Marc P. Baggelaar

Cannabinoid CB2 receptor ligand profiling reveals biased signalling and off-target activity

The cannabinoid CB2 receptor (CB2R) represents a promising therapeutic target for various forms of tissue injury and inflammatory diseases. Although numerous compounds have been developed and widely used to target CB2R, their selectivity, molecular mode of action and pharmacokinetic properties have been poorly characterized. Here we report the most extensive characterization of the molecular pharmacology of the most widely used CB2R ligands to date. In a collaborative effort between multiple academic and industry laboratories, we identify marked differences in the ability of certain agonists to activate distinct signalling pathways and to cause off-target effects. We reach a consensus that HU910, HU308 and JWH133 are the recommended selective CB2R agonists to study the role of CB2R in biological and disease processes. We believe that our unique approach would be highly suitable for the characterization of other therapeutic targets in drug discovery research.

Activity-based protein profiling reveals off-target proteins of the FAAH inhibitor BIA 10-2474

A clue to a drugs neurotoxicity? The drug BIA 10-2474 inhibits fatty acid amide hydrolase (FAAH), a lipase that degrades a specific endocannabinoid. On the basis of this activity, BIA 10-2474 was being developed as a potential treatment for anxiety and pain. In a phase 1 trial of the drug, one subject died, and four others suffered brain damage. As an initial step in investigating whether inhibition of off-target proteins by BIA 10-2474 might contribute to its clinical neurotoxicity, van Esbroeck et al. used activity-based proteomic assays to identify proteins targeted by the drug. Studying human cells and brain samples from subjects not associated with the trial, they found that BIA 10-2474 targeted several different lipases in addition to FAAH. It also substantially altered lipid metabolism in cultured neurons. Science, this issue p. 1084 A drug that was unexpectedly neurotoxic in a clinical trial has off-target activities in chemical proteomic assays. A recent phase 1 trial of the fatty acid amide hydrolase (FAAH) inhibitor BIA 10-2474 led to the death of one volunteer and produced mild-to-severe neurological symptoms in four others. Although the cause of the clinical neurotoxicity is unknown, it has been postulated, given the clinical safety profile of other tested FAAH inhibitors, that off-target activities of BIA 10-2474 may have played a role. Here we use activity-based proteomic methods to determine the protein interaction landscape of BIA 10-2474 in human cells and tissues. This analysis revealed that the drug inhibits several lipases that are not targeted by PF04457845, a highly selective and clinically tested FAAH inhibitor. BIA 10-2474, but not PF04457845, produced substantial alterations in lipid networks in human cortical neurons, suggesting that promiscuous lipase inhibitors have the potential to cause metabolic dysregulation in the nervous system.

Rapid and profound rewiring of brain lipid signaling networks by acute diacylglycerol lipase inhibition

Significance Lipid transmitters, such as endocannabinoid and eicosanoids, play important roles in the nervous system and regulate behaviors that include pain, emotionality, and addiction. Chemical probes that perturb lipid transmitter biosynthesis are needed to understand the functions of these pathways in the nervous system. Here, we describe selective and in vivo active inhibitors of the diacylglycerol lipases DAGLα and DAGLβ, which biosynthesize the endocannabinoid 2-arachidonoylglycerol (2-AG). We show that these inhibitors produce rapid and dramatic changes in a brain lipid signaling network, comprising not only 2-AG, but also eicosanoids and diacylglycerols. These lipid changes are accompanied by impairments in synaptic plasticity and attenuation of neuroinflammatory responses in vivo, underscoring the broad role that DAGLs play in nervous system metabolism and function. Diacylglycerol lipases (DAGLα and DAGLβ) convert diacylglycerol to the endocannabinoid 2-arachidonoylglycerol. Our understanding of DAGL function has been hindered by a lack of chemical probes that can perturb these enzymes in vivo. Here, we report a set of centrally active DAGL inhibitors and a structurally related control probe and their use, in combination with chemical proteomics and lipidomics, to determine the impact of acute DAGL blockade on brain lipid networks in mice. Within 2 h, DAGL inhibition produced a striking reorganization of bioactive lipids, including elevations in DAGs and reductions in endocannabinoids and eicosanoids. We also found that DAGLα is a short half-life protein, and the inactivation of DAGLs disrupts cannabinoid receptor-dependent synaptic plasticity and impairs neuroinflammatory responses, including lipopolysaccharide-induced anapyrexia. These findings illuminate the highly interconnected and dynamic nature of lipid signaling pathways in the brain and the central role that DAGL enzymes play in regulating this network.

