Cannabinoid CB2 receptor ligand profiling reveals biased signalling and off-target activity

RAMP and MRAP accessory proteins have selective effects on expression and signalling of the CB1, CB2, GPR18 and GPR55 cannabinoid receptors

BACKGROUND AND PURPOSE

Receptor activity-modifying proteins (RAMPs) and melanocortin receptor accessory proteins (MRAPs) modulate expression and signalling of calcitonin and melanocortin GPCRs. Interactions with other GPCRs have also been reported. The cannabinoid receptors, CB1 and CB2, and two putative cannabinoid receptors, GPR18 and GPR55, exhibit substantial intracellular expression and there are discrepancies in ligand responsiveness between studies. We investigated whether interactions with RAMPs or MRAPs could explain these phenomena.

EXPERIMENTAL APPROACH

Receptors and accessory proteins were co-expressed in HEK-293 cells. Selected receptors were studied at basal expression levels and also with enhanced expression produced by incorporation of a preprolactin signal sequence/peptide (pplss). Cell surface and total expression of receptors and accessory proteins were quantified using immunocytochemistry. Signalling was measured using cAMP (CAMYEL) and G protein dissociation (TRUPATH Gα13) biosensors.

KEY RESULTS

MRAP2 enhanced surface and total expression of GPR18. Pplss-GPR18 increased detection of cell surface MRAP2. MRAP1α and MRAP2 reduced GPR55 surface and total expression, correlating with reduced constitutive, but not agonist-induced, signalling. GPR55, pplss-CB1 and CB2 reduced detection of MRAP1α at the cell surface. Pplss-CB1 agonist potency was reduced by MRAP2 in Gα13 but not cAMP assays, consistent with MRAP2 reducing pplss-CB1 expression. Some cannabinoid receptors increased RAMP2 or RAMP3 total expression without influencing surface expression.

CONCLUSIONS AND IMPLICATIONS

Mutual influences on expression and/or function for specific accessory protein-receptor pairings raises the strong potential for physiological and disease-relevant consequences. Sequestration and/or hetero-oligomerisation of cannabinoid receptors with accessory proteins is a possible novel mechanism for receptor crosstalk.

LINKED ARTICLES

This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Cannabinoid CB2 receptor orthologues; in vitro function and perspectives for preclinical to clinical translation

Cannabinoid CB2 receptor agonists are in development as therapeutic agents, including for immune modulation and pain relief. Despite promising results in rodent preclinical studies, efficacy in human clinical trials has been marginal to date. Fundamental differences in ligand engagement and signalling responses between the human CB2 receptor and preclinical model species orthologues may contribute to mismatches in functional outcomes. This is a tangible possibility for the CB2 receptor in that there is a relatively large degree of primary amino acid sequence divergence between human and rodent. Here, we summarise CB2 receptor gene and protein structure, assess comparative molecular pharmacology between CB2 receptor orthologues, and review the current status of preclinical to clinical translation for drugs targeted at the CB2 receptor, focusing on comparisons between human, mouse and rat receptors. We hope that raising wider awareness of, and proposing strategies to address, this additional challenge in drug development will assist in ongoing efforts toward successful therapeutic translation of drugs targeted at the CB2 receptor. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Potent, Selective Agonists for the Cannabinoid-like Orphan G Protein-Coupled Receptor GPR18: A Promising Drug Target for Cancer and Immunity

The human orphan G protein-coupled receptor GPR18, activated by Δ9-tetrahydrocannabinol (THC), constitutes a promising drug target in immunology and cancer. However, studies on GPR18 are hampered by the lack of suitable tool compounds. In the present study, potent and selective GPR18 agonists were developed showing low nanomolar potency at human and mouse GPR18, determined in β-arrestin recruitment assays. Structure-activity relationships were analyzed, and selectivity versus cannabinoid (CB) and CB-like receptors was assessed. Compound 51 (PSB-KK1415, EC50 19.1 nM) was the most potent GPR18 agonist showing at least 25-fold selectivity versus CB receptors. The most selective GPR18 agonist 50 (PSB-KK1445, EC50 45.4 nM) displayed >200-fold selectivity versus both CB receptor subtypes, GPR55, and GPR183. The new GPR18 agonists showed minimal species differences, while THC acted as a weak partial agonist at the mouse receptor. The newly discovered compounds represent the most potent and selective GPR18 agonists reported to date.

Patent review of cannabinoid receptor type 2 (CB2R) modulators (2016-present)

INTRODUCTION

Cannabinoid receptor type 2 (CB2R), predominantly expressed in immune tissues, is believed to play a crucial role within the body's protective mechanisms. Its modulation holds immense therapeutic promise for addressing a wide spectrum of disbiotic conditions, including cardiovascular, gastrointestinal, liver, kidney, neurodegenerative, psychiatric, bone, skin, and autoimmune diseases, as well as lung disorders, cancer, and pain management.

AREAS COVERED

This review is an account of patents from 2016 up to 2023 which describes novel CB2R ligands, therapeutic applications, synthesis as well as formulations of CB2R modulators.

EXPERT OPINION

The patents cover a vast, structurally diverse chemical space. The focus of CB2R ligand development has shifted from unselective dual cannabinoid receptor type 1 (CB1R) and 2 agonists toward agonists with high selectivity over CB1R, particularly for indications associated with inflammation and tissue injury. Currently, there are at least eight CB2R agonists and one antagonist in active clinical development. A better understanding of the endocannabinoid system (ECS) and in particular of CB2R pharmacology is required to unlock the receptor's full therapeutic potential.

