Cholesterol is an essential structural component of cellular membranes and serves as a precursor for several classes of signaling molecules. Cholesterol exerts its effects and is, itself, regulated in large part by engaging in specific interactions with proteins. The full complement of sterol-binding proteins that exist in mammalian cells, however, remains unknown. Here, we describe a chemoproteomic strategy that uses clickable, photoreactive sterol probes in combination with quantitative mass spectrometry to globally map cholesterol-protein interactions directly in living cells. We identified over 250 cholesterol-binding proteins, including many established and previously unreported interactions with receptors, channels, and enzymes. Prominent among the newly identified interactions were enzymes that regulate sugars, glycerolipids, and cholesterol itself, as well as those involved in vesicular transport and protein glycosylation and degradation, pointing to key nodes in biochemical pathways that may couple sterol concentrations to the control of other metabolites and protein localization and modification.

Eukaryotic and prokaryotic organisms possess huge numbers of uncharacterized enzymes. Selective inhibitors offer powerful probes for assigning functions to enzymes in native biological systems. Here, we discuss how the chemical proteomic platform activity-based protein profiling (ABPP) can be implemented to discover selective and in vivo-active inhibitors for enzymes. We further describe how these inhibitors have been used to delineate the biochemical and cellular functions of enzymes, leading to the discovery of metabolic and signaling pathways that make important contributions to human physiology and disease. These studies demonstrate the value of selective chemical probes as drivers of biological inquiry.

Summary Lipids play central roles in physiology and disease, where their structural, metabolic, and signaling functions often arise from interactions with proteins. Here, we describe a set of lipid-based chemical proteomic probes and their global interaction map in mammalian cells. These interactions involve hundreds of proteins from diverse functional classes and frequently occur at sites of drug action. We determine the target profiles for several drugs across the lipidinteraction proteome, revealing that its ligandable content extends far beyond traditionally defined categories of druggable proteins. In further support of this finding, we describe a selective ligand for the lipid-binding protein nucleobindin-1 (NUCB1) and show that this compound perturbs the hydrolytic and oxidative metabolism of endocannabinoids in cells. The described chemical proteomic platform thus provides an integrated path to both discover and pharmacologically characterize a wide range of proteins that participate in lipid pathways in cells.

Chemical probes are critical tools for elucidating the biological functions of proteins and can lead to new medicines for treating disease. The pharmacological validation of protein function requires verification that chemical probes engage their intended targets in vivo. Here we discuss technologies, both established and emergent, for measuring target engagement in living systems and propose that determining this parameter should become standard practice for chemical probe and drug discovery programs.

The endocannabinoids 2-arachidonoyl glycerol (2-AG) and N-arachidonoyl ethanolamine (anandamide) are principally degraded by monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), respectively. The recent discovery of O-aryl carbamates such as JZL184 as selective MAGL inhibitors has enabled the functional investigation of 2-AG signaling pathways in vivo. Nonetheless, JZL184 and other reported MAGL inhibitors still display low-level cross-reactivity with FAAH and peripheral carboxylesterases, which can complicate their use in certain biological studies. Here, we report a distinct class of O-hexafluoroisopropyl (HFIP) carbamates that inhibit MAGL in vitro and in vivo with excellent potency and greatly improved selectivity, including showing no detectable cross-reactivity with FAAH. These findings designate HFIP-carbamates as a versatile chemotype for inhibiting MAGL and should encourage the pursuit of other serine hydrolase inhibitors that bear reactive groups resembling the structures of natural substrates.

BACKGROUND AND PURPOSESince monoacylglycerol lipase (MAGL) has been firmly established as the predominant catabolic enzyme of the endocannabinoid 2-arachidonoylglycerol (2-AG), a great need has emerged for the development of highly selective MAGL inhibitors. Here, we tested the in vivo effects of one such compound, KML29 (1,1,1,3,3,[1,3]dioxol-5-yl)(hydroxy)methyl)piperidine-1-carboxylate). EXPERIMENTAL APPROACHIn the present study, we tested KML29 in murine inflammatory (i.e. carrageenan) and sciatic nerve injury pain models, as well as the diclofenac-induced gastric haemorrhage model. KML29 was also evaluated for cannabimimetic effects, including measurements of locomotor activity, body temperature, catalepsy, and cannabinoid interoceptive effects in the drug discrimination paradigm. KEY RESULTSKML29 attenuated carrageenan-induced paw oedema and completely reversed carrageenan-induced mechanical allodynia. These effects underwent tolerance after repeated administration of high-dose KML29, which were accompanied by cannabinoid receptor 1 (CB1) receptor desensitization. Acute or repeated KML29 administration increased 2-AG levels and concomitantly reduced arachidonic acid levels, but without elevating anandamide (AEA) levels in the whole brain. Furthermore, KML29 partially reversed allodynia in the sciatic nerve injury model and completely prevented diclofenacinduced gastric haemorrhages. CB1 and CB2 receptors played differential roles in these pharmacological effects of KML29. In contrast, KML29 did not elicit cannabimimetic effects, including catalepsy, hypothermia and hypomotility. Although KML29 did not substitute for Δ 9 -tetrahydrocannabinol (THC) in C57BL/6J mice, it fully and dose-dependantly substituted for AEA in fatty acid amide hydrolase (FAAH) (−/−) mice, consistent with previous work showing that dual FAAH and MAGL inhibition produces THC-like subjective effects. CONCLUSIONS AND IMPLICATIONSThese results indicate that KML29, a highly selective MAGL inhibitor, reduces inflammatory and neuropathic nociceptive behaviour without occurrence of cannabimimetic side effects. LINKED ARTICLESThis article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx

