Abstract 3608: Prostaglandin E-2 promotes resistance to oxaliplatin in colorectal cancer cells

Abstract

Abstract Oxaliplatin, a platinum-based DNA crosslinking agent, has been used successfully as a first-line chemotherapeutic agent for the treatment of metastatic colorectal cancer (CRC). However, long-term treatment with oxaliplatin results in resistance in nearly all patients, limiting its therapeutic efficacy. Previous studies have shown that treatment of CRC cells with selective inhibitors of the enzyme Cyclooxygenase-2 (COX-2) leads to the development of drug resistance. One of the terminal products of the COX-2 pathway, prostaglandin E-2 (PGE2), is a pro-inflammatory lipid that has been implicated in colorectal tumorigenesis; however, it is unknown whether PGE2 plays a role in the development of drug resistance. In this study, we have begun to investigate the relationship between PGE2 and oxaliplatin resistance using the human CRC cell lines, HT29 and HCT116. Oxaliplatin-resistant HT29 cells (HT29-OXR) were generated by continuous exposure of parental HT29 cells to increasing concentrations of oxaliplatin over a period of 3 months. We have found that HT29-OXR cells produce significantly higher levels of PGE2 (3-fold increase, p<0.05) compared to the parental HT29 cell line. In addition, we have observed concomitantly elevated levels of the terminal PGE2 synthase, microsomal prostaglandin E synthase-1 (mPGES-1). Furthermore, we have demonstrated that the addition of exogenous PGE2 to both parental HT29 and HCT116 cells significantly (p<0.0001) decreased their sensitivity (IC50) to oxaliplatin, measured by the MTT cell viability assay. These findings suggest that PGE2 promotes resistance to oxaliplatin in CRC cells. FACS analysis showed that co-treatment of HT29 cells with exogenous PGE2 for 24 hours leaded to 27% reduction in oxaliplatin-induced Annexin V staining for early apoptosis, while exogenous PGE2 maintained G2/M arrest and simultaneously reduced the proportion of dead sub-G1 cells by approximately 80.4% in parental HCT116 cells. Our findings reveal a role for PGE2 in oxaliplatin resistance, possibly via regulation of apoptosis, and provide new data suggesting that targeting mPGES-1 may be a useful strategy for overcoming oxaliplatin resistance. Citation Format: Huakang Huang, Daniel W. Rosenberg. Prostaglandin E-2 promotes resistance to oxaliplatin in colorectal cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3608. doi:10.1158/1538-7445.AM2015-3608