In vitro activity: Finasteride binds to the type 2 isozyme-NADPH complex to form a ternary complex with Ki of 1.19 nM, which then rearranges to a high affinity complex (E:I) with a pseudo first order rate constant of 1.62 ms. Finasteride dose-dependently inhibits the growth rate of the LnCap cell line. Finasteride markedly inhibits prostate-specific antigen (PSA) secretion and expression in LNCaP cells.

Kinase Assay: Finasteride is an orally active testosterone 5-alpha-reductase inhibitor (Ki= 10 nM). Target: 5-alpha Reductase Approved: 1992 Finasteride, a synthetic 4-azasteroid antiandrogen compound, is a specific inhibitor of steroid Type II 5α-reductase, an intracellular enzyme that converts the androgen testosterone into 5α-dihydrotestosterone (DHT). Finasteride is used in the treatment of prostate cancer, benign prostatic hyperplasia, and androgenetic alopecia (male pattern baldness). In benign prostatic hyperplasia, finasteride inhibits 5alpha-reductase activity in epithelium for Ki of 10 nM, significantly lower than in stroma (Ki = 33nM).