The CB1 Neutral Antagonist AM4113 Retains the Therapeutic Efficacy of the Inverse Agonist Rimonabant for Nicotine Dependence and Weight Loss with Better Psychiatric Tolerability

Involvement of CB1R and CB2R Ligands in Sleep Disorders and Addictive Behaviors in the Last 25 Years

Over the last three decades, the decriminalization and legalization of therapeutic and recreational marijuana consumption have increased. Consequently, the availability of marijuana-based products associated with its therapeutic use has increased. These developments have stimulated research on cannabinoids involving a wide range of animal models and clinical trials. Also, it is reported that cannabinoids promote sleep in animal models and naïve human participants, and they seem to improve insomnia and sleep apnea in patients. However, evidence from rigorous clinical trials is needed. In addition, among several physiological processes, cannabinoid receptors modulate dopamine synthesis and release. In this regard, the side effects of marijuana and marijuana derivatives must not be ignored. The chronic consumption of marijuana could reduce dopamine responsivity, increase negative emotionality, and induce anhedonia. Research on the neurobiological changes associated with cannabinoid ligands in animal models, in regard to the consumption of both marijuana and marijuana-based compounds, must improve and the effectiveness of the therapeutic outcomes in clinical trials must be guaranteed. In this review, we include a detailed description of the mechanisms of action of cannabinoids on the brain and their impact on sleep disorders and addictive behaviors to emphasize the need to understand the potential risks and benefits of their therapeutic and recreational use. Evidence from basic research and clinical trials from papers published between 2000 and 2024 are included. The pharmacodynamics of these compounds is discussed in terms of sleep-wake regulation, drug addiction, and addictive behaviors.

Cannabinoid-based Pharmacology for the Management of Substance Use Disorders

In the last two decades, the endocannabinoid system has emerged as a crucial modulator of motivation and emotional processing. Due to its widespread neuroanatomical distribution and characteristic retrograde signaling nature, cannabinoid type I receptors and their endogenous ligands finely orchestrate somatic and axon terminal activity of dopamine neurons. Owing to these unique features, this signaling system is a promising pharmacological target to ameliorate dopamine-mediated drug-seeking behaviors while circumventing the adverse side effects of, for instance, dopaminergic antagonists. Despite considerable preclinical efforts, an agreement on the efficacy of endocannabinoid-targeting compounds for treating drug substance use disorders in humans has not been reached. In the following chapter, we will summarize preclinical and clinical evidence addressing the therapeutic potential of cannabinoids and endocannabinoid-targeting compounds in substance use disorders. To bridge the gap between animal and clinical research, we capitalize on studies evaluating the impact of endocannabinoid-targeting compounds in relevant settings, such as the management of drug relapse. Finally, we discuss the therapeutic potential of novel cannabinoid compounds that hold promise for treating substance use disorders.

Chemical Probes for Investigating the Endocannabinoid System

Cannabis sativa has been used therapeutically since early civilizations, with key cannabinoids Δ9-tetrahydrocannabinol (THC) 3.1 and cannabidiol characterized in the 1960s, leading to the discovery of cannabinoid receptors type 1 (CB1R) and type 2 (CB2R) and the endocannabinoid system (ECS) in the 1990s. The ECS, involving endogenous ligands like 2-arachidonoylglycerol (2-AG) 1.1, anandamide (N-arachidonoylethanolamine (AEA)) 1.2, and various proteins, regulates vital processes such as sleep, appetite, and memory, and holds significant therapeutic potential, especially for neurological disorders. Small molecule-derived pharmacological tools, or chemical probes, target key components of the ECS and are crucial for target validation, mechanistic studies, pathway elucidation, phenotypic screening, and drug discovery. These probes selectively interact with specific proteins or pathways, enabling researchers to modulate target activity and observe biological effects. When they carry an additional reporter group, they are referred to as labeled chemical probes. Developed through medicinal chemistry, structural biology, and high-throughput screening, effective chemical probes must be selective, potent, and depending on their purpose meet additional criteria such as cell permeability and metabolic stability.This chapter describes high-quality labeled and unlabeled chemical probes targeting ECS constituents that have been successfully applied for various research purposes. CB1R and CB2R, class A G protein-coupled receptors, are activated by 2-AG 1.1, AEA 1.2, and THC 3.1, with numerous ligands developed for these receptors. Imaging techniques like single-photon emission computed tomography, positron emission tomography, and fluorescently labeled CB1R and CB2R probes have enhanced CB receptor studies. CB2R activation generally results in immunosuppressive effects, limiting tissue injury. AEA 1.2 is mainly degraded by fatty acid amide hydrolase (FAAH) or N-acylethanolamine acid amidase (NAAA) into ethanolamine and arachidonic acid (AA) 1.3. FAAH inhibitors increase endogenous fatty acid amides, providing analgesic effects without adverse effects. NAAA inhibitors reduce inflammation and pain in animal models. Diacylglycerol lipase (DAGL) is essential for 2-AG 1.1 biosynthesis, while monoacylglycerol lipase (MAGL) degrades 2-AG 1.1 into AA 1.3, thus regulating cannabinoid signaling. Multiple inhibitors targeting FAAH and MAGL have been generated, though NAAA and DAGL probe development lags behind. Similarly, advancements in inhibitors targeting endocannabinoid (eCB) cellular uptake or trafficking proteins like fatty acid-binding proteins have been slower. The endocannabinoidome (eCBome) includes the ECS and related molecules and receptors, offering therapeutic opportunities from non-THC cannabinoids and eCBome mediators. Ongoing research aims to refine chemical tools for ECS and eCBome study, addressing unmet medical needs in central nervous system disorders and beyond.

Cannabis use disorder: from neurobiology to treatment

Cannabis has been legalized for medical and recreational purposes in multiple countries. A large number of people are using cannabis and some will develop cannabis use disorder (CUD). There is a growing recognition that CUD requires specific interventions. This Review will cover this topic from a variety of perspectives, with a particular emphasis on neurobiological findings and innovative treatment approaches that are being pursued. We will first describe the epidemiology and burden of disease of CUD, including risk factors associated with CUD (both in terms of general risk and genetic risk variants). Neurobiological alterations identified in brain imaging studies will be presented. Several psychosocial interventions that are useful for the management of CUD, including motivational enhancement therapy, behavioral and cognitive therapy, and contingency management, will be covered. Although no pharmacological interventions are yet approved for CUD, we present the most promising pharmacological interventions being tested.

AM6527, a neutral CB1 receptor antagonist, suppresses opioid taking and seeking, as well as cocaine seeking in rodents without aversive effects

Preclinical research has demonstrated the efficacy of CB1 receptor (CB1R) antagonists in reducing drug-taking behavior. However, clinical trials with rimonabant, a CB1R antagonist with inverse agonist profile, failed due to severe adverse effects, such as depression and suicidality. As a result, efforts have shifted towards developing novel neutral CB1R antagonists without an inverse agonist profile for treating substance use disorders. Here, we assessed AM6527, a CB1R neutral antagonist, in addiction animal models. Our findings revealed that AM6527 did not affect cocaine self-administration under fixed-ratio reinforcement schedules but dose-dependently inhibited it under progressive-ratio reinforcement schedules. Additionally, AM6527 dose-dependently inhibited heroin self-administration under both fixed-ratio and progressive-ratio reinforcement schedules and oral sucrose self-administration under a fixed-ratio reinforcement schedule, as well as cocaine- or heroin-triggered reinstatement of drug-seeking behavior in rats. However, chronic AM6527 administration for five consecutive days significantly inhibited heroin self-administration only during the initial two days, indicating tolerance development. Notably, AM6527 did not produce rewarding or aversive effects by itself in classical electrical intracranial self-stimulation and conditioned place preference tests. However, in optical intracranial self-stimulation (oICSS) maintained by optogenetic stimulation of midbrain dopamine neurons in DAT-cre mice, both AM6527 and rimonabant dose-dependently inhibited dopamine-dependent oICSS behavior. Together, these findings suggest that AM6527 effectively reduces drug-taking and seeking behaviors without rimonabant-like adverse effects. Thus, AM6527 warrants further investigation as a potential pharmacotherapy for opioid and cocaine use disorders.

