Mechanism-Based Inhibition of Human Steroid 5-Reductase by Finasteride: Enzyme-Catalyzed Formation of NADP-Dihydrofinasteride, a Pot
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- 作者：Herbert G. Bull ; Margarita Garcia-Calvo ; Stefan Andersson ; Walter F. Baginsky ; H. Karen Chan ; Dina E. Ellsworth ; Randall R. Miller ; Ralph A. Stearns ; Raman K. Bakshi ; Gary H. Rasmusson ; Richard L. Tol
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：March 13, 1996
- 年：1996
- 卷：118
- 期：10
- 页码：2359 - 2365
- 全文大小：180K
- 年卷期：v.118,no.10(March 13, 1996)
- ISSN：1520-5126
文摘
Finasteride is employed in treatment of benignprostatic hyperplasia in man, where its target enzyme issteroid 5
-reductase. It is a novel, potent mechanism-basedinhibitor of the human prostate (type 2) isozyme.Althoughit is accepted as an alternate substrate and is ultimately reduced todihydrofinasteride, this proceeds through anenzyme-bound NADP-dihydrofinasteride adduct. Finasteride isprocessed with a second-order rate constant,ki/Ki= 1 × 106 M-1s-1, that approacheskcat/Km for reduction oftestosterone, 3 × 106 M-1s-1, and essentially everycatalytic event is lethal (partition ratio 
1.07). Themembrane-bound enzyme-inhibitor complex formed from[3H]finasteride appears to release[3H]dihydrofinasteride with a half-life of 1 monthat 37 
C (k = (2.57 ± 0.03) ×10-7 s-1), as identified by massspectroscopy. The intermediate NADP-dihydrofinasteride adductcan be recoveredintact by denaturation of the enzyme-inhibitor complex and has beenpurified. Free in solution, it likewise decomposesto dihydrofinasteride (half-life = 11 days). An extremely potentbisubstrate analog inhibitor, this NADP-dihydrofinasteride adduct binds to the free enzyme with a second-orderrate constant equal tokcat/Km for turnoveroftestosterone and has a dissociation constant Ki 1 × 10-13 M. Finasteride is also amechanism-based inhibitor ofthe human skin (type 1) isozyme, but it is processed with a muchsmaller second-order rate constant,ki/Ki = 3 ×103M-1 s-1, whichattenuates its activity against this isozyme in vivo. Themechanism explains the exceptional potencyand specificity of finasteride in treatment of benign prostatichyperplasia, and the concept may have application toother pyridine nucleotide-linked enzymes.
-reductase. It is a novel, potent mechanism-basedinhibitor of the human prostate (type 2) isozyme.Althoughit is accepted as an alternate substrate and is ultimately reduced todihydrofinasteride, this proceeds through anenzyme-bound NADP-dihydrofinasteride adduct. Finasteride isprocessed with a second-order rate constant,ki/Ki= 1 × 106 M-1s-1, that approacheskcat/Km for reduction oftestosterone, 3 × 106 M-1s-1, and essentially everycatalytic event is lethal (partition ratio 1.07). Themembrane-bound enzyme-inhibitor complex formed from[3H]finasteride appears to release[3H]dihydrofinasteride with a half-life of 1 monthat 37 C (k = (2.57 ± 0.03) ×10-7 s-1), as identified by massspectroscopy. The intermediate NADP-dihydrofinasteride adductcan be recoveredintact by denaturation of the enzyme-inhibitor complex and has beenpurified. Free in solution, it likewise decomposesto dihydrofinasteride (half-life = 11 days). An extremely potentbisubstrate analog inhibitor, this NADP-dihydrofinasteride adduct binds to the free enzyme with a second-orderrate constant equal tokcat/Km for turnoveroftestosterone and has a dissociation constant Ki 1 × 10-13 M. Finasteride is also amechanism-based inhibitor ofthe human skin (type 1) isozyme, but it is processed with a muchsmaller second-order rate constant,ki/Ki = 3 ×103M-1 s-1, whichattenuates its activity against this isozyme in vivo. Themechanism explains the exceptional potencyand specificity of finasteride in treatment of benign prostatichyperplasia, and the concept may have application toother pyridine nucleotide-linked enzymes.