Signalling profiles of a structurally diverse panel of synthetic cannabinoid receptor agonists

The impact of piperazine and antipsychotic co-exposures and CB1 blockade on the effects elicited by AMB-FUBINACA, a synthetic cannabinoid, in mice

BACKGROUND & PURPOSE

The constant emergence and broad toxicological effects of synthetic cannabinoids create a discernible public health threat. The synthetic cannabinoid AMB-FUBINACA (AMB-FUB) is a potent agonist at the CB1 receptor and has been associated with numerous fatalities. Synthetic cannabinoids are commonly abused alongside other drugs and medications, including a "party pill" drug, para-fluorophenylpiperazine (pFPP), and the antipsychotic risperidone. This research aimed to investigate the mechanisms underpinning AMB-FUB toxicity and the impact of clinically relevant co-exposures in vivo.

EXPERIMENTAL APPROACH

Male and female C57Bl/6 mice received a single dose of AMB-FUB (3 or 6 mg kg-1), pFPP (10 or 20 mg kg-1) or vehicle intraperitoneally. Mice were co-exposed to AMB-FUB (3 mg kg-1) and pFPP (10 mg kg-1) or risperidone (0.5 mg kg-1) to investigate these drug combinations. To study receptor-dependency and potential rescue of AMB-FUB toxicity, rimonabant (3 mg kg-1) was administered both pre- and post-AMB-FUB. Adverse effects caused by drug administration, including hypothermia and convulsions, were recorded.

KEY RESULTS

AMB-FUB induced CB1-dependent hypothermia and convulsions in mice. The combination of AMB-FUB and pFPP significantly potentiated hypothermia, as did risperidone pre-treatment. Interestingly, risperidone provided significant protection from AMB-FUB-induced convulsions in female mice. Pre- and post-treatment with rimonabant was able to significantly attenuate both hypothermia and convulsions in mice administered AMB-FUB.

CONCLUSION & IMPLICATIONS

Factors such as dose, CB1 signalling, and substance co-exposure significantly contribute to the toxicity of AMB-FUBINACA. Mechanistic understanding of synthetic cannabinoid toxicity and fatality can help inform overdose treatment strategies and identify vulnerable populations of synthetic cannabinoid users.

Potent, Selective Agonists for the Cannabinoid-like Orphan G Protein-Coupled Receptor GPR18: A Promising Drug Target for Cancer and Immunity

The human orphan G protein-coupled receptor GPR18, activated by Δ9-tetrahydrocannabinol (THC), constitutes a promising drug target in immunology and cancer. However, studies on GPR18 are hampered by the lack of suitable tool compounds. In the present study, potent and selective GPR18 agonists were developed showing low nanomolar potency at human and mouse GPR18, determined in β-arrestin recruitment assays. Structure-activity relationships were analyzed, and selectivity versus cannabinoid (CB) and CB-like receptors was assessed. Compound 51 (PSB-KK1415, EC50 19.1 nM) was the most potent GPR18 agonist showing at least 25-fold selectivity versus CB receptors. The most selective GPR18 agonist 50 (PSB-KK1445, EC50 45.4 nM) displayed >200-fold selectivity versus both CB receptor subtypes, GPR55, and GPR183. The new GPR18 agonists showed minimal species differences, while THC acted as a weak partial agonist at the mouse receptor. The newly discovered compounds represent the most potent and selective GPR18 agonists reported to date.

GPCR kinase subtype requirements for arrestin-2 and -3 translocation to the cannabinoid CB1 receptor and the consequences on G protein signalling

Arrestins are key negative regulators of G Protein-Coupled Receptors (GPCRs) through mediation of G protein desensitisation and receptor internalisation. Arrestins can also contribute to signal transduction by scaffolding downstream signalling effectors for activation. GPCR kinase (GRK) enzymes phosphorylate the intracellular C-terminal domain, or intracellular loop regions of GPCRs to promote arrestin interaction. There are seven different GRK subtypes, which may uniquely phosphorylate the C-terminal tail in a type of 'phosphorylation barcode,' potentially differentially contributing to arrestin translocation and arrestin-dependent signalling. Such contributions may be exploited to develop arrestin-biased ligands. Here, we examine the effect of different GRK subtypes on the ability to promote translocation of arrestin-2 and arrestin-3 to the cannabinoid CB1 receptor (CB1) with a range of ligands. We find that most GRK subtypes (including visual GRK1) can enhance arrestin-2 and -3 translocation to CB1, and that GRK-dependent changes in arrestin-2 and arrestin-3 translocation were broadly shared for most agonists tested. GRK2/3 generally enhanced arrestin translocation more than the other GRK subtypes, with some small differences between ligands. We also explore the interplay between G protein activity and GRK2/3-dependent arrestin translocation, highlighting that high-efficacy G protein agonists will cause GRK2/3 dependent arrestin translocation. This study supports the hypothesis that arrestin-biased ligands for CB1 must engage GRK5/6 rather than GRK2/3, and G protein-biased ligands must have inherently low efficacy.

Pharmacological evaluation of new generation OXIZID synthetic cannabinoid receptor agonists

Synthetic cannabinoid receptor agonists (SCRAs) remain one the largest classes of new psychoactive substances, and are increasingly associated with severe adverse effects and death compared to the phytocannabinoid Δ9-tetrahydrocannabinol (THC). In the attempt to circumvent the rapid emergence of novel SCRAs, several nations have implemented 'generic' legislations, or 'class-wide' bans based on common structural scaffolds. However, this has only encouraged the incorporation of new chemical entities, including distinct core and linker structures, for which there is a dearth of pharmacological data. The current study evaluated five emergent OXIZID SCRAs for affinity and functional activity at the cannabinoid CB1 receptor (CB1) in HEK 293 cells, as well as pharmacological equivalence with THC in drug discrimination in mice. All OXIZID compounds behaved as agonists in Gαi protein activation and β-arrestin 2 translocation assays, possessing low micromolar affinity at CB1. All ligands also substituted for THC in drug discrimination, where potencies broadly correlated with in vitro activity, with the methylcyclohexane analogue BZO-CHMOXIZID being the most potent. Notably, MDA-19 (BZO-HEXOXIZID) exhibited partial efficacy in vitro, generating an activity profile most similar to that of THC, and partial substitution in vivo. Overall, the examined OXIZIDs were comparatively less potent and efficacious than previous generations of SCRAs. Further toxicological data will elucidate whether the moderate cannabimimetic activity for this series of SCRAs will translate to severe adverse health effects as seen with previous generations of SCRAs.

