Stratification of Cannabinoid 1 Receptor (CB1R) Agonist Efficacy: Manipulation of CB1R Density through Use of Transgenic Mice Reveals Congruence between In Vivo and In Vitro Assays

Pharmaco-toxicological effects of the synthetic cannabinoids 4F-ABUTINACA, SDB-005, and JWH-018 in mice. In vitro and in vivo studies

BACKGROUND

Synthetic cannabinoids (SCs) are currently one of the most severely abused new psychoactive substances in the world. However, there remains a notable lack of pharmacological data on the newly emerged synthetic cannabinoids. In the present study, the in vitro and in vivo pharmacological effects of the fourth-generation synthetic cannabinoids 4F-ABUTINACA and SDB-005 are determined and compared to those of the first-generation synthetic cannabinoid JWH-018.

METHODS

In this study, the affinities of three SCs for CB1 receptors were evaluated using surface plasmon resonance (SPR) experiments. The acute toxicity of these three SCs was assessed through the up-and-down procedure, while their cannabinoid-specific pharmacological effects were determined through tetrad assays, which examined parameters such as temperature regulation, analgesia, locomotor activity, and catalepsy. Additionally, conditioned place preference (CPP) experiments and a precipitated withdrawal tests were conducted to assess the psychoactive effects and physical dependence of the SCs.

RESULTS

SPR experiments and acute toxicity tests demonstrated that in vitro KD values were positively correlated with in vivo ED50 potency estimates. All SCs were found to induce the classical "tetrad effects" in a dose-dependent manner. Notably, all SCs displayed significant biphasic effects in CPP experiments. Following the administration of the CB1 receptor antagonist rimonabant, a significant increase in head twitches and paw tremors was observed, indicating that the physical dependence manifested after the ingestion of SCs is mediated by the CB1 receptor.

CONCLUSIONS

These findings suggest that these SCs have cannabinoid-specific pharmacological effects and abuse potential, providing robust experimental data to support future regulatory efforts.

A critical assessment of the abuse, dependence and associated safety risks of naturally occurring and synthetic cannabinoids

Various countries and US States have legalized cannabis, and the use of the psychoactive1 and non-psychoactive cannabinoids is steadily increasing. In this review, we have collated evidence from published non-clinical and clinical sources to evaluate the abuse, dependence and associated safety risks of the individual cannabinoids present in cannabis. As context, we also evaluated various synthetic cannabinoids. The evidence shows that delta-9 tetrahydrocannabinol (Δ9-THC) and other psychoactive cannabinoids in cannabis have moderate reinforcing effects. Although they rapidly induce pharmacological tolerance, the withdrawal syndrome produced by the psychoactive cannabinoids in cannabis is of moderate severity and lasts from 2 to 6 days. The evidence overwhelmingly shows that non-psychoactive cannabinoids do not produce intoxicating, cognitive or rewarding properties in humans. There has been much speculation whether cannabidiol (CBD) influences the psychoactive and potentially harmful effects of Δ9-THC. Although most non-clinical and clinical investigations have shown that CBD does not attenuate the CNS effects of Δ9-THC or synthetic psychoactive cannabinoids, there is sufficient uncertainty to warrant further research. Based on the analysis, our assessment is cannabis has moderate levels of abuse and dependence risk. While the risks and harms are substantially lower than those posed by many illegal and legal substances of abuse, including tobacco and alcohol, they are far from negligible. In contrast, potent synthetic cannabinoid (CB1/CB2) receptor agonists are more reinforcing and highly intoxicating and pose a substantial risk for abuse and harm. 1 "Psychoactive" is defined as a substance that when taken or administered affects mental processes, e.g., perception, consciousness, cognition or mood and emotions.

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

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

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

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

The cannabinoid agonist CB-13 produces peripherally mediated analgesia in mice but elicits tolerance and signs of central nervous system activity with repeated dosing

ABSTRACT

Activation of cannabinoid receptor type 1 (CB 1 ) produces analgesia in a variety of preclinical models of pain; however, engagement of central CB 1 receptors is accompanied by unwanted side effects, such as psychoactivity, tolerance, and dependence. Therefore, some efforts to develop novel analgesics have focused on targeting peripheral CB 1 receptors to circumvent central CB 1 -related side effects. In the present study, we evaluated the effects of acute and repeated dosing with the peripherally selective CB 1 -preferring agonist CB-13 on nociception and central CB 1 -related phenotypes in a model of inflammatory pain in mice. We also evaluated cellular mechanisms underlying CB-13-induced antinociception in vitro using cultured mouse dorsal root ganglion neurons. CB-13 reduced inflammation-induced mechanical allodynia in male and female mice in a peripheral CB 1 -receptor-dependent manner and relieved inflammatory thermal hyperalgesia. In cultured mouse dorsal root ganglion neurons, CB-13 reduced TRPV1 sensitization and neuronal hyperexcitability induced by the inflammatory mediator prostaglandin E 2 , providing potential mechanistic explanations for the analgesic actions of peripheral CB 1 receptor activation. With acute dosing, phenotypes associated with central CB 1 receptor activation occurred only at a dose of CB-13 approximately 10-fold the ED 50 for reducing allodynia. Strikingly, repeated dosing resulted in both analgesic tolerance and CB 1 receptor dependence, even at a dose that did not produce central CB 1 -receptor-mediated phenotypes on acute dosing. This suggests that repeated CB-13 dosing leads to increased CNS exposure and unwanted engagement of central CB 1 receptors. Thus, caution is warranted regarding therapeutic use of CB-13 with the goal of avoiding CNS side effects. Nonetheless, the clear analgesic effect of acute peripheral CB 1 receptor activation suggests that peripherally restricted cannabinoids are a viable target for novel analgesic development.

Sex-specific mechanisms of tolerance for the cannabinoid agonists CP55,940 and delta-9-tetrahydrocannabinol (Δ9-THC)

RATIONALE

Tolerance to cannabinoids could limit their therapeutic potential. Male mice expressing a desensitization-resistant form (S426A/S430A) of the type-1 cannabinoid receptor (CB1R) show delayed tolerance to delta-9-tetrahydrocannabinol (∆9-THC) but not CP55,940. With more women than men using medical cannabis for pain relief, it is essential to understand sex differences in cannabinoid antinociception, hypothermia, and resultant tolerance.

