Bispecific antibody-drug conjugates against her3 and c-met

Abstract

The present disclosure provides bispecific antibody-drug conjugates comprising an anti-HER3 / anti-c-MET bispecific antibody and a cytotoxic drug moiety, and methods of using them to treat HER3-expressing and / or c-MET-expressing cancers.

Description

BISPECIFIC ANTIBODY-DRUG CONJUGATES AGAINST HER3 AND C-METCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Patent Application 63 / 737,755, filed December 22, 2024. The disclosure of this priority application is incorporated by reference herein in its entirety.SEQUENCE LISTING

[0002] The instant application contains a Sequence Listing which has been submitted electronically in .XML format, is part of the specification, and is hereby incorporated by reference herein in its entirety. Said .XML copy, created on December 19, 2025, is named 125587.WO004.xml and is 41,263 bytes in size.BACKGROUND OF THE INVENTION

[0003] Receptor tyrosine kinases (RTK) play an important role in development and can contribute to the proliferation, metastasis, and survival of certain cancers. One of the RTKs, human epidermal growth factor receptor 3 (HER3), is typically expressed in epithelial, mesenchymal, cardiac, and neuronal tissues and plays a key role in cellular proliferation. Overexpression of HER3 has been reported in several types of cancer including breast, colorectal, cervical, head and neck, lung, melanoma, and prostate cancers. Another RTK, c- MET, also known as hepatocyte growth factor (HGF) receptor, plays a significant role in activation of signaling pathways, mediating wound healing, embryogenesis, tissue regeneration, and the formation of nerve muscle. Like HER3, aberrant activity of c-MET has been associated with the development and progression of cancers such as breast, colon, liver, lung, ovarian, pancreatic, and prostate cancers. Accordingly, HER3 and c-MET are of interest as targets for anti -cancer immunotherapies. There is a need for new cancer therapies that co-target HER3 and c-MET.SUMMARY OF THE INVENTION

[0004] The present disclosure provides an antibody-drug conjugate (ADC) comprising a bispecific antibody (Ab) conjugated, optionally at a cysteine residue therein, to a cytotoxin through a linker, wherein the bispecific antibody comprises a first antigen-binding portionspecific for human HER3, and a second antigen-binding portion specific for human c-MET, wherein the ADC comprises the structure shown in Formula (I):Formula (I) optionally wherein n is from 1 to 8.

[0005] In some embodiments, the first (anti-HER3) antigen-binding portion comprises heavy chain complementarity-determining regions (HCDR) 1, 2, 3 and light chain complementarity-determining regions (LCDR) 1, 2, 3 comprising SEQ ID NOs: 32, 33, 34, 35, 36, and 37, respectively, or comprising SEQ ID NOs: 38, 39, 40, 41, 42, and 37, respectively. In further embodiments, the first antigen-binding portion comprises a heavy chain variable domain (VH) and a light chain variable domain (VL) comprising SEQ ID NOs: 43 and 44, respectively.

[0006] In some embodiments, the second (anti-c-MET) antigen-binding portion comprises heavy chain CDR1-3 and light chain CDR1-3 comprising SEQ ID NOs: 1, 2, 3, 4, 5, and 6, respectively, or comprising SEQ ID NOs: 7, 8, 9, 10, 11, and 6, respectively. In further embodiments, the second antigen-binding portion comprises a VH and a VL comprising SEQ ID NOs: 12 and 13, respectively.

[0007] In alternative embodiments, the second (anti-c-MET) antigen-binding portion comprises HCDR1-3 and LCDR1-3 comprising SEQ ID NOs: 16, 17, 18, 19, 20, and 21, respectively, or comprising SEQ ID NOs: 22, 23, 24, 25, 26, and 27, respectively. In further embodiments, the second antigen-binding portion comprises a VH and a VL comprising SEQ ID NOs: 28 and 29, respectively.

[0008] In some embodiments, the bispecific antibody is of human IgG isotype. In further embodiments, the bispecific antibody is of human IgGi or IgG4 isotype subtype. In certain embodiments, the bispecific antibody comprises in its Fc domain one or more mutations that reduce effector functions of the bispecific antibody and / or knobs-in-holes mutations.

[0009] In some embodiments, the first or second antigen-binding portion is a CrossMab, i.e., comprising a VL linked to a light chain constant region (CL) and a VL linked to a Cm. In further embodiments, the bispecific antibody comprises four polypeptides (a), (b), (c), and(d), wherein polypeptide (a) comprises the VL of the first antigen-binding portion linked to a human CL, and polypeptide (b) comprises the VH of the first antigen-binding portion linked to a human IgGi constant region, wherein polypeptides (a) and (b) pair to form the first antigenbinding portion, polypeptide (c) comprises the VH of the second antigen-binding portion linked to a human CL, and polypeptide (d) comprises the VL of the second antigen-binding portion linked to a human IgGi constant region, wherein polypeptides (c) and (d) pair to form the second antigen-binding portion, and polypeptides (b) and (d) pair to form an antibody Fc domain. In particular embodiments, polypeptides (a), (b), (c), and (d) comprise SEQ ID NOs:46, 45, 15, and 14, respectively. In other particular embodiments, polypeptides (a), (b), (c), and (d) comprise SEQ ID NOs:46, 45, 31, and 30, respectively.

[0010] In some embodiments, the first and / or second antigen-binding portions in the bispecific antibody are an scFv.

[0011] In one aspect, the present disclosure provides a pharmaceutical composition comprising the ADC described herein and a pharmaceutically acceptable excipient.

[0012] In another aspect, the present disclosure provides a method of treating cancer in a human patient in need thereof, comprising administering to the patient a therapeutically effective amount of the present ADC or pharmaceutical composition; the present ADC or pharmaceutical composition for use in treating cancer in a human patient in need thereof; and the use of the present ADC or pharmaceutical composition in the manufacture of a medicament for treating cancer in a human patient in need thereof. In some embodiments, the cancer expresses HER3 and / or c-MET. In further embodiments, the cancer is head and neck cancer, lung cancer, esophageal cancer, gastric cancer, hepatic cancer, pancreatic cancer, colorectal cancer, breast cancer, endometrial cancer, ovarian cancer, soft-tissue sarcoma, bladder cancer, prostate cancer, renal cancer, or melanoma. In certain embodiments, the cancer is lung cancer, gastric cancer, colorectal cancer, pancreatic cancer, or breast cancer. In certain embodiments, the lung cancer is non-small cell lung cancer (NSCLC). In some embodiments, the patient is also administered an additional therapy, such as immunotherapy, chemotherapy, or radiotherapy.