Synthesis and Functional Evaluation of Synthetic Cannabinoid Receptor Agonists Related to ADB-HEXINACA

ADB-HEXINACA has been recently reported as a synthetic cannabinoid receptor agonist (SCRA), one of the largest classes of new psychoactive substances (NPSs). This compound marks the entry of the n-hexyl tail group into the SCRA landscape, which has continued in the market with recent, newly detected SCRAs. As such, a proactive characterization campaign was undertaken, including the synthesis, characterization, and pharmacological evaluation of ADB-HEXINACA and a library of 41 closely related analogues. Two in vitro functional assays were employed to assess activity at CB1 and CB2 cannabinoid receptors, measuring Gβγ-coupled agonism through a fluorescence-based membrane potential assay (MPA) and β-arrestin 2 (βarr2) recruitment via a live cell-based nanoluciferase complementation reporter assay. ADB-HEXINACA was a potent and efficacious CB1 agonist (CB1 MPA pEC50 = 7.87 ± 0.12 M; Emax = 124 ± 5%; βarr2 pEC50 = 8.27 ± 0.14 M; Emax = 793 ± 42.5), as were most compounds assessed. Isolation of the heterocyclic core and alkyl tails allowed for the comprehensive characterization of structure-activity relationships in this compound class, which were rationalized in silico via induced fit docking experiments. Overall, most compounds assessed are possibly emerging NPSs.

Investigating selectivity and bias for G protein subtypes and β-arrestins by synthetic cannabinoid receptor agonists at the cannabinoid CB1 receptor

The cannabinoid CB1 receptor (CB1) is a G protein-coupled receptor (GPCR) with widespread expression in the central nervous system. This canonically G⍺i/o-coupled receptor mediates the effects of Δ9-tetrahydrocannabinol (THC) and synthetic cannabinoid receptor agonists (SCRAs). Recreational use of SCRAs is associated with serious adverse health effects, making pharmacological research into these compounds a priority. Several studies have hypothesised that signalling bias may explain the different toxicological profiles between SCRAs and THC. Previous studies have focused on bias between G protein activation measured by cyclic adenosine monophosphate (cAMP) inhibition and β-arrestin translocation. In contrast, the current study characterises bias between G⍺ subtypes of the G⍺i/o family and β-arrestins; this method facilitates a more accurate assessment of ligand bias by assessing signals that have not undergone major amplification. We have characterised G protein dissociation and translocation of β-arrestin 1 and 2 using real-time BRET reporters. The responses produced by each SCRA across the G protein subtypes tested were consistent with the responses produced by the reference ligand AMB-FUBINACA. Ligand bias was probed by applying the operational analysis to determine biases within the G⍺i/o family, and between G protein subtypes and β-arrestins. Overall, these results confirm SCRAs to be balanced, high-efficacy ligands compared to the low efficacy ligand THC, with only one SCRA, 4CN-MPP-BUT7IACA, demonstrating statistically significant bias in one pathway comparison (towards β-arrestin 1 when compared with G⍺oA/oB). This suggests that the adverse effects caused by SCRAs are due to high potency and efficacy at CB1, rather than biased agonism.

Somatic and anxiety-like behaviors in male and female rats during withdrawal from the non-selective cannabinoid agonist WIN 55,212-2

Synthetic cannabinoids are associated with higher risk of dependence and more intense withdrawal symptoms than plant-derived Δ9-tetrahydrocannabinol (THC). Avoidance of withdrawal symptoms, including anxiogenic effects, can contribute to continued cannabinoid use. Adult male and female Long-Evans rats were given escalating doses of WIN 55,212-2 (WIN) via twice daily intrajugular infusions. Precipitated withdrawal was elicited with SR 141716 (rimonabant) 4 h after the final infusion. Global withdrawal scores (GWS) were compiled by summing z-scores of observed somatic behaviors over a 30-min period with locomotor activity simultaneously collected via beam breaks. Rimonabant precipitated withdrawal in female and male rats at 3 or 10 mg/kg, respectively, but the individual behaviors contributing to GWS were not identical. 3 mg/kg rimonabant did not impact locomotor behavior in females, but 10 mg/kg decreased locomotion in male controls. Spontaneous withdrawal observed between 6 and 96 h after the final infusion was quantifiable up to 24 h following WIN administration. Individual behaviors contributing to GWS varied by sex and time point. Males undergoing spontaneous withdrawal engaged in more locomotion than females undergoing withdrawal. Separate groups of rats were subjected to a battery of anxiety-like behavioral tests (elevated plus maze, open field test, and marble burying test) one or two weeks after WIN or vehicle infusions. At one week abstinence, sex-related effects were noted in marble burying and the open field test but were unrelated to drug treatment. At two weeks abstinence, females undergoing withdrawal spent more time grooming during marble burying and performed more marble manipulations than their male counterparts. WIN infusions did not impact estrous cycling, and GWS scores were not correlated with estrous at withdrawal. Collectively, these results show qualitative sex differences in behaviors contributing to the behavioral experience of cannabinoid withdrawal supporting clinical findings from THC.

The synthetic cannabinoids menace: a review of health risks and toxicity

Synthetic cannabinoids (SCs) are chemically classified as psychoactive substances that target the endocannabinoid system in many body organs. SCs can initiate pathophysiological changes in many tissues which can be severe enough to damage the normal functionality of our body systems. The majority of SCs-related side effects are mediated by activating Cannabinoid Receptor 1 (CB1R) and Cannabinoid Receptor 2 (CB2R). The activation of these receptors can enkindle many downstream signalling pathways, including oxidative stress, inflammation, and apoptosis that ultimately can produce deleterious changes in many organs. Besides activating the cannabinoid receptors, SCs can act on non-cannabinoid targets, such as the orphan G protein receptors GPR55 and GPR18, the Peroxisome Proliferator-activated Receptors (PPARs), and the Transient receptor potential vanilloid 1 (TRPV1), which are broadly expressed in the brain and the heart and their activation mediates many pharmacological effects of SCs. In this review, we shed light on the multisystem complications found in SCs abusers, particularly discussing their neurologic, cardiovascular, renal, and hepatic effects, as well as highlighting the mechanisms that intermediate SCs-related pharmacological and toxicological consequences to provide comprehensive understanding of their short and long-term systemic effects.

