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The cannabinoid CB 2 receptor (CB 2 R) represents a promising therapeutic target for various forms of tissue injury and inflammatory diseases. Although numerous compounds have been developed and widely used to target CB 2 R, their selectivity, molecular mode of action and pharmacokinetic properties have been poorly characterized. Here we report the most extensive characterization of the molecular pharmacology of the most widely used CB 2 R ligands to date. In a collaborative effort between multiple academic and industry laboratories, we identify marked differences in the ability of certain agonists to activate distinct signalling pathways and to cause off-target effects. We reach a consensus that HU910, HU308 and JWH133 are the recommended selective CB 2 R agonists to study the role of CB 2 R in biological and disease processes. We believe that our unique approach would be highly suitable for the characterization of other therapeutic targets in drug discovery research. CB 2 receptor agonists are developed as potential analgesics or immune-modulatory compounds. Here, the authors characterize the pharmacological properties of widely used CB 2 receptor agonists and antagonists, recommending three that appear most suitable for in vitro and in vivo studies.

The entourage effect was a proposed explanation for biological observations that endocannabinoid ligand activities can be modified by other lipids released from cells at the same time. An increasing volume of anecdotal reports and interest in the plant have provoked research into the activity of minor chemical constituents of the plant-including volatile terpenoids such as myrcene, α- and β- pinene, β-caryophyllene, and limonene. However, to date, no clear interaction has been identified. The current study was designed to determine whether terpenes in the cannabis plant have detectable receptor-mediated activity, or modify the activity of Δ -tetrahydrocannabinol, cannabidiol, or the endocannabinoid 2-arachidonylglycerol at the cannabinoid receptors. In addition, we have utilized a standard radioligand binding paradigm with ability to detect orthosteric and allosteric interactions of test compounds. With the possible exception of a weak interaction of β-caryophyllene with CB2, no data were produced to support the hypothesis that any of the five terpenes tested (either alone or in mixtures) have direct interactions with CB1 or CB2, as the binding of radioligand ([ H]-CP55,940), Δ -tetrahydrocannabinol, and cannabidiol were unaltered by the presence of terpenes. Similarly, terpene functional effects were also not detected, either alone or in combination with Δ -tetrahydrocannabinol, cannabidiol, or 2-arachidonoylglycerol. This study adds to the evidence that the putative entourage effect cannot be explained by direct effects at CB1 or CB2.

Arrestin translocation and signaling have come to the fore of the G protein-coupled receptor molecular pharmacology field. Some receptor-arrestin interactions are relatively well understood and considered responsible for specific therapeutic or adverse outcomes. Coupling of arrestins with cannabinoid receptors 1 (CB ) and 2 (CB ) has been reported, though the majority of studies have not systematically characterized the differential ligand dependence of this activity. In addition, many prior studies have utilized bovine (rather than human) arrestins, and the most widely applied assays require reporter-tagged receptors, which prevent meaningful comparison between receptor types. We have employed a bioluminescence resonance energy transfer (BRET) method that does not require the use of tagged receptors and thereby allows comparisons of arrestin translocation between receptor types, as well as with cells lacking the receptor of interest - an important control. The ability of a selection of CB and CB agonists to stimulate cell surface translocation of human and bovine β-arrestin-1 and -2 was assessed. We find that some CB ligands induce moderate β-arrestin-2 translocation in comparison with vasopressin V receptor (a robust arrestin recruiter); however, CB coupling with β-arrestin-1 and CB with either arrestin elicited low relative efficacies. A range of efficacies between ligands was evident for both receptors and arrestins. Endocannabinoid 2-arachidonoylglycerol stood out as a high efficacy ligand for translocation of β-arrestin-2 via CB . Δ -tetrahydrocannabinol was generally unable to elicit translocation of either arrestin subtype via CB or CB ; however, control experiments revealed translocation in cells not expressing CB /CB , which may assist in explaining some discrepancy with the literature. Overexpression of GRK2 had modest influence on CB /CB -induced arrestin translocation. Results with bovine and human arrestins were largely analogous, but a few instances of inconsistent rank order potencies/efficacies between bovine and human arrestins raise the possibility that subtle differences in receptor conformation stabilized by these ligands manifest in disparate affinities for the two arrestin species, with important potential consequences for interpretation in ligand bias studies. As well as contributing important information regarding CB /CB ligand-dependent arrestin coupling, our study raises a number of points for consideration in the design and interpretation of arrestin recruitment assays.

Model simplification is a process to simplify large‐scale mathematical models to enable easy applications such as simulation and parameter estimation. A novel heuristic machine analogy method of model simplification was developed and applied to a motivating example of a model for cAMP signaling switch induced by Gi/Gs pathway competition for the CB1 receptor (consisting of 31 species and 76 parameters) to enable its use in estimation. The method first acquired an understanding of the mechanism by full model simulation, and then the mechanism was ed to a machine analogy. The machine analogy included signal start, signal mode selector, signal size regulator, and final effector, representing functions of different parts of the full model. The simplified minimal model (consisting of 11 species and 13 estimated parameters) was used for parameter estimation for Gi/Gs signaling of six CB1 agonists. The results of the minimal model suggested that six CB1 agonists have similar ratios of Gi/Gs activation, indicating Gi/Gs preference was more of a system effect rather than a ligand‐specific effect. In conclusion, the novel machine analogy method can be used to heuristically simplify a larger‐scale model while maintaining the important mechanisms. In the example here, the full Gi/Gs model of CB1 was successfully simplified, and the results indicated Gi/Gs preference is a system‐dependent effect.