Flipping the GPCR Switch: Structure-Based Development of Selective Cannabinoid Receptor 2 Inverse Agonists

We report a blueprint for the rational design of G protein coupled receptor (GPCR) ligands with a tailored functional response. The present study discloses the structure-based design of cannabinoid receptor type 2 (CB2R) selective inverse agonists (S)-1 and (R)-1, which were derived from privileged agonist HU-308 by introduction of a phenyl group at the gem-dimethylheptyl side chain. Epimer (R)-1 exhibits high affinity for CB2R with Kd = 39.1 nM and serves as a platform for the synthesis of a wide variety of probes. Notably, for the first time these fluorescent probes retain their inverse agonist functionality, high affinity, and selectivity for CB2R independent of linker and fluorophore substitution. Ligands (S)-1, (R)-1, and their derivatives act as inverse agonists in CB2R-mediated cAMP as well as G protein recruitment assays and do not trigger β-arrestin-receptor association. Furthermore, no receptor activation was detected in live cell ERK1/2 phosphorylation and Ca2+-release assays. Confocal fluorescence imaging experiments with (R)-7 (Alexa488) and (R)-9 (Alexa647) probes employing BV-2 microglial cells visualized CB2R expressed at endogenous levels. Finally, molecular dynamics simulations corroborate the initial docking data in which inverse agonists restrict movement of toggle switch Trp2586.48 and thereby stabilize CB2R in its inactive state.

Structural basis of Δ9-THC analog activity at the Cannabinoid 1 receptor

Δ9-tetrahydrocannabinol (THC) is the principal psychoactive compound derived from the cannabis plant Cannabis sativa and approved for emetic conditions, appetite stimulation and sleep apnea relief. THC's psychoactive actions are mediated primarily by the cannabinoid receptor CB1. Here, we determine the cryo-EM structure of HU210, a THC analog and widely used tool compound, bound to CB1 and its primary transducer, Gi1. We leverage this structure for docking and 1,000 ns molecular dynamics simulations of THC and 10 structural analogs delineating their spatiotemporal interactions at the molecular level. Furthermore, we pharmacologically profile their recruitment of Gi and β-arrestins and reversibility of binding from an active complex. By combining detailed CB1 structural information with molecular models and signaling data we uncover the differential spatiotemporal interactions these ligands make to receptors governing potency, efficacy, bias and kinetics. This may help explain the actions of abused substances, advance fundamental receptor activation studies and design better medicines.

Enantiomeric Agonists of the Type 2 Cannabinoid Receptor Reduce Retinal Damage during Proliferative Vitreoretinopathy and Inhibit Hyperactive Microglia In Vitro

Microglia are resident immune cells of the central nervous system (CNS) and propagate inflammation following damage to the CNS, including the retina. Proliferative vitreoretinopathy (PVR) is a condition that can emerge following retinal detachment and is characterized by severe inflammation and microglial proliferation. The type 2 cannabinoid receptor (CB2) is an emerging pharmacological target to suppress microglial-mediated inflammation when the eyes or brain are damaged. CB2-knockout mice have exacerbated inflammation and retinal pathology during experimental PVR. We aimed to assess the anti-inflammatory effects of CB2 stimulation in the context of retinal damage and also explore the mechanistic roles of CB2 in microglia function. To target CB2, we used a highly selective agonist, HU-308, as well as its enantiomer, HU-433, which is a putative selective agonist. First, β-arrestin2 and Gαi recruitment was measured to compare activation of human CB2 in an in vitro heterologous expression system. Both agonists were then utilized in a mouse model of PVR, and the effects on retinal damage, inflammation, and cell death were assessed. Finally, we used an in vitro model of microglia to determine the effects of HU-308 and HU-433 on phagocytosis, cytokine release, migration, and intracellular signaling. We observed that HU-308 more strongly recruited both β-arrestin2 and Gαi compared to HU-433. Stimulation of CB2 with either drug effectively blunted LPS- and IFNγ-mediated signaling as well as NO and TNF release from microglia. Furthermore, both drugs reduced IL-6 accumulation, total caspase-3 cleavage, and retinal pathology following the induction of PVR. Ultimately, this work supports that CB2 is a valuable target for drugs to suppress inflammation and cell death associated with infection or sterile retinopathy, although the magnitude of effector recruitment may not be predictive of anti-inflammatory capacity.

Involvement of CB1 and CB2 receptors in neuroprotective effects of cannabinoids in experimental TDP-43 related frontotemporal dementia using male mice

BACKGROUND

The elevation of endocannabinoid levels through inhibiting their degradation afforded neuroprotection in CaMKIIα-TDP-43 mice, a conditional transgenic model of frontotemporal dementia. However, which cannabinoid receptors are mediating these benefits is still pending to be elucidated.

METHODS

We have investigated the involvement of the CB1 and the CB2 receptor using chronic treatments with selective ligands in CaMKIIα-TDP-43 mice, analysis of their cognitive deterioration with the Novel Object Recognition test, and immunostaining for neuronal and glial markers in two areas of interest in frontotemporal dementia.

RESULTS

Our results confirmed the therapeutic value of activating either the CB1 or the CB2 receptor, with improvements in the animal performance in the Novel Object Recognition test, preservation of pyramidal neurons, in particular in the medial prefrontal cortex, and attenuation of glial reactivity, in particular in the hippocampus. In addition, the activation of both CB1 and CB2 receptors reduced the elevated levels of TDP-43 in the medial prefrontal cortex of CaMKIIα-TDP-43 mice, an effect exerted by mechanisms that are currently under investigation.