Evaluating signaling bias for synthetic cannabinoid receptor agonists at the cannabinoid CB2 receptor

The rapid structural evolution and emergence of novel synthetic cannabinoid receptor agonists (SCRAs) in the recreational market remains a key public health concern. Despite representing one of the largest classes of new psychoactive substances, pharmacological data on new SCRAs is limited, particularly at the cannabinoid CB2 receptor (CB2 ). Hence, the current study aimed to characterize the molecular pharmacology of a structurally diverse panel of SCRAs at CB2 , including 4-cyano MPP-BUT7AICA, 4F-MDMB-BUTINACA, AMB-FUBINACA, JWH-018, MDMB-4en-PINACA, and XLR-11. The activity of SCRAs was assessed in a battery of in vitro assays in CB2 -expressing HEK 293 cells: G protein activation (Gαi3 and GαoB ), phosphorylation of ERK1/2, and β-arrestin 1/2 translocation. The activity profiles of the ligands were further evaluated using the operational analysis to identify ligand bias. All SCRAs activated the CB2 signaling pathways in a concentration-dependent manner, although with varying potencies and efficacies. Despite the detection of numerous instances of statistically significant bias, compound activities generally appeared only subtly distinct in comparison with the reference ligand, CP55940. In contrast, the phytocannabinoid THC exhibited an activity profile distinct from the SCRAs; most notably in the translocation of β-arrestins. These findings demonstrate that CB2 is able to accommodate a structurally diverse array of SCRAs to generate canonical agonist activity. Further research is required to elucidate whether the activation of CB2 contributes to the toxicity of these compounds.

Subtle Structural Modification of a Synthetic Cannabinoid Receptor Agonist Drastically Increases its Efficacy at the CB1 Receptor

The emergence of synthetic cannabinoid receptor agonists (SCRAs) as illicit psychoactive substances has posed considerable public health risks, including fatalities. Many SCRAs exhibit much higher efficacy and potency compared with the phytocannabinoid Δ9-tetrahydrocannabinol (THC) at the cannabinoid receptor 1 (CB1R), leading to dramatic differences in signaling levels that can be toxic. In this study, we investigated the structure-activity relationships of aminoalkylindole SCRAs at CB1Rs, focusing on 5F-pentylindoles containing an amide linker attached to different head moieties. Using in vitro bioluminescence resonance energy transfer assays, we identified a few SCRAs exhibiting significantly higher efficacy in engaging the Gi protein and recruiting β-arrestin than the reference CB1R full agonist CP55940. Importantly, the extra methyl group on the head moiety of 5F-MDMB-PICA, as compared to that of 5F-MMB-PICA, led to a large increase in efficacy and potency at the CB1R. This pharmacological observation was supported by the functional effects of these SCRAs on glutamate field potentials recorded in hippocampal slices. Molecular modeling and simulations of the CB1R models bound with both of the SCRAs revealed critical structural determinants contributing to the higher efficacy of 5F-MDMB-PICA and how these subtle differences propagated to the receptor-G protein interface. Thus, we find that apparently minor structural changes in the head moiety of SCRAs can cause major changes in efficacy. Our results highlight the need for close monitoring of the structural modifications of newly emerging SCRAs and their potential for toxic drug responses in humans.

The synthetic cannabinoid 5F-MDMB-PICA enhances the metabolic activity and angiogenesis in human brain microvascular endothelial cells by upregulation of VEGF, ANG-1, and ANG-2

Brain angiogenesis, the formation of new blood vessels from existing brain vasculature, has been previously associated with neural plasticity and addictive behaviors related to substances. Synthetic cannabinoids (SCs) have become increasingly popular due to their ability to mimic the effects of cannabis, offering high potency and easy accessibility. In the current study, we reveal that the SC 5F-MDMB-PICA, the most common SC in the United States in 2019, increases cell metabolic activity and promotes angiogenesis in human brain microvascular endothelial cells (HBMECs). First, we performed an MTT assay to evaluate the effects of 5F-MDMB-PICA treatment at various concentrations (0.0001 μM, 0.001 μM, 0.01 μM, 0.1 μM, and 1 μM) on HBMECs metabolic activity. The results demonstrated higher concentrations of the SC improved cell metabolic activity. Furthermore, 5F-MDMB-PICA treatment enhanced tube formation and migration of HBMECs in a dosage-dependent manner. Additionally, the mRNA, secreted protein, and intracellular protein levels of vascular endothelial growth factor, angiopoietin-1, and angiopoietin-2, which are involved in the regulation of angiogenesis, as well as the protein levels of cannabinoid receptor type-1, were all increased following treatment with 5F-MDMB-PICA. Notably, the phosphorylation levels at Serine 9 residue of glycogen synthase kinase-3β were also increased in the 5F-MDMB-PICA treated HBMECs. Collectively, our findings demonstrate that 5F-MDMB-PICA can enhance angiogenesis in HBMECs, suggesting the significant role of angiogenesis in the response to SCs. Manipulating this interaction may pave the way for innovative treatments targeting SC addiction and angiogenesis-related conditions.

A subtle structural modification of a synthetic cannabinoid receptor agonist drastically increases its efficacy at the CB1 receptor

The emergence of synthetic cannabinoid receptor agonists (SCRAs) as illicit psychoactive substances has posed considerable public health risks that include fatalities. Many SCRAs exhibit much higher efficacy and potency, compared with the phytocannabinoid Δ9-tetrahydrocannabinol (THC), at the cannabinoid receptor 1 (CB1R), a G protein-coupled receptor involved in modulating neurotransmitter release. In this study, we investigated structure activity relationships (SAR) of aminoalkylindole SCRAs at CB1Rs, focusing on 5F-pentylindoles containing an amide linker attached to different head moieties. Using in vitro bioluminescence resonance energy transfer (BRET) assays, we identified a few of SCRAs exhibiting significantly higher efficacy in engaging the Gi protein and recruiting β-arrestin than the reference CB1R full agonist CP55940. Importantly, adding a methyl group at the head moiety of 5F-MMB-PICA yielded 5F-MDMB-PICA, an agonist exhibiting a large increase in efficacy and potency at the CB1R. This pharmacological observation was supported by a functional assay of the effects of these SCRAs on glutamate field potentials recorded in hippocampal slices. Molecular modeling and simulations of the CB1R bound with either of the SCRAs revealed critical structural determinants contributing to the higher efficacy of 5F-MDMB-PICA, and how these subtle differences propagated to the receptor-G protein interface. Thus, we find that apparently minor structural changes in the head moiety of SCRAs can cause major changes in efficacy. Our results highlight the need for close monitoring of structural modifications of newly emerging SCRAs and their potential for toxic drug responses in humans.

