MCF-7 cells were transiently transfected with pGL2-ERE2x-TK-luciferase plasmid. After a 6 h transfection, cells were treated with compounds (DMSO, daidzein and daidzein analogues) and incubated overnight. Data are represented as relative light units (RLUs) normalized to E2 (100 ± SEM). The values are the means and the SEM of triplicates from a single experiment and representative for at least three independent experiments. a, significant difference from daidzein, p<0.05, b, significant difference from daidzein, p < 0.01, c, significant difference from daidzein, p < 0.001.