Upregulation of CYP2S1 by oxaliplatin is associated with p53 status in colorectal cancer cell lines

Oxaliplatin displays a wide spectrum of antitumor activities and is widely used in the treatment of metastatic colorectal cancer (CRC). However, tumor responses to this agent are variable, and the underlying mechanisms are poorly understood. In the present study, oxaliplatin was found to strongly inhibit the growth of HCT116 cells harboring wild-type p53 but to only weakly inhibit SW480 cells, HT29 cells or p53−/− HCT116 cells, which all lack p53 expression. Administration of oxaliplatin significantly induced p53 accumulation and enhanced expression of CYP2S1 in HCT116 cells with wild-type p53. CYP2S1 knockdown conferred a cell survival advantage after oxaliplatin treatment to cells harboring wild-type p53 in vitro and in vivo. Interestingly, enzyme immunoassays, TOPFlash/FOPFlash reporter activity assays and western blotting analysis demonstrated oxaliplatin-mediated downregulation of PGE2 and Wnt/β-catenin signaling in a manner dependent on p53. Moreover, oxaliplatin treatment of mice with subcutaneous tumor xenografts drastically reduced the volume of wild-type p53 HCT116 tumors but had no effect on isogenic p53−/− HCT116 tumors. These results suggest that oxaliplatin exerts its inhibitory effects in human CRC cells via upregulation of CYP2S1 expression in a p53-dependent manner.