amino acid changes (“LC AA Change”) relative to the parental burosumab light chain amino acid sequence of SEQ ID NO: 2, or has one or more variable region light chain amino acid changes (“VL AA Change”) relative to the variable region light chain amino acid sequence of the parental burosumab light chain of SEQ ID NO: 4, and / or has one or more heavy chain amino acid changes (“HC AA Change”) relative to the heavy chain amino acid sequence of Petition 870250099897, dated 10 / 31 / 2025, pp. 137 / 177 133 / 140 burosumab parent of SEQ ID NO: 1 or has one or more amino acid changes in the variable heavy chain region (“VH AA Change”) relative to the amino acid sequence of the variable heavy chain region of burosumab parent of SEQ ID NO: 3. In Table 22, the “AKA” column refers to alternative identifiers assigned to certain AS IDs provided herein. Sequence identification numbers (“SID#s”) are provided for the respective heavy chain (HC), light chain (LC), variable heavy chain (VH), and variable light chain (VL) amino acid sequences disclosed herein. Table 22. Summary of burosumab antibody variants rationally designed to have improved affinity to human FGF23. ID AS Alteração de AA de LC / VL Alteração de AA de HC / VH Também conhecido como SID# HC SID# LC SID# VH SID# VL UGX001 Q27F parental - 654 655 656 657 UGX002 Q27R parental - 658 659 660 661 UGX003 G28D parental - 662 663 664 665 UGX004 G28Q parental - 666 667 668 669 UGX005 G28R parental - 670 671 672 673 UGX006 G28Y parental - 674 675 676 677 UGX007 S30D parental UGX103 678 679 680 681 UGX008 S30F parental UGX105 682 683 684 685 UGX009 S30R parental - 686 687 688 689 UGX010 S30Y parental UGX108 690 691 692 693 UGX011 S31F parental UGX111 694 695 696 697 UGX012 S31Y parental UGX113 698 699 700 701 UGX013 D50E parental - 702 703 704 705 UGX014 D50Q parental UGX120 706 707 708 709 UGX015 D50R parental UGX121 710 711 712 713 UGX016 D50Y parental - 714 715 716 717 UGX017 S52E parental UGX127 718 719 720 721 UGX018 S52Q parental - 722 723 724 725 UGX019 S52R parental UGX387 726 727 728 729 UGX020 S52Y parental - 730 731 732 733 UGX021 S53R parental UGX132 734 735 736 737 UGX022 S53Y parentalUGX133 738 739 740 741 UGX023 L54E parental - 742 743 744 745 Petition 870250099897, dated 10 / 31 / 2025, pp. 138 / 177 134 / 140 UGX024 L54Y parental - 746 747 748 749 UGX025 E55R parental - 750 751 752 753 UGX026 E55Y parental - 754 755 756 757 UGX027 S67E parental - 758 759 760 761 UGX028 S67R parental - 762 763 764 765 UGX029 S67Y parental - 766 767 768 769 UGX030 T69R parental - 770 771 772 773 UGX031 T69Y parental - 774 775 776 777 UGX032 F91E parental - 778 779 780 781 UGX033 F91R parental - 782 783 784 785 UGX034 N92E parental UGX136 786 787 788 789 UGX035 N92F parental UGX137 790 791 792 793 UGX036 N92Q parental - 794 795 796 797 UGX037 N92R parental UGX360 798 799 800 801 UGX038 N92Y parental UGX139 802 803 804 805 UGX039 D93F parental UGX140 806 807 808 809 UGX040 D93R parental - 810 811 812 813 UGX041 D93Y parental - 814 815 816 817 UGX042 Y94E parental UGX145 818 819 820 821 UGX043 Y94R parental - 822 823 824 825 UGX044 parental T28Y - 826 827 828 829 UGX045 parental T30K - 830 831 832 833 UGX046 parental H32K - 834 835 836 837 UGX047 parental H32Y - 838 839 840 841 UGX048 parental Y33D - 842 843 844845 UGX049 parental Y33L - 846 847 848 849 UGX050 parental Y33R - 850 851 852 853 UGX051 parental N52E - 854 855 856 857 UGX052 parental N52Q - 858 859 860 861 UGX053 parental N52R - 862 863 864 865 UGX054 parental S55E - 866 867 868 869 UGX055 parental S55F - 870 871 872 873 UGX056 parental S55I - 874 875 876 877 UGX057 parental S55Q - 