Abstract 218: Ginsenoside Rh2 induced bcl2 family proteins mediated apoptosis in vitro and xenograft in vivo

Abstract

Abstract Natural products have received increasing attention in recent years for the discovery of novel cancer preventive and therapeutic agents. The root of Panax ginseng has been used for thousands of years in Korean medicine practice for treatment of diverse ailments. More recent studies have indicated that ginsenoside saponins, a constituents of Panax ginseng can induce retardation of growth and cell death of cancer in culture and in vivo. In this study, we used two human breast cancer cells, MCF7 (wild type p53, ER responsive), MDA-MB-231 (mutated p53, ER-independent) and xenograft nude mouse model to investigate further insights into the mechanism of Ginsenoside Rh2-induced cell death. It was observed that Rh2 treatment significantly decreases viability at 40 to 60 μM concentrations as judged by trypan blue dye exclusion assay in both two cell lines. Rh2 treatment also increased in a concentration- and time-dependent cell death in cytoplasmic histone-associated DNA fragmentation assay. Bcl-2 family proteins have emerged as critical regulators of apoptosis by functioning either as promoters (e.g., Bax and Bak) or inhibitors (e.g., Bcl-2 and Bcl-xL) of the cell death process. Rh2-induced apoptosis was correlated with induction of Bax and Bak and a decrease in Bcl-xL and Bcl-2 protein levels in both two cell lines. Transient transfection of MCF7 cells with Bak- and Bax-targeted siRNAs conferred partial yet significant protection against ginsenoside Rh2-induced apoptosis. The increased expression level of Bax was associated with initiation of intrinsic apoptotic pathway. The pathway initiated translocation of Bax from cytosol following release of mitochondrial cytochrome c dependent on ginsenoside Rh2 treatment time. To test whether Rh2-mediated inhibition of MDA-MB-231 xenograft growth in vivo at the 2mg dose was due to increased apoptosis, tumor tissues from control and Rh2-treated mice were examined for histologic evidence of apoptosis. The tumors from Rh2-treated mice exhibited markedly higher count of apoptotic bodies and reduced proliferation index. The tumor section also exhibited the changed protein level compared with control one in specific for Bax or Bcl-2 immunohistochemistry. It was consistent in RT-PCR using appropriate Bcl2- family gene primers. In conclusion, our data suggests Rh2-mediated suppression of MDA-MB-231 xenograft growth in vivo and MF7 cells in vitro highly correlates with increased apoptosis. The results of the present study show that the ability of Rh2 to inhibit cell growth or cause apoptotic cell death in two human breast cancer cells is not influenced by either p53 functional status or ER responsiveness. 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 218.