title: A Modeling and Experimental Investigation of the Effects of Antigen Density, Binding Affinity, and Antigen Expression Ratio on Bispecific Antibody Binding to Cell Surface Targets.
abstract: Despite the increasing number of multivalent antibodies, bispecific antibodies, fusion proteins, and targeted nanoparticles that have been generated and studied, the mechanism of multivalent binding to cell surface targets is not well understood. Here, we describe a conceptual and mathematical model of multivalent antibody binding to cell surface antigens. Our model predicts that properties beyond 1:1 antibody:antigen affinity to target antigens have a strong influence on multivalent binding. Predicted crucial properties include the structure and flexibility of the antibody construct, the target antigen(s) and binding epitope(s), and the density of antigens on the cell surface. For bispecific antibodies, the ratio of the expression levels of the two target antigens is predicted to be critical to target binding, particularly for the lower expressed of the antigens. Using bispecific antibodies of different valencies to cell surface antigens including MET and EGF receptor, we have experimentally validated our modeling approach and its predictions and observed several nonintuitive effects of avidity related to antigen density, target ratio, and antibody affinity. In some biological circumstances, the effect we have predicted and measured varied from the monovalent binding interaction by several orders of magnitude. Moreover, our mathematical framework affords us a mechanistic interpretation of our observations and suggests strategies to achieve the desired antibody-antigen binding goals. These mechanistic insights have implications in antibody engineering and structure/activity relationship determination in a variety of biological contexts.
authors.affiliation: From the Department of Drug Disposition, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285 rhoden_john_j@lilly.com.
authors.forename: John J
authors.initials: JJ
authors.lastname: Rhoden
authors.affiliation: From the Department of Drug Disposition, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285.
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Dyas
authors.affiliation: From the Department of Drug Disposition, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285.
authors.forename: Victor J
authors.identifier: http://orcid.org/0000-0002-0593-4350
authors.initials: VJ
authors.lastname: Wroblewski
mesh_terms: D000818:Animals; D018033:Antibodies, Bispecific / Q000737:chemistry / Q000378:metabolism; D000915:Antibody Affinity; D000937:Antigen-Antibody Reactions; D000954:Antigens, Surface / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D066246:ErbB Receptors / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D018448:Models, Immunological; D011485:Protein Binding; D019859:Proto-Oncogene Proteins c-met / Q000737:chemistry / Q000276:immunology / Q000378:metabolism
chemical_list: D018033:Antibodies, Bispecific; D000954:Antigens, Surface; D066246:ErbB Receptors; D019859:Proto-Oncogene Proteins c-met
keywords: antibody; antibody engineering; avidity; bispecific antibody; cooperativity; kinetics; mathematical modeling; multifunctional protein