878 879 880 881 UGX058 parental S55R - 882 883 884 885 UGX059 parental S55Y - 886 887 888 889 UGX060 parental S57E - 890 891 892 893 UGX061 parental S57F - 894 895 896 897 UGX062 parental S57R - 898 899 900 901 UGX063 parental S57Y - 902 903 904 905 Petição 870250099897, de 31 / 10 / 2025, pág. 139 / 177 135 / 140 UGX064 parental T58F - 906 907 908 909 UGX065 parental T58R - 910 911 912 913 UGX066 parental S59F UGX160 914 915 916 917 UGX067 parental S59R UGX340 918 919 920 921 UGX068 parental S59Y UGX166 922 923 924 925 UGX069 parental N60E - 926 927 928 929 UGX070 parental N60R - 930 931 932 933 UGX071 parental N60Y - 934 935 936 937 UGX072 parental A61F - 938 939 940 941 UGX073 parental A61R - 942 943 944 945 UGX074 parental A61Y - 946 947 948 949 UGX075 parental Q62L - 950 951 952 953 UGX076 parental Q62R - 954 955 956 957 UGX077 parental Q62Y - 958 959 960 961 UGX078 parental Q65E - 962 963 964 965 UGX079 parental Q65R - 966 967 968 969 UGX080 parental Q65Y - 970 971 972 973 UGX081 parental D99F - 974 975 976 977 UGX082 parental D99R - 978 979 980 981 UGX083 parental D99Y - 982 983 984 985 UGX084 parental I100E UGX168 986 987 988 989 UGX085 parental I100F UGX169 990 991 992 993 UGX086 parental I100Y - 994 995 996 997 UGX087 parental V101E UGX408 998 999 1000 1001 UGX088 parental V101F UGX1701002 1003 1004 1005 UGX089 parental V101L UGX172 1006 1007 1008 1009 UGX090 parental V101Q UGX407 1010 1011 1012 1013 UGX091 parental V101R UGX404 1014 1015 1016 1017 UGX092 parental D102E - 1018 1019 1020 1021 UGX093 parental D102F - 1022 1023 1024 1025 UGX094 parental D102K - 1026 1027 1028 1029 UGX095 parental D102R - 1030 1031 1032 1033 UGX096 parental D102Y - 1034 1035 1036 1037 UGX101 I29F parental - 1038 1039 1040 1041 UGX102 I29L parental - 1042 1043 1044 1045 UGX104 S30E parental - 1046 1047 1048 1049 UGX106 S30L parental - 1050 1051 1052 1053 UGX107 S30Q parental - 1054 1055 1056 1057 UGX109 S31D parental - 1058 1059 1060 1061 UGX110 S31E parental - 1062 1063 1064 1065 Petição 870250099897, de 31 / 10 / 2025, pág. 140 / 177 136 / 140 UGX112 S31Q parental - 1066 1067 1068 1069 UGX114 A32F parental - 1070 1071 1072 1073 UGX115 A32V parental - 1074 1075 1076 1077 UGX116 V34F parental - 1078 1079 1080 1081 UGX117 V34I parental - 1082 1083 1084 1085 UGX118 D50F parental - 1086 1087 1088 1089 UGX119 D50L parental - 1090 1091 1092 1093 UGX122 D50S parental - 1094 1095 1096 1097 UGX123 D50T parental - 1098 1099 1100 1101 UGX124 D50V parental - 1102 1103 1104 1105 UGX125 A51V parental - 1106 1107 1108 1109 UGX126 S52D parental - 1110 1111 1112 1113 UGX128 S52F parental - 1114 1115 1116 1117 UGX129 S53D parental - 1118 1119 1120 1121 UGX130 S53E parental - 1122 1123 1124 1125 UGX131 S53F parental - 1126 1127 1128 1129 UGX134 F91Y parental - 1130 1131 1132 1133 UGX135 N92D parental - 1134 1135 1136 1137 UGX138 N92S parental - 1138 1139 1140 1141 UGX141 D93Q parental - 1142 1143 1144 1145 UGX142 D93S parental - 1146 1147 1148 1149 UGX143 D93T parental - 1150 1151 1152 1153 UGX144 Y94D parental - 1154 1155 1156 1157 UGX146 Y94Fparental - 1158 1159 1160 1161 UGX147 Y94S parental - 1162 1163 1164 1165 UGX148 parental T30F - 1166 1167 1168 1169 UGX149 parental N31D - 1170 1171 1172 1173 UGX150 parental N31E - 1174 1175 1176 1177 UGX151 parental N31F - 1178 1179 1180 1181 UGX152 parental N31Q - 1182 1183 1184 1185 UGX153 parental N31R - 1186 1187 1188 1189 UGX154 parental N52F - 1190 1191 1192 1193 UGX155 parental N52Y - 1194 1195 1196 1197 UGX156 parental I54F - 1198 1199 1200 1201 UGX157 parental I54Y - 1202 1203 1204 1205 UGX158 parental S59D - 1206 1207 1208 1209 UGX159 parental S59E - 1210 