Abstract 4925: Promoter methylation of RASSF1A Tumor Suppressor Gene Modulates the Effect of Microtubule-Targeting Agent, docetaxl, in Breast Cancer

Abstract

Abstract RASSF1A has been previously demonstrated to be inactivated by CpG island methylation in breast cancer cell lines and primary tumor tissues. There have been evidences suggesting that methylation of this gene have a significant impact on biological characteristics of breast tumors and have a relationship with prognosis in breast cancer. The tumor suppressive effect of RASSF1A has been reported to be mediated by its 2 important roles in other cells; induction of cell cycle arrest and apoptosis. Therefore, it is possible that expression status of RASSF1A by promoter methylation may alter patient's sensitivity to chemotherapeutic agents affecting cell cycle. However, there is few data regarding the relationship between the methylation status of RASSF1A gene and clinical response to chemotherapeutic agents in breast cancer patients. In this current study, we show that RASSF1A gene expression was suppressed in the human breast cancer cell lines (MCF-7, MDA-MB-231, and ZR75-1) by the mechanism of promoter methylation using methylation -specific PCR. It was confirmed by the results that treatment with the DNA demethylating agent, 5-aza-2′-deoxycytidine, reactivated the expression of RASSF1A at the level of mRNA and protein. Re-expression of RASSF1A gene in breast cancer cell lines could decrease the cell growth and proliferation by both decreasing cyclin D1 expression and inducing cyclin A and B1 accumulation, then resulting in cell cycle arrest at G2/M phase. In addition, re-introduction of RASSF1A further increased docetaxel-induced cell death in breast cancer cells. We next questioned whether the methylation status of RASSF1A gene is associated with clinical response to taxane-based chemotherapy in breast cancer patients. Fresh frozen primary breast cancer tissues were ananlyzed for methylation status of RASSF1A gene using MS-PCR. Thirty three out of 39 patients (84.6%) showed RASSF1A methylation and 6 had un-methylated gene. Patients who had unmethylated or partially methylated RASSF1A gene showed some mRNA in RT-PCR analysis. And, the clinical response to taxane-based chemotherapy was significantly better in the un-, or partially-methylated patient group (100% vs 62.5%). These results suggest that hypermethylation of the CpG island promoter of RASSF1A may play an important role in breast cancer pathogenesis and is a modulating factor for docetaxel activity in breast cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4925.