Total Synthesis of the Triglycosyl Phenolic Glycolipid PGL-tb1 from Mycobacterium tuberculosis†

Mycobacterium tuberculosis (M. tb) is one of the most important pathogens. Despite the availability of antibiotics and a vaccine (BCG), one third of the world s population is infected with M. tb, causing 8 million casualties and 1.5 million deaths yearly. Synergy with HIV and the appearance of M. tb strains that are multi-drug resistant or hypervirulent, poses further threats. The search for novel drugs and more effective vaccines entered a new era with the publication of the genome sequence of M. tb H37Rv. Based on this sequence, genes that code for enzymes involved in the critical steps of host– pathogen interaction were identified. Many of these enzymes are involved in the synthesis and transport of complex lipids, in particular phthiocerol dimycocerosates (DIM or PDIM) present in the outer layer of the M. tb cell envelope. Furthermore, several M. tb strains synthesize closely related phenolic glycolipids (PGL-tb1, Figure 1) in which the phthiocerol is connected to a glycosylated phenol. It has been shown that DIM/PDIMs are required for multiplication and persistence of M. tb in vivo. Next to this, PGLtb1 (1, Figure 1) is suspected to be involved in hypervirulence of specific M. tb strains. The interplay of M. tb with the human host is very complex, with PGL-tb1 as one of the most unusual virulence factors modulating its defense systems and causing disease. Thus, there is a great need for antigens that permit to distinguish between prior BCG vaccination and infection. Recently, an enzyme-linked immunosorbent assay (ELISA) based on PGL-tb1 has shown potential for the diagnosis of TB in HIV-infected patients. Furthermore, a lipidomics platform has been established for chemotaxonomic analysis of M. tb. Thus, access to pure, chemically synthesized PGL-tb1 (1) has become crucial for reliable immunological studies. Preluded by the first synthesis of phthiocerol dimycocerosate PDIM A we now report the first total synthesis of PGLtb1. The size and complexity of PGL-tb1 is impressive. The parent phenylphthiocerol has four stereocenters and is esterified to two molecules of mycocerosic acid (2), a longchain quadruple methyl-branched fatty acid. Through the phenol terminus, the aglycon is linked to a linear trisaccharide. To get PGL-tb1 within reach, a strongly convergent synthetic strategy had to be designed (see Scheme 1). Esterification with mycocerosic acid was planned for a late stage because of its precious nature. Instead of the glycosylation of the phenol terminus with the trisaccharide construct, we chose to connect the trisaccharide in the form of a para-iodophenoxy-substituted glycan to a terminal alkyne through Sonogashira coupling. This strategy avoids a stereoselective glycosylation step with an activated trisaccharide in a late stage of the synthesis. The alkyne function should be fully reduced to the corresponding aliphatic fragment together with the removal of the benzyl protecting groups in the final step. An additional advantage is that the bifunctional “spacer” of the required length, equipped with a terminal alkyne, would be readily accessible from commercially available alkynol 5 in a few steps. The right-hand side of phenylphthiocerol was planned to be prepared by using our asymmetric conjugate addition– Figure 1. PGL-tb1 (1).

The novel, orally available and peripherally restricted selective cannabinoid CB2 receptor agonist LEI-101 prevents cisplatin-induced nephrotoxicity.

Here, we have characterized 3‐cyclopropyl‐1‐(4‐(6‐((1,1‐dioxidothiomorpholino)methyl)‐5‐fluoropyridin‐2‐yl)benzyl)imidazolidine‐2,4‐dione hydrochloride (LEI‐101) as a novel, peripherally restricted cannabinoid CB2 receptor agonist, using both in vitro and in vivo models.

A natural substrate-based fluorescence assay for inhibitor screening on diacylglycerol lipase α

The endocannabinoid 2-arachidonoylglycerol (2-AG) is predominantly biosynthesized by sn-1-diacylglycerol lipase α (DAGL-α) in the CNS. Selective inhibitors of DAGL-α will provide valuable insights in the role of 2-AG in endocannabinoid signaling processes and are potential therapeutics for the treatment of obesity and neurodegenerative diseases. Here, we describe the development of a natural substrate-based fluorescence assay for DAGL-α, using a coupled enzyme approach. The continuous setup of our assay allows monitoring of DAGL-α activity in real-time and in a 96-well plate format. This constitutes a major improvement to the currently available radiometric and LC/MS-based methods, which can be executed only in low-throughput formats. In addition, our assay circumvents the use of radioactive material. We demonstrate that our assay can be used to screen inhibitors of DAGL-α activity, using 1-stearoyl-2-arachidonoyl-sn-glycerol as the physiologically relevant natural substrate of DAGL-α. Furthermore, our method can be employed to measure DAGL activity and inhibition in the mouse brain membrane proteome. Consequently, our assay should serve as a valuable tool for rapid hit validation and lead optimization of DAGL-α inhibitors.

