Monoacylglycerol lipase (MAGL) constitutes a serine hydrolase that orchestrates endocannabinoid homeostasis and exerts its function by catalyzing the degradation of 2-arachidonoylglycerol (2-AG) to arachidonic acid (AA). As such, selective inhibition of MAGL represents a potential therapeutic and diagnostic approach to various pathologies including neurodegenerative disorders, metabolic diseases and cancers. Based on a unique 4-piperidinyl azetidine diamide scaffold, we developed a reversible and peripheral-specific radiofluorinated MAGL PET ligand [(18)F]FEPAD. Pharmacokinetics and binding studies on [(18)F]FEPAD revealed its outstanding specificity and selectivity towards MAGL in brown adipose tissue (BAT) - a tissue that is known to be metabolically active. We employed [(18)F]FEPAD in PET studies to assess the abundancy of MAGL in BAT deposits of mice and found a remarkable degree of specific tracer binding in the BAT, which was confirmed by post-mortem tissue analysis. Given the negative regulation of endocannabinoids on the metabolic BAT activity, our study supports the concept that dysregulation of MAGL is likely linked to metabolic disorders. Further, we now provide a suitable imaging tool that allows non-invasive assessment of MAGL in BAT deposits, thereby paving the way for detailed mechanistic studies on the role of BAT in endocannabinoid system (ECS)-related pathologies.
As a serine hydrolase, monoacylglycerol lipase (MAGL) is principally responsible for the metabolism of 2-arachidonoylglycerol (2-AG) in the central nervous system (CNS), leading to the formation of arachidonic acid (AA). Dysfunction of MAGL has been associated with multiple CNS disorders and symptoms, including neuroinflammation, cognitive impairment, epileptogenesis, nociception and neurodegenerative diseases. Inhibition of MAGL provides a promising therapeutic direction for the treatment of these conditions, and a MAGL positron emission tomography (PET) probe would greatly facilitate preclinical and clinical development of MAGL inhibitors. Herein, we design and synthesize a small library of fluoropyridyl-containing MAGL inhibitor candidates. Pharmacological evaluation of these candidates by activity-based protein profiling identified 14 as a lead compound, which was then radiolabeled with fluorine-18 via a facile S(N)Ar reaction to form 2-[(18)F]fluoropyridine scaffold. Good blood-brain barrier permeability and high in vivo specific binding was demonstrated for radioligand [(18)F]14 (also named as [(18)F]MAGL-1902). This work may serve as a roadmap for clinical translation and further design of potent (18)F-labeled MAGL PET tracers.
Monoacylglycerol lipase (MAGL) is a 33 kDa serine protease primarily responsible for hydrolyzing 2-arachidonoylglycerol into the proinflammatory eicosanoid precursor arachidonic acid in the central nervous system. Inhibition of MAGL constitutes an attractive therapeutic concept for treating psychiatric disorders and neurodegenerative diseases. Herein, we present the design and synthesis of multiple reversible MAGL inhibitor candidates based on a piperazinyl azetidine scaffold. Compounds 10 and 15 were identified as the best-performing reversible MAGL inhibitors by pharmacological evaluations, thus channeling their radiolabeling with fluorine-18 in high radiochemical yields and favorable molar activity. Furthermore, evaluation of [(18)F]10 and [(18)F]15 ([(18)F]MAGL-2102) by autoradiography and positron emission tomography (PET) imaging in rodents and nonhuman primates demonstrated favorable brain uptakes, heterogeneous radioactivity distribution, good specific binding, and adequate brain kinetics, and [(18)F]15 demonstrated a better performance. In conclusion, [(18)F]15 was found to be a suitable PET radioligand for the visualization of MAGL, harboring potential for the successful translation into humans.
Monoacylglycerol lipase (MAGL) is a serine hydrolase that degrades 2-arachidonoylglycerol (2-AG) in the endocannabinoid system (eCB). Selective inhibition of MAGL has emerged as a potential therapeutic approach for the treatment of diverse pathological conditions, including chronic pain, inflammation, cancer, and neurodegeneration. Herein, we disclose a novel array of reversible and irreversible MAGL inhibitors by means of "tail switching" on a piperazinyl azetidine scaffold. We developed a lead irreversible-binding MAGL inhibitor 8 and reversible-binding compounds 17 and 37, which are amenable for radiolabeling with (11)C or (18)F. [(11)C]8 ([(11)C]MAGL-2-11) exhibited high brain uptake and excellent binding specificity in the brain toward MAGL. Reversible radioligands [(11)C]17 ([(11)C]PAD) and [(18)F]37 ([(18)F]MAGL-4-11) also demonstrated excellent in vivo binding specificity toward MAGL in peripheral organs. This work may pave the way for the development of MAGL-targeted positron emission tomography tracers with tunability in reversible and irreversible binding mechanisms.
