Salinomycin Triggers Human Colorectal Cancer HCT116 Cell Death by Targeting Unfolded Protein Responses and Autophagy Pathways

Background: Autophagy and the unfolded protein response (UPR) are important pathways in colorectal tumorigenesis and drug resistance, rendering them as potential therapeutic targets for treating this cancer. As an ionophoric polyether antibiotic, salinomycin has anti-cancer effects and overcomes drug resistance in cancer cells. Considering the minimal information on the molecular action mechanism of salinomycin in colorectal cancer (CRC), this study was designed to investigate the effect of this compound on autophagy and UPR pathways in CRC cells. Methods: The in vitro cytotoxicity of salinomycin on CRC cell line HCT116 was determined using the MTT assay by treating the cells with different concentrations of salinomycin for 24 and 48 h. The gene expression analysis of three main autophagy biomarkers (Beclin1, LC3, and P62) and two UPR biomarkers (XBP-1s and CHOP) was performed using quantitative real-time polymerase chain reaction (RT-PCR). Data were analyzed with GraphPad Prism 8 software. Results: Salinomycin had cytotoxic effects on HCT116 cells in a time- and dose-dependent manner. The expression analysis of the UPR and autophagy-related genes showed UPR activation at both 24 h and 48 h (increase of XBP-1s and CHOP), autophagy activation at 24 h (increase of Beclin 1, LC3II, and decrease of P62), and autophagy flux inhibition at 48 h (increase of Beclin 1, LC3II and P62). Conclusion: The anti-cancer activity of salinomycin against the HCT116 cell line seems to be through triggering cell death by targeting UPR and autophagy pathways. Further studies are required to confirm our results.