Isoflavones inhibit intestinal epithelial cell proliferation and induce apoptosis in vitro

There have been many reports that high soya-based diets reduce the risk of certain types of cancer. This effect may be due to the presence of high lev els of isoflavones derived from the soyabean, particularly genistein which has been shown to be a protein tyrosine kinase (PTK) inhibitor and have bot h oestrogenic and anti-oestrogenic properties. We have examined the effect of genistein and a number of novel synthetic analogues on both normal (IEC6 , IEC18) and transformed (SW620, HT29) intestinal epithelial cell lines. Re sponses were compared to those elicited by oestradiol, the anti-oestrogen t amoxifen, and the tyrosine kinase inhibitor tyrphostin. Genistein and tamox ifen were potent inhibitors of cell proliferation. Of seven novel isoflavon es tested, none were more potent inhibitors than genistein, and all display ed similar relative activities across the different cell lines. In addition to inhibiting cell proliferation, cell death via apoptosis was observed wh en the cells were exposed to the isoflavones and all but one exhibited PTK inhibitory activity. These data suggest that by reducing proliferation and inducing apoptosis, possibly due in part to PTK inhibition, isoflavones may have a role in protecting normal intestinal epithelium from tumour develop ment (reducing the risk) and may reduce colonic tumour growth.