Novel two mechanisms for acquired EGFR-TKI resistance in lung cancer cells harboring EGFR activating mutation

Abstract

EGF receptor (EGFR) tyrosine kinase inhibitors, including gefitinib and erlotinib, exert potent therapeutic efficacy in non-small cell lung cancers (NSCLC) harboring EGFR-activating mutations. However, most patients ultimately develop resistance to these drugs. Here, we report two kinds of mechanisms of acquired resistance to EGFR tyrosine kinase inhibitors. In this study, we established gefitinib or erlotinib-resistant NSCLC cells from PC-9 cell line harboring del EGFR mutation. In gefitinib-resistant lung cancer cells, they showed a marked downregulation of PTEN expression and increased Akt phosphorylation. Knockdown of PTEN expression using small interfering RNA specific for PTEN in PC-9 cells resulted in drug resistance to gefitinib and erlotinib. Reduced PTEN expression was also observed in tumor samples from patients with gefitinib-refractory NSCLC. On the other hand, in erlotinib-resistant lung cancer cells, they showed marked expressions of Src, integrin beta 1, alpha 2, and alpha 5 along with enhanced cell adhesion activity. RNAi-mediated silencing of integrin beta 1 restored erlotinib sensitivity and reduced activation of Src and Akt after erlotinib treatment. Increased expression of integrin beta 1, alpha 5, and/or alpha 2 was also observed in tumor samples from patients with lung cancer treated with erlotinib and/or gefitinib. Together, we present our novel two mechanisms, PTEN loss and integrin beta 1/Src activation, involving acquired resistance to EGFR TKI in lung cancer cells. Our findings suggested that acquired Akt activation by a variety of ways contributes to gefitinib and erlotinib resistance in NSCLC.