OBJECTIVE

Our objective was to determine whether female mice rely on the same molecular mechanisms for tolerance to the antinociceptive and/or hypothermic effects of cannabinoids that we have previously reported in males. We determined whether the S426A/S430A mutation differentially disrupts antinociceptive and/or hypothermic tolerance to CP55,940 and/or Δ9-THC in male and female S426A/S430A mutant and wild-type littermates.

RESULTS

The S426A/S430A mutation conferred an enhanced antinociceptive response for ∆9-THC and CP55,940 in both male and female mice. While the S426A/S430A mutation conferred partial resistance to ∆9-THC tolerance in male mice, disruption of CB1R desensitization had no effect on tolerance to ∆9-THC in female mice. The mutation did not alter tolerance to the hypothermic effects of ∆9-THC or CP55,940 in either sex. Interestingly, female mice were markedly less sensitive to the antinociceptive effects of 30 mg/kg ∆9-THC and 0.3 mg/kg CP55,940 compared with male mice.

CONCLUSIONS

Our results suggest that disruption of the GRK/βarrestin2 pathway of desensitization alters tolerance to Δ9-THC but not CP55,940 in male but not female mice. As tolerance to Δ9-THC appears to develop differently in males and females, sex should be considered when assessing the therapeutic potential and dependence liability of cannabinoids.

Medicinal Cannabis and Central Nervous System Disorders

Cannabinoids, including those found in cannabis, have shown promise as potential therapeutics for numerous health issues, including pathological pain and diseases that produce an impact on neurological processing and function. Thus, cannabis use for medicinal purposes has become accepted by a growing majority. However, clinical trials yielding satisfactory endpoints and unequivocal proof that medicinal cannabis should be considered a frontline therapeutic for most examined central nervous system indications remains largely elusive. Although cannabis contains over 100 + compounds, most preclinical and clinical research with well-controlled dosing and delivery methods utilize the various formulations of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), the two most abundant compounds in cannabis. These controlled dosing and delivery methods are in stark contrast to most clinical studies using whole plant cannabis products, as few clinical studies using whole plant cannabis profile the exact composition, including percentages of all compounds present within the studied product. This review will examine both preclinical and clinical evidence that supports or refutes the therapeutic utility of medicinal cannabis for the treatment of pathological pain, neurodegeneration, substance use disorders, as well as anxiety-related disorders. We will predominately focus on purified THC and CBD, as well as other compounds isolated from cannabis for the aforementioned reasons but will also include discussion over those studies where whole plant cannabis has been used. In this review we also consider the current challenges associated with the advancement of medicinal cannabis and its derived potential therapeutics into clinical applications.

Medicinal Cannabis and Central Nervous System Disorders

Cannabinoids, including those found in cannabis, have shown promise as potential therapeutics for numerous health issues, including pathological pain and diseases that produce an impact on neurological processing and function. Thus, cannabis use for medicinal purposes has become accepted by a growing majority. However, clinical trials yielding satisfactory endpoints and unequivocal proof that medicinal cannabis should be considered a frontline therapeutic for most examined central nervous system indications remains largely elusive. Although cannabis contains over 100 + compounds, most preclinical and clinical research with well-controlled dosing and delivery methods utilize the various formulations of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), the two most abundant compounds in cannabis. These controlled dosing and delivery methods are in stark contrast to most clinical studies using whole plant cannabis products, as few clinical studies using whole plant cannabis profile the exact composition, including percentages of all compounds present within the studied product. This review will examine both preclinical and clinical evidence that supports or refutes the therapeutic utility of medicinal cannabis for the treatment of pathological pain, neurodegeneration, substance use disorders, as well as anxiety-related disorders. We will predominately focus on purified THC and CBD, as well as other compounds isolated from cannabis for the aforementioned reasons but will also include discussion over those studies where whole plant cannabis has been used. In this review we also consider the current challenges associated with the advancement of medicinal cannabis and its derived potential therapeutics into clinical applications.

Astroglial CB1 Cannabinoid Receptors Mediate CP 55,940-Induced Conditioned Place Aversion Through Cyclooxygenase-2 Signaling in Mice

Cannabinoids (CBs), such as phytocannabinoids, synthetic CBs, and endogenous CBs, can be neuroprotective, rewarding, or aversive. The aversive effects of CBs may hinder their medical and recreational applications. It is unknown which type of CB receptors mediates the direct aversive effects of synthetic CB CP 55,940 which is an analog of Δ9-tetrahydrocannabinol, the major psychoactive component of marijuana. In this study, we address this question by taking the advantage of systematic type 1 CB receptor (CB1R) knockout mice and conditional reinstatement of this receptor only in astrocytes. We show that CP 55,940 at a concentration of 1 mg/kg induces conditioned place aversion (CPA) and the CPA effect of CP 55,940 is mediated by the astroglial CB1Rs. Inhibiting cyclooxygenase-2 (COX-2) eliminates CP 55,940-induced CPA in mice that only express CB1Rs in astrocytes. These findings conclude that CPA effect of CP 55,940 is mediated by the astroglial CB1Rs through COX-2 signaling, suggesting that selective COX-2 inhibition or precise isolation of astroglial CB1R activity may be the strategy for treating aversive response of medical and recreational administrations of marijuana.

Computational Approach Reveals Pronociceptive Potential of Cannabidiol in Osteoarthritis: Role of Transient Receptor Potential Channels

Systems pharmacology employs computational and mathematical methods to study the network of interactions a drug may have within complex biological pathways. These tools are well suited for research on multitarget drugs, such as natural compounds, in diseases with complex etiologies, such as osteoarthritis (OA). The present study focuses on cannabidiol (CBD), a non-psychoactive constituent of cannabis, targeting over 60 distinct molecular targets as a potential treatment for OA, a degenerative joint disease leading to chronic pain with a neuropathic component. We successfully identified molecular targets of CBD that were relevant in the context of OA treatment with both beneficial and detrimental effects. Our findings were confirmed by in vivo and molecular studies. A key role of PPARγ in mediating the therapeutic potential of CBD was revealed, whereas upregulation of multiple transient receptor potential channels demasked CBD-induced heat hyperalgesia. Our findings pave the way for novel CBD-based therapy with improved therapeutic potential but also encourage the use of bioinformatic tools to predict the mechanism of action of CBD in different conditions. We have also created an accessible web tool for analogous analysis of CBD pharmacology in the context of any disease of interest and made it publicly available.

