Design of Negative and Positive Allosteric Modulators of the Cannabinoid CB2 Receptor Derived from the Natural Product Cannabidiol

In silico exploration of CB2 receptor agonist in the management of neuroinflammatory conditions by pharmacophore modeling

Endocannabinoid system plays a pivotal role in controlling neuroinflammation, and modulating this system may not only aid in managing symptoms of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Multiple sclerosis, Epilepsy, Central and Peripheral neuropathic pain, but also, have the potential to target these diseases at an early-stage. In the present study, six different pharmacophore hypotheses were generated from Cannabidiol (CBD)-Cannabinoid Receptor subtype-2 (CB2) and then Zinc database was screened for identification of hit molecules. Identified 215 hit molecules were subjected to preliminary screening with ADMET and drug likeness properties, and about 48 molecules were found with no violations and toxicity properties. In molecular docking studies, six compounds showed better binding energy than CBD and β-caryophyllene (known inhibitor of CB2). These six molecules were designated as leads and subjected to re-docking with glide tool and Lead1 (ZINC000078815430) showed docking score of -9.877 kcal/mol, whereas CBD and β-caryophyllene showed score of -9.664 and -8.499 kcal/mol, respectively. Lead1 and CBD were evaluated for stability studies with Desmond tool by molecular dynamic simulation studies. Lead1 showed better stability than CBD in all studied parameters such as RMSD, RMSF, SSE, Rg, SASA, etc. In MM-GBSA free energy calculations, ΔGbinding energy of CB2-CBD complex and CB2-Lead1 were found to be -103.13±11.19 and -107.94±5.42 kcal/mol, respectively. Six lead molecules stated in the study hold promise with respect to CBD agonistic activity for treating and/or managing chronic conditions and can be explored as an alternative for early-stage cure, which has not yet been experimentally explored.

Discovery of a CB2 and 5-HT1A receptor dual agonist for the treatment of depression and anxiety

Cannabinoid CB2R agonists have gained considerable attention as potential novel therapies for psychiatric disorders due to their non-psychoactive nature, in contrast to CB1R agonists. In this study, we employed molecular docking to design and synthesize 23 derivatives of cannabidiol (CBD) with the aim of discovering potent CB2R agonists rather than CB2R antagonists or inverse agonists. Structure-activity relationship (SAR) investigations highlighted the critical importance of the amide group at the C-3' site and the cycloalkyl group at the C-4' site for CB2R activation. Interestingly, three CBD derivatives, namely 2o, 6g, and 6h, exhibited substantial partial agonistic activity towards the CB2 receptor, in contrast to the inverse agonistic property of CBD. Among these, 2o acted as a CB2R and 5-HT1AR dual agonist, albeit with some undesired antagonist activity for CB1R. It demonstrated significant CB2R partial agonism while maintaining a level of 5-HT1AR agonistic and CB1R antagonistic activity similar to CBD. Pharmacokinetic experiments confirmed that 2o possesses favorable pharmacokinetic properties. Behavioral studies further revealed that 2o elicits significant antidepressant-like and anxiolytic-like effects while maintaining a good safety profile.

Cannabidiol at Nanomolar Concentrations Negatively Affects Signaling through the Adenosine A2A Receptor

Cannabidiol (CBD) is a phytocannabinoid with potential as a therapy for a variety of diseases. CBD may act via cannabinoid receptors but also via other G-protein-coupled receptors (GPCRs), including the adenosine A2A receptor. Homogenous binding and signaling assays in Chinese hamster ovary (CHO) cells expressing the human version of the A2A receptor were performed to address the effect of CBD on receptor functionality. CBD was not able to compete for the binding of a SCH 442416 derivative labeled with a red emitting fluorescent probe that is a selective antagonist that binds to the orthosteric site of the receptor. However, CBD reduced the effect of the selective A2A receptor agonist, CGS 21680, on Gs-coupling and on the activation of the mitogen activated kinase signaling pathway. It is suggested that CBD is a negative allosteric modulator of the A2A receptor.

