In Vitro Cell-Based Assays to Predict Pharmacokinetics and Brain Penetration of Biologics

Abstract

The present disclosure relates to methods and compositions useful for measuring the transcytosis or recycling of molecules. In particular, the present disclosure relates to in vitro receptor-mediated transcytosis or recycling assays for assessing the clearance rate of therapeutic antibody molecules and Fc fusion proteins in humans and animals.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 174,913, filed April 14, 2021, and U.S. Provisional Patent Application No. 63 / 187,750, filed May 12, 2021, the contents of which are incorporated by reference in their entireties herein. Sequence Listing

[0002] This application contains a Sequence Listing that has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. The ASCII copy created on March 15, 2022 is named "P36572-WO_SL.txt" and is 16,584 bytes in size.

[0003] The present disclosure relates to the method and composition useful for measuring the recycling of molecules through cell layers.In particular, the present disclosure relates to the in vitro receptor-dependent recycling assay, and the recycling and transcytosis assay for evaluating the in vivo pharmacokinetic profile (e.g., clearance rate and / or half-life) and tissue penetration of molecules that interact with FcRn, such as therapeutic antibodies, Fc fusion molecules, and molecules linked to albumin. [Background technology]

[0004] Therapeutic monoclonal antibodies (mAbs) have become a major class of pharmaceutical products worldwide due to their proven efficacy in treating various diseases and their desirable pharmacological properties. One of the favorable pharmacological properties of mAb drugs is their typically long circulating half-life. Prolonging the half-life of biopharmaceuticals allows for less frequent administration and / or lower dosage of the drug, which may reduce medical costs, improve patient compliance, and / or reduce concentration-dependent cytotoxicity / adverse events.

[0005] Significant progress has been made in understanding the pharmacokinetic (PK) profiles of mAb drugs in animals and humans. Although many mAb drugs exhibit PK behavior similar to endogenous IgG, substantial heterogeneity in the nonspecific clearance rates of mAb drugs in humans is still commonly observed. Thus, evaluation and selection of clinical candidates for desirable PK properties is an early and critical step during drug development. A wide range of techniques involving in silico, in vitro and in vivo analyses have been used to evaluate and / or predict the PK behavior of mAbs in humans (Dostalek et al., 2017, MAbs 9(5):756-766). However, the translation of PK data from animals to humans and from in vitro assays to in vivo readouts remains elusive to drug developers (Vugmeyster et al., 2012, World J Biol Chem 3(4):73-92). Furthermore, several animal models, such as human FcRn transgenic mice (Avery et al., 2016, MAbs, 8(6), 1064-1078) and non-human primates (Deng et al., 2011, Drug Metab Dispos 38(4):600-605), have been successfully used to predict human PK of mAbs, but these studies are usually time-consuming, expensive, and involve animal sacrifice.

[0006] There are many complexities in predicting human PK of mAbs from animal studies and in vitro assays. Target-mediated drug disposition (TMDD) is known to affect the dose-dependent PK behavior of mAbs, resulting in nonlinear distribution and elimination. In the absence of TMDD, mAbs are expected to exhibit linear elimination and nonspecific clearance rates reflecting target-independent, molecule-specific drug catabolism. Nonspecific clearance of mAbs is primarily mediated by lysosomal degradation in the reticuloendothelial system, where the neonatal Fc receptor (FcRn)-mediated Savage pathway plays a major role. Structurally, FcRn is a heterodimer, composed of a transmembrane heavy chain homologous to major histocompatibility complex (MHC) class I-like molecules (FCGRT) and a soluble light chain, β2-microglobulin (B2M). FcRn binds to the Fc domain of endogenous IgG at acidic pH (<6.5) but only minimally at neutral or basic pH (>7.0). This unique property allows FcRn to protect Fc-containing molecules from degradation by binding in acidic endosomes after uptake of the molecules into cells, and then transport them back to the cell surface and release into the circulation at physiological pH. In contrast, internalized molecules that are not bound to FcRn are targeted to lysosomes for degradation (see FIG. 1 and Roopenian et al., Nat Rev Immunol. 2007 Sep;7(9):715-25).

[0007] Although the contribution of FcRn in extending the half-life of Fc-containing proteins is well recognized (Roopenian et al., 2003, J Immunol, 170(7), 3528-3533), reports of a lack of correlation between FcRn binding and PK for mAb drugs in humans (Suzuki, 2010; Zheng, 2011; Hotzel, 2012) suggest that binding affinity to FcRn is not the sole determinant of the clearance rate of Fc-containing proteins. Considering the function of FcRn in intracellular trafficking, the kinetics of endosomal sorting and trafficking of Fc-containing molecules / FcRn complexes likely affect the overall efficiency of the FcRn-mediated salvage mechanism and, therefore, the nonspecific clearance rate of the molecule. In addition, the processes of cellular uptake by pinocytosis or endocytosis, as well as degradation in lysosomes, may also play a role in determining the rate and extent of mAb degradation (Junghans and Anderson, 1996, PNAS 93(11), 5512-5516). Finally, biochemical characteristics such as charge / pI, hydrophobicity, non-specific binding and other factors have been reported to affect the pharmacokinetics of mAbs (Datta-Mannan et al., 2015, MAbs 7(3), 483-493; Igawa et al., 2010 Protein Eng Des Sel 23(5), 385-392; Sharma et al., 2014 PNAS 111(52); Hotzel et al., 2012 MAbs 4(6), 753-760). These molecular features may themselves affect mAb structure so as to alter the "true" interaction with FcRn in vivo, or may contribute to non-specific cell surface binding that alters the mode / rate of internalization and the relative proportions of FcRn-mediated intracellular trafficking pathways, including recycling and transcytosis.

[0008] In vivo animal studies performed in rodents and non-human primates are commonly used to predict the PK of therapeutic antibodies in humans (Avery et al., MAbs, 2016, 8(6), 1064-1078; Deng et al., MAbs 2011, 3(1), 61-66). These approaches require sacrificing animals, are not cost-effective, and cannot be performed in a high-throughput manner. Based on empirical scaling methods, it has been demonstrated that in some cases, PK in animal studies cannot faithfully predict cross-species differences in PK in humans, due to species differences in FcRn binding, target-mediated drug pharmacokinetics, and elicitation of differential immune responses (Wang et al., 2016, Biopharm Drug Dispos, 37(2), 51-65). Approaches to in vitro assays have been used to assess PK in a time- and cost-saving and animal-sparing approach. Most of these methodologies take into account one or a subset of molecular properties that may affect PK, such as nonspecific binding (Hotzel et al., MAbs 2012, 4(6), 753-760), FcRn interactions (Schlothauer et al., MAbs 2013, 5(4), 576-586; Souders et al., MAbs 2015, 7(5), 912-921) and heparin or extracellular matrix (de Ridder et al., Cerebrovasc Dis 2013, 35(1), 60-63; Kraft et al., MAbs 2020, 12(1)). These methods usually rely on cut-off thresholds and occasionally have only limited success in direct PK prediction and have had to be combined with other methods to improve prediction accuracy.

[0009] The lack of in vitro models for the actual behavior of antibodies is particularly problematic in the context of brain penetration. Central nervous system (CNS) disorders are a serious health burden, and for decades there has been a strong motivation to develop effective treatments for CNS disorders. The blood-brain barrier is a highly specialized tissue that contains endothelial cells (and others) with tight junctions, regulating the passage of molecules into the brain, including preventing the transport of most current therapeutics from the bloodstream to the CNS. Although there are various methods to modify the brain penetration of molecules, it is very difficult to apply these methods in preclinical drug development without a robust model to evaluate their efficacy. Due to the low correlation between existing models and in vivo results, brain penetration of potential therapeutics must often be tested empirically, which is time-consuming and expensive.

[0010] A human microvascular endothelial cell (HMEC1) line engineered to express human FcRn was developed and evaluated, and the recycled / residual mAb ratio was found to correlate with their serum half-life in human FcRn transgenic mice (Grevys et al., Nat Commun 2018, 9(1), 621). However, the dataset was limited to engineered IgGs with much enhanced FcRn binding affinity, but did not include the normal IgG framework more commonly used in therapeutic antibodies. Furthermore, cells were cultured in regular cell culture plates, which are not ideal for cell polarization and may result in transcytosis components contaminating the recycled sample.

[0011] Thus, there remains a need for methods to predict the in vivo PK properties (e.g., clearance, half-life, etc.) and brain penetration of therapeutic molecules that can be performed quickly and at reasonable cost to aid in the evaluation and selection of therapeutic molecules. Summary of the Invention

[0012] The present disclosure relates to methods, assays, assay systems, kits and compositions useful for measuring the movement or transport of a molecule of interest to and from a cell membrane, including recycling and transcytosis of the molecule of interest. In particular, the present disclosure provides an in vitro receptor-dependent transcytosis and recycling assay for the evaluation of the in vivo pharmacokinetic profile (including, for example, in vivo clearance (CL), volume of distribution (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin)) of molecules that interact with molecular transport receptors (e.g., FcRn), including molecules such as therapeutic antibodies, Fc fusion molecules, and molecules linked to albumin. The methods and assays provided herein can more fully encompass multiple factors that may affect the in vivo PK behavior of test molecules (including antibodies), such as non-specific binding and interaction with cell surfaces, pH-dependent binding (e.g., FcRn binding) and intracellular transport pathways, compared to other methods. The methods and assays provided herein may better predict and / or model in vivo tissue penetration (such as brain penetration) of molecules of interest (including antibodies) compared to other methods. Methods and assays are provided that may further provide improved apical-basolateral polarization of cells and / or clearer assessment of recycling to transcytosis components compared to other methods and / or assays.

[0013] In certain embodiments, the present disclosure relates to a method for determining the recycling of a plurality of molecules. For example, determining can include: introducing a plurality of molecules into a first chamber, the first chamber being separated from a second chamber by a cell layer, and the first chamber and the second chamber comprising an aqueous solution; incubating the plurality of molecules in the first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of the plurality of molecules released from the cell layer into the first chamber; the aqueous solution is at physiological pH, and the cell layer comprises cells expressing receptors that mediate molecular transport.

[0014] In certain embodiments, the method further comprises measuring transcytosis of the plurality of molecules across the cell layer, hi certain embodiments, measuring transcytosis comprises measuring the amount of the plurality of molecules in the second chamber after the aqueous solution is exchanged.

[0015] In certain embodiments, the method includes incubating a plurality of molecules in a first chamber in the presence of an agent and determining whether the agent affects recycling of the plurality of molecules.

[0016] In certain embodiments, the present disclosure relates to a method for determining tissue permeability of a plurality of molecules, comprising: a) introducing a plurality of molecules into a first chamber, the first chamber being separated from a second chamber by a cell layer, the first chamber and the second chamber comprising an aqueous solution; the aqueous solution being at a physiological pH, and the cell layer comprising cells expressing a receptor that mediates molecular transport; b) measuring the amount of the plurality of molecules recycled from the first chamber to the cell layer and back to the first chamber; c) measuring the amount of the plurality of molecules transcytosed from the first chamber to the second chamber; and d) determining the tissue permeability of the plurality of molecules based on a ratio of transcytosed molecules to recycled molecules. In some embodiments, the tissue permeability is brain permeability.

[0017] In certain embodiments, measuring the number of molecules recycled includes introducing the number of molecules into the first chamber, followed by incubating the number of molecules in the first chamber; exchanging aqueous solutions in both the first chamber and the second chamber; and measuring the amount of the number of molecules released from the cell layer into the first chamber.

[0018] In certain embodiments, measuring the number of molecules that are transcytosed includes introducing the number of molecules into the first chamber, followed by incubating the number of molecules in the first chamber; exchanging aqueous solution in both the first chamber and the second chamber; and measuring the amount of molecules released from the cell layer into the second chamber.

[0019] In certain embodiments, measuring the amount of molecules recycled and measuring the amount of molecules transcytosed independently include using enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, mass spectrometry, or any combination thereof. In certain embodiments, the tissue permeability is brain permeability.

[0020] In certain embodiments, the method includes incubating a plurality of molecules in a first chamber in the presence of an agent and determining whether the agent affects tissue permeability of the plurality of molecules.

[0021] In certain embodiments, the present disclosure relates to a method of determining a pharmacokinetic (PK) parameter of a plurality of molecules, the method comprising: a) introducing a plurality of molecules into a first chamber, the first chamber being separated from a second chamber by a cell layer, the first chamber and the second chamber comprising an aqueous solution; the aqueous solution being at physiological pH, the cell layer comprising cells expressing a receptor that mediates molecular transport; b) measuring an amount of the plurality of molecules that is recycled from the first chamber to the cell layer and back to the first chamber; and c) determining the PK parameter based on the amount of the plurality of molecules that is recycled.

[0022] In certain embodiments, measuring the number of molecules recycled includes introducing the number of molecules into the first chamber, followed by incubating the number of molecules in the first chamber; exchanging aqueous solutions in both the first chamber and the second chamber; and measuring the amount of the number of molecules released from the cell layer into the first chamber.

[0023] In certain embodiments, the cells express a heterologous FcRn. In certain embodiments, measuring the amount of recycled molecules comprises using enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, or mass spectrometry.

[0024] In certain embodiments, the PK parameters are measurements of in vivo clearance, volume of distribution, area under the curve (AUC), bioavailability, or in vivo half-life of multiple molecules.

[0025] In certain embodiments, the method includes incubating a plurality of molecules in a first chamber in the presence of an agent and determining whether the agent affects a PK parameter of the plurality of molecules.

[0026] In certain embodiments, the plurality of molecules is a plurality of single molecules. In certain embodiments, the plurality of molecules is a plurality of separate molecules. In certain embodiments, the cell layer comprises a cell monolayer. In certain embodiments, the receptor that mediates molecular transport is a receptor that mediates intracellular transport of molecules. In certain embodiments, the receptor that mediates molecular transport is a transferrin receptor, an Fc receptor, megalin, or cubulin. In certain embodiments, the receptor that mediates molecular transport is neonatal Fc receptor (FcRn).

[0027] In certain embodiments, the cell is a eukaryotic cell, a mammalian cell, or a kidney cell, hi certain embodiments, the cell is a Madin-Darby canine kidney (MDCK) cell.

[0028] In certain embodiments, measuring the amount of the plurality of molecules released from the cell layer into the first chamber comprises the use of enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, or mass spectrometry.

[0029] In certain embodiments, the plurality of molecules is incubated in the first chamber for about 1 hour to about 48 hours. In certain embodiments, the plurality of molecules is incubated in the first chamber for about 1 hour to about 30 hours. In certain embodiments, exchanging the aqueous solution includes washing the first chamber. In certain embodiments, the method further includes incubating the first chamber and the second chamber with a replacement aqueous solution prior to measurement. In certain embodiments, the first chamber and the second chamber are incubated with the replacement aqueous solution for 1 hour to 6 hours prior to measurement. In certain embodiments, the incubation is performed at a temperature of about 35° C. to about 39° C.

[0030] In certain embodiments, the plurality of molecules are Fc-containing molecules. In certain embodiments, the Fc-containing molecules are receptor-Fc fusion molecules. In certain embodiments, the plurality of molecules are antibodies. In certain embodiments, the antibodies are monoclonal antibodies. In certain embodiments, the FcRn is selected from the group consisting of human FcRn, mouse FcRn, rat FcRn, and cynomolgus FcRn.

[0031] In certain embodiments, the physiological pH is about 7.4.

[0032] In certain embodiments, the present disclosure relates to an assay system comprising: a) a first chamber and a second chamber, each chamber comprising an aqueous solution at physiological pH; b) a cell layer separating the first chamber and the second chamber, the cell layer capable of mediating recycling of molecules from the first chamber into the cell layer and back into the first chamber; c) a detector for detecting the presence of a molecule in the first chamber; the assay system configured to determine recycling of a plurality of molecules, the determining comprising: introducing a plurality of molecules into the first chamber; incubating the plurality of molecules in the first chamber; exchanging aqueous solutions in both the first chamber and the second chamber; and measuring the amount of the plurality of molecules released from the cell layer into the first chamber.

[0033] In certain embodiments, the assay system further comprises a detector for detecting the presence of a molecule in the second chamber; the cell layer is capable of mediating transcytotic transport of a molecule from the first chamber to the second chamber; and is configured to determine transcytotic transport of a plurality of molecules across the cell layer, wherein determining transcytotic transport comprises measuring the amount of the plurality of molecules in the second chamber after the aqueous solution is exchanged.