Molecular Mechanisms of Action of Novel Psychoactive Substances (NPS). A New Threat for Young Drug Users with Forensic-Toxicological Implications

Novel psychoactive substances (NPS) represent a severe health risk for drug users. Even though the phenomenon has been growing since the early 2000s, the mechanisms of action of NPS at the receptors and beyond them are still scarcely understood. The aim of the present study was to provide a systematic review of the updated knowledge regarding the molecular mechanisms underlying the toxicity of synthetic opioids, cannabinoids, cathinones, and stimulants. The study was conducted on the PubMed database. Study eligibility criteria included relevance to the topic, English language, and time of publication (2010–2020). A combined Mesh and free-text protocols search was performed. Study selection was performed on the title/abstract and, in doubtful cases, on the full texts of papers. Of the 580 records identified through PubMed searching and reference checking, 307 were excluded by title/abstract and 78 additional papers were excluded after full-text reading, leaving a total of 155 included papers. Molecular mechanisms of synthetic opioids, synthetic cannabinoids, stimulants, psychedelics, and hallucinogens were reviewed and mostly involved both a receptor-mediated and non-receptor mediated cellular modulation with multiple neurotransmitters interactions. The molecular mechanisms underlying the action of NPS are more complex than expected, with a wide range of overlap among activated receptors and neurotransmitter systems. The peculiar action profile of single compounds does not necessarily reflect that of the structural class to which they belong, accounting for possible unexpected toxic reactions.

Behavioral Battery for Testing Candidate Analgesics in Mice. II. Effects of Endocannabinoid Catabolic Enzyme Inhibitors and ∆9-Tetrahydrocannabinol

Enhanced signaling of the endocannabinoid (eCB) system through inhibition of the catabolic enzymes monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) has received increasing interest for development of candidate analgesics. This study compared effects of MAGL and FAAH inhibitors with effects of ∆9-tetrahydrocannabinol (THC) using a battery of pain-stimulated, pain-depressed, and pain-independent behaviors in male and female mice. Intraperitoneal injection of dilute lactic acid (IP acid) served as an acute visceral noxious stimulus to stimulate two behaviors (stretching, facial grimace) and depress two behaviors (rearing, nesting). Nesting and locomotion were also assessed in the absence of IP acid as pain-independent behaviors. THC and a spectrum of six eCB catabolic enzyme inhibitors ranging from MAGL- to FAAH-selective were assessed for effectiveness to alleviate pain-related behaviors at doses that did not alter pain-independent behaviors. The MAGL-selective inhibitor MJN110 produced the most effective antinociceptive profile, with 1.0 mg/kg alleviating IP acid effects on stretching, grimace, and nesting without altering pain-independent behaviors. MJN110 effects on IP acid-depressed nesting had a slow onset and long duration (40 minutes to 6 hours), were blocked by rimonabant, and tended to be greater in females. As inhibitors increased in FAAH selectivity, antinociceptive effectiveness decreased. PF3845, the most FAAH-selective inhibitor, produced no antinociception up to doses that disrupted locomotion. THC decreased IP acid-stimulated stretching and grimace at doses that did not alter pain-independent behaviors; however, it did not alleviate IP acid-induced depression of rearing or nesting. These results support further consideration of MAGL-selective inhibitors as candidate analgesics for acute inflammatory pain. SIGNIFICANCE STATEMENT: This study characterized a spectrum of endocannabinoid catabolic enzyme inhibitors ranging in selectivity from monoacylglycerol lipase-selective to fatty acid amide hydrolase-selective in a battery of pain-stimulated, pain-depressed, and pain-independent behaviors previously pharmacologically characterized in a companion paper. This battery provides a method for prioritizing candidate analgesics by effectiveness to alleviate pain-related behaviors at doses that do not alter pain-independent behaviors, with inclusion of pain-depressed behaviors increasing translational validity and decreasing susceptibility to motor-depressant false positives.

Untapped endocannabinoid pharmacological targets: Pipe dream or pipeline?

It has been established that the endogenous cannabinoid (endocannabinoid) system plays key modulatory roles in a wide variety of pathological conditions. The endocannabinoid system comprises both cannabinoid receptors, their endogenous ligands including 2-arachidonoylglycerol (2-AG), N-arachidonylethanolamine (anandamide, AEA), and enzymes that regulate the synthesis and degradation of endogenous ligands which include diacylglycerol lipase alpha (DAGL-α), diacylglycerol lipase beta (DAGL-β), fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), α/β hydrolase domain 6 (ABHD6). As the endocannabinoid system exerts considerable involvement in the regulation of homeostasis and disease, much effort has been made towards understanding endocannabinoid-related mechanisms of action at cellular, physiological, and pathological levels as well as harnessing the various components of the endocannabinoid system to produce novel therapeutics. However, drug discovery efforts within the cannabinoid field have been slower than anticipated to reach satisfactory clinical endpoints and raises an important question into the validity of developing novel ligands that therapeutically target the endocannabinoid system. To answer this, we will first examine evidence that supports the existence of an endocannabinoid system role within inflammatory diseases, neurodegeneration, pain, substance use disorders, mood disorders, as well as metabolic diseases. Next, this review will discuss recent clinical studies, within the last 5 years, of cannabinoid compounds in context to these diseases. We will also address some of the challenges and considerations within the cannabinoid field that may be important in the advancement of therapeutics into the clinic.

