Structural Optimization of 4-Chlorobenzoylpiperidine Derivatives for the Development of Potent, Reversible, and Selective Monoacylglycerol Lipase (MAGL) Inhibitors

4,4-Dimethylsterols Reduces Fat Accumulation via Inhibiting Fatty Acid Amide Hydrolase In Vitro and In Vivo

4,4-Dimethylsterols constitute a unique class of phytosterols responsible for regulating endogenous cannabinoid system (ECS) functions. However, precise mechanism through which 4,4-dimethylsterols affect fat metabolism and the linkage to the ECS remain unresolved. In this study, we identified that 4,4-dimethylsterols, distinct from 4-demethseterols, act as inhibitors of fatty acid amide hydrolases (FAAHs) both in vivo and in vitro. Genetic ablation of FAAHs (faah-1) abolishes the effects of 4,4-dimethylsterols on fat accumulation and locomotion behavior in a Caenorhabditis elegans model. We confirmed that dietary intervention with 4,4-dimethylsterols in a high-fat diet (HFD) mouse model leads to a significant reduction in body weight (>11.28%) with improved lipid profiles in the liver and adipose tissues and increased fecal triacylglycerol excretion. Untargeted and targeted metabolomics further verified that 4,4-dimethylsterols influence unsaturated fatty acid biosynthesis and elevate oleoyl ethanolamine levels in the intestine. We propose a potential molecular mechanism in which 4,4-dimethylsterols engage in binding interactions with the catalytic pocket (Ser241) of FAAH-1 protein due to the shielded polarity, arising from the presence of 2 additional methyl groups (CH3). Consequently, 4,4-dimethylsterols represent an unexplored class of beneficial phytosterols that coordinate with FAAH-1 activity to reduce fat accumulation, which offers new insight into intervention strategies for treating diet-induced obesity.

The Benzoylpiperidine Fragment as a Privileged Structure in Medicinal Chemistry: A Comprehensive Review

The phenyl(piperidin-4-yl)methanone fragment (here referred to as the benzoylpiperidine fragment) is a privileged structure in the development of new drugs considering its presence in many bioactive small molecules with both therapeutic (such as anti-cancer, anti-psychotic, anti-thrombotic, anti-arrhythmic, anti-tubercular, anti-parasitic, anti-diabetic, and neuroprotective agents) and diagnostic properties. The benzoylpiperidine fragment is metabolically stable, and it is also considered a potential bioisostere of the piperazine ring, thus making it a feasible and reliable chemical frame to be exploited in drug design. Herein, we discuss the main therapeutic and diagnostic agents presenting the benzoylpiperidine motif in their structure, covering articles reported in the literature since 2000. A specific section is focused on the synthetic strategies adopted to obtain this versatile chemical portion.

Discovery of a novel class of reversible monoacylglycerol lipase inhibitors for potential treatment of depression

Biological studies on the endocannabinoid system (ECS) have suggested that monoacylglycerol lipase (MAGL), an essential enzyme responsible for the hydrolysis of 2-arachidonoylglycerol (2-AG), is a novel target for developing antidepressants. A decrease of 2-AG levels in the hippocampus of the brain has been observed in depressive-like models induced by chronic stress. Herein, employing a structure-based approach, we designed and synthesized a new class of (piperazine-1-carbonyl) quinolin-2(1H)-one derivatives as potent, reversible and selective MAGL inhibitors. And detailed structure-activity relationships (SAR) studies were discussed. Compound 27 (IC50 = 10.3 nM) exhibited high bioavailability (92.7%) and 2-AG elevation effect in vivo. Additionally, compound 27 exerted rapid antidepressant effects caused by chronic restraint stress (CRS) and didn't show signs of addictive properties in the conditioned place preference (CPP) assays. Our study is the first to report that reversible MAGL inhibitors can treat chronic stress-induced depression effectively, which may provide a new potential therapeutic strategy for the discovery of an original class of safe, rapid antidepressant drugs.

