EFFECTS OF DIETARY DAIDZEIN AND ITS METABOLITE, EQUOL, AT PHYSIOLOGICAL CONCENTRATIONS ON THE GROWTH OF ESTROGEN-DEPENDENT HUMAN BREAST CANCER (MCF-7) TUMORS IMPLANTED IN OVARIECTOMIZED ATHYMIC MICE

Genistein and daidzein are the main isoflavones in legumes. Equol is an intestinal bacterial metabolite of daidzein. In this study, we evaluated the estrogenic potential of daidzein and synthetic (±)-equol to stimulate growth of estrogen-dependent breast cancer (MCF-7) in vitro and in vivo. We hypothesize that estrogenic effects of daidzein and (±)-equol could modulate the growth of MCF-7 cells both in vitro and also once implanted into ovariectomized athymic mice. At concentrations between 0.001 and 50 μM, daidzein and (±)-equol stimulated the growth of MCF-7 cells with maximal stimulation at 1 μM in vitro. To evaluate their effects on the growth of MCF-7 cells implanted in ovariectomized athymic mice, two dietary dose–response studies [daidzein (125, 250, 500 and 1000 p.p.m.) and (±)-equol (250, 500 and 1000 p.p.m.)] were conducted. Tumor size and body weight were monitored weekly during the study