Abstract 4458: EGFR endocytosis is associated with susceptibility to gefitinib in lung cancer cells with wild-type EGFR.
Authors: Jo Ukhyun , Whang Young Mi , Sung Jae Sook , Park Kyong Hwa , Kim Seung Tae , Kim Yeul Hong 
Published: August 2014

Abstract
Although epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) is a rational targeted drug with dramatic survival benefit in lung cancer, susceptibility to the drug is restricted in lung cancer with activating mutations of EGFR. Nevertheless, the EGFR-TKI still remains an attractive anticancer drug in lung cancer with wild-type EGFR (wtEGFR). Therefore, in this study, we aimed to investigate unknown mechanism which can contribute to response of the EGFR targeted therapy using gefitinib, a well-known EGFR-TKI, in eight lung cancer cells with wtEGFR. We first examined differential effects of gefitinib on cell survival, morphology, motility, cell cycle and EGFR signaling between the TKI-sensitive and -resistant cells. As a result, although the TKI-resistant cells did not show any changes in cell phenotype by gefitinib treatment, phosphorylation of EGF induced EGFR and downstream effectors was inhibited by the drug treatment as if those in the TKI-sensitive cells. Additionally, we found difference in cellular distribution of EGF induced EGFR after gefitinib treatment between the TKI-sensitive and -resistant cells and it was associated with EGFR endocytosis. Based on our results, we next investigated that regulation of EGFR endocytosis could affect on the response of gefitinib in lung cancer cells with wtEGFR. Inhibition of EGFR endocytosis by combination treatment with gefitinib and two endocytosis inhibitors, dynasore and dynole 34-2, led to significantly decreased cell viability in the TKI-resistant cells compared with treatment of these drugs alone. Moreover, the reduced cell survival after the combination treatment was concerned with increased apoptotic cell death, accompanying by elevated cleavage of poly ADP ribose polymerase (PARP) and decreased myeloid cell leukemia-1 (Mcl-1), X-linked inhibitor of apoptosis protein (XIAP), Survivin and Livin among anti-apoptotic proteins. In addition, we found differentially expressed Rab25, a member of the RAS superfamily of small GTPases, between the TKI-sensitive and-resistant cells through genome-wide gene expression analysis. The expression status of Rab25 was partially associated with response of gefitinib in lung cancer cells with wtEGFR. Furthermore, the silencing of Rab25 in the TKI-sensitive cells with its normal expression reversed sensitivity to gefitinib treatment. In conclusion, our results provided molecular evidences that EGFR endocytosis might contribute to cell survival and response to the EGFR-TKI as a bypass survival mechanism in lung cancer with wtEGFR. Thus, targeting EGFR endocytosis could help us to overcome therapeutic limitation of EGFR-TKI in lung cancer with wtEGFR and Rab25 expression may be an important tool for predicting efficacy of the drug treatment.
Citation Format: Ukhyun Jo, Young Mi Whang, Jae Sook Sung, Kyong Hwa Park, Seung Tae Kim, Yeul Hong Kim. EGFR endocytosis is associated with susceptibility to gefitinib in lung cancer cells with wild-type EGFR. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4458. doi:10.1158/1538-7445.AM2013-4458