[0034] In certain embodiments, the present disclosure relates to kits comprising the assay systems and / or methods of the present disclosure. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 shows a schematic diagram of the mechanism of action of FcRn, including pH-dependent capture and release, and intracellular trafficking pathways including recycling, transcytosis, and lysosomal degradation.

[0036] [Diagram 2] FIG. 2 shows a schematic diagram of a particular embodiment of the recycling assay of the present disclosure.

[0037] [Figure 3A]FIG. 3A shows a schematic diagram of the sensitive human IgG-specific enzyme-linked immunosorbent assay (ELISA) used to quantitate recycling as described in the Examples.

[0038] [Figure 3B] FIG. 3B provides a standard curve for the ELISA assay shown in FIG. 3A, indicating the lower limit of detection.

[0039] [Figure 4] FIG. 4 shows that the recycling and transcytosis output of various humanized IgG1 antibodies with differential Fc-FcRn binding affinities is affected by human FcRn.

[0040] [Diagram 5] Figures 5A-5B provide a comparison of time-dependent recycling measurements demonstrating similar recycling kinetics for four therapeutic antibodies, with Figure 5A providing non-normalized data and Figure 5B providing normalized data.

[0041] [Figure 6] FIG. 6 shows the transcytosis / recycling (T / R) ratio for the wild-type (WT) BACE-1 antibody molecule and several sequence variants.

[0042] [Figure 7] FIG. 7 shows the relationship between the transcytosis / recycling (T / R) ratio and the brain serum ratio in cynomolgus monkeys for five anti-BACE1 mAb variants.

[0043] [Figure 8] Figures 8A-8D show clearance rates in humans compared to calculated pI (Figure 8A), Fv charge (Figure 8B), HI sum (Figure 8C), and normalized recycling assay output performed according to the methods and assays described herein for a series of therapeutic antibodies. In Figures 8A-8C, there is low or no correlation between clearance rates and the compared parameters. Figure 8D shows the correlation between clearance rates and normalized recycling output. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] In practicing the subject matter of the present disclosure, many conventional techniques in molecular biology, microbiology, cell biology, biochemistry and immunology will be used. These techniques are described in further detail, for example, in Molecular Cloning: a Laboratory Manual, 3rd ed., J.F. Sambrook and D.W. Russell, eds., Cold Spring Harbor Laboratory Press 2001; Recombinant Antibodies for Immunotherapy, Melvyn Little, ed., Cambridge University Press 2009; "Oligonucleotide Synthesis" (M.J. Gait, ed., 1984); "Animal Cell Culture" (R.I. Freshney, ed., 1987); "Methods in Enzymology" (Academic Press, Inc.); "Current Protocols in Molecular Biology" (F.M.Ausubel et al., eds., 1987, and periodic updates); "PCR: The Polymerase Chain Reaction," (Mullis et al., eds., 1994); "A Practical Guide to Molecular Cloning" (Perbal Bernard V., 1988); "Phage Display: A Laboratory Manual" (Barbas et al., 2001). The contents of these references, as well as other references containing standard protocols, including manufacturer's instructions, that are widely known and relied upon by those of skill in the art, are incorporated herein by reference as part of this disclosure.

[0045] 1.Definition Unless otherwise specified, all technical terms, notations, and other scientific terms used herein are intended to have the meaning commonly understood by those skilled in the art to which this disclosure pertains. In some cases, terms having a commonly understood meaning are defined herein for clarity and / or ease of reference, and the inclusion of such definitions herein should not necessarily be construed as representing a substantial difference to what is commonly understood in the art.

[0046] As used herein, the terms "comprise(s), "include(s)", "having", "has", "can", "contain(s)", and variations thereof are intended to be open-ended transitional phrases, terms, or words that do not exclude the possibility of additional acts or structures. The singular forms "a", "an", and "the" include plural referents unless the context clearly indicates otherwise. The present disclosure also contemplates other embodiments that "comprise", "consist of", and "consist essentially of" the embodiments or elements presented herein, whether or not expressly stated.

[0047] As used herein, the term "about" or "approximately" means within an acceptable error range of a particular value as determined by a person skilled in the art, which depends in part on the method of measuring or determining the value, i.e., the limitations of the measurement system. For example, "about" can mean within 3 or more standard deviations per one practice in the art in certain embodiments. Alternatively, "about" can mean within a range of up to 20%, up to 10%, up to 5%, or up to 1% of a given value in certain embodiments. Alternatively, particularly with respect to biological systems or processes, the term can mean within an order of magnitude of a value, for example within 5-fold, or within 2-fold.

[0048] As used herein, the terms "culture medium" and "cell culture medium" refer to a nutrient source used to grow or maintain cells. As will be understood by those skilled in the art, the nutrient source may contain components required by cells for growth and / or survival or may contain components that support cell growth and / or survival. Vitamins, essential or non-essential amino acids (e.g., cysteine ​​and cystine), and trace elements (e.g., copper) are examples of medium components. Any medium provided herein may be supplemented with any one or more of insulin, vegetable hydrolysates, and animal hydrolysates.

[0049] As used herein, the phrase "pharmacokinetic (PK) parameter" refers to any of a variety of PK parameters known in the art, including, but not limited to, in vivo clearance (CL), volume of distribution (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin), or in vivo half-life (t1 / 2) of multiple molecules.

[0050] As used herein, the term "clearance" refers to the rate at which a molecule or polypeptide is removed from the bloodstream of an animal. The animal may be a mammal, such as, for example, a rodent (mouse, rat, hamster, guinea pig, or other rodent), a non-human primate (such as a cynomolgus monkey), a dog, or a human.

[0051] As used herein, the term "physiological pH" refers to a pH of about 6.5 to about 8.0. In certain embodiments, the physiological pH value is any value between about 6.5 and about 8.0, such as about 6.6, about 6.7, about 6.8, about 6.9, about 7.0, about 7.1, about 7.2, about 7.3, about 7.4, about 7.5, about 7.6, about 7.7, about 7.8, or about 7.9, or any range within the range of about 6.5 to about 8.0.

[0052] "Culturing" a cell means contacting the cell with a cell culture medium under conditions suitable for the survival and / or growth and / or proliferation of the cell.

[0053] As used herein, "molecule" generally refers to the molecule that is the subject of the assay. For example, but not limited to, the molecule can be any molecule that naturally binds to FcRn (e.g., polypeptide, antibody, Fc-containing molecule, etc.) or that is engineered to bind to FcRn, such as, but not limited to, albumin-containing molecule, molecule that is engineered to bind to FcRn via peptide tag or other amino acid sequence, antibody, antibody fragment, or polyclonal or monoclonal antibody as defined below. Such polypeptide, protein, antibody, antibody fragment, or polyclonal or monoclonal antibody can include non-naturally occurring aspects, including, but not limited to, non-naturally occurring amino acids, non-amino acid linkers or spacers, and can include conjugates with other compositions, such as small or large molecule therapeutic agents.

[0054] As used herein, "polypeptide" generally refers to peptides and proteins having more than about 10 amino acids. The polypeptide can be homologous to the host cell, or preferably, exogenous. The latter means that it is heterologous, i.e., foreign, to the host cell utilized, e.g., a human protein produced by a Chinese hamster ovary cell, or a yeast polypeptide produced by a mammalian cell. In certain embodiments, mammalian polypeptides (polypeptides originally derived from a mammalian organism) are used, and in certain embodiments, the polypeptides of the invention are secreted directly into the medium.

[0055] The term "protein" refers to a sequence of amino acids with sufficient chain length to generate higher order tertiary and / or quaternary structure. This is to distinguish it from "peptides" or other low molecular weight drugs that do not have such structure. Typically, proteins herein have a molecular weight of at least about 15-20 kD, and in certain embodiments, at least about 20 kD. Examples of proteins encompassed by the definition herein generally include all mammalian proteins, particularly therapeutic and diagnostic proteins, such as therapeutic and diagnostic antibodies, and proteins that contain one or more disulfide bonds, including multi-chain polypeptides that contain one or more inter-chain and / or intra-chain disulfide bonds.

[0056] The term "antibody" is used herein in the broadest sense and encompasses various types of antibodies and antibody structures, including, but not limited to, polyclonal or monoclonal antibodies, human, humanized or chimeric antibodies, multispecific antibodies, e.g., bispecific antibodies, and antibody fragments that exhibit the desired antigen-binding activity.

[0057] As used herein, an "antibody fragment," "antigen-binding portion" (or simply "antibody portion") of an antibody, or an "antigen-binding fragment" of an antibody refers to a molecule other than an intact antibody that comprises a portion of an intact antibody that binds to an antigen and / or epitope. Examples of antibody fragments include, but are not limited to, Fv, Fab, Fab', Fab'-SH, and F(ab')2. Included are antibody fragments formed from diabodies; linear antibodies; single-chain antibody molecules (e.g., scFv); and multispecific antibodies, e.g., bispecific antibodies.

[0058] As used herein, the term "monoclonal antibody" or "mAb" refers to an antibody obtained from a population of substantially homogeneous antibodies, i.e., the individual antibodies comprising the population are identical and / or bind the same epitope, except for variant antibodies that may contain, for example, naturally occurring mutations or arise during the production of a monoclonal antibody preparation, and such variants are generally present in small amounts. Each monoclonal antibody of a monoclonal antibody preparation is directed against a single determinant on the antigen, in contrast to polyclonal antibody preparations, which typically contain different antibodies against different determinants (epitopes). Thus, the modifier "monoclonal" indicates the character of the antibody as being obtained from a substantially homogeneous population of antibodies, and should not be construed as requiring the production of the antibody by any particular method. For example, monoclonal antibodies used in accordance with the subject matter disclosed in the present invention may be produced by a variety of techniques, including, but not limited to, hybridoma methods, recombinant DNA methods, phage display methods, and methods utilizing transgenic animals containing all or part of the human immunoglobulin locus, and such methods and other exemplary methods for producing monoclonal antibodies are described herein.

[0059] The term "hybridoma" refers to a hybrid cell line produced by the fusion of an immortalized immunogenic cell line with an antibody-producing cell. The term encompasses the progeny of a heterohybrid myeloma fusion resulting from the fusion of a human cell with a mouse myeloma cell line, followed by a plasma cell commonly known as a trioma cell line. In addition, the term is meant to include any immortalized hybrid cell line that produces antibodies, such as quadromas. See, e.g., Milstein et al., Nature, 537:3053 (1983).

[0060] As used herein, the term "cell" refers to animal cells, mammalian cells, cultured cells, host cells, recombinant cells, and recombinant host cells. Such cells are generally cell lines obtained from or derived from mammalian tissues that are capable of proliferation and viability when placed in medium containing the appropriate nutrients and / or growth factors.

[0061] As used herein, the term "heterologous gene" refers to a gene that encodes a protein that is foreign to the host cell being utilized, such as a gene encoding a human protein produced by Chinese hamster ovary cells, or a gene encoding a yeast polypeptide produced in a mammalian cell.

[0062] As used herein, "multiple molecules" includes multiple single molecules and multiple different molecules. Multiple single molecules can be, for example, two or more physical molecules of the same antibody, two or more physical molecules of the same antibody fragment, two or more physical molecules of the same polypeptide, or two or more physical molecules of the same Fc-containing molecule, or two or more physical molecules of another molecule of interest. Multiple different molecules can include mixtures of one molecule type (e.g., physical molecules of at least two different antibodies, physical molecules of at least two different antibody fragments, physical molecules of at least two different polypeptides, or physical molecules of at least two Fc-containing molecules), but can also include mixtures between molecule types (e.g., physical molecules of one or more antibodies and one or more polypeptides; or one or more antibody fragments, one or more polypeptides, and one or more Fc-containing molecules, etc.).

[0063] As used herein, "test molecule" and "molecule of interest" refer to the identity of multiple molecules evaluated in the assays, methods, kits, and systems described herein. As described for multiple molecules, such terms encompass both a single type of molecule (e.g., one antibody, antibody fragment, polypeptide, or Fc-containing molecule) and more than one type of molecule (e.g., two or more antibodies, antibody fragments, polypeptides, or Fc-containing molecules, or a combination of categories).

[0064] As used herein, a "small molecule" refers to a molecule other than a protein or polypeptide having a molecular weight below about 2000 daltons, or preferably below about 500 daltons.

[0065] 2. Overview The present disclosure relates to methods, assays, assay systems, kits and compositions useful for measuring the movement or transport of a molecule of interest to and from a cell membrane, such as the recycling of the molecule of interest (as shown in FIG. 1). The present disclosure further relates to methods, assays, assay systems, kits and compositions useful for measuring the transcytosis and recycling of a molecule of interest (as shown in FIG. 1). In particular, the present disclosure relates to in vitro receptor-dependent recycling and transcytosis assays for evaluating PK parameters such as the clearance rate and / or half-life of therapeutic antibody molecules. As disclosed in detail herein, the recycling of a molecule of interest (e.g., an antibody, an antibody fragment, a polypeptide or an Fc-containing molecule), optionally further combined with transcytosis, measured by the method of the present disclosure can be highly related to the PK properties of the cell, such as the in vivo clearance of the molecule. Thus, the claimed methods for measuring the recycling, and in some cases the combination of transcytosis and recycling, of a molecule of interest may be used to assess the in vivo clearance of the molecule, as well as other PK parameters, such as half-life, volume of distribution (Vd), area under the curve (AUC), bioavailability, and maximum / minimum plasma concentration (Cmax / Cmin) of multiple molecules. Furthermore, the recycling of a molecule of interest (e.g., an antibody or antibody fragment thereof), optionally further combined with transcytosis, measured by the methods of the present disclosure may be highly correlated with the tissue penetration of the molecule of interest in vivo. Thus, in some embodiments, the claimed methods for measuring the recycling, and in some cases the combination of transcytosis and recycling, of a molecule of interest may be used to assess the in vivo tissue penetration of the molecule of interest. Tissue penetration may include, for example, brain penetration.

[0066] In certain embodiments, the method includes measuring the transcellular recycling of a plurality of the same molecules of interest from a first chamber to the same chamber by measuring the uptake of one or more molecules from a solution in the first chamber and the return of those molecules to the first chamber after the original solution is exchanged with a second solution, each of the first chamber and the second chamber having a physiological pH value (e.g., pH=about 7.4). In some embodiments, the intercellular transport of a plurality of the same molecules of interest from the first chamber to the second chamber is also evaluated. In other embodiments, the method includes measuring the intercellular recycling of a plurality of different molecules of interest (e.g., two, three, four, five, or more molecules of interest), which may optionally include evaluating the intercellular transport of a plurality of different molecules of interest from the first chamber to the second chamber. The use of the assay is performed using a cell layer separating the first chamber and the second chamber. In certain embodiments, the cell layer stably expresses one or more receptors that mediate molecular transport. Such receptors can be any receptor of interest, including, but not limited to, the transferrin receptor, an Fc receptor, megalin, or cubulin.

[0067] Thus, for example, in one aspect, a cell-based assay is provided herein that uses MDCK cells stably expressing human FcRn and β2-microglobulin genes to measure the recycling efficiency and optionally transcytosis of polypeptides, antibodies, or other FcRn-binding molecules under conditions related to the FcRn-mediated IgG salvage pathway. This transcytosis and recycling assay is performed under physiological pH conditions and is designed to evaluate the results from the combined effects of two or more of the following: non-specific binding of IgG to cells, uptake by pinocytosis, pH-dependent interaction with FcRn, and the kinetics of intracellular trafficking and sorting processes. In this particular embodiment, the expression of FcRn is necessary to promote the transcytosis and recycling of the test molecules in the assay, directly contributing to the observed correlation. Furthermore, assays such as those provided herein could correctly rank the clearance rates of charge or glycosylation variants of Fc-containing molecules in preclinical species. The results provided in the Examples support the utility of the assays disclosed herein as cost-effective, animal-conserving screening tools for the evaluation of polypeptides, antibodies, or other FcRn-binding molecules, including antibody drug candidates during lead selection and optimization, and process development for desirable pharmacokinetic properties.