Serine hydrolases are one of the largest and most diverse enzyme classes in Nature. Inhibitors of serine hydrolases are used to treat many diseases, including obesity, diabetes, cognitive dementia, and bacterial and viral infections. Nonetheless, the majority of the 200+ serine hydrolases in mammals still lack selective inhibitors for their functional characterization. We and others have shown that activated carbamates, through covalent reaction with the conserved serine nucleophile of serine hydrolases, can serve as useful inhibitors for members of this enzyme family. The extent to which carbamates, however, cross-react with other protein classes remains mostly unexplored. Here, we address this problem by investigating the proteome-wide reactivity of a diverse set of activated carbamates in vitro and in vivo using a combination of competitive and click chemistry (CC)-activity-based protein profiling (ABPP). We identify multiple classes of carbamates, including O-aryl, O-hexafluoroisopropyl (HFIP), and O-N-hydroxysuccinimidyl (NHS) carbamates that react selectively with serine hydrolases across entire mouse tissue proteomes in vivo. We exploit the proteome-wide specificity of HFIP carbamates to create in situ imaging probes for the endocannabinoid hydrolases monoacylglycerol lipase (MAGL) and alpha-beta hydrolase-6 (ABHD6). These findings, taken together, designate the carbamate as a privileged reactive group for serine hydrolases that can accommodate diverse structural modifications to produce inhibitors that display exceptional potency and selectivity across the mammalian proteome.Serine hydrolases comprise about ~1% of all proteins in most eukaryotic and prokaryotic organisms, including humans, (1) and perform a diverse array of crucial physiological functions including the regulation of bacterial cell wall biosynthesis, (2) viral replication, (3) inflammation, (4) nutrient digestion (5) and metabolism, (6) blood clotting (7) and neuronal signaling. (8,9) Because of this, serine hydrolases have been the focus of drug discovery programs, which have yielded new medicines to treat human disorders such as obesity, (10) diabetes, (11,12) dementia associated with Alzheimer's disease (13) and infectious diseases. (3,14) Despite these advances, selective and in vivo-active inhibitors are still lacking for most of the 200+ serine hydrolases in the human proteome (15) and, consequently many of these enzyme remain poorly characterized in terms of their endogenous biochemical and cellular functions. Thus, there is a great need for new pharmacological tools that target serine hydrolases with good selectivity in vivo, which would serve not only as chemical probes to investigate the function of these enzymes in cell and animal models, but also as potential leads for drug development. (15,16) * Correspondence: mniphak@scripps.edu (M.J.N.), cravatt@scripps.edu (B.F.C.).Supporting Information Synthetic procedures, 1 H NMR, 13 C NMR and HRMS data are provided for the compounds reported herein. This material is availab...

Monoacylglycerol lipase (MAGL) is a principal metabolic enzyme responsible for hydrolyzing the endogenous cannabinoid (endocannabinoid) 2-arachidonoylglycerol (2-AG). Selective inhibitors of MAGL offer valuable probes to further understand the enzyme's function in biological systems and may lead to drugs for treating a variety of diseases, including psychiatric disorders, neuroinflammation, and pain. N-Hydroxysuccinimidyl (NHS) carbamates have recently been identified as a promising class of serine hydrolase inhibitors that shows minimal cross-reactivity with other proteins in the proteome. Here, we explore NHS carbamates more broadly and demonstrate their potential as inhibitors of endocannabinoid hydrolases and additional enzymes from the serine hydrolase class. We extensively characterize an NHS carbamate 1a (MJN110) as a potent, selective, and in-vivo-active MAGL inhibitor. Finally, we demonstrate that MJN110 alleviates mechanical allodynia in a rat model of diabetic neuropathy, marking NHS carbamates as a promising class of MAGL inhibitors.