Leveraging allostery to improve G protein-coupled receptor (GPCR)-directed therapeutics: cannabinoid receptor 1 as a discovery target.


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“Allosteric modulators of G-protein coupled receptors (GPCRs) hold the promise of improved pharmacology and safety over typical orthosteric GPCR ligands.

These features are particularly relevant to the cannabinoid receptor 1 (CB1R) GPCR, since typical orthosteric CB1R ligands are associated with adverse events that limit their translational potential.

Areas covered: The contextual basis for applying allostery to CB1R is considered from pharmacological, drug-discovery, and medicinal standpoints.

Rational design of small-molecule CB1R allosteric modulators as potential pharmacotherapeutics would be greatly facilitated by direct experimental characterization of structure-function correlates underlying the biological activity of chemically-diverse CB1R allosteric modulators, CB1R allosteric ligand-binding binding pockets, and amino acid contact residues critical to allosteric ligand engagement and activity.

In these regards, designer covalent probes exhibiting well-characterized molecular pharmacology as CB1R allosteric modulators are emerging as valuable molecular reporters enabling experimental interrogation of CB1R allosteric site(s) and informing the design of new CB1R agents as drugs.

Expert opinion: Synthesis and pharmacological profiling of CB1R allosteric ligands will continue to provide valuable insights into CB1R structure-function correlates. The resulting data should expand the repertoire of novel agents capable of exerting therapeutic benefit by modulating CB1R-dependent signaling.”

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Intrathecal cannabinoid-1 receptor agonist prevents referred hyperalgesia in acute acrolein-induced cystitis in rats.

“We investigated the capacity of intrathecal arachidonyl-2′-chloroethylamide (ACEA), a cannabinoid-1 receptor (CB1R) agonist, to inhibit referred hyperalgesia and increased bladder contractility resulting from acute acrolein-induced cystitis in rats…

These findings suggest that pain arising from cystitis may be inhibited by activation of spinal CB1R but the acute local response of the bladder appeared to be unaffected by stimulation of spinal CB1R.”


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Differential Pharmacological Regulation of Sensorimotor-Gating Deficit in CB1 Knockout Mice and Associated Neurochemical and Histological Alterations.

“The endocannabinoid system has been widely involved in the pathophysiology of sensorimotor gating deficits. The present study is aimed to evaluate the pharmacological modulation of the sensorimotor gating impairment induced by cannabinoid CB1 receptor (CB1r) deletion…

These data further support the important role of CB1r in sensorimotor gating regulation and the therapeutic usefulness of methylphenidate for the treatment of psychiatric disorders with associated pre-attentional deficits.”


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Endocannabinoid-mediated modulation of Gq/11 protein-coupled receptor signaling-induced vasoconstriction and hypertension.

“Activation of G protein-coupled receptors (GPCRs) can induce vasoconstriction via calcium signal-mediated and Rho-dependent pathways…

Our aim was to provide evidence that GPCR signaling-induced 2-AG production and activation of vascular type1 cannabinoid receptors (CB1R) is capable of reducing agonist-induced vasoconstriction and hypertension…

Pharmacological or genetic loss of CB1R function augmented AngII-induced blood pressure rise in mice.

These data demonstrate that vasoconstrictor effect of GPCR agonists is attenuated via Gq/11-mediated vascular endocannabinoid formation.

Agonist-induced endocannabinoid-mediated CB1R activation is a significant physiological modulator of vascular tone.

Thus, the selective modulation of GPCR signaling-induced endocannabinoid release has a therapeutic potential in case of increased vascular tone and hypertension.”



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Changes in Cerebral CB1 Receptor Availability after Acute and Chronic Alcohol Abuse and Monitored Abstinence.

“Involvement of the type 1 cannabinoid receptor (CB1R) in the effects of alcohol on the brain is supported by animal experiments…

In conclusion, whereas the acute alcohol effect is an increase in CB1R availability, chronic heavy drinking leads to reduced CB1R availability that is not reversible after 1 month of abstinence. Longer follow-up is required to differentiate whether this is a compensatory effect of repeated endocannabinoid overstimulation or an enduring trait-like feature.

An enhanced CB1R signaling may offer a new therapeutic direction for treatment of the negative affective state produced by alcohol withdrawal and abstinence, which is critical for the maintenance of alcohol addiction.”


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Pre- and postsynaptic type-1 cannabinoid receptors control the alterations of glutamate transmission in experimental autoimmune encephalomyelitis.