CONCLUSIONS

These data reinforce the notion that the activation of CB1 and CB2 receptors may represent a promising therapy against TDP-43-induced neuropathology in frontotemporal dementia. Future studies will have to confirm these benefits, in particular with one of the selective CB2 agonists used here, which has been thoroughly characterized for clinical development.

A highly potent, orally bioavailable pyrazole-derived cannabinoid CB2 receptor-selective full agonist for in vivo studies

The cannabinoid CB2 receptor (CB2R) is a potential therapeutic target for distinct forms of tissue injury and inflammatory diseases. To thoroughly investigate the role of CB2R in pathophysiological conditions and for target validation in vivo , optimal pharmacological tool compounds are essential. Despite the sizable progress in the generation of potent and selective CB2R ligands, pharmacokinetic parameters are often neglected for in vivo studies. Here, we report the generation and characterization of a tetra-substituted pyrazole CB2R full agonist named RNB-61 with high potency ( K i 0.13-1.81 nM, depending on species) and a peripherally restricted action due to P-glycoprotein mediated efflux from the brain. 3 H and 14 C labelled RNB-61 showed apparent K d values < 4 nM towards human CB2R in both cell and tissue experiments. The >6000-fold selectivity over CB1 receptors and negligible off-targets in vitro , combined with high oral bioavailability and suitable systemic pharmacokinetic (PK) properties, prompted the assessment of RNB-61 in a mouse ischemia-reperfusion model of acute kidney injury (AKI) and in a rat model of chronic kidney injury/inflammation and fibrosis (CKI) induced by unilateral ureteral obstruction. RNB-61 exerted dose-dependent nephroprotective and/or antifibrotic effects in the AKI/CKI models. Thus, RNB-61 is an optimal CB2R tool compound for preclinical in vivo studies with superior biophysical and PK properties over generally used CB2R ligands.

Discovery and development of macrocyclic peptide modulators of the cannabinoid 2 receptor

The cannabinoid type 2 receptor (CB2R), a G protein-coupled receptor, is an important regulator of immune cell function and a promising target to treat chronic inflammation and fibrosis. While CB2R is typically targeted by small molecules, including endo-, phyto-, and synthetic cannabinoids, peptides-owing to their size-may offer a different interaction space to facilitate differential interactions with the receptor. Here, we explore plant-derived cyclic cystine-knot peptides as ligands of the CB2R. Cyclotides are known for their exceptional biochemical stability. Recently, they gained attention as G protein-coupled receptor modulators and as templates for designing peptide ligands with improved pharmacokinetic properties over linear peptides. Cyclotide-based ligands for CB2R were profiled based on a peptide-enriched extract library comprising nine plants. Employing pharmacology-guided fractionation and peptidomics, we identified the cyclotide vodo-C1 from sweet violet (Viola odorata) as a full agonist of CB2R with an affinity (Ki) of 1 μM and a potency (EC50) of 8 μM. Leveraging deep learning networks, we verified the structural topology of vodo-C1 and modeled its molecular volume in comparison to the CB2R ligand binding pocket. In a fragment-based approach, we designed and characterized vodo-C1-based bicyclic peptides (vBCL1-4), aiming to reduce size and improve potency. Opposite to vodo-C1, the vBCL peptides lacked the ability to activate the receptor but acted as negative allosteric modulators or neutral antagonists of CB2R. This study introduces a macrocyclic peptide phytocannabinoid, which served as a template for the development of synthetic CB2R peptide modulators. These findings offer opportunities for future peptide-based probe and drug development at cannabinoid receptors.

Type 2 cannabinoid receptor expression on microglial cells regulates neuroinflammation during graft-versus-host disease

Neuroinflammation is a recognized complication of immunotherapeutic approaches such as immune checkpoint inhibitor treatment, chimeric antigen receptor therapy, and graft versus host disease (GVHD) occurring after allogeneic hematopoietic stem cell transplantation. While T cells and inflammatory cytokines play a role in this process, the precise interplay between the adaptive and innate arms of the immune system that propagates inflammation in the central nervous system remains incompletely understood. Using a murine model of GVHD, we demonstrate that type 2 cannabinoid receptor (CB2R) signaling plays a critical role in the pathophysiology of neuroinflammation. In these studies, we identify that CB2R expression on microglial cells induces an activated inflammatory phenotype that potentiates the accumulation of donor-derived proinflammatory T cells, regulates chemokine gene regulatory networks, and promotes neuronal cell death. Pharmacological targeting of this receptor with a brain penetrant CB2R inverse agonist/antagonist selectively reduces neuroinflammation without deleteriously affecting systemic GVHD severity. Thus, these findings delineate a therapeutically targetable neuroinflammatory pathway and have implications for the attenuation of neurotoxicity after GVHD and potentially other T cell-based immunotherapeutic approaches.

Novel pyrrole based CB2 agonists: New insights on CB2 receptor role in regulating neurotransmitters' tone

The cannabinoid system is one of the most investigated neuromodulatory systems because of its involvement in multiple pathologies such as cancer, inflammation, and psychiatric diseases. Recently, the CB2 receptor has gained increased attention considering its crucial role in modulating neuroinflammation in several pathological conditions like neurodegenerative diseases. Here we describe the rational design of pyrrole-based analogues, which led to a potent and pharmacokinetically suitable CB2 full agonist particularly effective in improving cognitive functions in a scopolamine-induced amnesia murine model. Therefore, we extended our study by investigating the interconnection between CB2 activation and neurotransmission in this experimental paradigm. To this purpose, we performed a MALDI imaging analysis on mice brains, observing that the administration of our lead compound was able to revert the effect of scopolamine on different neurotransmitter tones, such as acetylcholine, serotonin, and GABA, shedding light on important networks not fully explored, so far.