Dual allosteric and orthosteric pharmacology of synthetic analog cannabidiol-dimethylheptyl, but not cannabidiol, on the cannabinoid CB2 receptor

Cannabinoid CB2 receptor (CB2R) is a class A G protein-coupled receptor (GPCR) involved in a broad spectrum of physiological processes and pathological conditions. For that reason, targeting CB2R might provide therapeutic opportunities in neurodegenerative disorders, neuropathic pain, inflammatory diseases, and cancer. The main components from Cannabis sativa, such as Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), have been therapeutically exploited and synthetically-derived analogs have been generated. One example is cannabidiol-dimethylheptyl (CBD-DMH), which exhibits anti-inflammatory effects. Nevertheless, its pharmacological mechanism of action is not yet fully understood and is hypothesized for multiple targets, including CB2R. The aim of this study was to further investigate the molecular pharmacology of CBD-DMH on CB2R while CBD was taken along as control. These compounds were screened in equilibrium and kinetic radioligand binding studies and various functional assays, including G protein activation, inhibition of cAMP production and ß-arrestin-2 recruitment. In dissociation studies, CBD-DMH allosterically modulated the radioligand binding. Furthermore, CBD-DMH negatively modulated the G protein activation of reference agonists CP55,940, AEA and 2-AG, but not the agonist-induced ß-arrestin-2 recruitment. Nevertheless, CBD-DMH also displayed competitive binding to CB2R and partial agonism on G protein activation, inhibition of cAMP production and ß-arrestin-2 recruitment. CBD did not exhibit such allosteric behavior and only very weakly bound CB2R without activation. This study shows a dual binding mode of CBD-DMH, but not CBD, to CB2R with the suggestion of two different binding sites. Altogether, it encourages further research into this dual mechanism which might provide a new class of molecules targeting CB2R.

Generation of Cannabigerolic Acid Derivatives and Their Precursors by Using the Promiscuity of the Aromatic Prenyltransferase NphB

NphB is an aromatic prenyltransferase with high promiscuity for phenolics including flavonoids, isoflavonoids, and plant polyketides. It has been demonstrated that cannabigerolic acid is successfully formed by the reaction catalysed by NphB using geranyl diphosphate and olivetolic acid as substrates. In this study, the substrate specificity of NphB was further determined by using olivetolic acid derivatives as potential substrates for the formation of new synthetic cannabinoids. The derivatives differ in the hydrocarbon chain attached to C6 of the core structure. We performed in silico experiments, including docking of olivetolic acid derivatives, to identify differences in their binding modes. Substrate acceptance was predicted. Based on these results, a library of olivetolic acid derivatives was constructed and synthesized by using different organic synthetic routes. Conversion was monitored in in vitro assays with purified NphB versions. For the substrates leading to a high conversion olivetolic acid-C8, olivetolic acid-C2 and 2-benzyl-4,6-dihydroxybenzoic acid, the products were further elucidated and identified as cannbigerolic acid derivatives. Therefore, these substrates show potential to be adapted in cannabinoid biosynthesis.

The Leu/Val6.51 Side Chain of Cannabinoid Receptors Regulates the Binding Mode of the Alkyl Chain of Δ9-Tetrahydrocannabinol