Manipulating Pharmacodynamic Efficacy with Agonist + Antagonist Mixtures: In Vitro and In Vivo Studies with Opioids and Cannabinoids

Pharmacodynamic efficacy of drugs to activate their receptors is a key determinant of drug effects, and intermediate-efficacy agonists are often useful clinically because they retain sufficient efficacy to produce therapeutically desirable effects while minimizing undesirable effects. Molecular mechanisms of efficacy are not well understood, so rational drug design to control efficacy is not yet possible; however, receptor theory predicts that fixed-proportion mixtures of an agonist and antagonist for a given receptor can be adjusted to precisely control net efficacy of the mixture in activating that receptor. Moreover, the agonist proportion required to produce different effects provides a quantitative scale for comparing efficacy requirements across those effects. To test this hypothesis, the present study evaluated effectiveness of fixed-proportion agonist/antagonist mixtures to produce in vitro and in vivo effects mediated by μ-opioid receptors (MOR) and cannabinoid type 1 receptors (CB1R). Mixtures of 1) the MOR agonist fentanyl and antagonist naltrexone and 2) the CB1R agonist CP55,940 and antagonist/inverse agonist rimonabant were evaluated in an in vitro assay of ligand-stimulated guanosine 5'-O-(3-[35S]thio)triphosphate binding and an in vivo assay of thermal nociception in mice. For both agonist/antagonist pairs in both assays, increasing agonist proportions produced graded increases in maximal mixture effects, and lower agonist proportions were sufficient to produce in vivo than in vitro effects. These findings support the utility of agonist-antagonist mixtures as a strategy to control net efficacy of receptor activation and to quantify and compare efficacy requirements across a range of in vitro and in vivo endpoints. SIGNIFICANCE STATEMENT: Manipulation of agonist proportion in agonist/antagonist mixtures governs net mixture efficacy at the target receptor. Parameters of agonist/antagonist mixture effects can provide a quantitative metric for comparison of efficacy requirements across a wide range of conditions.

Further evidence of anxiety- and depression-like behavior for total genetic ablation of cannabinoid receptor type 1

Cannabinoid receptor type 1 (CB1R) is the most abundant cannabinoid receptor in central nervous system. Clinical studies and animal models have shown that the attenuation of endocannabinoid system signaling correlates with the development of psychiatric disorders such as anxiety, depression and schizophrenia. In the present work, multiple behavioral tests were performed to evaluate behaviors related to anxiety and depression in CB1R^+/- and CB1R^-/-. CB1R^+/- mice had anxiety-related behavior similar to wild type (CB1R^+/+) mice, whereas CB1R^-/- mice displayed an anxious-like phenotype, which indicates that lower expression of CB1R is sufficient to maintain the neural circuits modulating anxiety. In addition, CB1R^-/- mice exhibited alterations in risk assessment and less exploration, locomotion, grooming, body weight and appetite. These phenotypic characteristics observed in CB1R^-/- mice could be associated with symptoms observed in human psychiatric disorders such as depression. A better knowledge of the neuromodulatory role of CB1R may contribute to understand scope and limitations of the development of medical treatments.

Δ9-tetrahydrocannabinol: Drug discrimination abuse liability testing in female Lister Hooded rats: Trials, tribulations and triumphs

INTRODUCTION

The assessment of the abuse potential of CNS-active drugs is a regulatory requirement. Drug discrimination is one of the nonclinical tests that contribute to this assessment by providing information on a drug's potential to induce a discriminative stimulus comparable to that of a known drug of abuse.

AIM

The objective was to validate drug discrimination in the rat for the purpose of supporting regulatory submissions for novel drugs with potential cannabinoid-like activity.

METHODS

Ten female Lister hooded rats were trained to discriminate no-drug from Δ⁹-THC (1.5 mg/kg, IP) under a FR10 schedule of reinforcement. Once trained, a Δ⁹-THC dose-response curve was obtained using doses of 0.25, 0.75, 1.5, and 3 mg/kg, IP. This was followed by evaluation of amphetamine (0.3 mg/kg, SC); morphine (3 mg/kg, IP); midazolam (2.5 mg/kg, PO); and the synthetic cannabinoids WIN55,212-2 (0.75 to 2 mg/kg, IP), CP-47,497 (0.5 to 2 mg/kg, IP), and JWH-018 (1 mg/kg, IP) for their discriminative stimulus similarity to Δ⁹-THC.

RESULTS

Pharmacological specificity was demonstrated by achieving the anticipated dose-response curve for Δ⁹-THC, and a vehicle-like response for the non-cannabinoid drugs. Although full generalisation was obtained for JWH-018, in contrast to published literature, WIN55,212-2 and CP-47,497 failed to generalise to Δ⁹-THC.

DISCUSSION

Based on the literature review performed in light of the results obtained, contrasting and unpredictable behavioural responses produced by cannabinoids in animals and humans raises the question of the reliability and relevance of including drug discrimination and self-administration studies within an abuse potential assessment for novel cannabinoid-like drugs.

Heteromer formation between cannabinoid type 1 and dopamine type 2 receptors is altered by combination cannabinoid and antipsychotic treatments

The cannabinoid type 1 (CB₁ ) receptor and the dopamine type 2 (D₂ ) receptor are co-localized on medium spiny neuron terminals in the globus pallidus where they modulate neural circuits involved in voluntary movement. Physical interactions between the two receptors have been shown to alter receptor signaling in cell culture. The objectives of the current study were to identify the presence of CB₁ /D₂ heteromers in the globus pallidus of C57BL/6J male mice, define how CB₁ /D₂ heteromer levels are altered following treatment with cannabinoids and/or antipsychotics, and determine if fluctuating levels of CB₁ /D₂ heteromers have functional consequences. Using in situ proximity ligation assays, we observed CB₁ /D₂ heteromers in the globus pallidus of C57BL/6J mice. The abundance of the heteromers increased following treatment with the nonselective cannabinoid receptor agonist, CP55,940. In contrast, treatment with the typical antipsychotic haloperidol reduced the number of CB₁ /D₂ heteromers, whereas the atypical antipsychotic olanzapine treatment had no effect. Co-treatment with CP55,940 and haloperidol had similar effects to haloperidol alone, whereas co-treatment with CP55,940 and olanzapine had similar effects to CP55,940. The observed changes were found to have functional consequences as the differential effects of haloperidol and olanzapine also applied to γ-aminobutyric acid release in STHdh^Q7/Q7 cells and motor function in C57BL/6J male mice. This work highlights the clinical relevance of co-exposure to cannabinoids and different antipsychotics over acute and prolonged time periods.

The short-acting synthetic cannabinoid AB-FUBINACA induces physical dependence in mice

BACKGROUND

Recent years have seen a rise in the diversity and use of synthetic cannabinoids. The present study evaluated the behavioral effects of the third-generation indazole-3-carboxamide-type synthetic cannabinoid, AB-FUBINACA.

