INHIBITION OF THE ACTIVITY OF BASIC 5-ALPHA-REDUCTASE (TYPE-1) DETECTED IN DU 145 CELLS AND EXPRESSED IN INSECT CELLS

The purpose of this study was 2-fold: (1) to identify the 5 alpha-redu ctase (5 alpha-R) isozyme(s) present in DU 145 cells, a human cell-lin e of low androgen sensitivity derived from a cerebral metastasis of an epithelial prostate cancer; and (2) to compare the inhibitory potenci es of three compounds on the 'basic' 5 alpha-R isozyme expressed in a baculovirus-directed insect cell system. Conversion of testosterone (T ) into 5 alpha-dihydrotestosterone (DHT) in DU 145 cells was measured by HPLC coupled to a Flo-one HP radioactivity detector. DU 145 cells e xhibited 5 alpha-R activity (21 pmol DHT/min/mg protein) at pH 7.4 whi ch disappeared at pH 5.5 suggesting that, of the two genomically disti nct human isozymes identified so far, type 1 5 alpha-R is expressed in DU 145 cells. This was confirmed by at least two observations: first, 5 alpha-R activity in DU 145 cells was inhibited with much higher pot ency by 4-MA than by finasteride which is known to be a very poor comp etitor of the 'basic' enzyme (IC(50)s = 2.8 +/- 0.2 and 264 +/- 55 nM, respectively). Second, only the type 1 5 alpha-R cDNA and not type 2 5 alpha-R cDNA hybridized with DU 145 RNA. A high potency differential was also recorded for the inhibition of 'basic' type 1 5 alpha-R expr essed in a baculovirus-directed-insect cell system by these two compou nds, 4-MA being considerably more active than finasteride (K-i = 8.4 /- 2.3 and 330 +/- 9 nM, respectively). This inhibition was competitiv e. On the other hand, inhibition by an n-hexane lipid/sterol extract o f Serenoa repens (LSESr) was non-competitive and, when expressed in te rms of recommended therapeutic doses, was 3-fold greater for LSESr tha n for finasteride. These studies suggest that LSESr might exert a regu latory inhibitory activity due to its specific lipid/sterol compositio n.