Cannabinoid Receptor Ligands Research Articles

Endocannabinoid regulation of inward rectifier potassium (Kir) channels.

The inward rectifier potassium channel Kir2.1 (KCNJ2) is an important regulator of resting membrane potential in both excitable and non-excitable cells. The functions of Kir2.1 channels are dependent on their lipid environment, including the availability of PI(4,5)P2, secondary anionic lipids, cholesterol and long-chain fatty acids acyl coenzyme A (LC-CoA). Endocannabinoids are a class of lipids that are naturally expressed in a variety of cells, including cardiac, neuronal, and immune cells. While these lipids are identified as ligands for cannabinoid receptors there is a growing body of evidence that they can directly regulate the function of numerous ion channels independently of CBRs. Here we examine the effects of a panel of endocannabinoids on Kir2.1 function and demonstrate that a subset of endocannabinoids can alter Kir2.1 conductance to varying degrees independently of CBRs. Using computational and Surface plasmon resonance analysis, endocannabinoid regulation of Kir2.1 channels appears to be the result of altered membrane properties, rather than through direct protein-lipid interactions. Furthermore, differences in endocannabinoid effects on Kir4.1 and Kir7.1 channels, indicating that endocannabinoid regulation is not conserved among Kir family members. These findings may have broader implications on the function of cardiac, neuronal and/or immune cells.

Exploring Cannabinoids with Enhanced Binding Affinity for Targeting the Expanded Endocannabinoid System: A Promising Therapeutic Strategy for Alzheimer's Disease Treatment.

Despite decades of rigorous research and numerous clinical trials, Alzheimer's disease (AD) stands as a notable healthcare challenge of this century, with effective therapeutic solutions remaining elusive. Recently, the endocannabinoid system (ECS) has emerged as an essential therapeutic target due to its regulatory role in different physiological processes, such as neuroprotection, modulation of inflammation, and synaptic plasticity. This aligns with previous research showing that cannabinoid receptor ligands have the potential to trigger the functional structure of neuronal and brain networks, potentially impacting memory processing. Therefore, our study aims to assess the effects of prolonged, intermittent exposure (over 90 days) to JWH-133 (0.2 mg/kg) and an EU-GMP certified Cannabis sativa L. (Cannabixir® Medium Flos, 2.5 mg/kg) on recognition memory, as well as their influence on brain metabolism and modulation of the expanded endocannabinoid system in APP/PS1 mice. Chronic therapy with cannabinoid receptor ligands resulted in reduced anxiety-like behavior and partially reversed the cognitive deficits. Additionally, a reduction was observed in both the number and size of Aβ plaque deposits, along with decreased cerebral glucose metabolism, as well as a decline in the expression of mTOR and CB2 receptors. Furthermore, the study revealed enlarged astrocytes and enhanced expression of M1 mAChR in mice subjected to cannabinoid treatment. Our findings highlight the pivotal involvement of the extended endocannabinoid system in cognitive decline and pathological aspects associated with AD, presenting essential preclinical evidence to support the continued exploration and assessment of cannabinoid receptor ligands for AD treatment.

A Robust and Efficient FRET-Based Assay for Cannabinoid Receptor Ligands Discovery.

The identification of new modulators for Cannabinoid Receptors (CBRs) has garnered significant attention in drug discovery over recent years, owing to their manifold pathophysiological implications. In the context of hit identification, the availability of robust and sensitive high-throughput screening assays is essential to enhance the likelihood of success. In this study, we present the development and validation of a Tag-lite® binding assay designed for screening hCB1/hCB2 binding, employing a dual fluorescent ligand, CELT-335. Representative ligands for CBRs, exhibiting diverse affinity and functional profiles, were utilized as reference compounds to validate the robustness and efficiency of the newly developed Tag-lite® binding assay protocol. The homogeneous format, coupled with the sensitivity and optimal performance of the fluorescent ligand CELT-335, establishes this assay as a viable and reliable method for screening in hit and lead identification campaigns.

