A three-step kinetic mechanism for selective inhibition of cyclo-oxygenase-2 by diarylheterocyclic inhibitors

Cyclo-oxygenase (COX) enzymes are the targets for non-steroidal anti-inflammatory drugs (NSAIDs). These drugs demonstrate a variety of inhibitory mechanisms, which include simple competitive, as well as slow binding and irreversible inhibition. In general, most NSAIDs inhibit COX-1 and -2 by similar mechanisms. A unique class of diarylheterocyclic inhibitors has been developed that is highly selective for COX-2 by virtue of distinct inhibitory mechanisms for each isoenzyme. Several of these inhibitors, with varying selectivity, have been utilized to probe the mechanisms of COX inhibition. Results from analysis of both steady-state and time-dependent inhibition were compared. A generalized mechanism for inhibition, consisting of three sequential reversible steps, can account for the various types of kinetic behaviour observed with these inhibitors.