[0013] In another aspect, the present disclosure provides a method of making an antibodydrug conjugate, comprising: providing a bispecific antibody as defined in any one of claims 1-16, and contacting the antibody with a compound comprising a structure of Formula (II) to allow the compound to be conjugated to the bispecific antibody at one or more cysteine in theantibody:Formula (II).

[0014] Other features, objectives, and advantages of the invention are apparent in the detailed description that follows. It should be understood, however, that the detailed description, while indicating embodiments and aspects of the invention, is given by way of illustration only, not limitation. Various changes and modification within the scope of the invention will become apparent to those skilled in the art from the detailed description.BRIEF DESCRIPTION OF THE FIGURES

[0015] FIGs. 1A-J are diagrams illustrating various configurations of the bispecific antibodies of the present disclosure. Interchain disulfide bonds, if any, are not shown. FIGs. 1B-G show CrossMab configurations. FIGs. 1H-J show scFv as one or both of the antigenbinding arms.

[0016] FIG. 2 is a line graph showing the binding of anti-c-Met, anti-HER3, and bispecific anti-c-MET / anti-HER3 antibody-drug conjugates to MDA-MD-453 breast cancer cells as measured by flow cytometry. BiADC: bispecific antibody-drug conjugate. The two BiADCs have an HER3 -binding arm from the same parental antibody, but their c-MET- binding arms are derived from parental antibodies anti-c-MET-A and anti-c-MET-B, respectively. All ADCs herein comprise the linker / payload structure shown in Formula (I). MFI: mean fluorescent intensity.

[0017] FIG. 3 is a line graph showing the binding of the indicated ADCs to NUGC-4 stomach cancer cells as measured by flow cytometry. All ADCs have the structure shown in Formula (I).

[0018] FIG. 4 is a line graph showing the binding of the indicated ADCs to A549 lung cancer cells as measured by flow cytometry. All ADCs have the structure shown in Formula (I).

[0019] FIG. 5 is a line graph showing the mean tumor volume over time in a murine model of pancreatic cancer following treatment on Days 0, 7, and 14 with the indicated ADCs.

[0020] FIG. 6 is a line graph showing the mean tumor volume over time in a murine model of colorectal cancer following treatment on Days 0, 7, and 14 with the indicated ADCs.

[0021] FIG. 7 is a line graph showing the mean tumor volume over time in a murine model of HR+ / HER2- breast cancer following treatment on Days 0 and 7 with the indicated ADCs.

[0022] FIG. 8 is a line graph showing the mean tumor volume over time in a murine model of non-small cell lung cancer following treatment on Days 0 and 7 with the indicted ADCs.

[0023] FIG. 9 is a line graph showing the mean tumor volume over time in a murine model of non-small cell lung cancer following treatment on Days 1, 8, and 15 with the indicated ADCs.

[0024] FIG. 10 is a line graph showing the mean tumor volume over time in a murine model of pancreatic cancer following treatment on Days 0, 8, and 14 with the indicated ADCs.DETAILED DESCRIPTION

[0025] The present disclosure provides bispecific antibody-drug conjugates (BiADCs) targeting cancer cells that are HER3-positive and / or c-MET-positive. The BiADCs comprise the cytotoxin exatecan linked to a bispecific antibody against HER3 and c-MET through a cleavable linker. These BiADCs can be used to treat cancer in human patients in need thereof.I. Bispecific Antibody-Drug Conjugates

[0026] The bispecific antibody of the present disclosure has two antigen-binding portions, the first portion is specific for human HER3 and the second portion is specific for human c- MET. Exemplary human HER3 and c-MET amino acid sequences are available at UniProt under Accession Nos. P21860 and P08581, respectively. An antibody or an antigen-binding portion (or fragment) thereof is said to specifically bind to an antigen when the KD for the binding is < 100 nM, e.g., < 10 nM, or < 1 nM. A KD binding affinity constant can be measured, e.g., by surface plasmon resonance (Biacore™) using the Biacore™ T200 system,the IBIS MX96 SPR system from IBIS Technologies, or the Carterra LSA SPR platform, or by bio-layer interferometry, for example using the Octet™ system from ForteBio.A. Bispecific Antibody Overall Structure

[0027] Production of a bispecific antibody requires dimerization of cognate VH and VL pairs. That is, the VH and VL of the anti-HER3 antigen-binding portion should pair with each other, and the VH and VL of the anti-c-MET antigen-binding portion should pair with each other. However, simultaneous expression of two different heavy chains and two different light chains can lead to noncognate pairing, i.e., pairing of an anti-HER3 light chain with an anti-c-MET heavy chain or pairing of an anti-c-MET light chain and an anti-HER3 heavy chain. Homodimerization of the heavy chains, i.e., pairing of two anti-HER3 heavy chains, and pairing of two anti-c-MET heavy chains, would further lower the manufacturing yield of the desired bispecific antibody, which requires heterodimerization of an anti-HER3 heavy chain and an anti-c-MET heavy chain (FIG. 1A).

[0028] Thus, in some embodiments, the bispecific antibody of the present disclosure adopts a CrossMab configuration in which one antigen-binding portion has a VH-VL swap, a CL-CHI swap, or a Fab swap. See, e.g., Schaefer et al., PNAS (2011) 108(27): 11187-92. Exemplary CrossMab configurations are illustrated in FIGs. 1B-G.

[0029] FIG. IB shows a configuration with a VH-VL swap in the anti-c-MET arm of a bispecific antibody comprising four polypeptide chains (a), (b), (c), and (d). Polypeptide (a) comprises the VL of the anti-HER3 antigen-binding portion linked to a human light chain constant region CL (e.g., kappa constant region), and polypeptide (b) comprises the VH of the anti-HER3 antigen-binding portion linked to a human IgG (e.g., IgGi or IgG-t) constant region (Cm, Cm, and Cm), where polypeptides (a) and (b) pair to form the anti-HER3 antigen-binding portion. Polypeptide (c) comprises the VH of the anti-c-MET antigenbinding portion linked to a human light chain constant region CL (e.g., kappa constant region) and polypeptide (d) comprises the VL of the anti-c-MET antigen-binding portion linked to a human IgG (e.g., IgGi or IgG4) constant region (Cm, Cm, and Cm), where polypeptides (c) and (d) pair to form the second antigen-binding portion. Polypeptides (b) and (d) pair to form an antibody Fc domain.