Steatosis in metabolic diseases: A focus on lipolysis and lipophagy

Fatty acids (FAs), as part of lipids, are involved in cell membrane composition, cellular energy storage, and cell signaling. FAs can also be toxic when their concentrations inside and/or outside the cell exceed physiological levels, which is called "lipotoxicity", and steatosis is a form of lipotoxity. To facilitate the storage of large quantities of FAs in cells, they undergo a process called lipolysis or lipophagy. This review focuses on the effects of lipolytic enzymes including cytoplasmic "neutral" lipolysis, lysosomal "acid" lipolysis, and lipophagy. Moreover, the impact of related lipolytic enzymes on lipid metabolism homeostasis and energy conservation, as well as their role in lipid-related metabolic diseases. In addition, we describe how they affect lipid metabolism homeostasis and energy conservation in lipid-related metabolic diseases with a focus on hepatic steatosis and cancer and the pathogenesis and therapeutic targets of AMPK/SIRTs/FOXOs, PI3K/Akt, PPARs/PGC-1α, MAPK/ERK1/2, TLR4/NF-κB, AMPK/mTOR/TFEB, Wnt/β-catenin through immune inflammation, oxidative stress and autophagy-related pathways. As well as the current application of lipolytic enzyme inhibitors (especially Monoacylglycerol lipase (MGL) inhibitors) to provide new strategies for future exploration of metabolic programming in metabolic diseases.

MAGL inhibitor NanoMicellar formulation (MAGL-NanoMicellar) for the development of an antiglaucoma eye drop

The ocular endocannabinoid system (ECS) including enzymes and CB1/CB2 receptors determines various substantial effects, such as anti-inflammatory activity and reduction of the intraocular pressure (IOP). The modulation of 2-arachidonoylglycerol (2-AG) levels obtained via MAGL inhibition is considered as a promising pharmacological strategy to activate the ECS. Within the scope of this study, the effect of a selective monoacylglycerol lipase (MAGL) inhibitor (MAGL17b) was investigated by measuring the IOP reduction in normotensive rabbits after performing a solubilisation process of the molecule with non-ionic surfactants, to produce suitable eye drops containing the highest possible concentration of the drug. Furthermore, the study involved the evaluation of cytotoxicity and of in vitro/ex vivo corneal permeation of MAG17b of selected formulations based on polyoxyl(35)castor oil (C-EL) and polyethylene glycol (80) sorbitan monolaurate (TW80). The solubilisation of 0.5 mM MAGL17b with 3% w/w TW80 (TW80/3-17b), through the formation of NanoMicellar structures (diameter of 12.3 nm), determined a significant permeation of MAGL17b, both through excised rabbits corneas and reconstituted corneal epithelium, with a limited corneal epithelial cells death. The blockade of MAGL activity induced a IOP reduction up to 4 mmHg in albino and pigmented rabbits after topical instillation, thus confirming the potential efficacy of the MAGL inhibition approach in the treatment of ocular pathologies.

Reversible Monoacylglycerol Lipase Inhibitors: Discovery of a New Class of Benzylpiperidine Derivatives

Monoacylglycerol lipase (MAGL) is the enzyme responsible for the metabolism of 2-arachidonoylglycerol in the brain and the hydrolysis of peripheral monoacylglycerols. Many studies demonstrated beneficial effects deriving from MAGL inhibition for neurodegenerative diseases, inflammatory pathologies, and cancer. MAGL expression is increased in invasive tumors, furnishing free fatty acids as pro-tumorigenic signals and for tumor cell growth. Here, a new class of benzylpiperidine-based MAGL inhibitors was synthesized, leading to the identification of 13, which showed potent reversible and selective MAGL inhibition. Associated with MAGL overexpression and the prognostic role in pancreatic cancer, derivative 13 showed antiproliferative activity and apoptosis induction, as well as the ability to reduce cell migration in primary pancreatic cancer cultures, and displayed a synergistic interaction with the chemotherapeutic drug gemcitabine. These results suggest that the class of benzylpiperidine-based MAGL inhibitors have potential as a new class of therapeutic agents and MAGL could play a role in pancreatic cancer.

A review on structurally diversified synthesized molecules as monoacylglycerol lipase inhibitors and their therapeutic uses

Monoacylglycerol is a metabolic key serine hydrolase, engaged in the regulation of signalling network system of endocannabinoids, which is associated with various physiological processes like pain, inflammation, feeding cognition and neurodegenerative diseases like Alzheimer, Parkinson's disease. The monoacylglycerol also found to act as a regulator and the free fatty acid provider in the proliferation of cancer cells, numerous aggressive tumours such as colorectal cancer, neuroblastoma and nasopharyngeal carcinoma. It also played an important role in increasing the concentration of specific lipids derived from free fatty acids like phosphatidic acid, lysophosphatidic acid, sphingosine-1-phosphate and prostaglandin E2. These signalling lipids are associated with cell proliferation, survival, tumour cell migration, contributing to tumour development, maturation and metastases. In the present study here, we are presenting a review on structurally diverse MAGL inhibitors, their development and their evaluation for different pharmacological activities.

