Abstract LB355: ICP-B794, a B7H3-targeting ADC with a novel linker-payload, demonstrated superior anti-tumor activity and large therapeutic window in preclinical studies

Abstract The B7H3-targeted antibody-drug conjugates (ADCs) have shown encouraging clinical efficacy in the treatment of multiple solid tumors. Here, we present a new B7H3-ADC, ICP-B794 created based on a novel linker-payload platform, which was able to overcome the resistant of cancer to DS-7300 in an in vivo xenograft model and exhibited large safety window. The novel ADC linker-payload platform consists of an irreversible connector, a proprietary hydrophilic linker via introducing PEG and a novel highly potent TOPO1 inhibitor payload with low P-gp sensitivity. The B7H3-ADC ICP-B794 based on this novel platform exhibited excellent drug-to-antibody ratio (DAR) value stability and low payload release in human plasma. In the in vitro cellular assays, ICP-B794 demonstrated significantly improved potency than DS-7300. To compare the in vivo anti-tumor efficacy of other B7H3-ADCs with ICP-B794, the linker-payloads from multiple ADC platforms were conjugated to the same B7H3 antibody used in ICP-B794, and the in vivo anti-tumor activities of the resulting ADCs and ICP-B794 were evaluated head-to-head in a xenograft model. ICP-B794 demonstrated superior in vivo efficacy to B7H3-ADCs generated from other platforms in a NCI-H1155 NSCLC xenograft model. The minimum effective dose (MED) of ICP-B794 in the NCI-H1155 CDX model is 0. 15 mg/kg. The NCI-H1155 model is resistant to DS-7300 treatment at 10 mg/kg, however, ICP-B794 treatment at 5 mg/kg following treatment of DS-7300 at 10 mg/kg still achieved complete tumor regression, indicating that ICP-B794 overcame the resistance of lung cancer to DS-7300. In the GLP toxicology study in monkeys, ICP-B794 administered via intravenously injection once every 3 weeks for 3 doses exhibited approximate dose-proportional PK and high stability in circulation. The highest non-severely toxic dose (HNSTD) was defined as 10 mg/kg and no interstitial inflammation or other lung toxicities were observed. The safety window of ICP-B794 HNSTD in monkey vs MED in NCI-H1155 model in mice was 267 folds, which is much higher than reported safety window of DS7300 (40 folds calculated based on HNSTD of 30 mg/kg in monkeys vs MED of 3 mg/kg in NCI-H526 model in mice). In summary, ICP-B794 created based on a novel ADC platform exhibited a favorable preclinical profile, including high potency in the in vitro assays, efficacious at very dose level in the in vivo xenograft models, overcoming resistance to DS-7300 and a larger safety window. ICP-B794 is currently being evaluated in a Phase I first-in-human clinical trial (NCT07136558). Citation Format: Dongliang Mo, Yingxiang Gao, Xiaoyan Wang, Yuan Qian, Hongjuan Zhang, Yingrui Han, Richard Liu, Junjian Liu, Charles Wang, Xiangyang Chen, Bin Zhang. ICP-B794, a B7H3-targeting ADC with a novel linker-payload, demonstrated superior anti-tumor activity and large therapeutic window in preclinical studies abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86 (8Suppl): Abstract nr LB355.