Discovery of a Photoaffinity Probe that Captures the Active Conformation of the Cannabinoid CB2 Receptor

The cannabinoid receptor type 2 (CB2R) is a G protein-coupled receptor with therapeutic potential for the treatment of inflammatory disorders. Fluorescent probes are desirable to study its receptor localization, expression and occupancy. Previously, we have reported a photoaffinity probe LEI-121 that stabilized the inactive conformation of the CB2R. Here, we report the structure-based design of a novel bifunctional probe that captures the active conformation of the CB2R upon irradiation with light. An alkyne handle was incorporated to visualize the receptor using click-chemistry with fluorophore-azides. These probes may hold promise to study different receptor conformations in relation to their cellular localization and function.

Cardiotoxic effects of common and emerging drugs: role of cannabinoid receptors

Drug-induced cardiotoxicity has become one of the most common and detrimental health concerns, which causes significant loss to public health and drug resources. Cannabinoid receptors (CBRs) have recently achieved great attention for their vital roles in the regulation of heart health and disease, with mounting evidence linking CBRs with the pathogenesis and progression of drug-induced cardiotoxicity. This review aims to summarize fundamental characteristics of two well-documented CBRs (CB1R and CB2R) from aspects of molecular structure, signaling and their functions in cardiovascular physiology and pathophysiology. Moreover, we describe the roles of CB1R and CB2R in the occurrence of cardiotoxicity induced by common drugs such as antipsychotics, anti-cancer drugs, marijuana, and some emerging synthetic cannabinoids. We highlight the 'yin-yang' relationship between CB1R and CB2R in drug-induced cardiotoxicity and propose future perspectives for CBR-based translational medicine toward cardiotoxicity curation and clinical monitoring.

Roadmap for the expression of canonical and extended endocannabinoid system receptors and metabolic enzymes in peripheral organs of preclinical animal models

The endocannabinoid system is widely expressed throughout the body and is comprised of receptors, ligands, and enzymes that maintain metabolic, immune, and reproductive homeostasis. Increasing interest in the endocannabinoid system has arisen due to these physiologic roles, policy changes leading to more widespread recreational use, and the therapeutic potential of Cannabis and phytocannabinoids. Rodents have been the primary preclinical model of focus due to their relative low cost, short gestational period, genetic manipulation strategies, and gold-standard behavioral tests. However, the potential for lack of clinical translation to non-human primates and humans is high as cross-species comparisons of the endocannabinoid system have not been evaluated. To bridge this gap in knowledge, we evaluate the relative gene expression of 14 canonical and extended endocannabinoid receptors in seven peripheral organs of C57/BL6 mice, Sprague-Dawley rats, and non-human primate rhesus macaques. Notably, we identify species- and organ-specific heterogeneity in endocannabinoid receptor distribution where there is surprisingly limited overlap among the preclinical models. Importantly, we determined there were no receptors with identical expression patterns among mice (three males and two females), rats (six females), and rhesus macaques (four males). Our findings demonstrate a critical, yet previously unappreciated, contributor to challenges of rigor and reproducibility in the cannabinoid field, which has implications in hampering progress in understanding the complexity of the endocannabinoid system and development of cannabinoid-based therapies.

The effect of cannabinoids on wound healing: A review

Background and Aims

Cannabis and its various derivatives are commonly used for both recreational and medicinal purposes. Cannabinoids have been shown to have anti-inflammatory properties. Inflammation is an important component of wound healing and the effect of cannabinoids on wound healing has become a recent topic of investigation. The objective of this article is to perform a comprehensive review of the literature to summarize the effects of cannabinoids on wound healing of the skin and to guide future avenues of research.

Methods

A comprehensive literature review was performed to evaluate the effects of cannabinoids on cutaneous wound healing.

Results

Cannabinoids appear to improve skin wound healing through a variety of mechanisms. This is supported through a variety of in vitro and animal studies. Animal studies suggest application of cannabinoids may improve the healing of postsurgical and chronic wounds. There are few human studies which evaluate the effects of cannabinoids on wound healing and many of these are case series and observational studies. They do suggest cannabinoids may have some benefit. However, definitive conclusions cannot be drawn from them.

Conclusion

While further human studies are needed, topical application of cannabinoids may be a potential therapeutic option for postsurgical and chronic wounds.

Role of the CB2 Cannabinoid Receptor in the Regulation of Food Intake: A Systematic Review

The CB2 cannabinoid receptor has been found in brain areas that are part of the reward system and has been shown to play a role in food intake regulation. Herein, we conducted a systematic review of studies assessing the role of the CB2 receptor in food intake regulation. Records from the PubMed, Scopus, and EBSCO databases were screened, resulting in 13 studies that were used in the present systematic review, following the PRISMA guidelines. A risk of bias assessment was carried out using the tool of the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE). The studies analyzed used two main strategies: (1) the intraperitoneal or intracerebroventricular administration of a CB2 agonist/antagonist; and (2) depletion of CB2 receptors via knockout in mice. Both strategies are useful in identifying the role of the CB2 receptor in food intake in standard and palatable diets. The conclusions derived from animal models showed that CB2 receptors are necessary for modulating food intake and mediating energy balance.