(-)-Δ9-trans-tetrahydrocannabinol (THC), which is the principal psychoactive constituent of Cannabis, mediates its action by binding to two members of the G-protein-coupled receptor (GPCR) family: the cannabinoid CB1 (CB1R) and CB2 (CB2R) receptors. Molecular dynamics simulations showed that the pentyl chain of THC could adopts an I-shape conformation, filling an intracellular cavity between Phe3.36 and Trp6.48 for initial agonist-induced receptor activation, in CB1R but not in CB2R. This cavity opens to the five-carbon chain of THC by the conformational change of the γ-branched, flexible, Leu6.51 side chain of CB1R, which is not feasible by the β-branched, mode rigid, Val6.51 side chain of CB2R. In agreement with our computational results, THC could not decrease the forskolin-induced cAMP levels in cells expressing mutant CB1RL6.51V receptor but could activate the mutant CB2RV6.51L receptor as efficiently as wild-type CB1R. Additionally, JWH-133, a full CB2R agonist, contains a branched dimethyl moiety in the ligand chain that bridges Phe3.36 and Val6.51 for receptor activation. In this case, the substitution of Val6.51 to Leu in CB2R makes JWH-133 unable to activate CB2RV6.51L. In conclusion, our combined computational and experimental results have shown that the amino acid at position 6.51 is a key additional player in the initial mechanism of activation of GPCRs that recognize signaling molecules derived from lipid species.

Diastereoselective and Scalable Synthesis of 6-(S)-Hydroxycannabidivarin

The synthesis of 6-(S)-hydroxycannabidivarin was required to assess its biological activity in the treatment of neurological disorders. A novel and scalable synthesis has been developed where the key step involves a Friedel-Crafts alkylation of phloroglucinol with (1S,2R,5R)-2-hydroxy-2-methyl-5-(prop-1-en-2-yl)cyclohex-3-en-1-ylbenzoate. Careful optimization of the reaction conditions identified trifluoromethanesulfonic acid in isopropyl acetate as the best catalyst/solvent combination, providing optimum regioselectivity, diastereoselectivity, and yield for this step. This enabled the multigram synthesis of 6-(S)-hydroxycannabidivarin in 10 steps from S-(+)-carvone.

Neuroprotection afforded by targeting G protein-coupled receptors in heteromers and by heteromer-selective drugs

G protein-coupled receptors (GPCRs) are the target of hundreds of approved drugs. Although these drugs were designed to target individual receptors, it is becoming increasingly apparent that GPCRs interact with each other to form heteromers. Approved drug targets are often part of a GPCR heteromer, and therefore new drugs can be developed with heteromers in mind. This review presents several strategies to selectively target GPCRs in heteromeric contexts, namely, taking advantage of i) heteromer-mediated biased agonism/signalling, ii) discovery of drugs with higher affinity for the receptor if it is part of a heteromer (heteromer selective drugs), iii) allosteric compounds directed against the interacting transmembrane domains and, eventually, iv) antagonists that block both GPCRs in a heteromer. Heteromers provide unique allosteric sites that should help designing a new type of drug that by definition would be a heteromer selective drug. The review also provides examples of rhodopsin-like class A receptors in heteromers that could be targeted to neuroprotect and/or delay the progression of diseases such as Parkinson's and Alzheimer's. GPCRs in heteromers (GriH) with the potential to address dyskinesias, a common complication of dopaminergic replacement therapy in parkinsonian patients, are also described.

Synthetic Pathways to Non-Psychotropic Phytocannabinoids as Promising Molecules to Develop Novel Antibiotics: A Review

Due to the rapid emergence of multi drug resistant (MDR) pathogens against which current antibiotics are no longer functioning, severe infections are becoming practically untreatable. Consequently, the discovery of new classes of effective antimicrobial agents with novel mechanism of action is becoming increasingly urgent. The bioactivity of Cannabis sativa, an herbaceous plant used for millennia for medicinal and recreational purposes, is mainly due to its content in phytocannabinoids (PCs). Among the 180 PCs detected, cannabidiol (CBD), Δ⁸ and Δ⁹-tetrahydrocannabinols (Δ⁸-THC and Δ⁹-THC), cannabichromene (CBC), cannabigerol (CBG), cannabinol (CBN) and some of their acidic precursors have demonstrated from moderate to potent antibacterial effects against Gram-positive bacteria (MICs 0.5-8 µg/mL), including methicillin-resistant Staphylococcus aureus (MRSA), epidemic MRSA (EMRSA), as well as fluoroquinolone and tetracycline-resistant strains. Particularly, the non-psychotropic CBG was also capable to inhibit MRSA biofilm formation, to eradicate even mature biofilms, and to rapidly eliminate MRSA persiter cells. In this scenario, CBG, as well as other minor non-psychotropic PCs, such as CBD, and CBC could represent promising compounds for developing novel antibiotics with high therapeutic potential. Anyway, further studies are necessary, needing abundant quantities of such PCs, scarcely provided naturally by Cannabis plants. Here, after an extensive overture on cannabinoids including their reported antimicrobial effects, aiming at easing the synthetic production of the necessary amounts of CBG, CBC and CBD for further studies, we have, for the first time, systematically reviewed the synthetic pathways utilized for their synthesis, reporting both reaction schemes and experimental details.

