Dutasteride and Enzalutamide Synergistically Suppress Prostate Tumor Cell Proliferation

Purpose: Dihydrotestosterone is the main active androgen in the prostate and it has a role in prostate cancer progression. After androgen deprivation therapy androgen receptor signaling is still active in tumor cells. Persistent intratumor steroidogenesis and androgen receptor changes are responsible for this continued activity, which influences the efficacy of prostate cancer treatment. We hypothesized that combining a 5 alpha-reductase inhibitor and an antiandrogen would block intratumor androgen synthesis and androgen receptor protein activity. Thus, it would act synergistically to reduce tumor cell proliferation. Materials and Methods: The expression level of 5 alpha-reductase and androgen receptor in endocrine therapy naive prostate cancer and castration resistant prostate cancer tissues, and cell line models was determined by microarray and quantitative polymerase chain reaction analysis. Intracellular androgen was measured with radioimmunoassay. Tumor cell proliferation was determined using coloric MTT assay. The synergistic effects of combination treatments on tumor cell proliferation were calculated using the Chou-Talalay equation. Results: In all prostate cancer cases 5 alpha-reductase-1 and 3 were up-regulated. Androgen receptor was up-regulated in metastatic prostate cancer and castration resistant prostate cancer cases. The 5 alpha-reductase inhibitor dutasteride effectively decreased dihydrotestosterone production in prostate cancer and castration resistant prostate cancer cell lines. Furthermore, dutasteride combined with the novel antiandrogen enzalutamide synergistically suppressed endocrine therapy naive prostate cancer and castration resistant prostate cancer cell proliferation. Conclusions: In this study the combination of a 5 alpha-reductase inhibitor and (novel) antiandrogens synergistically inhibited tumor cell proliferation. These findings support clinical studies of combinations of a 5 alpha-reductase inhibitor and (novel) antiandrogens as first line treatment of prostate cancer and castration resistant prostate cancer.