Novel Peripherally Selective Cannabinoid Receptor 1 Neutral Antagonist Improves Metabolic Dysfunction-Associated Steatotic Liver Disease in Mice

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) is increasing globally. MASLD is characterized by clinically significant liver steatosis, and a subset of patients progress to more severe metabolic-disorder-associated steatohepatitis (MASH) with liver inflammation and fibrosis. Cannabinoid receptor 1 (CB1) antagonism is a proven therapeutic strategy for the treatment of the phenotypes that underlie MASLD, though work on early centrally penetrant compounds largely ceased following adverse psychiatric indications in humans. We present here preclinical testing of a CB1 neutral antagonist, N-[1-[8-(2-Chlorophenyl)-9-(4-chlorophenyl)-9H-purin-6-yl]-4-phenylpiperidin-4l]methanesulfonamide (RTI-348), with minimal brain exposure when administered to mice. In a diet-induced model of MASLD-induced MASH, administration of RTI-348 decreased the total body and liver weight gain. Animals treated with RTI-348 showed reduced steatosis. Furthermore, they produced lower plasma alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH), biomarkers associated with liver damage. Mice maintained on the MASH diet had elevated expression of genes associated with profibrogenesis, immune response, and extracellular matrix remodeling, and treatment with RTI-348 mitigated these diet-induced changes in gene expression. Using an intracranial electrical self-stimulation model, we also demonstrated that RTI-348 does not produce an anhedonia response, as seen with the first-generation CB1 inverse agonist rimonabant. Altogether, the results herein point to RTI-348 as a promising neutral antagonist for MASH.

Neurobiology of Stress-Induced Nicotine Relapse

Tobacco smoking is the leading cause of preventable death and disease. Although there are some FAD-approved medicines for controlling smoking, the relapse rate remains very high. Among the factors that could induce nicotine relapse, stress might be the most important one. In the last decades, preclinical studies have generated many new findings that lead to a better understanding of stress-induced relapse of nicotine-seeking. Several molecules such as α3β4 nicotinic acetylcholine receptor, α2-adrenergic receptors, cannabinoid receptor 1, trace amine-associated receptor 1, and neuropeptide systems (corticotropin-releasing factor and its receptors, dynorphine and kappa opioid receptor) have been linked to stress-induced nicotine relapse. In this review, we discuss recent advances in the neurobiology, treatment targets, and potential therapeutics of stress-induced nicotine relapse. We also discuss some factors that may influence stress-induced nicotine relapse and that should be considered in future studies. In the final section, a perspective on some research directions is provided. Further investigation on the neurobiology of stress-induced nicotine relapse will shed light on the development of new medicines for controlling smoking and will help us understand the interactions between the stress and reward systems in the brain.

Dysregulation of the endogenous cannabinoid system following opioid exposure

Rates of opioid-related deaths and overdoses in the United States are at record-high levels. Thus, novel neurobiological targets for the treatment of OUD are greatly needed. Given the close interaction between the endogenous opioid system and the endocannabinoid system (ECS), targeting the ECS may have therapeutic potential in OUD. The various components of the ECS, including cannabinoid receptors, their lipid-derived endogenous ligands (endocannabinoids [eCBs]), and the related enzymes, present potential targets for developing new medications in OUD treatment. The purpose of this paper is to review the clinical and preclinical literature on the dysregulation of the ECS after exposure to opioids. We review the evidence of ECS dysregulation across various study types, exposure protocols, and measurement protocols and summarize the evidence for dysregulation of ECS components at specific brain regions. Preclinical research has shown that opioids disrupt various ECS components that are region-specific. However, the results in the literature are highly heterogenous and sometimes contradictory, possibly due to variety of different methods used. Further research is needed before a confident conclusion could be made on how exposure to opioids can affect ECS components in various brain regions.

Effects of the CB1 receptor antagonists AM6545 and AM4113 on metabolic syndrome-induced prostatic hyperplasia in rats

Metabolic syndrome (MetS) is a combination of metabolic disorders that can predispose individuals to benign prostatic hyperplasia (BPH). The inhibition of the cannabinoid 1 (CB1) receptor has been used to treat metabolic disorders in animal models. This study reports the use of a peripherally restricted CB1 antagonist (AM6545) and a neutral CB1 antagonist (AM4113) to improve MetS-related BPH in rats. Animals were divided into three control groups to receive either a normal rodent diet, AM6545, or AM4113. MetS was induced in the fourth, fifth, and sixth groups using a concentrated fructose solution and high-salt diet delivered as food pellets for eight weeks. The fifth and sixth groups were further given AM6545 or AM4113 for additional four weeks. Body and prostate weights were measured and prostate sections were stained with hematoxylin eosin. Cyclin D1, markers of oxidative stress and inflammation, and levels of the endocannabinoids were recorded. BPH in rats with MetS was confirmed through increased prostate weight and index, as well as histopathology. Treatment with either AM6545 or AM4113 significantly decreased prostate weight, improved prostate histology, and reduced cyclin D1 expression compared with the MetS group. Groups treated with CB1 antagonists experienced reduced lipid peroxidation, recovered glutathione depletion, restored catalase activity, and had lower inflammatory markers interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α). MetS rats treated with either AM6545 or AM4113 showed reduced concentrations of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) in the prostate compared with the MetS group. In conclusion, the CB1 antagonists AM6545 and AM4113 protect against MetS-induced BPH through their anti-proliferative, antioxidant, and anti-inflammatory effects.

Goods and Bads of the Endocannabinoid System as a Therapeutic Target: Lessons Learned after 30 Years

The cannabis derivative marijuana is the most widely used recreational drug in the Western world and is consumed by an estimated 83 million individuals (∼3% of the world population). In recent years, there has been a marked transformation in society regarding the risk perception of cannabis, driven by its legalization and medical use in many states in the United States and worldwide. Compelling research evidence and the Food and Drug Administration cannabis-derived cannabidiol approval for severe childhood epilepsy have confirmed the large therapeutic potential of cannabidiol itself, Δ9-tetrahydrocannabinol and other plant-derived cannabinoids (phytocannabinoids). Of note, our body has a complex endocannabinoid system (ECS)-made of receptors, metabolic enzymes, and transporters-that is also regulated by phytocannabinoids. The first endocannabinoid to be discovered 30 years ago was anandamide (N-arachidonoyl-ethanolamine); since then, distinct elements of the ECS have been the target of drug design programs aimed at curing (or at least slowing down) a number of human diseases, both in the central nervous system and at the periphery. Here a critical review of our knowledge of the goods and bads of the ECS as a therapeutic target is presented to define the benefits of ECS-active phytocannabinoids and ECS-oriented synthetic drugs for human health. SIGNIFICANCE STATEMENT: The endocannabinoid system plays important roles virtually everywhere in our body and is either involved in mediating key processes of central and peripheral diseases or represents a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of the components of this complex system, and in particular of key receptors (like cannabinoid receptors 1 and 2) and metabolic enzymes (like fatty acid amide hydrolase and monoacylglycerol lipase), will advance our understanding of endocannabinoid signaling and activity at molecular, cellular, and system levels, providing new opportunities to treat patients.

Development of a membrane-based Gi-CASE biosensor assay for profiling compounds at cannabinoid receptors

Introduction: The cannabinoid receptor (CBR) subtypes 1 (CB1R) and 2 (CB2R) are key components of the endocannabinoid system (ECS), playing a central role in the control of peripheral pain, inflammation and the immune response, with further roles in the endocrine regulation of food intake and energy balance. So far, few medicines targeting these receptors have reached the clinic, suggesting that a better understanding of the receptor signalling properties of existing tool compounds and clinical candidates may open the door to the development of more effective and safer treatments. Both CB1R and CB2R are Gαi protein-coupled receptors but detecting Gαi protein signalling activity reliably and reproducibly is challenging. This is due to the inherent variability in live cell-based assays and restrictions around the use of radioactive [35S]-GTPγS, a favoured technology for developing higher-throughput membrane-based Gαi protein activity assays. Methods: Here, we describe the development of a membrane-based Gαi signalling system, produced from membrane preparations of HEK293TR cells, stably overexpressing CB1R or CB2R, and components of the Gαi-CASE biosensor. This BRET-based system allows direct detection of Gαi signalling in both cells and membranes by monitoring bioluminescence resonance energy transfer (BRET) between the α and the βγ subunits. Cells and membranes were subject to increasing concentrations of reference cannabinoid compounds, with 10 μM furimazine added to generate RET signals, which were detected on a PHERAstar FSX plate reader, then processed using MARS software and analysed in GraphPad PRISM 9.2. Results: In membranes expressing the Gi-CASE biosensor, the cannabinoid ligands profiled were found to show agonist and inverse agonist activity. Agonist activity elicited a decrease in the BRET signal, indicative of receptor activation and G protein dissociation. Inverse agonist activity caused an increase in BRET signal, indicative of receptor inactivation, and the accumulation of inactive G protein. Our membrane-based Gi-CASE NanoBRET system successfully characterised the potency (pEC50) and efficacy (Emax) of CBR agonists and inverse agonists in a 384-well screening format. Values obtained were in-line with whole-cell Gi-CASE assays and consistent with literature values obtained in the GTPγS screening format. Discussion: This novel, membrane-based Gαi protein activation assay is applicable to other Gαi-coupled GPCRs, including orphan receptors, allowing real-time higher-throughput measurements of receptor activation.