1211 1212 1213 UGX161 parental S59I - 1214 1215 1216 1217 UGX162 parental S59L - 1218 1219 1220 1221 UGX163 parental S59Q - 1222 1223 1224 1225 Petição 870250099897, de 31 / 10 / 2025, pág. 141 / 177 137 / 140 UGX164 parental S59T - 1226 1227 1228 1229 UGX165 parental S59V - 1230 1231 1232 1233 UGX167 parental I100D - 1234 1235 1236 1237 UGX171 parental V101I - 1238 1239 1240 1241 UGX173 parental A103D - 1242 1243 1244 1245 UGX174 parental A103F - 1246 1247 1248 1249 UGX175 parental A103S - 1250 1251 1252 1253 UGX176 parental A103T - 1254 1255 1256 1257 UGX177 S31E, D50F parental - 1258 1259 1260 1261 UGX178 parental N31F, S59F - 1262 1263 1264 1265 UGX179 D50F, S53E parental - 1266 1267 1268 1269 UGX180 S31F, S52E parental - 1270 1271 1272 1273 UGX181 D50F V101I - 1274 1275 1276 1277 UGX182 parental S59D, V101I - 1278 1279 1280 1281 UGX183 S31F, S53E parental - 1282 1283 1284 1285 UGX184 N92E, D93F parental - 1286 1287 1288 1289 UGX185 S31E, S53E parental - 1290 1291 1292 1293 UGX186 S31F, D50F parental - 1294 1295 1296 1297 UGX187 parental N31E,S59E - 1298 1299 1300 1301 UGX188 parental S57E, S59D - 1302 1303 1304 1305 UGX189 parental N31E, I54F - 1306 1307 1308 1309 UGX190 parental S59T,V101L - 1310 1311 1312 1313 UGX191 parental I54Y, V101F - 1314 1315 1316 1317 UGX192 parental N52F, V101I - 1318 1319 1320 1321 UGX193 N92D, D93F parental - 1322 1323 1324 1325 UGX194 parental N52F, V101L - 1326 1327 1328 1329 UGX195 S31F, D50E parental - 1330 1331 1332 1333 UGX196 Y94D S59D UGX301 1334 1335 1336 1337 UGX201 N92F S59E - 1338 1339 1340 1341 UGX202 N92Y S59E - 1342 1343 1344 1345 UGX203 S52D S59E - 1346 1347 1348 1349 UGX204 S52E S59E - 1350 1351 1352 1353 UGX205 Y94D S59E - 1354 1355 1356 1357 UGX206 Y94E S59E - 1358 1359 1360 1361 UGX302 Y94D S59Q - 1362 1363 1364 1365 UGX303 Y94E S59D - 1366 1367 1368 1369 UGX304 Y94E S59Q - 1370 1371 1372 1373 UGX305 Y94Q S59D - 1374 1375 1376 1377 UGX306 Y94Q S59E - 1378 1379 1380 1381 UGX307 Y94Q S59Q - 1382 1383 1384 1385, Petição 870250099897, de 31 / 10 / 2025, pág. 142 / 177 138 / 140 UGX308 parental S59E, I54Y - 1386 1387 1388 1389 UGX309 parental S59D, I54Y - 1390 1391 1392 1393 UGX310 parental S59Q, I54Y - 1394 1395 1396 1397 UGX311 Y94D I54Y - 1398 1399 1400 1401 UGX312 Y94E I54Y - 1402 1403 1404 1405 UGX313 Y94Q I54Y - 1406 1407 1408 1409 UGX314 N92Y S59D - 1410 1411 1412 1413 UGX315 N92Y S59Q - 1414 1415 1416 1417 UGX316 N92F S59D - 1418 1419 1420 1421 UGX317 N92F S59Q - 1422 1423 1424 1425 UGX318 N92L S59D - 1426 1427 1428 1429 UGX319 N92L S59E - 1430 1431 1432 1433 UGX320 N92L S59Q - 1434 1435 1436 1437 UGX321 N92I S59D - 1438 1439 1440 1441 UGX322 N92I S59E - 1442 1443 1444 1445 UGX323 N92I S59Q - 1446 1447 1448 1449 UGX324 N92T S59D - 1450 1451 1452 1453 UGX325 N92T S59E - 1454 1455 1456 1457 UGX326 N92T S59Q - 1458 1459 1460 1461 UGX327 parental I54A - 1462 1463 1464 1465 UGX328 parental I54L - 1466 1467 1468 1469 UGX329 parental I54V - 1470 1471 1472 1473 UGX330 parental I54R - 1474 1475 1476 1477 UGX331 parental I54D - 1478 1479 1480 1481 UGX332parental I54G - 1482 1483 1484 1485 UGX333 parental I54H - 1486 1487 1488 1489 UGX334 parental I54K - 1490 1491 1492 1493 UGX335 parental I54M - 1494 1495 1496 1497 UGX336 parental I54N - 1498 1499 1500 1501 UGX337 parental I54P - 1502 1503 1504 1505 UGX338 parental I54W - 1506 1507 1508 1509 UGX339 parental S59A - 1510 1511 1512 1513 UGX341 parental S59N - 1514 1515 1516 1517 UGX342 parental S59G - 1518 1519 1520 1521 UGX343 parental S59H - 1522 1523 1524 1525 UGX344 parental S59K - 1526 1527 1528 1529 UGX345 parental S59M - 1530 1531 1532 1533 UGX346 parental S59P - 1534 1535 1536 