Targeting the endocannabinoid system: Structural determinants and molecular mechanism of allosteric modulation

Although drugs targeting the orthosteric binding site of cannabinoid receptors (CBRs) have several therapeutic effects on human physiological and pathological conditions, they can also cause serious adverse effects. Only a few orthosteric ligands have successfully passed clinical trials. Recently, allosteric modulation has become a novel option for drug discovery, with fewer adverse effects and the potential to avoid drug overdose. In this review, we highlight novel findings related to the drug discovery of allosteric modulators (AMs) targeting CBRs. We summarize newly synthesized AMs and the reported/predicted allosteric binding sites. We also discuss the structural determinants of the AMs binding as well as the molecular mechanism of CBR allostery.

Endocannabinoid signaling in the central nervous system

It is hard to overestimate the influence of the endocannabinoid signaling (ECS) system on central nervous system (CNS) function. In the 40 years since cannabinoids were found to trigger specific cell signaling cascades, studies of the ECS system continue to cause amazement, surprise, and confusion! CB1 cannabinoid receptors are expressed widely in the CNS and regulate cell-cell communication via effects on the release of both neurotransmitters and gliotransmitters. CB2 cannabinoid receptors are difficult to detect in the CNS but seem to "punch above their weight" as compounds targeting these receptors have significant effects on inflammatory state and behavior. Positive and negative allosteric modulators for both receptors have been identified and examined in preclinical studies. Concentrations of the endocannabinoid ligands, N-arachidonoylethanolamine and 2-arachidonoylglycerol (2-AG), are regulated by a combination of enzymatic synthesis and degradation and inhibitors of these processes are available and making their way into clinical trials. Importantly, ECS regulates many essential brain functions, including regulation of reward, anxiety, inflammation, motor control, and cellular development. While the field is on the cusp of preclinical discoveries providing impactful clinical and therapeutic insights into many CNS disorders, there is still much to be learned about this remarkable and versatile modulatory system.

A Single Point Mutation Blocks the Entrance of Ligands to the Cannabinoid CB2 Receptor via the Lipid Bilayer

Molecular dynamic (MD) simulations have become a common tool to study the pathway of ligand entry to the orthosteric binding site of G protein-coupled receptors. Here, we have combined MD simulations and site-directed mutagenesis to study the binding process of the potent JWH-133 agonist to the cannabinoid CB₂ receptor (CB₂R). In CB₂R, the N-terminus and extracellular loop 2 fold over the ligand binding pocket, blocking access to the binding cavity from the extracellular environment. We, thus, hypothesized that the binding pathway is a multistage process consisting of the hydrophobic ligand diffusing in the lipid bilayer to contact a lipid-facing vestibule, from which the ligand enters an allosteric site inside the transmembrane bundle through a tunnel formed between TMs 1 and 7 and finally moving from the allosteric to the orthosteric binding cavity. This pathway was experimentally validated by the Ala282^7.36Phe mutation that blocks the entrance of the ligand, as JWH-133 was not able to decrease the forskolin-induced cAMP levels in cells expressing the mutant receptor. This proposed ligand entry pathway defines transient binding sites that are potential cavities for the design of synthetic modulators.