A carrier free delivery system of a monoacylglycerol lipase hydrophobic inhibitor

Monoacylglycerol lipase (MAGL) is an emerging therapeutic target for cancer. It is involved in lipid metabolism and its inhibition impairs many hallmarks of cancer including cell proliferation, migration/invasion and tumor growth. For these reasons, our group has recently developed a potent reversible MAGL inhibitor (MAGL23), which showed promising anticancer activities. Here in, to improve its pharmacological properties, a nanoformulation based on nanocrystals coated with albumin was prepared for therapeutic applications. MAGL23 was solubilized by a nanocrystallization method with Pluronic F-127 as surfactant into an organic solvent and was recovered as nanocrystals in water after solvent evaporation. Finally, the solubilized nanocrystals were stabilized by human serum albumin to create a smart delivery carrier. An in-silico prediction (lipophilicity, structure at different pH and solubility in water), as well as experimental studies (solubility), have been performed to check the chemical properties of the inhibitor and nanocrystals. The solubility in water increases from less than 0.01 mg/mL (0.0008 mg/mL, predicted) up to 0.82 mg/mL in water. The formulated inhibitor maintained its potency in ovarian and colon cancer cell lines as the free drug. Furthermore, the system was thoroughly observed at each step of the solubilization process till the final formulation stage by different spectroscopic techniques and a comparative study was performed to check the effects of Pluronic F-127 and CTAB as surfactants. The formulated system is favorable to release the drug at physiological pH conditions (at pH 7.4, after 24 h, less than 20% of compound is released). In vivo studies have shown that albumin-complexed nanocrystals increase the therapeutic window of MAGL23 along with a favorable biodistribution. As per our knowledge, we are reporting the first ever nanoformulation of a MAGL inhibitor, which is promising as a therapeutic system where the MAGL enzyme is involved, especially for cancer therapeutic applications.

Novel Reversible-Binding PET Ligands for Imaging Monoacylglycerol Lipase Based on the Piperazinyl Azetidine Scaffold

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 [¹⁸F]10 and [¹⁸F]15 ([¹⁸F]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 [¹⁸F]15 demonstrated a better performance. In conclusion, [¹⁸F]15 was found to be a suitable PET radioligand for the visualization of MAGL, harboring potential for the successful translation into humans.

Targeting Monoacylglycerol Lipase in Pursuit of Therapies for Neurological and Neurodegenerative Diseases

Neurological and neurodegenerative diseases are debilitating conditions, and frequently lack an effective treatment. Monoacylglycerol lipase (MAGL) is a key enzyme involved in the metabolism of 2-AG (2-arachidonoylglycerol), a neuroprotective endocannabinoid intimately linked to the generation of pro- and anti-inflammatory molecules. Consequently, synthesizing selective MAGL inhibitors has become a focus point in drug design and development. The purpose of this review was to summarize the diverse synthetic scaffolds of MAGL inhibitors concerning their potency, mechanisms of action and potential therapeutic applications, focusing on the results of studies published in the past five years. The main irreversible inhibitors identified were derivatives of hexafluoroisopropyl alcohol carbamates, glycol carbamates, azetidone triazole ureas and benzisothiazolinone, whereas the most promising reversible inhibitors were derivatives of salicylketoxime, piperidine, pyrrolidone and azetidinyl amides. We reviewed the results of in-depth chemical, mechanistic and computational studies on MAGL inhibitors, in addition to the results of in vitro findings concerning selectivity and potency of inhibitors, using the half maximal inhibitory concentration (IC₅₀) as an indicator of their effect on MAGL. Further, for highlighting the potential usefulness of highly selective and effective inhibitors, we examined the preclinical in vivo reports regarding the promising therapeutic applications of MAGL pharmacological inhibition.

Design and Synthesis of Novel Spiro Derivatives as Potent and Reversible Monoacylglycerol Lipase (MAGL) Inhibitors: Bioisosteric Transformation from 3-Oxo-3,4-dihydro-2H-benzo[b][1,4]oxazin-6-yl Moiety

The therapeutic potential of monoacylglycerol lipase (MAGL) inhibitors in central nervous system-related diseases has attracted attention worldwide. However, the availability of reversible-type inhibitor is still limited to clarify the pharmacological effect. Herein, we report the discovery of novel spiro chemical series as potent and reversible MAGL inhibitors with a different binding mode to MAGL using Arg57 and His121. Starting from hit compound 1 and its co-crystal structure with MAGL, structure-based drug discovery (SBDD) approach enabled us to generate various spiro scaffolds like 2a (azetidine-lactam), 2b (cyclobutane-lactam), and 2d (cyclobutane-carbamate) as novel bioisosteres of 3-oxo-3,4-dihydro-2H-benzo[b][1,4]oxazin-6-yl moiety in 1 with higher lipophilic ligand efficiency (LLE). Optimization of the left hand side afforded 4f as a promising reversible MAGL inhibitor, which showed potent in vitro MAGL inhibitory activity (IC₅₀ 6.2 nM), good oral absorption, blood-brain barrier penetration, and significant pharmacodynamic changes (2-arachidonoylglycerol increase and arachidonic acid decrease) at 0.3-10 mg/kg, po. in mice.