Triazole Ureas Act as Diacylglycerol Lipase Inhibitors and Prevent Fasting-Induced Refeeding

Triazole ureas constitute a versatile class of irreversible inhibitors that target serine hydrolases in both cells and animal models. We have previously reported that triazole ureas can act as selective and CNS-active inhibitors for diacylglycerol lipases (DAGLs), enzymes responsible for the biosynthesis of 2-arachidonoylglycerol (2-AG) that activates cannabinoid CB1 receptor. Here, we report the enantio- and diastereoselective synthesis and structure-activity relationship studies. We found that 2,4-substituted triazole ureas with a biphenylmethanol group provided the most optimal scaffold. Introduction of a chiral ether substituent on the 5-position of the piperidine ring provided ultrapotent inhibitor 38 (DH376) with picomolar activity. Compound 38 temporarily reduces fasting-induced refeeding of mice, thereby emulating the effect of cannabinoid CB1-receptor inverse agonists. This was mirrored by 39 (DO34) but also by the negative control compound 40 (DO53) (which does not inhibit DAGL), which indicates the triazole ureas may affect the energy balance in mice through multiple molecular targets.

Comprehensive Analysis of Structure–Activity Relationships of α-Ketoheterocycles as sn-1-Diacylglycerol Lipase α Inhibitors

Diacylglycerol lipase α (DAGLα) is responsible for the formation of the endocannabinoid 2-arachidonoylglycerol (2-AG) in the central nervous system. DAGLα inhibitors are required to study the physiological role of 2-AG. Previously, we identified the α-ketoheterocycles as potent and highly selective DAGLα inhibitors. Here, we present the first comprehensive structure-activity relationship study of α-ketoheterocycles as DAGLα inhibitors. Our findings indicate that the active site of DAGLα is remarkably sensitive to the type of heterocyclic scaffold with oxazolo-4N-pyridines as the most active framework. We uncovered a fundamental substituent effect in which electron-withdrawing meta-oxazole substituents increased inhibitor potency. (C6-C9)-acyl chains with a distal phenyl group proved to be the most potent inhibitors. The integrated SAR data was consistent with the proposed binding pose in a DAGLα homology model. Altogether, our results may guide the design of future DAGLα inhibitors as leads for molecular therapies to treat neuroinflammation, obesity, and related metabolic disorders.

Chemical Proteomics Maps Brain Region Specific Activity of Endocannabinoid Hydrolases

The biosynthetic and catabolic enzymes of the endocannabinoids tightly regulate endocannabinoid-mediated activation of the cannabinoid CB1 receptor. Monitoring the activities of these endocannabinoid hydrolases in different brain regions is, therefore, key to gaining insight into spatiotemporal control of CB1 receptor-mediated physiology. We have employed a comparative chemical proteomics approach to quantitatively map the activity profile of endocannabinoid hydrolases in various mouse brain regions at the same time. To this end, we used two different activity-based probes: fluorophosphonate-biotin (FP-biotin), which quantifies FAAH, ABHD6, and MAG-lipase activity, and MB108, which detects DAGL-α, ABHD4, ABHD6, and ABHD12. In total, 32 serine hydrolases were evaluated in the frontal cortex, hippocampus, striatum, and cerebellum. Comparison of endocannabinoid hydrolase activity in the four brain regions revealed that FAAH activity was highest in the hippocampus, and MAGL activity was most pronounced in the frontal cortex, whereas DAGL-α was most active in the cerebellum. Comparison of the activity profiles with a global proteomics data set revealed pronounced differences. This could indicate that post-translational modification of the endocannabinoid hydrolases is important to regulate their activity. Next, the effect of genetic deletion of the CB1 receptor was studied. No difference in the enzymatic activity was found in the cerebellum, striatum, frontal cortex, and hippocampus of CB1 receptor knockout animals compared to wild type mice. Our results are in line with previous reports and indicate that the CB1 receptor exerts no regulatory control over the basal production and degradation of endocannabinoids and that genetic deletion of the CB1 receptor does not induce compensatory mechanisms in endocannabinoid hydrolase activity.

Catalytic asymmetric total synthesis of (S)-(-)-zearalenone, a novel lipoxygenase inhibitor

A catalytic asymmetric synthesis of (S)-(-)-zearalenone is reported using asymmetric allylic alkylation for the introduction of the stereocenter. (S)-(-)-Zearalenone turned out to be a novel lipoxygenase inhibitor.