Effects of new 17α-hydroxylase/C17,20-lyase inhibitors on LNCaP prostate cancer cell growth in vitro and in vivo

Our laboratory has been developing new inhibitors of a key regulatory enzyme of testicular and adrenal androgen synthesis 17 alpha-hydroxylase/C-17.20-lyase (P450c17), with the aim of improving prostate cancer treatment. We designed and evaluated two groups of azolyl steroids: Delta 5-non-competitive inhibitors (Delta 5NCls), VN/63-1, VN/85-1, VN/87-1 and their corresponding Delta 4 derivatives (Delta 4NCls), VN/107-1, VN/108-1 and VN/109-1. The human P450c17 gene was transfected into LNCaP human prostate cancer cells. and the resultant LNCaP-CYP17 cells were utilized to evaluate the inhibitory potency of the new azolyl steroids. VN/85-1 and VN/108-1 had the lowest IC50 values of 1.25 +/- 0.44 nM and 2.96 +/- 0.78 nM respectively, which are much lower than that of the known P450 inhibitor ketoconazole (80.7 +/- 1.8 nM). To determine whether the compounds had direct actions on proliferation of wild-type LNCaP cells, cell growth studies were performed. All of the Delta 5NCls and VN/108-1 blocked the growth-stimulating effects of androgens, In steroid-free media, the Delta 5NCls decreased the proliferation of LNCaP cells by 35-40%, while all of the Delta 4NCls stimulated LNCaP cells growth 1.5- to 2-fold, In androgen receptor (AR) binding studies, carried out to determine the mechanism of this effect, all of the Delta 4NCls (5 mu M) displaced 77-82% of synthetic androgen R1881 (5 nM) from the LNCaP AR. The anti-androgen flutamide and the Delta 5NCls displaced 53% and 32-51% of R1881 bound to AR respectively. These results suggested that the Delta 5NCls may also be acting as anti-androgens. We further evaluated our inhibitors in male severe combined immunodeficient mice bearing LNCaP tumour xenografts. In this model VN/85-1 was as effective as finasteride at inhibiting tumor growth (26% and 28% inhibition, respectively) and the inhibitory effect of VN/87-1 was similar to that of castration (33% and 36% inhibition respectively). These results suggest that VN/85-1 and VN/87-1 may be potential candidates for treatment of prostate cancer. (C) 1999 Cancer Research Campaign.