[0068] The present disclosure also relates to methods and compositions useful for determining tissue permeability of a plurality of molecules by determining the transcytosis / recycling (T / R) ratio of the plurality of molecules. In certain embodiments, the method includes determining the brain permeability of a plurality of molecules based on the ratio of transcytosis to recycling. The claimed methods for measuring the transcytosis and recycling of a molecule of interest and determining the T / R ratio may be used to evaluate the brain permeability and other PK parameters such as half-life of the molecule. In vitro assays as provided herein have demonstrated correlation with brain permeability of Fc-containing molecules in preclinical species. Thus, the results provided in the Examples support the utility of the assays disclosed herein as cost-effective, animal-conserving screening tools for evaluating polypeptides, antibodies, or other FcRn binding molecules, including antibody drug candidates during lead selection and optimization, and process development for desired tissue permeability properties.

[0069] The disclosure relates to a method, assay, assay system, kit, and composition provided herein that may be used to assess the movement or transport (e.g., recycling, or recycling and transcytosis), one or more PK parameters, and / or tissue permeability (e.g., brain permeability) of a plurality of the same molecules of interest (e.g., antibodies, antibody fragments, polypeptides, or Fc-containing molecules of the same type) or a plurality of two or more molecules of interest (e.g., two or more molecules of interest selected from antibodies, antibody fragments, polypeptides, Fc-containing molecules, or any mixture thereof).

[0070] 3. Recycling Assay, Recycling and Transcytosis Assay Recycling refers to vesicular transport of macromolecules from one side of the cell to the same side. Recycling is a mechanism for transport through cells in which cells surround extracellular material in invaginations of the cell membrane to form vesicles, then move the vesicles intracellularly and expel the material through the same cell membrane by the reverse process. See Figure 1.

[0071] Transcytosis, which refers to the vesicular transport of macromolecules from one side of a cell to the other, is a strategy used by multicellular organisms to selectively move materials between two environments without changing the native composition of those environments. Transcytosis is a mechanism for transcytosis in which cells encapsulate extracellular materials in invaginations of the cell membrane to form vesicles, then move the vesicles across the cell to eject the material through the opposite cell membrane by the reverse process. See FIG. 1.

[0072] In a typical FcRn-mediated transcytosis assay, FcRn-expressing MDCK cells are grown to confluency on a filter membrane in a transwell plate, and a pH gradient is created by filling the inner chamber with an acidic assay buffer (pH<6.0) and the outer chamber with a basic assay buffer (pH>7.4) prior to the assay. This assay design exploits the pH-dependent binding properties of FcRn to promote cellular uptake of the test molecule via binding to FcRn on the cell surface under acidic pH and release of the test molecule under basic pH, both of which improve the robustness and sensitivity of the assay. However, the assay could be used to improve the predictive assessment of the PK behavior of the test molecule. Because transfected cells typically express high levels of FcRn on the cell surface and test antibodies are incubated with the cells in an acidic environment, test molecules (such as antibodies) that exhibit high binding affinity for FcRn at acidic pH are expected to readily bind to FcRn and enter the cells via FcRn-mediated endocytosis. This is in contrast to what typically occurs in vivo, where polypeptides or antibodies minimally bind to cell surface FcRn under physiological pH and cellular uptake is primarily mediated by nonspecific pinocytosis. As a result, without wishing to be bound by theory, it is believed that the output of a pH gradient transcytosis assay may be significantly influenced by the FcRn binding affinity of the polypeptide or antibody at acidic pH and therefore may not necessarily fully reflect the contribution of other factors that affect PK, such as electrostatic interactions and intracellular trafficking parameters. Furthermore, artificial pH conditions may be inherently harmful to cells, limiting the duration of the assay and potentially resulting in further assay artifacts.

[0073] Thus, as described in more detail in the Examples, improved methods are provided herein for assessing the transport of molecules within a cellular environment, which can be further used to more accurately determine or measure one or more PK parameters (e.g., in vivo clearance (CL), volume of distribution (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin) or in vivo half-life (t1 / 2)) or tissue penetrance (such as brain penetrance). Thus, for example, in certain embodiments, the present disclosure provides methods for determining or measuring the recycling of multiple molecules. For example, determining or measuring may include introducing a plurality of molecules (e.g., including an antibody, an antibody fragment, a polypeptide, or an Fc-containing molecule) into a first chamber, the first chamber being separated from a second chamber by a cell layer, the first chamber and the second chamber comprising an aqueous solution; introducing the plurality of molecules into the first chamber and incubating the plurality of molecules; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of the plurality of molecules released from the cell layer into the first chamber; the aqueous solution is at a physiological pH, and the cell layer comprises cells expressing a receptor that mediates molecular transport.

[0074] In certain embodiments of the methods, assays and systems provided herein, the physiological pH value is about 6.5 to about 8.0. In certain embodiments, the physiological pH value is any value between about 6.5 and about 8.0, such as about 6.6, about 6.7, about 6.8, about 6.9, about 7.0, about 7.1, about 7.2, about 7.3, about 7.4, about 7.5, about 7.6, about 7.7, about 7.8 or about 7.9, or any range within the range of about 6.5 to about 8.0. In certain embodiments, the pH of each chamber can be different, so long as both chambers have a physiological pH. For example, and not by way of limitation, the first chamber can have a pH of 6.5, while the second chamber can have a pH of 8.0, or vice versa. In certain embodiments, the physiological pH can be about 7.4.

[0075] In certain embodiments, the present disclosure relates to a method for determining a pharmacokinetic (PK) parameter of a plurality of molecules (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules), comprising: a) introducing the plurality of molecules into a first chamber, the first chamber being separated from a second chamber by a cell layer, the first chamber and the second chamber comprising an aqueous solution; the aqueous solution being at a physiological pH, and the cell layer comprising cells expressing a receptor that mediates molecular transport; b) measuring the amount of the plurality of molecules recycled from the first chamber to the cell layer and back to the first chamber; and c) determining the PK parameter based on the amount of the plurality of molecules recycled. In certain embodiments, measuring the plurality of molecules recycled (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules) comprises incubating the plurality of molecules in the first chamber after introducing the plurality of molecules into the first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of the plurality of molecules released from the cell layer into the first chamber. In certain embodiments, the plurality of molecules (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules) are incubated in the second chamber for about 1 hour to about 48 hours, about 1 hour to about 30 hours, about 1 hour to about 24 hours, about 1 hour to about 12 hours, about 1 hour to about 6 hours, or about 1 hour to about 4 hours, or any value therein, such as about 1 hour, about 2 hours, about 4 hours, about 6 hours, about 8 hours, about 12 hours, or about 18 hours. In certain embodiments, exchanging the aqueous solution includes washing the first chamber. In certain embodiments, the method further includes incubating the first chamber and the second chamber with a replacement aqueous solution prior to measurement. In certain embodiments, the first and second chambers are incubated with the replacement aqueous solution for about 10 minutes to about 12 hours, about 20 minutes to about 12 hours, about 30 minutes to about 6 hours, about 20 minutes to about 5 hours, or about 1 hour to about 4 hours, or any value therein, such as 30 minutes, 1 hour, 2 hours, 3 hours, or 4 hours, prior to measurement. In certain embodiments, the incubation is performed at a temperature of about 35°C to about 39°C, such as about 37°C.In some embodiments, a quantification method is used that has a lower limit of quantification (LLOQ) of at least 200 pg / mL, at least 100 pg / mL, at least 50 pg / mL, or a single digit pg / mL. Such methods may include, for example, ELISA using a high affinity capture reagent that may be biotinylated mouse anti-human IgG-Fc, for example biotin-R10Z. In certain embodiments, the plurality of molecules is a plurality of the same molecules (e.g., the same type of antibody, antibody fragment, polypeptide, or Fc-containing molecule), and in other embodiments, the plurality of molecules is a mixture of molecules (e.g., one or more different antibodies, antibody fragments, polypeptides, or Fc-containing molecules, or mixtures thereof).

[0076] In certain embodiments, the measure of recycling may be determined by measuring the uptake of one or more molecules (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules) from a solution in a first chamber and their return to the first chamber after the original solution is replaced with a second solution. In some embodiments in which transcytosis is also assessed, the measure of transcytosis may be determined by measuring the transcytosis of one or more molecules (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules) from a solution in a first chamber to a solution in a second chamber, the first and second chambers being separated by a cell monolayer, and the solutions in each chamber being at physiological pH. In certain embodiments, the plurality of cells are derived from a eukaryotic organism, such as a mammal, for example a rodent (e.g., mouse, rat, guinea pig, hamster, or other mammal), dog, non-human primate (such as cynomolgus monkey), or human. Cells that may be used are described in more detail herein. In certain embodiments, the cell or cells may be Madin-Darby canine kidney (MDCK) cells. In some embodiments, the cells are wild type. In other embodiments, the cells express one or more heterologous receptors of interest. In certain embodiments, the cells include at least one heterologous gene. In certain embodiments, the at least one heterologous gene may be selected from the group consisting of FCGRT gene and B2M gene. In certain embodiments, the cells may express a heterologous cell surface protein. In certain embodiments, the heterologous cell surface protein may include neonatal Fc receptor (FcRn). In certain embodiments, measuring the recycling and optionally transcytosis of molecules includes the use of enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, or a fluorescence reader system. In some embodiments, measuring the recycling and optionally transcytosis of molecules includes the use of a quantitative method that can assess sub-nanomolar concentrations of the molecule of interest. In some embodiments, a method of quantification is used that has a lower limit of quantification (LLOQ) of at least 200 pg / mL, at least 100 pg / mL, or at least 50 pg / mL.Such methods may include, for example, ELISA using a high affinity capture reagent, which may be biotinylated mouse anti-human IgG-Fc, e.g., biotin-R10Z. Such highly sensitive ELISA methods are described in the Examples section of this disclosure. In some aspects, such highly sensitive quantification methods are used to measure recycling, but less sensitive methods are used to evaluate transcytosis (e.g., with a nanomolar LLOQ). In some embodiments, highly sensitive automated immunoassay platforms are used to quantify recycled and / or transcytosis molecules (e.g., from Quanterix, Gyrolab, or Singulex). In certain embodiments, the methods of the present disclosure may further include determining the in vivo clearance (CL), volume of distribution (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin), or in vivo half-life (t1 / 2) of a plurality of molecules based on the amount of the molecules measured. In certain aspects, the molecule can be a molecule that naturally binds to a receptor of interest or a molecule that is engineered to bind to a receptor of interest, where the receptor of interest is expressed by multiple cells.Thus, in some embodiments, the molecule can be a molecule that naturally binds to FcRn or a molecule that is engineered to bind to FcRn.In certain embodiments, the molecule can be an Fc-containing molecule.In certain embodiments, the molecule can be an antibody.In certain embodiments, the antibody can be a monoclonal antibody.In certain embodiments, the antibody can be an anti-IgE antibody, an anti-VEGF antibody, an anti-integrin antibody (e.g., an anti-α4β7 integrin antibody), an anti-IL-6 antibody, an anti-TNFa antibody, an anti-BACE1 antibody, or an anti-gD antibody.In some embodiments, the antibody is omalizumab, bevacizumab, vedolizumab, tocilizumab, adalimumab, anti-BACE1 It can be WT, anti-BACE1 variant YEY (mutations: M252Y; N286E; N434Y), anti-BACE1 variant YQAY (mutations: M252Y; T307Q; Q311A; N434Y), anti-BACE1 variant YPY (mutations: M252Y; V308P; N434Y), anti-BACE1 variant YY (mutations: M252Y; N434Y), anti-BACE1 variant YLY1 (Q6) (mutations: M252Y; M428L; N434Y; Y436I), or anti-BACE1 variant YIY (T3) (mutations: M252Y; Q311I; N434Y). In certain embodiments, the molecule can be an albumin-containing molecule. In certain embodiments, the physiological pH value is about 6.5 to about 8.0. In certain embodiments, the physiological pH value is any value between about 6.5 and about 8.0, such as about 6.6, about 6.7, about 6.8, about 6.9, about 7.0, about 7.1, about 7.2, about 7.3, about 7.4, about 7.5, about 7.6, about 7.7, about 7.8 or about 7.9, or any range within the range of about 6.5 to about 8.0. In certain embodiments, the pH of each chamber can be different, so long as both chambers have a physiological pH. For example, but not by way of limitation, the first chamber can have a pH of 6.5, while the second chamber can have a pH of 8.0, or vice versa. In certain embodiments, the physiological pH can be about 7.4. In certain embodiments, PK parameters are determined, such as measures of in vivo clearance (CL), volume of distribution (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin) or in vivo half-life (t1 / 2) of multiple molecules. In other embodiments, tissue permeability, such as brain permeability, is determined, either separately or in combination.

[0077] In certain embodiments, the present disclosure relates to an assay system comprising: a) a first chamber and a second chamber, each chamber containing an aqueous solution at physiological pH; b) a cell layer separating the first chamber and the second chamber, the cell layer being capable of mediating the recycling of molecules from the first chamber into the cell layer and back into the first chamber; c) a detector for detecting the presence of molecules in the second chamber, the assay system being configured to determine the recycling of a plurality of molecules, the determining comprising: introducing a plurality of molecules (e.g., including an antibody, an antibody fragment, a polypeptide, or an Fc-containing molecule) into the first chamber; incubating the plurality of molecules in the first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of the plurality of molecules released from the cell layer into the first chamber. The cells forming the cell layer may be any that can be stably grown to form a cell layer, as further described herein. In certain embodiments, the cells are in a cell growth medium at a concentration of about 1×10 5The cells may be seeded at a density of 100 cells / well. The cell growth medium may be any suitable medium for growing the selected cells. In certain embodiments, the cell growth medium may be DMEM high glucose supplemented with 10% FBS, 100 units penicillin / streptomycin, and 5 μg / mL puromycin. In some embodiments, the volume of medium in the inner and outer chambers is independently 25 μL to 500 μL, or 50 μL to 350 μL, or 50 μL to 200 μL. In certain embodiments, the medium in the inner chamber may be 100 μL and the medium in the outer chamber may be 200 μL. In certain embodiments, the cells may be used 2 days after plating. In certain embodiments, the test molecule may be added to a final concentration of about 100 μg / mL (0.67 μM) and incubated in a 37° C. tissue culture incubator for 24 hours. In certain embodiments, Lucifer Yellow (Lucifer Yellow CH, dilithium salt; Sigma Aldrich; St. Louis, MO) may be prepared in cell growth medium and added during the last 90 minutes of the 24-hour assay incubation. In certain embodiments, the level of passive passage of Lucifer Yellow during the assay may be calculated by dividing the fluorescent signal in the sample from the outer chamber by that of the inner chamber. In certain embodiments, transcytosis and recycling results from wells that show more than 0.1% passive passage of Lucifer Yellow in the outer chamber, i.e., wells where less than 0.1% passive passage of Lucifer Yellow is used, may be discarded. In some embodiments, the detector system is capable of evaluating sub-nanomolar concentrations of the molecule of interest (including, for example, antibodies, antibody fragments, polypeptides, or Fc-containing molecules), such as with an LLOQ of at least 200 pg / mL, at least 100 pg / mL, or at least 50 pg / mL. In some embodiments, the detector system comprises an ELISA assay using a high affinity capture reagent, which can be, for example, a biotinylated mouse anti-human IgG-Fc, such as biotin-R10Z. Such a sensitive method is described in the Examples herein.

[0078] In certain embodiments, test molecules (including, for example, antibodies, antibody fragments, polypeptides, or Fc-containing molecules) may be added to the outer or inner chamber of a transwell assay, and recycling may be detected by measuring the amount of test molecule present in the same chamber (e.g., the outer or inner chamber, respectively) after a suitable incubation period (pulse step), removing the medium, and replacing it (chase step). In some embodiments, transcytosis of the test molecule is also detected by measuring the amount of test molecule present in the opposite chamber (e.g., the inner or outer chamber, respectively). In certain embodiments, the test molecule is recycled from a chamber exposed to the apical membrane of the cell to the same chamber. In some embodiments, the test molecule is recycled from a chamber exposed to the basolateral membrane of the cell to the same chamber. In still further embodiments, the test molecule is transcytosis from a chamber exposed to the apical membrane of the cell to a chamber exposed to the basolateral membrane of the cell.