METHODS

Adult male and female C57BL/6J mice were treated with AB-FUBINACA (0-3 mg/kg, i.p.) and tested repeatedly in the tetrad battery measuring catalepsy, antinociception, hypothermia, and locomotor activity. Mice treated with AB-FUBINACA (≥2 mg/kg, i.p.) displayed classic cannabinoid effects in the tetrad that were blocked by the CB₁ receptor selective antagonist rimonabant. To address tolerance and withdrawal effects, a second group of mice was injected with AB-FUBINACA (3 mg/kg, s.c.) or vehicle consisting of 5% ethanol, 5% Kolliphor EL, and 90 % saline every 12 h and tested daily in modified tetrad over the course of 5 days. On the 6th day, withdrawal was precipitated using rimonabant (3 mg/kg, s.c.), and somatic signs of withdrawal (i.e., head twitches and paw tremors) were quantified.

RESULTS

Although mice did not develop tolerance to AB-FUBINACA or cross-tolerance to Δ⁹-tetrahydrocannabinol (THC; 50 mg/kg, i.p.), somatic precipitated withdrawal signs were observed. Repeated tetrad testing up to 48 h post injection indicated that AB-FUBINACA effects are relatively short-lived, as compared with THC. Brain levels of AB-FUBINACA, as quantified by UHPLC-MS/MS, were undetectable 4 h post injection.

CONCLUSIONS

These data indicate that the cannabinoid effects of AB-FUBINACA are relatively short-lived, yet sufficient to induce dependence in mice.

In vitro and in vivo pharmacological evaluation of the synthetic cannabinoid receptor agonist EG-018

Synthetic cannabinoid receptor agonists (SCRAs) possess high abuse liability and complex toxicological profiles, making them serious threats to public health. EG-018 is a SCRA that has been detected in both illicit products and human samples, but it has received little attention to date. The current studies investigated EG-018 at human CB₁ and CB₂ receptors expressed in HEK293 cells in [³H]CP55,940 competition binding, [³⁵S]GTPγS binding and forskolin-stimulated cAMP production. EG-018 was also tested in vivo for its ability to produce cannabimimetic and abuse-related effects in the cannabinoid tetrad and THC drug discrimination, respectively. EG-018 exhibited high affinity at CB₁ (21 nM) and at CB₂ (7 nM), but in contrast to typical SCRAs, behaved as a weak partial agonist in [³⁵S]GTPγS binding, exhibiting lower efficacy but greater potency, than that of THC at CB₁ and similar potency and efficacy at CB₂. EG-018 inhibited forskolin-stimulated cAMP with similar efficacy but lower potency, compared to THC, which was likely due to high receptor density facilitating saturation of this signaling pathway. In mice, EG-018 (100 mg/kg, 30 min) administered intraperitoneally (i.p.) did not produce effects in the tetrad or drug discrimination nor did it shift THC's ED₅₀ value in drug discrimination when administered before THC, suggesting EG-018 has negligible occupancy of brain CB₁ receptors following i.p. administration. Following intravenous (i.v.) administration, EG-018 (56 mg/kg) produced hypomotility, catalepsy, and hypothermia, but only catalepsy was blocked by the selective CB₁ antagonist rimonabant (3 mg/kg, i.v.). Additional studies of EG-018 and its structural analogues could provide further insight into how cannabinoids exert efficacy through the cannabinoid receptors.

In vitro and in vivo pharmacological evaluation of the synthetic cannabinoid receptor agonist EG-018

Synthetic cannabinoid receptor agonists (SCRAs) possess high abuse liability and complex toxicological profiles, making them serious threats to public health. EG-018 is a SCRA that has been detected in both illicit products and human samples, but it has received little attention to date. The current studies investigated EG-018 at human CB₁ and CB₂ receptors expressed in HEK293 cells in [³H]CP55,940 competition binding, [³⁵S]GTPγS binding and forskolin-stimulated cAMP production. EG-018 was also tested in vivo for its ability to produce cannabimimetic and abuse-related effects in the cannabinoid tetrad and THC drug discrimination, respectively. EG-018 exhibited high affinity at CB₁ (21 nM) and at CB₂ (7 nM), but in contrast to typical SCRAs, behaved as a weak partial agonist in [³⁵S]GTPγS binding, exhibiting lower efficacy but greater potency, than that of THC at CB₁ and similar potency and efficacy at CB₂. EG-018 inhibited forskolin-stimulated cAMP with similar efficacy but lower potency, compared to THC, which was likely due to high receptor density facilitating saturation of this signaling pathway. In mice, EG-018 (100 mg/kg, 30 min) administered intraperitoneally (i.p.) did not produce effects in the tetrad or drug discrimination nor did it shift THC's ED₅₀ value in drug discrimination when administered before THC, suggesting EG-018 has negligible occupancy of brain CB₁ receptors following i.p. administration. Following intravenous (i.v.) administration, EG-018 (56 mg/kg) produced hypomotility, catalepsy, and hypothermia, but only catalepsy was blocked by the selective CB₁ antagonist rimonabant (3 mg/kg, i.v.). Additional studies of EG-018 and its structural analogues could provide further insight into how cannabinoids exert efficacy through the cannabinoid receptors.

Molecular Mechanism and Cannabinoid Pharmacology

Since antiquity, Cannabis has provoked enormous intrigue for its potential medicinal properties as well as for its unique pharmacological effects. The elucidation of its major cannabinoid constituents, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), led to the synthesis of new cannabinoids (termed synthetic cannabinoids) to understand the mechanisms underlying the pharmacology of Cannabis. These pharmacological tools were instrumental in the ultimate discovery of the endogenous cannabinoid system, which consists of CB1 and CB2 cannabinoid receptors and endogenously produced ligands (endocannabinoids), which bind and activate both cannabinoid receptors. CB1 receptors mediate the cannabimimetic effects of THC and are highly expressed on presynaptic neurons in the nervous system, where they modulate neurotransmitter release. In contrast, CB2 receptors are primarily expressed on immune cells. The endocannabinoids are tightly regulated by biosynthetic and hydrolytic enzymes. Accordingly, the endocannabinoid system plays a modulatory role in many physiological processes, thereby generating many promising therapeutic targets. An unintended consequence of this research was the emergence of synthetic cannabinoids sold for human consumption to circumvent federal laws banning Cannabis use. Here, we describe research that led to the discovery of the endogenous cannabinoid system and show how knowledge of this system benefitted as well as unintentionally harmed human health.

