Abstract 4888: Decitabine and vorinostat cooperate to sensitize metastatic human colon carcinoma cells to Fas-mediated apoptosis

Abstract

Abstract The death receptor Fas and its physiological ligand, FasL, which is expressed on the surface of cytotoxic T-cells (CTLs), regulate apoptosis of cancerous cells. While normal colon epithelial cells express high levels of Fas, Fas expression is diminished in colon carcinomas. Metastatic colon cancers acquire an apopotosis-resistant phenotype often due to the loss of Fas expression and function. Previous studies have implicated Fas-mediated apoptosis as an important contributor of tumor regression. Therefore, targeting Fas resistance is of critical importance in treating colon cancer through Fas-based cancer therapy and immunotherapy. In this study, we explore whether epigenetic pharmacological agents can restore Fas expression and re-establish sensitivity to Fas-mediated apoptosis in metastatic human colon carcinoma cells. First we determined that the epigenetic drugs Decitabine, a DNA methyltransferase inhibitor, and Vorinostat, a HDAC inhibitor, each are capable of up-regulating Fas expression. When combined, these two inhibitors cooperate to increase Fas expression to an even greater extent than each agent alone. Pre-treatment with decitabine, vorinostat, or both drugs followed by incubation with FasL, was able to overcome resistance to FasL-induced apoptosis. Analysis of bisulfite-modified genomic DNA, isolated from human metastatic colon carcinoma cells revealed that the Fas promoter is sporadically methylated; therefore sensitization of Fas receptor expression on the cell surface by decitabine was unlikely through direct inhibition of Fas promoter meythlation. Although the Fas promoter was not heavily methylated, the promoters for BNIP3 and Bik, which are downstream of Fas signaling, were methylated. After treatment with these pharmacological epigenetic inhibitors, alone or in combination, protein levels of both BNIP3 and Bik were increased. Our data suggest that combined modalities of chemotherapy and Fas-based immunotherapy may be an effective approach for the suppression of colon cancer metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4888. doi:1538-7445.AM2012-4888