Modulation of type 1 cannabinoid receptor activity by cannabinoid by-products from Cannabis sativa and non-cannabis phytomolecules

Cannabis sativa contains more than 120 cannabinoids and 400 terpene compounds (i.e., phytomolecules) present in varying amounts. Cannabis is increasingly available for legal medicinal and non-medicinal use globally, and with increased access comes the need for a more comprehensive understanding of the pharmacology of phytomolecules. The main transducer of the intoxicating effects of Cannabis is the type 1 cannabinoid receptor (CB1R). ∆⁹-tetrahydrocannabinolic acid (∆⁹-THCa) is often the most abundant cannabinoid present in many cultivars of Cannabis. Decarboxylation converts ∆⁹-THCa to ∆⁹-THC, which is a CB1R partial agonist. Understanding the complex interplay of phytomolecules—often referred to as “the entourage effect”—has become a recent and major line of inquiry in cannabinoid research. Additionally, this interest is extending to other non-Cannabis phytomolecules, as the diversity of available Cannabis products grows. Here, we chose to focus on whether 10 phytomolecules (∆⁸-THC, ∆^6a,10a-THC, 11-OH-∆⁹-THC, cannabinol, curcumin, epigallocatechin gallate, olivetol, palmitoylethanolamide, piperine, and quercetin) alter CB1R-dependent signaling with or without a co-treatment of ∆⁹-THC. Phytomolecules were screened for their binding to CB1R, inhibition of forskolin-stimulated cAMP accumulation, and βarrestin2 recruitment in Chinese hamster ovary cells stably expressing human CB1R. Select compounds were assessed further for cataleptic, hypothermic, and anti-nociceptive effects on male mice. Our data revealed partial agonist activity for the cannabinoids tested, as well as modulation of ∆⁹-THC-dependent binding and signaling properties of phytomolecules in vitro and in vivo. These data represent a first step in understanding the complex pharmacology of Cannabis- and non-Cannabis-derived phytomolecules at CB1R and determining whether these interactions may affect the physiological outcomes, adverse effects, and abuse liabilities associated with the use of these compounds.

Regulation of Expression of Cannabinoid CB2 and Serotonin 5HT1A Receptor Complexes by Cannabinoids in Animal Models of Hypoxia and in Oxygen/Glucose-Deprived Neurons

Background: Cannabidiol (CBD) is a phytocannabinoid with potential in one of the most prevalent syndromes occurring at birth, the hypoxia of the neonate. CBD targets a variety of proteins, cannabinoid CB₂ and serotonin 5HT_1A receptors included. These two receptors may interact to form heteromers (CB₂–5HT_1A-Hets) that are also a target of CBD. Aims: We aimed to assess whether the expression and function of CB₂–5HT_1A-Hets is affected by CBD in animal models of hypoxia of the neonate and in glucose- and oxygen-deprived neurons. Methods: We developed a quantitation of signal transduction events in a heterologous system and in glucose/oxygen-deprived neurons. The expression of receptors was assessed by immuno-cyto and -histochemistry and, also, by using the only existing technique to visualize CB₂–5HT_1A-Hets fixed cultured cells and tissue sections (in situ proximity ligation PLA assay). Results: CBD and cannabigerol, which were used for comparative purposes, affected the structure of the heteromer, but in a qualitatively different way; CBD but not CBG increased the affinity of the CB₂ and 5HT_1A receptor–receptor interaction. Both cannabinoids regulated the effects of CB₂ and 5HT_1A receptor agonists. CBD was able to revert the upregulation of heteromers occurring when neurons were deprived of oxygen and glucose. CBD significantly reduced the increased expression of the CB₂–5HT_1A-Het in glucose/oxygen-deprived neurons. Importantly, in brain sections of a hypoxia/ischemia animal model, administration of CBD led to a significant reduction in the expression of CB₂–5HT_1A-Hets. Conclusions: Benefits of CBD in the hypoxia of the neonate are mediated by acting on CB₂–5HT_1A-Hets and by reducing the aberrant expression of the receptor–receptor complex in hypoxic-ischemic conditions. These results reinforce the potential of CBD for the therapy of the hypoxia of the neonate.

