Estradiol suppresses tissue androgens and prostate cancer growth in castration resistant prostate cancer

Background: Estrogens suppress tumor growth in prostate cancer which progresses despite anorchid serum androgen levels, termed castration resistant prostate cancers (CRPC), although the mechanisms are unclear. We hypothesize that estrogen inhibits CRPC in anorchid animals by suppressing tumoral androgens, an effect independent of the estrogen receptor. Methods: The human CRPC xenograft LuCaP 35V was implanted into orchiectomized male SCID mice and established tumors were treated with placebo, 17 beta-estradiol or 17 beta-estradiol and estrogen receptor antagonist ICI 182,780. Effects of 17 beta-estradiol on tumor growth were evaluated and tissue testosterone (T) and dihydrotestosterone (DHT) evaluated by mass spectrometry. Results: Treatment of LuCaP 35V with 17 beta-estradiol slowed tumor growth compared to controls (tumor volume at day 21: 785 +/- 81 mm(3) vs. 1195 +/- 84 mm(3), p = 0.002). Survival was also significantly improved in animals treated with 17 beta-estradiol (p = 0.03). The addition of the estrogen receptor antagonist ICI 182,780 did not significantly change survival or growth. 17 beta-estradiol in the presence and absence of ICI 182,780 suppressed tumor testosterone (T) and dihydrotestosterone (DHT) as assayed by mass spectrometry. Tissue androgens in placebo treated LuCaP 35V xenografts were; T = 0.71 +/- 0.28 pg/mg and DHT = 1.73 +/- 0.36 pg/mg. In 17 beta-estradiol treated LuCaP35V xenografts the tissue androgens were, T = 0.20 +/- 0.10 pg/mg and DHT = 0.15 +/- 0.15 pg/mg, (p < 0.001 vs. controls). Levels of T and DHT in control liver tissue were < 0.2 pg/mg. Conclusions: CRPC in anorchid animals maintains tumoral androgen levels despite castration. 17 beta- estradiol significantly suppressed tumor T and DHT and inhibits growth of CRPC in an estrogen receptor independent manner. The ability to manipulate tumoral androgens will be critical in the development and testing of agents targeting CRPC through tissue steroidogenesis.