Abstract 4945: Targeting ErbB3-addicted cancers across the HER2 spectrum

ErbB3 is a critical activator of phosphoinositide 3-kinase (PI3K) signaling in EGFR-, HER2-, and MET-addicted cancers, and ligand-driven activation of ErbB3 is a prominent method by which cancers become resistant to targeted inhibitors of ErbB signaling, as well as anti-hormonal and chemotherapeutic agents. With the goals of inhibiting survival signaling in cancer cells, delaying the onset of resistance to standard-of-care therapies, and re-sensitizing cancer cells to prior therapies, we developed an anti-ErbB3 monoclonal antibody, MM-121, that effectively blocks ligand-dependent activation of ErbB3 and induces internalization and degradation of the receptor. The activity of single-agent MM-121 was examined in xenograft models and a machine-learning algorithm was developed that accurately predicts which preclinical models of cancer will respond to MM-121 based on five protein-based biomarkers. By simulating ErbB3 inhibition using a computational model of ErbB signaling, we predicted that a bispecific molecule that docks onto HER2 and subsequently binds to ErbB3 would effectively block ErbB3-driven signaling in HER2-amplified tumors. We therefore developed a bispecific antibody comprising two human scFv antibodies linked by a modified form of human serum albumin. The resulting molecule, MM-111, forms a trimeric complex with HER2 and ErbB3, effectively inhibiting ErbB3 signaling and demonstrating antitumor activity in preclinical models that are dependent on HER2 overexpression. Both MM-121 and MM-111 are now in early stages of clinical development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4945. doi:1538-7445.AM2012-4945