Autophagy inhibition facilitates erlotinib cytotoxicity in lung cancer cells through modulation of endoplasmic reticulum stress

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have revolutionized the treatment for non-small cell lung cancer patients, but acquired resistance limit the efficiency of this treatment. As a homeostatic cellular recycling mechanism, autophagy has been proposed to participate in the EGFR-TKI resistance. However, the role of autophagy in lung cancer treatment and the underlying mechanisms have not been clarified. In this study, we found the sensitivity to erlotinib, a well-used EGFR-TKI, was correlated with basal autophagy level. Erlotinib was able to induce autophagy not only in TKI-sensitive, but also TKI-resistant cancer cells. Inhibition of autophagy significantly enhanced cytotoxicity of erlotinib in TKI-resistant cancer cells via modulation of endoplasmic reticulum (ER) stress induced apoptosis. In this process, CCAAT/enhancer binding protein homologous protein (CHOP) acted as an executioner. Downregulation of CHOP with siRNA blocked the autophagy inhibition and erlotinib co-treatment induced apoptosis and prevented cancer cells from this co-treatment-induced cell death. Our findings suggest that autophagy inhibition overcomes erlotinib resistance through modulation of ER stress mediated apoptosis.