Pharmacological insights emerging from the characterization of a large collection of synthetic cannabinoid receptor agonists designer drugs

Synthetic cannabinoid receptor agonists (SCRAs) constitute the largest and most defiant group of abuse designer drugs. These new psychoactive substances (NPS), developed as unregulated alternatives to cannabis, have potent cannabimimetic effects and their use is usually associated with episodes of psychosis, seizures, dependence, organ toxicity and death. Due to their ever-changing structure, very limited or nil structural, pharmacological, and toxicological information is available to the scientific community and the law enforcement offices. Here we report the synthesis and pharmacological evaluation (binding and functional) of the largest and most diverse collection of enantiopure SCRAs published to date. Our results revealed novel SCRAs that could be (or may currently be) used as illegal psychoactive substances. We also report, for the first time, the cannabimimetic data of 32 novel SCRAs containing an (R) configuration at the stereogenic center. The systematic pharmacological profiling of the library enabled the identification of emerging Structure-Activity Relationship (SAR) and Structure-Selectivity Relationship (SSR) trends, the detection of ligands exhibiting incipient cannabinoid receptor type 2 (CB₂R) subtype selectivity and highlights the significant neurotoxicity of representative SCRAs on mouse primary neuronal cells. Several of the new emerging SCRAs are currently expected to have a rather limited potential for harm, as the evaluation of their pharmacological profiles revealed lower potencies and/or efficacies. Conceived as a resource to foster collaborative investigation of the physiological effects of SCRAs, the library obtained can contribute to addressing the challenge posed by recreational designer drugs.

Cannabinoids as multifaceted compounds

Since ancient times, Cannabis and its preparations have found various applications such as for medical, recreational and industrial purposes. Subsequently the 1930s, legislation in many countries has restricted its use due to its psychotropic properties. More recently, the discovery of endocannabinoid system, including new receptors, ligands, and mediators, its role in maintaining the homeostasis of the human body and the possible implication in various physiological and pathophysiological processes has also been understood. Based on this evidence, researchers were able to develop new therapeutic targets for the treatment of various pathological disorders. For this purpose, Cannabis and cannabinoids were subjected for the evaluation of their pharmacological activities. The renewed interest in the medical use of cannabis for its potential therapeutic application has prompted legislators to take action to regulate the safe use of cannabis and products containing cannabinoids. However, each country has an enormous heterogeneity in the regulation of laws. Here, we are pleased to show a general and prevailing overview of the findings regarding cannabinoids and the multiple research fields such as chemistry, phytochemistry, pharmacology and analytics in which they are involved.

Cannabinoid 1 (CB1 ) receptor arrestin subtype-selectivity and phosphorylation dependence

BACKGROUND AND PURPOSE

Arrestin or G protein bias may be desirable for novel cannabinoid therapeutics. Arrestin-2 and arrestin-3 translocation to CB₁ receptor have been suggested to mediate different functions that may be exploited with biased ligands. Here, the requirement of a recently described phosphorylation motif 'pxxp' (where 'p' denotes phosphorylatable serine or threonine and 'x' denotes any other amino acid) within the CB₁ receptor C-terminus for interaction with different arrestin subtypes was examined.

EXPERIMENTAL APPROACH

Site-directed mutagenesis was conducted to generate nine different phosphorylation-impaired CB₁ receptor C-terminal mutants. Bioluminescence resonance energy transfer (BRET) was employed to measure arrestin-2/3 translocation and G protein dissociation of a high efficacy agonist for each mutant. Immunocytochemistry was used to quantify receptor expression.

KEY RESULTS

The effects of each mutation were shared for arrestin-2 and arrestin-3 translocation to CB₁ receptor pxxp motifs are partially required for arrestin-2/3 translocation, but translocation was not completely inhibited until all phosphorylation sites were mutated. The rate of arrestin translocation was reduced with simultaneous mutation of S425 and S429. Desensitisation of G protein dissociation was inhibited in different mutants proportional to the extent of their respective loss of arrestin translocation.

CONCLUSIONS AND IMPLICATIONS

These data do not support the existence of an 'essential' pxxp motif for arrestin translocation to CB₁ receptor. These data also identify that arrestin-2 and arrestin-3 have equivalent phosphorylation requirements within the CB₁ receptor C-terminus, suggesting arrestin subtype-selective biased ligands may not be viable and that different regions of the C-terminus contribute differently to arrestin translocation.

The piperazine analogue para-fluorophenylpiperazine alters timing of the physiological effects of the synthetic cannabinoid receptor agonist AMB-FUBINACA, without changing its discriminative stimulus, signalling effects, or metabolism

AMB-FUBINACA is a synthetic cannabinoid receptor agonist (SCRA), which has been associated with substantial abuse and health harm since 2016 in many countries including New Zealand. A characteristic of AMB-FUBINACA use in New Zealand has included the observation that forensic samples (from autopsies) and drugs seized by police have often been found to contain para-fluorophenylpiperazine (pFPP), a relatively little-characterised piperazine analogue that has been suggested to act through 5HT1a serotonin receptors. In the current study, we aimed to characterise the interactions of these two agents in rat physiological endpoints using plethysmography and telemetry, and to examine whether pFPP altered the subjective effects of AMB-FUBINACA in mice trained to differentiate a cannabinoid (THC) from vehicle. Though pFPP did not alter the ability of AMB-FUBINACA to substitute for THC, it did appear to abate some of the physiological effects of AMB-FUBINACA in rats by delaying the onset of AMB-FUBINACA-mediated hypothermia and shortening duration of bradycardia. In HEK cells stably expressing the CB1 cannabinoid receptor, 5HT1a, or both CB1 and 5HT1a, cAMP signalling was recorded using a BRET biosensor (CAMYEL) to assess possible direct receptor interactions. Although low potency pFPP agonism at 5HT1a was confirmed, little evidence for signalling interactions was detected in these assays: additive or synergistic effects on potency or efficacy were not detected between pFPP and AMB-FUBINACA-mediated cAMP inhibition. Experiments utilising higher potency, classical 5HT1a ligands (agonist 8OH-DPAT and antagonist WAY100635) also failed to reveal evidence for mutual CB1/5HT1a interactions or cross-antagonism. Finally, the ability of pFPP to alter the metabolism of AMB-FUBINACA in rat and human liver microsomes into its primary carboxylic acid metabolite via carboxylesterase-1 was assessed by HPLC; no inhibition was detected. Overall, the effects we have observed do not suggest that increased harm/toxicity would result from the combination of pFPP and AMB-FUBINACA.

