title: Impact of mechanism-based enzyme inactivation on inhibitor potency: implications for rational drug discovery.
abstract: Mechanism-based enzyme inactivators (MBEIs) have unique kinetic actions that make predictions of potency, selectivity, and potential for metabolic drug interactions more complex than for competitive antagonists. We have derived a mathematical relationship that links the influence of substrate concentration and binding constant ([S] and K(m), respectively), inhibitor concentration and binding constant ([I] and K(I), respectively), and inactivation rate constant (k(inact)) to enzyme activity (v) and maximal activity (V(max)) at any time (t). The kinetic behavior of this relationship was validated in murine-macrophage cell cultures using MBEIs of nitric oxide synthase (NOS). This initial equation was also used in the derivation of a new relationship that directly links the kinetic parameters of mechanism-based inactivation to inhibitory potency at a particular time (IC((t))(50)). Using this direct relationship, we observed that the predicted rank inhibitory potency of a series of MBEIs was improved over that predicted by the K(I) parameter alone. These relationships offer a fundamental understanding of the kinetics of MBEI action and may be useful in the evaluation of these compounds during the discovery process.
authors.affiliation: Department of Pharmaceutics, School of Pharmacy, University at Buffalo, State University of New York, Buffalo, New York 14260-1200, USA. tristan_s_maurer@groton.pfizer.com
authors.forename: T S
authors.initials: TS
authors.lastname: Maurer
authors.forename: M A
authors.initials: MA
authors.lastname: Tabrizi-Fard
authors.forename: H L
authors.initials: HL
authors.lastname: Fung
mesh_terms: D002460:Cell Line; D015195:Drug Design; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics*; D008956:Models, Chemical; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D019323:omega-N-Methylarginine / Q000493:pharmacokinetics*
chemical_list: D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D019001:Nitric Oxide Synthase