ZFIN ID: ZDB-PUB-160603-2
Phytoestrogen Bakuchiol Exhibits In Vitro and In Vivo Anti-breast Cancer Effects by Inducing S Phase Arrest and Apoptosis
Li, L., Chen, X., Liu, C.C., Lee, L.S., Man, C., Cheng, S.H.
Phytoestrogen has been proposed as an alternative to hormone replacement therapy, which has been demonstrated to promote a high risk of breast cancer. However, the effect of phytoestrogen on breast cancer development has not been fully understood. Bakuchiol is an active ingredient of a traditional Chinese herbal medicine Fructus Psoraleae, the dried ripe fruit of Psoralea corylifolia L. (Fabaceae). The in vitro and in vivo estrogenic activities and anti-breast cancer effects of bakuchiol have not been well-studied. We found that bakuchiol induced the GFP expression in transgenic medaka (Oryzias melastigma, Tg, Chg:GFP) dose-dependently (0-1 μg/ml), demonstrating its in vivo estrogenic activity. Low dose of bakuchiol (1 μg/ml) induced the cell proliferation and ERα expression in MCF-7 cells, which could be blocked by the anti-estrogen ICI 182780, suggesting the in vitro estrogenic activity of bakuchiol. Our data indicated that high doses of bakuchiol (>2 μg/ml) inhibited breast cancer cell growth, with a stronger anti-proliferative effect than resveratrol, a widely studied analog of bakuchiol. High doses of bakuchiol (4, 7, and 10 μg/ml) were used for the further in vitro anti-breast cancer studies. Bakuchiol induced ERβ expression and suppressed ERα expression in MCF-7 cells. It also induced S phase arrest in both MCF-7 and MDA-MB-231 cells, which could be rescued by caffeine. Knock-down of p21 also marginally rescued S phase arrest in MCF-7 cells. The S phase arrest was accompanied by the upregulation of ATM, P-Cdc2 (Tyr15), Myt1, P-Wee1 (Ser642), p21 and Cyclin B1, suggesting that blocking of Cdc2 activation may play an important role in bakuchiol-induced S phase arrest. Furthermore, bakuchiol induced cell apoptosis and disturbed mitochondrial membrane potential in MCF-7 cells. The bakuchiol-induced apoptosis was associated with increased expression of Caspase family and Bcl-2 family proteins, suggesting that bakuchiol may induce apoptosis via intrinsic apoptotic pathway. The in vivo anti-breast cancer effect of bakuchiol was further proved in zebrafish (Danio rerio, wild-type AB) xenografts. 0.5 μg/ml of bakuchiol significantly reduced the MCF-7 cell mass in zebrafish xenografts. Overall, these results suggested the potential of using bakuchiol in HRT and breast cancer treatment.