Neutral CB1 Receptor Antagonists as Pharmacotherapies for Substance Use Disorders: Rationale, Evidence, and Challenge

Cannabinoid receptor 1 (CB1R) has been one of the major targets in medication development for treating substance use disorders (SUDs). Early studies indicated that rimonabant, a selective CB1R antagonist with an inverse agonist profile, was highly promising as a therapeutic for SUDs. However, its adverse side effects, such as depression and suicidality, led to its withdrawal from clinical trials worldwide in 2008. Consequently, much research interest shifted to developing neutral CB1R antagonists based on the recognition that rimonabant’s side effects may be related to its inverse agonist profile. In this article, we first review rimonabant’s research background as a potential pharmacotherapy for SUDs. Then, we discuss the possible mechanisms underlying its therapeutic anti-addictive effects versus its adverse effects. Lastly, we discuss the rationale for developing neutral CB1R antagonists as potential treatments for SUDs, the supporting evidence in recent research, and the challenges of this strategy. We conclude that developing neutral CB1R antagonists without inverse agonist profile may represent attractive strategies for the treatment of SUDs.

Off-label and investigational drugs in the treatment of alcohol use disorder: A critical review

Compounds known to be successful in the treatment of alcohol use disorder include the aversive agent, Disulfiram, the glutamatergic NMDA receptor antagonist, Acamprosate, and the opioid receptor antagonists, Naltrexone and Nalmefene. Although all four are effective in maintaining abstinence or reduction of alcohol consumption, only a small percentage of patients receive pharmacological treatment. In addition, many other medications have been investigated for their therapeutic potential in the treatment of alcohol use disorder. In this review we summarize and compare Baclofen, Gabapentin, Topiramate, Ondansetron, Varenicline, Aripiprazole, Quetiapine, Clozapine, Antidepressants, Lithium, Neuropeptide Y, Neuropeptide S, Corticotropin-releasing factor antagonists, Oxytocin, PF-05190457, Memantine, Ifenprodil, Samidorphan, Ondelopran, ABT-436, SSR149415, Mifepristone, Ibudilast, Citicoline, Rimonabant, Surinabant, AM4113 and Gamma-hydroxybutyrate While some have shown promising results in the treatment of alcohol use disorder, others have disappointed and should be excluded from further investigation. Here we discuss the most promising results and highlight medications that deserve further preclinical or clinical study. Effective, patient-tailored treatment will require greater understanding provided by many more preclinical and clinical studies.

Cannabigerol (CBG) attenuates mechanical hypersensitivity elicited by chemotherapy-induced peripheral neuropathy

BACKGROUND

Cannabigerol (CBG) is a non-psychoactive phytocannabinoid produced by the plant Cannabis sativa with affinity to various receptors involved in nociception. As a result, CBG is marketed as an over-the-counter treatment for many forms of pain. However, there is very little research-based evidence for the efficacy of CBG as an anti-nociceptive agent.

METHODS

To begin to fill this knowledge gap, we assessed the anti-nociceptive effects of CBG in C57BL/6 mice using three different models of pain; cisplatin-induced peripheral neuropathy, the formalin test, and the tail-flick assay.

RESULTS

Using the von Frey test, we found that CBG-attenuated mechanical hypersensitivity evoked by cisplatin-induced peripheral neuropathy in both male and female mice. Additionally, we observed that this CBG-induced reduction in mechanical hypersensitivity was attenuated by the α₂ -adrenergic receptor antagonist atipamezole (3 mg/kg, i.p.) and the CB₁ R antagonist, AM4113 (3 mg/kg, i.p.), and blocked by the CB₂ R antagonist/inverse agonist, SR144528 (10 mg/kg, i.p.). We found that the TRPV1 antagonist, SB705498 (20 mg/kg, i.p.) was unable to prevent CBG actions. Furthermore, we show that CBG:CBD oil (10 mg/kg, i.p.) was more effective than pure CBG (10 mg/kg) at reducing mechanical hypersensitivity in neuropathic mice. Lastly, we show that pure CBG and CBG:CBD oil were ineffective at reducing nociception in other models of pain, including the formalin and tail flick assays.

CONCLUSIONS

Our findings support the role of CBG in alleviating mechanical hypersensitivity evoked by cisplatin-induced peripheral neuropathy, but highlight that these effects may be limited to specific types of pain.

SIGNIFICANCE

There are few effective treatments for neuropathic pain and neuropathic pain is projected to increase with the aging population. We demonstrate that CBG (cannabigerol) and CBG:CBD oil attenuate neuropathy-induced mechanical hypersensitivity mice. Second, we identify receptor targets that mediate CBG-induced reduction in mechanical hypersensitivity in neuropathic mice. Third, we demonstrate that an acute injection of CBG is anti-nociceptive specifically for neuropathic pain rather than other forms of pain, including persistent pain and thermal pain.

Cannabidiol in the context of substance use disorder treatment: A systematic review

INTRODUCTION

Cannabidiol (CBD) is a phytocannabinoid found in the Cannabis plant. CBD has received significant medical attention in relation to its anticonvulsant, anxiolytic, and antipsychotic characteristics. An increasing number of studies focusing on the anti-addictive properties of CBD have recently been published. In this systematic review, we aim to offer a comprehensive overview of animal and human studies regarding the impact of CBD on substance use disorders (SUDs).

METHODS

A systematic search was performed on the PubMed database in February 2021. We included all articles assessing the effects of CBD on substance use disorders.

RESULTS

The current systematic review suggests that CBD might offer promising therapeutic potential for the treatment of SUD, based on available animal and human studies. Animal studies showed a positive impact of CBD in the context of alcohol, opioids, and methamphetamine use (e.g., diminishing of drug-seeking behaviors). The results for cocaine use were mixed among reviewed studies, and CBD was not found to have an effect in animal studies on cannabis use. No animal study was identified that focused on the impact of CBD on nicotine use. Human studies showed a positive impact of CBD in the context of nicotine, cannabis, and opioid use (e.g., frequency and quantity of consumption). In contrast, CBD was not found to have an effect in human studies on cocaine or alcohol use. No human study was identified that investigated the impact of CBD on methamphetamine use.

CONCLUSIONS

CBD might offer promising therapeutic potential for the treatment of SUD, especially for nicotine, cannabis, and opioid use disorders, based on available human studies. The available research evidence is, however, sparse and more research on humans is needed.

Therapeutic potential of PIMSR, a novel CB1 receptor neutral antagonist, for cocaine use disorder: evidence from preclinical research

Cannabinoid CB1 receptors (CB1Rs) have been major targets in medication development for the treatment of substance use disorders. However, clinical trials with rimonabant, a CB1R antagonist/inverse agonist, failed due to severe side effects. Here, we evaluated the therapeutic potential of PIMSR, a neutral CB1R antagonist lacking an inverse agonist profile, against cocaine's behavioral effects in experimental animals. We found that systemic administration of PIMSR dose-dependently inhibited cocaine self-administration under fixed-ratio (FR5), but not FR1, reinforcement, shifted the cocaine self-administration dose-response curve downward, decreased incentive motivation to seek cocaine under progressive-ratio reinforcement, and reduced cue-induced reinstatement of cocaine seeking. PIMSR also inhibited oral sucrose self-administration. Importantly, PIMSR alone is neither rewarding nor aversive as assessed by place conditioning. We then used intracranial self-stimulation (ICSS) to explore the possible involvement of the mesolimbic dopamine system in PIMSR's action. We found that PIMSR dose-dependently attenuated cocaine-enhanced ICSS maintained by electrical stimulation of the medial forebrain bundle in rats. PIMSR itself failed to alter electrical ICSS, but dose-dependently inhibited ICSS maintained by optical stimulation of midbrain dopamine neurons in transgenic DAT-Cre mice, suggesting the involvement of dopamine-dependent mechanisms. Lastly, we examined the CB1R mechanisms underlying PIMSR's action. We found that PIMSR pretreatment attenuated Δ⁹-tetrahydrocannabinol (Δ⁹-THC)- or ACEA (a selective CB1R agonist)-induced reduction in optical ICSS. Together, our findings suggest that the neutral CB1R antagonist PIMSR deserves further research as a promising pharmacotherapeutic for cocaine use disorder.

