Huang M.-H.JIH-HSIANG LEEChang Y.-J.Tsai H.-H.Lin Y.-L.Lin A.M.Y.CHIH-HSIN YANG2020-05-262020-05-2620131574-7891https://www.scopus.com/inward/record.uri?eid=2-s2.0-84872491067&doi=10.1016%2fj.molonc.2012.09.002&partnerID=40&md5=9dce309fff85e9326ab252301893ceachttps://scholars.lib.ntu.edu.tw/handle/123456789/495050Lung adenocarcinoma cells harboring epidermal growth factor receptor (EGFR) mutations are sensitive to EGFR tyrosine kinase inhibitors (TKIs), including gefitinib. Acquired resistance to EGFR-TKIs develops after prolonged treatments. The study was prompt to explore effective strategies against resistance to EGFR-TKIs. We established gefitinib resistant PC-9 cells which harbor EGFR exon 19 deletion. Known mechanisms for intrinsic or acquired EGFR-TKI resistance, including KRAS mutation, HER2 mutation, EGFR T790M mutation and MET gene amplification, were studied, and we did not observe any known mechanisms for intrinsic or acquired resistance to EGFR-TKIs in the resistant cells. In the parental PC-9 cells, labeled as PC-9/wt, gefitinib completely inhibited EGF-induced phosphorylation of EGFR, AKT and ERK. Gefitinib inhibited EGFR phosphorylation, but was unable to block EGF-induced phosphorylation of ERK in resistant cells, labeled as PC-9/gef cells, including PC-9/gefB4, PC-9/gefE3, and PC-9/gefE7 subclones. We detected NRAS Q61K mutation in the PC-9/gef cells but not the PC-9/wt cells. MEK inhibitors, either AZD6244 or CI1040, inhibited ERK phosphorylation and sensitized gefitinib-induced cytotoxicity in PC-9/gef cells. Whereas MEK inhibitors or gefitinib alone did not activate caspases in PC-9/gef cells, combination of gefitinib and AZD6244 or CI1040 induced apoptosis. Our in vivo studies showed that gefitinib inhibited growth of PC-9/wt xenografts but not PC-9/gef xenografts. Furthermore, combination of a MEK inhibitor and gefitinib inhibited growth of both PC-9/wt xenografts and PC-9/gefB4 xenografts. To conclude, persistent activation of ERK pathway contributes to the acquired gefitinib-resistance. Combined treatment of gefitinib and MEK inhibitors may be therapeutically useful for acquired gefitinib-resistance lung adenocarcinoma cells harboring EGFR mutations. ? 2012 Federation of European Biochemical Societies.[SDGs]SDG32 (2 chloro 4 iodoanilino) n cyclopropylmethoxy 3,4 difluorobenzamide; caspase; epidermal growth factor receptor; epidermal growth factor receptor 2; gefitinib; K ras protein; methionine; mitogen activated protein kinase inhibitor; protein kinase B; scatter factor receptor; selumetinib; threonine; animal experiment; animal model; apoptosis; article; cancer growth; controlled study; cytotoxicity; drug inhibition; exon; gene amplification; gene deletion; gene mutation; genetic analysis; human; human cell; in vivo study; lung adenocarcinoma; male; mouse; nonhuman; priority journal; protein phosphorylation; tumor xenograft; Western blottingjournal article10.1016/j.molonc.2012.09.002231027282-s2.0-84872491067