Monoacylglycerol lipase (MAGL) inhibitors based on a diphenylsulfide-benzoylpiperidine scaffold

Monoacylglycerol lipase (MAGL) is an enzyme belonging to the endocannabinoid system that mainly metabolizes the endocannabinoid 2-arachidonoylglycerol (2-AG). Numerous studies have shown the involvement of this enzyme in various pathological conditions such as pain, cancer progression, Parkinson's and Alzheimer's disease, thus encouraging the development of new MAGL modulators. In this context, we developed new diphenylsulfide-benzoylpiperidine derivatives characterized by a high enzymatic MAGL inhibition activity in the low nanomolar range, a reversible mechanism of action and selectivity. The three most active compounds (15-17) induced an appreciable inhibition of cell viability in a panel of nine cancer cell lines, with IC₅₀ values ranging between 0.32 and 10 μM, thus highlighting their potential as novel anticancer agents.

Development of a highly-specific 18F-labeled irreversible positron emission tomography tracer for monoacylglycerol lipase mapping

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_NAr reaction to form 2-[¹⁸F]fluoropyridine scaffold. Good blood–brain barrier permeability and high in vivo specific binding was demonstrated for radioligand [¹⁸F]14 (also named as [¹⁸F]MAGL-1902). This work may serve as a roadmap for clinical translation and further design of potent ¹⁸F-labeled MAGL PET tracers.

Discovery of novel reversible monoacylglycerol lipase inhibitors via docking-based virtual screening

Monoacylglycerol lipase (MAGL) is the major enzyme that catalyzes the hydrolysis of monoacylglycerols (MAGs). MAGL is responsible for degrading 2-arachidonoylglycerol (2-AG) to arachidonic acid (AA) and glycerol in the brain and specific tissues. The inhibition of MAGL could attenuate the inflammatory response. Here, we report a series of reversible non-covalent MAGL inhibitors via virtual screening combined with biochemical analysis. The hit, DC630-8 showed low-micromolar activity against MAGL in vitro, and exhibited significant anti-inflammatory effects.

From Anti-infective Agents to Cancer Therapy: a Drug Repositioning Study Revealed a New Use for Nitrofuran Derivatives

BACKGROUND

The progression of ovarian cancer seems to be related to HDAC1, HDAC3 and HDAC6 activity. A possible strategy for improving therapies for treating ovarian carcinoma, minimizing the preclinical screenings, is the repurposing of already approved pharmaceutical products as inhibitors of these enzymes.

OBJECTIVE

This work was aimed to implement a computational strategy for identifying new HDAC inhibitors for ovarian carcinoma treatment among approved drugs.

METHOD

The CHEMBL database was used to construct training, test and decoys sets for performing and validating HDAC1, HDAC3 and HDAC6 3D-QSAR models obtained by using FLAP program. Docking and MD simulations were used in combination with the generated models to identify novel potential HDAC inhibitors. Cell viability assays and Western blot analyses were performed on normal and cancer cells for a direct evaluation of the anti-proliferative activity and an in vitro estimation of HDAC inhibition of the compounds selected through in silico screening.

RESULT

The best quantitative prediction was obtained for the HDAC6 3D-QSAR model. The screening of approved drugs highlighted a new potential use as HDAC inhibitors for some compounds, in particular nitrofuran derivatives, usually known for their antibacterial activity, and frequently used as antimicrobial adjuvant therapy in cancer treatment. Experimental evaluation of these derivatives highlighted a significant antiproliferative activity against cancer cell lines overexpressing HDAC6, and an increase in acetylated alpha-tubulin levels.

CONCLUSION

Experimental results support the hypothesis of a potential direct interaction of nitrofuran derivatives with HDACs. In addition to the possible repurposing of already approved drugs, this work suggests the nitro group as a new zinc binding group, able to interact with the catalytic zinc ion of HDACs.

