In-vitro test system for the evaluation of cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) inhibitors based on a single HPLC run with UV detection using bovine aortic coronary endothelial cells (BAECs)

Q3 · MEDICINE

Article

Author: G. Dannhardt ; H. Ulbrich

OBJECTIVE AND DESIGNThe aim of this study was to develop a new, whole-cell test system which is easy to handle and requires a standard equipment for the parallel screening of COX-1 and COX-2 inhibitors.MATERIALSBovine aortic endothelial cells (BAECs).TREATMENT AND METHODSUnstimulated bovine aortic coronary endothelial cells (BAECs) were used as a source of COX-1 and BAECs pretreated with ASA (100 microM) and activated with phorbol myristate acetate (PMA) were used as a source of COX-2. The time- and concentration-dependent induction of COX-2 expression in the BAECs was evaluated by a kinetic profile (HPLC analysis) and detected by Western-Blot analysis using polyclonal antibodies against COX-1 and COX-2.RESULTSIn BAECs, diclofenac and meloxicam showed balanced inhibition of COX-1 (IC50: 0.01/0.4 microM) and COX-2 (IC50: 0.03/0.6 microM). Indomethacin inhibited COX-1 more potently than COX-2 (IC50: 0.008/0.04 microM). Aceclofenac inhibited COX-2 more potently than COX-1 (IC50: 3.0/7.3 microM). DFU and Cl-SC57666 [16] inhibited COX-2 (IC50: 0.04/0.001 microM) highly selectively but did not inhibit COX-1 (IC50: >100 microM).CONCLUSIONSIn summary an assay has been developed, for the determination of IC50-values for inhibitors of COX-1/2 on cells of the same origin, in line with values in the literature. Moreover, new insights have been gained into the relationship of COX-1/2 and lipoxygenase pathways in BAECs by detecting 15- and 12-HETE: Inhibition of COX-1 by the NSAIDs mostly resulted in an enhancement of 15-HETE and 12-HETE release. In contrast inhibition of COX-2 decreased 15-HETE release.

01 Mar 1998·Journal of Biological ChemistryQ2 · BIOLOGY

The Dynamics of Prostaglandin H Synthases

Q2 · BIOLOGY

Article

Author: Liliana E. Scarafia ; Ondine H. Callan ; Amy Y. Mak ; On-Yee So ; David C. Swinney

Prostaglandin H synthases (PGHSs) catalyze the conversion of arachidonic acid to prostaglandins. In this report, we describe the effect of a PGHS2 Y355F mutation on the dynamics of PGHS2 catalysis and inhibition. Tyr355 is part of a hydrogen-bonding network located at the entrance to the cyclooxygenase active site. The Y355F mutant exhibited allosteric activation kinetics in the presence of arachidonic acid that was defined by a curved Eadie-Scatchard plot and a Hill coefficient of 1.36 +/- 0.05. Arachidonic acid-induced allosteric activation has not been directly observed with wild type PGHS2. The mutation also decreased the observed time-dependent inhibition by indomethacin, flurbiprofen, RS-57067, and SC-57666. Detailed kinetic analysis showed that the Y355F mutation decreased the transition state energy associated with slow-binding inhibition (EIdouble dagger) relative to the energy associated with catalysis (ESdouble dagger) by 1.33, 0.67, and 1.06 kcal/mol, respectively, for indomethacin, flurbiprofen, and RS-57067. These observations show Tyr355 to be involved in the molecular mechanism of time-dependent inhibition. We interpret these results to indicate that slow binding inhibitors and the Y355F mutant slow the rate and unmask intrinsic, dynamic events associated with product formation. We hypothesize that the dynamic events are the equilibrium between relaxed and tightened organizations of the hydrogen-bonding network at the entrance to the cyclooxygenase active site. It is these rearrangements that control the rate of substrate binding and ultimately the rate of prostaglandin formation.

01 Jan 1997·Canadian Journal of Physiology and PharmacologyQ4 · MEDICINE

Comparison of the cyclooxygenase-1 inhibitory properties of nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors, using sensitive microsomal and platelet assays

Q4 · MEDICINE

Article

Author: Jocelyne Guay ; Elizabeth Wong ; Denis Riendeau ; Joseph A. Mancini ; Wanda Cromlish ; Stella Charleson

Two forms of cyclooxygenase (COX) activity are involved in the synthesis of prostaglandins, prostacyclins, and thromboxanes in mammalian cells. There is now convincing evidence, obtained with a number of structurally distinct inhibitors, that selective COX-2 inhibitors possess anti-inflammatory effects with an improved gastrointestinal tolerability compared with conventional nonsteroidal anti-inflammatory drugs (NSAIDs) affecting both COX-1 and COX-2. As more selective COX-2 inhibitors are being developed, assays with a high degree of sensitivity to inhibition are needed to compare the relative effects of compounds on COX-1 activity. In the present report, we describe a sensitive assay for the inhibition of human COX-1 based on the production of prostaglandin E2 by microsomes from U937 cells incubated with a subsaturating concentration of arachidonic acid. More than 45 NSAIDs and selective COX-2 inhibitors were tested in this assay. IC50 values ranged from 1 nM for flunixin and flurbiprofen to about 200-500 microM for salicylate and acetaminophen. Potent and nonselective NSAIDs such as sulindac sulfide, diclofenac, and indomethacin showed IC50 values of < 20 nM. Among the compounds that have been reported to show selectivity for COX-2, the rank order of potency against COX-1 was DuP 697 > SC-58451 > celecoxib > nimesulide-meloxicam-piroxicam-NS-398-RS-57067 > SC-57666 > SC-58125 > flosulide > etodolac > L-745,337 > DFU-T-614, with IC50 values ranging from 7 nM to 17 microM. A good correlation was obtained between the IC50 values for the inhibition of microsomal COX-1 and both the inhibition of TXB2 production by Ca2+ ionophore challenged platelets and the inhibition of prostaglandin E2 production by CHO cells stably expressing human COX-1. However, the microsomal assay was more sensitive to inhibition than cell-based assays and allowed the detection of inhibitory effects on COX-1 for all NSAIDs and selective COX-2 inhibitors examined with discrimination of their potency under conditions of limited availability of arachidonic acid.

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Indication	Highest Phase	Country/Location	Organization	Date
Rheumatic Diseases	Phase 1	-	Pfizer Inc.	-
Rheumatic Diseases	Phase 1	US	Pharmacia Corp.	-

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