Disruption of an enhancer associated with addictive behaviour within the cannabinoid receptor-1 gene suggests a possible role in alcohol intake, cannabinoid response and anxiety-related behaviour

The cannabinoid-1 receptor (CB₁) plays a critical role in a number of biological processes including nutrient intake, addiction and anxiety-related behaviour. Numerous studies have shown that expression of the gene encoding CB1 (CNR1) is highly dynamic with changes in the tissue specific expression of CNR1 associated with brain homeostasis and disease progression. However, little is known of the mechanisms regulating this dynamic expression. To gain a better understanding of the genomic mechanisms modulating the expression of CNR1 in health and disease we characterised the role of a highly conserved regulatory sequence (ECR1) in CNR1 intron 2 that contained a polymorphism in linkage disequilibrium with disease associated SNPs. We used CRISPR/CAS9 technology to disrupt ECR1 within the mouse genome. Disruption of ECR1 significantly reduced CNR1 expression in the hippocampus but not in the hypothalamus. These mice also displayed an altered sex-specific anxiety-related behavioural profile (open field test), reduced ethanol intake and a reduced hypothermic response following CB₁ agonism. However, no significant changes in feeding patterns were detected. These data suggest that, whilst not all of the expression of CNR1 is modulated by ECR1, this highly conserved enhancer is required for appropriate physiological responses to a number of stimuli. The combination of comparative genomics and CRISPR/CAS9 disruption used in our study to determine the functional effects of genetic and epigenetic changes on the activity of tissue-specific regulatory elements at the CNR1 locus represent an important first step in gaining a mechanistic understanding of cannabinoid regulatory pharmacogenetics.

Synthetic cannabinoids nano-micelles for the management of triple negative breast cancer

Triple-negative breast cancer (TNBC) is a highly heterogeneous disease with poor prognosis and inadequate therapeutic outcome. This contribution reports the use of a cannabinoid derivative, WIN55,212-2 (WIN) on the growth of TNBC in a 4T1 syngeneic mouse model. To reduce the well-known psychoactive side effects of cannabinoids, we prepared a nanomicellar formulation of WIN (SMA-WIN). In vivo biodistribution, in silico ADME predictions, anticancer activity, and psychoactive effect of WIN and SMA-WIN studies suggest that SMA-WIN formulation can reduce to greater extent tumor growth with milder psychoactive side effects when compared to free drug. Finally, the effects of WIN and SMA-WIN in combination with doxorubicin (Doxo), an established chemotherapeutic agent for the treatment of TNBC, were investigated in vitro and in vivo. SMA-WIN in combination with Doxo showed therapeutic efficacy and was able to reduce the tumor volume of TNBC murine model drastically. Moreover, SMA-WIN, while favoring drug tumor accumulation, minimized the adverse psychoactive effects that have impeded the use of this agent in the clinic. To our knowledge, this is the first report for the assessment of cannabinoid nanoparticles in vivo for the treatment of TNBC and its enhanced anticancer effect at low doses with Doxo. These findings suggest a new therapeutic strategy in the management of TNBC.

Finding order in chemical chaos - Continuing characterization of synthetic cannabinoid receptor agonists

Diversion of synthetic cannabinoids from the lab to drugs of abuse has become increasingly prevalent in recent years. Moreover, as earlier synthetic cannabinoids were banned, manufacturers introduced a new supply of novel compounds to serve as replacements. Hence, the chemical diversity of synthetic cannabinoid analogs has also rapidly increased. The present study examined 8 new synthetic cannabinoids: AM-1220, AM-2232, AM-2233, AM-679, EAM-2201, JWH-210, JHW-251, and MAM-2201. Each compound was assessed for binding affinity and functional activation of CB₁ and CB₂ receptors, and pharmacological equivalence with Δ⁹-tetrahydrocannabinol (THC) in THC drug discrimination. All compounds bound to and activated CB₁ and CB₂ receptors, although efficacy at the CB₂ receptor was reduced compared to that for the CB₁ receptor. Similarly, all compounds stimulated [³⁵S]GTPγS binding through the CB₁ receptor, and all compounds except AM-1220 and AM-2233 stimulated [³⁵S]GTPγS binding through the CB₂ receptor. Furthermore, these compounds, along with CP55,940, substituted for THC in THC drug discrimination. Rank order of potency in drug discrimination was correlated with CB₁ receptor binding affinity. Together, these results suggest that all test compounds share the THC-like subjective effects of marijuana. Interestingly, the most potent compounds in CB₁ binding in the present study were also the compounds that have been found recently in the U.S., MAM-2201, EAM-2201, JWH-210, AM-2233, and AM-1220. These results indicate that the evolution of the synthetic cannabinoid drug market may be focused toward compounds with increased potency. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'

Application of Receptor Theory to the Design and Use of Fixed-Proportion Mu-Opioid Agonist and Antagonist Mixtures in Rhesus Monkeys

Receptor theory predicts that fixed-proportion mixtures of a competitive, reversible agonist (e.g., fentanyl) and antagonist (e.g., naltrexone) at a common receptor [e.g., mu-opioid receptors (MORs)] will result in antagonist proportion-dependent decreases in apparent efficacy of the agonist/antagonist mixtures and downward shifts in mixture dose-effect functions. The present study tested this hypothesis by evaluating behavioral effects of fixed-proportion fentanyl/naltrexone mixtures in a warm-water tail-withdrawal procedure in rhesus monkeys (n = 4). Fentanyl (0.001-0.056 mg/kg) alone, naltrexone (0.032-1.0 mg/kg, i.m.) alone, and fixed-proportion mixtures of fentanyl/naltrexone (1:0.025, 1:0.074, and 1:0.22) were administered in a cumulative-dosing procedure, and the proportions were based on published fentanyl and naltrexone Kd values at MOR in monkey brain. Fentanyl alone produced dose-dependent antinociception at both 50 and 54°C thermal intensities. Up to the largest dose tested, naltrexone alone did not alter nociception. Consistent with receptor theory predictions, naltrexone produced a proportion-dependent decrease in the effectiveness of fentanyl/naltrexone mixtures to produce antinociception. The maximum effects of fentanyl, naltrexone, and each mixture were also used to generate an efficacy-effect scale for antinociception at each temperature, and this scale was evaluated for its utility in quantifying 1) efficacy requirements for antinociception at 50 and 54°C and 2) relative efficacy of six MOR agonists that vary in their efficacies to produce agonist-stimuated GTPγS binding in vitro (from lowest to highest efficacy: 17-cyclopropylmethyl-3,14β-dihyroxy-4,5α-epoxy-6α-[(3'-isoquinolyl)acetamindo]morphine, nalbuphine, buprenorphine, oxycodone, morphine, and methadone). These results suggest that fixed-proportion agonist/antagonist mixtures may offer a useful strategy to manipulate apparent drug efficacy for basic research or therapeutic purposes.