Visible-Light Photoswitchable Benzimidazole Azo-Arenes as β-Arrestin2-Biased Selective Cannabinoid 2 Receptor Agonists

The cannabinoid 2 receptor (CB2 R) has high therapeutic potential for multiple pathogenic processes, such as neuroinflammation. Pathway-selective ligands are needed to overcome the lack of clinical success and to elucidate correlations between pathways and their respective therapeutic effects. Herein, we report the design and synthesis of a photoswitchable scaffold based on the privileged structure of benzimidazole and its application as a functionally selective CB2 R "efficacy-switch". Benzimidazole azo-arenes offer huge potential for the broad extension of photopharmacology to a wide range of optically addressable biological targets. We used this scaffold to develop compound 10 d, a "trans-on" agonist, which serves as a molecular probe to study the β-arrestin2 (βarr2) pathway at CB2 R. βΑrr2 bias was observed in CB2 R internalization and βarr2 recruitment, while no activation occurred when looking at Gα16 or mini-Gαi . Overall, compound 10 d is the first light-dependent functionally selective agonist to investigate the complex mechanisms of CB2 R-βarr2 dependent endocytosis.

Evaluating signaling bias for synthetic cannabinoid receptor agonists at the cannabinoid CB2 receptor

The rapid structural evolution and emergence of novel synthetic cannabinoid receptor agonists (SCRAs) in the recreational market remains a key public health concern. Despite representing one of the largest classes of new psychoactive substances, pharmacological data on new SCRAs is limited, particularly at the cannabinoid CB2 receptor (CB2 ). Hence, the current study aimed to characterize the molecular pharmacology of a structurally diverse panel of SCRAs at CB2 , including 4-cyano MPP-BUT7AICA, 4F-MDMB-BUTINACA, AMB-FUBINACA, JWH-018, MDMB-4en-PINACA, and XLR-11. The activity of SCRAs was assessed in a battery of in vitro assays in CB2 -expressing HEK 293 cells: G protein activation (Gαi3 and GαoB ), phosphorylation of ERK1/2, and β-arrestin 1/2 translocation. The activity profiles of the ligands were further evaluated using the operational analysis to identify ligand bias. All SCRAs activated the CB2 signaling pathways in a concentration-dependent manner, although with varying potencies and efficacies. Despite the detection of numerous instances of statistically significant bias, compound activities generally appeared only subtly distinct in comparison with the reference ligand, CP55940. In contrast, the phytocannabinoid THC exhibited an activity profile distinct from the SCRAs; most notably in the translocation of β-arrestins. These findings demonstrate that CB2 is able to accommodate a structurally diverse array of SCRAs to generate canonical agonist activity. Further research is required to elucidate whether the activation of CB2 contributes to the toxicity of these compounds.

Neuroprotection and Beyond: The Central Role of CB1 and CB2 Receptors in Stroke Recovery

The endocannabinoid system, with its intricate presence in numerous cells, tissues, and organs, offers a compelling avenue for therapeutic interventions. Central to this system are the cannabinoid receptors 1 and 2 (CB1R and CB2R), whose ubiquity can introduce complexities in targeted treatments due to their wide-ranging physiological influence. Injuries to the central nervous system (CNS), including strokes and traumatic brain injuries, induce localized pro-inflammatory immune responses, termed neuroinflammation. Research has shown that compensatory immunodepression usually follows, and these mechanisms might influence immunity, potentially affecting infection risks in patients. As traditional preventive treatments like antibiotics face challenges, the exploration of immunomodulatory therapies offers a promising alternative. This review delves into the potential neuroprotective roles of the cannabinoid receptors: CB1R's involvement in mitigating excitotoxicity and CB2R's dual role in promoting cell survival and anti-inflammatory responses. However, the potential of cannabinoids to reduce neuroinflammation must be weighed against the risk of exacerbating immunodepression. Though the endocannabinoid system promises numerous therapeutic benefits, understanding its multifaceted signaling mechanisms and outcomes remains a challenge.

Cannabinoid CB2 receptor agonist reduces local and systemic inflammation associated with pneumonia-induced sepsis in mice

Sepsis is a severe condition secondary to dysregulated host response to infection leading to tissue damage and organ dysfunction. Cannabinoid CB2 receptor has modulatory effects on the immune response. Therefore, this study investigated the effects of a cannabinoid CB2 receptor agonist on the local and systemic inflammatory process associated with pneumonia-induced sepsis. Pneumonia-induced sepsis was induced in mice by intratracheal inoculation of Klebsiella pneumoniae. Tissue and bronchoalveolar lavage (BAL) were collected 6, 24, or 48 h after surgery. Mice were treated with CB2 agonist (AM1241, 0.3 and 3 mg/kg, i.p.) and several parameters of inflammation were evaluated 24 h after sepsis induction. Polymorphonuclear cell migration to the infectious focus peaked 24 h after pneumonia-induced sepsis induction in male and female animals. Septic male mice presented a significant reduction of cannabinoid CB2 receptor density in the lung tissue after 24 h, which was not observed in females. CB2 expression in BAL macrophages was also reduced in septic animals. Treatment of septic mice with AM1241 reduced cell migration, local infection, myeloperoxidase activity, protein extravasation, and NOS-2 expression in the lungs. In addition, the treatment reduced plasma IL-1β, increased IL-10 and reduced the severity and mortality of septic animals. These results suggest that AM1241 promotes an interesting balance in the inflammatory response, maintaining lung function and preventing organ injury. Therefore, cannabinoid CB2 receptors are potential targets to control the excessive inflammatory process that occurs in severe conditions, and agonists of these receptors can be considered promising adjuvants in pneumonia-induced sepsis treatment.

