Quercetin synergizes with 2-methoxyestradiol inhibiting cell growth and inducing apoptosis in human prostate cancer cells

Lack of effective treatment options for castration-resistant prostate cancer reinforces the great need to develop novel drug therapies. Quercetin is a plant-derived flavonoid that can induce apoptosis in prostate cancer cells. 2-Methoxyestradiol (2-ME) is an endogenous estrogenic metabolite that also has antineoplastic activity. However, these two agents have limited bioavailability. Herein, we explored the antiproliferative and proapoptotic activities of quercetin combined with 2-ME in both androgen-dependent LNCaP and androgen-independent PC-3 human prostate cancer cell lines. Compared to quercetin and 2-ME alone, combining quercetin with 2-ME at appropriate concentrations i) showed synergistic antiproliferative and proapoptotic activities; ii) increased G2/M phase population of cells; iii) decreased the ratio of Bcl-2/Bax significantly. The combination of quercetin and 2-ME is a new clinically relevant treatment regimen which has the potential of enhancing the antitumor effect on prostate cancer and lessening the side effect of either quercetin or 2-ME alone.