AbstractNovel Multispecific Antibody with Superior Activity in TNBC INTRO: TNBC (Triple Negative Breast Cancer) has a diverse etiology and high unmet need. We created a novel multispecific antibody with unique 2:1:1 ratio of EGFR:cMet:VEGF binding arms with excellent activity against TNBC. METHOD: Multiple in vitro EGFR & cMet signaling pathway inhibition, proliferation inhibition, and ADCC, ADCP, and CDC were conducted. Various in vivo studies using the TNBC cell lines (MDA-MB-468, MDA-MB-231, HCC70, BT20) with diverse levels of EGFR and cMet receptor density levels were tested. RESULTS: Strong tumor growth inhibition was found in multiple TNBC animal models (56% tumor growth inhibition (TGI) in BT20, 26% TGI in HCC70, 62% TGI in MDA-MB-231). Tavo412 demonstrated better activity than comparator molecules in several in vivo models using lung, gastric, and pancreatic cancer cell lines (data not shown). A one month GLP toxicity study in cynomolgus monkeys has been completed with well-expected tolerability and pharmacokinetic profiles. Besides shutting down three important cancer pathways, TAVO412 showed high potency because it also has strong EGFR and VEGF binding at pH 6 in the tumor microenvironment. Moreover, Tavo412 has exemplary Fc effector function engaging the innate immune responses that include ADCC, ADCP, and CDC. There is also a synergistic tumor growth inhibition in the presence of a standard of care molecule such as doxorubicin (61% in HCC70 with TAVO412 + doxorubicin, 66% TGI in BT20 with TAVO412 + doxorubicin, 71% TGI in MDA-MB-231 with TAVO412 + doxorubicin). In addition, gastric, pancreatic, and lung cancer in vivo models showed excellent TGI profiles. CONCLUSIONS: Tavo412 has the potential activity to be a superior multispecific antibody to treat patients with triple negative breast cancer. Phase 1 clinical testing in patients is anticipated in early 2023.Citation Format: Mark Chiu. TAVO412 - A Novel Trispecific cMet x EGFR x VEGF Antibody for Triple Negative Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-24-05.