“Type-1 cannabinoid receptors (CB1R) are important regulators of the neurodegenerative damage in multiple sclerosis (MS) and in experimental autoimmune encephalomyelitis (EAE). In GABAergic striatal neurons, CB1R stimulation exerts protective effects by limiting inflammation…

Our results provide further evidence that CB1R are involved in EAE pathophysiology, and suggest that both pre- and postsynaptic alterations of glutamate transmission are important to drive excitotoxic neurodegeneration typical of this disorder.”


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Association between a Genetic Variant of Type-1 Cannabinoid Receptor and Inflammatory Neurodegeneration in Multiple Sclerosis

“Genetic ablation of type-1 cannabinoid receptors (CB1Rs) exacerbates the neurodegenerative damage of experimental autoimmune encephalomyelitis, the rodent model of multiple sclerosis (MS)…

Our results demonstrate the biological relevance of the (AAT)n CNR1 repeats in the inflammatory neurodegenerative damage of MS…

In conclusion, our study points to CB1R as an interesting molecular target for preventing neuronal loss and cognitive impairment in MS as well as in other CNS disorders in which inflammation-driven neurodegeneration process play a role.”


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Transient changes in the endocannabinoid system after acute and chronic ethanol exposure and abstinence in the rat: a combined PET and microdialysis study.

“Recent biochemical and post-mortem evidence suggests involvement of the endocannabinoid system in alcohol drinking behaviour and dependence…


This study provides in vivo evidence that acute ethanol consumption is associated with enhanced endocannabinoid signalling in the NAcc, indicated by an increased CB1R binding and AEA content. In addition, chronic ethanol exposure leads to regional dysfunctions in CB1R levels, involving the hippocampus and caudate-putamen that are reversible within 2 weeks in this animal model.”


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Enhancement of endocannabinoid neurotransmission through CB1 cannabinoid receptors counteracts the reinforcing and psychostimulant effects of cocaine.


“Cannabinoids, in contrast to typical drugs of abuse, have been shown to exert complex effects on behavioural reinforcement and psychomotor function. We have shown that cannabinoid agonists lack reinforcing/rewarding properties in the intracranial self-stimulation (ICSS) paradigm and that the CB1 receptor (CB1R) agonist WIN55,212-2 attenuates the reward-facilitating actions of cocaine. We sought to determine the effects of the endocannabinoid neurotransmission enhancer AM-404 (1, 3, 10, 30 mg/kg) on the changes in ICSS threshold and locomotion elicited by cocaine and extend the study of the effects of WIN55,212-2 (0.3, 1, 3 mg/kg) on cocaine-induced hyperlocomotion. AM-404 did not exhibit reward-facilitating properties, and actually increased self-stimulation threshold at the highest dose. Cocaine significantly reduced self-stimulation threshold, without altering maximal rates of responding. AM-404 (10 mg/kg) attenuated this action of cocaine, an effect which was reversed by pretreatment with the selective CB1R antagonist SR141716A. WIN55,212-2 decreased locomotion at the two highest doses, an effect that was blocked by SR141716A; AM-404 had no effect on locomotion. Cocaine caused a significant, dose-dependent increase in locomotion, which was reduced by WIN55,212-2 and AM-404. SR141716A blocked the effects of WIN55,212-2 and AM-404 on cocaine-induced hyperlocomotion. SR141716A alone had no effect on ICSS threshold or locomotion. These results indicate that cannabinoids may interfere with brain reward systems responsible for the expression of acute reinforcing/rewarding properties of cocaine, and provide further evidence that the cannabinoid system could be explored as a potential drug discovery target for the treatment of psychostimulant addiction and pathological states associated with psychomotor overexcitability.”


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Cannabinoid CB1 receptor antagonists as potential pharmacotherapies for drug abuse disorders.


“Since the discovery of the cannabinoid CB1 receptor (CB1R) in 1988, and subsequently of the CB2 receptor (CB2R) in 1993, there has been an exponential growth of research investigating the functions of the endocannabinoid system. The roles of CB1Rs have been of particular interest to psychiatry because of their selective presence within the CNS and because of their association with brain-reward circuits involving mesocorticolimbic dopamine systems. One potential role that has become of considerable focus is the ability of CB1Rs to modulate the effects of the drugs of abuse. Many drugs of abuse elevate dopamine levels, and the ability of CB1R antagonists or inverse agonists to modulate these elevations has suggested their potential application as pharmacotherapies for treating drug abuse disorders. With the identification of the selective CB1R antagonist, rimonabant, in 1994, and subsequently of other CB1R antagonists, there has been a rapid expansion of research investigating their ability to modulate the effects of the drugs of abuse. This review highlights some of the preclinical and clinical studies that have examined the effects of CB1R antagonists under conditions potentially predictive of their therapeutic efficacy as treatments for drug abuse disorders.”


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