COMPARISON OF THE CYCLOOXYGENASE-1 INHIBITORY PROPERTIES OF NONSTEROIDAL ANTIINFLAMMATORY DRUGS (NSAIDS) AND SELECTIVE COX-2 INHIBITORS, USING SENSITIVE MICROSOMAL AND PLATELET ASSAYS
D. Riendeau et al., COMPARISON OF THE CYCLOOXYGENASE-1 INHIBITORY PROPERTIES OF NONSTEROIDAL ANTIINFLAMMATORY DRUGS (NSAIDS) AND SELECTIVE COX-2 INHIBITORS, USING SENSITIVE MICROSOMAL AND PLATELET ASSAYS, Canadian journal of physiology and pharmacology, 75(9), 1997, pp. 1088-1095
Two forms of cyclooxygenase (COX) activity are involved in the synthes
is of prostaglandins, prostacyclins, and thromboxanes in mammalian cel
ls. There is now convincing evidence, obtained with a number of struct
urally distinct inhibitors, that selective COX-2 inhibitors possess an
ti-inflammatory effects with an improved gastrointestinal tolerability
compared with conventional nonsteroidal anti-inflammatory drugs (NSAI
Ds) affecting both COX-1 and COX-2. As more selective COX-2 inhibitors
are being developed, assays with a high degree of sensitivity to inhi
bition are needed to compare the relative effects of compounds on COX-
1 activity. In the present report, we describe a sensitive assay for t
he inhibition of human COX-1 based on the production of prostaglandin
E-2 by microsomes from U937 cells incubated with a subsaturating conce
ntration 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 mu M for salicylate and ac
etaminophen. Potent and nonselective NSAIDs such as sulindac sulfide,
diclofenac, and indomethacin showed IC50 values of <20 nM. Among the c
ompounds that have been reported to show selectivity for COX-2, the ra
nk order of potency against COX-1 was DuP 697 > SC-58451 > celecoxib >
nimesulide similar to meloxicam similar to piroxicam similar to NS-39
8 similar to RS-57067 > SC-57666 > SC-58125 > flosulide > etodolac > L
-745,337 > DFU similar to T-614, with IC50 values ranging from 7 nM to
17 mu M. A good correlation was obtained between the IC50 values for
the inhibition of microsomal COX-1 and both the inhibition of TXB2 pro
duction by Ca2+ ionophore challenged platelets and the inhibition of p
rostaglandin E-2 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 C
OX-1 for all NSAIDs and selective COX-2 inhibitors examined with discr
imination of their potency under conditions of limited availability of
arachidonic acid.