Prostate cancer (PCA) is the most frequently diagnosed malignancy in elderly men, and is rated as second leading cause of cancer deaths in men. The malignancy has long latent period of development from pre-neoplastic lesion to full-blown cancer providing ample time to intervene or alter the progression of this disease employing chemopreventive strategies. Additionally, numerous studies have shown that the risk for certain cancers could be lowered by dietary manipulations, especially by increased consumption of fruits and vegetables. Accordingly, there has been serious interest in identifying diets or dietary constituents (both nutritive and non-nutritive phytochemicals) for their potential use as chemopreventive agents. Grape seed extract (GSE), a rich and commercially available source of proanthocyanidins (also known as procyanidins), is usually consumed as a health supplement for its wide range of beneficial effects. Regarding cancer, several studies by us and others have demonstrated the anti-cancer and chemopreventive efficacy of GSE against various epithelial malignancies including PCA cells. Since GSE represents a complex mixture of polyphenols, the central focus of the studies during the last funding period was to isolate and characterize active component(s) in GSE to carry out detailed mechanistic and efficacy studies for anticancer activity employing pure and defined agents. We recently isolated and characterized procyanidin B2- 3,3'-di-O-gallate (B2-G2) as an active compound from GSE with strong anti-cancer activity against human prostate carcinoma DU145 cells. Further studies with this compound revealed that it is taken up by PCA cells and that it causes both cytotoxic as well as cell growth inhibitory effects. Additional studies revealed that B2-G2 causes both cell cycle arrest and apoptosis induction in human PCA cells carrying functional androgen receptor;these cells specifically represent majority of human prostate tumors. Importantly, B2-G2 did not show cytotoxicity in normal human prostate epithelial and stromal cells, showing its selectivity in human PCA cells. Since uncontrolled proliferation due to deregulated cell cycle progression and loss of apoptotic function are the major underlying defects in most of the cancers including PCA and since B2-G2 exerts strong cell cycle arrest and apoptotic responses in PCA cells, our central hypothesis is that procyanidin B2-3,3'-di-O-gallate selectively induces cell cycle arrest and apoptosis in neoplastic prostate epithelial cells which collectively leads to its preventive and therapeutic efficacy against PCA.
Our specific aims are to: 1) prepare B2-G2 needed for planned mechanistic, bioavailability and efficacy studies, 2) conduct in vitro studies to address mechanism of action of B2-G2 involved in cell cycle arrest and apoptosis, and 3) determine efficacy and bioavailability of B2-G2 employing an in vivo transgenic carcinoma of the mouse prostate (TRAMP) model, which closely and naturally mimics the progression of prostatic carcinoma in humans. Overall, our long term goal is to develop procyanidin B2-3,3'-di- O-gallate as a mechanism-based potential chemopreventive agent against PCA. 7. PROJECT NARRATIVE Prostate cancer is second leading cause of cancer-related deaths in United States, and thus is an important public health issue. Use of chemopreventive agents seems to be more effective approach for the control of prostate cancer as it has long latent period of development;sometimes over decade from precursor lesions to full blown disease. Current grant proposal focuses on the development of one such agent, which has been isolated from grape seed extract, a widely consumed health supplement. Outcomes of our proposed research will provide a mechanism-based agent for the prevention of prostate cancer in humans.
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