Cannabinoid type-2 receptors: An emerging target for regulating schizophrenia-relevant brain circuits

Although the cannabinoid type-2 receptor (CB2) is highly expressed in the immune system, emerging evidence points to CB2 playing a key role in regulating neuronal function in the central nervous system. Recent anatomical studies, combined with electrophysiological studies, indicate that CB2 receptors are expressed in specific dopaminergic and glutamatergic brain circuits that are hyperactive in schizophrenia patients. The ability of CB2 receptors to inhibit dopaminergic and hippocampal circuits, combined with the anti-inflammatory effects of CB2 receptor activation, make this receptor an intriguing target for treating schizophrenia, a disease where novel interventions that move beyond dopamine receptor antagonists are desperately needed. The development of new CB2-related pharmacological and genetic tools, including the first small molecule positive allosteric modulator of CB2 receptors, has greatly advanced our understanding of this receptor. While more work is needed to further elucidate the translational value of selectively targeting CB2 receptors with respect to schizophrenia, the studies discussed below could suggest that CB2 receptors are anatomically located in schizophrenia-relevant circuits, where the physiological consequence of CB2 receptor activation could correct circuit-based deficits commonly associated with positive and cognitive deficits.

Design, Synthesis, and Biological Activity of New CB2 Receptor Ligands: from Orthosteric and Allosteric Modulators to Dualsteric/Bitopic Ligands

The design of dualsteric/bitopic agents as single chemical entities able to simultaneously interact with both the orthosteric and an allosteric binding site represents a novel approach in medicinal chemistry. Biased dualsteric/bitopic agents could enhance certain signaling pathways while diminishing the others that cause unwanted side effects. We have designed, synthesized, and functionally characterized the first CB2R heterobivalent bitopic ligands. In contrast to the parent orthosteric compound, our bitopic ligands selectively target CB2R versus CB1R and show a functional selectivity for the cAMP signaling pathway versus βarrestin2 recruitment. Moreover, the most promising bitopic ligand FD-22a displayed anti-inflammatory activity in a human microglial cell inflammatory model and antinociceptive activity in vivo in an experimental mouse model of neuropathic pain. Finally, computational studies clarified the binding mode of these compounds inside the CB2R, further confirming their bitopic nature.

Effect of Fatty Acid Amide Hydrolase Inhibitor URB597 on Orofacial Pain Perception in Rats

Endocannabinoids act as analgesic agents in a number of headache models. However, their effectiveness varies with the route of administration and the type of pain. In this study, we assessed the role of the fatty acid amide hydrolase inhibitor URB597 in an animal model of orofacial pain based on tooth pulp stimulation. More specifically, we assessed the effects of intracerbroventricular (i.c.v.) and intraperitoneal (i.p.) administration of URB597 on the amplitude of evoked tongue jerks (ETJ) in rats. The levels of the investigated mediators anandamide (AEA), 2-arachidonyl glycerol (2-AG), Substance P (SP), calcitonin-gene-related peptide (CGRP), endomorphin-2 (EM-2) and fatty acid amide hydrolase (FAAH) inhibitor by URB597 and receptors cannabinoid type-1 receptors (CB1R), cannabinoid type-2 receptors (CB2R) and µ-opioid receptors (MOR) were determined in the mesencephalon, thalamus and hypothalamus tissues. We have shown that increasing endocannabinoid AEA levels by both central and peripheral inhibition of FAAH inhibitor by URB597 has an antinociceptive effect on the trigemino-hypoglossal reflex mediated by CB1R and influences the activation of the brain areas studied. On the other hand, URB597 had no effect on the concentration of 2-AG in the examined brain structures and caused a significant decrease in CB2R mRNA expression in the hypothalamus only. Tooth pulp stimulation caused in a significant increase in SP, CGRP and EM-2 gene expression in the midbrain, thalamus and hypothalamus. In contrast, URB597 administered peripherally one hour before stimulation decreased the mRNA level of these endogenous neuropeptides in comparison with the control and stimulation in all examined brain structures. Our results show that centrally and peripherally administered URB597 is effective at preventing orofacial pain by inhibiting AEA catabolism and reducing the level of CGRP, SP and EM-2 gene expression and that AEA and 2-AG have different species and model-specific regulatory mechanisms. The data presented in this study may represent a new promising therapeutic target in the treatment of orofacial pain.

