Monoacylglycerol lipase (MAGL) is one of the key enzymes in the endocannabinoid system. Inhibition of MAGL has been proposed as an attractive approach for the treatment of various diseases. In this study, we designed and successfully synthesized two series of piperazinyl pyrrolidin-2-one derivatives as novel reversible MAGL inhibitors. (R)-[(18)F]13 was identified through the preliminary evaluation of two carbon-11-labeled racemic structures [(11)C]11 and [(11)C]16. In dynamic positron-emission tomography (PET) scans, (R)-[(18)F]13 showed a heterogeneous distribution and matched the MAGL expression pattern in the mouse brain. High brain uptake and brain-to-blood ratio were achieved by (R)-[(18)F]13 in comparison with previously reported reversible MAGL PET radiotracers. Target occupancy studies with a therapeutic MAGL inhibitor revealed a dose-dependent reduction of (R)-[(18)F]13 accumulation in the mouse brain. These findings indicate that (R)-[(18)F]13 ([(18)F]YH149) is a highly promising PET probe for visualizing MAGL non-invasively in vivo and holds great potential to support drug development.
Monoacylglycerol lipase (MAGL) is a serine hydrolase that plays an important role in the endocannabinoid degradation in the brain. It has recently emerged as a promising therapeutic target in the treatment of neuroinflammatory and neurodegenerative diseases, such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. Development of MAGL-specific radioligands for non-invasive imaging by positron-emission tomography (PET) would deepen our knowledge on the relevant pathological changes in diseased states and accelerate drug discovery. In this study, we report the selection and synthesis of two morpholine-3-one derivatives as potential reversible MAGL PET tracer candidates based on their multiparameter optimization scores. Both compounds ([(11)C]1, [(11)C]2) were radiolabeled by direct [(11)C]CO(2) fixation and the in vitro autoradiographic studies demonstrated their specificity and selectivity towards MAGL. Dynamic PET imaging using MAGL knockout and wild-type mice confirmed the in vivo specificity of [(11)C]2. Our preliminary results indicate that morpholine-3-one derivative [(11)C]2 ([(11)C]RO7279991) binds to MAGL in vivo, and this molecular scaffold could serve as an alternative lead structure to image MAGL in the central nervous system.
Chronic inflammation and blood-brain barrier dysfunction are key pathological hallmarks of neurological disorders such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. Major drivers of these pathologies include pro-inflammatory stimuli such as prostaglandins, which are produced in the central nervous system by the oxidation of arachidonic acid in a reaction catalyzed by the cyclooxygenases COX1 and COX2. Monoacylglycerol lipase hydrolyzes the endocannabinoid signaling lipid 2-arachidonyl glycerol, enhancing local pools of arachidonic acid in the brain and leading to cyclooxygenase-mediated prostaglandin production and neuroinflammation. Monoacylglycerol lipase inhibitors were recently shown to act as effective anti-inflammatory modulators, increasing 2-arachidonyl glycerol levels while reducing levels of arachidonic acid and prostaglandins, including PGE2 and PGD2. In this study, we characterized a novel, highly selective, potent and reversible monoacylglycerol lipase inhibitor (MAGLi 432) in a mouse model of lipopolysaccharide-induced blood-brain barrier permeability and in both human and mouse cells of the neurovascular unit: brain microvascular endothelial cells, pericytes and astrocytes. We confirmed the expression of monoacylglycerol lipase in specific neurovascular unit cells in vitro, with pericytes showing the highest expression level and activity. However, MAGLi 432 did not ameliorate lipopolysaccharide-induced blood-brain barrier permeability in vivo or reduce the production of pro-inflammatory cytokines in the brain. Our data confirm monoacylglycerol lipase expression in mouse and human cells of the neurovascular unit and provide the basis for further cell-specific analysis of MAGLi 432 in the context of blood-brain barrier dysfunction caused by inflammatory insults.
Synthesis and SAR are described for a structurally distinct class of DPP-IV inhibitors based on aminobenzo[a]quinolizines bearing (hetero-)aromatic substituents in the S1 specificity pocket. The m-(fluoromethyl)-phenyl derivative (S,S,S)-2g possesses the best fit in the S1 pocket. However, (S,S,S)-2i, bearing a more hydrophilic 5-methyl-pyridin-2-yl residue as substituent for the S1 pocket, displays excellent in vivo activity and superior drug-like properties.
Design, synthesis, and SAR are described for a class of DPP-IV inhibitors based on aminobenzo[a]quinolizines with non-aromatic substituents in the S1 specificity pocket. One representative thereof, carmegliptin (8p), was chosen for clinical development. Its X-ray structure in complex with the enzyme and early efficacy data in animal models of type 2 diabetes are also presented.
Title: Molecular recognition of ligands in dipeptidyl peptidase IV Kuhn B, Hennig M, Mattei P Ref: Curr Top Med Chem, 7:609, 2007 : PubMed
The serine protease dipeptidyl peptidase IV (DPP-IV) is a clinically validated target for the treatment of type II diabetes and has received considerable interest from the pharmaceutical industry over the last years. Concomitant with a large variety of published small molecule DPP-IV inhibitors almost twenty co-crystal structures have been released to the public as of May 2006. In this review, we discuss the structural characteristics of the DPP-IV binding site and use the available X-ray information together with published structure-activity relationship data to identify the molecular interactions that are most important for tight enzyme-inhibitor binding. Optimized interactions with the two key recognition motifs, i.e. the lipophilic S1 pocket and the negatively charged Glu 205/206 pair, result in large gains in binding free energy, which can be further improved by additional favorable contacts to side chains that flank the active site. First examples show that the lessons learned from the X-ray structures can be successfully incorporated into the design of novel DPP-IV inhibitors.
In a search for novel DPP-IV inhibitors, 2-aminobenzo[a]quinolizines were identified as submicromolar HTS hits. Due to the difficult synthetic access to this compound class, 1,3-disubstituted 4-aminopiperidines were used as model compounds for optimization. The developed synthetic methodology and the SAR could be transferred to the 2-aminobenzo[a]quinolizine series, leading to highly active DPP-IV inhibitors.
The influence of aromatic substitution on a newly discovered class of inhibitors of dipeptidyl peptidase IV was investigated. A 10(5)-fold increase in potency was achieved by the optimization of aromatic substituents in a parallel chemistry program. The observed SAR could be explained by an X-ray structure of the protein-ligand complex.
