Manipulation of Cell-Type Selective Antibody Internalization by a Guide-Effector Bispecific Design

摘要

Cell-type-specific intracellular payload delivery is desired for antibody-based-targeted therapy development. However, tumor-specific internalizing antigens are rare to find, and even rarer for those that are expressed at uniformly high levels. We constructed a bispecific antibody that is com posed of a rapidly internalizing antibody binding to a tumor-associated antigen, ephrin receptor A2 (EphA2), and a nonintemalizing antibody binding to a highly expressed tumor-associated antigen, activated leukocyte cell adhesion molecule (ALCAM). We found that the overall internalization property of the bispedfic is profoundly impacted by the relative surface expression level (antigen density ratio) of EphA2 versus ALCAM. When the EphA2-to-ALCAM ratio is greater than a threshold level (1:5), the amount of the bispedfic taken into the tumor cell exceeds what is achieved by either the monoclonal internalizing antibody or a mixture of the two antibodies, showing a bispeci ticdependent amplification effect where a small amount of the internalizing antigen EphA2 induces internalization of a larger amount of the noninternalizing antigen ALCAM. When the ratio is below the threshold, EphA2 can be rendered nonintemalizing by the presence of excess ALCAM on the same cell surface. We constructed a bispedfic antibody-drug conjugate (ADC) based on the above bispecific design and found that the bispecific ADC is more potent than monospecific ADCs in tumor cell killing both in vitro and in vivo. Thus, the internalizing property of a cell surface antigen can be manipulated in either direction by a neighboring antigen, and this phenomenon can be exploited for therapeutic targeting.