IUPHAR review- Preclinical models of neuropathic pain: Evaluating multifunctional properties of natural cannabinoid receptors ligands

Neuropathic pain remains prevalent and challenging to manage and is often comorbid with depression and anxiety. The new approach that simultaneously targets neuropathic pain and the associated comorbidities, such as depression and anxiety, is timely and critical, given the high prevalence and severity of neuropathic pain and the lack of effective analgesics. In this review, we focus on the animal models of neuropathic pain that researchers have used to investigate the analgesic effects of cannabidiol (CBD) and Beta-Caryophyllene (BCP) individually and in combination while addressing the impact of these compounds on the major comorbidity (e.g., depression, anxiety) associated with neuropathic pain. We also addressed the potential targets/mechanisms by which CBD and BCP produce analgesic effects in neuropathic pain models. The preclinical studies examined in this review support CBD and BCP individually and combined as potential alternative analgesics for neuropathic pain while showing beneficial effects on depression and anxiety.

Non-Intoxicating Cannabinoids in Visceral Pain.

Cannabis and cannabis products are becoming increasingly popular options for symptom management of inflammatory bowel diseases, particularly abdominal pain. While anecdotal and patient reports suggest efficacy of these compounds for these conditions, clinical research has shown mixed results. To date, clinical research has focused primarily on delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is a ligand of classical cannabinoid receptors (CBRs). CBD is one of a large group of nonintoxicating cannabinoids (niCBs) that mediate their effects on both CBRs and through non-CBR mechanisms of action. Because they are not psychotropic, there is increasing interest and availability of niCBs. The numerous niCBs show potential to rectify abnormal intestinal motility as well as have anti-inflammatory and analgesic effects. The effects of niCBs are frequently not mediated by CBRs, but rather through actions on other targets, including transient receptor potential channels and voltage-gated ion channels. Additionally, evidence suggests that niCBs can be combined to increase their potency through what is termed the entourage effect. This review examines the pre-clinical data available surrounding these niCBs in treatment of abdominal pain with a focus on non-CBR mechanisms.

Cannabinoid CB2 receptor ligands disrupt the sequential regulation of p-MEK1/2 to p-ERK1/2 in mouse brain cortex

Aim: The sequential phosphorylation of mitogen-activated protein (MAP) kinases MEK-ERK is the most relevant cellular signaling pathway. This study quantified the parallel in vivo regulation of brain phosphorylation-MEK1/2 (p-MEK1/2) to p-ERK1/2 by mechanistically different cannabinoid 2 (CB2) receptor ligands, i.e., direct (and endogenous) agonists and inverse agonists. Methods: Groups of Swiss albino CD1 IGS male adult mice were treated (i.p.) with the CB2 agonist JWH133 (1 mg/kg and 3 mg/kg, 1 h, n = 8) or the CB2 inverse agonist/antagonist AM630 (0.3 mg/kg and 1 mg/kg, 1.5 h, n = 8–9), and 0.9% NaCl (2 mL/kg, 1 h, n = 4–10) as vehicle control. Transgenic male mice overexpressing cortical CB2 receptors [messenger RNA (mRNA) and protein] on a Swiss ICR congenic background (CB2xP) and the corresponding littermates age-matched wild-type (WT) controls were used. Protein forms (total MEK and ERK p-kinases) were resolved by electrophoresis [sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) minigels] followed by immunoblotting standard procedures. Results: The selective CB2 agonist JWH133 (1 mg/kg and 3 mg/kg, i.p., 1 h) modestly decreased MEK (17%, n = 8) and upregulated ERK (25%, n = 8) activities. The endogenous CB2 agonists (acting on promoted overexpressed receptors) decreased MEK (44%, n = 9) and upregulated ERK (67%, n = 10) activities. The inverse agonist/antagonist AM630 (0.3 mg/kg and 1 mg/kg, i.p., 1.5 h) increases MEK activity (27%, n = 8) without significantly altering that of ERK (5%, n = 9). Conclusions: Acute treatments of mice with mechanistically different CB2 receptor ligands (i.e., direct agonists, endogenous agonists, and inverse agonists) resulted in disruption of MEK (p-MEK/total-MEK ratio) to ERK (p-ERK/total-ERK ratio) signals in the brain cortex. This striking disruption of MEK to ERK parallel regulation in the cannabinoid CB2 receptor system in the brain could be relevant to the postulated role of CB2 receptors in various central nervous system (CNS) diseases.