Synthetic Cannabinoids: A Pharmacological and Toxicological Overview

Synthetic cannabinoids (SCs) are a chemically diverse group of new psychoactive substances (NPSs) that target the endocannabinoid system, triggering a plethora of actions (e.g., elevated mood sensation, relaxation, appetite stimulation) that resemble, but are more intense than, those induced by cannabis. Although some of these effects have been explored for therapeutic applications, anticipated stronger psychoactive effects than cannabis and reduced risk perception have increased the recreational use of SCs, which have dominated the NPS market in the United States and Europe over the past decade. However, rising SC-related intoxications and deaths represent a major public health concern and embody a major challenge for policy makers. Here, we review the pharmacology and toxicology of SCs. A thorough characterization of SCs' pharmacodynamics and toxicodynamics is important to better understand the main mechanisms underlying acute and chronic effects of SCs, interpret the clinical/pathological findings related to SC use, and improve SC risk awareness.

In vitro and in vivo pharmacology of nine novel synthetic cannabinoid receptor agonists

Synthetic cannabinoid receptor agonists (SCRAs) are novel psychoactive substances that bind to and activate CB1 receptors in the brain. The structural manipulations observed in newer SCRAs suggest that manufacturers have incorporated modern drug development techniques into their repertoire, often producing higher CB1 receptor affinity than Δ9-tetrahydrocannabinol (Δ9-THC). This study examined nine SCRAs recently detected by forensic surveillance, some of which caused fatalities: 5F-MDMB-PICA, FUB-144, 5F-MMB-PICA, MMB-4en-PICA, MMB-FUBICA, 5F-EDMB-PINACA, APP-BINACA, MDMB-4en-PINACA, and FUB-AKB48. Compounds were evaluated for CB1 and CB2 receptor binding affinity and functional activation and for their effects on body temperature, time course, and pharmacological equivalence with Δ9-THC in Δ9-THC drug discrimination in mice. All SCRAs bound to and activated CB1 and CB2 receptors with high affinity, with similar or greater affinity for CB2 than CB1 receptors and stimulated [35S]GTPγS binding in CB1 and CB2 expressing cell membranes. All compounds produced hypothermia, with shorter latency to peak effects for SCRAs than Δ9-THC. All SCRAs fully substituted for Δ9-THC in drug discrimination at one or more doses. Rank order potency in producing in vivo effects mostly aligned with rank order CB1 receptor affinities. Potencies for Δ9-THC-like discriminative stimulus effects were similar across sex except Δ9-THC was more potent in females and 5F-MMB-PICA was more potent in males. In summary, 5F-EMDB-PINACA, 5F-MDMB-PICA, MDMB-4en-PINACA, FUB-144, FUB-AKB48, 5F-MMB-PICA, MMB-4en-PICA, and MMB-FUBICA are potent and efficacious SCRAs with pharmacology like that of past SCRAs that have been abused in humans. In contrast, APP-BINACA was efficacious, but had lower potency than most past SCRAs.

Analysis of synthetic cannabinoids in wastewater of major cities in China

Synthetic cannabinoids (SCs) could pose serious health risks to its users. It is necessary to monitor its community consumption. Wastewater-based epidemiology is a potentially useful approach in this regard. However, limited research has been conducted to investigate the occurrence of SCs in wastewater. In this study, liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was optimized to analyze 8 SCs and metabolites (in total 16 analytes) in wastewater. The limit of quantification for this method for certain analytes in wastewater was as low as 0.03 ng L^-1. The validated method was used to examine the stability of the analytes under different conditions and to examine their occurrence in wastewater collected from 31 major cities across China. The overwhelming majority of the analytes were stable within 24 h, even at room temperature. However, 5-fluoro MDMB-PICA and MDMB-4en-PINACA butanoic acid metabolite showed significant degradation within 120 days even when stored at -20 °C or -80 °C. At least one cannabinoid or their metabolite was detected in 21 cities. In the city with the highest detection rate, at least one synthetic cannabinoid or metabolite was detected in 95% of samples of the city. MDMB-4en-PINACA butanoic acid metabolite had the highest detection frequency (in 13.4% of the samples). These results indicated that SCs were used in a significant number of Chinese cities. A few parent drugs (MDMB-4en-PINACA, ADB-BUTINACA, 5-fluoro MDMB-PICA, 4-fluoro MDMB-BUTINACA) were detected in a small fraction of wastewater samples, possibly due to release from manufacturing of these cannabinoids or illegal addition of electronic cigarettes.

Behavioral pharmacology of five novel synthetic cannabinoids

Newly emerging synthetic cannabinoid compounds continue to be found in the designer drug market. They are often targeted as a 'legal high' alternative to traditional cannabinoids via 'darknet' markets and their increased potency and efficacy are becoming a growing concern internationally. The purpose of this study was to determine whether 4-CN-CUMYL-BUTINACA, 4F-MDMB-BINACA, 5F-AEB, 5F-CUMYL-P7AICA and EMB-FUBINACA exhibited similar behavioral effects as Δ9-tetrahydrocannabinol (Δ9-THC). Locomotor activity was assessed in an open-field assay using Swiss-Webster mice. Male Sprague-Dawley rats were trained to discriminate between intraperitoneal injections of Δ9-THC (3 mg/kg) and vehicle. Following successful training, substitution tests for 4-CN-CUMYL-BUTINACA, 4F-MDMB-BINACA, 5F-AEB, 5F-CUMYL-P7AICA and EMB-FUBINACA were conducted. All of the test compounds decreased locomotor activity. 4-CN-CUMYL-BUTINACA (ED50 = 0.26 mg/kg), 4F-MDMB-BINACA (ED50 = 0.019 mg/kg), 5F-CUMYL-P7AICA (ED50 = 0.13 mg/kg) and EMB-FUBINACA (ED50 = 0.13 mg/kg) each fully substituted for the discriminative stimulus effects of the training dose of Δ9-THC, whereas 5F-AEB produced only a maximum of 67% drug-appropriate responding at 0.5 mg/kg. Higher doses produced piloerection, exophthalmos and convulsions. 4-CN-CUMYL-BUTINACA, 4F-MDMB-BINACA, 5F-CUMYL-P7AICA and EMB-FUBINACA are likely to produce similar subjective effects in humans as those produced by abused synthetic cannabinoids, and may therefore share similar abuse liability. In contrast, 5F-AEB may have a reduced abuse liability given its weaker THC-like discriminative stimulus effects but maybe more dangerous due to the adverse effects observed at doses needed to produce discriminative stimulus effects.