Anticancer Potential of Small-Molecule Inhibitors of Fatty Acid Amide Hydrolase and Monoacylglycerol Lipase

Recently fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) inhibitors have been in the limelight due to their anticancer potential. Both FAAH and MAGL are the endocannabinoid degrading enzymes that hydrolyze several endogenous ligands, mainly anandamide (AEA) and 2-arachidonic glycerol (2-AG), which regulate various pathophysiological conditions in the body such as emotion, cognition, energy balance, pain sensation, neuroinflammation, and cancer cell proliferation. FAAH and MAGL inhibitors block the metabolism of AEA and 2-AG, increase endogenous levels of fatty acid amides, and exert various therapeutic effects including chronic pain, metabolic disorders, psychoses, nausea and vomiting, depression, and anxiety disorders. FAAH and MAGL are primarily neurotherapeutic targets, but their contribution to various types of carcinomas are significant. Inhibitors of these enzymes either alone or as multitarget agents, or with supra-additive effects show the potential effect in ovarian, breast, prostate, and colorectal cancers. Besides highlighting the role of FAAH and MAGL in cancer progression, this review provides an update on the anticancer capabilities of known and newly discovered FAAH and MAGL inhibitors and also provides further directions to develop FAAH and MAGL inhibitors as new candidates for cancer therapy.

Analgesic and Anticancer Activity of Benzoxazole Clubbed 2-Pyrrolidinones as Novel Inhibitors of Monoacylglycerol Lipase

Ten benzoxazole clubbed 2-pyrrolidinones (11–20) as human monoacylglycerol lipase inhibitors were designed on the criteria fulfilling the structural requirements and on the basis of previously reported inhibitors. The designed, synthesized, and characterized compounds (11–20) were screened against monoacylglycerol lipase (MAGL) in order to find potential inhibitors. Compounds 19 (4-NO₂ derivative) and 20 (4-SO₂NH₂ derivative), with an IC₅₀ value of 8.4 and 7.6 nM, were found most active, respectively. Both of them showed micromolar potency (IC₅₀ value above 50 µM) against a close analogue, fatty acid amide hydrolase (FAAH), therefore considered as selective inhibitors of MAGL. Molecular docking studies of compounds 19 and 20 revealed that carbonyl of 2-pyrrolidinone moiety sited at the oxyanion hole of catalytic site of the enzyme stabilized with three hydrogen bonds (~2 Å) with Ala51, Met123, and Ser122, the amino acid residues responsible for the catalytic function of the enzyme. Remarkably, the physiochemical and pharmacokinetic properties of compounds 19 and 20, computed by QikProp, were found to be in the qualifying range as per the proposed guideline for good orally bioactive CNS drugs. In formalin-induced nociception test, compound 20 reduced the pain response in acute and late stages in a dose-dependent manner. They significantly demonstrated the reduction in pain response, having better potency than the positive control gabapentin (GBP), at 30 mg/kg dose. Compounds 19 and 20 were submitted to NCI, USA, for anticancer activity screening. Compounds 19 (NSC: 778839) and 20 (NSC: 778842) were found to have good anticancer activity on SNB-75 cell line of CNS cancer, exhibiting 35.49 and 31.88% growth inhibition (% GI), respectively.

Structure-based molecular modeling in SAR analysis and lead optimization

In silico methods like molecular docking and pharmacophore modeling are established strategies in lead identification. Their successful application for finding new active molecules for a target is reported by a plethora of studies. However, once a potential lead is identified, lead optimization, with the focus on improving potency, selectivity, or pharmacokinetic parameters of a parent compound, is a much more complex task. Even though in silico molecular modeling methods could contribute a lot of time and cost-saving by rationally filtering synthetic optimization options, they are employed less widely in this stage of research. In this review, we highlight studies that have successfully used computer-aided SAR analysis in lead optimization and want to showcase sound methodology and easily accessible in silico tools for this purpose.

Discovery of Monoacylglycerol Lipase (MAGL) Inhibitors Based on a Pharmacophore-Guided Virtual Screening Study

Monoacylglycerol lipase (MAGL) is an important enzyme of the endocannabinoid system that catalyzes the degradation of the major endocannabinoid 2-arachidonoylglycerol (2-AG). MAGL is associated with pathological conditions such as pain, inflammation and neurodegenerative diseases like Parkinson’s and Alzheimer’s disease. Furthermore, elevated levels of MAGL have been found in aggressive breast, ovarian and melanoma cancer cells. Due to its different potential therapeutic implications, MAGL is considered as a promising target for drug design and the discovery of novel small-molecule MAGL inhibitors is of great interest in the medicinal chemistry field. In this context, we developed a pharmacophore-based virtual screening protocol combined with molecular docking and molecular dynamics simulations, which showed a final hit rate of 50% validating the reliability of the in silico workflow and led to the identification of two promising and structurally different reversible MAGL inhibitors, VS1 and VS2. These ligands represent a valuable starting point for structure-based hit-optimization studies aimed at identifying new potent MAGL inhibitors.

