Abstract 909: Mechanistic study of synergistic interaction between genistein and equol in MCF-7 human breast cancer cells in vitro

Abstract

Abstract Soy isoflavones, such as genistein, daidzein, glycitein and equol, a metabolite of daidzein, have been suggested to affect the growth of estrogen-receptor positive breast cancer cells in vitro, and thus considered to be involved in the prevention of breast cancer. We have recently reported that soy isoflavone component mixture has a greater preventive activity against breast cancer rather than genistein alone using chemically induced rat model of hormone-dependent mammary carcinoma. Therefore, we investigated here whether a synergistic interaction exists between genistein and other isoflavone components in estrogen receptor positive MCF-7 cells. Effects of genistein in combination with other isoflavone components on proliferation, apoptosis, cell cycle perturbation, and signal proteins for survival, proliferation, and apoptosis were evaluated by WST-1 assay, FACS analyses, and Western blotting. Synergistic anti-proliferative activity of genistein was observed in combination with three respective isoflavone components, with the most efficacious interaction observed in combination with equal. In FACS study, cells were arrested at the G2/M by genistein but G1/S by equol. However, when these components were combined, cells were arrested at the G2/M, indicating a dominant effect of genistein over equol. Although apoptosis was not evident when cells were treated with either genistein or equol alone, combination treatment markedly induced apoptosis, with demonstrable cleavage of PARP. Upon combination treatment, constitutive activities of Erk1/2 were enhanced, but those of Akt were significantly inhibited, with subsequent reductions of activities of downstream mTOR. Reduced expression of anti-apoptotic Bcl-xL and enhanced expression of proapoptotic Bax were also demonstrated. These data indicate that synergic mechanism of genistein in combination with equol would be mediated by enhanced apoptosis induction through inactivation of Akt and its downstream molecule mTOR, followed by subsequent upregulation of Bax and downregulation of Bcl-xL, thus providing mechanistic rationale for soy isoflavone for the prevention of human breast cancer. Citation Format: MISAKI ONO, KAORU EJIMA, MIKAKO TAKESHIMA, TAKAKO HIGUCHI, REI WAKIMOTO, SHUJI NAKANO. Mechanistic study of synergistic interaction between genistein and equol in MCF-7 human breast cancer cells in vitro. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 909. doi:10.1158/1538-7445.AM2015-909