Molecular Understanding of the Activation of CB1 and Blockade of TRPV1 Receptors: Implications for Novel Treatment Strategies in Osteoarthritis

Osteoarthritis (OA) is a joint disease in which cartilage degenerates as a result of mechanical and biochemical changes. The main OA symptom is chronic pain involving both peripheral and central mechanisms of nociceptive processing. Our previous studies have implicated the benefits of dual- over single-acting compounds interacting with the endocannabinoid system (ECS) in OA treatment. In the present study, we focused on the specific molecular alterations associated with pharmacological treatment. OA was induced in Wistar rats by intra-articular injection of 3 mg of monoiodoacetate (MIA). Single target compounds (URB597, an FAAH inhibitor, and SB366791, a TRPV1 antagonist) and a dual-acting compound OMDM198 (FAAH inhibitor/TRPV1 antagonist) were used in the present study. At day 21 post-MIA injection, rats were sacrificed 1 h after i.p. treatment, and changes in mRNA expression were evaluated in the lumbar spinal cord by RT-qPCR. Following MIA administration, we observed 2-4-fold increase in mRNA expression of targeted receptors (Cnr1, Cnr2, and Trpv1), endocannabinoid degradation enzymes (Faah, Ptgs2, and Alox12), and TRPV1 sensitizing kinases (Mapk3, Mapk14, Prkcg, and Prkaca). OMDM198 treatment reversed some of the MIA effects on the spinal cord towards intact levels (Alox12, Mapk14, and Prkcg). Apparent regulation of ECS and TRPV1 in response to pharmacological intervention is a strong justification for novel ECS-based multi-target drug treatment in OA.

Gender-specific association of functional prodynorphin 68 bp repeats with cannabis exposure in an African American cohort

BACKGROUND

Cannabis use disorders (CUDs) cause substantial neuropsychiatric morbidity and comorbidity. There is evidence for gender-based differences in CUDs, for instance, a greater prevalence in males than in females. The main active component of cannabis is delta 9-tetrahydrocannabinol (delta 9-THC), a partial agonist of the cannabinoid type 1 receptor. Preclinical studies show that genetic or pharmacological manipulation of the kappa opioid receptor/dynorphin system modulates the effects of delta 9-THC.

METHODS

In this case-control study of adult African Americans (n=476; 206 females, 270 males), we examined the association of the functional prodynorphin 68 bp (PDYN 68 bp) promoter repeats with categorical diagnoses of cannabis dependence (Diagnostic and Statistical Manual of Mental Disorders-IV criteria), as well as with a rapid dimensional measure of maximum lifetime cannabis exposure (the Kreek-McHugh-Schluger-Kellogg cannabis scale).

RESULTS

The PDYN 68 bp genotype (examined as short-short [SS], short-long [SL], or long-long [LL], based on the number of repeats) was not significantly associated with categorical cannabis-dependence diagnoses, either in males or in females. However, in males, the PDYN 68 bp SS+SL genotype was associated with both greater odds of any use of cannabis (p<0.05) and earlier age of first cannabis use, compared to the LL genotype (ie, 15 versus 16.5 years of age; p<0.045). Males in the SS+SL group also had greater odds of high lifetime exposure to cannabis, compared to the LL group (p<0.045). Of interest, none of the aforementioned genetic associations were significant in females.

CONCLUSION

This study provides the first data on how the PDYN 68 bp genotype is associated with gender-specific patterns of exposure to cannabis. Overall, this study shows that PDYN 68 bp polymorphisms affect behaviors involved in early stages of nonmedical cannabis use and potentially lead to increasing self-exposure. These data may eventually lead to improvements in personalized medicine for the prevention and treatment of highly prevalent CUDs and neuropsychiatric comorbidities.

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.

Finding order in chemical chaos - Continuing characterization of synthetic cannabinoid receptor agonists

Diversion of synthetic cannabinoids from the lab to drugs of abuse has become increasingly prevalent in recent years. Moreover, as earlier synthetic cannabinoids were banned, manufacturers introduced a new supply of novel compounds to serve as replacements. Hence, the chemical diversity of synthetic cannabinoid analogs has also rapidly increased. The present study examined 8 new synthetic cannabinoids: AM-1220, AM-2232, AM-2233, AM-679, EAM-2201, JWH-210, JHW-251, and MAM-2201. Each compound was assessed for binding affinity and functional activation of CB₁ and CB₂ receptors, and pharmacological equivalence with Δ⁹-tetrahydrocannabinol (THC) in THC drug discrimination. All compounds bound to and activated CB₁ and CB₂ receptors, although efficacy at the CB₂ receptor was reduced compared to that for the CB₁ receptor. Similarly, all compounds stimulated [³⁵S]GTPγS binding through the CB₁ receptor, and all compounds except AM-1220 and AM-2233 stimulated [³⁵S]GTPγS binding through the CB₂ receptor. Furthermore, these compounds, along with CP55,940, substituted for THC in THC drug discrimination. Rank order of potency in drug discrimination was correlated with CB₁ receptor binding affinity. Together, these results suggest that all test compounds share the THC-like subjective effects of marijuana. Interestingly, the most potent compounds in CB₁ binding in the present study were also the compounds that have been found recently in the U.S., MAM-2201, EAM-2201, JWH-210, AM-2233, and AM-1220. These results indicate that the evolution of the synthetic cannabinoid drug market may be focused toward compounds with increased potency. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'

Approaches to Assess Biased Signaling at the CB1R Receptor

G protein-coupled receptors, such as the cannabinoid type 1 receptor (CB1R), have been shown to interact with multiple binding partners to transmit signals. In both transfected cell systems and in endogenously expressing cell lines, CB1R signaling has been described as multifaceted. The question remains as to how this highly widely expressed receptor signals in a given cell at a given time in vivo. The concept of functional selectivity, or biased agonism, describes the ability of an agonist to engage the receptor in a manner that preferentially engages certain signaling interactions (e.g., G proteins) over others (e.g., β-arrestins), presumably by stabilizing certain receptor conformations. There is growing interest in using such properties of ligands to direct signaling downstream of CB1R toward desirable therapeutic outcomes and to avoid adverse side effects. While it is not currently clear what pathways should be engaged and which should be avoided, the development of biased agonist tool compounds will aid in answering these questions. In this chapter, we discuss the approaches and caveats to assessing biased agonism at the CB1R.

