Abstract 3625: Exogenous short-term activation of c-Met and EGFR sensitizes them to kinase inhibitors

Abstract

Abstract Activation of the c-Met and EGFR receptor tyrosine kinases induces brain tumor malignancy and is associated with poor clinical outcome of brain tumor patients. Consequently, c-Met and EGFR are promising targets for the therapy of brain tumors and clinically applicable inhibitors of these receptors have been developed by biotechnology and pharmaceutical companies. We tested the effects of a specific and potent c-Met kinase inhibitor (PF-2341066) on glioma cells and glioma stem cells. Surprisingly, we found that the inhibitor induced significantly greater cell death when c-Met was shortly pre-activated with its ligand hepatocyte growth factor (HGF). Glioblastoma cells (U87, U373), primary glioblastoma cells (GBM10) and glioblastoma stem cells (1228, 0308) were pre-treated with 20 ng/ml HGF for 2h, 4h, 6h, 8h, 16h or 24h prior to treatment with PF-2341066 (100 nM for established and primary cells and 300 nM for cancer stem cells) for 24 hr. The cells were subsequently assessed for apoptosis using annexin-V flow cytometry. The results showed that the inhibitor induced significantly greater (34-79%) absolute cell death in pre-activated cells than in non-activated cells. The optimal time of pre-activation that achieved greatest sensitization of the receptor to kinase inhibitor-induced cell death was 2-4 hours. Using a similar experimental approach, we also tested the effects of EGFR pre-activation on EGFR inhibitor erlotinib-induced cell death in glioma cells. Glioma cells were pre-treated with EGF (100ng/ml) for 3h, 6h, 16h or 24h prior to treatment with erlotinib (2.5 µM) for 24 hrs and assessment of cell death by annexin V flow cytometry. EGFR pre-activation led to significantly greater (138 %) erlotinib-induced cell death than without pre-activation. Based on the above findings, we hypothesize that short-term exogenous activation of c-Met, EGFR and possibly also other receptor tyrosine kinases can trigger fast oncogene addiction that sensitizes tumor cells to death induced by receptor tyrosine kinase inhibitors. We are currently testing this hypothesis using in vivo glioblastoma animal models. Verification of this new hypothesis would imply that quick short-term activation of tyrosine kinase receptors by bolus delivery of receptor tyrosine kinase ligands would sensitize tumors to kinase inhibitors and therefore improve the efficacy of these inhibitors in cancer therapy. 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 3625.