Abstract 1730: Transient PI3K inhibition induces apoptosis and overcomes HGF-mediated resistance to EGFR-TKIs in EGFR mutant lung cancer

Abstract

Abstract Purpose: Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), such as gefitinib and erlotinib, show favorable response to EGFR mutant lung cancer. However, the responders acquire resistance almost without exception. We recently reported that hepatocyte growth factor (HGF) induces EGFR-TKI resistance by activating MET which restores downstream MAPK-ERK1/2 and PI3K-Akt signaling. The purpose of this study was to determine whether inhibition of PI3K, a downstream molecule of both EGFR and MET, could overcome HGF-mediated EGFR-TKI resistance in EGFR mutant lung cancer cells, PC-9 and HCC827. Experimental Design: We explored therapeutic effect of a class I PI3K inhibitor PI-103 on HGF-induced EGFR-TKI resistance in vitro and in vivo. Results: Unlike gefitinib or erlotinib, continuous exposure with PI-103 inhibited proliferation of PC-9 and HCC827 cells, even in the presence of HGF. On the other hand, in gefitinib-resistant xenograft model using PC-9 cells mixed with HGF high producing fibroblasts, PI-103 monotherapy did not inhibit tumor growth. However, PI-103 combined with gefitinib successfully regressed gefitinib-resistant tumor. In vitro experiments considering short half life of PI-103 reveal that transient exposure of PI-103 combined with gefitinib caused sustained inhibition of Akt phosphorylation, but not ERK1/2 phosphorylation, resulting in induction of tumor cell apoptosis even in the presence of HGF. Conclusions: These results indicate that transient blockade of PI3K-Akt pathway by PI-103 and gefitinib could overcome HGF-mediated resistance to EGFR-TKIs by inducing apoptosis, further suggesting usefulness of double blockade of PI3K-Akt signaling at upstream (EGFR) and downstream (PI3K) for more successful treatment of EGFR mutant lung cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1730. doi:10.1158/1538-7445.AM2011-1730