Pregnenolone stimulates LNCaP prostate cancer cell growth via the mutated androgen receptor

Pregnenolone (P-5), a common precursor of many steroids, is present in the blood of normal adult men at concentrations of 1-3 nM. In vitro, P-5 was fo und to stimulate LNCaP-cell proliferation 7-8-fold at a physiological conce ntration (2 nM), and 3-4-fold at a subphysiological concentration (0.2 nM). Growth stimulation at the 2-nM concentration was comparable with that of t he androgen, dihydrotestosterone at its physiological concentration (0.5 nM : 9-10-fold increase in cell number). To determine whether P-5 or its metab olites were mediating this growth response, LNCaP cells were incubated with [H-3]P-5 and high-performance liquid chromatography (HPLC) was performed. After a 48-h exposure, two unidentified metabolites were detected. Although , the P-5 metabolites slightly increased LNCaP-cell growth in vitro, their effect was significantly less than P-5 alone, suggesting that the growth st imulation was mediated by P, itself. We further showed that P, sustained it s proliferative: activity in vivo and stimulated the growth of LNCaP-tumor xenografts in intact male SCID mice as well as in castrated animals. In ord er to determine whether P, was binding to a specific site in LNCaP cells, r eceptor binding studies were performed. Scatchard analysis predicted for a single class of binding sites with K-d=1.4 nM. Studies were performed to de termine the effects of P-5 on transcription mediated by wild-type and LNCaP androgen receptors. P, was shown to activate transcription through the: LN CaP androgen receptor (AR), but not the wild-type AR. This implies that P, most likely stimulates LNCaP-cell proliferation through binding to the cell ular mutated AR present in LNCaP cells. We have also demonstrated that drug s designed to be antagonists of the androgen, progesterone and estrogen rec eptors, and one of our novel compounds designed to be an inhibitor of andro gen synthesis, were potent inhibitors of the AR-mediated transcriptional ac tivity induced by P-5, and were able to inhibit LNCaP-cell proliferation. T hese findings suggest that some prostate cancer patients who appear to beco me hormone-independent may have tumors which are stimulated by P, via a mut ated AR and that these patients could benefit from treatment with antiestro gens, antiprogestins, or with some of our novel androgen synthesis inhibito rs. (C) 2001 Elsevier Science Ltd. All rights reserved.