Therapeutic modulation of cannabinoid lipid signaling: metabolic profiling of a novel antinociceptive cannabinoid-2 receptor agonist

AM1241 inhibits chondrocyte inflammation and ECM degradation through the Nrf2/HO-1 and NF-κB pathways and alleviates osteoarthritis in mice

BACKGROUND

This study aimed to investigate the impact of AM1241 on lipopolysaccharide (LPS)-induced chondrocyte inflammation in mice and its potential mechanism for improving osteoarthritis (OA).

METHODS

The OA mice model was established employing the refined Hulth method. The impact of different concentrations of AM1241 on mice chondrocyte activity was detected using CCK-8. Changes in the levels of LPS-induced inflammatory factors and cartilage extracellular matrix (ECM) degradation in chondrocytes were determined by western blot, RT-qPCR, ELISA, and immunofluorescence assays, respectively. The specific action modes and binding sites of AM1241 with NEMO/IκB kinases (IKKs) in the NF-κB pathway and Keap1 protein in the Nrf2 pathway were predicted via molecular docking and molecular dynamics simulation, and the NF-κB and Nrf2 pathways were detected using western blot and immunofluorescence. In vivo, the impact of AM1241 on OA mice was analyzed through safranin-fast green staining, IHC staining, Mankin score, and microCT.

RESULTS

AM1241 inhibited the levels of LPS-induced transforming growth factor-β (TGF-β1), tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), matrix metalloproteinase-13 (MMP-13), and a disintegrin and metalloproteinase with thrombospondin motif 5 (ADAMTS-5) and diminished the degradation of type II collagen and Aggrecan. For the mechanism, AM1241 regulated the NF-kB and Nrf2/HO-1 signaling pathways by binding to NEMO/IKKβ and Keap1 target proteins and suppressed the activation of the NF-κB signaling pathway by activating the Nrf2 in chondrocytes. In vivo, AM1241 inhibited bone anabolism, mitigated articular cartilage hyperplasia and wear, and reduced the Mankin score in mice, thereby hindering the development of OA.

CONCLUSION

AM1241 inhibited activation of the NF-κB signaling pathway via activating Nrf2. It suppressed the expression of inflammation factors and the degradation of ECM in vitro, and improved OA in mice in vivo, suggesting its potential as an effective drug candidate for the treatment of OA. The remarkable efficacy of AM1241 in alleviating murine OA positions it as a potential therapeutic strategy in the clinical management of OA diseases.

Design and Synthesis of Highly Potent and Specific ABHD6 Inhibitors

Fine-tuning than complete disruption of 2-arachidonoylglycerol (2-AG) metabolism in the brain represents a promising pharmacological approach to limit potential untoward effects associated with complete blockade of monoacylglycerol lipase (MGL), the primary hydrolase of 2-AG. This could be achieved through a/b-hydrolase domain containing 6 (ABHD6) inhibition, which will provide a smaller and safer contribution to 2-AG regulation in the brain. Pharmacological studies with ABHD6 inhibitors have recently been reported, where modulation of ABHD6 activity either through CB1R-dependent or CB1R-independent processes showed promise in preclinical models of epilepsy, neuropathic pain and inflammation. Furthermore in the periphery, ABHD6 modulates 2-AG and other fatty acid monoacylglycerols (MAGs) and is implicated in Type-2 diabetes, metabolic syndrome and potentially other diseases. Herein, we report the discovery of single-digit nanomolar potent and highly specific ABHD6 inhibitors with >1000-fold selectivity against MGL and FAAH. The new ABHD6 inhibitors provide early leads to develop therapeutics for neuroprotection and the treatment of inflammation and diabetes.

Design and Structure-Activity Relationships of Isothiocyanates as Potent and Selective N-Acylethanolamine-Hydrolyzing Acid Amidase Inhibitors

N-Acylethanolamines are signaling lipid molecules implicated in pathophysiological conditions associated with inflammation and pain. N-Acylethanolamine acid amidase (NAAA) favorably hydrolyzes lipid palmitoylethanolamide, which plays a key role in the regulation of inflammatory and pain processes. The synthesis and structure-activity relationship studies encompassing the isothiocyanate pharmacophore have produced potent low nanomolar inhibitors for hNAAA, while exhibiting high selectivity (>100-fold) against other serine hydrolases and cysteine peptidases. We have followed a target-based structure-activity relationship approach, supported by computational methods and known cocrystals of hNAAA. We have identified systemically active inhibitors with good plasma stability (t_1/2 > 2 h) and microsomal stability (t_1/2 ∼ 15-30 min) as pharmacological tools to investigate the role of NAAA in inflammation, pain, and drug addiction.

