Type I Insulin-like Growth Factor Receptor (IGF-1R) is a tyrosine kinase receptor that is activated by binding to IGF-1 and IGF-II ligands; IGF-1R has been shown to play a role in cancer development and progression and therapies targeting IGF-1R have resulted in clinical benefit in cancer patients. Insulin Receptor (IR) which is closely related to IGF-1R, is expressed in normal tissues and tumors, and is expressed as two isoforms, IR-A and IR-B. IR-A exhibits mitogenic activity and is preferentially found in fetal tissue and cancer cells, whereas IR-B regulates glucose metabolism in response to insulin. Both IR isoforms bind insulin, and IR-A also binds IGF-II. Several cancer cell types that express IR-A also overexpress IGF-II, suggesting a possible autocrine loop that enhances tumor survival. Since IGF-1R antibodies bind specifically to IGF-1R and not to IR, IR signaling could represent a potential escape mechanism to antibody treatment through the IR-A pathway. BMS-754807, a small molecule inhibitor with dual activity against IGF-1R and IR, recently entered clinical development. It is anticipated that BMS-754807 can prevent or overcome therapeutic resistance resulting from increased IR-activated signaling. The goal of the presented studies was to demonstrate whether dual IGF-1R/IR inhibition by BMS-754807 may prevent IR-mediated resistance to IGF-1R inhibition.

To test this hypothesis, a human rhabdomyosarcoma cell line, Rh41 expressing IGF-1R, but little IR, was engineered to express either IR-A (Rh41-IR-A) or IR-B (Rh41-IR-B). IR expression was confirmed by PCR analysis of specific IR isoforms. Rh41-IR-A cells showed phosphorylation of IR after stimulation with IGF-II and/or insulin. MAB391, a neutralizing monoclonal antibody to IGF-1R, inhibited the proliferation of parental Rh41 and Rh41-IR-B cells in vitro, but Rh41-IR-A cells exhibited no sensitivity to the IGF-1R mAb. Combination treatment with both IGF-1R and IR antibodies in Rh41-IR-A cells were strongly synergistic, suggesting dual receptor blocking is required for enhanced anti-tumor efficacy. Inhibition of IGF-1R and IR with BMS-754807 showed the same inhibitory activity in Rh41-IR-A cells as was observed in the parental Rh41 cells. Therefore, dual IGF-1R/IR inhibition by BMS-754807 treatment may overcome the ability of cancer cells to utilize the IR-A pathway and provide an advantage over IGF-1R specific antibodies in the treatment of cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 363.