The role of autophagy in erlotinib‐resistant lung cancer and the synergistic induction of cell death with combination cisplatin and erlotinib treatment by Atg3 modulation

Abstract

ObjectiveErlotinib resistance (ER) in non‐small cell lung cancer (NSCLC) is a major problem clinically. Therefore, in this study we tested whether combination of low dose erlotinib and cisplatin is effective against ER and specifically examined the role of autophagy in ER.MethodsPC9 cells were used to establish erlotinib resistant cells (PC9ER). Cell survival was quantified with Alamar blue assay. LC3II and regulatory proteins of autophagy were measured by western blot. SiRNA was used to modulate protein translation.ResultsCombination of low dose erlotinib‐cisplatin induced synergistic cell death in PC9ER cells and this response was related to a decrease in autophagy. Concordantly, rapamycin increased ER and 3‐MA sensitized cell death response in PC9ER cells. Western blot analysis of autophagy regulatory proteins showed significantly higher baseline levels of LC3II and Atg3 in ER cells as compared to the sensitive PC9 and a significant decrease in Atg3 level was seen with combination treatment. Atg3 SiRNA transfection resulted in the reversal of the resistance in PC9ER cells to both erlotinib‐alone and combination treatment.ConclusionsOur data suggests that ER lung cancer cells are responsive to combined low dose erlotinib‐cisplatin treatment by targeting the baseline over production of Atg3 and that Atg3 is a key regulator/promoter of ER in NSCLC.This research was supported by NIH‐T32 grant.