Cannabinoid Receptor 2 (CB 2 ) is a promising therapeutic target for modulating inflammation. Canonical signalling responses to receptor ligands are critically dependent on cell surface receptor expression. However, it is also now appreciated that intracellular G protein-coupled receptors can contribute to signalling responses and influence functional outcomes. Therefore, understanding how the subcellular distribution of receptors is controlled is also highly pertinent. CB 2 is observed to be expressed at the cell surface as well as having a considerable proportion expressed intracellularly. Despite this distribution being well established, little is known about the regulation of CB 2 anterograde trafficking and subcellular distribution. We report that sustained treatment with a range of CB 2 agonists and inverse agonists stimulates a distinct population of CB 2 to be delivered to the cell surface, at various expression levels and despite agonists concurrently internalising cell surface CB 2 . We present evidence that this ligand-stimulated anterograde trafficking is a result of CB 2 agonists, as well as inverse agonists, acting as pharmacological chaperones. We also report that a di-lysine (KK) motif in the CB 2 C-terminal tail is required for basal delivery to the cell surface. Corroborating the hypothesis that CB 2 ligands can act as pharmacological chaperones, sustained CB 2 ligand stimulation induces cell surface expression of the mutated receptor and alters maturation states as measured by western blotting. Our finding that prolonged exposure to CB 2 ligands can induce CB 2 cell surface delivery via pharmacological chaperoning may well have important implications for optimal design of CB 2 -targeted therapeutics.

Background: Inhaled delivery of cannabidiol (CBD) through dry powder inhalers is a promising approach for achieving optimal drug concentrations in the lungs. Spray drying is a commonly employed technique to prepare inhalable powders with particle sizes ideally ranging from 1 to 5 µm, for deep lung deposition. However, formulating aerosolizable CBD dry powders remains challenging due to the thermolabile nature of CBD and the cohesive behaviour of micron-sized particles, which affects powder dispersibility, reduces de-agglomeration during inhalation, and causes inefficient lung deposition. These challenges can be overcome by the inclusion of excipients that can stabilize CBD during processing and enhance the dispersion and aerosolization of the powder. Objectives and methods: This study investigates the role of different amino acids (lysine, cysteine, arginine, and phenylalanine) in combination with inulin, a sugar-based excipient, on the in vitro aerosolization performance, stability, and cytotoxicity of inhalable CBD dry powders. Results and conclusion: The prepared CBD dry powders exhibited a size range of 1–5 µm. Amino-acid-free CBD powder showed an irregular and flaky morphology, while in association with amino acids, CBD dry powder showed spherical morphology with a dimpled surface. The ATR-FTIR spectra confirmed no interactions between CBD and amino acids in the dry powder formulations. CBD dry powder formulations containing amino acids demonstrated a better aerosolization profile compared to amino-acid-free CBD powder, with the lysine-containing formulation achieving the highest fine particle fraction (FPF) of 56.6%. Additionally, all the formulations were stable under low and high humidity (<15% RH and 53% RH) conditions for 28 days. Cytotoxicity studies on A549 alveolar basal epithelial cells showed that the amino acids were non-toxic, while the CBD formulations with/without amino acids showed comparable levels of cytotoxicity.

G protein-coupled receptors (GPCRs) are important therapeutic targets and therefore extensively studied. Like most transmembrane proteins, there has been considerable difficulty in developing reliable specific antibodies for them. To overcome this, epitope tags are often used to facilitate antibody recognition in studies on fundamental receptor signalling and trafficking. In our study of cannabinoid CB 1 /dopamine D 2 interactions we sought to generate HEK293 cells expressing FLAG-tagged D 2 for use in antibody-based assays of GPCR localisation and trafficking activity, however observed that stable FLAG-hD 2 expression was particularly challenging to maintain. In contrast, when expressed in cell lines expressing hCB 1 robust and stable FLAG-hD 2 expression was observed. We hypothesised that co-expression of CB 1 might stabilise surface FLAG-hD2 expression, and therefore investigated this further. Here, we describe the observation that co-expression of either cannabinoid CB 1 or CB 2 receptors in HEK293 decreases the sulfation of a FLAG epitope appended at the N-terminus of the dopamine D 2 receptor. Sulfation alters epitope recognition by some anti-FLAG antibodies, leading to the detection of fewer receptors, even though expression is maintained. This demonstrates that cannabinoid receptor expression modifies posttranslational processing of the FLAG-hD 2 receptor, and importantly, has wider implications for the utilisation and interpretation of receptor studies involving epitope tags.