[0079] In certain embodiments, the present disclosure provides a method for determining or predicting PK parameters of one or more molecules (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules), comprising: a) introducing the molecule into a first of two chambers, the first chamber being separated from the second chamber by one or more cells, and each of the first and second chambers having a physiological pH value; and measuring the number of molecules recycled from the first chamber to the first chamber. In certain embodiments, the physiological pH value is about 6.5 to about 8.0. In certain embodiments, the physiological pH value is any value between about 6.5 and about 8.0, such as about 6.6, about 6.7, about 6.8, about 6.9, about 7.0, about 7.1, about 7.2, about 7.3, about 7.4, about 7.5, about 7.6, about 7.7, about 7.8, or about 7.9, or any range within the range of about 6.5 to about 8.0. In certain embodiments, the pH of each chamber can be different as long as both chambers have physiological pH.For example, but not by way of limitation, the first chamber can have a pH of 6.5, while the second chamber can have a pH of 8.0, or vice versa.In certain embodiments, the physiological pH can be about 7.4.In some aspects, the PK parameter is in vivo clearance (CL), distribution volume (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin) or in vivo half-life (t1 / 2).In certain embodiments, the PK parameter is in vivo clearance.

[0080] In certain embodiments, the assay system further comprises a detector for detecting the presence of a molecule in the first chamber; the cell layer may mediate the recycling of the molecule from the first chamber to the first chamber; the assay system is configured to determine the recycling of the plurality of molecules from the cell layer to the first chamber, and determining the recycling comprises measuring the amount of the plurality of molecules in the first chamber after the aqueous solution is exchanged. In some embodiments, transcytosis is also measured. In certain embodiments, the assay system further comprises a detector for detecting the presence of a molecule in the second chamber; the cell layer may mediate the transcytosis of the molecule from the first chamber to the second chamber; and the assay system is configured to determine the transcytosis of the plurality of molecules across the cell layer, and determining the transcytosis comprises measuring the amount of the plurality of molecules in the second chamber after the aqueous solution is exchanged. In some embodiments, the detector for detecting the presence of the molecule in the first chamber can evaluate sub-nanomolar concentrations of the molecule of interest (e.g., including an antibody, antibody fragment, polypeptide, or Fc-containing molecule), such as with an LLOQ of at least 200 pg / mL, at least 100 pg / mL, or at least 50 pg / mL. In some embodiments, the detector for detecting the presence of the molecule in the second chamber has a similar sensitivity. In other embodiments, the detector may not have an LLOQ, for example, in the nanomolar range.

[0081] In certain embodiments, the present disclosure provides an assay for measuring transcytosis of the same or different molecules, comprising a first chamber and a second chamber, each of the first chamber and the second chamber having a physiological pH value, the first chamber being configured to receive the molecules, allow transcytosis of the molecules to the second chamber, and recycle the molecules to the first chamber. In certain embodiments, the physiological pH value is about 6.5 to about 8.0. In certain embodiments, the physiological pH value is any value between about 6.5 and about 8.0, such as about 6.6, about 6.7, about 6.8, about 6.9, about 7.0, about 7.1, about 7.2, about 7.3, about 7.4, about 7.5, about 7.6, about 7.7, about 7.8, or about 7.9, or any range within the range of about 6.5 to about 8.0. In certain embodiments, the pH of each chamber can be different, so long as both chambers have a physiological pH. For example, and not by way of limitation, the first chamber may have a pH of 6.5 while the second chamber may have a pH of 8.0, or vice versa. In certain embodiments, the physiological pH may be about 7.4.

[0082] In certain embodiments, the present disclosure provides an assay for determining or predicting one or more PK parameters of one or more molecules, comprising a first chamber and a second chamber, each of the first chamber and the second chamber having a physiological pH value, the first chamber being configured to receive a plurality of molecules and to allow recycling of the molecules from the first chamber to the first chamber, and optionally to allow transcytosis of the molecules from the first chamber to the second chamber. In certain embodiments, the physiological pH value is about 7.4. In some aspects, the PK parameter is in vivo clearance (CL), distribution volume (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin) or in vivo half-life (t1 / 2). In some embodiments, the PK parameter is in vivo clearance.

[0083] In certain embodiments, the first chamber may contain a monolayer of cells. In certain embodiments, the cells used in the assay are selected from the list provided in Section 4 below entitled "Cells". In certain embodiments, the cells used in the assay are eukaryotic cells. In some embodiments, the eukaryotic cells are mammalian cells. In certain embodiments, the mammalian cells are kidney cells. In some embodiments, the kidney cells are rodent, non-human primate, human or canine cells. In some embodiments, the cells are MDCK cells. In certain embodiments, the cells used in the methods described in this disclosure may contain at least one heterologous gene. In certain embodiments, the at least one heterologous gene may be selected from the group consisting of FCGRT and B2M genes. In certain embodiments, the cells used in the methods described in this disclosure may express a cell surface protein. In certain embodiments, the cell surface protein comprises an Fc receptor (FcR). In certain embodiments, the cell surface protein comprises a neonatal Fc receptor (FcRn).

[0084] In certain embodiments, the molecules can be labeled or unlabeled. Non-limiting examples of labeled molecules include 3H-labeled, fluorescently labeled molecules, or radioisotopes, such as I-125 and P-32.

[0085] In certain embodiments, the method of the present disclosure includes measuring the number of recycled and optionally transcytosed molecules. In certain non-limiting embodiments, measuring the number of recycled or transcytosed molecules may be performed by enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, confocal microscopy, or a live cell imaging system, or any combination thereof. The use of different detection methods for recycled and transcytosed molecules is contemplated. In some embodiments, the measurement method is a method that can assess the concentration of a molecule of interest (including, for example, an antibody, antibody fragment, polypeptide, or Fc-containing molecule) at sub-nanomolar concentrations, for example, with an LLOQ of at least 200 pg / mL, at least 100 pg / mL, or at least 50 pg / mL. In some embodiments, the detector system includes an ELISA assay that uses a high affinity capture reagent, which may be, for example, a biotinylated mouse anti-human IgG-Fc, such as biotin-R10Z. In certain embodiments, different methods are used, where the method used to measure recycling may assess sub-nanomolar concentrations and the method used to measure transcytosis may not. Highly sensitive automated immunoassay platforms (e.g., from Quanterix, Gyrolab, or Singulex) may be used to quantify recycled and / or transcytosis molecules.

[0086] In certain embodiments, the present disclosure provides an FcRn-dependent cell-based assay for measuring the recycling and optionally transcytosis of a molecule of interest (e.g., one or more antibodies, antibody fragments, polypeptides, or Fc-containing molecules) through MDCK cells expressing human FcRn and B2M under conditions similar to the FcRn-mediated IgG salvage pathway. In certain embodiments, the output of the assay includes not only Fc-FcRn interactions at physiological conditions, but also non-specific binding, cellular uptake, sorting, and intracellular trafficking processes associated with the in vivo PK behavior of the molecule of interest. In some embodiments, the molecule of interest is an IgG mAb, such as those described elsewhere herein. In some embodiments, the assay measures the recycling and optionally transcytosis of two or more molecules of interest.

[0087] In certain embodiments, the disclosure provides methods and assays for correlating the recycling with one or more PK properties in animals of molecules of interest (e.g., antibodies, antibody fragments, polypeptides, or Fc-containing molecules) with diverse structures, functions, and pharmacological properties. In certain embodiments, the PK properties are in vivo clearance (CL), volume of distribution (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin), or half-life (t1 / 2) in vivo. In some embodiments, the PK parameter is in vivo clearance. In some embodiments, the animal is a mammal, such as a human, or a non-human primate, such as a cynomolgus monkey. In certain embodiments, the disclosure provides methods and assays for correlating the transcytosis and recycling with tissue permeability in animals of molecules of interest (e.g., antibodies, antibody fragments, polypeptides, or Fc-containing molecules) with diverse structures, functions, and pharmacological properties. In some embodiments, the tissue permeability is brain permeability. In some embodiments, the animal is a mammal, such as a human, or a non-human primate, such as a cynomolgus monkey.

[0088] In certain embodiments, expression of FcRn may be required to facilitate recycling, and possibly transcytosis (if also assessed), of a molecule of interest such as a mAb in an assay (including, for example, an antibody, antibody fragment, polypeptide, or Fc-containing molecule), and contribute to the observed association between recycling and PK parameters or tissue penetration assessed. In certain embodiments, the methods and assays described in this disclosure may rank order clearance rates of charge or glycosylation variants of Fc-containing molecules in preclinical species. In certain embodiments, the methods and assays described in this disclosure may be used as a time-efficient, cost-effective, and animal-sparing tool for evaluation of drug candidates (including, for example, antibodies, antibody fragments, polypeptides, or Fc-containing molecules) during lead selection and optimization, as well as process development for desired pharmacokinetic properties.

[0089] In certain embodiments, the present disclosure provides cell-based assays and methods for measuring the recycling efficiency of drugs (including, for example, antibodies, antibody fragments, polypeptides, or Fc-containing molecules) under physiologically relevant conditions. In certain embodiments, MDCK cells stably expressing human FcRn and β2-microglobulin genes are used in conjunction with the assays described herein.

[0090] In certain embodiments, the present disclosure provides methods and assays that are performed at physiological pH in normal cell culture medium supplemented with fetal bovine serum that provides bovine albumin, which is known to bind to human FcRn (Chaudhury C. et al., 2003, J. Exp. Med. 197, 315-322).

[0091] In certain embodiments, the disclosure provides methods and assays in which molecules are taken up by cells via non-specific pinocytosis, interact with human FcRn in the presence of albumin, and recycled by cells under conditions relevant to FcRn-mediated mechanisms of action. In some embodiments, at least some of the molecules are recycled to the side of the cell layer in which they were taken up. In some embodiments, at least some of the molecules are transcytosed to the opposite side of the cell layer. In certain embodiments, the disclosure provides methods and assays for determining or predicting the clearance of a molecule of interest (including, for example, an antibody, an antibody fragment, a polypeptide, or an Fc-containing molecule) in a mammal due to the ability of the methods and / or assays to assess the combined effects of non-specific binding to cells, pinocytic uptake, pH-dependent interactions with FcRn, and / or the kinetics of intracellular trafficking and sorting processes. In some embodiments, the mammal is a non-human primate, such as a cynomolgus monkey. In some embodiments, the mammal is a human.

[0092] In certain embodiments, the disclosure provides methods and assays for determining or predicting tissue permeability of a molecule of interest (including, for example, an antibody, an antibody fragment, a polypeptide, or an Fc-containing molecule). In certain embodiments, the tissue is brain tissue. In certain embodiments, the disclosure provides methods and assays for determining or predicting tissue permeability of a molecule of interest by determining the T / R ratio of the molecule. In certain embodiments, the disclosure provides methods and assays for determining or predicting tissue permeability of a molecule of interest (including, for example, an antibody, an antibody fragment, a polypeptide, or an Fc-containing molecule) in a mammal by the ability of the method and / or assay to assess the combined effects of non-specific binding to cells, pinocytic uptake, pH-dependent interactions with FcRn, and / or the kinetics of intracellular trafficking and sorting processes to determine the T / R ratio of the molecule of interest. In some embodiments, the mammal is a non-human primate, such as a cynomolgus monkey. In some embodiments, the mammal is a human.

[0093] In certain embodiments, the present disclosure provides methods and assays used to correlate the recycling and optionally transcytosis output obtained with PK parameters of a molecule of interest (e.g., including an antibody, antibody fragment, polypeptide, or Fc-containing molecule) in a mammal. In some embodiments, the PK parameters are in vivo clearance (CL), volume of distribution (Vd), area under the curve (AUC), bioavailability, maximum / minimum plasma concentration (Cmax / Cmin) or half-life in vivo (t1 / 2). In certain embodiments, the output of the methods and assays of the present disclosure can be the concentration (ng / mL) of the recycled molecule in the medium of the inner chamber (e.g., the first chamber), or optionally even the concentration of the transcytosis molecule in the medium of the outer chamber (e.g., the second chamber), and the reportable value of the assay can be the average concentration of at least two replicate wells from the same plate. In certain embodiments, the output of the method and / or assay can be a measure of the recycling rate or a measure of the relative recycling of the recycled molecule to a control molecule. In certain embodiments, the output of the assay may be a measure of the rate of transcytosis, or a measure of the relative transcytosis of the transcytosed molecule compared to a control molecule. In still further embodiments, the output of the assay may be a calculation based on recycling and optionally transcytosis, such as a ratio of recycling to transcytosis or a ratio of transcytosis to recycling, either alone or relative to a control molecule. In some embodiments, the mammal is a non-human primate, such as a cynomolgus monkey. In some embodiments, the mammal is a human.

[0094] In still further embodiments, the present disclosure provides methods and assays for use in determining the effect of one or more agents other than the test molecule on recycling, transcytosis, tissue permeability, PK parameters or other characteristics of the test molecule (including, for example, an antibody, an antibody fragment, a polypeptide or an Fc-containing molecule). Such agents (sometimes referred to as secondary molecules) may be, for example, small molecules (e.g., not proteins or polypeptides), such as small molecule drugs, or may be peptides, or may be polypeptides, or may be antibodies or fragments thereof, or multiples or combinations of such molecules. Such agents may bind to the test molecule or be suspected to bind to the test molecule, or may modulate the binding of the test molecule to a receptor that mediates molecular transport, such as modulating the binding of the test molecule to FcRn; or may be a ligand for a receptor of interest in the system being evaluated (e.g., a ligand for a receptor expressed by one or more cells of the cell layer); or may be known or suspected to interact with the test molecule or a receptor expressed by the cell layer. The agents may be therapeutic molecules, such as prescription or over-the-counter (OTC) drugs, or may be supplements, vitamins, research reagents, imaging reagents, or other agents of interest. The therapeutic agents may include those used to treat disorders or conditions of the immune system, cardiovascular system, endocrine system, gastrointestinal tract, renal system, respiratory system, or central nervous system, or to treat cancer or other malignancies (including chemotherapeutic and immunotherapeutic agents), viral infections, bacterial infections, fungal infections, or parasitic infections. Combinations of two or more agents of interest may also be evaluated. Thus, in some embodiments, the methods provided herein include evaluating the recycling, or recycling and transcytosis, of a test molecule in the presence of one or more agents. The one or more agents may be in the first chamber but not in the second chamber, or in the second chamber but not in the first chamber, or in both chambers, or in the first solution in the first chamber but not present when the solution is replaced, or combinations thereof.In some embodiments, the assay output is further compared to recycling, or recycling and transcytosis in the absence of one or more agents. The ability to assess the effect of one or more agents on the recycling, or recycling and transcytosis of a test molecule according to the methods and assays described herein can be useful, for example, to determine how one or more agents affect one or more PK parameters of the test molecule, or how they affect the tissue permeability (e.g., brain permeability) of the test molecule. The methods and assays described herein can be used, for example, to understand the effect of commonly co-administered drugs on the PK parameters and / or tissue permeability of a molecule of interest. The methods and assays described herein can be used, for example, to investigate the mechanism of intracellular transport, PK parameters and / or tissue permeability.

[0095] The present disclosure also provides methods and assays for use in determining the effect of changing one or more environmental conditions on the recycling, transcytosis, tissue permeability, PK parameters or other properties of a test molecule (including, for example, an antibody, an antibody fragment, a polypeptide or an Fc-containing molecule). Such environmental conditions can include, for example, the presence, absence or concentration of one or more cell culture medium components, or temperature, or pH, or oxidation, or a combination thereof. In some embodiments, the tissue permeability is brain permeability.

[0096] In certain embodiments, the selection of test molecules (including, for example, antibodies, antibody fragments, polypeptides, or Fc-containing molecules) for the methods and assays of the present disclosure may be based on, but not limited to, clinical grade materials and the availability of animal PK data and / or animal tissue permeation data from reliable sources such as prescribing information, published reports based on population PK or tissue permeation models, or in-house clinical trials where linear PK or tissue permeation data were generated. In certain embodiments, the use of clinical grade materials may ensure that the quality of the test materials may be consistent with those used in the clinical trials where human PK or tissue permeation data were generated.

[0097] In certain embodiments, the methods and assays described in this disclosure may be used as tools for in vitro assessment of potential liability in nonspecific clearance of drug candidates (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules) to aid in lead selection and optimization with the goal of ranking candidates, reducing the number of molecules tested in animal models, and / or reducing the number of animal models required.