[0030] FIG. 1C shows a configuration with a CHI-CL swap in the anti-c-MET arm of the bispecific antibody. In this configuration, polypeptides (a) and (b) are the same as in the configuration of FIG. IB. But compared to the conventional configuration of FIG. 1A, polypeptide (c) has a Cm, rather than the native CL, as the constant region, while polypeptide (d) has its native Cm domain replaced by a CL.

[0031] FIG. ID shows a configuration with a VH-VL swap in the anti-HER3 arm of a bispecific antibody comprising four polypeptide chains (a), (b), (c), and (d). Polypeptide (a) comprises the VH of the anti-HER3 antigen-binding portion linked to a human light chain constant region CL (e.g., kappa constant region), and polypeptide (b) comprises the VL of the anti-HER3 antigen-binding portion linked to a human IgG (e.g., IgGi or IgG-t) constant region (Cm, Cm, and Cm), where polypeptides (a) and (b) pair to form the anti-HER3 antigen-binding portion. Polypeptide (c) comprises the VL of the anti-c-MET antigenbinding portion linked to a human light chain constant region CL (e.g., kappa constant region) and polypeptide (d) comprises the VH of the anti-c-MET antigen-binding portion linked to a human IgG (e.g., IgGi or IgG4) constant region (Cm, Cm, and Cm), where polypeptides (c) and (d) pair to form the second antigen-binding portion. Polypeptides (b) and (d) pair to form an antibody Fc domain.

[0032] FIG. IE shows a configuration with a CHI-CL swap in the anti-HER3 arm of the bispecific antibody. In this configuration, polypeptides (c) and (d) are the same as in the configuration of FIG. ID. But compared to the configuration of FIG. 1A, polypeptide (a) has a Cm, rather than the native CL, as the constant region, while polypeptide (b) has its native Cm domain replaced by a CL.

[0033] FIG. IF shows a configuration with a Fab swap in the anti-HER3 arm of the bispecific antibody, in which the VL / CL domains and the VH / CHI domains switch positions such that the VL / CL domains are joined to the rest of the heavy chain, and the VH / CHI domains are no longer joined to the rest of the heavy chain. FIG. 1G shows a configuration where the Fab swap takes place in the anti-c-MET arm instead.

[0034] In some embodiments, charge mutations may be made in the light and heavy chains of a bispecific antibody to promote correct pairing of VH and VL and / or to promote heterodimerization of two different heavy chains. See, e.g., Gunasekaran et al., J Biol Chem. (2010) 285: 19637-46; and Liu et al., J Biol Chem. (2015) 290(12):7535-62.

[0035] In some embodiments, the antigen-binding portion of a bispecific antibody is an antibody fragment such as an scFv, as illustrated in FIGs. 1H-J. In FIG. 1H, the anti-HER3 arm is an scFv, with either the VH or the VL positioned at the N-terminus. In FIG. II, the anti-c-MET arm is an scFv, with either the VH or the VL positioned at the N-terminus. In FIG. 1 J, the anti-HER3 is an scFv with either the VH or the VL positioned at the N-terminus, and the anti-c-MET arms is also an scFv with either the VH or the VL positioned at the N- terminus.

[0036] In some embodiments, the Fc domain of the bispecific antibody described hereinmay comprise knobs-in-holes mutations to promote heavy chain heterodimerization. In some embodiments, the knobs-into-holes mutations may comprise a T366Y “knob” mutation on a polypeptide chain of the Fc domain, and a Y407T “hole” mutation in the other polypeptide of the Fc domain. In some embodiments, the knobs-into-holes mutations comprise Y349C and / or T366W mutations in the CH3 domain of the “knob chain” and E356C, T366S, L368A, and / or Y407V mutations in the CH3 domain of the “hole chain.” In certain embodiments, the knobs-into-holes mutations comprise T366W mutations in the CH3 domain of the “knob chain” and T366S, L368A, and Y407V mutations in the CH3 domain of the “hole chain.”

[0037] In some embodiments, the present bispecific antibody may comprise other mutations that confer desired properties to the proteins, e.g., increased serum half-life, altered (e.g., reduced) immunogenicity in humans, and / or engineered sites for covalent or non- covalent binding to another molecule (e.g., a cytotoxic, radioactive, or detectable agent). These mutations may be introduced in the framework (FR) regions, the CDRs, or other parts of the antibody. In some embodiments, the antibody may comprise at least one mutation in the Fc region. A number of different Fc mutations are known, where these mutations alter, e.g., the antibody’s effector functions or half-life. For example, the Fc domain may comprise mutations that improve the therapeutic potential of the antibody, such as mutations (e.g., “effectorless” mutations) that reduce or eliminate effector functions of the antibody. An antibody may comprise, for instance, a human IgGi constant region with the mutation L235E, “LALA” mutations (L234A / L235A), “LALAGA” mutations (L234A / L235A / G237A), “LALAGR” mutations (L234A / L235A / G236R), or “LALAPG” mutations (L234A / L235A / P329G). In some embodiments, the constant region may comprise L234F / L235E / P331S (“FES”), L234F / L235Q / K322Q (“FQQ”), A330S / P331S, L234A / G237A, L234A / L235A / G237A, L234A / L235A / G237A / P238S / H268A / A330S / P330S, L234A / L235E, G236R / L328R, or L234A / L235A / K322A mutations.

[0038] Unless otherwise indicated, the amino acid position numbers in the Fc domain referred to in the present disclosure are Eu numbers.

[0039] As used herein, a VH is still referred to as VH even after it is “crossed” over to the light chain and becomes linked to a CL and the CDRs therein are still referred to as HCDRs. Likewise, a VL is still referred to as VL even after it is “crossed” over to the heavy chain and becomes linked to a Cm and the CDRs therein are still referred to as LCDRs.B. Bispecific Antibody Sequences

[0040] In some embodiments, the anti-HER3 antigen-binding portion of the present bispecific antibody comprises heavy chain complementarity-determining regions (HCDR) 1- 3 and light chain complementarity-determining regions (LCDR) 1-3 having the amino acid sequences of SEQ ID NOs: 32, 33, 34, 35, 36, and 37, respectively (CDRs defined by the Kabat system), or comprising the amino acid sequences of SEQ ID NOs: 38, 39, 40, 41, 42, and 37, respectively (CDRs defined by the IMGT® system). In some embodiments, the anti- HER3 antigen-binding portion comprises a heavy chain variable domain (VH) having the amino acid sequence of SEQ ID NO:43 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto, and a light chain variable domain (VL) having the amino acid sequence of SEQ ID NO:44 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto. In certain embodiments, the VH and VL of the anti-HER3 antigen-binding portion comprise SEQ ID NOs:43 and 44, respectively, i.e., comprise the same VH and a VL as the parental HER3 antibody described herein.

