Kinetic inhibitory profile of BIA 3-202, a novel fast tight-binding, reversible and competitive catechol-O-methyltransferase inhibitor

The present study reports the kinetic inhibitory profile of 1-[3,4-dihydroxy-5-nitroplienyl]-2-phenyl-ethanone (BIA 3-202), a novel inhibitor of soluble catechol-O-methyltransferase (COMT) in rat liver. After an oral single dose (30 mg kg(-1)), there was a time-dependent recovery of enzyme activity from 98 +/- 2% inhibition at 30 min to total recovery at 24 It after treatment. The inhibitory effect produced by BIA 3-202 on soluble COMT was reversible after gel filtration of the samples. BIA 3-202 acted as a fast inhibitor of rat liver soluble COMT, interacting immediately with the enzyme after mixing. No differences were observed in the metanephrine formation rates (in nmol mg protein(-1) min(-1)) obtained without and with a 60-min preincubation with 30 nNI of BIA 3-202 (1.30 +/- 0.02 and 1.35 +/- 0.03, respectively). The tight-binding nature of the inhibition produced by BIA 3-202 was evaluated by performing an Ackermann-Potter plot. The true K-i for BIA 3-202, derived from the nonlinear regression analysis, was 0.19 +/- 0.02 nM. In substrate competition studies, an increase in the concentration of adrenaline resulted in a linear increase in IC50 values for BIA 3-202. In conclusion, BIA 3-202 behaves as a reversible, potent and fast tight-binding COMT inhibitor that acts competitively at the substrate binding site of rat liver soluble COMT. (C) 2002 Elsevier Science B.V. All rights reserved.