Colorectal cancer (CRC) is the second most common cause of cancer deaths in humans, and about 5% of the US population will develop CRC in their life times. Overall, CRC growth, progression and metastasis involve a gradual accumulation of genetic and epigenetic changes over a period of years. One approach to control CRC growth and metastasis could be its prevention by phytochemicals present in diet and those consumed as dietary supplement, which inhibit one or more events of neoplastic stages and reduce overall cancer risk. Grape seed extract (GSE) is a widely consumed dietary supplement in the United States for its several health benefits, and is a rich source of standardized phytochemicals known as proanthocyanidins. Recently, we observed that GSE significantly inhibits growth, causes cell cycle arrest and induces apoptosis in human colon carcinoma HT29, SW480 and LoVo cells, and that GSE feeding significantly inhibits HT29 tumor xenograft growth in nude mice and prevents polyp formation and its growth in APCmin mice without any apparent signs of toxicity as measured in terms of animal body weight and diet consumption. Mechanistic studies in human CRC cell lines showed that GSE very strongly induces Cip1/p21 levels, together with a decrease in CDKs and cyclins;p21 induction was also observed in GSE-treated HT29 xenografts. Other studies found that GSE causes strong caspase 3 and PARP cleavage in CRC cell lines. We also observed that GSE inhibits ligand-induced AKT activation in CRC cells. Recent studies have also shown that GSE feeding prevents azoxymethane (AOM)-induced colon carcinogenesis in rat model, which was associated with its in vivo anti-proliferative and apoptotic effects. Together, based on these studies, we hypothesize that GSE is a novel colon cancer chemopreventive dietary supplement agent, which targets cell cycle progression and cell survival signaling leading to its anti-proliferative and apoptotic efficacy against CRC.
Our specific aims are to: I) further assess and establish GSE efficacy in AOM-induced rat CRC model, II) establish the role of Cip1/p21 induction by GSE in its biological efficacy against CRC, III) assess and define GSE effect on mitogenic and cell survival signaling, and APC/p-catenin/ TCF4 pathway, and IV) further examine and define the effects of GSE on apoptosis regulators. We anticipate that proposed studies will identify GSE as a mechanism-based dietary supplement agent for the prevention of CRC, and will establish its in vivo efficacy in pre-clinical CRC models. As a practical and translational approach, the long- range goal of these studies would be to define and establish the usefulness of GSE for the prevention and intervention of human CRC.
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