GPR18, GPR55 and GPR119 in GtoPdb v.2023.1

GPR18, GPR55 and GPR119 (provisional nomenclature), although showing little structural similarity to CB1 and CB2 cannabinoid receptors, respond to endogenous agents analogous to the endogenous cannabinoid ligands, as well as some natural/synthetic cannabinoid receptor ligands [104]. Although there are multiple reports to indicate that GPR18, GPR55 and GPR119 can be activated in vitro by N-arachidonoylglycine, lysophosphatidylinositol and N-oleoylethanolamide, respectively, there is a lack of evidence for activation by these lipid messengers in vivo. As such, therefore, these receptors retain their orphan status.

Novel putative ligands of cannabinoid receptors: synthesis and effects on cell signaling and neuronal functions

Cannabinoid ligands are known to possess neuroprotective actions and may have utility in the treatment of neurodegeneration. The major targets for cannabinoids include the classical CB1 cannabinoid receptor, as well as the novel cannabinoid receptor GPR55 which binds to many synthetic cannabinoid ligands. In this study, novel thiopyranothiazoles 1, 3, 4, 6, and 7 were synthesized and their pharmacological activity as potential cannabinoid-like ligands was evaluated in glioblastoma cells, cultured cortical neurons, and cells of HEK293 line expressing GPR55. Stimulation of protein kinase ERK1/2, MAP-kinases and cAMP response element binding protein (CREB) was evaluated using Western-blot analysis, CREB activation was additionally monitored by means of confocal imaging of nuclear phospho-CREB labeling. Docking simulation confirmed the good affinity of the synthesized compounds to CB1 and CB2 receptors. Striking effects of the chromeno[4′,3′:4,5]thiopyrano[2,3-d][1,3]thiazol with ethylacetate moiety (3) and isothiochromeno[4a,4-d]thiazole with phenazone fragment (7) on pCREB activation as the indicator of stimulation of the pathway beneficial for neurons survival were observed. Keywords: cAMP response element binding protein (CREB), CB1, CB2, cultured cortical neurons, putative cannabinoid ligands, thiopyranothiazoles

Endocannabinoid regulation of inward rectifier (Kir2.1) channels.

The inward rectifier potassium channel Kir2.1 (KCNJ2) is an important regulator of resting membrane potential in both excitable and non-excitable cells. The function of Kir2.1 channels are dependent on their lipid environment, including the availability of PI(4,5)P2, secondary anionic lipids, cholesterol and long-chain fatty acids acyl coenzyme A (LC-CoA). Endocannabinoids are a class of lipids that are naturally expressed in a variety of cells, including cardiac, neuronal, and immune cells. While these lipids are identified as ligands for cannabinoid receptors (CBRs), there is a growing body of evidence that they can directly regulate the function of numerous ion channels independently of CBRs. Here we examine the effects of a panel of endocannabinoids on Kir2.1 function, and demonstrate that a subset of endocannabinoids can alter Kir2.1 conductance to varying degrees independently of CBRs. These findings may have broader implications on the function of cardiac, neuronal and/or immune cells.

Development of Yin-Yang ligand for cannabinoid receptors

Cannabinoid receptors (CBs), including CB1 and CB2, are the key components of a lipid signaling endocannabinoid system (ECS). Development of synthetic cannabinoids has been attractive to modulate ECS functions. CB1 and CB2 are structurally closely related subtypes but with distinct functions. While most efforts focus on the development of selective ligands for single subtype to circumvent the undesired off-target effect, Yin-Yang ligands with opposite pharmacological activities simultaneously on two subtypes, offer unique therapeutic potential. Herein we report the development of a new Yin-Yang ligand which functions as an antagonist for CB1 and concurrently an agonist for CB2. We found that in the pyrazole-cored scaffold, the arm of N1-phenyl group could be a switch, modification of which yielded various ligands with distinct activities. As such, the ortho-morpholine substitution exerted the desired Yin-Yang bifunctionality which, based on the docking study and molecular dynamic simulation, was proposed to be resulted from the hydrogen bonding with S173 and S285 in CB1 and CB2, respectively. Our results demonstrated the feasibility of structure guided ligand evolution for challenging Yin-Yang ligand.