Exploring the 1,3-benzoxazine chemotype for cannabinoid receptor 2 as a promising anti-cancer therapeutic

The discovery of selective agonists of cannabinoid receptor 2 (CB2) is strongly pursued to successfully tuning endocannabinoid signaling for therapeutic purposes. However, the design of selective CB2 agonists is still challenging because of the high homology with the cannabinoid receptor 1 (CB1) and for the yet unclear molecular basis of the agonist/antagonist switch. Here, the 1,3-benzoxazine scaffold is presented as a versatile chemotype for the design of CB2 agonists from which 25 derivatives were synthesized. Among these, compound 7b5 (CB2 EC50 = 110 nM, CB1 EC50 > 10 μM) demonstrated to impair proliferation of triple negative breast cancer BT549 cells and to attenuate the release of pro-inflammatory cytokines in a CB2-dependent manner. Furthermore, 7b5 abrogated the activation of extracellular signal-regulated kinase (ERK) 1/2, a key pro-inflammatory and oncogenic enzyme. Finally, molecular dynamics studies suggested a new rationale for the in vitro measured selectivity and for the observed agonist behavior.

Interaction of Synthetic Cannabinoid Receptor Agonists with Cannabinoid Receptor I: Insights into Activation Molecular Mechanism

Synthetic cannabinoid receptor agonists (SCRAs) have become a wide group of new psychoactive substances since the 2010s. For the last few years, the X-ray structures of the complexes of cannabinoid receptor I (CB1) with SCRAs as well as the complexes of CB1 with its antagonist have been published. Based on those data, SCRA-CB1 interactions are analyzed in detail, using molecular modeling and molecular dynamics simulations. The molecular mechanism of the conformational transformation of the transmembrane domain of CB1 caused by its interaction with SCRA is studied. These conformational changes allosterically modulate the CB1-Gi complex, providing activation of the Gi protein. Based on the X-ray-determined structures of the CB1-ligand complexes, a stable apo conformation of inactive CB1 with a relatively low potential barrier of receptor activation was modeled. For that model, molecular dynamic simulations of SCRA binding to CB1 led to the active state of CB1, which allowed us to explore the key features of this activation and the molecular mechanism of the receptor's structural transformation. The simulated CB1 activation is in accordance with the previously published experimental data for the activation at protein mutations or structural changes of ligands. The key feature of the suggested activation mechanism is the determination of the stiff core of the CB1 transmembrane domain and the statement that the entire conformational transformation of the receptor to the active state is caused by a shift of alpha helix TM7 relative to this core. The shift itself is caused by protein-ligand interactions. It was verified via steered molecular dynamics simulations of the X-ray-determined structures of the inactive receptor, which resulted in the active conformation of CB1 irrespective of the placement of agonist ligand in the receptor's active site.

A type II cannabis extract and a 1:1 blend of Δ(9)-tetrahydrocannabinol and cannabidiol display distinct antinociceptive profiles and engage different endocannabinoid targets when administered into the subarachnoid space

Introduction: Cannabis extracts are being increasingly used to mitigate chronic pain. Current guidelines for their prescription rely on Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) content as well as the ratio of these major cannabinoids present in the blend. Here we assessed whether these descriptors were representative of product effectiveness to produce a desired outcome such as analgesia. Methods: In this study, we used a rat model of diabetic neuropathy and assessed the reduction in mechanical allodynia following intrathecal injection of pure THC, pure CBD, a 1:1 mix of these compounds and a "balanced" chemotype II cannabis extract. Engagement of endocannabinoid targets by different treatments was investigated using CB1 (AM251) and CB2 (AM630) receptor antagonists as well as a TRPV1 channel blocker (capsazepine). Results: Antinociceptive responses induced by an equivalent amount of THC administered in its pure form, as a THC:CBD mix or as a "balanced" extract were distinct. Furthermore, the 1:1 THC:CBD mix and the balanced extract had not only different response profiles but their relative engagement of CB1, CB2 receptors and TRPV1 channels was distinct. Discussion: These findings indicate that antinociceptive responses and targets engaged by blended cannabinoids are composition-specific, and cannot be simply inferred from THC and CBD contents. This information may have implications in relation to the way medicinal cannabis products are prescribed.

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.

MICROGLIAL CELL EXPRESSION OF THE TYPE 2 CANNABINOID RECEPTOR REGULATES IMMUNE-MEDIATED NEUROINFLAMMATION

Neuroinflammation is a recognized complication of immunotherapeutic approaches such as immune checkpoint inhibitor treatment, chimeric antigen receptor therapy, and graft versus host disease (GVHD) occurring after allogeneic hematopoietic stem cell transplantation. While T cells and inflammatory cytokines play a role in this process, the precise interplay between the adaptive and innate arms of the immune system that propagates inflammation in the central nervous system remains incompletely understood. Using a murine model of GVHD, we demonstrate that type 2 cannabinoid receptor (CB2R) signaling plays a critical role in the pathophysiology of neuroinflammation. In these studies, we identify that CB2R expression on microglial cells induces an activated inflammatory phenotype which potentiates the accumulation of donor-derived proinflammatory T cells, regulates chemokine gene regulatory networks, and promotes neuronal cell death. Pharmacological targeting of this receptor with a brain penetrant CB2R inverse agonist/antagonist selectively reduces neuroinflammation without deleteriously affecting systemic GVHD severity. Thus, these findings delineate a therapeutically targetable neuroinflammatory pathway and has implications for the attenuation of neurotoxicity after GVHD and potentially other T cell-based immunotherapeutic approaches.

