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Functional Analysis of Cyclooxygenase-2

Lawrence J Marnett

1 Collaborator(s)

Funding source

National Cancer Institute (NIH)
Cyclooxygenase-2 (COX-2) plays a key role in the conversion of arachidonic acid (AA) to prostaglandins, which are an important class of bioactive lipids. COX-2 is highly expressed in inflamed tissue, premalignant lesions, and cancers but not in adjacent normal tissue. COX-2 inhibitors, whether isoform-selective or non- selective, exhibit anti-inflammatory, cancer preventive, and adjuvant cancer therapeutic activities as well as cardiovascular side effects in human clinical trials. COX-2 also oxygenates ester and amide derivatives of AA including 2-arachidonoylglycerol (2-AG) and arachidonoylethanolamide (AEA). 2-AG and AEA are the two best characterized endogenous ligands for the cannabinoid receptors - CB1 and CB2 - and exert a plethora of effects through these receptors. The major focus of endocannabinoid biology has been on the nervous system, but increasing evidence indicates that 2-AG and AEA exert anti-inflammatory and cancer preventive effects. We hypothesize that COX-2-dependent metabolism of 2-AG and AEA lowers endocannabinoid levels, thereby contributing to the development of inflammation and cancer. Our laboratory has studied the structural and functional basis of the interaction of COX-2 with substrates and inhibitors in order to generate detailed insights into the chemical biology of COX-2 and to use this information to synthesize novel agents with which to study or manipulate COX-2 function in vivo. We recently discovered that non-steroidal anti-inflammatory drugs (NSAIDs) that are weak, competitive inhibitors of AA oxygenation by COX-2 are potent, non-competitive inhibitors of 2-AG and AEA oxygenation. This is most dramatic for the (R)-enantiomers of arylpropionic acid NSAIDs (profens), such as (R)-flurbiprofen, (R)-naproxen, and (R)-ibuprofen. While essentially inactive as inhibitors of AA oxygenation, these compounds are moderately potent, substrate-selective inhibitors of COX-2 oxygenation of 2-AG and AEA. These insights provide opportunities to develop chemical probes to investigate the in vivo importance of COX-2 oxygenation of endocannabinoids and may explain the reported anti-inflammatory and cancer preventive activities of (R)-profens. Thus, we propose to (1) use X-ray crystallography, site-directed mutagenesis, and enzyme kinetics studies to determine the structural and functional basis for (R)-profen binding to COX-2 in order to (2) design and synthesize more potent and selective inhibitors of endocannabinoid oxygenation in vitro and in vivo. The optimized molecules will be used to (3) test the hypothesis that COX-2 lowers endocannabinoid levels in models of colonic inflammation and cancer and that endocannabinoid levels can be restored by substrate-selective inhibitors of COX-2. These substrate-selective inhibitors may represent candidate cancer chemopreventive agents that lack the gastrointestinal and cardiovascular side effects of currently marketed NSAIDs.

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