Cannabinoids: new friends in bone fracture and in joint disease prevention?

n recent years the endocannabinoid system (ES) has been recognized to play an important role in the regulation of several physiological processes, including pain perception, appetite control, and motor function development. This system has recently been recognized to be present in bone and joint tissues, playing a role in the regulation of bone and joint physiology. The ES seems to play its role mainly by acting on its receptors and thanks to the demonstrated ability of bone cells to synthesize the principal endocannabinoids (i.e., anandamide and 2-arachidonoylglycerol), which can act on bone remodeling and metabolism. Cannabinoids have also been shown to be produced within synovial tissues, and recent studies have shown that cannabinoid receptor ligands are effective in the treatment of inflammatory arthritis. In recent years synthetic endocannabinoid-like compounds and phytocannabinoids, which are the principal components of Cannabis sativa, have also started to be studied as molecules that could play a role not only in bone physiology, but also in the pathogenesis of osteoporosis, the most common bone disease, and in the inflammatory processes underlying osteoarthritis. Accumulating evidence that cannabinoids and their receptors play an important role in bone metabolism and in the regulation of the immune response is now starting to show us the true future therapeutic potential of cannabinoids, and of the phytocannabinoids contained in Cannabis sativa, in the treatment of bone loss and joint diseases. Here we summarize the role of the cannabinoids and their receptors in bone metabolism, osteoporosis, and joint disease.

Multi-omics gut microbiome signatures in obese women: role of diet and uncontrolled eating behavior

BackgroundObesity and related co-morbidities represent a major health challenge nowadays, with a rapidly increasing incidence worldwide. The gut microbiome has recently emerged as a key modifier of human health that can affect the development and progression of obesity, largely due to its involvement in the regulation of food intake and metabolism. However, there are still few studies that have in-depth explored the functionality of the human gut microbiome in obesity and even fewer that have examined its relationship to eating behaviors.MethodsIn an attempt to advance our knowledge of the gut-microbiome-brain axis in the obese phenotype, we thoroughly characterized the gut microbiome signatures of obesity in a well-phenotyped Italian female cohort from the NeuroFAST and MyNewGut EU FP7 projects. Fecal samples were collected from 63 overweight/obese and 37 normal-weight women and analyzed via a multi-omics approach combining 16S rRNA amplicon sequencing, metagenomics, metatranscriptomics, and lipidomics. Associations with anthropometric, clinical, biochemical, and nutritional data were then sought, with particular attention to cognitive and behavioral domains of eating.ResultsWe identified four compositional clusters of the gut microbiome in our cohort that, although not distinctly associated with weight status, correlated differently with eating habits and behaviors. These clusters also differed in functional features, i.e., transcriptional activity and fecal metabolites. In particular, obese women with uncontrolled eating behavior were mostly characterized by low-diversity microbial steady states, with few and poorly interconnected species (e.g., Ruminococcus torques and Bifidobacterium spp.), which exhibited low transcriptional activity, especially of genes involved in secondary bile acid biosynthesis and neuroendocrine signaling (i.e., production of neurotransmitters, indoles and ligands for cannabinoid receptors). Consistently, high amounts of primary bile acids as well as sterols were found in their feces.ConclusionsBy finding peculiar gut microbiome profiles associated with eating patterns, we laid the foundation for elucidating gut-brain axis communication in the obese phenotype. Subject to confirmation of the hypotheses herein generated, our work could help guide the design of microbiome-based precision interventions, aimed at rewiring microbial networks to support a healthy diet-microbiome-gut-brain axis, thus counteracting obesity and related complications.

Docking and Molecular Dynamic Investigations of Phenylspirodrimanes as Cannabinoid Receptor-2 Agonists.

Cannabinoid receptor ligands are renowned as being therapeutically crucial for treating diverse health disorders. Phenylspirodrimanes are meroterpenoids with unique and varied structural scaffolds, which are mainly reported from the Stachybotrys genus and display an array of bioactivities. In this work, 114 phenylspirodrimanes reported from Stachybotrys chartarum were screened for their CB2 agonistic potential using docking and molecular dynamic simulation studies. Compound 56 revealed the highest docking score (-11.222 kcal/mol) compared to E3R_6KPF (native agonist, gscore value -12.12 kcal/mol). The molecular docking and molecular simulation results suggest that compound 56 binds to the putative binding site in the CB2 receptor with good affinity involving key interacting amino acid residues similar to that of the native ligands, E3R. The molecular interactions displayed π-π stacking with Phe183 and hydrogen bond interactions with Thr114, Leu182, and Ser285. These findings identified the structural features of these metabolites that might lead to the design of selective novel ligands for CB2 receptors. Additionally, phenylspirodrimanes should be further investigated for their potential as a CB2 ligand.