1537 UGX347 parental S59W - 1538 1539 1540 1541 UGX348 Y94A parental - 1542 1543 1544 1545 Petição 870250099897, de 31 / 10 / 2025, pág. 143 / 177 139 / 140 UGX349 Y94N parental - 1546 1547 1548 1549 UGX350 Y94G parental - 1550 1551 1552 1553 UGX351 Y94H parental - 1554 1555 1556 1557 UGX352 Y94I parental - 1558 1559 1560 1561 UGX353 Y94L parental - 1562 1563 1564 1565 UGX354 Y94K parental - 1566 1567 1568 1569 UGX355 Y94M parental - 1570 1571 1572 1573 UGX356 Y94P parental - 1574 1575 1576 1577 UGX357 Y94W parental - 1578 1579 1580 1581 UGX358 Y94V parental - 1582 1583 1584 1585 UGX359 N92A parental - 1586 1587 1588 1589 UGX361 N92G parental - 1590 1591 1592 1593 UGX362 N92H parental - 1594 1595 1596 1597 UGX363 N92I parental - 1598 1599 1600 1601 UGX364 N92L parental - 1602 1603 1604 1605 UGX365 N92K parental - 1606 1607 1608 1609 UGX366 N92M parental - 1610 1611 1612 1613 UGX367 N92P parental - 1614 1615 1616 1617 UGX368 N92W parental - 1618 1619 1620 1621 UGX369 N92V parental - 1622 1623 1624 1625 UGX370 parental A103I - 1626 1627 1628 1629 UGX371 parental A103L - 1630 1631 1632 1633 UGX372 parental A103R - 1634 1635 1636 1637 UGX373parental A103N - 1638 1639 1640 1641 UGX374 parental A103G - 1642 1643 1644 1645 UGX375 parental A103H - 1646 1647 1648 1649 UGX376 parental A103K - 1650 1651 1652 1653 UGX377 parental A103M - 1654 1655 1656 1657 UGX378 parental A103P - 1658 1659 1660 1661 UGX379 parental A103W - 1662 1663 1664 1665 UGX380 parental A103V - 1666 1667 1668 1669 UGX381 S52D S59Q - 1670 1671 1672 1673 UGX382 S52D S59D - 1674 1675 1676 1677 UGX383 S52E S59Q - 1678 1679 1680 1681 UGX384 S52E S59D - 1682 1683 1684 1685 UGX385 S52Q S59E - 1686 1687 1688 1689 UGX386 S52A parental - 1690 1691 1692 1693 UGX388 S52N parental - 1694 1695 1696 1697 UGX389 S52G parental - 1698 1699 1700 1701 UGX390 S52H parental - 1702 1703 1704 1705 Petição 870250099897, de 31 / 10 / 2025, pág. 144 / 177 140 / 140 UGX391 S52I parental - 1706 1707 1708 1709 UGX392 S52L parental - 1710 1711 1712 1713 UGX393 S52K parental - 1714 1715 1716 1717 UGX394 S52M parental - 1718 1719 1720 1721 UGX395 S52P parental - 1722 1723 1724 1725 UGX396 S52W parental - 1726 1727 1728 1729 UGX397 S52V parental - 1730 1731 1732 1733 UGX398 parental S59E, V101I - 1734 1735 1736 1737 UGX399 parental S59D, V101L - 1738 1739 1740 1741 UGX400 parental S59Q, V101I - 1742 1743 1744 1745 UGX401 parental S59D, V101S - 1746 1747 1748 1749 UGX402 parental S59E,V101S - 1750 1751 1752 1753 UGX403 parental V101A - 1754 1755 1756 1757 UGX405 parental V101N - 1758 1759 1760 1761 UGX406 parental V101D - 1762 1763 1764 1765 UGX409 parental V101G - 1766 1767 1768 1769 UGX410 parental V101H - 1770 1771 1772 1773 UGX411 parental V101K - 1774 1775 1776 1777 UGX412 parental V101M - 1778 1779 1780 1781 UGX413 parental V101P - 1782 1783 1784 1785 UGX414 parental V101S - 1786 1787 1788 1789 UGX415 parental V101W - 1790 1791 1792 1793 UGX416 parental I54Y, A103S - 1794 1795 1796 1797 UGX417 parental I54F, A103S - 1798 1799 1800 1801 UGX418 Y94D A103S - 1802 1803 1804 1805 UGX419 Y94E A103S - 1806 1807 1808 1809 UGX420 N92F A103S - 1810 1811 1812 1813 UGX421 N92Y A103S - 1814 1815 1816 1817 UGX422 S52D A103S - 1818 1819 1820 1821 UGX423 S52E A103S - 1822 1823 1824 1825 UGX424 parental S59D, A103S - 1826 1827 1828 1829 UGX425 parental S59E, A103S - 1830 1831 1832 1833 UGX426 parental S59Q,A103S - 1834 1835 1836 1837 UGX427 N92Y I54Y - 1838 1839 1840 1841 UGX428 N92F I54Y - 1842 1843 1844 1845 UGX429 parent V101I, I54F - 1846 1847 1848 1849 UGX430 parent V101I, I54Y - 1850 1851 1852 1853, Petition 870250099897, dated 10 / 31 / 2025, pp. 145 / 177

