COX-3 the enzyme and the concept: steps towards highly specialized pathways and precision therapeutics?

Cyclooxygenases (COXs) catalyse the key rate-limiting step in prostanoid and thromboxane biosynthesis and are targets of non-steroidal anti-inflammatory drugs (NSAIDs). Until recently, the presence of only two isoforms—COX-1 and COX-2—remained in question because the potent anti-pyretic and analgesic effects of acetaminophen (paracetamol, tylenol^® ben-u-ron^®) could not be explained by either COX-1 or COX-2 blockades. A novel COX-1 splice variant termed COX-3, sensitive to acetaminophen, was recently discovered by Simmons et al., and is considered to play a key role in the biosynthesis of prostanoids known to be important mediators in pain and fever. Drugs that preferential block COX-1 also appear to act at COX-3. However the existence of COX-3 at the nucleotide sequence level in humans has been called to question. A functional COX-3 in humans is still to come underlining that the concept of COX-3 is still attractive. Here, we discuss some of the implications drawn from the identification of additional functional cyclooxygenase members in the generation of bioactive autacoids.