[0041] In some embodiments, the anti-c-MET antigen-binding portion of the present disclosure comprises HCDR1-3 and LCDR1-3 having the amino acid sequences of SEQ ID NOs: 1, 2, 3, 4, 5, and 6, respectively (CDRs defined by the Kabat system), or comprising SEQ ID NOs: 7, 8, 9, 10, 11, and 6, respectively (CDR defined by the IMGT® system). In some embodiments, the anti-c-MET antigen-binding portion comprises a VH having the amino acid sequence of SEQ ID NO: 12 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto, and a light chain variable domain (VL) having the amino acid sequence of SEQ ID NO: 13 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto. In certain embodiments, the VH and VL of the anti-c-MET antigen-binding portion comprise SEQ ID NOs: 12 and 13, respectively, i.e., comprise the same VH and a VL as anti-c-MET-A antibody.

[0042] In alternative embodiments, the anti-c-MET antigen-binding portion of the present disclosure comprises HCDR1-3 and LCDR1-3 having the amino acid sequences of SEQ ID NOs: 16, 17, 18, 19, 20, and 21, respectively (CDRs defined by the Kabat system), or comprising SEQ ID NOs:22, 23, 24, 25, 26, and 27, respectively (CDR defined by the IMGT® system). In some embodiments, the anti-c-MET antigen-binding portion comprises a VH having the amino acid sequence of SEQ ID NO:28 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto, and a light chain variable domain (VL) having the amino acid sequence of SEQ ID NO:29 or an amino acidsequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto. In certain embodiments, the VH and VL of the anti-c-MET antigen-binding portion comprise SEQ ID NOs:28 and 29, respectively, i.e., comprise the same VH and a VL as anti-c-MET-B antibody.

[0043] In further embodiments, the bispecific antibody herein comprises four polypeptides (a), (b), (c), and (d), where polypeptide (a) comprise SEQ ID NO:46, or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto; polypeptide (b) comprises SEQ ID NO:45 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto; polypeptide (c) comprises SEQ ID NO: 15 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto; and polypeptide (d) comprise SEQ ID NO: 14 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto.In these embodiments, polypeptides (a) and (b) pair to form an anti-HER3 antigen-binding domain, polypeptides (c) and (d) pair to form an anti-c-MET antigen-binding domain (i.e., the anti-c-MET antigen-binding domain that is the same as anti-c-MET-A antibody), and polypeptides (b) and (d) pair to form an antibody Fc domain. In certain embodiments, polypeptides (a), (b), (c), and (d) comprise SEQ ID NOs:46, 45, 15, and 14, respectively.

[0044] In other further embodiments, the bispecific antibody herein comprises four polypeptides (a), (b), (c), and (d), where polypeptide (a) comprise SEQ ID NO:46, or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto; polypeptide (b) comprises SEQ ID NO:45 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto; polypeptide (c) comprises SEQ ID NO:31 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto; and polypeptide (d) comprise SEQ ID NO: 30 or an amino acid sequence at least 90% (e.g., at least 91, 92, 93, 94, 95, 96, 97, 98, or 99%) identical thereto.In these embodiments, polypeptides (a) and (b) pair to form an anti-HER3 antigen-binding domain, polypeptides (c) and (d) pair to form an anti-c-MET antigen-binding domain (i.e., the anti-c-MET antigen-binding domain that is the same as anti-c-MET-B antibody), and polypeptides (b) and (d) pair to form an antibody Fc domain. In certain embodiments, polypeptides (a), (b), (c), and (d) comprise SEQ ID NOs:46, 45, 31, and 30, respectively.C. Production of Bispecific Antibodies

[0045] The BiADCs may be produced recombinantly using isolated nucleic acid molecules such as expression constructs encoding each chain of the proteins. Biomolecules (e.g., nucleic acid or polypeptide) molecules referred to herein as “isolated” or “purified” are those that (1) have been separated away from the biomolecules (e.g., nucleic acids of the genomic DNA or cellular RNA, or polypeptides) of their source of origin; and / or (2) do not occur in nature. The coding sequences for each polypeptide chain may be cloned into a single vector or cloned into separate vectors.

[0046] The present antibodies may be produced in, e.g., mammalian host cells, using appropriate expression constructs. Mammalian cell lines available as hosts for expression include many immortalized cell lines and may include, inter alia, Chinese hamster ovary (CHO) cells, NSO cells, SP2 cells, HEK-293T cells, 293 Freestyle cells (Invitrogen), NIH- 3T3 cells, HeLa cells, baby hamster kidney (BHK) cells, African green monkey kidney cells (COS), human hepatocellular carcinoma cells (e.g., Hep G2), A549 cells, and a number of other cell lines. The binding proteins may be isolated and purified from the host cell culture using well known methods, such as centrifugation, ultracentrifugation, protein A, protein G, protein A / G, or protein L purification, and / or ion exchange chromatography.D. Linker / Payload

[0047] In some embodiments, the bispecific antibody of the present disclosure is conjugated at one or more (e.g., 1, 2, 3, 4, 5, 6, 7, or 8) of its cysteine residues (e.g., cysteine residues that normally form interchain disulfide bonds) to a cytotoxin such as exatecan or a derivative thereof through a cleavable linker. The cleavable linker may comprise, for example, a short peptide (e.g., a di-, tri-, or tetra-peptide), a self-immolative spacer, and PEG units. In some embodiments, the linker / payload moiety of the Bi ADC has the structure shown within the parenthesis in Formula (I) below, wherein the bispecific antibody is shown as “Ab,” and wherein “n” refers to the number of the linker / payload moieties per antibody.Formula (I)

[0048] In some embodiments, the average drug-to-antibody ratio (DAR) of the Bi ADC is 1, or at least 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8, 9, or 10. In some embodiments, the DAR is between 3 and 8. For example, the DAR may be about 3.0, 3.5, 4, 4.5, 7, 7.4, 7.5, 7.6, 7.8, 7.9, or 8. The DAR may be about 1, about 2, about 3, about 4, about 5, about 6, about 7, or about 8. In some embodiments, the DAR is about 2. In some embodiments, the DAR is about 4. In some embodiments, the DAR is about 6. In some embodiments, the DAR is about 8.