Claims

1 / 16 CLAIMS 1. An isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable region heavy chain (VH) amino acid sequence according to SEQ ID NO: 3, but comprising one or more amino acid changes relative to SEQ ID NO: 3, wherein one or more amino acid changes are selected from T30E, T30F, T30Q, T30S, T30Y, N31D, N31E, N31F, N31Q, N31R, N31Y, H32E, H32F, H32Q, H32S, H32T, I50D, I50E, I50F, I50S, I50T, I50Y, N52E, N52F, N52Q, N52Y, I54E, I54F, I54L, I54Q, I54S, I54T, I54V, I54Y, S55E, S55F, S55Q, S55T, S55Y, S59D, S59E, S59F, S59I, S59L, S59Q, S59T, S59V, S59Y, D99E, D99Q, D99Y, I100D, I100E, I100F, I100L, I100Q, I100V, I100Y, V101F, V101I, V101L, V101T, V101Y, D102E, D102F, D102I, D102L, D102Q, D102Y, A103D, A103E, A103F, A103Q, A103S, A103T and A103Y.

2. An isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable light chain (VL) region amino acid sequence according to SEQ ID NO: 4, but comprising one or more amino acid changes relative to SEQ ID NO: 4, wherein one or more amino acid changes are selected from A25L, A25V, I29F, I29L, I29V, S30D, S30E, S30F, S30I, S30L, S30Q, S30T, S30V, S30Y, S31D, S31E, S31F, S31I, S31L, S31Q, S31T, S31V, S31Y, A32F, A32I, A32L, A32T, A32V, A32Y, V34F, V34I, V34L, V34Y, D50E, D50F, D50I, D50L, D50Q, D50R, D50S, D50T, D50V, A51F, A51I, A51L, A51S, A51T, A51V, S52D, S52E, S52F, S52Q, S52T, S52Y, S53D, S53E, S53F, S53I, S53L, S53Q, S53R, S53T, S53V, S53Y, Q90F, Q90Y, Petition 870250099897, dated 10 / 31 / 2025, page.146 / 177 2 / 16 F91K, F91R, F91Y, N92D, N92E, N92F, N92Q, N92S, N92T, N92Y, D93E, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94D, Y94E, Y94F, Y94Q, Y94S e Y94T.

3. An isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a VH amino acid sequence according to SEQ ID NO: 3 and a VL amino acid sequence according to SEQ ID NO: 4, wherein the VH amino acid sequence comprises one or more amino acid alterations selected from T30E, T30F, T30Q, T30S, T30Y, N31D, N31E, N31F, N31Q, N31R, N31Y, H32E, H32F, H32Q, H32S, H32T, I50D, I50E, I50F, I50S, I50T, I50Y, N52E, N52F, N52Q, N52Y, I54E, I54F, I54L, I54Q, I54S, I54T, I54V, I54Y, S55E, S55F, S55Q, S55T, S55Y, S59D, S59E, S59F, S59I, S59L, S59Q, S59T, S59V, S59Y, D99E, D99Q, D99Y, I100D, I100E, I100F, I100L, I100Q, I100V, I100Y, V101F, V101I, V101L, V101T, V101Y, D102E, D102F, D102I, D102L, D102Q, D102Y, A103D, A103E, A103F, A103Q, A103S, A103T and A103Y,and wherein the VL amino acid sequence comprises one or more amino acid alterations selected from A25L, A25V, I29F, I29L, I29V, S30D, S30E, S30F, S30I, S30L, S30Q, S30T, S30V, S30Y, S31D, S31E, S31F, S31I, S31L, S31Q, S31T, S31V, S31Y, A32F, A32I, A32L, A32T, A32V, A32Y, V34F, V34I, V34L, V34Y, D50E, D50F, D50I, D50L, D50Q, D50R, D50S, D50T, D50V, A51F, A51I, A51L, A51S, A51T, A51V, S52D, S52E, S52F, S52Q, S52T, S52Y, S53D, S53E, S53F, S53I, S53L, S53Q, S53R, S53T, S53V, S53Y, Q90F, Q90Y, F91K, F91R, F91Y, N92D, N92E, N92F, N92Q, N92S, N92T, N92Y, D93E, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94D, Y94E, Y94F, Y94Q, Y94S and Y94T.

4. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a heavy chain complementarity-determining region 1 (HCDR1) according to an amino acid sequence selected from SEQ ID NOS: 22-32.

5. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a heavy chain complementarity-determining region 2 (HCDR2) according to an amino acid sequence selected from SEQ ID NOS: 33-65.

6. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a heavy chain complementarity-determining region 3 (HCDR3) according to an amino acid sequence selected from SEQ ID NOS: 66-93.

7. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a light chain complementarity-determining region 1 (LCDR1) according to an amino acid sequence selected from SEQ ID NOS: 94-126.

8. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a light chain complementarity-determining region 2 (LCDR2) according to an amino acid sequence selected from SEQ ID NOs: 127-158.

9. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a complementarity-determining light chain 3 (LCDR3) region according to an amino acid sequence selected from SEQ ID NOS: 159-185.

10. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises an HCDR1, an HCDR2, an HCDR3, an LCDR1, an LCDR2 and an LCDR3, in which: HCDR1 comprises an amino acid sequence selected from SEQ ID NO: 11 and SEQ ID NOs: 22-32; HCDR2 comprises an amino acid sequence selected from SEQ ID NO: 12 and SEQ ID NOs: 33-65; HCDR3 comprises an amino acid sequence selected from SEQ ID NO: 13 and SEQ ID NOs: 66-93; LCDR1 comprises an amino acid sequence selected from SEQ ID NO: 14 and SEQ ID NOs: 94-126; LCDR2 comprises an amino acid sequence selected from SEQ ID NO: 15 and SEQ ID NOs: 127-158; and LCDR3 comprises an amino acid sequence selected from SEQ ID NO: 16 and SEQ ID Nos: 159-185.

11. Isolated antibody or fragment thereof according to any one of claims 1 to 10, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region and a variable light chain (VL) region, wherein the VH comprises an amino acid sequence that has at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or Petition 870250099897, dated 10 / 31 / 2025, p. 149 / 177 5 / 16 wherein the VL comprises an amino acid sequence that has at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

12. Isolated antibody or fragment thereof according to any one of claims 1 to 11, wherein the antibody or fragment thereof is characterized in that it comprises a VH comprising an amino acid sequence that has at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the antibody or fragment thereof comprises a VL comprising an amino acid sequence that has at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

13. Isolated antibody or fragment thereof according to any one of claims 1 to 12, wherein the antibody or fragment thereof is characterized in that it comprises a VH comprising an amino acid sequence that has at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the antibody or fragment thereof comprises a VL comprising an amino acid sequence that has at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

14. Isolated antibody or fragment thereof according to any one of claims 1 to 13, wherein the antibody or fragment thereof is characterized in that it comprises a VH and a VL, and wherein the VH comprises an amino acid sequence that has at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL comprises an amino acid sequence that has at least 80% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

15. Isolated antibody or fragment thereof according to any one of claims 1 to 14, wherein the antibody or fragment thereof is characterized in that it comprises a VH and a VL, and wherein the VH comprises an amino acid sequence that has at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL comprises an amino acid sequence that has at least 90% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

16. Isolated antibody or fragment thereof according to any one of claims 1 to 15, wherein the antibody or fragment thereof is characterized in that it comprises a VH and a VL, and wherein the VH comprises an amino acid sequence that has at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, and the VL comprises an amino acid sequence that has at least 95% sequence identity with an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

17. Isolated antibody or fragment thereof according to any one of claims 1 to 16, wherein the antibody or fragment thereof is characterized in that it comprises a VH and a VL, and wherein the VH comprises an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270, or the VL comprises an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

18. Isolated antibody or fragment thereof according to any one of claims 1 to 16, wherein the antibody or fragment thereof is characterized in that it comprises a VH and a VL, and wherein the VH comprises an amino acid sequence selected from SEQ ID NO: 3 and SEQ ID NOs: 186-270; and the VL comprises an amino acid sequence selected from SEQ ID NO: 4 and SEQ ID NOs: 271-368.

19. Isolated antibody or fragment thereof according to any one of claims 1 to 18, wherein the antibody or fragment thereof is characterized in that it comprises an amino acid sequence of variable heavy chain (VH) region according to SEQ ID NO: 3 and a variable light chain (VL) region according to SEQ ID NO: 4, but comprising at least two amino acid changes in the VH and / or VL sequences, wherein the at least two amino acid changes are selected from VL:S31E / VL:D50F, VH:N31F / VH:S59F, VL:D50F / VL:S53E, VH:S59D / VH:V101I, VL:S31E / VL:S53E, VH:S57E / VH:S59D, VH:I54Y / VH:V101F, VH:N52F / VH:V101L, VL:Y94D / VH:S59E, VL:S31F / VL:S52E, VL:S31F / VL:S53E, VL:S31F / VL:D50F, VH:N31E / VH:I54F, VH:N52F / VH:V101I, VL:S31F / VL:D50E, VL:N92F / VH:S59E, VL:D50F / VH:V101I, VL:N92E / VL:D93F, VH:N31E / VH:S59E, VH:S59T / VH:V101L, VL:N92D / VL:D93F, VL:Y94D / VH:S59D, VL:N92Y / VH:S59E, VL:Y94E / VH:S59E, VL:S52D / VH:S59E and VL:S52E / VH:S59E.

20. Isolated antibody or fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a VH amino acid sequence according to SEQ ID NO: 3 and a VL amino acid sequence according to SEQ ID NO: 4, wherein the VH amino acid sequence comprises one or more amino acid alterations selected from I54F, I54Y, S59D, S59E, V101I and A103S compared to SEQ ID NO:

3.

21. Isolated antibody or fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a VH amino acid sequence according to SEQ ID NO: 3 and a VL amino acid sequence according to SEQ ID NO: 4, wherein the VL amino acid sequence comprises one or more amino acid changes selected from S52D, S52E, N92F, N92Y, Y94D and Y94E compared to SEQ ID NO:

4.

22. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-027 (UGX126).

23. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-066 (UGX144).

24. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-001 and a variable light chain (VL) region according to VL-067 (UGX145).

25. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-028 and a variable light chain (VL) region according to VL-001 (UGX156).

26. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-029 and a variable light chain (VL) region according to VL-001 (UGX157).

27. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-061 and a variable light chain (VL) region according to VL-001 (UGX175).

28. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-055 and a variable light chain (VL) region according to VL-001 (UGX182).

29. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-050 (UGX201).

30. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-054 (UGX202).

31. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-027 (UGX203).

32. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-030 (UGX204).

33. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-066 (UGX205).

34. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region according to VH-031 and a variable light chain (VL) region according to VL-067 (UGX206).

35. An isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a heavy chain (HC) amino acid sequence according to SEQ ID NO: 1 and a light chain (LC) amino acid sequence according to SEQ ID NO: 2, wherein the antibody or fragment thereof comprises one or more HC amino acid changes relative to SEQ ID NO: 1 and / or one or more LC amino acid changes relative to SEQ ID NO: 2, wherein one or more HC amino acid changes are selected from T28Y, T30F, T30K, N31D, N31E, N31F, N31Q, N31R, H32K, H32Y, Y33D, Y33L, Y33R, N52E, N52F, N52Q, N52R, N52Y, I54A, I54D, I54F, I54G, I54H, I54K, I54L, I54M, I54N, I54P, I54R, I54V, I54W, I54Y, S55E, S55F, S55I, S55Q, S55R, S55Y, S57E, S57F, S57R, S57Y, T58F, T58R, S59A, S59D, S59E, S59F, S59G, S59H, S59I, S59K, S59L, S59M, S59N, S59P, S59Q,S59R, S59T, S59V, S59W, S59Y, N60E, N60R, N60Y, A61F, A61R, A61Y, Q62L, Q62R, Q62Y, Q65E, Q65R, Q65Y, D99F, D99R, D99Y, I100D, I100E, I100F, I100Y, V101A, V101D, V101E, V101F, V101G, V101H, V101I, V101K, V101L, V101M, V101N, V101P, V101Q, V101R, V101S, V101W, D102E, D102F, D102K, D102R, D102Y, A103D, A103F, A103G, A103H, A103I, A103K, A103L, A103M, A103N, A103P, A103R, A103S, A103T, A103V and A103W, and one or more LC amino acid changes are selected from Q27F, Q27R, G28D, G28Q, G28R, G28Y, I29F, I29L, S30D, S30E, S30F, S30L, S30Q, S30R, S30Y, S31D, S31E, S31F, S31Q, S31Y, Petition 870250099897, dated 10 / 31 / 2025, page. 156 / 177 12 / 16 A32F, A32V, V34F, V34I, D50E, D50F, D50L, D50Q, D50R, D50S, D50T, D50V, D50Y, A51V, S52A, S52D, S52E, S52F, S52G, S52H, S52I, S52K, S52L, S52M, S52N, S52P, S52Q, S52R, S52V, S52W, S52Y, S53D, S53E, S53F, S53R, S53Y, L54E, L54Y, E55R, E55Y, S67E, S67R, S67Y, T69R, T69Y, F91E, F91R, F91Y, N92A, N92D, N92E, N92F, N92G, N92H, N92I, N92K, N92L, N92M, N92P,N92Q, N92R, N92S, N92T, N92V, N92W, N92Y, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94A, Y94D, Y94E, Y94F, Y94G, Y94H, Y94I, Y94K, Y94L, Y94M, Y94N, Y94P, Y94Q, Y94R, Y94S, Y94V, Y94W.

36. Isolated antibody or a fragment thereof that specifically binds to a human fibroblast growth factor 23 (FGF23) polypeptide, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region amino acid sequence according to SEQ ID NO: 3 and a variable light chain (VL) region amino acid sequence according to SEQ ID NO: 4, wherein the antibody or fragment thereof comprises one or more VH amino acid changes relative to SEQ ID NO: 3 and / or one or more VL amino acid changes relative to SEQ ID NO: 4, wherein one or more VH amino acid changes are selected from T28Y, T30F, T30K, N31D, N31E, N31F, N31Q, N31R, H32K, H32Y, Y33D, Y33L, Y33R, N52E, N52F, N52Q, N52R, N52Y, I54A, I54D, I54F, I54G, I54H, I54K, I54L, I54M, I54N, I54P, I54R, I54V, I54W, I54Y, S55E, S55F, S55I, S55Q, S55R, S55Y, S57E, S57F, S57R, S57Y, T58F, T58R, S59A, S59D, S59E, S59F, S59G, S59H,S59I, S59K, S59L, S59M, S59N, S59P, S59Q, S59R, S59T, S59V, S59W, S59Y, N60E, N60R, N60Y, A61F, A61R, A61Y, Q62L, Q62R, Q62Y, Q65E, Q65R, Q65Y, D99F, D99R, D99Y, I100D, I100E, I100F, I100Y, V101A, V101D, V101E, V101F, V101G, V101H, V101I, V101K, V101L, V101M, V101N, V101P, V101Q, V101R, V101S, V101W, D102E, D102F, D102K, D102R, D102Y, A103D, A103F, A103G, Petition 870250099897, dated 10 / 31 / 2025, page. 157 / 177 13 / 16 A103H, A103I, A103K, A103L, A103M, A103N, A103P, A103R, A103S, A103T, A103V and A103W, and one or more VL amino acid changes are selected from Q27F, Q27R, G28D, G28Q, G28R, G28Y, I29F, I29L, S30D, S30E, S30F, S30L, S30Q, S30R, S30Y, S31D, S31E, S31F, S31Q, S31Y, A32F, A32V, V34F, V34I, D50E, D50F, D50L, D50Q, D50R, D50S, D50T, D50V, D50Y, A51V, S52A, S52D, S52E, S52F, S52G, S52H, S52I, S52K, S52L, S52M, S52N, S52P, S52Q, S52R, S52V, S52W, S52Y, S53D, S53E, S53F, S53R, S53Y, L54E, L54Y, E55R, E55Y, S67E, S67R, S67Y, T69R, T69Y, F91E, F91R, F91Y, N92A, N92D, N92E, N92F,N92G, N92H, N92I, N92K, N92L, N92M, N92P, N92Q, N92R, N92S, N92T, N92V, N92W, N92Y, D93F, D93Q, D93R, D93S, D93T, D93Y, Y94A, Y94D, Y94E, Y94F, Y94G, Y94H, Y94I, Y94K, Y94L, Y94M, Y94N, Y94P, Y94Q, Y94R, Y94S, Y94V and Y94W.

37. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide with higher binding affinity compared to burosumab, wherein the antibody or fragment thereof is characterized in that it comprises a variable heavy chain (VH) region amino acid sequence and a variable light chain (VL) region amino acid sequence as per Table 22.

38. Isolated antibody or a fragment thereof that binds specifically to a human fibroblast growth factor 23 (FGF23) polypeptide with higher binding affinity compared to burosumab, wherein the antibody or fragment thereof is characterized in that it comprises a heavy chain (HC) amino acid sequence and a light chain (LC) amino acid sequence as per Table 22.

39. Isolated antibody or fragment thereof according to any of claims 1 to 38, wherein the antibody or fragment thereof is characterized by the fact that it has a higher affinity for human FGF23 compared to burosumab.

40. Isolated antibody or fragment thereof according to any one of claims 1 to 39, wherein the antibody or fragment thereof is characterized in that it has approximately 2 to 10 times greater binding affinity for human FGF23 compared to burosumab.

41. Isolated antibody or fragment thereof according to any one of claims 1 to 40, characterized in that the binding affinity of the antibody or fragment thereof to human FGF23 (Kd) is between about 1*10-12 M and about 7*10-12 M.

42. Isolated antibody or fragment thereof according to any one of claims 1 to 41, characterized in that it is intended for use in a method for reducing serum FGF23 in a subject in need thereof.

43. Isolated antibody or fragment thereof according to any one of claims 1 to 41, characterized in that it is intended for use in a method for increasing the maximum renal threshold for phosphate reabsorption (TmP) in a subject in need thereof.

44. Isolated antibody or fragment thereof according to any one of claims 1 to 41, characterized in that it is intended for use in a method for increasing serum inorganic phosphorus (Pi) in a subject in need thereof.

45. Isolated antibody or fragment thereof according to any one of claims 1 to 41, characterized in that it is intended for use in a method for increasing the serum concentration of 1,25-dihydroxyvitamin D (1,25[OH]2D) in a subject in need thereof.

46. ​​Isolated antibody or fragment thereof according to any of claims 1 to 41, characterized in that it is intended for use in a method for treating a hypophosphatemic condition in a subject in need thereof.

47. Isolated antibody or fragment thereof for use, as defined in any of claims 42 to 46, characterized in that the subject is diagnosed with X-linked hypophosphatemia (XLH) or tumor-induced osteomalacia (TIO).

48. A method for lowering serum FGF23 in a subject in need thereof, wherein the method is characterized by comprising administering to the subject the isolated antibody or a fragment thereof, as defined in any of claims 1-41.

49. A method for increasing the maximum renal threshold for phosphate reabsorption (TmP) in a subject in need thereof, wherein the method is characterized by comprising administering to the subject the isolated antibody or a fragment thereof, as defined in any of claims 1-41.

50. Method for increasing serum inorganic phosphorus (Pi) in a subject in need thereof, wherein the method is characterized in that it comprises administering to the subject the isolated antibody or a fragment thereof, as defined in any of claims 141.

51. A method for increasing the serum concentration of 1,25-dihydroxyvitamin D (1,25[OH]2D) in a subject in need thereof, wherein the method is characterized in that it comprises administering to the subject the isolated antibody or a fragment thereof, as defined in any one of claims 1-41.

52. Method for treating a hypophosphatemic condition in a subject in need thereof, wherein the method is characterized by the fact that it comprises administering to the subject the isolated antibody or a fragment thereof, as defined in any of the claims 1- Petition 870250099897, of 10 / 31 / 2025, pp. 160 / 177 16 / 16 41.

53. Method according to any one of claims 48 to 52, characterized in that the subject is diagnosed with X-linked hypophosphatemia (XLH) or tumor-induced osteomalacia (TIO). Petition 870250099897, dated 10 / 31 / 2025, pp. 161 / 177

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