Cannabidiol and periodontal inflammatory disease: A critical assessment

Cannabidiol (CBD), a non-psychotropic cannabinoid produced by the genus Cannabis, is a phytoceutical that activates the endocannabinoid system (ECS) through binding to CB1 and CB2 receptors. The ECS is involved in cellular homeostasis and regulates metabolic processes in virtually all mammalian tissues. Published studies on CBD focus, inter alia, on its use in prophylaxis and as an anti-inflammatory agent. Here the authors present a critical assessment of the effects of CBD on inflammatory periodontal diseases caused by bacterial virulence factors, and evaluate critically the possible benefits and drawbacks of CBD use in dentistry. Particular attention is paid to the interaction of CBD with microbially colonized oral tissues, the inflammatory response in relation to the immune response, and the destruction/regeneration of hard and soft tissues of the periodontium.

Targeting CB2 and TRPV1: Computational Approaches for the Identification of Dual Modulators

Both metabotropic (CBRs) and ionotropic cannabinoid receptors (ICRs) have implications in a range of neurological disorders. The metabotropic canonical CBRs CB1 and CB2 are highly implicated in these pathological events. However, selective targeting at CB2 versus CB1 offers optimized pharmacology due to the absence of psychoactive outcomes. The ICR transient receptor potential vanilloid type 1 (TRPV1) has also been reported to play a role in CNS disorders. Thus, activation of both targets, CB2 and TRPV1, offers a promising polypharmacological strategy for the treatment of neurological events including analgesia and neuroprotection. This brief research report aims to identify chemotypes with a potential dual CB2/TRPV1 profile. For this purpose, we have rationalized key structural features for activation and performed virtual screening at both targets using curated chemical libraries.

The Binding Mode to Orthosteric Sites and/or Exosites Underlies the Therapeutic Potential of Drugs Targeting Cannabinoid CB2 Receptors

The classical terms agonists and antagonists for G protein coupled receptors (GPCRs) have often become misleading. Even the biased agonism concept does not describe all the possibilities already demonstrated for GPCRs. The cannabinoid CB₂ receptor (CB₂R) emerged as a promising target for a variety of diseases. Reasons for such huge potential are centered around the way drugs sit in the orthosteric and/or exosites of the receptor. On the one hand, a given drug in a specific CB₂R conformation leads to a signaling cascade that differs qualitatively and/or quantitatively from that triggered by another drug. On the other hand, a given drug may lead to different signaling outputs in two different tissues (or cell contexts) in which the conformation of the receptor is affected by allosteric effects derived from interactions with other proteins or with membrane lipids. This highlights the pharmacological complexity of this receptor and the need to further unravel the binding mode of CB₂R ligands in order to fine-tune signaling effects and therapeutic propositions.

New Insights and Potential Therapeutic Targeting of CB2 Cannabinoid Receptors in CNS Disorders

