Osimertinib, a third-generation epidermal growth factor receptor - tyrosine kinase inhibitor (EGFR-TKI), shows great efficacy in EGFR-mutant non-small cell lung cancer (NSCLC); however, the resistance is inevitable. Osimertinib induces autophagy in NSCLC cells, but the role of autophagy in osimertinib resistance is not clear. We discovered that enhanced autophagy is associated with osimertinib resistance in vitro and in vivo. Inhibition of autophagy enhanced osimertinib cytotoxicity in both osimertinib-resistant and sensitive cells. Moreover, osimertinib-resistant cells exhibited stem cell-like properties, whereas autophagy inhibition decreased the stemness by downregulating the expression of SOX2 and ALDH1A1. Further, we found that knockdown of Beclin-1 inhibited the stem cell-like properties and restored osimertinib cytotoxicity. Osimertinib combined with chloroquine inhibited tumor growth more effectively than alone in xenograft mice. These results reveal that autophagy plays an adverse role in osimertinib cytotoxicity through inducing stem cell-like properties. Combination therapy of EGFR-TKI and autophagy inhibitor could provide a promising strategy to improve osimertinib cytotoxicity.
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