The endocannabinoid system and drug-associated contextual memories

Drug abuse and addiction can be initiated and reinstated by contextual stimuli previously paired with the drug use. The influence exerted by the context on drug-seeking behaviour can be modelled in experimental animals with place-conditioning protocols. Here, we review the effects of cannabinoids in place conditioning and the therapeutic potential of the endocannabinoid system for interfering with drug-related memories. The phytocannabinoid Δ9-tetrahydrocannabinol (THC) tends to induce conditioned place preference (CPP) at low doses and conditioned place aversion at high doses; cannabidiol is devoid of any effect, yet it inhibits CPP induced by some drugs. Synthetic CB1 receptor agonists tend to recapitulate the biphasic profile observed with THC, whereas selective antagonists/inverse agonists inhibit CPP induced by cocaine, nicotine, alcohol and opioids. However, their therapeutic use is limited by potential psychiatric side effects. The CB2 receptor has also attracted attention, because selective CB2 receptor agonists inhibit cocaine-induced CPP. Inhibitors of endocannabinoid membrane transport and hydrolysis yield mixed results. In targeting the endocannabinoid system for developing new treatments for drug addiction, future research should focus on 'neutral' CB1 receptor antagonists and CB2 receptor agonists. Such compounds may offer a well-tolerated pharmacological profile and curb addiction by preventing drug-seeking triggered by conditioned contextual cues.

Tobacco and nicotine use

Tobacco smoking is a major determinant of preventable morbidity and mortality worldwide. More than a billion people smoke, and without major increases in cessation, at least half will die prematurely from tobacco-related complications. In addition, people who smoke have a significant reduction in their quality of life. Neurobiological findings have identified the mechanisms by which nicotine in tobacco affects the brain reward system and causes addiction. These brain changes contribute to the maintenance of nicotine or tobacco use despite knowledge of its negative consequences, a hallmark of addiction. Effective approaches to screen, prevent and treat tobacco use can be widely implemented to limit tobacco's effect on individuals and society. The effectiveness of psychosocial and pharmacological interventions in helping people quit smoking has been demonstrated. As the majority of people who smoke ultimately relapse, it is important to enhance the reach of available interventions and to continue to develop novel interventions. These efforts associated with innovative policy regulations (aimed at reducing nicotine content or eliminating tobacco products) have the potential to reduce the prevalence of tobacco and nicotine use and their enormous adverse impact on population health.

Endocannabinoid system contributions to sex-specific adolescent neurodevelopment

With an increasing number of countries and states adopting legislation permitting the use of cannabis for medical purposes, there is a growing interest among health and research professionals into the system through which cannabinoids principally act, the endocannabinoid system (ECS). Much of the seminal research into the ECS dates back only 30 years and, although there has been tremendous development within the field during this time, many questions remain. More recently, investigations have emerged examining the contributions of the ECS to normative development and the effect of altering this system during important critical periods. One such period is adolescence, a unique period during which brain and behaviours are maturing and reorganizing in preparation for adulthood, including shifts in endocannabinoid biology. The purpose of this review is to discuss findings to date regarding the maturation of the ECS during adolescence and the consequences of manipulations of the ECS during this period to normative neurodevelopmental processes, as well as highlight sex differences in ECS function, important technical considerations, and future directions. Because most of what we know is derived from preclinical studies on rodents, we provide relevant background of this model and some commentary on the translational relevance of the research in this area.

New Insights in the Involvement of the Endocannabinoid System and Natural Cannabinoids in Nicotine Dependence

Nicotine, the main psychoactive component in tobacco smoke, plays a major role in tobacco addiction, producing a high morbidity and mortality in the world. A great amount of research has been developed to elucidate the neural pathways and neurotransmitter systems involved in such a complex addictive behavior. The endocannabinoid system, which has been reported to participate in the addictive properties of most of the prototypical drugs of abuse, is also implicated in nicotine dependence. This review summarizes and updates the main behavioral and biochemical data involving the endocannabinoid system in the rewarding properties of nicotine as well as in nicotine withdrawal and relapse to nicotine-seeking behavior. Promising results from preclinical studies suggest that manipulation of the endocannabinoid system could be a potential therapeutic strategy for treating nicotine addiction.

The Endocannabinoid System: A Potential Target for the Treatment of Various Diseases

The Endocannabinoid System (ECS) is primarily responsible for maintaining homeostasis, a balance in internal environment (temperature, mood, and immune system) and energy input and output in living, biological systems. In addition to regulating physiological processes, the ECS directly influences anxiety, feeding behaviour/appetite, emotional behaviour, depression, nervous functions, neurogenesis, neuroprotection, reward, cognition, learning, memory, pain sensation, fertility, pregnancy, and pre-and post-natal development. The ECS is also involved in several pathophysiological diseases such as cancer, cardiovascular diseases, and neurodegenerative diseases. In recent years, genetic and pharmacological manipulation of the ECS has gained significant interest in medicine, research, and drug discovery and development. The distribution of the components of the ECS system throughout the body, and the physiological/pathophysiological role of the ECS-signalling pathways in many diseases, all offer promising opportunities for the development of novel cannabinergic, cannabimimetic, and cannabinoid-based therapeutic drugs that genetically or pharmacologically modulate the ECS via inhibition of metabolic pathways and/or agonism or antagonism of the receptors of the ECS. This modulation results in the differential expression/activity of the components of the ECS that may be beneficial in the treatment of a number of diseases. This manuscript in-depth review will investigate the potential of the ECS in the treatment of various diseases, and to put forth the suggestion that many of these secondary metabolites of Cannabis sativa L. (hereafter referred to as "C. sativa L." or "medical cannabis"), may also have potential as lead compounds in the development of cannabinoid-based pharmaceuticals for a variety of diseases.

The endocannabinoid system in social anxiety disorder: from pathophysiology to novel therapeutics

Social anxiety disorder (SAD) is a highly prevalent psychiatric disorder that presents with an early age of onset, chronic disease course, and increased risk of psychiatric comorbidity. Current treatment options for SAD are associated with low response rates, suboptimal efficacy, and possible risk of adverse effects. Investigation of new neurobiological mechanisms may aid in the identification of more specific therapeutic targets for the treatment of this disorder. Emerging evidence suggests that the endogenous cannabinoid system, also referred to as the endocannabinoid system (ECS), could play a potential role in the pathophysiology of SAD. This review discusses the known pathophysiological mechanisms of SAD, the potential role of the ECS in this disorder, current drugs targeting the ECS, and the potential of these novel compounds to enhance the therapeutic armamentarium for SAD. Further investigational efforts, specifically in human populations, are warranted to improve our knowledge of the ECS in SAD.

The Cannabinoid Receptor 1 Reverse Agonist AM251 Ameliorates Radiation-Induced Cognitive Decrements

Despite advancements in the radiotherapeutic management of brain malignancies, resultant sequelae include persistent cognitive dysfunction in the majority of survivors. Defining the precise causes of normal tissue toxicity has proven challenging, but the use of preclinical rodent models has suggested that reductions in neurogenesis and microvascular integrity, impaired synaptic plasticity, increased inflammation, and alterations in neuronal structure are contributory if not causal. As such, strategies to reverse these persistent radiotherapy-induced neurological disorders represent an unmet medical need. AM251, a cannabinoid receptor 1 reverse agonist known to facilitate adult neurogenesis and synaptic plasticity, may help to ameliorate radiation-induced CNS impairments. To test this hypothesis, three treatment paradigms were used to evaluate the efficacy of AM251 to ameliorate radiation-induced learning and memory deficits along with disruptions in mood at 4 and 12 weeks postirradiation. Results demonstrated that acute (four weekly injections) and chronic (16 weekly injections) AM251 treatments (1 mg/kg) effectively alleviated cognitive and mood dysfunction in cranially irradiated mice. The beneficial effects of AM251 were exemplified by improved hippocampal- and cortical-dependent memory function on the novel object recognition and object in place tasks, while similar benefits on mood were shown by reductions in depressive- and anxiety-like behaviors on the forced swim test and elevated plus maze. The foregoing neurocognitive benefits were associated with significant increases in newly born (doublecortin+) neurons (1.7-fold), hippocampal neurogenesis (BrdU+/NeuN+mature neurons, 2.5-fold), and reduced expression of the inflammatory mediator HMGB (1.2-fold) in the hippocampus of irradiated mice. Collectively, these findings indicate that AM251 ameliorates the effects of clinically relevant cranial irradiation where overall neurological benefits in memory and mood coincided with increased hippocampal cell proliferation, neurogenesis, and reduced expression of proinflammatory markers.

