In vitro activity: Genistein is an ATP competitive inhibitor. Genistein inhibits tyrosine phosphorylation in isolated enzyme and receptor preparations and in whole cells including platelets, lymphocytes and a variety of cultured cells. It also inhibits EGF-stimulated phosphorylation in cultured cells as well as inhibition of Topo II (topoisomerase II). Genistein inhibits EGF-stimulated tyrosine phosphorylation in cultured A431 epidermoid carcinoma cells. Inhibition is competitive with ATP and noncompetitive with substrate. Genistein blocks the mitogenic effect mediated by EGF, insulin and thrombin on NIH-3T3 cells. Genistein also acts as an agonist at the GPR30 receptor and binds to PPARγ and estrogen receptors. Genistein also binds to PPARγ, acting as an agonist at this receptor with Ki of 5.7 μM.

Kinase Assay: Genistein inhibits serum-stimulated growth of MCF-7 and T47D ER+ cells with IC50 values of 7.6 and 8.7 μg/mL by dye exclusion, respectively, and 8.7 and 10.6 μg/mL by [3H]thymidmne incorporation, respectively. These values are similar to the IC50 values of 9.4 and 7 μg/mL for MCF-7 and T47D ER+ cells, respectively, obtained with the MTT assay. Additionally, Genistein at concentrations up to 20 μg/mL does not alter MTT mitochondrial reduction when compared to control cells in an 8 h incubation period. Furthermore, neither biochanin A or daidzein are found to interfere with the MTT assay at IC50 concentrations. Therefore, the MTT assay is valid for determining growth inhibition by Genistein at concentrations under 20 μg/mL in the systems studied.

Cell Assay: The IC50 values for Genistein are determined by the MTT assay. Briefly, the MTT assay is a colorimetric assay that is based on the ability of living but not dead cells to reduce a tetrazolium-based compound to a blue formazan product. The formazan crystals are solubilized in DMSO, and the absorbance is measured at 540 nm. The absorbance at 540 nm is proportional to the number of viable cells. The lC50 values obtained with the MTT assay are compared with the lC50 values obtained by counting viable cells using trypan blue dye exclusion and by tritiated thymidine incorporation into DNA.

Rats: Male 8-week-old Wistar rats (150-180g) are used. After one week acclimation, all rats are randomly divided into 8 groups with 10 rats per group and treated for 35 weeks as follows: (1) STD group is fed with rodent standard chow diet (STD); (2) STD-BPA group is fed with STD and administered with BPA (50 μg/kg/day); (3) STD-(BPA+G) group is fed with STD and administered with BPA (50 μg/kg/day) plus Genistein (10 mg/kg/day); (4) STD-G group is fed with STD and administered with Genistein (10 mg/kg/day); (5) HFD group received high-fat diet (HFD); (6) HFD-BPA group is fed with HFD and administered with BPA (50 μg/kg/day); (7) STD-(BPA+G) group is fed with HFD and administered with BPA (50 μg/kg/day) plus Genistein (10 mg/kg/day); (8) HFD-G group is fed with HFD and administrated with Genistein (10 mg/kg/day). All the male genitors are treated for 35 weeks consecutively. The details of BPA (50 μg/kg/day) and Genistein (10 mg/kg/day) treatment methods have been described previously: BPA is dissolved in corn oil and diluted with three stock solutions (20, 40, 80, and 120 μg/mL).