We have recently studied the ability of a hydrolyzable tannin, gallotannin (GT), and a condensed tannin, red alder (RA) bark extract, to inhibit 1,2-dimethylhydrazine (DMH)-induced colonic aberrant crypt foci (ACF) and tumors in Balb-c mice. The multiplicity, size and distribution of ACF and tumors was significantly inhibited by both tannins, even when these compounds were administered for only two weeks prior to a 24-week treatment with the carcinogen DMH, suggesting a potential role for these drugs as preventive agents against colon cancer. This project aims at determining the cellular and molecular mechanisms by which tannins exert their cancer preventive effects using human colon cancer cells. To achieve this goal, we will investigate the effects of tannins on the growth, proliferation and genomic alteration in human xenografted tumors. We will also investigate the effect of tannins on colon cancer cell growth and study their ability to induce apoptosis, affect cell cycle phase distribution, and modulate the MAP kinase signaling pathway.