[0049] In some embodiments, the antibody (Ab) in Formula I comprise four polypeptides of the amino acid sequences of SEQ ID NOs:46, 45, 15, and 14, respectively. In other embodiments, the antibody (Ab) in Formula I comprise four polypeptides of the amino acid sequences of SEQ ID NOs:46, 45, 31, and 30, respectively.

[0050] To generate a Bi ADC shown in Formula (I), a bispecific antibody of the present disclosure may be conjugated to the linker / payload precursor of Formula (II) through chemical reaction between a cysteine on the antibody and the maleimide group at the left terminus of the linker / payload precursor.Formula (II)

[0051] As used herein, a linker / payload precursor refers to a linker / payload unit prior to the chemical reaction to link the antibody and the drug (cytotoxic agent or payload). It will be apparent to the skilled person in the ADC art whether a certain chemical entity disclosed herein is a linker precursor based on its reactive capabilities, or a linker component in the final immunoconjugate product.II. Pharmaceutical Compositions

[0052] The present disclosure also provides a pharmaceutical composition comprising a BiADC described herein and a pharmaceutically acceptable excipient. “Pharmaceutically acceptable excipients” may include appropriate solvents, buffering agents, antioxidants,isotonic agents, detergents, preservatives, and the like. Examples of pharmaceutically acceptable excipients are water and saline (e.g., phosphate-buffered saline).

[0053] The pharmaceutical compositions herein may be used to treat cancer, e.g., HER3- expressing and / or c-MET-expressing cancer.

[0054] A pharmaceutical composition of the present disclosure may comprise a therapeutically effective amount of a Bi ADC described herein. A “therapeutically effective amount” is an amount of the drug (e.g., a Bi ADC described herein) or a pharmaceutical composition comprising it that will relieve to some extent one or more of the symptoms of the disease being treated. A therapeutically effective amount of an anti -cancer therapeutic may, for example, result in delayed tumor growth, elimination of cancer cells, tumor shrinkage, increased patient survival, slowed or decreased metastasis, or other clinical endpoints desired by healthcare professionals.

[0055] The pharmaceutical compositions described herein may be delivered to a patient through parenteral administration. In particular, parenteral administration is contemplated to include, but is not limited to, subcutaneous, intraperitoneal, intramuscular, intrasternal, intracisternal, intravenous, intraarterial, intrathecal, intraurethral, intracranial, intratumoral, and intrasynovial injection or infusions. In some embodiments, the pharmaceutical composition is delivered intravenously (e.g., through intravenous infusion) or subcutaneously (e.g., through subcutaneous injection).III. Therapeutic Uses

[0056] The anti-HER3 / c-MET Bi ADCs of the present disclosure may be used to treat cancer in a human patient in need thereof. In certain embodiments, the cancer is a HER3- expressing and / or c-MET-expressing cancer, e.g., HER3+ / cMET+cancer, HER3+ / cMET' cancer, and HER37cMET+cancer. The BiADC may be administered alone or in combination with other therapeutic agents.

[0057] In some embodiments, the cancer treated by the Bi ADCs of the present disclosure may be a solid tumor or a hematopoietic cancer. The cancer may be, e.g., melanoma, skin basal cell cancer, glioblastoma, glioma, gliosarcoma, astrocytoma, meningioma, neuroblastoma, adrenocortical cancer, head and neck cancer (e.g., cancer of the head, neck, nasal cavity, paranasal sinuses, nasopharynx, oral cavity, oropharynx, larynx, hypopharynx, and / or salivary glands, and paragangliomas), oral cancer, salivary gland cancer, nasopharyngeal cancer, breast cancer (e.g., triple negative breast cancer), lung cancer (e.g., non-small cell lung cancer (NSCLC), small cell lung cancer, or squamous cell lung cancer),esophageal cancer, gastroesophageal junction cancer, gastric cancer, gastrointestinal cancer, primary peritoneal cancer, liver cancer, hepatocellular carcinoma, gallbladder cancer, biliary tract cancer, cholangiocarcinoma, colon cancer, rectal cancer, colorectal carcinoma, ovarian cancer, fallopian tube cancer, bladder cancer, upper urinary tract cancer, urothelial cancer, renal cell carcinoma, kidney cancer, genitourinary cancer, cervical cancer, testicular cancer, prostate cancer, fibrosarcoma, liposarcoma, rhabdomyosarcoma (e.g., embryonal rhabdomyosarcoma), leiomyosarcoma, neurofibrosarcoma, synovial sarcoma, liposarcoma, alveolar soft part sarcoma, osteosarcoma, histiocytoma (e.g., malignant fibrous histiocytoma), pancreatic cancer, endometrial cancer, cancer of the appendix, thyroid cancer, advanced Merkel cell cancer, multiple myeloma, sarcomas, choriocarcinoma, leukemia (e.g., erythroleukemia, acute lymphoblastic leukemia, acute monocytic leukemia, acute promyelocytic leukemia, acute myeloid leukemia, acute myelogenous leukemia, chronic myeloid leukemia, chronic myelogenous leukemia, chronic lymphocytic leukemia, acute lymphoblastic leukemia, or mast cell leukemia), lymphoma (e.g., small lymphocytic lymphoma, Burkitt’s lymphoma, Hodgkin’s lymphoma, non -Hodgkin’s lymphoma, diffuse large B cell lymphoma, lymphoplasmacytoid lymphoma, mucosa-associated lymphoid tissue lymphoma, mantle cell lymphoma, T-cell anaplastic large cell lymphoma, follicular lymphoma, monocytic lymphoma, or HTLV-associated T cell leukemia / lymphoma), or mesothelioma. In certain embodiments, the cancer is selected from the group consisting of head and neck cancer, bone cancer (e.g., osteosarcoma), Ewing sarcoma, squamous cell carcinoma, lung cancer (e.g., non-small cell lung cancer or small cell lung cancer), kidney cancer, urethral cancer, colorectal cancer, prostate cancer, glioblastoma multiforme, ovarian cancer, cervical cancer, pancreatic cancer, breast cancer (e.g., triple negative breast cancer), melanoma, liver cancer, bladder cancer, stomach cancer, esophageal cancer, and chronic myelogenous leukemia. In particular embodiments, the cancer is selected from the group consisting of head and neck cancer, lung cancer, esophageal cancer, gastric cancer, hepatic cancer, pancreatic cancer, colorectal cancer, breast cancer, endometrial cancer, ovarian cancer, soft-tissue sarcoma, bladder cancer, prostate cancer, renal cancer, and melanoma. In further embodiments, the cancer is selected from the group consisting of lung cancer, gastric cancer, colorectal cancer, pancreatic cancer, and breast cancer. In certain embodiments, the lung cancer is non-small cell lung cancer (NSCLC). In certain embodiments, the NSCLC is EGFR-wildtype NSCLC. In certain embodiments, the NSCLC is EGFR-mutated NSCLC. The cancer may be, e.g., at an early, intermediate, late, locally advanced, or metastatic stage, and may be relapsed or refractory to other therapeutics, or there may be no standard therapyavailable.

