Capsaicin Exerts Therapeutic Effects by targeting tNOX-SIRT1 Axis and Augmenting ROS-Dependent Cytotoxic Autophagy in Melanoma Cancer Cells
Abstract Background: Although considered a rare form of skin cancer, malignant melanoma has steadily increased internationally and is a main cause of cancer-associated death worldwide. The treatment options for malignant melanoma are very limited. Accumulating data suggest that the natural compound, capsaicin, exhibits preferential anticancer properties to act as a nutraceutical agent. Here, we explored the underlying molecular events involved in the inhibitory effects of capsaicin on the growth of melanoma cells.Methods: The cellular thermal shift assay (CETSA) and isothermal dose response fingerprint (ITDRFCETSA) were utilized to validate the binding of capsaicin with the tumor-associated NADH oxidase, tNOX (ENOX2) in melanoma cells. We also assessed the cellular impact of capsaicin-targeting of tNOX on A375 cells by flow cytometry and protein analysis. The essential role of tNOX in tumor- and melanoma-growth limiting abilities of capsaicin was evaluated in C57BL/6 mice.Results: Our data show that capsaicin directly targets cellular tNOX to inhibit its enzymatic activity and enhance protein degradation capacity. The inhibition of tNOX by capsaicin is accompanied by the attenuation of SIRT1, a NAD+-dependent deacetylase that enhances ULK1 acetylation to induce ROS-dependent autophagy in melanoma cells. Capsaicin treatment of mice implanted with melanoma cancer cells suppressed tumor growth by down-regulating tNOX and SIRT1, which was also seen in an in vivo xenograft study with tNOX-depleted melanoma cells. Conclusions: Together, our findings suggest that tNOX expression is important for the growth of melanoma cancer cells both in vitro and in vivo, and that inhibition of the tNOX-SIRT1 axis contributes to inducting cytotoxic ROS-dependent autophagy in melanoma cells.