CHARACTERIZATION OF TYPE-I 5-ALPHA-REDUCTASE ACTIVITY IN DU145 HUMAN PROSTATIC ADENOCARCINOMA CELLS

The conversion of testosterone (T) to dihydrotestosterone (DHT) has be en demonstrated to be catalysed by at least two isoforms of human ster oid 5 alpha-reductase, designated types I and II. Type II 5 alpha-redu ctase expression predominates in human accessory sex tissues, localize d to the fibromuscular stromal compartment. The type I isoform predomi nates in skin, prostatic epithelia and, to a lesser extent, in prostat ic fibromuscular stroma. The significance of the type I isoform to pro static cellular growth and function remains undefined. In cultured DU1 45 cells, we evaluated the metabolism of [C-14]-T and demonstrated the time-dependent formation of [C-14]-DHT. Oxidative metabolism (convers ion of [C-14]-T to [C-14]-androstenedione) and the formation of conjug ated androgen metabolites occurred at a relatively low rate in the DU1 45 cells. Using human type I 5 alpha-reductase cDNA, Northern blot ana lysis of DU145 cell mRNA revealed high levels of type I isoform expres sion. Analogous probing of the DU145 cells with a human 5 alpha-reduct ase II cDNA failed to reveal expression of the type II isoform. The ex pression of functional type I activity has been confirmed pharmacologi cally using isoform-selective 5 alpha-reductase inhibitors. Reductive metabolism of [H-3]-T in the DU145 cells was inhibited in a concentrat ion-dependent manner by LY306089, a potent non-steroidal type I-select ive inhibitor (IC50 = 10.0 nM). SKF105657, a steroidal type II-specifi c inhibitor was distinctly less active at inhibiting [H-3]-DHT formati on. LY306089 was a non-competitive inhibitor of type I 5 alpha-reducta se in DU145 cellular homogenates with an apparent K-i value of 4.0 nM. These studies have identified and pharmacologically defined type I 5 alpha-reductase activity in an androgen-insensitive prostatic cancer c ell line and provide the basis for additional investigations into the significance of type I 5 alpha-reductase to human prostatic pathophysi ology. Copyright (C) 1996 Elsevier Science Ltd.