Abstract LB055: IBI3001: A potentially first-in-class site-specifically conjugated B7-H3/EGFR bispecific ADC for multiple solid tumors

Abstract B7-H3 and EGFR are both clinically validated TAAs in solid tumors. We previously demonstrated in IBI334 (B7-H3/EGFR bsAb) study that (1) B7-H3 and EGFR are co-expressed in multiple solid tumors; (2) B7-H3-aided EGFR signaling inhibition was significantly more potent than Zalutumumab (EGFR mAb) and Amivantamab (c-met/EGFR bsAb) ; and (3) IBI334 has favorable safety profile in cynomolgus monkey at 120 mg/kg/week. Building on this optimized bispecific antibody, we site-specifically conjugated IBI334 with Exatecan (drug-antibody-ratio = 4) using the clinically validated SyntecanE platform. The resulting bispecific ADC, IBI3001, has multiple mechanism of actions: (1) enhanced EGFR signaling blockage; (2) EGFR- and B7-H3-aided payload internalization and cytotoxicity; and (3) bystander killing effects of ADC. More importantly, the optimized B7-H3 arm not only enhances the EGFR signaling blockage but also reduces EGFR on-target toxicities. IBI3001 demonstrated potent in vitro cytotoxicity in all B7-H3LowEGFRLow, B7-H3HighEGFRLow, B7-H3LowEGFRHigh and B7-H3HighEGFRHigh cancer cells across multiple solid tumors, including lung cancer, colorectal cancer, pancreatic cancer, breast cancer, head and neck cancer, and stomach cancer. In addition, it had strong bystander effects, killing both EGFR+ B7-H3+ cancer cells and EGFR- B7-H3- cancer cells. All in vitro studies were further validated in vivo with robust tumor growth inhibition in NCI-H508 (colorectal cancer), JIMT-1 (breast cancer), BxPC3 (pancreatic cancer) and NCI-1975 (lung cancer) xenograft models. IBI3001 has a favorable PK profile in BALB/c mice with the half-life at 282 hours, and is well-tolerated in cynomolgus monkeys up to 90 mg/kg/week. In conclusion, IBI3001 is a novel bispecific ADC that demonstrated strong anti-tumor efficacy cross multiple solid tumors, and has excellent PK and safety profile. Citation Format: Jian Guan, Xiao Zhang, Weiwei Wu, Lei Cao, Zhengguang Liao, Tianyu Zhu, Chentao Liu, Shuaixiang Zhou, Jia Lu, Ninghuan Li, Nana Luo, Ying Zhang, Kang Dian, Tiong Sun Chia, Bingliang Chen, Kaijie He. IBI3001: A potentially first-in-class site-specifically conjugated B7-H3/EGFR bispecific ADC for multiple solid tumors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr LB055.