Design and synthesis of cyanamides as potent and selective N-acylethanolamine acid amidase inhibitors

N-acylethanolamine acid amidase (NAAA) inhibition represents an exciting novel approach to treat inflammation and pain. NAAA is a cysteine amidase which preferentially hydrolyzes the endogenous biolipids palmitoylethanolamide (PEA) and oleoylethanolamide (OEA). PEA is an endogenous agonist of the nuclear peroxisome proliferator-activated receptor-α (PPAR-α), which is a key regulator of inflammation and pain. Thus, blocking the degradation of PEA with NAAA inhibitors results in augmentation of the PEA/PPAR-α signaling pathway and regulation of inflammatory and pain processes. We have prepared a new series of NAAA inhibitors exploring the azetidine-nitrile (cyanamide) pharmacophore that led to the discovery of highly potent and selective compounds. Key analogs demonstrated single-digit nanomolar potency for hNAAA and showed >100-fold selectivity against serine hydrolases FAAH, MGL and ABHD6, and cysteine protease cathepsin K. Additionally, we have identified potent and selective dual NAAA-FAAH inhibitors to investigate a potential synergism between two distinct anti-inflammatory molecular pathways, the PEA/PPAR-α anti-inflammatory signaling pathway,^1-4 and the cannabinoid receptors CB1 and CB2 pathways which are known for their antiinflammatory and antinociceptive properties.^5-8 Our ligand design strategy followed a traditional structure-activity relationship (SAR) approach and was supported by molecular modeling studies of reported X-ray structures of hNAAA. Several inhibitors were evaluated in stability assays and demonstrated very good plasma stability (t_1/2 > 2 h; human and rodents). The disclosed cyanamides represent promising new pharmacological tools to investigate the potential role of NAAA inhibitors and dual NAAA-FAAH inhibitors as therapeutic agents for the treatment of inflammation and pain.

Oxidative burst and Dectin-1-triggered phagocytosis affected by norepinephrine and endocannabinoids: implications for fungal clearance under stress

A prolonged stress burden is known to hamper the efficiency of both the innate and the adaptive immune systems and to attenuate the stress responses by the catecholaminergic and endocannabinoid (EC) systems. Key mechanisms of innate immunity are the eradication of pathogens through phagocytosis and the respiratory burst. We tested the concentration-dependent, spontaneous and stimulated (via TNFα and N-formylmethionine-leucyl-phenylalanine) release of reactive oxygen species (ROS) by human polymorphonuclear leukocytes (PMNs) in vitro in response to norepinephrine (NE) and AM1241, a pharmacological ligand for the EC receptor CB2. We evaluated phagocytosis of Dectin-1 ligating zymosan particles and tested the cytokine response against Candida antigen in an in vitro cytokine release assay. Increasing concentrations of NE did not affect phagocytosis, yet stimulated ROS release was attenuated gradually reaching maximum suppression at 500 nM. Adrenergic receptor (AR) mechanisms using non-AR-selective (labetalol) as well as specific α-(prazosin) and β-(propranolol) receptor antagonists were tested. Results show that only labetalol and propranolol were able to recuperate cytotoxicity in the presence of NE, evidencing a β-receptor-mediated effect. The CB2 agonist, AM1241, inhibited phagocytosis at 10 µM and spontaneous peroxide release by PMNs. Use of the inverse CB2 receptor agonist SR144528 led to partial recuperation of ROS production, confirming the functional role of CB2. Additionally, AM1241 delayed early activation of monocytes and induced suppression of IL-2 and IL-6 levels in response to Candida via lower activity of mammalian target of rapamycin (mTOR). These findings provide new insights into key mechanisms of innate immunity under stressful conditions where ligands to the sympatho-adrenergic and EC system are released.

