In vitro effect of low dose resveratrol and tri-acetyl resveratrol on Wnt signaling in colon-derived and colon cancer cell lines

AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA 5534 BACKGROUND: Resveratrol (RES) is a bioflavonoid found in the skin of dark grapes and red wine which has antioxidant and pro-apoptotic activity, has been shown to inhibit colon cancer cell proliferation at high dosages (> 100uM) in vitro, and has cancer prevention activity in animal models. It has been proposed for use in colon cancer prevention in humans. However, it is unclear if a biologically equivalent concentration could be achieved in humans when considering dosages utilized in vitro and in animal models. We have examined the activity of low dose RES on cell proliferation and on Wnt signaling in vitro and compared this to a chemically modified derivative, tri-acetyl resveratrol (TAR). TAR has increased hydrophobicity which would facilitate cellular uptake of the compound both in vitro, and in vivo by colonic mucosa. METHODS: The effects of low dose (< 40uM) RES and TAR on proliferation and Wnt signaling were examined in a normal-derived colon cell line (NCM460) and a colon cancer cell line lacking intrinsic Wnt pathway activation (RKO) by MTT assay and a luminescence-based LEF/TCF reporter assay respectively. RESULTS: Neither RES nor TAR affected proliferation of NCM460 at concentrations from 2.5uM to 40uM. Proliferation of RKO was inhibited by both RES and TAR at 20uM and 40uM, with TAR exhibiting a slightly greater inhibitory effect at each concentration. The effects of RES and TAR on Wnt throughput were measured following treatment of cells with Wnt3a conditioned medium (CM) to augment basal Wnt signaling. Both NCM460 and RKO had significantly increased Wnt throughput following Wnt3a CM. At 20uM, neither RES nor TAR inhibited Wnt throughput in NCM460. 20uM TAR, but not RES, significantly inhibited the Wnt3a CM induced increase in Wnt throughput in RKO (p=0.025). A non-significant trend toward inhibition was seen with RES in these cells. CONCLUSIONS: We have demonstrated that low concentrations of RES and TAR can inhibit proliferation of colon tumor-derived cells. TAR, but not RES, inhibited Wnt signaling in RKO colon cancer cells but had no effect on the normal-derived colonic mucosal cells, NCM460. This is the first report demonstrating activity of a chemically modified analog of RES on Wnt signaling. The increased efficacy of TAR may be related to improved cellular uptake. Further research on chemically modified analogs of RES on Wnt signaling and on colon cancer is indicated.