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.

Pharmacological blockade of cannabinoid receptor 2 signaling does not affect LPS/IFN-γ-induced microglial activation

Cannabinoid receptor 2 (CB2) signaling modulates microglial responses to inflammatory stimuli. Our previous studies demonstrated that genetic deletion of CB2 inhibits microglial activation during inflammatory stimulation of toll-like receptors (TLRs) or in neurodegenerative conditions. However, we cannot exclude developmental effects of the constitutive CB2 knockout (CB2-/-), which could mediate compensatory outcomes in CB2-/- mice. In the present study, we therefore tested whether acute pharmacological inhibition of CB2 receptor has a similar effect on microglial activation as in CB2-/- in response to inflammatory stimulation. Our findings suggest that the CB2-specific antagonist SR144528 has little or no effect on LPS/IFN-γ-induced activation in primary microglia or organotypic hippocampal slice cultures at nanomolar concentrations. We show that SR144528 did not alter LPS/IFN-γ-mediated microglial cytokine secretion, Iba1 and CD68 staining intensity or morphology at 1 and 10 nM. Although SR144528 suppressed LPS/IFN-γ-induced microglial activation at 1 µM, this anti-inflammatory effect was not dependent on CB2 receptors and exceeded the Ki on CB2 receptors by more than a thousand-fold. Thus, SR144528 does not mimic the anti-inflammatory effects observed in the CB2-/- microglia after LPS/IFN-γ stimulation. Therefore, we propose that the deletion of CB2 probably triggered an adaptive mechanism, making microglia less responsive to inflammatory stimulation.

Roadmap For The Expression Of Canonical and Extended Endocannabinoid System Receptors and Proteins in Peripheral Organs of Preclinical Animal Models

The endocannabinoid system is widely expressed throughout the body and is comprised of receptors, ligands, and enzymes that maintain metabolic, immune, and reproductive homeostasis. Increasing interest in the endocannabinoid system has arisen due to these physiologic roles, policy changes leading to more widespread recreational use, and the therapeutic potential of Cannabis and phytocannabinoids. Rodents have been the primary preclinical model of focus due to their relative low cost, short gestational period, genetic manipulation strategies, and gold-standard behavioral tests. However, the potential for lack of clinical translation to non-human primates and humans is high as cross-species comparisons of the endocannabinoid system has not been evaluated. To bridge this gap in knowledge, we evaluate the relative gene expression of 14 canonical and extended endocannabinoid receptors in seven peripheral organs of C57/BL6 mice, Sprague-Dawley rats, and non-human primate rhesus macaques. Notably, we identify species- and organ-specific heterogeneity in endocannabinoid receptor distribution where there is surprisingly limited overlap among the preclinical models. Importantly, we determined there were only five receptors (CB2, GPR18, GPR55, TRPV2, and FAAH) that had identical expression patterns in mice, rats, and rhesus macaques. Our findings demonstrate a critical, yet previously unappreciated, contributor to challenges of rigor and reproducibility in the cannabinoid field, which has profound implications in hampering progress in understanding the complexity of the endocannabinoid system and development of cannabinoid-based therapies.

Endocannabinoid modulation of allergic responses: Focus on the control of FcεRI-mediated mast cell activation

Allergic reactions are highly prevalent pathologies initiated by the production of IgE antibodies against harmless antigens (allergens) and the activation of the high-affinity IgE receptor (FcεRI) expressed in the surface of basophils and mast cells (MCs). Research on the mechanisms of negative control of those exacerbated inflammatory reactions has been intense in recent years. Endocannabinoids (eCBs) show important regulatory effects on MC-mediated immune responses, mainly inhibiting the production of pro-inflammatory mediators. However, the description of the molecular mechanisms involved in eCB control of MC activation is far from complete. In this review, we aim to summarize the available information regarding the role of eCBs in the modulation of FcεRI-dependent activation of that cell type, emphasizing the description of the eCB system and the existence of some of its elements in MCs. Unique characteristics of the eCB system and cannabinoid receptors (CBRs) localization and signaling in MCs are mentioned. The described and putative points of cross-talk between CBRs and FcεRI signaling cascades are also presented. Finally, we discuss some important considerations in the study of the effects of eCBs in MCs and the perspectives in the field.

Sphingosine Kinases at the Intersection of Pro-Inflammatory LPS and Anti-Inflammatory Endocannabinoid Signaling in BV2 Mouse Microglia Cells

Microglia, the resident immune cells of the central nervous system, play important roles in brain homeostasis as well as in neuroinflammation, neurodegeneration, neurovascular diseases, and traumatic brain injury. In this context, components of the endocannabinoid (eCB) system have been shown to shift microglia towards an anti-inflammatory activation state. Instead, much less is known about the functional role of the sphingosine kinase (SphK)/sphingosine-1-phosphate (S1P) system in microglia biology. In the present study, we addressed potential crosstalk of the eCB and the S1P systems in BV2 mouse microglia cells challenged with lipopolysaccharide (LPS). We show that URB597, the selective inhibitor of fatty acid amide hydrolase (FAAH)-the main degradative enzyme of the eCB anandamide-prevented LPS-induced production of tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β), and caused the accumulation of anandamide itself and eCB-like molecules such as oleic acid and cis-vaccenic acid ethanolamide, palmitoylethanolamide, and docosahexaenoyl ethanolamide. Furthermore, treatment with JWH133, a selective agonist of the eCB-binding cannabinoid 2 (CB₂) receptor, mimicked the anti-inflammatory effects of URB597. Interestingly, LPS induced transcription of both SphK1 and SphK2, and the selective inhibitors of SphK1 (SLP7111228) and SphK2 (SLM6031434) strongly reduced LPS-induced TNFα and IL-1β production. Thus, the two SphKs were pro-inflammatory in BV2 cells in a non-redundant manner. Most importantly, the inhibition of FAAH by URB597, as well as the activation of CB₂ by JWH133, prevented LPS-stimulated transcription of SphK1 and SphK2. These results present SphK1 and SphK2 at the intersection of pro-inflammatory LPS and anti-inflammatory eCB signaling, and suggest the further development of inhibitors of FAAH or SphKs for the treatment of neuroinflammatory diseases.