Synthesis and evaluation of potent and selective MGL inhibitors as a glaucoma treatment

Monoacylglycerol lipase (MGL) inhibition provides a potential treatment approach to glaucoma through the regulation of ocular 2-arachidonoylglycerol (2-AG) levels and the activation of CB1 receptors. Herein, we report the discovery of new series of carbamates as highly potent and selective MGL inhibitors. The new inhibitors showed potent nanomolar inhibitory activity against recombinant human and purified rat MGL, were selective (>1000-fold) against serine hydrolases FAAH and ABHD6 and lacked any affinity for the cannabinoid receptors CB1 and CB2. Protein-based ¹H NMR experiments indicated that inhibitor 2 rapidly formed a covalent adduct with MGL with a residence time of about 6 h. This interconversion process "intrinsic reversibility" was exploited by modifications of the ligand's size (length and bulkiness) to generate analogs with "tunable' adduct residence time (τ). Inhibitor 2 was evaluated in a normotensive murine model for assessing intraocular pressure (IOP), which could lead to glaucoma, a major cause of blindness. Inhibitor 2 was found to decrease ocular pressure by ∼4.5 mmHg in a sustained manner for at least 12 h after a single ocular application, underscoring the potential for topically-administered MGL inhibitors as a novel therapeutic target for the treatment of glaucoma.

In vitro metabolism of synthetic cannabinoid AM1220 by human liver microsomes and Cunninghamella elegans using liquid chromatography coupled with high resolution mass spectrometry

Purpose

Identifying intake of synthetic cannabinoids generally requires the metabolism data of the drugs so that appropriate metabolite markers can be targeted in urine testing. However, the continuous appearance of new cannabinoids during the last decade has made it difficult to keep up with all the compounds including {1-[(1-methylpiperidin-2-yl)methyl]-1H-indol-3-yl}(naphthalen-1-yl)methanone (AM1220). In this study, metabolism of AM1220 was investigated with human liver microsomes and the fungus Cunninghamella elegans.

Methods

Metabolic stability of AM1220 was analysed by liquid chromatography–tandem mass spectrometry in multiple reaction monitoring mode after 1 µM incubation in human liver microsomes for 30 min. Tentative structure elucidation of metabolites was performed on both human liver microsome and fungal incubation samples using liquid chromatography–high-resolution mass spectrometry.

Results

Half-life of AM1220 was estimated to be 3.7 min, indicating a high clearance drug. Nine metabolites were detected after incubating human liver microsomes while seven were found after incubating Cunninghamella elegans, leading to 11 metabolites in total (five metabolites were common to both systems). Demethylation, dihydrodiol formation, combination of the two, hydroxylation and dihydroxylation were the observed biotransformations.

Conclusions

Three most abundant metabolites in both human liver microsomes and Cunninghamella elegans were desmethyl, dihydrodiol and hydroxy metabolites, despite different isomers of dihydrodiol and hydroxy metabolites in each model. These abundant metabolites can potentially be useful markers in urinalysis for AM1220 intake.

Probing the carboxyester side chain in controlled deactivation (-)-δ(8)-tetrahydrocannabinols

We recently reported on a controlled deactivation/detoxification approach for obtaining cannabinoids with improved druggability. Our design incorporates a metabolically labile ester group at strategic positions within the THC structure. We have now synthesized a series of (−)-Δ⁸-THC analogues encompassing a carboxyester group within the 3-alkyl chain in an effort to explore this novel cannabinergic chemotype for CB receptor binding affinity, in vitro and in vivo potency and efficacy, as well as controlled deactivation by plasma esterases. We have also probed the chain’s polar characteristics with regard to fast onset and short duration of action. Our lead molecule, namely 2-[(6aR,10aR)-6a,7,10,10a-tetrahydro-1-hydroxy-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-3-yl]-2-methyl-propanoic acid 3-cyano-propyl ester (AM7438), showed picomolar affinity for CB receptors and is deactivated by plasma esterases while the respective acid metabolite is inactive. In further in vitro and in vivo experiments, the compound was found to be a remarkably potent and efficacious CB1 receptor agonist with relatively fast onset/offset of action.

Controlled-deactivation cannabinergic ligands

We report an approach for obtaining novel cannabinoid analogues with controllable deactivation and improved druggability. Our design involves the incorporation of a metabolically labile ester group at the 2'-position on a series of (-)-Δ(8)-THC analogues. We have sought to introduce benzylic substituents α to the ester group which affect the half-lives of deactivation through enzymatic activity while enhancing the affinities and efficacies of individual ligands for the CB1 and CB2 receptors. The 1'-(S)-methyl, 1'-gem-dimethyl, and 1'-cyclobutyl analogues exhibit remarkably high affinities for both CB receptors. The novel ligands are susceptible to enzymatic hydrolysis by plasma esterases in a controllable manner, while their metabolites are inactive at the CB receptors. In further in vitro and in vivo experiments key analogues were shown to be potent CB1 receptor agonists and to exhibit CB1-mediated hypothermic and analgesic effects.