Therapeutic potential of cannabinoids for stroke: scoping review protocol

Introduction: Each year, approximately 795,000 people experience a new or recurrent stroke, either ischemic or hemorrhagic. The current therapeutical approach for acute ischemic stroke includes thrombolysis and mechanical thrombectomy; still, no neuroprotective treatment options currently exist to improve its neurological outcome. Some components of the endocannabinoid system are altered after ischemic stroke. It is considered that cannabinoids may exert neuroprotective effects; however, the use of cannabinoid receptor ligands is a major concern due to its psychotropic properties. Regardless that there are many studies describing the benefit of administering cannabinoids for experimental stroke several unanswered questions remain since most of the information point up in non-human species. A previous systematic review detected significant heterogeneity among studies, so it is appropriate to perform a scoping review to evaluate the feasibility of performing an updated systematic review and meta-analysis. This scoping review aims to evaluate the therapeutic potential of modulating the endocannabinoid system for stroke. Methods: Published studies (all publication types) will be retrieved from Web of Science, PubMed, Scopus, Ovid, EBSCOhost, and Google Scholar. Eligibility criteria: Clinical or preclinical studies reporting endocannabinoid levels or their effects, or reporting administration of cannabinoid modulators (stimulating or inhibiting their synthesis or metabolism, phytocannabinoids, or synthetic cannabinoids), in patients or models of stroke will be considered for inclusion. Studies written in languages different than Spanish or English that could not be appropriately translated, or whose full-text files could not be retrieved will be excluded. Data charting: Results will be summarized in tabular form. This protocol complies with PRISMA-P.

Therapeutic potential of cannabinoids for stroke: scoping review protocol

Introduction: Each year, approximately 795,000 people experience a new or recurrent stroke, either ischemic or hemorrhagic. The current therapeutical approach for acute ischemic stroke includes thrombolysis and mechanical thrombectomy; still, no neuroprotective treatment options currently exist to improve its neurological outcome. Some components of the endocannabinoid system are altered after ischemic stroke. It is considered that cannabinoids may exert neuroprotective effects; however, the use of cannabinoid receptor ligands is a major concern due to its psychotropic properties. Regardless that there are many studies describing the benefit of administering cannabinoids for experimental stroke several unanswered questions remain since most of the information point up in non-human species. A previous systematic review detected significant heterogeneity among studies, so it is appropriate to perform a scoping review to evaluate the feasibility of performing an updated systematic review and meta-analysis. This scoping review aims to evaluate the therapeutic potential of modulating the endocannabinoid system for stroke. Methods: Published studies (all publication types) will be retrieved from Web of Science, PubMed, Scopus, Ovid, EBSCOhost, and Google Scholar. Eligibility criteria: Clinical or preclinical studies reporting endocannabinoid levels or their effects, or reporting administration of cannabinoid modulators (stimulating or inhibiting their synthesis or metabolism, phytocannabinoids, or synthetic cannabinoids), in patients or models of stroke will be considered for inclusion. Studies written in languages different than Spanish or English that could not be appropriately translated, or whose full-text files could not be retrieved will be excluded. Data charting: Results will be summarized in tabular form. This protocol complies with PRISMA-P.

Non-Canonical Cannabinoid Receptors with Distinct Binding and Signaling Properties in Prostate and Other Cancer Cell Types Mediate Cell Death.

Cannabinoids exert anti-cancer actions; however, the underlying cytotoxic mechanisms and the cannabinoid receptors (CBRs) involved remain unclear. In this study, CBRs were characterized in several cancer cell lines. Radioligand binding screens surprisingly revealed specific binding only for the non-selective cannabinoid [3H]WIN-55,212-2, and not [3H]CP-55,940, indicating that the expressed CBRs exhibit atypical binding properties. Furthermore, [3H]WIN-55,212-2 bound to a single site in all cancer cells with high affinity and varying densities. CBR characteristics were next compared between human prostate cancer cell lines expressing low (PC-3) and high (DU-145) CBR density. Although mRNA for canonical CBRs was detected in both cell lines, only 5 out of 15 compounds with known high affinity for canonical CBRs displaced [3H]WIN-55,212-2 binding. Functional assays further established that CBRs in prostate cancer cells exhibit distinct signaling properties relative to canonical Gi/Go-coupled CBRs. Prostate cancer cells chronically exposed to both CBR agonists and antagonists/inverse agonists produced receptor downregulation, inconsistent with actions at canonical CBRs. Treatment of DU-145 cells with CBR ligands increased LDH-release, decreased ATP-dependent cell viability, and produced mitochondrial membrane potential depolarization. In summary, several cancer cell lines express CBRs with binding and signaling profiles dissimilar to canonical CBRs. Drugs selectively targeting these atypical CBRs might exhibit improved anti-cancer properties.

