We now know that progastrins (PG) and insulin-like growth factors (IGFs) exert potent proliferative and anti- apoptotic effects on colon cancer (CRC) cells and can potentially function as co-carcinogens during all phases of colorectal carcinogenesis. Dietary agents, such as curcumin, inhibit the growth of CRC cells and inhibit colon carcinogenesis at both the pre-malignant and post-malignant stages of the disease. It is, however, not known if curcumin can inhibit the growth factor effects of autocrine and/or endocrine PG and IGF-II during colon carcinogenesis. Our preliminary studies suggest that the inhibitory effects of curcumin are attenuated in the presence of growth factors, such as IGF-II and PG; surprisingly the degree of attenuation was significantly higher in the presence of IGF-II than in the presence of PG. Therefore, the major hypothesis of our grant proposal is that the inhibitory efficacy of curcumin will be dictated by either the circulating growth factor profile of animal models or by the autocrine growth factors in CRC cells. To address this hypothesis, in Aim 1, we will develop isogenic cell lines that either express PG or IGF-II, and examine the pro-apoptotic and anti-proliferative potency of curcumin on these cells. Inhibitory effects of curcumin on intact colonic crypt cells, prepared from either transgenic mice over-expressing PG or IGFs or prepared from wild type mice, will also be examined.
In Aim 2, we will examine dose-dependent effects of dietary curcumin against all phases of colon carcinogenesis in transgenic mice over-expressing PG or IGF-II, either in the circulation or locally within the intestinal mucosa. The intracellular pathways that mediate anti-apoptotic vs proliferative effects of PG and IGFs, on CRC and intestinal epithelial (IEC) cells, are being currently examined in our laboratory. The mechanisms by which curcumin inhibits the growth factor effects of IGFs and PG are unknown at the present time.
In Aim 3 we will examine the effect of curcumin on the phosphorylation/dephosphorylation of several kinases/phosphatases that are activated in response to PG or IGF-II in isogenic CRC and IEC cells. The above experiments will allow us to learn for the first time the relative effectiveness of curcumin on colon carcinogenesis in the presence of growth factors relevant to the etiology of the disease. The results of these studies are expected to help in developing mechanism-based strategies for preventative/treatment protocols for CRCusing curcumin like agents.
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