Melatonin promotes apoptosis of oxaliplatin-resistant colorectal cancer cells through inhibition of cellular prion protein

Background/Aim: Drug resistance restricts the efficacy of chemotherapy in colorectal cancer. However, the detailed molecular mechanism of drug resistance in colorectal cancer cells remains unclear. Materials and Methods: The level of cellular prion protein (PrP^C) in oxaliplatin-resistant colorectal cancer (SNU-C5/Oxal-R) cells was assessed. Results: PrP^C level in SNU-C5/Oxal-R cells was significantly increased compared to that in wild-type (SNU-C5) cells. Superoxide dismutase and catalase activities were higher in SNU-C5/Oxal-R cells than in SNU-C5 cells. Treatment of SNU-C5/Oxal-R cells with oxaliplatin and melatonin reduced PrP^C expression, while suppressing antioxidant enzyme activity and increasing superoxide anion generation. In SNU-C5/Oxal-R cells, endoplasmic reticulum stress and apoptosis were significantly increased following co-treatment with oxaliplatin and melatonin compared to treatment with oxaliplatin alone. Conclusion: Co-treatment with oxaliplatin and melatonin increased endoplasmic reticulum stress in and apoptosis of SNU-C5/Oxal-R cells through inhibition of PrP^C, suggesting that PrP^C could be a key molecule in oxaliplatin resistance of colorectal cancer cells.