An updated patent review of monoacylglycerol lipase (MAGL) inhibitors (2018-present)

INTRODUCTION

Monoacylglycerol lipase (MAGL) belongs to the endocannabinoid system and is responsible for the inactivation of endocannabinoid 2-arachidonoylglycerol. Importantly, it was found that MAGL degradation of lipids in cancer cells enhances the availability of free fatty acids for new cellular membrane formation and pro-oncogenic lipid modulators. The multifaceted role of MAGL has greatly stimulated the search for MAGL inhibitors, which could be effective to treat diseases, such as inflammation, neurodegeneration and cancer.

AREAS COVERED

This review covers patents published since 2018 up to now, concerning new MAGL inhibitors and their potential therapeutic applications.

EXPERT OPINION

In the years 2018-2020, several well-known chemical scaffolds of MAGL inhibitors have been further optimized and developed and some new chemical classes have also been identified as MAGL inhibitors. Moreover, an increasing number of scientific publications covering MAGL inhibitors is focused on MAGL-specific positron emission tomography (PET) ligands. The numerous efforts of pharmaceutical companies and academic research groups finalized to find new potent MAGL inhibitors confirm that this research area is rapidly growing. Nevertheless, most of the patented compounds still belong to the large group of irreversible MAGL inhibitors, highlighting that the development of reversible MAGL inhibitors is still an unmet pharmaceutical need.

Design, synthesis and biological evaluation of second-generation benzoylpiperidine derivatives as reversible monoacylglycerol lipase (MAGL) inhibitors

An interesting enzyme of the endocannabinoid system is monoacylglycerol lipase (MAGL). This enzyme, which metabolizes the endocannabinoid 2-arachidonoylglycerol (2-AG), has attracted great interest due to its involvement in several physiological and pathological processes, such as cancer progression. Experimental evidences highlighted some drawbacks associated with the use of irreversible MAGL inhibitors in vivo, therefore the research field concerning reversible inhibitors is rapidly growing. In the present manuscript, the class of benzoylpiperidine-based MAGL inhibitors was further expanded and optimized. Enzymatic assays identified some compounds in the low nanomolar range and steered molecular dynamics simulations predicted the dissociation itinerary of one of the best compounds from the enzyme, confirming the observed structure-activity relationship. Biological evaluation, including assays in intact U937 cells and competitive activity-based protein profiling experiments in mouse brain membranes, confirmed the selectivity of the selected compounds for MAGL versus other components of the endocannabinoid system. An antiproliferative ability in a panel of cancer cell lines highlighted their potential as potential anticancer agents. Future studies on the potential use of these compounds in the clinical setting are also supported by the inhibition of cell growth observed both in cancer organoids derived from high grade serous ovarian cancer patients and in pancreatic ductal adenocarcinoma primary cells, which showed genetic and histological features very similar to the primary tumors.

Pyrrolidin-2-one linked benzofused heterocycles as novel small molecule monoacylglycerol lipase inhibitors and antinociceptive agents

Eighteen pyrrolidin-2-one linked benzothiazole, and benzimidazole derivatives (10-27) were designed and synthesized. The structure of the compounds was confirmed by elemental and spectral (IR, ¹ H-NMR and MS) data analysis. All the compounds were screened by human monoacylglycerol lipase (hMAGL) inhibition assay. Three benzimidazole compounds, 22 (4-Cl phenyl), 23 (3-Cl,4-F phenyl) and 25 (4-methoxy phenyl) were found to be the most potent, having an IC₅₀ value of 8.6, 8.0 and 9.4 nm, respectively. Among them, the halogen-substituted phenyl derivatives, compound 22 (4-Cl phenyl) and compound 23 (3-Cl,4-F phenyl), showed micromolar potency against fatty acid amide hydrolase (FAAH), having an IC₅₀ value of 35 and 24 µm, respectively. Benzimidazole derivative having 4-methoxyphenyl substitution (compound 25) was found to be a selective MAGL inhibitor (IC₅₀  = 9.4 nm), with an IC₅₀ value above 50 µm against FAAH. In the formalin-induced nociception test, compound 25 showed a dose-dependent reduction of pain response in both acute and late phases. At 30 mg/kg dose, it significantly reduced the pain response and showed greater potency than the reference drug gabapentin (GBP).