Structure-activity relationships for 5F-MDMB-PICA and its 5F-pentylindole analogs to induce cannabinoid-like effects in mice

Synthetic cannabinoid receptor agonists (SCRAs) are an evolving class of new psychoactive substances found on recreational drug markets worldwide. The indole-containing compound, 5F-MDMB-PICA, is a popular SCRA associated with serious medical consequences, including overdose and hospitalizations. In vitro studies reveal that 5F-MDMB-PICA is a potent agonist at cannabinoid type 1 receptors (CB₁), but little information exists regarding in vivo pharmacology of the drug. To this end, we examined the in vitro and in vivo cannabinoid-like effects produced by 5F-MDMB-PICA and related 5F-pentylindole analogs with differing composition of the head group moiety (i.e., 5F-NNEI, 5F-SDB-006, 5F-CUMYL-PICA, 5F-MMB-PICA). In mouse brain membranes, 5F-MDMB-PICA and its analogs inhibited binding to [³H]rimonabant-labeled CB₁ and displayed agonist actions in [³⁵S]GTPγS functional assays. 5F-MDMB-PICA exhibited the highest CB₁ affinity (K_i = 1.24 nM) and functional potency (EC₅₀ = 1.46 nM), but head group composition markedly influenced activity in both assays. For example, the 3,3-dimethylbutanoate (5F-MDMB-PICA) and cumyl (5F-CUMYL-PICA) head groups engendered high CB₁ affinity and potency, whereas a benzyl (5F-SDB-006) head group did not. In C57BL/6J mice, all 5F-pentylindole SCRAs produced dose- and time-dependent hypothermia, catalepsy, and analgesia that were reversed by rimonabant, indicating CB₁ involvement. In vitro K_i and EC₅₀ values were positively correlated with in vivo ED₅₀ potency estimates. Our findings demonstrate that 5F-MDMB-PICA is a potent SCRA, and subtle alterations to head group composition can have profound influence on pharmacological effects at CB₁. Importantly, measures of CB₁ binding and efficacy in mouse brain tissue seem to accurately predict in vivo drug potency in this species.

Exploring determinants of agonist efficacy at the CB1 cannabinoid receptor: Analogues of the synthetic cannabinoid receptor agonist EG-018

Neutral antagonists of GPCRs remain relatively rare—indeed, a large majority of GPCR antagonists are actually inverse agonists. The synthetic cannabinoid receptor agonist (SCRA) EG‐018 was recently reported as a low efficacy cannabinoid receptor agonist. Here we report a comparative characterization of EG‐018 and 13 analogues along with extant putative neutral antagonists of CB₁. In HEK cells stably expressing human CB₁, assays for inhibition of cAMP were performed by real‐time BRET biosensor (CAMYEL), G protein cycling was quantified by [³⁵S]GTPγS binding, and stimulation of pERK was characterized by AlphaLISA (PerkinElmer). Signaling outcomes for the EG‐018 analogues were highly variable, ranging from moderate efficacy agonism with high potency, to marginal agonism at lower potency. As predicted by differing pathway sensitivities to differences in ligand efficacy, most EG‐018‐based compounds were completely inactive in pERK alone. The lowest efficacy analogue in cAMP assays, 157, had utility in antagonism assay paradigms. Developing neutral antagonists of the CB₁ receptor has been a long‐standing research goal, and such compounds would have utility both as research tools and in therapeutics. Although these results emphasize again the importance of system factors in determining signaling outcomes, some compounds characterized in this study appear among the lowest efficacy agonists described to date and therefore suggest that development of neutral antagonists is an achievable goal for CB₁.

In vivo Evidence for Brain Region-Specific Molecular Interactions Between Cannabinoid and Orexin Receptors

The endocannabinoid and orexin neuromodulatory systems serve key roles in many of the same biological functions such as sleep, appetite, pain processing, and emotional behaviors related to reward. The type 1 cannabinoid receptor (CB1R) and both subtypes of the orexin receptor, orexin receptor type 1 (OX1R) and orexin receptor type 2 (OX2R) are not only expressed in the same brain regions modulating these functions, but physically interact as heterodimers in recombinant and neuronal cell cultures. In the current study, male and female C57BL/6 mice were co-treated with the cannabinoid receptor agonist CP55,940 and either the OX2R antagonist TCS-OX2-29 or the dual orexin receptor antagonist (DORA) TCS-1102. Mice were then evaluated for catalepsy, body temperature, thermal anti-nociception, and locomotion, after which their brains were collected for receptor colocalization analysis. Combined treatment with the DORA TCS-1102 and CP55,940 potentiated catalepsy more than CP55,940 alone, but this effect was not observed for changes in body temperature, nociception, locomotion, or via selective OX2R antagonism. Co-treatment with CP55,940 and TCS-1102 also led to increased CB1R-OX1R colocalization in the ventral striatum. This was not seen following co-treatment with TCS-OX2-29, nor in CB1R-OX2R colocalization. The magnitude of effects following co-treatment with CP55,940 and either the DORA or OX2R-selective antagonist was greater in males than females. These data show that CB1R-OX1R colocalization in the ventral striatum underlies cataleptic additivity between CP55,940 and the DORA TCS-1102. Moreover, cannabinoid-orexin receptor interactions are sex-specific with regards to brain region and functionality. Physical or molecular interactions between these two systems may provide valuable insight into drug-drug interactions between cannabinoid and orexin drugs for the treatment of insomnia, pain, and other disorders.

Delineating the interactions between the cannabinoid CB2 receptor and its regulatory effectors; β-arrestins and G protein-coupled receptor kinases

BACKGROUND AND PURPOSE

The cannabinoid CB₂ receptor (CB₂ ) is a promising therapeutic target for modulating inflammation. However, little is known surrounding the mechanisms underpinning CB₂ desensitisation and regulation, particularly the role of G protein-coupled receptor kinases (GRKs). Here, we evaluated the role of six GRK isoforms in β-arrestin recruitment to CB₂ . Mutagenesis of several distal C-terminal aspartic acid residues was also performed in an attempt to delineate additional structural elements involved in the regulation of CB₂ .

EXPERIMENTAL APPROACH

In CB₂ -expressing HEK 293 cells, β-arrestin translocation was measured using real-time BRET assays. G protein dissociation BRET assays were performed to assess the activation and desensitisation of CB₂ in the presence of β-arrestin 2.

KEY RESULTS

Overexpression of GRK isoforms 1-6 failed to considerably improve translocation of either β-arrestin 1 or β-arrestin 2 to CB₂ . Consistent with this, inhibition of endogenous GRK2/3 did not substantially reduce β-arrestin 2 translocation. Mutagenesis of C-terminal aspartic acid residues resulted in attenuation of β-arrestin 2 translocation, which translated to a reduction in desensitisation of G protein activation.

CONCLUSION AND IMPLICATIONS

Our findings suggest that CB₂ does not adhere to the classical GPCR regulatory paradigm, entailing GRK- and β-arrestin-mediated desensitisation. Instead, C-terminal aspartic acid residues may act as phospho-mimics to induce β-arrestin activation. This study provides novel insights into the regulatory mechanisms of CB₂ , which may aid in our understanding of drug tolerance and dependence.