Understanding neuronal mechanisms underlying aggression in patients with autism spectrum disorder (ASD) could lead to better treatments and prognosis. The NL3R451C mouse model of ASD, has a heightened aggressive phenotype, however the biological mechanisms underlying this behaviour are unknown. It is well established that NL3R451C mice have imbalanced excitatory and inhibitory synaptic activity in the hippocampus and somatosensory cortex. The amygdala plays a major role in modulating aggressive behaviour, however potential changes in synaptic activity in this region have not previously been assessed in this model. We investigated whether aggressive behaviour is robustly present in mice expressing the R451C mutation, following back-crossing onto a congenic background strain. Endocannabinoids influence social interaction and aggressive behaviour, therefore we also studied the effects of cannabinoid receptor 1 (CB1) agonist on NL3R451C mice. We report that NL3R451C mice have increased amplitude of miniature excitatory postsynaptic currents (EPSCs) with a concomitant decrease in the amplitude of inhibitory postsynaptic currents (IPSCs) in the basolateral amygdala. Importantly, we demonstrated that NL3R451C mice bred on a C57Bl/6 background strain exhibit an aggressive phenotype. Following non-sedating doses (0.3 and 1.0 mg/kg) of the CB1 receptor agonist WIN55,212-2 (WIN), we observed a significant reduction in aggressive behaviour in NL3R451C mice. These findings demonstrate altered synaptic activity in the basolateral amygdala and suggest that the NL3R451C mouse model is a useful preclinical tool to understand the role of CB1 receptor function in aggressive behaviour. Furthermore, this data supports the CB1 receptor as a promising target for new therapeutic approaches to treat aggression.

The orphan receptor GPR18 has become a research target following the discovery of a putative endogenous agonist, N-arachidonoyl glycine (NAGly). Chemical similarity between NAGly and the endocannabinoid anandamide suggested the hypothesis that GPR18 is a third cannabinoid receptor. GPR18-mediated cellular signalling through inhibition of cyclic adenosine monophosphate (cAMP) and phosphorylation of extracellular signal-regulated kinase (ERK), in addition to physiological consequences such as regulation of cellular migration and proliferation/apoptosis have been described in response to both NAGly and anandamide. However, discordant findings have also been reported. Here we sought to describe the functional consequences of GPR18 activation in heterologously-expressing HEK cells. GPR18 expression was predominantly intracellular in stably transfected cell lines, but moderate cell surface expression could be achieved in transiently transfected cells which also had higher overall expression. Assays were employed to characterise the ability of NAGly or anandamide to inhibit cAMP or induce ERK phosphorylation through GPR18, or induce receptor trafficking. Positive control experiments, which utilised cells expressing hCB1 receptors (hCB1R), were performed to validate assay design and performance. While these functional pathways in GPR18-expressing cells were not modified on treatment with a panel of putative GPR18 ligands, a constitutive phenotype was discovered for this receptor. Our data reveal that GPR18 undergoes rapid constitutive receptor membrane trafficking—several-fold faster than hCB1R, a highly constitutively active receptor. To enhance the likelihood of detecting agonist-mediated receptor signalling responses, we increased GPR18 protein expression (by tagging with a preprolactin signal sequence) and generated a putative constitutively inactive receptor by mutating the hGPR18 gene at amino acid site 108 (alanine to asparagine). This A108N mutant did cause an increase in surface receptor expression (which may argue for reduced constitutive activity), but no ligand-mediated effects were detected. Two glioblastoma multiforme cell lines (which endogenously express GPR18) were assayed for NAGly-induced pERK phosphorylation, with negative results. Despite a lack of ligand-mediated responses in all assays, the constitutive trafficking of GPR18 remains an interesting facet of receptor function and will have consequences for understanding the role of GPR18 in physiology.

Positive allosteric modulators (PAMs) of the cannabinoid CB1 receptor (CB1) offer potential therapeutic advantages in the treatment of neuropathic pain and addiction by avoiding the adverse effects associated with orthosteric CB1 activation. Here, molecular modeling and mutagenesis were used to identify residues central to PAM activity at CB1. Six putative allosteric binding sites were identified in silico, including novel sites previously associated with cholesterol binding, and key residues within each site were mutated to alanine. The recently determined ZCZ011 binding site was found to be essential for allosteric agonism, as GAT228, GAT229 and ZCZ011 all increased wild-type G protein dissociation in the absence of an orthosteric ligand; activity that was abolished in mutants F191A3.27 and I169A2.56. PAM activity was demonstrated for ZCZ011 in the presence of the orthosteric ligand CP55940, which was only abolished in I169A2.56. In contrast, the PAM activity of GAT229 was reduced for mutants R220A3.56, L404A8.50, F191A3.27 and I169A2.56. This indicates that allosteric modulation may represent the net effect of binding at multiple sites, and that allosteric agonism is likely to be mediated via the ZCZ011 site. This study underlines the need for detailed understanding of ligand receptor interactions in the search for pure CB1 allosteric modulators.