3H-3000, AN FGFR2B-SPECIFIC MONOCLONAL ANTIBODY, SHOWS SUPERIOR TUMOR KILLING IN VIVO

Abstract Background and significance Fibroblast growth factor receptor 2b (FGFR2b), a splice isoform of FGFR2, is found to overexpress across multiple cancers types and promotes dysregulated tyrosine kinase activation, resulting in tumor cell proliferation and unchecked malignancy. Cohort studies reveal FGFR2b overexpression and/or amplification in Gastric cancer (~30.2%), squamous non-small cell lung cancer (~20.8%), and endometrial carcinoma (~40%). About 80–85% patients who have advanced HER2-negative gastro-esophageal cancer undergoes approximately 12-14 months of median overall survival (mOS). Thus, there is an urgent need for novel and effective molecular targeted agents. With the recent advancement of mechanistic studies, however, FGFR2b is becoming the optimal target of multiple modalities such as mAb, bispecifics, or antibody-drug conjugate. Bemarituzumab, a FGFR2b blocking antibody, developed by Five Prime clinically demonstrates the safety of FGFR2b target and exhibits preliminary efficacy in advanced GE/GEJ adenocarcinoma patients with overexpression of FGFR2 in at least 5% or 10% of tumor cells. 3H Pharmaceuticals developed a FGFR2b-specific mAb, 3H-3000, of high-affinity, differentiated epitope and enhanced ADCC effect for FGFR2b-overexpressing gastric cancer or other FGFR2b-associated cancer types. In the meantime, we will also explore the versatility of this mAb in other format and in the combination with small molecules that will bring about a wider therapeutic spectrum. Method and Result 3H-3000 is a humanized IgG1kappa antibody with a single digit nM affinity for FGFR2b and no binding to other FGFR2 isoforms. 3H-3000 shows potent proliferation-inhibitive effects on FGFR2b-overexpressing human tumor cells. In gastric cancer cell line SNU16, 3H-3000 can fully inhibit FGF7-induced phosphorylation of FGFR2b and SNU16 proliferation in vitro. On top of signaling blocking, we strongly believe efficacy of antibody-dependent cell cytotoxicity (ADCC) is another viable mechanism for growth factor-targeting therapy. Therefore, 3H-3000 was further engineered with a 20-fold ADCC enhancement which is validated through a CD16-F158 variant-based reporter system. In FGFR2b-overexpressing human gastric cancer SNU16 or OCUM-2M xenograft model, 3H-3000 was shown to inhibit tumor growth and even induce regression, which is rather unexpected given the relative low expression of FGFR2b on SNU16 and none of the competitors exhibit similar phenomenon. With potent efficacy of tumor inhibition and killing, and excellent biophysical characteristics and developability of 3H-3000, we expect to push the molecule to clinical development in the middle of 2024. Conclusion 3H-3000 is a potent FGFR2b blocker with well-defined ADCC efficacy enhancement. It demonstrates strong blocking activity of FGFR2 signaling, strikingly enhanced ADCC activity in vitro and potent efficacy of tumor inhibition in vivo. These data strongly support its clinical development in FGFR2b-overexpressing cancers. In parallel, 3H Pharmaceuticals are also developing FGFR2- selectively tyrosine kinase inhibitors targeting FGFR2 mutations or fusion. We propose a combination of small molecule FGFR2 inhibitors and mAb of FGFR2b specificity will significantly broaden the therapeutic spectrum of heterogenous tumors where mechanism is centered around FGFR2b alteration including mutation, fusion, and overexpression.