[0058] “ Treat,” “treating,” and “treatment” refer to a method of alleviating or abrogating a biological disorder and / or at least one of its attendant symptoms. As used herein, to “alleviate” a disease, disorder or condition means reducing the severity and / or occurrence frequency of the symptoms of the disease, disorder, or condition. In certain embodiments, therapeutic use of a Bi ADC described herein inhibits tumor growth by at least 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100%. In certain embodiments, therapeutic use of a BiADC described herein provides partial tumor regression of at least 10, 20, 30, 40, 50, 60, 70, 80, or 90%, or complete tumor regression.

[0059] The Bi ADCs of the present disclosure may be administered without additional therapeutic treatments, i.e., as a stand-alone therapy (monotherapy). Alternatively, treatment with the BiADCs of the present disclosure may include at least one additional therapeutic treatment (combination therapy), e.g., an immunomodulatory agent, an anti -cancer agent (such as a chemotherapeutic agent, an anti-neoplastic agent, or an anti -angiogenic agent), a vaccine (such as a tumor vaccine), or radiation therapy.

[0060] In some embodiments, the additional therapeutic treatment may comprise an anticancer agent such as, for example, an agent selected from the group consisting of alkylating agents (e.g., platinum derivatives such as cisplatin, carboplatin and / or oxaliplatin); plant alkoids (e.g., paclitaxel, docetaxel and / or irinotecan); antitumor antibiotics (e.g., doxorubicin, adriamycin, daunorubicin, epirubicin, idarubicin mitoxantrone, dactinomycin, bleomycin, actinomycin, luteomycin, and / or mitomycin); topoisomerase inhibitors (e.g., topotecan); antimetabolites (e.g., fluorouracil and / or other fluoropyrimidines); kinase inhibitors such as tyrosine kinase inhibitors (e.g., acalabrutinib, ibrutinib, imatinib, sorafenib, lapatinib, etc.); or any combination thereof.

[0061] Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. Exemplary methods and materials are described below, although methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure. In case of conflict, the present specification, including definitions, will control. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular. Throughout this specification and embodiments, the words “have” and “comprise,” or variations such as “has,” “having,” “comprises,” or “comprising,” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group ofintegers. All publications and other references mentioned herein are incorporated by reference in their entirety, as if each individual reference were specifically and individually indicated to be incorporated by reference in its entirety. Although a number of documents are cited herein, this citation does not constitute an admission that any of these documents forms part of the common general knowledge in the art. As used herein, the term “approximately” or “about” as applied to one or more values of interest refers to a value that is similar to a stated reference value. In certain embodiments, the term refers to a range of values that fall within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context.

[0062] According to the present disclosure, back-references in the dependent claims are meant as short-hand writing for a direct and unambiguous disclosure of each and every combination of claims that is indicated by the back-reference. Further, headers herein are created for ease of organization and are not intended to limit the scope of the claimed invention in any manner.

[0063] In order that this invention may be better understood, the following examples are set forth. These examples are for purposes of illustration only and are not to be construed as limiting the scope of the invention in any manner.EXAMPLESExample 1: Conjugation of Bispecific Anti-HER3 / Anti-c-MET ADC

[0064] To generate the anti-HER3 / anti-c-Met BiADC, the naked bispecific antibody and their monospecific parental antibody (parental HER3, anti-c-MET-A, anti-c-MET-B) in storage buffer (20 mM histidine-acetate, 150 mM NaCl, pH 5.5) at a concentration of 5-6 mg / mL were adjusted with Tris buffer pH 7.5 to a conjugation pH of 6-7. This was followed by the addition of 5 mM Tris (2-carboxy ethyl) phosphine (TCEP) hydrochloride solution (10 equiv.). The final antibody concentration in the reaction was 4.95 mg / mL. The reaction was incubated at 22°C for 18 hours. N,N-dimethylacetamide (DMA) was added to the reaction, followed by the addition of 10 mM of the linker-payload of Formula (II) in DMA solution (14 equiv.). The reaction was incubated at 22°C for 1 hour. The antibody concentration during conjugation was 4.46 mg / mL. The crude conjugation product was purified via Zeba™ Spin Desalting Column (40K, lOmL; ThermoFisher) followed by ultrafiltration (Amicon® Ultra Centrifugal Filter Unit 50K, 15mL) with 20 mM histidine, 8% sucrose, pH 6.0 buffer.The fractions were collected, filtered with 0.22 pm filter, and characterized for concentration, DAR value, SEC purity, endotoxin level, and free drug.Example 2: Binding of Bispecific ADC to Cancer Cells

[0065] MDA-MD-453 breast cancer cells, which are HER3+ / c-MET', were plated at a density of 100,000 cells / well in a 96-well plate in RPMI 1640 Medium + 10% FBS in the presence of 1% bovine serum albumin and in a final volume of 100 pL / well. Serial dilutions of the bispecific ADCs (BiADCs) and parental ADCs were prepared in 1% BSA in a final volume of 100 pL, added to the cells and incubated at 4°C for 1 hour. A secondary goat antihuman IgG-Fc- Alexa Fluor™ 647 antibody (Jackson ImmunoResearch) was added to the wells and incubated at 4°C for 30 minutes. The plate was read at 633 nm in a BD FACSCanto™ II flow cytometer and binding curves (FIG. 2) were derived from the histograms. The data show that the parental anti-c-MET ADCs did not bind MDA-MB-453 cells while the parental anti-HER3 ADC did. The two BiADCs showed strong binding to MDA-MB-453 cells.

[0066] Binding of the Bi ADCs and parental ADCs to NUGC-4 stomach cancer cells, which are HER3+ / c-MET+, was measured by the same method. The data show that the parental ADCs bound to NUGC-4 cells, but the two BiADCs showed stronger binding to NUGC-4 cells (FIG. 3).

