Abstract 830: ISU104, a fully human antibody targeting a specific epitope on the ErbB3, displays potent inhibition of tumor growth in multiple xenograft tumor models

Abstract Members of the epidermal growth factor receptor family (ErbB family) are known as potent mediators in the development and progression of cancer. Activated ErbBs recruit various adaptors and signaling molecules through the phosphorylated cytoplasmic domain, which further leads to activation of downstream oncogenic signaling pathways. There are approved therapeutics for ErbB1 (EGFR) and ErbB2 (HER2) in the treatment of human cancers, while monoclonal antibodies targeting ErbB3 are just undergoing clinical trials. ISU104 is a fully human anti-ErbB3 antibody isolated from phage display antibody library. We performed the hydrogen/deuterium exchange mass spectrometry (HDX-MS) analysis with ErbB3 extracellular domain and ISU104, and that indicated that ISU104 mainly binds with domain 3 and weakly interacts with domain 1 of ErbB3. The binding property of ISU104 induced dose-dependent inhibition of ligand (heregulin, HRG) binding, blocking of dimerization of ErbB3 with other ErbBs and subsequently inactivated the downstream signaling of ErbB3. Also, ISU104 occasioned internalization of ErbB3 from plasma membrane, and downregulated the expression level of ErbB3. We demonstrated the biologic effect of ISU104 in several ErbB3-expressing cancer cell lines, including head and neck squamous cell carcinoma (HNSCC) and breast cancers. ISU104 completely suppressed the HRG-induced ErbB3/AKT phosphorylation, reduced cell proliferation and survival. Next, we evaluated efficacy of ISU104 in multiple xenograft models. Mice were treated with 10 mg/kg of ISU104 twice weekly. ISU104 regressed tumor growth in FaDu HNSCC model, and showed more than 70% tumor growth inhibition (TGI) in CAL27 (HNSCC), BxPC3 (pancreatic cancer), MDA-MB-468 (breast cancer), A549 (skin cancer), and BT474 (breast cancer) models. Our results suggest that ISU104 effectively blocks activation of ErbB3 and the downstream pathway by ErbB3, and may provide clinical benefit to ErbB3-activated patients. Citation Format: Miyoung Kim, Youngmi Hur, Sohyeon Seo, Heynjeong Lim, Kyungyong Kim, Youngsoo Sohn, Seung-Beom Hong, Donggoo Bae. ISU104, a fully human antibody targeting a specific epitope on the ErbB3, displays potent inhibition of tumor growth in multiple xenograft tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 830.