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Background and Purpose: Activation of CB1 by exogenous agonists causes adverse effects in vivo. Positive allosteric modulation may offer improved therapeutic potential and a reduced on‐target adverse effect profile compared with orthosteric agonists, due to reduced desensitisation/tolerance, but this has not been directly tested. This study investigated the ability of PAMs/ago‐PAMs to induce receptor regulation pathways, including desensitisation and receptor internalisation. Experimental Approach: Bioluminescence resonance energy transfer (BRET) assays in HEK293 cells were performed to investigate G protein dissociation, ERK1/2 phosphorylation and β‐arrestin 2 translocation, while immunocytochemistry was performed to measure internalisation of CB1 in response to the PAMs ZCZ011, GAT229 and ABD1236 alone and in combination with the orthosteric agonists AEA, 2‐AG, and AMB‐FUBINACA. Key Results: ZCZ011, GAT229 and ABD1236 were allosteric agonists in all pathways tested. The ago‐PAM ZCZ011 induced a biphasic ERK1/2 phosphorylation time course compared to transient activation by orthosteric agonists. In combination with 2‐AG but not AEA or AMB‐FUBINACA, ZCZ011 and ABD1236 caused the transient peak of ERK1/2 phosphorylation to become sustained. All PAMs increased the potency and efficacy of AEA‐induced signalling in all pathways tested; however, no notable potentiation of 2‐AG or AMB‐FUBINACA was observed. Conclusion and Implications: Ago‐PAMs can potentiate endocannabinoid CB1 agonism by AEA to a larger extent compared with 2‐AG. However, all compounds were found to be allosteric agonists and induce activation of CB1 in the absence of endocannabinoid, including β‐arrestin 2 recruitment and internalisation. Thus, the spatiotemporal signalling of endogenous cannabinoids will not be retained in vivo. [ABSTRACT FROM AUTHOR]

Synthetic cannabinoids are a rapidly evolving, diverse class of new psychoactive substances. Synthetic cannabinoid use results in a higher likelihood of adverse events and hospitalization when compared to cannabis use. The mechanisms behind synthetic cannabinoid toxicity remain elusive. Furthermore, poly-substance use may be a significant contributing factor in many cases. This scoping review aimed to identify the key characteristics of synthetic cannabinoid co-exposure cases and discuss the potential implications of poly-substance use in humans. There were 278 human cases involving 64 different synthetic cannabinoids extracted from the databases. Cases involved a total of 840 individual co-exposures, with an average of four substances involved in each case. The most common co-exposures were alcohol (11.4%), opioids (11.2%), and cannabis (11.1%). When analyzed by case outcome, co-exposure to either antipsychotics/antidepressants, alcohol, or tobacco were significantly associated with mortality as an outcome (p < 0.05). Drug-use history (63.4%), mental illness (23.7%), and hypertensive and atherosclerotic cardiovascular disease (20.1%) were prevalent patient histories in the case cohort. There are several potential pharmacodynamic and pharmacokinetic interactions between co-exposure drugs and synthetic cannabinoids that could worsen clinical presentation and toxicity in synthetic cannabinoid users. Individuals with substance-use disorders or psychiatric illness would be especially vulnerable to these multi-drug interactions. Further research into these complex exposures is needed for the successful prevention and treatment of synthetic cannabinoid-related harms. [ABSTRACT FROM AUTHOR]

Background and Purpose: Orthosteric agonism of the CB1 receptor normally associates with Gi signalling resulting in a net inhibition of cAMP production. Empirical evidence shows CB1 causes a net cAMP stimulation through Gs coupling under two conditions: co‐stimulation with the D2 receptor and high‐level CB1 expression. Two hypotheses have been proposed to account for these paradoxical effects, (1) Gi is consumed by coupling to D2 or extra CB1 and excess CB1 binds to Gs and (2), the formation of dimers CB1‐CB1 or CB1‐D2 switches Gi/Gs preference. This study explored the mechanisms of Gi/Gs preference based on a mathematical model of the CB1 receptor. Experimental Approach: The model was based on Hypothesis 1 and known mechanisms. The model was calibrated to align with multiple types of data (cAMP, Gi dissociation and internalisation). The key step of Hypothesis 1 was examined by simulation from the model. An experiment was proposed to distinguish Hypothesis 1 and 2. Key Results: The model successfully descripted multiple types of data under Hypothesis 1. Simulations from the model indicated that precoupling of G protein with receptors is necessary for this hypothesis. The model designed experiments to distinguish Hypothesis 1 and 2 by increasing Gi & Gs in parallel with CB1 overexpression. The two hypotheses result in distinct cAMP responses. Conclusion and Implications: A mathematical model of CB1‐regulated Gi/Gs pathways was developed. It indicated Hypothesis 1 is feasible and G protein precoupling is a key step causing cAMP signalling switch. The model‐designed experiments provided guides for future experimentation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]