[0098] In certain embodiments, the methods and assays described in this disclosure may be used to aid in the development of new drugs (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing drugs) with improved recycling properties relevant to the investigation of molecules of interest (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules) that exhibit undesirable or atypical PK or tissue penetration behavior, or for specialized applications such as crossing the blood-brain barrier to promote brain exposure, or enhancing treatment in the tumor microenvironment for improved tumor targeting. Such "improved recycling properties" may include increased recycling compared to another molecule, which may in some embodiments increase serum half-life. In certain embodiments, the methods and assays described in this disclosure may be used to aid in the development of new drugs with improved transcytosis properties relevant to the investigation of molecules of interest (e.g., including antibodies, antibody fragments, polypeptides, or Fc-containing molecules) that exhibit undesirable or atypical PK behavior, or for specialized applications such as crossing the blood-brain barrier to promote brain exposure, or enhancing treatment in the tumor microenvironment for improved tumor targeting. Such "improved transcytosis properties" may include enhanced transcytosis properties compared to another molecule. Furthermore, in certain embodiments, the methods and assays described in this disclosure may be used to aid in the investigation of molecules of interest (including, for example, antibodies, antibody fragments, polypeptides, or Fc-containing molecules) that exhibit undesirable or atypical PK behavior, or to develop new drugs with improved transcytosis properties suitable for specialized applications such as crossing the blood-brain barrier to promote brain exposure, or enhancing treatment in the tumor microenvironment to improve tumor targeting. Such "improved transcytosis properties" may include increased transcytosis properties compared to another molecule. It is further contemplated to use the assays described herein to aid in the development of new drugs (including, for example, antibodies, antibody fragments, polypeptides, or Fc-containing molecules) with improved transcytosis to recycling ratios compared to another molecule. Such "improved transcytosis to recycling ratios" (T / R ratios) may include higher ratios than another molecule, for example due to increased transcytosis, decreased recycling, or both.A higher T / R ratio may result in better tissue penetration, e.g., better brain penetration, compared to another molecule. In some embodiments, the molecule of interest and / or drug is a mAb.

[0099] In certain embodiments, the methods and assays described in this disclosure can be used to develop improved mechanism-based PK models to assist in the design of optimal doses and administration schemes in clinical trials.In certain embodiments, the methods and assays described in this disclosure can be used to demonstrate the correlation between in vitro readout and in vivo PK data of test molecules (including, for example, antibodies, antibody fragments, polypeptides or Fc-containing molecules).Such PK models and / or data can include in vivo clearance (CL), in vivo half-life (t1 / 2), area under the curve (AUC), bioavailability, volume of distribution (Vd) or maximum / minimum plasma concentration (Cmax / Cmin).

[0100] In certain embodiments, the molecule of interest, the test molecule and / or the molecules may be antibodies. In certain embodiments, the antibodies may be monoclonal or polyclonal antibodies. In certain embodiments, the antibodies may have different structural compositions (chimeric, humanized, and fully human). In certain embodiments, the antibodies may consist of different heavy and light chain sequences (IgG1, IgG2 and IgG4 heavy chains, kappa and lambda light chains). In certain embodiments, the antibodies may recognize different types of targets (membrane-bound and soluble). In certain embodiments, the antibodies may exert different therapeutic mechanisms of action (agonistic, antagonistic, and cytotoxic). In certain embodiments, the antibodies are administered to the patient via different routes (e.g., intravenous, intramuscular, and subcutaneous). In certain embodiments, the antibodies are anti-IgE, anti-VEGF, anti-integrin antibodies (e.g., anti-α4β7 integrin antibodies), anti-IL-6, anti-TNFa, anti-BACE1, or anti-gD antibodies, or fragments thereof. In some embodiments, the antibody is omalizumab, bevacizumab, vedolizumab, tocilizumab, adalimumab, anti-BACE1 WT, anti-BACE1 variant YEY (mutations: M252Y; N286E; N434Y), anti-BACE1 variant YQAY (mutations: M252Y; T307Q; Q311A; N434Y), anti-BACE1 variant YPY (mutations: M252Y; V308P; N434Y), anti-BACE1 variant YY (mutations: M252Y; N434Y), anti-BACE1 variant YLY1(Q6) (mutations: M252Y; M428L; N434Y; Y436I), or anti-BACE1 variant YIY(T3) (mutations: M252Y; Q311I; N434Y), or fragments thereof. In some embodiments, more than one antibody is evaluated.

[0101] In certain embodiments, the molecule of interest, test molecule and / or molecules may have engineered mutations that may alter their effector function (e.g., but not limited to, atezolizumab, durvalumab), allow for association of bispecific half antibodies (e.g., but not limited to, emicizumab), or stabilize IgG4 Fab arms (e.g., but not limited to, nivolumab, pembrolizumab).

[0102] In certain embodiments, the molecule of interest, the test molecule, and / or the molecules may be an antibody that exhibits extreme FcRn binding affinity. In certain embodiments, the correlation observed between recycling readout and PK parameters in mammals (e.g., non-human primates, or humans) may be applicable to a wide range of antibodies with typical Fc regions. In certain embodiments, the test molecule may be an antibody that has been engineered to have altered FcRn binding activity. In certain embodiments, the molecule of interest, the test molecule, and / or the molecules may be an albumin-containing molecule, or any molecule engineered to bind to FcRn via a peptide tag or recombinant protein. In certain embodiments, the molecule of interest, the test molecule, and / or the molecules may be a molecule that naturally binds to FcRn. In certain embodiments, the molecule of interest, the test molecule, and / or the molecules may be a molecule engineered to bind to FcRn.

[0103] In certain embodiments, the methods and assays described in this disclosure may be used to show whether expression of human FcRn is required for efficient recycling, and in some embodiments, recycling and transcytosis, in recycling or recycling and transcytosis assays.

[0104] In certain embodiments, the disclosed methods and assays may be used to detect and / or show that interaction with FcRn contributes to the observed correlation between the recycling readout of a test molecule and a PK parameter, in some embodiments, in vivo clearance (CL), in vivo half-life (t1 / 2), area under the curve (AUC), bioavailability, volume of distribution (Vd), or maximum / minimum plasma concentration (Cmax / Cmin).

[0105] In certain embodiments, the disclosed method and assay can be used for binding analysis of a molecule of interest, a test molecule and / or a plurality of molecules to a receptor. In certain embodiments, the receptor can be an FcRn receptor. In certain embodiments, the test molecule can be an antibody. In certain embodiments, the receptor can be a transferrin receptor. In certain embodiments, the receptor is a human, mouse, rat or cynomolgus monkey transferrin receptor. In certain embodiments, the receptor is a transferrin 1 or transferrin 2 receptor. In certain embodiments, the receptor is a transferrin receptor described in UNIPROT P02786 (TFR1_HUMAN), UNIPROT Q9UP52 (TFR2_HUMAN), UNIPROT A0A2K5X958 (A0A2K5X958_MACFA, cyno), UNIPROT Q62351 (TFR1_MOUSE), UNIPROT Q9JKX3 (TFR2_MOUSE), UNIPROT Q99376 (TFR1_RAT), or UNIPROT B2GUY2 (TFR2_RAT). In some embodiments, the receptor is described in UNIPROT P02786 (TFR1_HUMAN), or UNIPROT Q9UP52 (TFR2_HUMAN). In certain embodiments, the receptor can be a megalin receptor. In certain embodiments, the receptor is a megalin receptor described in UNIPROT P98164 (LRP2_HUMAN), UNIPROT A2ARV4 (LRP2_MOUSE), or UNIPROT P98158 (LRP2_RAT). In certain aspects, the receptor can be a cubulin receptor. In some embodiments, the receptor is a cubulin receptor described in UNIPROT O60494 (CUBN_HUMAN), UNIPROT Q9JLB4 (CUBN_MOUSE), UNIPROT O70244 (CUBN_RAT), or UNIPROTA0A2K5USK6 (A0A2K5USK6_MACFA, cyno).

[0106] In a specific embodiment, the FcRn receptor of the methods, assays, assay systems and kits of the invention is a human FcRn receptor.

[0107] In a particular embodiment, the heavy chain of the human FcRn receptor of the methods, assays, assay systems and kits of the invention has the sequence: AESHLSLLYHLTAVSSPAPGTPAFWVSGWLGPQQYLSYNSLRGEAEPCGAWVWENQVSWYWEKETTDLRIKEKLFLEAFKALGGKGPYTLQGLLGCELGPDNTSVPTAKFALNGEEFMNFDLKQGTWGGDWPEALAISQRWQQQDKAANKELTFLLFSCPHRLREHLERGRGNLEWKEPPSMRLKARPSSPGFSVLTCSAFSFYPPELQLRFLRNGLAAGTGQGDFGPNSDGSFHASSSLTVKSGDEHHYCCIVQHAGLAQPLRVELESPAKSSVLVVGIVIGVLLLTAAAVGGALLWRRMRSGLPAPWISLRGDDTGVLLPTPGEAQDADLKDVNVIPATA (SEQ ID NO: 1).

[0108] In a particular embodiment, the light chain of the human FcRn receptor of the methods, assays, assay systems and kits of the invention has the following sequence: MSRSVALAVLALLSLSGLEAIQRTPKIQVYSRHPAENGKSNFLNCYVSGFHPSDIEVDLLKNGERIEKVEHSDLSFSKDWSFYLLYYTEFTPTEKDEYACRVNHVTLSQPKIVKWDRDM (SEQ ID NO: 2).

[0109] In a specific embodiment, the FcRn receptor of the methods, assays, assay systems and kits of the invention is a mouse FcRn receptor.

[0110] In a particular embodiment, the heavy chain of the mouse FcRn receptor of the methods, assays, assay systems and kits of the invention has the sequence: SETRPPLMYHLTAVSNPSTGLPSFWATGWLGPQQYLTYNSLRQEADPCGAWMWENQVSWYWEKETTDLKSKEQLFLEALKTLEKILNGTYTLQGLLGCELASDNSSVPTAVFALNGEEFMKFNPRIGNWTGEWPETEIVANLWMKQPDAARKESEFLLNSCPERLLGHLERGRRNLEWKEPPSMRLKARPGNSGSSVLTCAAFSFYPPELKFRFLRNGLASGSGNCSTGPNGDGSFHAWSLLEVKRGDEHHYQCQVEHEGLAQPLTVDLDSSARSSVPVVGIVLGLLLVVVAIAGGVLLWGRMRSGLPAPWLSLSGDDSGDLLPGGNLPPEAEPQGANAFPATS (SEQ ID NO: 3).

[0111] In a specific embodiment, the light chain of the mouse FcRn receptor of the methods, assays, assay systems and kits of the invention has the following sequence: MARSVTLVFLVLVSLTGLYAIQKTPQIQVYSRHPPENGKPNILNCYVTQFHPPHIEIQMLKNGKKIPKVEMSDMSFSKDWSFYILAHTEFTPTETDTYACRVKHDSMAEPKTVYWDRDM (SEQ ID NO: 4).

[0112] In a specific embodiment, the FcRn receptor of the methods, assays, assay systems and kits of the invention is a rat FcRn receptor.

[0113] In a particular embodiment, the heavy chain of the rat FcRn receptor of the methods, assays, assay systems and kits of the invention has the sequence: AEPRLPLMYHLAAVSDLSTGLPSFWATGWLGAQQYLTYNNLRQEADPCGAWIWENQVSWYWEKETTDLKSKEQLFLEAIRTLENQINGTFTLQGLLGCELAPDNSSLPTAVFALNGEEFMRFNPRTGNWSGEWPETDIVGNLWMKQPEAARKESEFLLTSCPERLLGHLERGRQNLEWKEPPSMRLKARPGNSGSSVLTCAAFSFYPPELKFRFLRNGLASGSGNCSTGPNGDGSFHAWSLLEVKRGDEHHYQCQVEHEGLAQPLTVDLDSPARSSVPVVGIILGLLLVVVAIAGGVLLWNRMRSGLPAPWLSLSGDDSGDLLPGGNLPPEAEPQGVNAFPATS (SEQ ID NO: 5).

[0114] In a specific embodiment, the light chain of the rat FcRn receptor of the methods, assays, assay systems and kits of the invention has the following sequence: MARSVTVIFLVLVSLAVVLAIQKTPQIQVYSRHPPENGKPNFLNCYVSQFHPPQIEIELLKNGKKIPNIEMSDLSFSKDWSFYILAHTEFTPTETDVYACRVKHVTLKEPKTVTWDRDM (SEQ ID NO: 6).

[0115] In a specific embodiment, the FcRn receptor of the methods, assays, assay systems and kits of the invention is the cynomolgus monkey (Macaca fascicularis) FcRn receptor.

[0116] In a particular embodiment, the heavy chain of the cynomolgus monkey FcRn receptor of the methods, assays, assay systems and kits of the invention has the sequence: AESHLSLLYHLTAVSSPAPGTPAFWVSGWLGPQQYLSYDSLRGQAEPCGAWVWENQVSWYWEKETTDLRIKEKLFLEAFKALGGKGPYTLQGLLGCELSPDNTSVPTAKFALNGEEFMNFDLKQGTWGGDWPEALAISQRWQQQDKAANKELTFLLFSCPHRLREHLERGRGNLEWKEPPSMRLKARPGNPGFSVLTCSAFSFYPPELQLRFLRNGMAAGTGQGDFGPNSDGSFHASSSLTVKSGDEHHYCCIVQHAGLAQPLRVELETPAKSSVLVVGIVIGVLLLTAAAVGGALLWRRMRSGLPAPWISLRGDDTGSLLPTPGEAQDADSKDINVIPATA (SEQ ID NO: 7).

[0117] In a particular embodiment, the light chain of the cynomolgus monkey FcRn receptor of the methods, assays, assay systems and kits of the invention has the following sequence: MSPSVALAVLALLSPSGLEAIQRTPKIQVYSRHPPENGKPNFLNCYVSGFHPSDIEVDLLKNGEKMGKVEHSDLSFSKDWSFYLLYYTEFTPNEKDEYACRVNHVTLSGPRTVKWDRDM (SEQ ID NO: 8).

[0118] In certain embodiments, the methods, assays, assay systems and kits of the present invention may be used to evaluate the contribution of multiple factors, including but not limited to, the kinetics of internalization, sorting and intracellular trafficking, and exocytosis, to the overall efficiency of the salvage process of a test molecule (including, for example, an antibody, an antibody fragment, a polypeptide or an Fc-containing molecule). In certain embodiments, the methods and assays of the present disclosure may be used to identify and / or detect multiple parameters involved in the FcRn-mediated salvage pathway to determine or predict the PK of a test molecule (including, for example, an antibody, an antibody fragment, a polypeptide or an Fc-containing molecule).

[0119] In certain embodiments, the disclosed methods, assays, assay systems, and kits may be used to detect correlations between in vitro recycling and in vivo clearance of a test molecule, including, for example, an antibody, antibody fragment, polypeptide, or Fc-containing molecule. In certain embodiments, the disclosed assays may be used to detect correlations between in vitro recycling and in vivo clearance of a molecule, as compared to BV ELISA or Fv charge / pI.

[0120] In certain embodiments, the disclosed methods, assays, assay systems and kits may be used to evaluate and / or investigate the role of glycosylation on the distribution and catabolism of a test molecule (e.g., including an antibody, antibody fragment, polypeptide or Fc-containing molecule) in vivo. In certain embodiments, the molecule may be a glycoform variant.

[0121] In certain embodiments, the disclosed methods, assays, assay systems and kits may be used to assess the role of sialic acid addition to molecules on intracellular trafficking parameters, hi certain embodiments, they may be used to analyze the involvement of additional mechanisms in the clearance of high mannose and high sialylated glycoform variants of molecules in vivo.

[0122] In certain embodiments, the methods, assays, assay systems and kits of the present disclosure may be used as tools for the study of FcRn-mediated transcytosis and recycling as an elimination mechanism of test molecules (including, for example, antibodies, antibody fragments, polypeptides or Fc-containing molecules) in relation to their PK.

[0123] In certain embodiments, the disclosed methods, assays, assay systems and kits may be used as tools for studying and elucidating the molecular mechanisms governing the distribution of IgG complexed to FcRn.

[0124] In certain embodiments, the disclosed methods, assays, assay systems, and kits may provide an output that reflects the target-independent, non-specific clearance mechanism of a test molecule (including, for example, an antibody, antibody fragment, polypeptide, or Fc-containing molecule) that has a typical FcRn binding affinity in humans.

[0125] In certain embodiments, the disclosed methods, assays, assay systems and kits may be used to analyze a diverse group of Fc-containing molecules and may be responsive to factors known to affect PK.

[0126] In certain embodiments, the methods, assays, assay systems and kits of the present embodiments may be used to analyze recycling assays and factors involved in recycling and transcytosis assays, to understand how these factors correlate with in vivo clearance, and to define the quantitative nature of this correlation.