CB1 receptor neutral antagonist treatment epigenetically increases neuropeptide Y expression and decreases alcohol drinking

Alcohol consumption is mediated by several important neuromodulatory systems, including the endocannabinoid and neuropeptide Y (NPY) systems in the limbic brain circuitry. However, molecular mechanisms through which cannabinoid-1 (CB1) receptors regulate alcohol consumption are still unclear. Here, we investigated the role of the CB1 receptor-mediated downstream regulation of NPY via epigenetic mechanisms in the amygdala. Alcohol drinking behavior was measured in adult male C57BL/6J mice treated with a CB1 receptor neutral antagonist AM4113 using a two-bottle choice paradigm while anxiety-like behavior was assessed in the light-dark box (LDB) test. The CB1 receptor-mediated changes in the protein levels of phosphorylated cAMP-responsive element binding protein (pCREB), CREB binding protein (CBP), H3K9ac, H3K14ac and NPY, and the mRNA levels of Creb1, Cbp, and Npy were measured in amygdaloid brain structures. Npy-specific changes in the levels of acetylated histone (H3K9/14ac) and CBP in the amygdala were also measured. We found that the pharmacological blockade of CB1 receptors with AM4113 reduced alcohol consumption and, in an ethanol-naïve cohort, reduced anxiety-like behavior in the LDB test. Treatment with AM4113 also increased the mRNA levels of Creb1 and Cbp in the amygdala as well as the protein levels of pCREB, CBP, H3K9ac and H3K14ac in the central and medial nucleus of amygdala, but not in the basolateral amygdala. Additionally, AM4113 treatment increased occupancy of CBP and H3K9/14ac at the Npy gene promoter, leading to an increase in both mRNA and protein levels of NPY in the amygdala. These novel findings suggest that CB1 receptor-mediated CREB signaling plays an important role in the modulation of NPY function through an epigenetic mechanism and further support the potential use of CB1 receptor neutral antagonists for the treatment of alcohol use disorder.

Evidence for the Endocannabinoid System as a Therapeutic Target in the Treatment of Cannabis Use Disorder

Purpose of Review

Cannabis use disorder (CUD) is highly prevalent. Psychotherapy alone is not adequately effective, with few individuals achieving abstinence. Pharmacotherapeutic supplementation may improve efficacy, and the endocannabinoid system presents a target specifically dysregulated by heavy cannabis use. This review compiles current literature evaluating endocannabinoid modulation as a treatment strategy for CUD, with implications for future research.

Recent Findings

Cannabinoid receptor agonists have been found to reduce cannabis withdrawal symptoms without a notable effect on relapse, and antagonists can produce severe psychiatric symptoms. Fatty acid amide hydrolase inhibitors and cannabidiol demonstrate the most promising efficacy in treating CUD thus far, but research with these compounds is still preliminary.

Summary

Components of the endocannabinoid system may serve as unique treatment targets with differential efficacy for the treatment of cannabis use disorder as a whole. Further research is needed exploring novel methods for targeting endocannabinoid dysfunction in CUD.

Exploring the impact of adolescent exposure to cannabinoids and nicotine on psychiatric risk: insights from translational animal models

Adolescence represents a highly sensitive period of mammalian neurodevelopment wherein critical synaptic and structural changes are taking place in brain regions involved in cognition, self-regulation and emotional processing. Importantly, neural circuits such as the mesocorticolimbic pathway, comprising the prefrontal cortex, sub-cortical mesolimbic dopamine system and their associated input/output centres, are particularly vulnerable to drug-related insults. Human adolescence represents a life-period wherein many individuals first begin to experiment with recreational drugs such as nicotine and cannabis, both of which are known to profoundly modulate neurochemical signalling within the mesocorticolimbic pathway and to influence both long-term and acute neuropsychiatric symptoms. While a vast body of epidemiological clinical research has highlighted the effects of adolescent exposure to drugs such as nicotine and cannabis on the developing adolescent brain, many of these studies are limited to correlative analyses and rely on retrospective self-reports from subjects, making causal interpretations difficult to discern. The use of pre-clinical animal studies can avoid these issues by allowing for precise temporal and dose-related experimental control over drug exposure during adolescence. In addition, such animal-based research has the added advantage of allowing for in-depth molecular, pharmacological, genetic and neuronal analyses of how recreational drug exposure may set up the brain for neuropsychiatric risk. This review will explore some of the advantages and disadvantages of these models, with a focus on the common, divergent and synergistic effects of adolescent nicotine and cannabis exposure on neuropsychiatric risk.

Cannabis use and cannabis use disorder

Cannabis use disorder (CUD) is an underappreciated risk of using cannabis that affects ~10% of the 193 million cannabis users worldwide. The individual and public health burdens are less than those of other forms of drug use, but CUD accounts for a substantial proportion of persons seeking treatment for drug use disorders owing to the high global prevalence of cannabis use. Cognitive behavioural therapy, motivational enhancement therapy and contingency management can substantially reduce cannabis use and cannabis-related problems, but enduring abstinence is not a common outcome. No pharmacotherapies have been approved for cannabis use or CUD, although a number of drug classes (such as cannabinoid agonists) have shown promise and require more rigorous evaluation. Treatment of cannabis use and CUD is often complicated by comorbid mental health and other substance use disorders. The legalization of non-medical cannabis use in some high-income countries may increase the prevalence of CUD by making more potent cannabis products more readily available at a lower price. States that legalize medical and non-medical cannabis use should inform users about the risks of CUD and provide information on how to obtain assistance if they develop cannabis-related mental and/or physical health problems.

Interference with TGFβ1-Mediated Inflammation and Fibrosis Underlies Reno-Protective Effects of the CB1 Receptor Neutral Antagonists AM6545 and AM4113 in a Rat Model of Metabolic Syndrome

The role of cannabinoid receptors in nephropathy is gaining much attention. This study investigated the effects of two neutral CB1 receptor antagonists, AM6545 and AM4113, on nephropathy associated with metabolic syndrome (MetS). MetS was induced in rats by high-fructose high-salt feeding for 12 weeks. AM6545, the peripheral silent antagonist and AM4113, the central neutral antagonist were administered in the last 4 weeks. At the end of study, blood and urine samples were collected for biochemical analyses while the kidneys were excised for histopathological investigation and transforming growth factor beta 1 (TGFβ1) measurement. MetS was associated with deteriorated kidney function as indicated by the elevated proteinuria and albumin excretion rate. Both compounds equally inhibited the elevated proteinuria and albumin excretion rate while having no effect on creatinine clearance and blood pressure. In addition, AM6545 and AM4113 alleviated the observed swelling and inflammatory cells infiltration in different kidney structures. Moreover, AM6545 and AM4113 alleviated the observed histopathological alterations in kidney structure of MetS rats. MetS was associated with a ten-fold increase in urine uric acid while both compounds blocked this increase. Furthermore, AM6545 and AM4113 completely prevented the collagen deposition and the elevated expression of the TGFβ1 seen in MetS animals. In conclusion, AM6545 and AM4113, possess reno-protective effects by interfering with TGFβ1-mediated renal inflammation and fibrosis, via peripheral action.

Negative allosteric modulators of cannabinoid receptor 1: Ternary complexes including CB1, orthosteric CP55940 and allosteric ORG27569

In October 2019, the first X-ray crystal structure of a ternary cannabinoid receptor 1 (CB1) complex (PDB ID: 6KQI) was published, including the well-known orthosteric agonist, CP55940, and the well-studied negative allosteric modulator, ORG27569. Prior to the release of 6KQI, we applied binding pocket analysis and molecular docking to carefully prepared computational models of the ternary CB1 complex, in order to predict the binding site for ORG27569 with the CP55940-bound CB1 receptor. We carefully studied the binding pose of agonist ligands in the CB1 orthosteric pocket, including CP55940. Our computational studies identified the most favorable binding site for ORG27569, in the CP55940-CB1 complex, to be at the intracellular end of the receptor. However, in the 6KQI structure, ORG27569 was found at an extrahelical, intramembrane site on the complex, a site that partially overlaps with the site predicted in our calculations to be second-best. We performed molecular dynamics simulations of the CP55940-bound CB1 complex with ORG27569 at different binding sites. Our analysis of the simulations indicated that ORG27569 bound favorably and stably in each simulation, but, as in the earlier calculations, bound best at the intracellular site, which is different than that found in the crystal structure. These results suggest that the intracellular site might serve as an alternative binding site in CB1. Our studies show that the computational techniques we used are valuable in identifying ligand-binding pockets in proteins, and could be useful for the study of the interaction mode of other allosteric modulators.