[0067] Binding of the BiADCs and parental ADCs to A549 lung cancer cells, which are HER37c-MET+, was measured by the same method, except that the cells were grown in F- 12K Nutrient Mixture medium + 10% FBS. The data show that the parental anti-HER3 ADC did not bind to A549 cells, while both parental anti-c-MET ADCs (A and B) did. The two BiADCs showed strong binding to A549 cells (FIG. 4).Example 3: Effects of BiADC Treatment in a Murine Model of Pancreatic Cancer

[0068] Female C.B-17 SCID mice were implanted subcutaneously in the right flank with 5 xlO6BxPC-3 human pancreatic cancer cells in a 100 pL cells + 100 pL Matrigel™ suspension. After tumor staging, mice were randomized to generate groups of 6 mice each with an average tumor volume of 150-200 mm3. Mice received 3 doses of the different test articles on Days 0, 7 and 14 at dose levels of either 3 mg / kg or 10 mg / kg. Tumor volumes and body weights of the animals were measured twice weekly. The data show that bothBiADcs resulted in significant tumor growth inhibition and were significantly more efficacious than each of the parental ADCs (FIG. 5).Example 4: Effects of BiADC Treatment in a Murine Model of Colorectal Cancer

[0069] Female C.B-17 SCID mice were implanted subcutaneously in the right flank with 2.5 xlO6SW620 human colorectal cancer cells in a 70 pL cells + 30 pL Matrigel™ suspension. After tumor staging, mice were randomized to generate groups of 6 mice each with an average tumor volume of 150-200 mm3. Mice received 3 doses of the different test articles on Days 0, 7 and 14 at dose levels of either 1 mg / kg or 3 mg / kg. Tumor volumes and body weights of the animals were measured twice weekly. The data show that both BiADCs resulted in complete tumor eradication (FIG. 6).Example 5: Effects of HER3 x c-MET-A BiADC on Tumor Growth in a Murine Model of HR+ / HER2- Breast Cancer

[0070] Female NPG mice were implanted subcutaneously in the right flank with 5 * 106MCF-7 cells in a 100 pL cells + 100 pL Matrigel™ suspension. After tumor staging, mice were randomized to generate groups of 5 mice each with an average tumor volume of approximately 200 mm3. Mice received two doses of Patritumab-DXd, Trastuzumab-DXd, Datopotamab-DXd or HER3 x c-MET-A BiADC on Day 0 and 7 at dose levels of either 1.5 mg / kg or 3 mg / kg. Tumor volumes were measured twice weekly. HER3 x c-MET-A Bi ADC treatment resulted in complete regression of the tumors. The HER3 x c-MET-A BiADC is more efficacious than the other ADCs directed against a single target (FIG 7).Example 6: Effects of HER3 x c-MET-A BiADC on Tumor Growth in a Murine Model of EGFR-wildtype Non Small Cell Lung Cancer

[0071] Female BALB / c mice were implanted subcutaneously in the right flank with 2 x 106NCI-H441 cells in a 100 pL cells + 100 pL Matrigel™ suspension. After tumor staging, mice were randomized to generate groups of 5 mice each with an average tumor volume of approximately 150 mm3. Mice received 3 mg / kg Patritumab-DXd or 1.5 mg / kg, 3 mg / kg or 5 mg / kg HER3 x c-MET-A BiADC on Day 0 and 7. Tumor volumes were measured twice weekly. HER3 x c-MET-A BiADC treatment resulted in complete regression of the tumors. The HER3 x c-MET-A BiADC is significantly more efficacious than Patritumab-Dxd (FIG.8)Example 7: Effects of HER3 x c-MET-A BiADC on Tumor Growth in a Murine Model of EGFR-mutated Non Small Cell Lung Cancer

[0072] Female CB17 SCID mice were implanted subcutaneously in the right flank with 5 X 106HCC4006 cells in a 100 pL cells + 100 pL Matrigel™ suspension. After tumor staging, mice were randomized to generate groups of 5 to 7 mice each with an average tumor volume of 152-163 mm3. Mice received 10 mg / kg Patritumab-DXd or 3 mg / kg or 10 mg / kg HER3 x c-MET-A Bi ADC on Day 1, 8 and 15. The tumors in the Patritumab-DXd treatment group were allowed to regrow for approximately 2 weeks after the last dose of Patritumab- DXd and were re-treated with 10 mg / kg HER3 x c-MET-A Bi ADC on Day 29 and 36. Tumor volumes were measured twice weekly. The HER3 x c-MET-A BiADC is significantly more efficacious than Patritumab-DXd and is effective at killing Patritumab- DXd-resistant tumors (FIG. 9).Example 8: Effects of HER3 x c-MET-A BiADC on Tumor Growth in a Murine Model of Pancreatic Cancer

[0073] Female NUNU mice were implanted subcutaneously in the right flank with 2 x 106Capan-2 cells in 100 pL culture medium. After tumor staging, mice were randomized to generate groups of 5 mice each with an average tumor volume of 197-220 mm3. Mice received 3 mg / kg Patritumab-DXd, 3 mg / kg Telisotuzumab-vedotin or 3 mg / kg HER3 x c- MET-A BiADC on Day 0, 8 and 14. Tumor volumes were measured twice weekly. HER3 x c-MET-A Bi ADC treatment resulted in complete regression of the tumors. The HER3 x c- MET-A BiADC is more efficacious than Patritumab-DXd and Telisotuzumab-vedotin (FIG. 10).SEQUENCES

[0074] Amino acid sequences provided in the present disclosure are listed below (SEQ: SEQ ID NO). Complementarity-determining regions (CDRs) are defined by the Kabat system or the IMGT® system.

Claims

CLAIMS1. An antibody-drug conjugate (ADC) comprising a bispecific antibody (Ab) conjugated, optionally at a cysteine residue therein, to a cytotoxin through a linker, wherein the bispecific antibody comprises a first antigen-binding portion specific for human HER3, and a second antigen-binding portion specific for human c-MET, wherein the first antigen-binding portion comprises heavy chain CDR1-3 and light chain CDR1-3 comprising SEQ ID NOs: 32, 33, 34, 35, 36, and 37, respectively, or comprising SEQ ID NOs: 38, 39, 40, 41, 42, and 37, respectively; the second antigen-binding portion comprises heavy chain CDR1-3 and light chain CDR1-3 comprising SEQ ID NOs: 1, 2, 3, 4, 5, and 6, respectively, or comprising SEQ ID NOs: 7, 8, 9, 10, 11, and 6, respectively; and the ADC comprises the structure shown in Formula (I):Formula (I) wherein n is from 1 to 8.