Monoacylglycerol lipase inhibitors: modulators for lipid metabolism in cancer malignancy, neurological and metabolic disorders

Monoacylglycerol lipase (MAGL) is a serine hydrolase that plays a crucial role catalysing the hydrolysis of monoglycerides into glycerol and fatty acids. It links the endocannabinoid and eicosanoid systems together by degradation of the abundant endocannabinoid 2-arachidaoylglycerol into arachidonic acid, the precursor of prostaglandins and other inflammatory mediators. MAGL inhibitors have been considered as important agents in many therapeutic fields, including anti-nociceptive, anxiolytic, anti-inflammatory, and even anti-cancer. Currently, ABX-1431, a first-in-class inhibitor of MAGL, is entering clinical phase 2 studies for neurological disorders and other diseases. This review summarizes the diverse (patho)physiological roles of MAGL and will provide an overview on the development of MAGL inhibitors. Although a large number of MAGL inhibitors have been reported, novel inhibitors are still required, particularly reversible ones.

ω-Quinazolinonylalkyl aryl ureas as reversible inhibitors of monoacylglycerol lipase

The serine hydrolase monoacylglycerol lipase (MAGL) is involved in a plethora of pathological conditions, in particular pain and inflammation, various types of cancer, metabolic, neurological and cardiovascular disorders, and is therefore a promising target for drug development. Although a large number of irreversible-acting MAGL inhibitors have been discovered over the past years, there are only few compounds known so far which inhibit the enzyme in a reversible manner. Therefore, much effort is put into the development of novel chemical entities showing reversible inhibitory behavior, which is thought to cause less undesired side effects. To explore a wide range of chemical structures as MAGL binders, we have applied a virtual screening approach by docking small molecules into the crystal structure of human MAGL (hMAGL) and envisaged a library of 45 selected compounds which were then synthesized. Biochemical investigations included the determination of the inhibitory potency on hMAGL and two related hydrolases, i.e. human fatty acid amide hydrolase (hFAAH) and murine cholesterol esterase (mCEase). The most promising candidates from theses analyses, i.e. three ω-quinazolinonylalkyl aryl ureas bearing alkyl spacers of three to five methylene groups, exhibited IC₅₀ values of 20-41 µM and reversible, detergent-insensitive behavior towards hMAGL. Among these compounds, the inhibitor 1-(3,5-bis(trifluoromethyl)phenyl)-3-(4-(4-oxo-3,4-dihydroquinazolin-2-yl)butyl)urea (96) was selected for further kinetic characterization, yielding a dissociation constant K_i = 15.4 µM and a mixed-type inhibition with a pronounced competitive component (α = 8.94). This mode of inhibition was further supported by a docking experiment, which suggested that the inhibitor occupies the substrate binding pocket of hMAGL.

Stereoselectivity of Aldose Reductase in the Reduction of Glutathionyl-Hydroxynonanal Adduct

The formation of the adduct between the lipid peroxidation product 4-hydroxy-2-nonenal (HNE) and glutathione, which leads to the generation of 3-glutathionyl-4-hydroxynonane (GSHNE), is one of the main routes of HNE detoxification. The aldo-keto reductase AKR1B1 is involved in the reduction of the aldehydic group of both HNE and GSHNE. In the present study, the effect of chirality on the recognition by aldose reductase of HNE and GSHNE was evaluated. AKR1B1 discriminates very modestly between the two possible enantiomers of HNE as substrates. Conversely, a combined kinetic analysis of the glutathionyl adducts obtained starting from either 4R- or 4S-HNE and mass spectrometry analysis of GSHNE products obtained from racemic HNE revealed that AKR1B1 possesses a marked preference toward the 3S,4R-GSHNE diastereoisomer. Density functional theory and molecular modeling studies revealed that this diastereoisomer, besides having a higher tendency to be in an open aldehydic form (the one recognized by AKR1B1) in solution than other GSHNE diastereoisomers, is further stabilized in its open form by a specific interaction with the enzyme active site. The relevance of this stereospecificity to the final metabolic fate of GSHNE is discussed.

Computationally driven discovery of phenyl(piperazin-1-yl)methanone derivatives as reversible monoacylglycerol lipase (MAGL) inhibitors

Monoacylglycerol lipase (MAGL) is an attractive therapeutic target for many pathologies, including neurodegenerative diseases, cancer as well as chronic pain and inflammatory pathologies. The identification of reversible MAGL inhibitors, devoid of the side effects associated to prolonged MAGL inactivation, is a hot topic in medicinal chemistry. In this study, a novel phenyl(piperazin-1-yl)methanone inhibitor of MAGL was identified through a virtual screening protocol based on a fingerprint-driven consensus docking (CD) approach. Molecular modeling and preliminary structure-based hit optimization studies allowed the discovery of derivative 4, which showed an efficient reversible MAGL inhibition (IC₅₀ = 6.1 µM) and a promising antiproliferative activity on breast and ovarian cancer cell lines (IC₅₀ of 31-72 µM), thus representing a lead for the development of new and more potent reversible MAGL inhibitors. Moreover, the obtained results confirmed the reliability of the fingerprint-driven CD approach herein developed.

