Activated Akt Prevents Antitumor Activity of Gefitinib in Renal Cancer Cells

ObjectivesTo investigate the mechanism of gefitinib resistance in renal cell carcinoma (RCC) cells. Although epidermal growth factor receptor (EGFR) is frequently overexpressed in RCC, gefitinib, a tyrosine kinase inhibitor of EGFR, has only a limited antitumor effect on RCC.MethodsThe effects of gefitinib on the activation status of EGFR and kinases downstream in its signaling cascade were examined in three gefitinib-resistant RCC cell lines: SKRC-44, KU20-01, and 786-O. The changes in signaling cascades and cell survival that were induced by gefitinib in combination with either the phosphatidylinositol 3-kinase inhibitor LY294002 or the knockdown of Akt expression by transient transfection with Akt small interfering RNA were examined in 786-O cells.ResultsGefitinib alone did not significantly reduce cell viability in any of the examined cell lines. Although in each line, the phosphorylation of EGFR and extracellular signal-regulated kinase was inhibited by 0.1 μM gefitinib, the phosphorylation of Akt was constitutive and was not inhibited by even 10 μM gefitinib. In 786-O cells, the phosphorylation of both extracellular signal-regulated kinase and Akt was inhibited by gefitinib used in combination with either LY294002 or the knockdown of Akt expression, and the viability of 786-O cells was suppressed significantly by gefitinib used in combination with LY294002 (P < .0001) or Akt small interfering RNA (P = .0044).ConclusionsConstitutively activated Akt might prevent the antitumor efficacy of gefitinib in renal cell carcinoma, and the therapeutic effectiveness of gefitinib might be improved by inhibiting Akt activation.