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Imbalance in the critical cellular processes like cell proliferation, differentiation and apoptosis leads to cancer development. In most cases, induction of apoptosis is an important therapeutic strategy to control the abnormal proliferation of cancer cells. Many chemopreventive agents of natural origin have shown this capacity in various cell culture and animal models of cancer. We have previously demonstrated the anti-cancer activity of grape seed extract, a mixture of polyphenols, against the androgen-dependent and -independent human prostate carcinoma cell lines. In the present study, we assessed the efficacy and the molecular mechanism of action of gallic acid, which was found to be a principle active constituent of grape seed extract, in human prostate carcinoma cell lines. We observed that treatment of DU145, PC-3 and 22Rv1 cells with gallic acid decreases the viability of these cells in a dose-dependent manner with IC50 of 57, 60 and 74 µM, respectively. Further studies conducted in these cell lines revealed that the decrease in cell viability was due to apoptosis induction by gallic acid. Additional studies next conducted in DU145 cells showed that gallic acid caused 70-80% of cells to undergo apoptotic death after 24h of treatment at 50 and 75µM doses as determined by Annexin V-PI staining. In mechanistic studies, western blot analysis revealed that treatment with gallic acid caused the activation of caspase-3 and caspase-9 along with the release of cytochrome-c and apoptosis inducing factor (AIF) from mitochondria in DU145 cells. Additionally, gallic acid treatment caused the decrease in the levels of anti-apoptotic proteins, Mcl-1 and survivin without affecting the levels of pro-apoptotic members, Bcl-XL, Bak and Bad. Treatment of DU145 cells with gallic acid also caused a strong activation of p38 MAPK pathway. Pretreatment with p38 inhibitor SB203580 significantly attenuated the apoptotic death induced by gallic acid, thereby suggesting that activation of p38 MAPK pathway is involved in the regulation of cell death induced by gallic acid in DU145 cells. Together these results suggest the involvement of both caspase-dependent and -independent pathways of apoptosis mediated through release of cytochrome-c and AIF from the mitochondria in gallic acid mediated death in DU145 cells via the activation of p38 MAPK pathway.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA