Cloning, Expression and Characterization of Rhesus Macaque Types 1 and 2 5Alpha-Reductase: Evidence for Mechanism-Based Inhibition by Finasteride

The rhesus macaque types 1 and 2 5alpha-reductase (5aR1 and 5aR2) were cloned and expressed in COS cells to facilitate comparison of rhesus and human 5aRs. The deduced protein sequences of the rhesus 5aRs shared 94% and 96% identity with the human type 1 and 2 isozymes, respectively. Despite a four amino acid insertion at the N-terminal region of rhesus 5aR1, the biochemical properties of rhesus and human homologs are very similar with respect to pH optimum, K_m values for testosterone and progesterone, and inhibition by a variety of inhibitors. As expected, the biochemical properties of the human and rhesus 5aR2 are also very similar. The mechanism of inhibition of the rhesus 5aR1 and 5aR2 by finasteride was investigated in more detail. Finasteride displays time dependent inhibition of the rhesus 5aR1 and 5aR2 with second order rate constants of 4 × 10³ M⁻¹ s⁻¹ and 5.2 × 10⁵ M⁻¹ s⁻¹. Inhibition of rhesus 5aR2 with ³H-finasteride resulted in ³H bound to the enzyme which is not released by dialysis. Heat denaturation of the [rhesus 5aR2:inhibitor] complex releases dihydrofinasteride, a breakdown product presumably related to the NADP⁺-adduct previously identified with the human 5aRs (Bull et al., Mechanism-based inhibition of human steroid 5-reductase by finasteride: Enzyme catalyzed formation of NADP-dihydrofinasteride, a potent bisubstrate analog inhibitor. J. Amer. Chem. Soc., 1996, 118, 2359-2365). Taken together, these results provide good evidence that the rhesus macaque is a suitable model to evaluate the pharmacological properties of finasteride and other 5aR inhibitors.