[0127] In certain embodiments, the methods, assays, assay systems and kits of the present embodiments may be used to analyze the factors involved in recycling assays and recycling and transcytosis assays, to understand how these factors correlate with tissue permeability, and to define the quantitative nature of this correlation. In some embodiments, the tissue permeability is brain permeability.

[0128] In certain embodiments, the disclosed methods, assays, assay systems and kits may be used to investigate the distribution of pinocytic or internalized test molecules (including, for example, antibodies, antibody fragments, polypeptides or Fc-containing molecules) among recycling pathways, transcytosis pathways in various cell types / tissue compartments, as well as the molecular mechanisms governing such distribution in cells involved in IgG clearance.

[0129] In certain embodiments, the present disclosure relates to a recycling assay system. In certain embodiments, the present disclosure relates to a recycling and transcytosis assay system. For example, but not limited to, such a system comprises a first chamber and a second chamber, each of which contains an aqueous solution at physiological pH; a cell layer separating the first chamber and the second chamber, the cell layer returning molecules introduced into the first chamber back to the cell layer and back to the first chamber; and a detector for detecting the presence of molecules in the first chamber. In certain embodiments, the assay system disclosed herein uses a cell layer of eukaryotic cells, such as mammalian cells, e.g., rodent, canine, non-human primate, or human cells. In some embodiments, the assay system disclosed herein uses a cell layer of kidney cells. In some embodiments, the assay system disclosed herein uses a cell layer of MDCK cells. In some embodiments, the cell layer is a single cell layer. In certain embodiments, the assay system disclosed herein uses cells that contain at least one heterologous gene. In certain embodiments, the assay system disclosed herein uses cells that contain at least one heterologous gene selected from the group consisting of FCGRT gene and B2M gene. In certain embodiments, the assay system disclosed herein uses cells that express heterologous cell surface proteins. In certain embodiments, the assay system disclosed herein uses cells that express heterologous cell surface proteins, where the heterologous cell surface proteins include neonatal Fc receptor (FcRn). In certain embodiments, the assay system disclosed herein can measure the number of recycled molecules through the use of enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, fluorescence reader systems, automated immunoassay platforms (e.g., Quanterix, Gyrolab, and Singulex), fluorescence imaging, or mass spectrometry.In certain embodiments, the assay system disclosed herein may measure the number of recycled molecules using a method with an LLOQ of at least 200 pg / mL, or at least 100 pg / mL, or at least 50 pg / mL, such as an ELISA assay using a high affinity capture reagent (e.g., biotinylated mouse anti-human IgG-Fc, e.g., biotin-R10Z). In certain embodiments, in the recycling and transcytosis assay system of the present disclosure, the cell layer may mediate transcytosis of molecules from the first chamber to the second chamber. In some embodiments, the assay system further comprises a detector for detecting the presence of molecules in the second chamber. Such a detector may be of the same type and / or have the same LLOQ as the detector for detecting the presence of molecules in the first chamber, or may be of a different type and / or different sensitivity, such as a low sensitivity type (e.g., having an LLOQ in the nanomolar range).

[0130] 4.Cells Suitable cells for use in the disclosed methods, assays, assay systems or kits include any prokaryotic or eukaryotic cell described herein.

[0131] In certain embodiments, vertebrate cells may be used. Non-limiting examples of useful mammalian cell lines include SV40 transformed monkey kidney CV1 line (COS-7); primary human endothelial cells; human umbilical vein endothelial cells (HUVEC); human brain microvascular endothelial cells (HBMEC); vascular endothelial cells (EA.hy926); human dermal microvascular endothelial cells (HMEC); human embryonic kidney cell lines (293 or, for example, Graham et al., J. Gen. 293 cells, described in, for example, Mather, Biol. Reprod. 36:59 (1977); baby hamster kidney cells (BHK); mouse Sertoli cells (e.g., TM4 cells, described in, for example, Mather, Biol. Reprod. 23:243-251 (1980); monkey kidney cells (CV1); African green monkey kidney cells (VERO-76); human cervical carcinoma cells (HELA); canine kidney cells (MDCK); buffalo rat hepatocytes (BRL3A); human lung cells (W138); human hepatocytes (HepG2); mouse mammary tumor (MMT060562); TRI cells, described in, for example, Mather et al., Annals N.Y. Acad. Sci. 383:44-68 (1982); MRC5 cells; and FS4 cells. Further non-limiting examples of useful mammalian cell lines include Chinese hamster ovary (CHO) cells, including DHFR-CHO cells (Urlaub et al., Proc. Natl. Acad. Sci. USA 77:4216 (1980)). In certain embodiments, the methods of the disclosure may use hybridoma cells. For example, but not by way of limitation, hybrid cell lines may be of any species, including human and mouse. In certain embodiments, the methods of the disclosure may use primary and established endothelial and / or epithelial cells.For example, but not limited to, endothelial and / or epithelial cells can be caco-2, T-84, HMEC-1, MHEC2.6, HUVEC, and induced pluripotent stem cell (iPSC) derived cells (see, e.g., Lidington, E. A., DL Moyes, et al. (1999), "A comparison of primary endothelial cells and endothelial cells lines for studies of immune interactions" Transpl Immunol 7(4):239-246, or Yamaura, Y, B. D. Chapron, et al. (2016), "Functional Comparison of Human Colonic Carcinoma Cell Lines and Primary Small Intestinal Epithelial Cells for Investigations of Intestinal Drug Permeability and First-Pass Metabolism," Drug Metab Dispos 44(3):329-335).

[0132] In certain embodiments, cells for use in the disclosed methods, assays, assay systems, or kits may contain a nucleic acid encoding a molecule, such as a receptor. In certain embodiments, the nucleic acid may be present in one or more vectors, such as expression vectors. One type of vector is a "plasmid," which refers to a circular double-stranded DNA loop into which additional DNA segments can be ligated. Another type of vector is a viral vector, in which additional DNA segments can be ligated into the viral genome. Certain vectors can replicate autonomously in the cells into which they are introduced (e.g., bacterial vectors with a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) integrate into the genome of the cell upon introduction into the cell, thereby replicating along with the host genome. In addition, certain vectors, expression vectors, can induce the expression of genes to which they are operably linked. In general, expression vectors utilized in recombinant DNA techniques are often in the form of plasmids (vectors). Further non-limiting examples of expression vectors for use in the present disclosure include viral vectors (e.g., replication-defective retroviruses, adenoviruses, and adeno-associated viruses) that serve equivalent functional roles.

[0133] In certain embodiments, the nucleic acid encoding the molecule, e.g., the receptor, can be introduced into the cell. In certain embodiments, the nucleic acid can be introduced into the cell by any method known in the art, including, but not limited to, transfection, electroporation, microinjection, infection with a viral or bacteriophage vector containing the nucleic acid sequence, cell fusion, chromosome-mediated gene transfer, microcell-mediated gene transfer, spheroplast fusion, etc. In certain embodiments, the cell is a eukaryotic organism, e.g., an MDCK cell.

[0134] 5. Chamber The disclosed method, assay, assay system or kit requires a first chamber and a second chamber, the first chamber and the second chamber being separated by a cell layer. Any suitable configuration of chambers that can hold aqueous solutions in two separate compartments that cross along the cell layer can be used. The chamber material can include, for example, plastic (e.g., polycarbonate), glass, ceramic, coating material (e.g., plasticized metal), or a mixture thereof. The chamber can be completely sealed or have one or more sides exposed, so long as it can hold sufficient aqueous solutions in both chambers and maintain the cell layer separating the chambers. The chamber can further include a configuration in which one chamber has a smaller volume than the other chamber, e.g., fits (e.g., is an insert) into the three-dimensional space of the other chamber separated by the cell layer. In some embodiments, the smaller chamber (which may be described as the "inner chamber") is the first chamber, and the larger chamber (which may be described as the "outer chamber") is the second chamber. However, such terms are not meant to limit the use of the currently described assays and systems to alternative chamber combinations (e.g., the outer chamber may be used as the first chamber and the inner chamber may be used as the second chamber). The test molecule is introduced into the first chamber, whichever configuration of chambers is used. In some embodiments, the chamber is a transwell system. Suitable transwell systems that may be used in the disclosed methods, assays, assay systems or kits include, but are not limited to, Boyden chambers, cell migration assays, cell invasion assays, microfluidic migration devices, in vitro scratch assays, extracellular matrix (ECM) protein assays. The disclosed methods may be performed utilizing a wide variety of assay platforms, including "universal" transwell platforms (e.g., 12-well, 24-well or 96-well multiwell arrays).Non-limiting examples of assay platforms include MILLICELL® cell culture inserts and insert plates, and CORNING® TRANSWELL® polycarbonate membrane cell culture inserts. Exemplary embodiments E1. A method comprising determining recycling of a plurality of molecules, the determining comprising: introducing a plurality of molecules into a first chamber, a first chamber separated from a second chamber by a cell layer; the first chamber and the second chamber containing an aqueous solution; incubating a plurality of molecules in a first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of a plurality of molecules released from the cell layer into the first chamber; The method, wherein the aqueous solution is at physiological pH and the cell layer comprises cells expressing a receptor that mediates molecular transport. E2. The method of E1, wherein the plurality of molecules is a plurality of single molecules. E3. The method of E1, wherein the plurality of molecules is a plurality of different molecules. E4. The method of any one of E1-E3, wherein the cell layer comprises a cell monolayer. E5. The method according to any one of E1 to E4, wherein the receptor mediating molecular transport is a receptor mediating intracellular transport of a molecule. E6. The method of any one of E1 to E4, wherein the receptor that mediates molecular transport is a transferrin receptor, an Fc receptor, megalin, or cubulin. E7. The method of any one of E1-E6, wherein the receptor mediating molecular transport is neonatal Fc receptor (FcRn). E8. The method of any one of E1-E7, wherein the cell is a eukaryotic cell or a mammalian cell. E9. The method according to any one of E1 to E7, wherein the cells are Madin-Darby canine kidney (MDCK) cells. E10. The method of any one of E1 to E9, wherein measuring the amount of multiple molecules released from the cell layer comprises using enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, or mass spectrometry. E11. The method of any one of E1-E10, wherein the plurality of molecules is incubated in the first chamber for about 1 hour to about 48 hours. E12. Any one of E1-E11, wherein the plurality of molecules is incubated in the first chamber for about 1 hour to about 30 hours. E13. The method of any one of E1-E12, wherein exchanging the aqueous solution includes washing the first chamber. E14. The method of any one of E1-E13, further comprising incubating the first chamber and the second chamber with a replacement aqueous solution prior to measuring. E15. The method according to E14, wherein the first and second chambers are incubated with the replacement aqueous solution for 1 hour to 6 hours before measurement. E16. The method according to any one of E1 to E15, wherein the incubation is carried out at a temperature of about 35°C to about 39°C. E17. The method of any one of E1-E15, wherein the plurality of molecules is an Fc-containing molecule. E18. The method of E17, wherein the Fc-containing molecule is a receptor-Fc fusion molecule. E19. The method of any one of E1-E15, wherein the plurality of molecules is an antibody. E20. The method of E19, wherein the antibody is a monoclonal antibody. E21. The method of E20, wherein the antibody is an anti-IgE antibody, an anti-VEGF antibody, an anti-integrin antibody, an anti-IL-6 antibody, an anti-TNFa antibody, an anti-BACE1 antibody, or an anti-gD antibody. E22. The method of E20, wherein the antibody is omalizumab, bevacizumab, tocilizumab, anti-BACE1 WT, anti-BACE1 variant YEY, anti-BACE1 variant YQAY, anti-BACE1 variant YPY, anti-BACE1 variant YY, anti-BACE1 variant YLY1(Q6), or anti-BACE1 variant YIY(T3). E23. The method according to E7, wherein FcRn is selected from the group consisting of human FcRn, mouse FcRn, rat FcRn and cynomolgus monkey FcRn. E24. The method according to any one of E1 to E23, wherein the physiological pH is about 7.4. E25. The method of any one of E1-E24, further comprising measuring transcellular transport of a plurality of molecules across the cell layer. E26. Measuring transcellular transport The method of E25, comprising measuring the amount of the plurality of molecules in the second chamber after the aqueous solution is exchanged in both the first chamber and the second chamber. E27. The method of any one of E1-E26, comprising incubating the plurality of molecules in the first chamber in the presence of an agent and determining whether the agent affects recycling of the plurality of molecules. E28. The method of E27, wherein the agent is a small molecule or a polypeptide. E29. A method for determining tissue permeability of a plurality of molecules, comprising: a) introducing a plurality of molecules into a first chamber, the first chamber being separated from a second chamber by a cell layer, the first chamber and the second chamber comprising an aqueous solution; introducing, wherein the aqueous solution is at physiological pH and the cell layer comprises cells expressing a receptor that mediates molecular transport; b) measuring the amount of a plurality of molecules that are recycled from the first chamber to the cell layer and back to the first chamber; c) measuring the amount of the plurality of molecules that are transcytosed from the first chamber to the second chamber; and d) determining tissue permeability of the plurality of molecules based on a ratio of transcytosed molecules to recycled molecules. E30. The method of E29, wherein measuring a plurality of recycled molecules comprises: introducing the plurality of molecules into the first chamber and then incubating the plurality of molecules in the first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of a plurality of molecules released from the cell layer into the first chamber. E31. The method of E29 or E30, wherein measuring a plurality of transcytosed molecules comprises: introducing the plurality of molecules into the first chamber and then incubating the plurality of molecules in the first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of the plurality of molecules released from the cell layer into the second chamber. E32. The method of E30 or E31, wherein the plurality of molecules is incubated in the first chamber for at least about 1 hour to about 48 hours. E33. The method of E30 or E31, wherein the plurality of molecules is incubated in the first chamber for about 1 hour to about 30 hours. E34. The method of any one of E30-E33, wherein exchanging the aqueous solution includes washing the first chamber. E35. The method of any one of E29-E34, further comprising incubating the first chamber and the second chamber with a replacement aqueous solution prior to measuring. E36. The method according to E35, wherein the first chamber and the second chamber are incubated with the replacement aqueous solution for 1 to 6 hours prior to measurement. E37. The method according to any one of E29 to E36, wherein the incubation is carried out at a temperature of about 35°C to about 39°C. E38. The method of any one of E29 to E36, wherein the plurality of molecules is a plurality of single molecules. E39. The method of any one of E29 to E36, wherein the plurality of molecules is a plurality of different molecules. E40. The method according to any one of E29 to E39, wherein the cell layer comprises a cell monolayer. E41. The method according to any one of E29 to E40, wherein the receptor mediating molecular transport is a receptor mediating intracellular transport of the molecule. E42. The method according to any one of E29 to E41, wherein the receptor mediating molecular transport is a transferrin receptor, an Fc receptor, megalin or cubulin. E43. The method according to any one of E29 to E42, wherein the receptor mediating molecular transport is neonatal Fc receptor (FcRn). E44. The method according to any one of E29 to E43, wherein the cell is a eukaryotic or mammalian cell. E45. The method of any one of E29 to E44, wherein the cells are Madin-Darby canine kidney (MDCK) cells. E46. The method of any one of E29 to E45, wherein measuring the amount of a plurality of molecules recycled and measuring the amount of a plurality of molecules transcytosed independently include the use of enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, mass spectrometry, or any combination thereof. E47. The method of any one of E29 to E46, wherein the plurality of molecules is an Fc-containing molecule. E48. The method of E47, wherein the Fc-containing molecule is a receptor-Fc fusion molecule. E49. The method of any one of E29 to E48, wherein the plurality of molecules is an antibody. E50. The method of E47, wherein the antibody is a monoclonal antibody. E51. The method of E50, wherein the antibody is an anti-IgE antibody, an anti-VEGF antibody, an anti-integrin antibody, an anti-IL-6 antibody, an anti-TNFa antibody, an anti-BACE1 antibody, or an anti-gD antibody. E52. The method of E50, wherein the antibody is omalizumab, bevacizumab, tocilizumab, anti-BACE1 WT, anti-BACE1 variant YEY, anti-BACE1 variant YQAY, anti-BACE1 variant YPY, anti-BACE1 variant YY, anti-BACE1 variant YLY1(Q6), or anti-BACE1 variant YIY(T3). E53. The method according to any one of E29 to E52, wherein the physiological pH is about 7.4. E54. The method according to any one of E29 to E53, wherein the tissue penetrance is brain penetrance. E55. The method of any one of E29-E54, comprising incubating the plurality of molecules in the first chamber in the presence of an agent and determining whether the agent affects tissue permeability of the plurality of molecules. E56. The method of E55, wherein the agent is a small molecule. E57. A method for determining pharmacokinetic (PK) parameters of a plurality of molecules, comprising: a) introducing a plurality of molecules into a first chamber, the first chamber being separated from a second chamber by a cell layer, the first chamber and the second chamber comprising an aqueous solution; introducing, wherein the aqueous solution is at physiological pH and the cell layer comprises cells expressing a receptor that mediates molecular transport; b) measuring the amount of the plurality of molecules that are recycled from the first chamber to the cell layer and back to the first chamber; and c) determining a PK parameter based on the amount of the plurality of molecules recycled. E58. The method according to E57, wherein measuring the number of recycled molecules comprises: introducing the plurality of molecules into the first chamber and then incubating the plurality of molecules in the first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of a plurality of molecules released from the cell layer into the first chamber. E59. The method of E58, wherein the plurality of molecules is incubated in the first chamber for at least about 1 hour to about 48 hours. E60. The method of E58, wherein the plurality of molecules is incubated in the first chamber for about 1 hour to about 30 hours. E61. The method of any one of E58-E60, wherein exchanging the aqueous solution includes washing the first chamber. E62. The method of any one of E54-E57, further comprising incubating the first chamber and the second chamber with a replacement aqueous solution prior to measuring. E63. The method of E62, wherein the first chamber and the second chamber are incubated with the replacement aqueous solution for about 1 hour to about 6 hours prior to measurement. E64. The method according to any one of E58 to E63, wherein the incubation is carried out at a temperature of about 35°C to about 39°C. E65. The method of any one of E57-E63, wherein the plurality of molecules is a plurality of single molecules. E66. The method according to any one of E57 to E64, wherein the plurality of molecules is a plurality of different molecules. E67. The method according to any one of E57 to E66, wherein the cell layer comprises a cell monolayer. E68. The method of any one of E57 to E67, wherein the cell expresses a heterologous FcRn. E69. The method according to any one of E57 to E68, wherein the cell is a Madin-Darby canine kidney (MDCK) cell. E70. The method of any one of E57 to E68, wherein measuring the amount of multiple molecules recycled comprises using an enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, or mass spectrometry. E71. The method of any one of E57 to E70, wherein the plurality of molecules is an Fc-containing molecule. E72. The method of E71, wherein the Fc-containing molecule is a receptor-Fc fusion molecule. E73. The method of any one of E57 to E72, wherein the plurality of molecules is an antibody. E74. The method of E73, wherein the antibody is a monoclonal antibody. E75. The method of E74, wherein the antibody is an anti-IgE antibody, an anti-VEGF antibody, an anti-integrin antibody, an anti-IL-6 antibody, an anti-TNFa antibody, an anti-BACE1 antibody, or an anti-gD antibody. E76. The method of E74, wherein the antibody is omalizumab, bevacizumab, tocilizumab, anti-BACE1 WT, anti-BACE1 variant YEY, anti-BACE1 variant YQAY, anti-BACE1 variant YPY, anti-BACE1 variant YY, anti-BACE1 variant YLY1(Q6), or anti-BACE1 variant YIY(T3). E77. The method of any one of E57 to E76, wherein the physiological pH is about 7.4. E78. The method of any one of E57 to E77, wherein the PK parameter is a measure of in vivo clearance, volume of distribution, area under the curve (AUC) or in vivo half-life of a plurality of molecules. E79. The method of any one of E57-E78, comprising incubating a plurality of molecules in the first chamber in the presence of an agent and determining whether the agent affects a PK parameter of the plurality of molecules. E80. The method of E79, wherein the agent is a small molecule. E81. An assay system comprising: a) a first chamber and a second chamber, each chamber containing an aqueous solution at physiological pH; b) a cell layer separating the first and second chambers, the cell layer being capable of mediating the recycling of molecules from the first chamber into the cell layer and back into the first chamber; c) an assay system comprising a detector for detecting the presence of a molecule in the first chamber; The assay system is configured to determine recycling of a plurality of molecules, determining comprising: introducing a plurality of molecules into a first chamber; incubating a plurality of molecules in a first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and An assay system comprising: measuring the amount of a plurality of molecules released from the cell layer into a first chamber. An assay system as described in E82.E81, comprising: further comprising a detector for detecting the presence of the molecule in the second chamber; the cell layer is capable of mediating transcellular transport of a molecule from the first chamber to the second chamber; and An assay system configured to determine transcytosis of a plurality of molecules across the cell layer, wherein determining the transcytosis comprises measuring an amount of the plurality of molecules in the second chamber after the aqueous solution is exchanged. E83. The assay system of E81 or E82, wherein the first chamber and the second chamber are components of a 96-well transwell plate. E84. A kit comprising the assay system according to any one of E81 to E83 and an instruction manual. EXAMPLES

