Abstract: Objective：To investigate the effect of equol on the proliferation of colom cancer cells and to explore the mechanisms. Methods: Colon cancer cells (DLD1,HCT15,COLO205,LOVO,SW480) were incubated, the cell proliferation was identified by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation assay. Reverse transcription PCR and Western blot were used to measure the mRNA and the protein expression of estrogen receptor and nuclear factor (erythroid-derived 2)-like 2 (Nrf2)in the colon cancer cells, respectively. Moreover, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation assay was used to investigate the effect of estrogen receptor(ER) inhibitor,ERα agonist, and estrogen receptor ERβagonist on the cell proliferation. Results: ERα was faintly expressed in the DLD-1 and HCT-15 cells. However, ERβ expression in DLD1, HCT15, COLO205, LOVO, and SW480 colon cancer cells. Different concentrations of equol (0, 0.5, 1, 5, 10 μmol/L) significantly inhibited the growth of HCT-15 cell with the expression of ERα and ERβ.More-over, different concentrations of equol (0, 0.5, 1, 5, 10 μmol/L) significantly inhibited the growth of LOVO, and SW480 cells with the ERβ expression in a dosedependent manner as demonstrated with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation assay. mRNA expressions of ERα and ERβ in HCT-15 were stimulated significantly. Western blotting proved that the protein expressions of ERα and ERβ increased with the increasing of equol dose. Moreover we found significant difference of Nrf2 protein expression in HCT-15 cell stimulated by different concentrationss of equol. After the similation of estrogen receptor inhibitor, ERα agonist, or ERβ agonist, we found that only dif-ferent concentrations of ERβ agonist(0, 1, 10, 100, 1 000, 10 000 nmol/L) significantly inhibited the growth of HCT-15, LOVO, and SW480 in adose-dependent manner. Estrogen receptor inhibitor and ERα agonistdid not present significant effect on the cell proliferation of HCT-15, LOVO, and SW480. Conclusion: Equol inhibited the colon cancer cell proliferation by its estrogenic activities and antioxidant activities.

Key words: Equol, Colon cancer, Estrogen receptor, Proliferation