Molecular signaling of synthetic cannabinoids: Comparison of CB1 receptor and TRPV1 channel activation

Recreational use of synthetic cannabinoids (SCs) is associated with desirable euphoric and relaxation effects as well as adverse effects including anxiety, agitation and psychosis. These SC-mediated actions represent a combination of potentiated cannabinoid receptor signaling and "off-target" receptor activity. The goal of this study was to compare the efficacy of various classes of SCs in stimulating CB1 receptors and activating "off-target" transient receptor potential (TRP) channels. Cannabinoid-type 1 (CB1) receptor activity was determined by measuring SC activation of G protein-gated inward rectifier K+ (GIRK) channels using a membrane potential-sensitive fluorescent dye assay. SC opening of vanilloid type-1 (TRPV1) channels was measured by recording intracellular Ca2+ transients. All of the SCs tested activated the GIRK channel with an efficacy of 4-fluoro MDMB-BUTINACA > 5-fluoro MDMB-PICA > MDMB-4en-PINACA ≈ WIN 55,212-2 > AB-FUBINACA > AM1220 ≈ JWH-122 N-(5-chloropentyl) > AM1248 > JWH-018 ≈ XLR-11 ≈ UR-144. The potency of the SCs at the CB1 receptor was 5-fluoro MDMB-PICA ≈ 4-fluoro MDMB-BUTINACA > AB-FUBINACA ≈ MDMB-4en-PINACA > JWH-018 > AM1220 > XLR-11 > JWH-122 N-(5-chloropentyl) > WIN 55,212-2 ≈ UR-144 > AM1248. In contrast, when tested at a SC concentration that produced a maximal effect on the Gi/GIRK channel, only XLR-11, UR-144 and AM1220 caused a significant activation of the TRPV1 channels. The TRPV1 channel/Ca2+ signal measured during application of 10 μM XLR-11 was similar to the signal induced by the endocannabinoid N-arachidonoylethanolamine (AEA). Thus, while various SCs share the ability to stimulate CB1 receptor/Gi signaling, they display limited efficacy in opening TRPV1 channels.

The endocannabinoid system - current implications for drug development

In this review, the state of the art for compounds affecting the endocannabinoid (eCB) system is described with a focus on the treatment of pain. Amongst directly acting CB receptor ligands, clinical experience with ∆⁹ -tetrahydracannabinol and medical cannabis in chronic non-cancer pain indicates that there are differences between the benefits perceived by patients and the at best modest effect seen in meta-analyses of randomized controlled trials. The reason for this difference is not known but may involve differences in the type of patients that are recruited, the study conditions that are chosen and the degree to which biases such as reporting bias are operative. Other directly acting CB receptor ligands such as biased agonists and allosteric receptor modulators have not yet reached the clinic. Amongst indirectly acting compounds targeting the enzymes responsible for the synthesis and catabolism of the eCBs anandamide and 2-arachidonoylglycerol, fatty acid amide hydrolase (FAAH) inhibitors have been investigated clinically but were per se not useful for the treatment of pain, although they may be useful for the treatment of post-traumatic stress disorder and cannabis use disorder. Dual-acting compounds targeting this enzyme and other targets such as cyclooxygenase-2 or transient potential vanilloid receptor 1 may be a way forward for the treatment of pain.

Assessment of select synthetic cannabinoid receptor agonist bias and selectivity between the type 1 and type 2 cannabinoid receptor

The first synthetic cannabinoid receptor agonists (SCRAs) were designed as tool compounds to study the endocannabinoid system's two predominant cannabinoid receptors, CB1R and CB2R. Unfortunately, novel SCRAs now represent the most rapidly proliferating novel psychoactive substances (NPS) of abuse globally. Unlike ∆9-tetrahydrocannabinol, the CB1R and CB2R partial agonist and the intoxicating constituent of Cannabis, many SCRAs characterized to date are full agonists of CB1R. Gaining additional insight into the pharmacological activity of these SCRAs is critical to assess and regulate NPSs as they enter the marketplace. The purpose of this study was to assess select SCRAs recently identified by Canadian police, border service agency, private companies and the illicit market as potential CB1R and CB2R agonists. To this end, fifteen SCRAs were screened for in vitro activity and in silico interactions at CB1R and CB2R. Several SCRAs were identified as being highly biased for cAMP inhibition or βarrestin2 recruitment and receptor subtype selectivity between CB1R and CB2R. The indazole ring and halogen-substituted butyl or pentyl moieties were identified as two structural features that may direct βarrestin2 bias. Two highly-biased SCRAs-JWH-018 2'-napthyl-N-(3-methylbutyl) isomer (biased toward cAMP inhibition) and 4-fluoro MDMB-BINACA (biased toward βarrestin2 recruitment) displayed unique and differential in vivo activity in mice. These data provide initial insight into the correlations between structure, signalling bias, and in vivo activity of the SCRAs.

Pharmacological selection of cannabinoid receptor effectors: Signalling, allosteric modulation and bias

The type-1 cannabinoid receptor (CB₁) is a promising drug target for a wide range of diseases. However, many existing and novel candidate ligands for CB₁ have shown only limited therapeutic potential. Indeed, no ligands are currently approved for the clinic except formulations of the phytocannabinoids Δ⁹-THC and CBD and a small number of analogues. A key limitation of many promising CB₁ ligands are their on-target adverse effects, notably including psychoactivity (agonists) and depression/suicidal ideation (inverse agonists). Recent drug development attempts have therefore focussed on altering CB₁ signalling profiles in two ways. Firstly, with compounds that enhance or reduce the signalling of endogenous (endo-) cannabinoids, namely allosteric modulators. Secondly, with compounds that probe the capability of selectively targeting specific cellular signalling pathways that may mediate therapeutic effects using biased ligands. This review will summarise the current paradigm of CB₁ signalling in terms of the intracellular transduction pathways acted on by the receptor. The development of compounds that selectively activate CB₁ signalling pathways, whether allosterically or via orthosteric agonist bias, will also be addressed.

