Abstract 1209: Istiratumab (MM-141), a bispecific antibody targeting IGF-1R and ErbB3, inhibits pro-survival signaling in vitro and potentiates the activity of standard of care chemotherapy in vivo in ovarian cancer models

Insulin-like growth factor receptor 1 (IGF-1R) signaling has been implicated in the pathogenesis of ovarian cancer. However, clinical trials evaluating monospecific IGF-1R inhibitors have demonstrated limited clinical efficacy. Our data indicate that ErbB3, a member of the ErbB receptor tyrosine kinase family, can activate pro-survival AKT signaling in response to IGF-1R blockade and may represent a potential escape route in the development of resistance to therapy. Istiratumab (MM-141), an IGF-1R and ErbB3 directed bispecific antibody, inhibits ligand activation of these signaling pathways and degrades IGF-1R and ErbB3 receptor-containing complexes, leading to inhibition of downstream pro-survival signaling. Here we tested the activity of istiratumab, alone and in combination with chemotherapy, in in vitro and in vivo models of ovarian cancer. Anti-proliferative activity of istiratumab monotherapy was evaluated in a panel of ovarian cancer cell lines in vitro. The effects of istiratumab and the ligands IGF-1 and heregulin on IGF-1R- and ErbB3-mediated survival signaling were tested by ELISA and immunoblotting. Co-treatment assays with istiratumab and chemotherapy investigated mechanisms of synergy and additivity. Anti-tumor activity of istiratumab, alone and in combination with chemotherapy, was tested in in vivo ovarian xenograft tumor models. Our results indicated that istiratumab monotherapy inhibits ovarian cancer cell line proliferation in vitro. In addition, istiratumab blocked ligand-mediated resistance to chemotherapy. Co-treatment of istiratumab, ligands or chemotherapy indicated a strong correlation between drug activity and IGF-1R expression. Furthermore, co-treatment of chemotherapies and ligands potentiated AKT activation, which was inhibited by istiratumab. In vivo studies showed that istiratumab potentiates the activity of chemotherapy in ovarian xenograft tumor models. Our findings demonstrate that co-inhibition of IGF-1R and ErbB3 signaling with istiratumab can potentiate standard of care chemotherapies in ovarian tumor models and warrant further investigation of istiratumab as a potential therapy for ovarian cancer patients. Citation Format: Michael D. Curley, Gege Tan, Isabel Yannatos, Adam Camblin, Sergio Iadevaia, Chrystal Louis, Alexey Lugovskoy. Istiratumab (MM-141), a bispecific antibody targeting IGF-1R and ErbB3, inhibits pro-survival signaling in vitro and potentiates the activity of standard of care chemotherapy in vivo in ovarian cancer models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1209.