Establishment of type II 5α-reductase over-expressing cell line as an inhibitor screening model

Dihydrotestosterone (DHT) is the most potent male hormone that causes androgenetic alopecia. The type II 5α-reductase is an enzyme that catalyzes the conversion of testosterone (T) to DHT, therefore it can be expected that specific inhibitors for type II 5α-reductase may improve the pathophysiologic status of androgenetic alopecia. In this study, we attempted to establish the reliable and convenient screening model for type II 5α-reductase inhibitors. After transfection of human cDNA for type II 5α-reductase into HEK293 cells, the type II 5α-reductase over-expressing stable cells were selected by G418 treatment. RT-PCR and Western blot analyses confirmed that type II 5α-reductase gene was expressed in the stable cells. In in vitro enzymatic assay, 10 μg of stable cell extract completely converted 1 μCi (∼0.015 nmol) of T into DHT. The type II 5α-reductase activity was inhibited by finasteride in a dose-dependent manner, confirming the reliability of screening system. In cell culture condition, 2 × 105 of stable cells completely converted all the input T (∼0.03 nmol) into DHT by 4 h incubation, demonstrating that the stable cell line can be used as a cell-based assay system. Using this system, we selected the extracts of Curcumae longae rhizoma and Mori ramulus as the potential inhibitors for type II 5α-reductase. These results demonstrate that the type II 5α-reductase over-expressing stable cell line is a convenient and reliable model for screening and evaluation of inhibitors.