Co-targeting autophagy and NRF2 signaling triggers mitochondrial superoxide to sensitize oral cancer stem cells for cisplatin-induced apoptosis

• Published in: Free radical biology & medicine 2023-10, Vol.207, p.72-88
• Main Authors: Praharaj, Prakash P., Singh, Amruta, Patra, Srimanta, Bhutia, Sujit K.
• Format: Article
• Language: English
• Subjects: Apoptosis; Autophagy; Cancer stem cell; mtROS; NRF2; Oral cancer
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2023.07.008

Cancer stem cell (CSC) populations are regulated by autophagy, which in turn modulates tumorigenicity and malignancy. In this study, we demonstrated that cisplatin treatment enriches the CSCs population by increasing autophagosome formation and speeding up autophagosome-lysosome fusion by recruiting RAB7 to autolysosomes. Further, cisplatin treatment stimulates lysosomal activity and increases autophagic flux in oral CD44+ cells. Interestingly, both ATG5- and BECN1-dependent autophagy are essential for maintaining cancer stemness, self-renewal, and resistance to cisplatin-induced cytotoxicity in oral CD44+ cells. Moreover, we discovered that autophagy-deficient (shATG5 and/or shBECN1) CD44+ cells activates nuclear factor, erythroid 2 like 2 (NRF2) signaling, which in turn reduces the elevated reactive oxygen species (ROS) level enhancing cancer stemness. Genetic inhibition of NRF2 (siNRF2) in autophagy-deficient CD44+ cells increases mitochondrial ROS (mtROS) level, reducing cisplatin-resistance CSCs, and pre-treatment with mitoTEMPO [a mitochondria-targeted superoxide dismutase (SOD) mimetic] lessened the cytotoxic effect enhancing cancer stemness. We also found that inhibiting autophagy (with CQ) and NRF2 signaling (with ML-385) combinedly increases cisplatin cytotoxicity, thereby suppressing the expansion of oral CD44+ cells; this finding has the potential to be clinically applicable in resolving CSC-associated chemoresistance and tumor relapse in oral cancer. A proposed mechanism by which CD44+ cells accelerate autophagic flux by increasing autophagosome formation and lysosomal activity. Autophagy-deficient CD44+ cells preserve cancer stemness by activating NRF2 signaling to keep mtROS levels low. Moreover, combined inhibition of autophagy and NRF2 signaling generates excessive mitochondrial superoxide which triggers apoptosis in oral CD44+ CSCs. [Display omitted] •Cisplatin treatment increases autophagosome biogenesis and autophagosome-lysosome fusion in oral CD44+ CSCs.•Oral CD44+ cells exhibit increased lysosomal activity and induce autophagic flux in response to cisplatin treatment.•ATG5-and BECN1-dependent autophagy protects oral CD44+ cells from cisplatin-induced apoptosis and maintains stemness.•NRF2 signaling limits mitochondrial superoxide production in autophagy-deficient oral CD44+ cells exposed to cisplatin.•CQ and ML-385 improve the therapeutic efficacy of cisplatin in oral CD44+ cells by inhibiting autophagy and NRF2 signaling.