2. The ADC of claim 1, wherein the first antigen-binding portion comprises a heavy chain variable domain (VH) and a light chain variable domain (VL) comprising SEQ ID NOs: 43 and 44, respectively; and the second antigen-binding portion comprises a VH and a VL comprising SEQ ID NOs: 12 and 13, respectively.

3. The ADC of claim 1 or 2, wherein the bispecific antibody is of human IgGi or IgG4 isotype subtype.

4. The ADC of claim 3, wherein the bispecific antibody comprises in its Fc domain one or more mutations that reduce effector functions of the bispecific antibody and / or knobs-in- holes mutations.

5. The ADC of any one of claims 1-4, wherein the first or second antigen-binding portion is a CrossMab comprising a VL linked to a light chain constant region (CL) and a VL linked to a Cm.

6. The ADC of claim 5, wherein the bispecific antibody comprises four polypeptides (a), (b), (c), and (d), wherein polypeptide (a) comprises the VL of the first antigen-binding portion linked to a human CL, and polypeptide (b) comprises the VH of the first antigen-binding portion linked to a human IgGi constant region, wherein polypeptides (a) and (b) pair to form the first antigenbinding portion, polypeptide (c) comprises the VH of the second antigen-binding portion linked to a human CL, and polypeptide (d) comprises the VL of the second antigen-binding portion linked to a human IgGi constant region, wherein polypeptides (c) and (d) pair to form the second antigen-binding portion, and polypeptides (b) and (d) pair to form an antibody Fc domain.

7. The ADC of claim 5, wherein polypeptides (a), (b), (c), and (d) comprise SEQ ID NOs:46, 45, 15, and 14, respectively.

8. The ADC of any one of claims 1-4, wherein the first and / or second antigen-binding portions are an scFv.

9. An antibody-drug conjugate (ADC) comprising a bispecific antibody (Ab) conjugated, optionally at a cysteine residue therein, to a cytotoxin through a linker, wherein the bispecific antibody comprises a first antigen-binding portion specific for human HER3, and a second antigen-binding portion specific for human c-MET, wherein the first antigen-binding portion comprises heavy chain CDR1-3 and light chain CDR1-3 comprising SEQ ID NOs: 32, 33, 34, 35, 36, and 37, respectively, or comprising SEQ ID NOs: 38, 39, 40, 41, 42, and 37, respectively; the second antigen-binding portion comprises heavy chain CDR1-3 and light chain CDR1-3 comprising SEQ ID NOs: 16, 17, 18, 19, 20, and 21, respectively, or comprising SEQ ID NOs: 22, 23, 24, 25, 26, and 27, respectively; and the ADC comprises the structure shown in Formula (I):Formula (I) wherein n is from 1 to 8.

10. The ADC of claim 9, wherein the first antigen-binding portion comprises a heavy chain variable domain (VH) and a light chain variable domain (VL) comprising SEQ ID NOs: 43 and 44, respectively; and the second antigen-binding portion comprises a VH and a VL comprising SEQ ID NOs: 28 and 29, respectively.

11. The ADC of claim 9 or 10, wherein the bispecific antibody is of human IgGi or IgG4 isotype subtype.

12. The ADC of claim 11, wherein the bispecific antibody comprises in its Fc domain one or more mutations that reduce effector functions and / or knobs-in-holes mutations.

13. The ADC of any one of claims 9-12, wherein the first or second antigen-binding portion is a CrossMab comprising a VL linked to a light chain constant region (CL) and a VL linked to a Cm.

14. The ADC of claim 13, wherein the bispecific antibody comprises four polypeptides (a), (b), (c), and (d), wherein polypeptide (a) comprises the VL of the first antigen-binding portion linked to a human CL, and polypeptide (b) comprises the VH of the first antigen-binding portion linked to a human IgGi constant region, wherein polypeptides (a) and (b) pair to form the first antigenbinding portion, polypeptide (c) comprises the VH of the second antigen-binding portion linked to a human CL, and polypeptide (d) comprises the VL of the second antigen-binding portion linked to a human IgGi constant region, wherein polypeptides (c) and (d) pair to form the second antigen-binding portion, and polypeptides (b) and (d) pair to form an antibody Fc domain.

15. The ADC of claim 14, wherein polypeptides (a), (b), (c), and (d) comprise SEQ ID NOs:46, 45, 31, and 30, respectively.

16. The ADC of any one of claims 9-12, wherein the first and / or second antigen-binding portions are an scFv.

17. A pharmaceutical composition comprising the ADC of any one of claims 1-16 and a pharmaceutically acceptable excipient.

18. A method of treating cancer in a human patient in need thereof, comprising administering to the patient a therapeutically effective amount of the ADC of any one of claims 1-16 or the pharmaceutical composition of claim 17.

19. The method of claim 18, wherein the cancer expresses HER3 and / or c-MET.

20. The method of claim 18 or 19, wherein the cancer is head and neck cancer, lung cancer, esophageal cancer, gastric cancer, hepatic cancer, pancreatic cancer, colorectal cancer, breast cancer, endometrial cancer, ovarian cancer, soft-tissue sarcoma, bladder cancer, prostate cancer, renal cancer, or melanoma, optionally wherein cancer is lung cancer, gastric cancer, colorectal cancer, pancreatic cancer, or breast cancer, further optionally wherein the lung cancer is non-small cell lung cancer (NSCLC).

21. The method of any one of claims 18-20, further comprising administering to the patient an additional therapy.

22. The method of claim 21, wherein the additional therapy is immunotherapy, chemotherapy, or radiotherapy.

23. The ADC of any one of claims 1-16 or the pharmaceutical composition of claim 17 for use in treating cancer in a method of any one of claims 18-22.

24. Use of the ADC of any one of claims 1-16 or the pharmaceutical composition of claim 17 in the manufacture of a medicament for treating cancer in a method of any one of claims 18-22.

25. A method of making an antibody-drug conjugate, comprising: providing a bispecific antibody as defined in any one of claims 1-16, and contacting the antibody with a compound comprising a structure of Formula (II) to allow the compound to be conjugated to the bispecific antibody at one or more cysteine in the antibody:Formula (II).

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