Decoding endocannabinoid signaling.

JZL184, is a covalent inactivator that exhibits a half-maximal inhibitory concentration (IC50) for MAGL of 8 nM (its IC50 for FAAH is 4 μM). JZL184 doesn’t inhibit any of 40 other serine hydrolases in the mouse brain membrane proteome. When administered to mice, JZL184 inhibits MAGL activity by 85% and induces a prolonged eightfold increase in the level of 2-AG in the brain while not increasing other acylglycerol or acylethanolamide levels. library of carbamates against a mouse brain membrane proteome that contains a range of serine hydrolases rather than against pure MAGL. They used activity-based protein profiling (ABPP) to covalently modify all the serine hydrolases with a fluorescent or biotinylated fluorophosphonate and screened for compounds that could selectively prevent labeling of MAGL. ABPP was used at each step of optimization to ensure that as more potent inhibitors were synthesized, they retained high Endocannabinoids—the endogenous ligands for the cannabinoid receptors—are attracting increasing attention as mediators of neurological, anti-inflammatory and proliferative effects1. There are two wellcharacterized endocannabinoids: arachidonoylethanolamide (AEA or anandamide) and 2arachidonoylglycerol (2-AG). 2-AG binds to the two cannabinoid receptors, CB1 and CB2, whereas AEA binds only to the CB1 receptor. CB1 and CB2 are seven-transmembrane G protein–coupled receptors that lower cyclic AMP levels following ligand binding. The CB1 receptor is abundant in the brain and the CB2 receptor is abundant in macrophages, but both receptors are being found in an increasing number of tissues. The brain CB1 receptor functions in a number of neurological responses, including postsynaptic desensitization of neuronal firing, which is mediated by 2-AG (Fig. 1). Both AEA and 2-AG are generated ondemand and then rapidly inactivated by hydrolysis. The ephemeral nature of these mediators makes studies of their role in complex biological responses challenging. Genetic deletion or pharmacological inhibition of the hydrolases that inactivate AEA and 2-AG are powerful approaches to defining endocannabinoid biology. Knockout animals and specific inhibitors of fatty acid amide hydrolase (FAAH) have been instrumental in elucidating the role of AEA in cell signaling2,3. Comparable reagents have not been available for monoacylglycerol lipase (MAGL), which inactivates 2-AG, but in this issue, Long et al. report the first potent and specific inhibitor of this enzyme4. The most daunting aspect of generating useful reagents is maintaining specificity as one increases potency. In many cases, the specificity of an inhibitor is inversely proportional to the number of enzymes against which it has been screened. Long et al. tackled the problem of specificity up-front by screening candidate compounds from a Decoding endocannabinoid signaling