Apparent CB1 Receptor Rimonabant Affinity Estimates: Combination with THC and Synthetic Cannabinoids in the Mouse In Vivo Triad Model

Synthetic cannabinoids (SCs) represent an emerging class of abused drugs associated with psychiatric complications and other substantial health risks. These ligands are largely sold over the internet for human consumption, presumably because of their high cannabinoid 1 receptor (CB1R) affinity and their potency in eliciting pharmacological effects similar to Δ9-tetrahydrocannabinol (THC), as well as circumventing laws illegalizing this plant. Factors potentially contributing to the increased prevalence of SC abuse and related hospitalizations, such as increased CB1R efficacy and non-CB1R targets, highlight the need for quantitative pharmacological analyses to determine receptor mediation of the pharmacological effects of cannabinoids. Accordingly, the present study used pA2 and pKB analyses for quantitative determination of CB1R mediation in which we utilized the CB1R-selective inverse agonist/antagonist rimonabant to elicit rightward shifts in the dose-response curves of five SCs (i.e., A-834,735D; WIN55,212-2; CP55,950; JWH-073; and CP47,497) and THC in producing common cannabimimetic effects (i.e., catalepsy, antinociception, and hypothermia). The results revealed overall similarity of pA2 and pKB values for these compounds and suggest that CB1Rs, and not other pharmacological targets, largely mediated the central pharmacological effects of SCs. More generally, affinity estimation offers a powerful pharmacological approach to assess potential receptor heterogeneity subserving in vivo pharmacological effects of SCs.

Thermolytic Degradation of Synthetic Cannabinoids: Chemical Exposures and Pharmacological Consequences

Synthetic cannabinoids are manufactured clandestinely with little quality control and are distributed as herbal "spice" for smoking or as bulk compound for mixing with a solvent and inhalation via electronic vaporizers. Intoxication with synthetic cannabinoids has been associated with seizure, excited delirium, coma, kidney damage, and other disorders. The chemical alterations produced by heating these structurally novel compounds for consumption are largely unknown. Here, we show that heating synthetic cannabinoids containing tetramethylcyclopropyl-ring substituents produced thermal degradants with pharmacological activity that varied considerably from their parent compounds. Moreover, these degradants were formed under conditions simulating smoking. Some products of combustion retained high affinity at the cannabinoid 1 (CB1) and CB2 receptors, were more efficacious than (-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol (CP55,940) in stimulating CB1 receptor-mediated guanosine 5'-O-(3-thiotriphosphate) (GTPγS) binding, and were potent in producing Δ9-tetrahydrocannabinol-like effects in laboratory animals, whereas other compounds had low affinity and efficacy and were devoid of cannabimimetic activity. Degradants that retained affinity and efficacy also substituted in drug discrimination tests for the prototypical synthetic cannabinoid 1-pentyl-3-(1-naphthoyl)indole (JWH-018), and are likely to produce psychotropic effects in humans. Hence, it is important to take into consideration the actual chemical exposures that occur during use of synthetic cannabinoid formulations to better comprehend the relationships between dose and effect.

Synthetic Pot: Not Your Grandfather's Marijuana

In the early 2000s in Europe and shortly thereafter in the USA, it was reported that 'legal' forms of marijuana were being sold under the name K2 and/or Spice. Active ingredients in K2/Spice products were determined to be synthetic cannabinoids (SCBs), producing psychotropic actions via CB1 cannabinoid receptors, similar to those of Δ9-tetrahydrocannabinol (Δ9-THC), the primary active constituent in marijuana. Often abused by adolescents and military personnel to elude detection in drug tests due to their lack of structural similarity to Δ9-THC, SCBs are falsely marketed as safe marijuana substitutes. Instead, SCBs are a highly structural diverse group of compounds, easily synthesized, which produce very dangerous adverse effects occurring by, as of yet, unknown mechanisms. Therefore, available evidence indicates that K2/Spice products are clearly not safe marijuana alternatives.

Comparison of the discriminative stimulus and response rate effects of Δ9-tetrahydrocannabinol and synthetic cannabinoids in female and male rats

BACKGROUND

Women report greater sensitivity to the subjective effects of Δ⁹-tetrahydrocannabinol (THC). Similarly, female rodents tend to be more sensitive to some pharmacological effects of THC and synthetic cannabinoids. This study examined sex differences in discriminative stimulus and response rate effects of THC and synthetic cannabinoids in rats.

METHODS

A cumulative dosing THC discrimination procedure was utilized to evaluate sex differences in the discriminative stimulus effects of THC and three synthetic cannabinoids: CP47,497, WIN55,212-2, and JWH-018. Sex differences in the effects of these four compounds and a degradant of A-834735 on response rates also were assessed in a food-reinforced discrete dosing procedure.

RESULTS

Females required a lower training dose than males for acquisition of the discrimination. Further, THC was more potent at producing rimonabant-reversible discriminative stimulus and response rate effects in females. While synthetic cannabinoids were more potent in producing THC-like effects than was THC in female rats, greater discrepancies were observed in male rats. Similar sensitivity to the response rate-decreasing effects induced by most, but not all (A-834735 degradant), synthetic cannabinoids was seen in both sexes.

CONCLUSIONS

This study represents one of the first direct comparisons of sex differences in THC discrimination. Females were more sensitive to THC's effects, which may be related, in part, to sex differences in THC metabolism. Synthetic cannabinoids were more potent than THC in both sexes, but were considerably more so in male than in female rats. Future research should emphasize further characterization of sex differences in cannabinoid pharmacology.