[0135] The following examples are merely illustrative of the subject matter disclosed herein and should not be construed as limiting in any way.

[0136] material and method MDCK cell line expressing human FcRn Clonal cell lines stably expressing both human FcRn heavy chain (FCGRT) and light chain (B2M) were generated as previously published (Chung, S. et al., 2019, MAbs, 11(5), 942-955). Briefly, cDNAs of the two genes FCGRT (UniProtKB-P55899, FCGRTN_HUMAN) and B2M (UniProtKB-P61769, B2MG_HUMAN) were introduced into MDCK cells using modified pPRK plasmids, then selected with puromycin and sorted by fluorescence-activated cell sorting (FACS). The final clones used in the assay were selected based on significant expression levels of both FCGRT and B2M proteins. MDCK-hFcRn cells were maintained in Dulbecco's modified minimal essential medium (DMEM) with GlutaMAX (Thermo Fisher Scientific, Waltham, MA) supplemented with 10% FBS (HyClone, Logan, UT), 5 μg / mL puromycin, and 1% penicillin-streptomycin (Thermo Fisher Scientific). Cells were cultured at 37°C and 5% CO2 and passaged every 2–3 days.

[0137] Test molecule The test molecules included a series of humanized IgG 1 antibodies - a panel of seven therapeutic antibodies with documented or published clearance values ​​in human studies, and anti-herpes simplex virus glycoprotein D wild type (anti-gD WT) with two of its variants with engineered mutations that alter Fc-FcRn binding affinity (anti-gD HAHQ and anti-gD YTE). Of the seven therapeutic antibodies, five were commercially available preparations, two of which (vedolizumab and adalimumab) were purchased from manufacturers. The remaining therapeutic antibodies (bevacizumab, omalizumab, tocilizumab, mAbX and mAbY), along with the anti-gD variants, were produced in engineered Chinese hamster ovary (CHO) cells at Genentech (South San Francisco, CA).

[0138] Recycling assay MDCK-hFcRn cells were cultured at 6 × 10 4 Cells were seeded into the inner chamber of a 96-well transwell plate (MilliporeSigma, Burlington, MA) at a density of 100 μL of growth medium in the inner chamber and 200 μL of growth medium in the outer chamber and cultured on the membrane filter for 3 days until confluence was reached. To measure recycling, the medium in the inner chamber was removed and 50 μL of test antibody was loaded into each inner chamber at a concentration of 100 μg / mL (0.67 μM), followed by incubation for 2 h at 37 °C in 5% CO2. The transwells were washed with growth medium to remove residual antibody in both chambers, and 100 μL / well of fresh cell culture medium was added to the inner chamber and 200 μL / well of medium was left in the outer chamber. Cells were incubated for an additional 4 h at 37 °C in 5% CO2, and recycling samples were taken from the inner chamber for the following quantification by human IgG-specific ELISA assay. In the final step of the experiment, the integrity of the cell monolayer was assessed with Lucifer Yellow (Sigma Aldrich, St. Louis, MO) by adding 20 mM Lucifer Yellow to the inner chamber and incubating for 1 h. Samples taken from the outer chamber were then measured for levels of Lucifer Yellow, and results from wells with passive flow path (measured by dividing the Lucifer Yellow signal from the outer chamber into that of the corresponding inner chamber) greater than 0.1% were considered invalid due to potential leakage of the cell monolayer and discarded. Each recycle assay measurement was performed in six to eight replicates, and reported values ​​are the average concentrations normalized by the recycle output of bevacizumab tested in parallel in the same transwell plate.

[0139] Samples taken from the inner chamber represent the recycled components, whereas samples from the outer chamber represent the transcytosis components. Samples were frozen at -70°C for quantification using ELISA.

[0140] Variations of this procedure may be used. For example, optionally, the lowest speed of the electronic pipette may be used in the washing procedure to recycle the components (inner chamber) to minimize disturbance / damage to the cell layer cultured on the filter. Optionally, the lower limit of quantification of the immunoassay may be two orders of magnitude to ensure that the sensitivity is rigorous enough to detect low concentrations of antibodies. Optionally, cells may be cultured under conditions that achieve a viability of more than 95%. Optionally, the cell culture medium may be adjusted depending on the type of cells being used and / or the test molecule being evaluated. Optionally, large transwell plates may be used (e.g., 12-well or 24-well). Further variations may be performed.

[0141] ELISA method Samples were evaluated using a semi-homogeneous bridging enzyme-linked immunosorbent assay (ELISA) using biotinylated mouse anti-human IgG-Fc (Biotin-R10Z, Genentech) as the capture molecule, horseradish peroxidase (HRP)-conjugated goat anti-human Fab (Jackson ImmunoResearch Laboratories, West Grove, PA) as the detection molecule, and 3,3',5,5'-tetramethylbenzidine (TMB) solution (Kirkegaard & Perry Laboratories, Gaithersburg, MD) for color development. Specifically, standards, controls, and samples were diluted with cell culture medium to their final concentrations, and other reagents were prepared in assay diluent (PBS / 0.5% BSA / 0.05% polysorbate 20 / 0.05% ProClin 300, pH 7.4 ± 0.1). Each therapeutic molecule standard was serially diluted from 4 ng / mL to 31.25 pg / mL (in-well concentration). For the assay, 60 μL / well of working standard, control, or sample was incubated overnight at ambient temperature with 60 μL / well of 1 μg / mL biotin-R10Z in a sealed 96-well polypropylene plate with gentle agitation. After overnight incubation, 100 μL / well of the mixture was added to a streptavidin-coated, preblocked plate (Roche Diagnostics Corporation, Indianapolis, IN). The plate was sealed and incubated for 1 h at ambient temperature with agitation. The plate was washed 4 times with wash buffer (PBS / 0.05% polysorbate 20, pH 7.34) at 400 μL / well per cycle. Then, 100 μL / well of 0.1 μg / mL HRP-conjugated goat anti-human was added, and the plate was sealed and incubated for 1 h at ambient temperature. Plates were washed four times with wash buffer at 300 μL / well per cycle, followed by the addition of 100 μL / well of peroxidase substrate solution B and TMB peroxidase substrate mix (Kirkegaard & Perry Laboratories, Gaithersburg, MD) and incubation for 15–20 min to allow plates to develop.To stop color development, 100 μL of 1M H3PO4 was added to each well. Plates were read on a SpectraMax340 plate reader (Molecular Devices, San Jose, CA) at 450 nm (detection wavelength) with a 630 nm reference filter. Data were analyzed using a four-parameter fit and weighted by 1 / y2 with the SoftMax Pro 6.5.1 software program.

[0142] Example 1: Development of a recycling assay An FcRn-dependent recycling assay was developed using a clonal MDCK cell line (MDCK-hFcRn) engineered to express both human FcRn heavy chain (FCGRT) and light chain (B2M). Expression levels, intracellular colocalization and functional readouts suggesting functional human FcRn in MDCK cell lines have been previously demonstrated (Chung, S. et al., 2019, MAbs, 11(5), 942-955). The recycling assay was designed with a pulse-chase experimental procedure (Figure 2), and a transwell culture system that allows for a more complete apical-basolateral polarization of cells. MDCK-hFcRn cells were seeded in 96-well transwell plates and cultured for 3 days until confluence. For the pulse step, antibodies were added to the inner chamber and incubated for 2 hours to provide time for the antibodies to be internalized by the cells and distributed and reach homeostasis among the intracellular pathways (recycling, transcytosis and degradation). After washing both the inner and outer chambers to remove pre-existing or transcytosed antibodies, fresh medium was added to both chambers and cells were incubated for 4 h. During this chase step, three possible outcomes were possible: intracellular antibodies were recycled to the inner chamber, transcytosed to the outer chamber, or degraded intracellularly. Antibodies appearing in the inner chamber represent recycled molecules. Therefore, the inner chamber solution was collected for analysis. Any antibodies that were transcytosed to the outer chamber were excluded from the samples to avoid contamination of the recycling assay with FcRn-mediated transcytosis. Monolayer integrity was assessed at the end of each experiment, and data from compromised monolayers were excluded from analysis.

[0143] Because the amount of recycled antibodies released from cells is low in a 96-well assay format, we developed a highly sensitive human IgG-specific enzyme-linked immunosorbent assay (ELISA). This sandwich ELISA uses biotinylated mouse anti-human IgG-Fc for capture, HRP-conjugated goat anti-human Fab for detection, and TMB solution for color development (Figure 3A), achieving a lower limit of quantification (LLOQ) of 50 pg / mL, allowing quantification of subnanomolar recycled outputs (Figure 3B).

[0144] Example 2: Recycling output of humanized IgG1 antibodies is highly dependent on FcRn-mediated mechanisms in cells expressing FcRn To demonstrate the involvement of FcRn-mediated mechanisms in the recycling assay, we compared a humanized IgG1 antibody-anti-herpes simplex virus glycoprotein D (anti-gD) wild type (WT) with two variants carrying Fc mutations that alter Fc-FcRn binding affinity. One of the anti-gDHAHQ variants carries H310A / H435Q mutations that abolish FcRn binding, while the other anti-gDYTE variant carries FcRn-binding enhancing mutations M252Y / S254T / T256E. The recycling output of anti-gDHAHQ was 0.6 ng / mL, significantly lower than that of anti-gDWT (1.2 ng / mL), whereas anti-gDYTE had an increased recycling output (1.9 ng / mL) (Figure 4). These results suggest that the primary mechanism reflected by the recycling output in this system is mediated by FcRn and support the use of this assay to evaluate FcRn-mediated IgG homeostasis.

