Genistein inhibits growth of estrogen-independent human breast cancer cells in culture but not in athymic mice

Abstract

The studies presented were conducted to assess the effect of the soy isoflavone genistein on proliferation of estrogen-independent human breast cancer cells (MDA-MB-231) in vitro and in vivo. Genistein (20 μmol/L) inhibited cell proliferation in vitro by ~50%. Cell cycle progression-was blocked in G2/M with 40 and 80 μmol/L genistein. To evaluate the effect of dietary genistein on tumor growth in vivo, genistein was fed to female athymic mice inoculated with MDA-MB-231 cells. After so lid tumor masses had formed, mice were fed genistein at a dose (750 μg/g AIN-93G diet), shown to produce a total plasma genistein concentration of ~1 μmol/L. This dose of genistein did not significantly (P > 0.05) alter tumor growth. Studies were then conducted to assess the effect of dietary genistein on initial tumor development and growth. Genistein (750 μg/g AIN-93G diet), fed 3 d before cells were inoculated into mice, did not significantly (P > 0.05) inhibit tumor formation or growth. The plasma concentration of genistein in mice fed this dose of dietary genistein (750 μg/g AIN-93G diet) does not appear sufficient to inhibit tumor formation or growth. Dietary genistein at 750 μg/g AIN-93G diet does not inhibit tumor formation or growth. Additional studies were conducted to determine the effect of dietary dosages ranging from 0 to 6000 μg/g AIN-93G diet on plasma genistein concentration. Plasma genistein concentration increased in a dose-dependent manner up to 7 μmol/L at 6000 μg/g AIN-93G diet. These data suggest that although genistein inhibits cancer cell growth in vitro, it is unlikely that the plasma concentration required to inhibit cancer cell growth in vivo can be achieved from a dietary dosage of genistein.