Endocannabinoid signaling regulates the reinforcing and psychostimulant effects of ketamine in mice

The abuse potential of ketamine limits its clinical application, but the precise mechanism remains largely unclear. Here we discovered that ketamine significantly remodels the endocannabinoid-related lipidome and activates 2-arachidonoylglycerol (2-AG) signaling in the dorsal striatum (caudate nucleus and putamen, CPu) of mice. Elevated 2-AG in the CPu is essential for the psychostimulant and reinforcing effects of ketamine, whereas blockade of the cannabinoid CB1 receptor, a predominant 2-AG receptor, attenuates ketamine-induced remodeling of neuronal dendrite structure and neurobehaviors. Ketamine represses the transcription of the monoacylglycerol lipase (MAGL) gene by promoting the expression of PRDM5, a negative transcription factor of the MAGL gene, leading to increased 2-AG production. Genetic overexpression of MAGL or silencing of PRDM5 expression in the CPu robustly reduces 2-AG production and ketamine effects. Collectively, endocannabinoid signaling plays a critical role in mediating the psychostimulant and reinforcing properties of ketamine.

Choosing the right drug: status and future of endocannabinoid research for the prevention of drug-seeking reinstatement

Prolonged exposure to drugs of abuse leads to severe alterations in mesocorticolimbic dopamine circuitry deeply implicated in substance use disorders. Despite considerable efforts, few medications to reduce relapse rates are currently available. To solve this issue, researchers are uncovering therapeutic opportunities offered by the endocannabinoid system. The cannabinoid receptor type 1 (CB₁R), and its endogenous ligands, participate in orchestration of cue-triggered and stress-triggered responses leading to obtain natural and drug rewards. Here, we review the evidence supporting the use of CB₁R neutral antagonists, allosteric modulators, indirect agonists, as well as multi-target compounds, as improved alternatives compared to classical CB₁R antagonists. The promising therapeutic value of other substrates participating in endocannabinoid signaling, like peroxisome proliferator-activated receptors, is also covered. Overall, a wide body of pre-clinical evidence avails novel pharmacological strategies interacting with the endocannabinoid system as clinically amenable candidates able to counteract drug-induced dopamine maladaptations contributing to increased risk of relapse.

The Cannabinoid CB1 Receptor in Schizophrenia

Converging lines of evidence from epidemiological, preclinical, and experimental studies indicate that the endocannabinoid system may be involved in the pathophysiology of schizophrenia and suggest that the cannabinoid CB₁ receptor may be a potential therapeutic target. In view of this, we first provide an overview of the endocannabinoid system and systematically review the evidence for CB₁ receptor alterations in animal models of schizophrenia and clinical studies in schizophrenia. MEDLINE, EMBASE, PsycArticles, and PsycINFO were systematically searched from inception until January 7, 2020. Of 1187 articles, 24 were included in the systematic review, including 8 preclinical studies measuring the CB₁ receptor in the context of an established animal model of schizophrenia and 16 clinical studies investigating the CB₁ receptor in schizophrenia. The majority of preclinical studies (6 of 8) have shown that the CB₁ receptor is reduced in the context of animal models of schizophrenia. Moreover, the majority of in vivo clinical imaging studies that used arterial blood sampling to quantify the radiotracer kinetics (3 of 4) have shown reduced CB₁ receptor availability in schizophrenia. However, mixed findings have been reported in ex vivo literature, including reports of no change in receptor levels (5 of 11), increased receptor levels (4 of 11), and decreased receptor levels (2 of 11). We review methodological reasons for these discrepancies and review how CB₁ receptor dysfunction may contribute to the pathophysiology of schizophrenia, drawing on the role of the receptor in regulating synaptic transmission and synaptic plasticity. We also discuss how the CB₁ receptor may be a potential therapeutic target.

Targeting the Endocannabinoid CB1 Receptor to Treat Body Weight Disorders: A Preclinical and Clinical Review of the Therapeutic Potential of Past and Present CB1 Drugs

Obesity rates are increasing worldwide and there is a need for novel therapeutic treatment options. The endocannabinoid system has been linked to homeostatic processes, including metabolism, food intake, and the regulation of body weight. Rimonabant, an inverse agonist for the cannabinoid CB1 receptor, was effective at producing weight loss in obese subjects. However, due to adverse psychiatric side effects, rimonabant was removed from the market. More recently, we reported an inverse relationship between cannabis use and BMI, which has now been duplicated by several groups. As those results may appear contradictory, we review here preclinical and clinical studies that have studied the impact on body weight of various cannabinoid CB1 drugs. Notably, we will review the impact of CB1 inverse agonists, agonists, partial agonists, and neutral antagonists. Those findings clearly point out the cannabinoid CB1 as a potential effective target for the treatment of obesity. Recent preclinical studies suggest that ligands targeting the CB1 may retain the therapeutic potential of rimonabant without the negative side effect profile. Such approaches should be tested in clinical trials for validation.

Neuronal nicotinic acetylcholine receptors mediate ∆9 -THC dependence: Mouse and human studies

Cessation from prolonged use of ∆9 -tetrahydrocannabinol (THC), the primary active compound responsible for the cannabimimetic effects of cannabis, results in a mild to moderate withdrawal syndrome in humans and laboratory animals. Whereas manipulations of the endogenous cannabinoid system (eg, cannabinoid receptors and endocannabinoid regulating enzymes) alter nicotine withdrawal, in this study we asked the reciprocal question. Do nicotinic acetylcholine receptors (nAChRs) modulate THC withdrawal? To assess the role of different nAChR subtypes in THC withdrawal, we used transgenic mouse, preclinical pharmacological, and human genetic correlation approaches. Our findings show that selective α3β4* nAChR antagonist, AuIB, and α3β4* nAChR partial agonist, AT-1001, dose-dependently attenuated somatic withdrawal signs in THC-dependent mice that were challenged with the cannabinoid-1 receptor antagonist rimonabant. Additionally, THC-dependent α5 and α6 nAChR knockout (KO) mice displayed decreased rimonabant precipitated somatic withdrawal signs compared with their wild-type counterparts. In contrast, β2 and α7 nAChR KO mice showed no alterations in THC withdrawal signs. Moreover, deletion of β2 nAChR did not alter the reduced expression of somatic signs by the preferred α6β4* antagonist, BulA [T5A;P60]. Finally, the human genetic association studies indicated that variations in the genes that code for the α5, α3, β4, and α6 nAChRs were associated with cannabis disorder phenotypes. Overall, these findings suggest that α3β4* and α6β4* nAChR subtypes represent viable targets for the development of medications to counteract THC dependence.

Δ8 -Tetrahydrocannabivarin has potent anti-nicotine effects in several rodent models of nicotine dependence

BACKGROUND AND PURPOSE

Both types of cannabinoid receptors-CB1 and CB2 -regulate brain functions relating to addictive drug-induced reward and relapse. CB1 receptor antagonists and CB2 receptor agonists have anti-addiction efficacy, in animal models, against a broad range of addictive drugs. Δ9 -Tetrahydrocannabivarin (Δ9 -THCV)-a cannabis constituent-acts as a CB1 antagonist and a CB2 agonist. Δ8 -Tetrahydrocannabivarin (Δ8 -THCV) is a Δ9 -THCV analogue with similar combined CB1 antagonist/CB2 agonist properties.

EXPERIMENTAL APPROACH

We tested Δ8 -THCV in seven different rodent models relevant to nicotine dependence-nicotine self-administration, cue-triggered nicotine-seeking behaviour following forced abstinence, nicotine-triggered reinstatement of nicotine-seeking behaviour, acquisition of nicotine-induced conditioned place preference, anxiety-like behaviour induced by nicotine withdrawal, somatic withdrawal signs induced by nicotine withdrawal, and hyperalgesia induced by nicotine withdrawal.

KEY RESULTS

Δ8 -THCV significantly attenuated intravenous nicotine self-administration and both cue-induced and nicotine-induced relapse to nicotine-seeking behaviour in rats. Δ8 -THCV also significantly attenuated nicotine-induced conditioned place preference and nicotine withdrawal in mice.

CONCLUSIONS AND IMPLICATIONS

We conclude that Δ8 -THCV may have therapeutic potential for the treatment of nicotine dependence. We also suggest that tetrahydrocannabivarins should be tested for possible anti-addiction efficacy in a broader range of preclinical animal models, against other addictive drugs, and eventually in humans.