Dysfunction of monoacylglycerol lipase (MAGL) is associated with several psychopathological disorders, including drug addiction and neurodegenerative diseases. Herein we design, synthesize, and evaluate several irreversible fluorine-containing MAGL inhibitors for positron emission tomography (PET) ligand development. Compound 6 (identified from a therapeutic agent) was advanced for (18)F-labeling via a novel spirocyclic iodonium ylide (SCIDY) strategy, which demonstrated high brain permeability and excellent specific binding. This work supports further development of novel (18)F-labeled MAGL PET probes.
Monoacylglycerol lipase (MAGL) is a cytosolic serine hydrolase involved in endocannabinoid and inflammatory signaling. Positron-emission tomography (PET) imaging of MAGL serves to validate target engagement of therapeutic MAGL inhibitors as well as to investigate MAGL levels under normal and disease conditions. However, PET radioligands with reversible binding kinetics for MAGL, which allow quantitative assessment of MAGL, are hitherto unavailable. In this study, we designed and synthesized fluoro-containing PET probes starting from a recently identified piperazinyl pyrrolidine-2-one derivative with reversible binding to MAGL. By tailoring the lipophilicity of the molecule to optimize nonspecific binding and blood-brain barrier permeability, we successfully identified two compounds that show high uptake to regions enriched with MAGL. PET imaging of wild-type and MAGL-deficient mice as well as a macaque monkey indicated that [(18)F]5 ((4 R)-1-{3-[2-((18)F)fluoro-4-methylpyridin-3-yl]phenyl}-4-[4-(1,3-thiazol-2-ylcarbo nyl)piperazin-1-yl]pyrrolidin-2-one, [(18)F]T-401) specifically binds to MAGL with adequate reversibility, yielding a high contrast for MAGL within an appropriate imaging time.
Monoacylglycerol lipase (MAGL) is the principle enzyme for metabolizing endogenous cannabinoid ligand 2-arachidonoyglycerol (2-AG). Blockade of MAGL increases 2-AG levels, resulting in subsequent activation of the endocannabinoid system, and has emerged as a novel therapeutic strategy to treat drug addiction, inflammation, and neurodegenerative diseases. Herein we report a new series of MAGL inhibitors, which were radiolabeled by site-specific labeling technologies, including (11)C-carbonylation and spirocyclic iodonium ylide (SCIDY) radiofluorination. The lead compound [(11)C]10 (MAGL-0519) demonstrated high specific binding and selectivity in vitro and in vivo. We also observed unexpected washout kinetics with these irreversible radiotracers, in which in vivo evidence for turnover of the covalent residue was unveiled between MAGL and azetidine carboxylates. This work may lead to new directions for drug discovery and PET tracer development based on azetidine carboxylate inhibitor scaffold.
Monoacylglycerol lipase (MAGL) is a main regulator of the endocannabinoid system within the central nervous system (CNS). Recently, [(11)C]SAR127303 was developed as a promising radioligand for MAGL imaging. In this study, we aimed to quantify regional MAGL concentrations in the rat brain using positron emission tomography (PET) with [(11)C]SAR127303. An irreversible two-tissue compartment model (2-TCMi, k4=0) analysis was conducted to estimate quantitative parameters (k3, Ki(2-TCMi), and lambdak3). These parameters were successfully obtained with high identifiability (<10 %COV) for the following regions ranked in order from highest to lowest: cingulate cortex>striatum>hippocampus>thalamus>cerebellum>hypothalamus approximately pons. In vitro autoradiographs using [(11)C]SAR127303 showed a heterogeneous distribution of radioactivity, as seen in the PET images. The Ki(2-TCMi) and lambdak3 values correlated relatively highly with in vitro binding (r>0.4, P<0.005). The Ki(2-TCMi) values showed high correlation and low underestimation (<10%) compared with the slope of a Patlak plot analysis with linear regression (Ki(Patlak)). In conclusion, we successfully estimated regional net uptake value of [(11)C]SAR127303 reflecting MAGL concentrations in rat brain regions for the first time.
