Phytoestrogens derived from Belamcanda chinensis have an antiproliferative effect on prostate cancer cells in vitro

Purpose: Phytoestrogens are nonsteroidal plant derived compounds with estrogenic activity that have been implicated in protecting against prostate cancer progression. We hypothesized that these compounds would alter cell number and increase the ability of antiandrogens to induce cell death in prostate cancer cells. Materials and Methods: RWPE-1, LNCaP and PC-3 cells were treated with or without an extract of Belamcanda chinensis, 2 purified phytoestrogens derived from this extract (irigenin and tectorigenin) and the antiandrogen bicalutamide. We assessed the effect on cell number, proliferation and apoptosis. Results: Phytoestrogens (50 to 100 muM) and bicalutamide (10 to 50 muM) alone decreased the cell number in all 3 cell lines. Phytoestrogens (50 muM) combined with bicalutamide (10 muM) further decreased the number of RWPE-1 and PC-3 cells compared to these agents alone. Tectorigenin and irigenin inhibited the proliferation of RWPE-1, LNCaP and PC-3 cells, causing G(1) arrest and the induction of p21 (WAF1) or p27(kip1) protein expression, whereas bicalutamide induced apoptosis in a dose dependent manner in all 3 cell lines. Phytoestrogens did not have antiandrogenic activity. Conclusions: These in vitro studies demonstrate a role for tectorigenin and irigenin in regulating prostate cancer cell number by inhibiting proliferation through cell cycle regulation.