Abstract 6365: The bispecific antibody KA-3008, targeting both EGFR and B7H3, increases internalization and minimizes on-target, off-tumor toxicity

Abstract EGFR and B7H3 are highly expressed in various solid tumors, as well as in different normal tissues. Targeting EGFR or B7H3 alone with inhibitory monoclonal antibodies or antibody-drug conjugates (ADCs) may result in on-target, off-tumor toxicity. In this study, we developed a bispecific antibody (BsAb) named KA-3008, targeting both EGFR and B7H3 using our common light chain antibody discovery platform. KA-3008, in IgG1 format, features a regular antibody structure with an identical light chain, developed through knob-into-hole technology. Compared to its parent antibodies, its affinities for both EGFR and B7H3 decrease by more than ten times. It binds to cell lines expressing EGFR or B7H3 alone with an EC50 of more than 10nM, while it binds to cell lines expressing both EGFR and B7H3 with an EC50 of less than 1nM. KA-3008 also blocks the binding of EGF to EGFR and increases internalization when binding to both EGFR and B7H3 compared to binding to EGFR or B7H3 alone. In human tumor mouse models, KA-3008 effectively suppresses the growth of NCI-H1568 tumors expressing both EGFR and B7H3, but does not affect the growth of MS751 tumors that only highly express EGFR with low expression of B7H3. Additionally, KA-3008 has a half-life of more than five days in the blood of Balb/c mice. Finally, we assessed the developability of this BsAb with different treatments such as high concentration, low pH, repeated freezing and thawing, and high temperature, and KA-3008 shows neither aggregation nor degradation. In conclusion, the BsAb KA-3008, developed with our common light chain antibody discovery platform, is stable and holds potential for the development of ADCs targeting both EGFR and B7H3. Citation Format: Guojin Wu, Li Ding, Hao Peng, Feng Hao, Feng He, Jinying Ning. The bispecific antibody KA-3008, targeting both EGFR and B7H3, increases internalization and minimizes on-target, off-tumor toxicity abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6365.