Breast cancer cell cultures were exposed to different concentrations of black cohosh, estradiol (E2), and tamoxifen to examine the effect on cell proliferation; cytotoxicity was assessed by using sulforhodamine B (SRB) dye solution. E2 (10−10–10−8 mol/L) markedly stimulated the proliferation of MCF-7 cells (p < 0.01). Tamoxifen stimulated MCF-7 cell proliferation at 10−6 mol/L and 10−5 mol/L (p < 0.005) but inhibited in a dose-dependent fashion the proliferative effect of E2 (p < 0.001). Black cohosh alone did not show any stimulatory effect, but exhibited a cytotoxic effect, which was significant at 103 μg/mL (p < 0.001). Adding black cohosh at 100–103 μg/mL to E2 at 10−9 mol/L also resulted in a dose-dependent inhibition of E2 proliferative effect. Interestingly, the combination of black cohosh (100–103 μg/mL) with increasing tamoxifen concentrations further inhibited MCF-7 cell growth. On MDA-MB-231 cells, neither E2 nor tamoxifen displayed any detectable effect. However, black cohosh inhibited MDA-MB-231 cell proliferation at 103 μg/mL (p < 0.05), and this inhibitory effect was enhanced by increasing tamoxifen concentrations. This study reveals a cytotoxic effect of black cohosh on both estrogen-sensitive and estrogen-insensitive breast cancer cells and a synergism with tamoxifen for inhibition of cancerous cell growth.
The antiestrogenic effects of black cohosh on BRCA1 and steroid receptors in breast cancer cells