The endocannabinoid system (ECS) is ubiquitous in most human tissues, and involved in the regulation of mental health. Consequently, its dysregulation is associated with neuropsychiatric and neurodegenerative disorders. Together, the ECS and the expanded endocannabinoidome (eCBome) are composed of genes coding for CB1 and CB2 cannabinoid receptors (CB1R, CB2R), endocannabinoids (eCBs), and the metabolic enzyme machinery for their synthesis and catabolism. The activation of CB1R is associated with adverse effects on the central nervous system (CNS), which has limited the therapeutic use of drugs that bind this receptor. The discovery of the functional neuronal CB2R raised new possibilities for the potential and safe targeting of the ECS for the treatment of CNS disorders. Previous studies were not able to detect CB2R mRNA transcripts in brain tissue and suggested that CB2Rs were absent in the brain and were considered peripheral receptors. Studies done on the role of CB2Rs as a potential therapeutic target for treating different disorders revealed the important putative role of CB2Rs in certain CNS disorders, which requires further clinical validation. This review addresses recent advances on the role of CB2Rs in neuropsychiatric and neurodegenerative disorders, including, but not limited to, anxiety, depression, schizophrenia, Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD) and addiction.

In Silico Prediction and Validation of CB2 Allosteric Binding Sites to Aid the Design of Allosteric Modulators

Although the 3D structures of active and inactive cannabinoid receptors type 2 (CB2) are available, neither the X-ray crystal nor the cryo-EM structure of CB2-orthosteric ligand-modulator has been resolved, prohibiting the drug discovery and development of CB2 allosteric modulators (AMs). In the present work, we mainly focused on investigating the potential allosteric binding site(s) of CB2. We applied different algorithms or tools to predict the potential allosteric binding sites of CB2 with the existing agonists. Seven potential allosteric sites can be observed for either CB2-CP55940 or CB2-WIN 55,212-2 complex, among which sites B, C, G and K are supported by the reported 3D structures of Class A GPCRs coupled with AMs. Applying our novel algorithm toolset-MCCS, we docked three known AMs of CB2 including Ec2la (C-2), trans-β-caryophyllene (TBC) and cannabidiol (CBD) to each site for further comparisons and quantified the potential binding residues in each allosteric binding site. Sequentially, we selected the most promising binding pose of C-2 in five allosteric sites to conduct the molecular dynamics (MD) simulations. Based on the results of docking studies and MD simulations, we suggest that site H is the most promising allosteric binding site. We plan to conduct bio-assay validations in the future.

Similarities and differences upon binding of naturally occurring Δ9-tetrahydrocannabinol-derivatives to cannabinoid CB1 and CB2 receptors

We have here assessed, using Δ⁹-tetrahydrocannabinol (Δ⁹-THC) for comparison, the effect of Δ⁹-tetrahydrocannabinolic acid (Δ⁹-THCA) and of Δ⁹-tetrahydrocannabivarin (Δ9-THCV) that is mediated by human versions of CB₁, CB₂, and CB₁-CB₂ receptor functional units, expressed in a heterologous system. Binding to the CB₁ and CB₂ receptors was addressed in living cells by means of a homogeneous assay. A biphasic competition curve for the binding to the CB₂ receptor, was obtained for Δ⁹-THCV in cells expressing the two receptors. Signaling studies included cAMP level determination, activation of the mitogen-activated protein kinase pathway and ß-arrestin recruitment were performed. The signaling triggered by Δ⁹-THCA and Δ⁹-THCV via individual receptors or receptor heteromers disclosed differential bias, i.e. the bias observed using a given phytocannabinoid depended on the receptor (CB₁, CB₂ or CB₁-CB₂) and on the compound used as reference to calculate the bias factor (Δ⁹-THC, a selective agonist or a non-selective agonist). These results are consistent with different binding modes leading to differential functional selectivity depending on the agonist structure, and the state (monomeric or heteromeric) of the cannabinoid receptor. In addition, on studying Gi-coupling we showed that Δ⁹-THCV and Δ⁹-THCA and Δ⁹-THCV were able to revert the effect of a selective CB₂ receptor agonist, but only Δ9-THCV, and not Δ9-THCA, reverted the effect of arachidonyl-2'-chloroethylamide (ACEA 100 nM) a selective agonist of the CB₁ receptor. Overall, these results indicate that cannabinoids may have a variety of binding modes that results in qualitatively different effects depending on the signaling pathway that is engaged upon cannabinoid receptor activation.