Escalating low-dose Δ9 -tetrahydrocannabinol exposure during adolescence induces differential behavioral and neurochemical effects in male and female adult rats

Cannabinoid administration during adolescence affects various physiological processes, such as motor and affective response, cognitive-related functions and modulates neurotransmitter activity. Literature remains scant concerning the parallel examination of the effects of adolescent escalating low-dose Δ⁹ -tetrahydrocannabinol (Δ⁹ -THC) on the behavioral and plasticity profile of adult rats in both sexes. Herein, we investigated the long-term behavioral, neurochemical and neurobiological effects of adolescent escalating low Δ⁹ -THC doses in adult male and female rats. In adult males, adolescent low-dose Δ⁹ -THC exposure led to increased spontaneous locomotor activity, impaired behavioral motor habituation and defective short-term spatial memory, paralleled with decreased BDNF protein levels in the prefrontal cortex. In this brain area, serotonergic activity was increased, as depicted by the increased serotonin turnover rate, while the opposite effect was observed in the hippocampus, a region where SERT levels were enhanced by Δ⁹ -THC, compared with vehicle. In adult females, adolescent Δ⁹ -THC treatment led to decreased spontaneous vertical activity and impaired short-term spatial memory, accompanied by increased BDNF protein levels in the prefrontal cortex. Present findings emphasize the key role of adolescent escalating low Δ⁹ -THC exposure in the long-term regulation of motor response, spatial-related cognitive functions and neuroplasticity indices in adulthood. In this framework, these changes could, at a translational level, contribute to clinical issues suggesting the development of psychopathology in a sex-differentiated manner following Δ⁹ -THC exposure during adolescence.

Overcoming the Psychiatric Side Effects of the Cannabinoid CB1 Receptor Antagonists: Current Approaches for Therapeutics Development

The Cannabinoid CB1 Receptor (CB1R) is involved in a variety of physiological pathways and has long been considered a golden target for therapeutic manipulation. A large body of evidence in both animal and human studies suggests that CB1R antagonism is highly effective for the treatment of obesity, metabolic disorders and drug addiction. However, the first-in-class CB1R antagonist/inverse agonist, rimonabant, though demonstrating effectiveness for obesity treatment and smoking cessation, displays serious psychiatric side effects, including anxiety, depression and even suicidal ideation, resulting in its eventual withdrawal from the European market. Several strategies are currently being pursued to circumvent the mechanisms leading to these side effects by developing neutral antagonists, peripherally restricted ligands, and allosteric modulators. In this review, we describe the progress in the development of therapeutics targeting the CB1R in the last two decades.

Potential of Cannabinoid Receptor Ligands as Treatment for Substance Use Disorders

Substance use disorder (SUD) is a major public health crisis worldwide, and effective treatment options are limited. During the past 2 decades, researchers have investigated the impact of a variety of pharmacological approaches to treat SUD, one of which is the use of medical cannabis or cannabinoids. Significant progress was made with the discovery of rimonabant, a selective CB1 receptor (CB1R) antagonist (also an inverse agonist), as a promising therapeutic for SUDs and obesity. However, serious adverse effects such as depression and suicidality led to the withdrawal of rimonabant (and almost all other CB1R antagonists/inverse agonists) from clinical trials worldwide in 2008. Since then, much research interest has shifted to other cannabinoid-based strategies, such as peripheral CB1R antagonists/inverse agonists, neutral CB1R antagonists, allosteric CB1R modulators, CB2R agonists, fatty acid amide hydrolase (FAAH) inhibitors, monoacylglycerol lipase (MAGL) inhibitors, fatty acid binding protein (FABP) inhibitors, or nonaddictive phytocannabinoids with CB1R or CB2R-binding profiles, as new therapeutics for SUDs. In this article, we first review recent progress in research regarding the endocannabinoid systems, cannabis reward versus aversion, and the underlying receptor mechanisms. We then review recent progress in cannabinoid-based medication development for the treatment of SUDs. As evidence continues to accumulate, neutral CB1R antagonists (such as AM4113), CB2R agonists (JWH133, Xie2-64), and nonselective phytocannabinoids (cannabidiol, β-caryophyllene, ∆9-tetrahydrocannabivarin) have shown great therapeutic potential for SUDs, as shown in experimental animals. Several cannabinoid-based medications (e.g., dronabinol, nabilone, PF-04457845) that entered clinical trials have shown promising results in reducing withdrawal symptoms in cannabis and opioid users.

The Cannabinoid CB1 Antagonist TM38837 With Limited Penetrance to the Brain Shows Reduced Fear-Promoting Effects in Mice

Rimonabant was the first selective CB1 antagonist/inverse agonist introduced into clinical practice to treat obesity and metabolic-related disorders. It was withdrawn from market due to the notably increased rates of psychiatric side effects. We have evaluated TM38837, a novel, largely peripherally restricted CB1 antagonist, in terms of fear-promoting consequences of systemic vs. intracerebral injections. Different groups of male C57BL/6 N mice underwent auditory fear conditioning, followed by re-exposure to the tone. Mice were treated per os (p.o.) with TM38837 (10, 30, or 100 mg/kg), rimonabant (10 mg/kg; a brain penetrating CB1 antagonist/inverse agonist which served as a positive control), or vehicle, 2 h prior the tone presentation. Only the high dose of TM38837 (100 mg/kg) induced a significant increase in freezing behavior, similar to that induced by rimonabant (10 mg/kg) (p < 0.001). If injected into the brain both TM38837 (10 or 30 μg/mouse) and rimonabant (1 or 10 μg/mouse) caused a sustained fear response to the tone, which was more pronounced after rimonabant treatment. Taken together, TM38837 was at least one order of magnitude less effective in promoting fear responses than rimonabant. Given the equipotency of the two CB1 antagonists with regard to weight loss and metabolic syndrome-like symptoms in rodent obesity models, our results point to a critical dose range in which TM3887 might be beneficial for indications such as obesity and metabolic disorders with limited risk of fear-promoting effects.

Cannabinoid CB1 receptor neutral antagonist AM4113 inhibits heroin self-administration without depressive side effects in rats

Cannabinoid CB₁ receptors (CB₁Rs) have been shown to be a promising target in medication development for the treatment of addiction. However, clinical trials with SR141716A (rimonabant, a selective CB₁R antagonist/inverse agonist) for the treatment of obesity and smoking cessation failed due to unwanted side effects, such as depression, anxiety, and suicidal tendencies. Recent preclinical studies suggest that the neutral CB₁R antagonist AM4113 may retain the therapeutic anti-addictive effects of SR141716A in nicotine self-administration models and possibly has fewer unwanted side effects. However, little is known about whether AM4113 is also effective for other drugs of abuse, such as opioids and psychostimulants, and whether it produces depressive side effects similar to SR141716A in experimental animals. In this study, we demonstrated that systemic administration of AM4113 (3 and 10 mg/kg) dose-dependently inhibited the self-administration of intravenous heroin but not cocaine or methamphetamine, whereas SR141716A (3 and 10 mg/kg) dose-dependently inhibited the self-administration of heroin and methamphetamine but not cocaine. In the electrical brain-stimulation reward (BSR) paradigm, SR141716A (3 and 10 mg/kg) dose-dependently increased the BSR stimulation threshold (i.e., decreased the stimulation reward), but AM4113 had no effect on BSR at the same doses, suggesting that SR141716A may produce aversive effects while AM4113 may not. Together, these findings show that neutral CB₁R antagonists such as AM4113 deserve further research as a new class of CB₁R-based medications for the treatment of opioid addiction without SR141716A-like aversive effects.

Anti-stress neuropharmacological mechanisms and targets for addiction treatment: A translational framework

Stress-related substance use is a major challenge for treating substance use disorders. This selective review focuses on emerging pharmacotherapies with potential for reducing stress-potentiated seeking and consumption of nicotine, alcohol, marijuana, cocaine, and opioids (i.e., key phenotypes for the most commonly abused substances). I evaluate neuropharmacological mechanisms in experimental models of drug-maintenance and relapse, which translate more readily to individuals presenting for treatment (who have initiated and progressed). An affective/motivational systems model (three dimensions: valence, arousal, control) is mapped onto a systems biology of addiction approach for addressing this problem. Based on quality of evidence to date, promising first-tier neurochemical receptor targets include: noradrenergic (α1 and β antagonist, α2 agonist), kappa-opioid antagonist, nociceptin antagonist, orexin-1 antagonist, and endocannabinoid modulation (e.g., cannabidiol, FAAH inhibition); second-tier candidates may include corticotropin releasing factor-1 antagonists, serotonergic agents (e.g., 5-HT reuptake inhibitors, 5-HT3 antagonists), glutamatergic agents (e.g., mGluR2/3 agonist/positive allosteric modulator, mGluR5 antagonist/negative allosteric modulator), GABA-promoters (e.g., pregabalin, tiagabine), vasopressin 1b antagonist, NK-1 antagonist, and PPAR-γ agonist (e.g., pioglitazone). To address affective/motivational mechanisms of stress-related substance use, it may be advisable to combine agents with actions at complementary targets for greater efficacy but systematic studies are lacking except for interactions with the noradrenergic system. I note clinically-relevant factors that could mediate/moderate the efficacy of anti-stress therapeutics and identify research gaps that should be pursued. Finally, progress in developing anti-stress medications will depend on use of reliable CNS biomarkers to validate exposure-response relationships.

