Targeting DHEA-S transport and steroid sulfatase for more efficient androgen deprivation therapy
INTRODUCTION
Androgen deprivation therapy (ADT) is used to treat locally advanced or metastatic prostate cancer (CaP). Patients treated with ADT respond well initially, but develop castration-resistant prostate cancer (CRPC) eventually. Failure of ADT is attributed to intra-tumoral steroidogenesis that produces testosterone (T) and dihydrotestosterone (DHT). Adrenal androgens dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEA-S) are the most abundant circulating androgens in adult males, with circulating DHEA-S and DHEA in the μM and nM ranges, respectively. ADT reduces only modestly circulating DHEA-S and DHEA levels. Tumor cells are believed to produce T/DHT from DHEA-S or DHEA through the "front-door" steroidogenesis pathway. The high concentration of DHEA-S in circulation suggests that DHEA-S is the most available substrate for intra-tumoral T/DHT production. However, whether, and to what extent, benign prostate tissue and CaP tissue produce T/DHT from DHEA-S remains unsettled. Demonstration of production of T/DHT from DHEA(-S) is critical to designing novel neo-adjuvant therapies to synergize with ADT based on inhibitors of androgen metabolizing/transport proteins.
METHODS
Fresh benign prostate tissue and CaP tissue specimens were received in phenol red-free RPMI1640 medium supplemented with 10% charcoal-stripped fetal bovine serum. Tissue specimens were cut into -3 mm3 pieces and 2-3 pieces were placed in each well of 48-well plates. Samples were treated with DHEA or DHEA-S for various numbers of days. Medium samples were collected at the end of experiments, and DHT and DHEA in the medium analyzed using ELISA.
RESULTS
1) DHEA-S at a physiological concentration (3.5 μM) was a suitable substrate for DHT production, resulting in final tissue DHT concentrations > 100 nM; 2) DHEA at a physiological concentration (10 nM) was not an effective substrate for DHT production; 3) DHEA at a supra-physiological concentration (3.5 μM) was an effective substrate for DHT production; 4) the steroid sulfatase (STS)inhibitor STX64 completely inhibited production of DHT from DHEA-S.
CONCLUSION
Benign prostate tissue and CaP tissue produced DHT from DHEA-S at physiologic concentrations, and DHEA only at supra-physiologic concentrations. Therefore, DHEA-S is the adrenal androgen most likely to be a substrate for intracrine DHT production, with STS critical to DHT production from DHEA-S. Therefore, targeting transport of DHEA-S from circulation into CaP cells or desulfation by STS represent significant new therapeutic targets.
Funding: NIH grant: 1R01CA193829-01A1.