[0145] Next, the kinetics of recycling measurements were evaluated by using a panel of conventional humanized therapeutic antibodies, including omalizumab, bevacizumab, vedolizumab, and tocilizumab. Recycling samples were taken at various time points (ranging from 20 min to 4 h) during the chase step. For each individual molecule, a cumulative increase in recycling was observed, with the recycling output being lowest at 20 min and highest at 4 h (Figure 5A). Three of the evaluated antibodies showed a maximum recycling amount of approximately 0.4-0.5 ng / ml, while tocilizumab had a higher recycling value, reaching 1.09 ng / ml at 4 h. Despite the differences in recycling output among the four molecules, the kinetics of recycling are similar and show little variation throughout the time course of the chase step (Figure 5B; recycling output was normalized to the 4 h data points of the same molecules. Data are summarized in Table 1B). The ranking of recycling output among the four molecules was further examined at each time point normalized to the recycling output of bevacizumab. Both the ranking order and normalized recycling output were similar across the four time points (Table 1A normalized to bevacizumab), suggesting that the relative recycling output was consistent regardless of chase time. The coefficient of variation (CV) across the four time points (20, 30, 60, and 240 min) was less than 20% for each molecule, suggesting that the relative recycling output between antibodies with different absolute recycling values ​​was consistent across the 4-h chase. Therefore, due to the high recycling output that is reliable for quantification, it was decided to select 4 h in the pulse step as the standard assay procedure for this system and to use bevacizumab as an internal control for normalization of the recycling output measured with other test molecules. [Table 1A] [Table 1B]

[0146] Example 3: Correlation of Transcytosis / Recycling (T / R) Ratio with In Vivo Brain-Serum Ratio in Cynomolgus Monkeys A panel of seven anti-BACE1 variants, including wild-type (WT) molecules and six variants, were tested in the transcytosis / recycling dual assay. The anti-BACE1 antibodies are further described in WO 2020 / 132230. The six variants have variants in their Fc region that significantly enhance the binding affinity to FcRn at neutral pH and reduce the Kd at pH 7.4 by 13.3-78.1 fold (Table 1). The higher the binding affinity to FcRn, the more the mAb will be protected and the more the mAb will be directed to the FcRn-mediated recycling and transcytosis pathways. Compared to the WT molecule, the pH 7.4 variants had both significantly increased recycling and transcytosis output. This finding is likely due to enhanced mAb internalization via FcRn receptor-mediated uptake for the pH 7.4 variants. Furthermore, the ratio between transcytosis and recycling was significantly increased among the pH 7.4 variants. The T / R ratio of the WT molecule was 0.026, whereas in the pH 7.4 variants the ratios ranged from 0.074 to 0.191 (Table 2 and Figure 6), indicating that the introduced mutations may result in a transcytosis pathway bias and facilitate antibody transport across the cell layer. [Table 2]

[0147] We then analyzed potential correlations between the assay output and in vivo brain penetration results from the cynomolgus monkey study (cynomolgus monkey data available for five molecules; Table 3). Transcytosis or recycling output alone did not show significant correlation with the brain-serum ratio. However, the T / R ratio showed a very strong correlation with the brain-serum ratio (Pearson's correlation coefficient 0.837). A higher T / R ratio indicates a biased intracellular pathway in favor of transcytosis and thus a higher brain penetration behavior in vivo (Figure 7). Thus, the T / R ratio is a meaningful biological parameter for the prediction of brain penetration ability of therapeutic candidates. [Table 3]

[0148] Example 3: Correlation between in vitro recycling output and in vivo clearance of mAbs in humans Seven therapeutic antibodies, including five marketed and two in development, were tested and evaluated for possible correlation with in vivo clearance in humans. The seven molecules are humanized antibodies of IgG1 / kappa isotype, reflecting diverse properties including mechanism of action, targeting properties and route of administration, but none have Fc mutations to modify PK properties or FcRn interactions. Based on drug prescribing information and previous publications, clearance values ​​cover a range of 2.2-8.5 mL / day / kg. Discrepancies in nonspecific clearance observed between similar antibody isotypes have been proposed to be due to molecular properties such as pI, charge or hydrophobicity (Hotzel, I. et al., (2012), MAbs, 4(6), 753-760). Using an established sequence-based algorithm, we calculated molecular parameters including (i) pI value, (ii) net Fv charge at pH 5.5, and (iii) the sum of hydrophobicity index values ​​(HIsum) on CDRL1, L3, H2, and H3 (Sharma, VK et al., (2014), PNAS, 111(52), 18601-18606). Extreme values ​​of these parameters have been shown to indicate fast-clearing antibodies, but consistent with previous findings, we found no clear trend of correlation between these parameters and clearance (Figure 8A-C; Table 4). To examine the correlation between recycling and clearance, seven molecules were evaluated in a recycling assay to provide a quantitative measure of the FcRn-mediated recycling process. The recycling output of each molecule was measured by the concentration of antibody returned to the inner chamber and normalized to the recycling value of bevacizumab run on the same 96-well transwell plate as a control. The results of the recycling assay with these molecules are shown in Table 4 along with their published clearance in humans. All seven molecules showed measurable recycling outputs, with molecules with faster clearance values ​​showing higher recycling outputs. The recycling outputs showed a strong positive correlation with clearance in humans (R for recycling). 2= 0.856; Figure 8D). The average intra-assay precision is 10.7% and the inter-assay precision is 12.3%. The results suggest recycling as a promising assay for prediction of the PK behavior of therapeutic antibodies or candidates under development. [Table 4]

[0149] The seven evaluated antibodies, each with a conventional Fc region, demonstrated a remarkable correlation between recycling output and clearance in humans, despite diverse Fab region characteristics. IgGs with identical Fc regions may have widely different Pk properties that are believed to be due to the Fv charge of the Fab arms, which may affect interactions with FcRn and affect fluid-phase pinocytosis during internalization. In this study, after normalization to the maximum value at 4 hours for each molecule, there was little variation between recycling kinetic curves among the four humanized therapeutic antibodies tested (omalizumab, bevacizumab, vedolizumab, and tocilizumab). Tocilizumab had identical rates of recycling (slope at each time point), but showed approximately two-fold higher recycling output values ​​than the other three antibodies at 4 hours. Without wishing to be bound by theory, the similar recycling kinetics suggests that FcRn-mediated transport through the recycling pathway may be similar for mAbs with conventional Fc regions, and thus the difference in measured amounts of recycling output may result from mechanisms upstream of FcRn-mediated transport. Although these four antibodies have comparable binding affinities for FcRn at pH 6.0, tocilizumab has a higher calculated PI value and a higher Fv charge. This may explain the higher recycling value and faster clearance of tocilizumab, as the positive charge may enhance nonspecific binding through electrostatic interactions with anionic heparan sulfate proteoglycans at the cell surface. These interactions may increase internalization of tocilizumab by fluid-phase pinocytosis. Previous studies have shown that FcRn-independent mechanisms may play a role in regulating the PK behavior of mAbs that share the same Fc but have different Fab regions.

[0150] Without wishing to be bound by theory, it was initially expected that a high recycling output might be inversely correlated with the clearance rate, as it is believed to be a salvage mechanism that rescues IgG from lysosomal degradation and returns it to the blood. Unexpectedly, it was observed that a higher recycling output corresponds to a faster clearance. Without wishing to be bound by theory, the positive correlation between clearance and FcRn-mediated recycling may be related to the fraction of antibodies that undergo clearance mechanisms during each internalization event. The recycling process removes antibodies from the circulation and returns them to the same compartment, but does not affect the net amount of serum concentration as a single factor. However, it has been previously demonstrated that recycling events may involve a small loss of antibodies due to degradation in lysosomes (Grevys et al., 2018). In the currently described transwell culture system, transcytosis may also function as a clearance pathway that directs antibodies away from recycling. Without wishing to be bound by theory, it is speculated that such losses (due to degradation and transcytosis) for each recycling event may reduce the amount recycled back to the circulation. Thus, for highly recycled molecules, the losses are exaggerated, leading to a faster decrease in serum concentration and faster clearance measurements. Interestingly, this observation seems to be reversed in the FcRn binding variant group, demonstrating a trend for a negative correlation between recycling output and clearance of Fc-engineered anti-gD variants. The YTE mutants that showed slower clearance had higher recycling output compared to the WT (see Example 2). Without wishing to be bound by theory, the highly enhanced binding to FcRn may be the primary biological factor, which may lead to a higher level of protection of the antibody, an extended serum half-life, and reduced lysosomal degradation. To explain the discrepancy between conventional and Fc-engineered mAbs, the dominant factors influencing the PK behavior may differ between the two scenarios depending on the design of the molecule. Therefore, the biochemical properties of the antibody and the Fc engineering should be considered when interpreting the results from this in vitro system.

[0151] The seven mAbs evaluated demonstrate that the recycle assay described herein was superior to other models that use antibody pI, charge or hydrophobicity parameters as predictors of PK properties of mAbs without Fc modifications, particularly clearance from the circulation in humans. The assay design uses a three-compartment in vitro model system (inner chamber, cell, and outer chamber) to mimic the in vivo situation (blood compartment, vesicle endothelial cell, and tissue compartment) and incorporates multiple biological events that may affect the cellular metabolism of antibodies. The recycle assay provides a holistic assessment of multiple biological factors that may affect the cellular metabolism of antibodies and may therefore better predict one or more PK properties compared to other published assays that only consider a single or a subset of factors, e.g., nonspecific binding, binding to extracellular matrix, and FcRn interactions.

[0152] Furthermore, without wishing to be bound by theory, the neutral pH used in both transwell chambers may be important for successful PK property prediction, as it is more physiologically relevant to the in vivo situation where antibodies are captured and released at neutral pH on the cell surface. This may explain the limited application of other FcRn-mediated cell-based assays that used acidic buffers in loading the cells with antibodies to take advantage of enhanced FcRn binding at acidic pH (Chung et al., (2018), J Immunol Methods, 462, 101-105; Jaramillo et al., 2017, MAbs, 9(5), 781-791; Sockolosky, JT et al., 2012, PNAS, 109(40), 16095-16100; Ying et al., 2015, MAbs, 7(5), 922-930). Some of these methods predicted the clearance or half-life of Fc-engineered molecules with enhanced FcRn binding, but were limited in their ability to predict the PK behavior of conventional mAbs, where changes to FcRn binding are more subtle. Furthermore, cell polarization may be considered an important factor, since both recycling and transcytosis are inherently polarized and are at least partially transported by independent processes at the apical and basolateral surfaces of polarized endothelial cells (Dickinson et al., 1999, J Clin Invest, 104(7), 903-911; Tzaban, S. et al., 2009, J Cell Biol, 185(4), 673-684). The assay described herein, utilizing a transwell cell culture system, allows for better polarization and separation of recycling from transcytosis components, which may more accurately evaluate conventional mAbs, compared to other recycling assays performed in regular cell culture plates (Grevys, A. Nat Commun, 9(1) 621).

[0153] All publications, patents, and other references cited herein are incorporated by reference in their entirety into this disclosure.

Claims

1. 16. A method comprising determining recycling of a plurality of molecules, the determining comprising: introducing the plurality of molecules into a first chamber, the first chamber being separated from the second chamber by a cell layer; introducing said first chamber and said second chamber containing an aqueous solution; incubating said plurality of molecules in said first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of the plurality of molecules released from the cell layer into the first chamber. The method, wherein the aqueous solution is at a physiological pH and the cell layer comprises cells expressing a receptor that mediates molecular transport.

2. The method of claim 1 , wherein the cell layer comprises a cell monolayer.

3. The method of claim 1 or 2, wherein the receptor that mediates molecular transport is a transferrin receptor, an Fc receptor, megalin or cubulin.

4. The method of claim 1 or 2, wherein the receptor that mediates molecular transport is the neonatal Fc receptor (FcRn).

5. The method of claim 1 or 2, wherein the cells are Madin-Darby canine kidney (MDCK) cells.

6. 3. The method of claim 1 or 2, wherein measuring the amount of the plurality of molecules released from the cell layer comprises using an enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, or mass spectrometry.

7. The method of claim 1 or 2, wherein the plurality of molecules are Fc-containing molecules.

8. The method of claim 1 or 2, wherein the plurality of molecules are antibodies.

9. The method of claim 4, wherein the FcRn is selected from the group consisting of human FcRn, mouse FcRn, rat FcRn and cynomolgus monkey FcRn.

10. The method of claim 1 or 2, further comprising measuring transcellular transport of said plurality of molecules across said cell layer.

11. Measuring the transcytosis 11. The method of claim 10, comprising measuring the amount of the plurality of molecules in the second chamber after the aqueous solution has been exchanged in both the first chamber and the second chamber.

12. 3. The method of claim 1, comprising incubating the plurality of molecules in the first chamber in the presence of an agent and determining whether the agent affects the recycling of the plurality of molecules.

13. 1. A method for determining tissue permeability of a plurality of molecules, comprising: a) introducing said plurality of molecules into a first chamber, said first chamber being separated from a second chamber by a cell layer, said first chamber and said second chamber comprising an aqueous solution; introducing, said aqueous solution being at a physiological pH and said cell layer comprising cells expressing a receptor that mediates molecular transport; b) measuring the amount of said plurality of molecules recycled from said first chamber to said cell layer and back to said first chamber; c) measuring the amount of the plurality of molecules that are transcytosed from the first chamber to the second chamber; and d) determining said tissue permeability of said plurality of molecules based on a ratio of transcytosed molecules to recycled molecules.

14. Measuring the plurality of molecules that are recycled after introducing said plurality of molecules into said first chamber, incubating said plurality of molecules in said first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and 14. The method of claim 13, comprising measuring the amount of the plurality of molecules released from the cell layer into the first chamber.

15. Measuring the plurality of molecules that are transcytosed, after introducing said plurality of molecules into said first chamber, incubating said plurality of molecules in said first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and 15. The method of claim 13 or 14, comprising measuring the amount of the plurality of molecules released from the cell layer into the second chamber.

16. The method of claim 13 or 14, wherein the cell layer comprises a cell monolayer.

17. The method of claim 13 or 14, wherein the receptor that mediates molecular transport is a transferrin receptor, an Fc receptor, megalin or cubulin.

18. The method of claim 13 or 14, wherein the receptor mediating molecular transport is the neonatal Fc receptor (FcRn).

19. 15. The method of claim 13 or 14, wherein the cell is a Madin-Darby canine kidney (MDCK) cell.

20. 15. The method of claim 13 or 14, wherein measuring the amount of the plurality of molecules that are recycled and measuring the amount of the plurality of molecules that are transcytosed independently comprise the use of enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, mass spectrometry, or any combination thereof.

21. The method of claim 13 or 14, wherein the plurality of molecules are Fc-containing molecules.

22. The method of claim 13 or 14, wherein the plurality of molecules are antibodies.

23. 23. The method of claim 22, wherein the antibody is an anti-IgE antibody, an anti-VEGF antibody, an anti-integrin antibody, an anti-IL-6 antibody, an anti-TNFa antibody, an anti-BACE1 antibody, or an anti-gD antibody.

24. 15. The method of claim 13 or 14, wherein the tissue penetrance is brain penetrance.

25. 15. The method of claim 13 or 14, comprising incubating the plurality of molecules in the first chamber in the presence of an agent and determining whether the agent affects the tissue permeability of the plurality of molecules.

26. 1. A method for determining pharmacokinetic (PK) parameters of a plurality of molecules, comprising: a) introducing said plurality of molecules into a first chamber, said first chamber being separated from a second chamber by a cell layer, said first chamber and said second chamber comprising an aqueous solution; introducing, said aqueous solution being at a physiological pH and said cell layer comprising cells expressing a receptor that mediates molecular transport; b) measuring the amount of the plurality of molecules recycled from the first chamber to the cell layer and back to the first chamber; and c) determining said PK parameter based on an amount of said plurality of molecules that is recycled.

27. Measuring the plurality of molecules that are recycled after introducing said plurality of molecules into said first chamber, incubating said plurality of molecules in said first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and 27. The method of claim 26, comprising measuring the amount of the plurality of molecules released from the cell layer into the first chamber.

28. 28. The method of claim 26 or 27, wherein the cell layer comprises a cell monolayer.

29. The method of claim 26 or 27, wherein the cell expresses a heterologous FcRn.

30. 28. The method of claim 26 or 27, wherein the cell is a Madin-Darby canine kidney (MDCK) cell.

31. 28. The method of claim 26 or 27, wherein measuring the amount of the plurality of molecules recycled comprises the use of enzyme-linked immunosorbent assay (ELISA), liquid scintillation counting (LSC), quantitative PCR, a fluorescence reader system, or mass spectrometry.

32. 28. The method of claim 26 or 27, wherein the plurality of molecules are Fc-containing molecules.

33. 28. The method of claim 26 or 27, wherein the plurality of molecules are antibodies.

34. 34. The method of claim 33, wherein the antibody is an anti-IgE antibody, an anti-VEGF antibody, an anti-integrin antibody, an anti-IL-6 antibody, an anti-TNFa antibody, an anti-BACE1 antibody, or an anti-gD antibody.

35. 28. The method of claim 26 or 27, wherein the PK parameter is a measure of in vivo clearance, volume of distribution, area under the curve (AUC) or in vivo half-life of the multiple molecules.

36. 28. The method of claim 26 or 27, comprising incubating the plurality of molecules in the first chamber in the presence of a drug and determining whether the drug affects the PK parameter of the plurality of molecules.

37. a) a first chamber and a second chamber, each chamber containing an aqueous solution at a physiological pH; b) a cell layer separating the first and second chambers, the cell layer being capable of mediating the recycling of molecules from the first chamber into the cell layer and back into the first chamber; c) a detector for detecting the presence of a molecule in the first chamber; The assay system is configured to determine recycling of a plurality of molecules, the determining comprising: introducing said plurality of molecules into said first chamber; incubating said plurality of molecules in said first chamber; exchanging the aqueous solution in both the first chamber and the second chamber; and measuring the amount of said plurality of molecules released from said cell layer into said first chamber.

38. The assay system comprises: further comprising a detector for detecting the presence of a molecule in the second chamber; the cell layer is capable of mediating transcellular transport of a molecule from the first chamber to the second chamber; and 38. The assay system of claim 37, wherein the assay system is configured to determine transcytosis of a plurality of molecules across the cell layer, and determining transcytosis comprises measuring the amount of the plurality of molecules in the second chamber after the aqueous solution is exchanged.

39. 39. The assay system of claim 37 or 38, wherein the first chamber and the second chamber are components of a 96-well transwell plate.

40. 39. A kit comprising the assay system of claim 37 or 38 and instructions for use.

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