Indexed on: 12 Apr '19Published on: 10 Apr '19Published in: Molecular cancer therapeutics
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 composed of a rapidly internalizing antibody binding to a tumor-associated antigen EphA2 and a non-internalizing antibody binding to a highly expressed tumor-associated antigen ALCAM. We found that the overall internalization property of the bispecific is profoundly impacted by the relative surface expression level (antigen density ratio) of EphA2 vs. ALCAM. When the EphA2 to ALCAM ratio is greater than a threshold level (1:5), the amount of the bispecific taken into the tumor cell exceeds what is achieved by either the monoclonal internalizing antibody or a mixture of the two antibodies, showing a bispecific-dependent amplification effect where a small amount of the internalizing antigen EphA2 induces internalization of a larger amount of non-internalizing antigen ALCAM. When the ratio is below the threshold, EphA2 can be rendered non-internalizing by the presence of excess ALCAM on the same cell surface. We constructed a bispecific 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. Copyright ©2019, American Association for Cancer Research.