We explored the effects of different lifetime exposures to soy isoflavone extracts on the growth of estrogen- dependent human breast cancer cells （MCF-7） implanted into athymic mice of different ovarian statuses. The athymic mice, ovariectomized or not, were implanted with MCF-7 cells. Mice were fed with low, moderate and high doses of soy isoflavone extract, at dietary concentrations of 6.25, 12.5 and 25 g/kg, in different reproductive models, respectively. The expression of ki-67 was detected by immunohistochemistry, pS2 expression in tumors was analyzed by real-time PCR. Estrogen level in the serum was measured by chemiluminescence enzyme im- munoassay. Total genistein and daidzein levels in serum and urine were determined by liquid chromatography- electrospray tandem mass spectrometry （LC-ES/MS/MS）. In Group A, on week 4, nude mice were exposed to different doses of soy iosflavone extracts. In Group B, the experimental diets were given to the nude mice follow- ing ovariectomy and tumor implantation. In both groups, 6.25 and 12.5 g/kg soy isoflavone extracts stimulated the growth of MCF-7 xenografts, increased pS2 expression, proliferation and estrogen level in serum. In both Group B （postmenopausal mouse model） and Group C （premenopausal mouse model）, soy isoflavone extracts at doses of 6.25 and 12.5 g/kg showed stimulatory effects on the growth of MCF-7 tumors. In conclusion, administration of soy isoflavone extracts at doses of 6.25 and 12.5 g/kg during adolescence or later in life stimulated tumor growth in both menopausal and postmenopausal mouse models.
In this study,we explored the effects of soy isoflavone extracts on the growth of estrogen-dependent human breast cancer (MCF-7) tumors implanted in ovariectomized athymic mice. The ovariectomized athymic mice were implanted with MCF-7 cells. They were fed with low,moderate and high doses of soy isoflavone extracts,at dietary concentrations of 6.25,12.5 and 25 g/kg,respectively. The expression of ki-67 was detected by immunohistochemistry. The pS2 expression in tumors was analyzed by real-time PCR. Estrogen level in the serum was measured by chemiluminescence enzyme immunoassay. Com-pared with the control group,dietary soy isoflavone extracts had a significant stimulatory effect on MCF-7 tumor growth in mice (P < 0.05). The ki-67 and pS2 mRNA expressions in tumors were signifi-cantly increased by 6.25 and 12.5 g/kg dose of soy isoflavone extracts (P < 0.05). And,estrogen level in serum of 6.25 and 12.5 g/kg dose groups was higher than that of control group (P > 0.05). In conclusion,in the tested dietary concentration range soy isoflavone extracts had a stimulatory effect on tumor growth. 6.25 and 12.5 g/kg doses of soy isoflavone extracts can increase the cell proliferation in tumors and induce estrogen-responsive pS2 expression.