Systematic evaluation of a panel of 30 synthetic cannabinoid receptor agonists structurally related to MMB-4en-PICA, MDMB-4en-PINACA, ADB-4en-PINACA, and MMB-4CN-BUTINACA using a combination of binding and different CB1 receptor activation assays: Part I-Synthesis, analytical characterization, and binding affinity for human CB1 receptors

Synthetic cannabinoid receptor agonists (SCRAs) are one of the largest and most structurally diverse classes of new psychoactive substances (NPS). Despite this, pharmacological data are often lacking following the identification of a new SCRA in drug markets. In this first of a three-part series, we describe the synthesis, analytical characterization, and binding affinity of a proactively generated, systematic library of 30 indole, indazole, and 7-azaindole SCRAs related to MMB-4en-PICA, MDMB-4en-PINACA, ADB-4en-PINACA, and MMB-4CN-BUTINACA featuring a 4-pentenyl (4en-P), butyl (B/BUT), or 4-cyanobutyl (4CN-B/BUT) tail and a methyl l-valinate (MMB), methyl l-tert-leucinate (MDMB), methyl l-phenylalaninate (MPP), l-valinamide (AB), l-tert-leucinamide (ADB), l-phenylalaninamide (APP), adamantyl (A), or cumyl head group. Competitive radioligand binding assays demonstrated that the indazole core conferred the highest CB₁ binding affinity (K_i  = 0.17-39 nM), followed by indole- (K_i  = 0.95-160 nM) and then 7-azaindole-derived SCRAs (K_i  = 5.4-271 nM). Variation of the head group had the greatest effect on binding, with tert-leucine amides and methyl esters (K_i  = 0.17-14 nM) generally showing the greatest affinities, followed by valine derivatives (K_i  = 0.72-180 nM), and then phenylalanine derivatives (K_i  = 2.5-271 nM). Adamantyl head groups (K_i  = 8.8-59 nM) were suboptimal for binding, whereas the cumyl analogues consistently conferred high affinity (K_i  = 0.62-36 nM). Finally, both butyl (K_i  = 3.1-163 nM) and 4-cyanobutyl (K_i  = 5.5-44 nM) tail groups were less favorable for CB₁ binding than their corresponding 4-pentenyl counterparts (K_i  = 0.72-25 nM).

Biased agonism at the cannabinoid receptors - Evidence from synthetic cannabinoid receptor agonists

The type 1 and type 2 cannabinoid receptors are G protein-coupled receptors implicated in a variety of physiological processes and diseases. Synthetic cannabinoid receptor agonists (SCRAs) were originally developed to explore the therapeutic benefits of cannabinoid receptor activation, although more recently, these compounds have been diverted to the recreational drug market and are increasingly associated with incidences of toxicity. A prominent concept in contemporary pharmacology is functional selectivity or biased agonism, which describes the ability of ligands to elicit differential activation of signalling pathways through stabilisation of distinct receptor conformations. Biased agonists may maximise drug effectiveness by reducing on-target adverse effects if they are mediated by signalling pathways distinct from those that drive the therapeutic effects. For the cannabinoid receptors, it remains unclear as to which signalling pathways mediate desirable and adverse effects. However, given their structural diversity and potential to induce a plethora of signalling effects, SCRAs provide the most promising prospect for detecting and studying bias at the cannabinoid receptors. This review summarises the emerging evidence of SCRA bias at the cannabinoid receptors.

Exploring Stereochemical and Conformational Requirements at Cannabinoid Receptors for Synthetic Cannabinoids Related to SDB-006, 5F-SDB-006, CUMYL-PICA, and 5F-CUMYL-PICA

Synthetic cannabinoid receptor agonists (SCRAs) represent the most rapidly expanding class of new psychoactive substances (NPSs). Despite the prevalence and potency of recent chiral indole-3-carboxamide SCRAs, few pharmacological data are available regarding the enantiomeric bias of these NPSs toward human CB1 and CB2 receptors. A series of homochiral indole-3-carboxamides derived from (S)- and (R)-α-methylbenzylamine and featuring variation of the 1-alkyl substituent were prepared, pharmacologically evaluated, and compared to related achiral congeners derived from cumyl- and benzylamine. Competitive binding assays demonstrated that all analogues derived from either enantiomer of α-methylbenzylamine (14-17) showed affinities for CB1 (K_i = 47.9-813 nM) and CB2 (K_i = 47.9-347 nM) that were intermediate to that of the corresponding benzylic (10-13, CB1 K_i = 550 nM to >10 μM; CB2 K_i = 61.7 nM to >10 μM) and cumyl derivatives (6-9, CB1 K_i = 12.6-21.4 nM; CB2 K_i = 2.95-24.5 nM). In a fluorometric membrane potential assay, all α-methylbenzyl analogues (excluding 17) were potent, efficacious agonists of CB1 (EC₅₀ = 32-464 nM; E_max = 89-104%) and low efficacy agonists of CB2 (EC₅₀ = 54-500 nM; E_max = 52-77%), with comparable or greater potency than the benzyl analogues and much lower potency than the cumyl derivatives, consistent with binding trends. The relatively greater affinity and potency of (S)-14-17 compared to (R)-14-17 analogues at CB1 highlighted an enantiomeric bias for this series of SCRAs. Molecular dynamics simulations provided a conformational basis for the observed differences in agonist potency at CB1 pending benzylic substitution.

Molecular Pharmacology of Synthetic Cannabinoids: Delineating CB1 Receptor-Mediated Cell Signaling

Synthetic cannabinoids (SCs) are a class of new psychoactive substances (NPSs) that exhibit high affinity binding to the cannabinoid CB1 and CB2 receptors and display a pharmacological profile similar to the phytocannabinoid (-)-trans-Δ9-tetrahydrocannabinol (THC). SCs are marketed under brand names such as K2 and Spice and are popular drugs of abuse among male teenagers and young adults. Since their introduction in the early 2000s, SCs have grown in number and evolved in structural diversity to evade forensic detection and drug scheduling. In addition to their desirable euphoric and antinociceptive effects, SCs can cause severe toxicity including seizures, respiratory depression, cardiac arrhythmias, stroke and psychosis. Binding of SCs to the CB1 receptor, expressed in the central and peripheral nervous systems, stimulates pertussis toxin-sensitive G proteins (Gi/Go) resulting in the inhibition of adenylyl cyclase, a decreased opening of N-type Ca2+ channels and the activation of G protein-gated inward rectifier (GIRK) channels. This combination of signaling effects dampens neuronal activity in both CNS excitatory and inhibitory pathways by decreasing action potential formation and neurotransmitter release. Despite this knowledge, the relationship between the chemical structure of the SCs and their CB1 receptor-mediated molecular actions is not well understood. In addition, the potency and efficacy of newer SC structural groups has not been determined. To address these limitations, various cell-based assay technologies are being utilized to develop structure versus activity relationships (SAR) for the SCs and to explore the effects of these compounds on noncannabinoid receptor targets. This review focuses on describing and evaluating these assays and summarizes our current knowledge of SC molecular pharmacology.