The miR‑625‑3p/AXL axis induces non‑T790M acquired resistance to EGFR‑TKI via activation of the TGF‑β/Smad pathway and EMT in EGFR‑mutant non‑small cell lung cancer

Gefitinib is currently the preferred treatment for nonsmall cell lung cancer (NSCLC) patients with epidermal growth factor receptor (EGFR)activating mutation. However, some patients gradually develop acquired resistance after receiving treatment. In addition to secondary T790M mutation, the remaining mechanisms contributing to nonT790M mutations need to be explored. In the present study, NSCLCderived HCC827 and PC9 cells and the corresponding gefitinibresistant cell lines (HCC827GR and PC9GR) were utilized. Nextgeneration DNA sequencing was performed on the HCC827GR and PC9GR cells. Under AXL receptor tyrosine kinase (AXL) knockdown or miR6253p overexpressing conditions, a cell growth inhibition assay was performed to evaluate gefitinib sensitivity. Wound healing and Transwell assays were used to examine the migratory and invasive abilities of the cells. Moreover, we also carried out western blot analysis to detect the altered downstream signaling pathway. Our study revealed markedly decreased miR6253p expression in the HCC827GR cell line, while its overexpression partly reversed gefitinib resistance. Integrated analysis based on Targetscan website showed that AXL can be potentially targeted by miR6253p and we further verified the hypothesis via dualluciferase reporter assays. Mechanistic analysis revealed that TGFbeta1induced EMT may contribute to the miR6253p/AXL axismediated gefitinib resistance. Our data demonstrated that miR6253p contributes to the acquired resistance of gefitinib, which may provide novel insight to combat resistance to EGFRTKIs.