Abstract 4769: Characterization of novel humanized FGFR2b antibody-based ADCs site-specifically conjugated with topoisomerase I inhibitor payload in preclinical tumor models
Authors: Fei Teng, Huanhuan Guo, Hongjun Li, Lizhi Qin, Xinlai Yao, Lei Shi, Yi Gu, Xueming Qian
Journal: Cancer Research (2025)

Abstract Background: Fibroblast growth factor receptor 2 IIIb (FGFR2b), one of the four FGFR family members that encode transmembrane receptor tyrosine kinases, is overexpressed in a variety of cancers, such as gastric/GEJ (29%), esophageal (41%), squamous NSCLC (31%), TNBC (13%), ovarian (40%), endometrial (86%), cervical (80%), colorectal (62%), and cholangiocarcinoma (22%). We have developed a FGFR2b-targeting ADC (TST105) with a novel topoisomerase I inhibitor payload by using glycotransferase mediated site-specific conjugation and characterized its in vitro and in vivo anti-tumor activity in preclinical tumor models. Methods: A novel anti-FGFR2b humanized antibody 38D4 was generated by hybridoma platform. The binding affinity was analyzed by Fortebio Octet, and the selectivity and species cross-reactivity were assessed by ELISA. Antibody internalization was conducted by using Fluoresence Image. Cytotoxicity of TST105 was tested in tumor cell lines with different levels of FGFR2b expression. The bystander effect was assessed in co-culture experiments with the FGFR2b-negative and -positive tumor cells. Anti-tumor efficacy was evaluated in FGFR2b-positive tumor cell line-derived xenograft (CDX) models in mice. Results: 38D4 specifically binds to FGFR2b with a higher affinity than the Bemarituzumab-analog. 38D4 binds with comparable affinity to human, cynomolgus, rat and mouse FGFR2b. Significant internalization of 38D4 was observed after 4 hour and 24 hour-culture at 37°C. In the gastric (SNU-16) and colorectal (SW480-FGFR2b) tumor cell lines, TST105 demonstrated specific killing activity with a potency between 0.3 nM and 0.4 nM in vitro, which was weaker than both 38D4-MMAE and Bema-MMAE (stochastic conjugated). However, a higher potent bystander effect of TST105 than them was observed, indicating the potential to treat tumors with heterogeneous target expression. Furthermore, in SNU-16 xenograft model, which endogenously expresses FGFR2b at a high level, TST105 induced a better anti-tumor efficacy than Bema-MMAE. TST105 had a tumor growth inhibition of 91.25% and overall response rate (ORR, 50% reduction of tumor volume from baseline) of 70% at 3 mg/kg QW, while Bema-MMAE only reduced tumor growth of 48.32% with no ORR. The similar superior tumor regression efficacy of TST105 was also observed in colorectal tumor model SW480-FGFR2b. This differentiation may be contributed by the glycotransferase site-specific conjugation, which can eliminate Fc function, thus reduces the non-specific endocytosis in normal cells and leads to ADC enrichment in the FGFR2b-positive tumors. Conclusions: FGFR2b ADC TST105 demonstrated the high potency, strong anti-tumor activity and bystander effect in the preclinical studies, which support further investigations of TST105 in FGFR2b positive solid tumors. Citation Format: Fei Teng, Huanhuan Guo, Hongjun Li, Lizhi Qin, Xinlai Yao, Lei Shi, Yi Gu, Xueming Qian. Characterization of novel humanized FGFR2b antibody-based ADCs site-specifically conjugated with topoisomerase I inhibitor payload in preclinical tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4769.