Abstract 652: GPX3 promoter hypermethylation predicts platinum sensitivity in colorectal cancer cells.

Abstract

Abstract An estimated 52,000 people will die from colorectal cancer (CRC) in 2012 in the U.S. Unfortunately, these tumors do not respond uniformly to the available chemotherapeutic agents and molecular heterogeneity in these tumors is an important factor in determining their sensitivity to the different agents. Epigenetic regulation of gene expression is a critical determinant of normal and tumor cellular phenotypes. By combining tumors’ epigenetic alterations with existing knowledge of drugs’ mechanisms, specific DNA methylation alterations can serve as predictive biomarkers for the efficacy of particular chemotherapeutic agents which can then direct patients’ treatments for improved outcomes. The glutathione peroxidase family of enzymes is a critical cellular antioxidant system and increased glutathione peroxidase activity has been linked to platinum resistance in tumors such as prostate and ovarian cancer. Using methylation-specific PCR (MSP), we demonstrate that the glutathione peroxidase 3 (GPX3) promoter is hypermethylated in six of nine colorectal cancer cell lines and those lines with methylated GPX3 have significantly decreased GPX3 mRNA expression by real-time polymerase chain reaction (RT-PCR). Importantly, the cisplatin IC50 for the CRC cell lines with methylated GPX3 and thus lower GPX3 expression ranges between 2.5 and 6 micromolar compared to 15-50 micromolar in the cell lines with unmethylated GPX3. Initial studies demonstrate similar findings with oxaliplatin. We also examined primary colorectal cancer xenografts and find that 11 of 42 (26%) have GPX3 promoter hypermethylation, with reduction in GPX3 expression also demonstrated for methylated tumors. Analysis is underway to assess the impact that methylated GPX3 has on these primary tumor samples’ sensitivity to platinum agents. To further define the importance of GPX3 promoter hypermethylation in platinum sensitivity, experiments using azacitidine to demethylate GPX3 in cells with methylated GPX3 will be used to determine if increased platinum sensitivity can be restored. Our studies suggest that epigenetically silenced GPX3 may serve as a valuable predictive biomarker for platinum agent sensitivity. Citation Format: Lorraine Pelosof, Sashidhar Yerram, Nilofer Azad, James Herman. GPX3 promoter hypermethylation predicts platinum sensitivity in colorectal cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 652. doi:10.1158/1538-7445.AM2013-652