Understanding the implications of the biobehavioral basis of nicotine addiction and its impact on the efficacy of treatment

INTRODUCTION

Tobacco use remains the leading cause of preventable death in the United States. There are efficacious behavioral and pharmacological options for smoking cessation including three FDA approved therapies - nicotine replacement therapy, varenicline and bupropion. Nevertheless, uptake of smoking cessation treatments continues to be poor and there is a need for novel smoking cessation treatments. Areas covered: This article reviews the biobehavioral basis of nicotine addiction, its implications for smoking cessation treatments, the various neurotransmitter systems involved in nicotine addictive effects, and their potential therapeutic value. Included are discussions around the role of genetic factors in predicting response to pharmacotherapy and what we know about appropriate application of pharmacotherapy and behavioral interventions for tobacco use disorder. The evidence for harm reduction measures in individuals who are not willing or able to quit smoking is also reviewed. Expert commentary: Many neurotransmitter system targets have been investigated as a result of our understanding of the underlying neurobiology of tobacco use disorder, and there remain important targets that have yet to be fully explored. rTMS or combination therapies are proposed as possible novel strategies to improve smoking cessation.

When and How to Treat Possible Cannabis Use Disorder

Cannabis (marijuana) is a drug product derived from the plant Cannabis sativa. Cannabinoid is a general term for all chemical constituents of the cannabis plant. Legalization of marijuana in numerous US states, the availability of cannabis of higher potency, and the emergence of synthetic cannabinoids may have contributed to increased demand for related medical services. The most effective available treatments for cannabis use disorder are psychosocial approaches. There is no pharmacotherapy approved treatment. This article reviews the current state of knowledge regarding effective treatments for cannabis use disorder.

Endocannabinoids in Body Weight Control

Maintenance of body weight is fundamental to maintain one's health and to promote longevity. Nevertheless, it appears that the global obesity epidemic is still constantly increasing. Endocannabinoids (eCBs) are lipid messengers that are involved in overall body weight control by interfering with manifold central and peripheral regulatory circuits that orchestrate energy homeostasis. Initially, blocking of eCB signaling by first generation cannabinoid type 1 receptor (CB1) inverse agonists such as rimonabant revealed body weight-reducing effects in laboratory animals and men. Unfortunately, rimonabant also induced severe psychiatric side effects. At this point, it became clear that future cannabinoid research has to decipher more precisely the underlying central and peripheral mechanisms behind eCB-driven control of feeding behavior and whole body energy metabolism. Here, we will summarize the most recent advances in understanding how central eCBs interfere with circuits in the brain that control food intake and energy expenditure. Next, we will focus on how peripheral eCBs affect food digestion, nutrient transformation and energy expenditure by interfering with signaling cascades in the gastrointestinal tract, liver, pancreas, fat depots and endocrine glands. To finally outline the safe future potential of cannabinoids as medicines, our overall goal is to address the molecular, cellular and pharmacological logic behind central and peripheral eCB-mediated body weight control, and to figure out how these precise mechanistic insights are currently transferred into the development of next generation cannabinoid medicines displaying clearly improved safety profiles, such as significantly reduced side effects.

Psychosocial and pharmacological interventions for the treatment of cannabis use disorder

Cannabis use has been continuously increasing, and cannabis use disorder (CUD) has become a public health issue. Some psychosocial interventions have demonstrated the ability to reduce cannabis use; however, there are no pharmacotherapies approved for the treatment of CUD. Some drugs have shown limited positive effects on use and withdrawal symptoms, but no controlled studies have been able to show strong and persistent effects on clinically meaningful outcomes. The aim of this review is to synthesize the evidence from the available literature regarding the effectiveness of psychosocial and pharmacological treatments for CUD among adults (that is, 18 years old or older). An analysis of the evidence shows that the current best psychosocial intervention to reduce cannabis use is the combination of motivational enhancement therapy and cognitive-behavioral therapy, preferably accompanied by a contingency management approach. In regard to pharmacological interventions, there are mostly unclear findings. Some drugs, such as CB1 agonists, gabapentin, and N-acetylcysteine, have been shown to produce improvements in some symptoms of CUD in single studies, but these have not been replicated. Other classes of medications, including antidepressants and antipsychotics, have been unsuccessful in producing such effects. There is an imminent need for more clinical trials to develop more effective treatments for CUD.

The Current State of Pharmacological Treatments for Cannabis Use Disorder and Withdrawal

Cannabis use disorder (CUD) commonly occurs and carries a notable economic and functional burden at both individual and societal levels. While there are no clearly efficacious medication treatments for CUD, 20 years of committed and high-quality research in the human laboratory and clinical settings have resulted in medications with demonstrated effectiveness in the treatment of cannabis withdrawal, the ability to reduce cannabis use, and results that point to promising future work. The current state of pharmacology research for CUD highlights the need to consider particular characteristics of patients, such as gender, impulsivity, and severity of cannabis use, when selecting a medication in the off-label treatment of CUD or cannabis withdrawal. As a field, the body of work also exposes some areas in need of improvement in study design, selection of outcome measures, interpretation of results, and the overall process of evaluating candidate medications. Coming to a consensus as a field and addressing these gaps in future research will likely lend itself to further advances in improving the lives of patients with CUD.

Preclinical Studies of Cannabinoid Reward, Treatments for Cannabis Use Disorder, and Addiction-Related Effects of Cannabinoid Exposure

Cannabis use has become increasingly accepted socially and legally, for both recreational and medicinal purposes. Without reliable information about the effects of cannabis, people cannot make informed decisions regarding its use. Like alcohol and tobacco, cannabis can have serious adverse effects on health, and some people have difficulty discontinuing their use of the drug. Many cannabis users progress to using and becoming addicted to other drugs, but the reasons for this progression are unclear. The natural cannabinoid system of the brain is complex and involved in many functions, including brain development, reward, emotion, and cognition. Animal research provides an objective and controlled means of obtaining information about: (1) how cannabis affects the brain and behavior, (2) whether medications can be developed to treat cannabis use disorder, and (3) whether cannabis might produce lasting changes in the brain that increase the likelihood of becoming addicted to other drugs. This review explains the tactics used to address these issues, evaluates the progress that has been made, and offers some directions for future research.

Medications for substance use disorders (SUD): emerging approaches

INTRODUCTION

Substance use disorders are a group of chronic relapsing disorders of the brain, which have massive public health and societal impact. In some disorders (e.g., heroin/prescription opioid addictions) approved medications have a major long-term benefit. For other substances (e.g., cocaine, amphetamines and cannabis) there are no approved medications, and for alcohol there are approved treatments, which are not in wide usage. Approved treatments for tobacco use disorders are available, and novel medications are also under study. Areas covered: Medication-based approaches which are in advanced preclinical stages, or which have reached proof-of concept clinical laboratory studies, as well as clinical trials. Expert opinion: Current challenges involve optimizing translation between preclinical and clinical development, and between clinical laboratory studies to therapeutic clinical trials. Comorbidities including depression or anxiety are challenges for study design and analysis. Improved pharmacogenomics, biomarker and phenotyping approaches are areas of interest. Pharmacological mechanisms currently under investigation include modulation of glutamatergic, GABA, vasopressin and κ-receptor function, as well as inhibition of monoamine re-uptake. Other factors that affect potential market size for emerging medications include stigma, availability of treatment settings, adoption by clinicians, and the prevalence of persons with SUD who are not actively treatment-seeking.

Cannabinoid-1 receptor neutral antagonist reduces binge-like alcohol consumption and alcohol-induced accumbal dopaminergic signaling

Binge alcohol (ethanol) drinking is associated with profound adverse effects on our health and society. Rimonabant (SR141716A), a CB1 receptor inverse agonist, was previously shown to be effective for nicotine cessation and obesity. However, studies using rimonabant were discontinued as it was associated with an increased risk of depression and anxiety. In the present study, we examined the pharmacokinetics and effects of AM4113, a novel CB1 receptor neutral antagonist on binge-like ethanol drinking in C57BL/6J mice using a two-bottle choice drinking-in-dark (DID) paradigm. The results indicated a slower elimination of AM4113 in the brain than in plasma. AM4113 suppressed ethanol consumption and preference without having significant effects on body weight, ambulatory activity, preference for tastants (saccharin and quinine) and ethanol metabolism. AM4113 pretreatment reduced ethanol-induced increase in dopamine release in nucleus accumbens. Collectively, these data suggest an important role of CB1 receptor-mediated regulation of binge-like ethanol consumption and mesolimbic dopaminergic signaling, and further points to the potential utility of CB1 neutral antagonists for the treatment of binge ethanol drinking.