Endocannabinoid regulation of Kir2.1 inward rectifier potassium channels

The inward rectifier potassium channel Kir2.1 (KCNJ2) is an important regulator of resting membrane potential in both excitable and non-excitable cells. The function of Kir2.1 channels is dependent on their lipid environment, including the availability of PI(4,5)P2, secondary anionic lipids, cholesterol and long-chain fatty acids acyl coenzyme A (LC-CoA). Endocannabinoids are a class of lipids that are naturally expressed in a variety of cells, including cardiac, neuronal, and immune cells. While these lipids are identified as ligands for cannabinoid receptors (CBRs), there is growing body of evidence that they can directly regulate the function of numerous ion channels independently of CBRs.

Age-related changes in CB1 receptor expression and function and the behavioral effects of cannabinoid receptor ligands

Cannabinoid use has increased among aging individuals. However, little information on age-related differences in the behavioral effects of these agents is available. To explore potential differences in the behavioral effects of cannabinoids, we determined effects of Δ9-tetrahydrocannabinol (THC, 1–10 mg/kg) or rimonabant (0.3–3.2 mg/kg) on operant fixed-ratio responding (FR10) for food in young adult (6 months) and aged (29 months) rats. THC dose-dependently decreased responding for food. Rimonabant alone had little or no effect on responding up to 1.0 mg/kg, but disrupted responding following a 3.2 mg/kg dose. Rimonabant (1.0 mg/kg) partially antagonized response disruption by THC. These effects were similar in young adult and aged rats. However, aging has been reported to change the neurobiology of cannabinoid CB1 receptors. To confirm our rats exhibited such differences, we assessed CB1 receptor binding sites and function in six subcortical (caudate, nucleus accumbens CA1, and CA2/CA3), and three cortical regions (medial prefrontal, temporal, entorhinal) in young adult (6 months) or aged (26 months) male Lewis rats using quantitative autoradiography. CB1 receptor binding sites were reduced in cortical, but not subcortical brain regions of aged rats. CB1 receptor function, at the level of receptor-G protein interaction, was not different in any region studied. Results indicate that down-regulation of CB1 receptor binding sites observed in cortical regions of aged rats was not accompanied by a commensurate decrease in CB1 receptor-stimulated [35S]GTPγS binding, suggesting a compensatory increase in receptor function in cortical areas. Together, our results provide additional evidence of age-related changes in central CB1 receptor populations. However, the functional compensation for decreased CB1 receptor binding may mitigate changes in behavioral effects of cannabinoids. With the rising use of cannabinoid-based therapeutics among aging populations, further evaluation of age-related changes in the cannabinoid system and the impact of these changes on effects of this class of drugs is warranted.

Endocannabinoid system components: A crucial role in regulation of disease

Endocannabinoids (ECs) are characterized as the endogenous ligands of cannabinoid recep-tors (CRs). The research in the field of the endocannabinoid system (ECS) has forecasted a promising role that ECS could play in developing an understanding and management of nu-merous physiological disorders and several diseases. There is a range of analytical techniques that have proved to be fruitful in diagnosing and learning the metabolic and pathological role of these receptors/mediators through various

Covalent cannabinoid receptor ligands - structural insight and selectivity challenges.

X-ray crystallography and cryogenic electronic microscopy have provided significant advancement in the knowledge of GPCR structure and have allowed the rational design of GPCR ligands. The class A GPCRs cannabinoid receptor type 1 and type 2 are implicated in many pathophysiological processes and thus rational design of drug and tool compounds is of great interest. Recent structural insight into cannabinoid receptors has already led to a greater understanding of ligand binding sites and receptor residues that likely contribute to ligand selectivity. Herein, classes of heterocyclic covalent cannabinoid receptor ligands are reviewed in light of the recent advances in structural knowledge of cannabinoid receptors, with particular discussion regarding covalent ligand selectivity and rationale design.