Many non-steroidal anti-inflammatory drugs （NSAIDs） are potent but non-selective inhibitors of both COX-1 and COX-2 in humans. CAY10404 is one of the most selective inhibitors of COX-2 which has been reported to date， with a selectivity index （SI； SI = IC50 COX-1/IC50 COX-2） of >500，000. （The COX-1 IC50 is >500 mM， and COX-2 IC50 is <1 nM.） As a reference point， the SI of celecoxib is about 400. Thus， CAY10404 has an SI which is several logs greater than the first generation of selective COX-2 inhibitors， and is comparable to the SI of second generation selective COX-2 inhibitors， such as valdecoxib and etoricoxib.