In silico screening of a novel scaffold for fructose-1,6-bisphosatase (FBPase) inhibitors

Fructose-1, 6-bisphosphatase (FBPase) has been regarded as an attractive drug target to control blood glucose against Type 2 diabetes (T2D). In this study, by using the strategy of pharmacophore-based virtual screening, a novel scaffold inhibitor targeted the AMP allosteric site of human liver FBPase were screened, their inhibitory activities were further tested. The experimental results showed that compound H27 exhibited high inhibitory activities with the IC₅₀ value of 5.3 μM. Therefore, compound H27 was chosen as the probe molecule, it's possible binding conformation targeted into FBPase was identified by using DOX2.0 strategy. The importance of key residues (T27, T31, K112 and R140) in allosteric site of FBPase for the binding inhibitors were validated by mutation experiments. The agreement between theory and experiment suggest that the interactional information of FBPase and inhibitors (H27) were reliable. On basis of these rational interactional information, the compound H29 was further designed to exhibit more potential FBPase inhibition (IC₅₀ = 2.5 μM).

Lipid-metabolizing serine hydrolases in the mammalian central nervous system: endocannabinoids and beyond

The metabolic serine hydrolases hydrolyze ester, amide, or thioester bonds found in broad small molecule substrates using a conserved activated serine nucleophile. The mammalian central nervous system (CNS) express a diverse repertoire of serine hydrolases that act as (phospho)lipases or lipid amidases to regulate lipid metabolism and signaling vital for normal neurocognitive function and CNS integrity. Advances in genomic DNA sequencing have provided evidence for the role of these lipid-metabolizing serine hydrolases in neurologic, psychiatric, and neurodegenerative disorders. This review briefly summarizes recent progress in understanding the biochemical and (patho)physiological roles of these lipid-metabolizing serine hydrolases in the mammalian CNS with a focus on serine hydrolases involved in the endocannabinoid system. The development and application of specific inhibitors for an individual serine hydrolase, if available, are also described. This article is part of a Special Issue entitled Novel functions of phospholipase A2 Guest Editors: Makoto Murakami and Gerard Lambeau.

Monoacylglycerol lipase (MAGL) as a promising therapeutic target

Monoacylglycerol lipase (MAGL) has been characterized as the main enzyme responsible for the inactivation of the most abundant brain endocannabinoid, 2-arachidonoylglycerol (2-AG). Besides this role, MAGL has progressively acquired a growing importance as an integrative metabolic hub that controls not only the in vivo levels of 2-AG but also of other monoacylglycerides and, indirectly, the levels of free fatty acids derived from their hydrolysis as well as other lipids with pro-inflammatory or pro-tumorigenic effects, coming from the further metabolism of fatty acids. All these functions have only started to be elucidated in the last years due to the progress made in the knowledge of the structure of MAGL and in the development of genetic and chemical tools. In this review we report the advances made in the field with a special focus on the last decade and how MAGL has become a promising therapeutic target for the treatment of several diseases that currently lack appropriate therapies.

Rational Development of MAGL Inhibitors

Hit identification and hit-to-lead optimization are key steps of the early drug discovery program. Starting from the X-ray crystal structure of the human monoacylglycerol lipase (hMAGL), we herein describe the computational and experimental procedures that we applied for identifying and optimizing a new active inhibitor of this target enzyme. A receptor-based virtual screening method is reported in details, together with enzymatic assays and a first round of hit optimization.

Development of terphenyl-2-methyloxazol-5(4H)-one derivatives as selective reversible MAGL inhibitors

Monoacylglycerol lipase is a serine hydrolase that plays a major role in the degradation of the endocannabinoid neurotransmitter 2-arachidonoylglycerol. A wide number of MAGL inhibitors are reported in literature; however, many of them are characterised by an irreversible mechanism of action and this behavior determines an unwanted chronic MAGL inactivation, which acquires a functional antagonism of the endocannabinoid system. The possible use of reversible MAGL inhibitors has only recently been explored, due to the lack of known compounds possessing efficient reversible inhibitory activities. In this work, we report a new series of terphenyl-2-methyloxazol-5(4H)-one derivatives characterised by a reversible MAGL-inhibition mechanism. Among them, compound 20b showed to be a potent MAGL reversible inhibitor (IC₅₀ = 348 nM) with a good MAGL/FAAH selectivity. Furthermore, this compound showed antiproliferative activities against two different cancer cell lines that overexpress MAGL.