Distinct activation mechanisms regulate subtype selectivity of Cannabinoid receptors

Design of cannabinergic subtype selective ligands is challenging because of high sequence and structural similarities of cannabinoid receptors (CB₁ and CB₂). We hypothesize that the subtype selectivity of designed selective ligands can be explained by the ligand binding to the conformationally distinct states between cannabinoid receptors. Analysis of ~ 700 μs of unbiased simulations using Markov state models and VAMPnets identifies the similarities and distinctions between the activation mechanism of both receptors. Structural and dynamic comparisons of metastable intermediate states allow us to observe the distinction in the binding pocket volume change during CB₁ and CB₂ activation. Docking analysis reveals that only a few of the intermediate metastable states of CB₁ show high affinity towards CB₂ selective agonists. In contrast, all the CB₂ metastable states show a similar affinity for these agonists. These results mechanistically explain the subtype selectivity of these agonists by deciphering the activation mechanism of cannabinoid receptors.

Medicinal cannabis products for the treatment of acute pain

For thousands of years, medicinal cannabis has been used for pain treatment, but its use for pain management is still controversial. Meta-analysis of the literature has shown contrasting results on the addition of cannabinoids to opioids compared with placebo/other active agents to reduce pain. Clinical studies are mainly focused on medicinal cannabis use in chronic pain management, for which the analgesic effect has been proven in many studies. This review focuses on the potential use of medical cannabis for acute pain management in preclinical studies, studies on healthy subjects and the few pioneering studies in the clinical setting.

Review of the oral toxicity of cannabidiol (CBD)

Information in the published literature indicates that consumption of CBD can result in developmental and reproductive toxicity and hepatotoxicity outcomes in animal models. The trend of CBD-induced male reproductive toxicity has been observed in phylogenetically disparate organisms, from invertebrates to non-human primates. CBD has also been shown to inhibit various cytochrome P450 enzymes and certain efflux transporters, resulting in the potential for drug-drug interactions and cellular accumulation of xenobiotics that are normally transported out of the cell. The mechanisms of CBD-mediated toxicity are not fully understood, but they may involve disruption of critical metabolic pathways and liver enzyme functions, receptor-specific binding activity, disruption of testosterone steroidogenesis, inhibition of reuptake and degradation of endocannabinoids, and the triggering of oxidative stress. The toxicological profile of CBD raises safety concerns, especially for long term consumption by the general population.

Treatment of Diet-Induced Obese Rats with CB2 Agonist AM1241 or CB2 Antagonist AM630 Reduces Leptin and Alters Thermogenic mRNA in Adipose Tissue

Diet-induced obesity (DIO) is a contributor to co-morbidities, resulting in alterations in hormones, lipids, and low-grade inflammation, with the cannabinoid type 2 receptor (CB₂) contributing to the inflammatory response. The effects of modulating CB₂ with pharmacological treatments on inflammation and adaptations to the obese state are not known. Therefore, we aimed to investigate the molecular mechanisms in adipose tissue of CB₂ agonism and CB₂ antagonism treatment in a DIO model. Male Sprague Dawley rats were placed on a high-fat diet (HFD) (21% fat) for 9 weeks, then received daily intraperitoneal injections with a vehicle, AM630 (0.3 mg/kg), or AM1241 (3 mg/kg), for a further 6 weeks. AM630 or AM1241 treatment in DIO rats did not alter their body weight, food intake, or liver weight, and it had no effect on their numerous circulating cytokines or peri-renal fat pad mass. AM1241 decreased heart weight and BAT weight; both treatments (AM630 or AM1241) decreased plasma leptin levels, while AM630 also decreased plasma ghrelin and GLP-1 levels. Both treatments decreased Adrb3 and TNF-α mRNA levels in eWAT and TNF-α levels in pWAT. AM630 treatment also decreased the mRNA levels of Cnr2, leptin, and Slc2a4 in eWAT. In BAT, both treatments decreased leptin, UCP1, and Slc2a4 mRNA levels, with AM1241 also decreasing Adrb3, IL1β, and PRDM16 mRNA levels, and AM630 increasing IL6 mRNA levels. In DIO, CB₂ agonist and CB₂ antagonist treatment reduces circulating leptin in the absence of weight loss and modulates the mRNA responsible for thermogenesis.

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.

Structural basis of selective cannabinoid CB2 receptor activation

Cannabinoid CB₂ receptor (CB₂R) agonists are investigated as therapeutic agents in the clinic. However, their molecular mode-of-action is not fully understood. Here, we report the discovery of LEI-102, a CB₂R agonist, used in conjunction with three other CBR ligands (APD371, HU308, and CP55,940) to investigate the selective CB₂R activation by binding kinetics, site-directed mutagenesis, and cryo-EM studies. We identify key residues for CB₂R activation. Highly lipophilic HU308 and the endocannabinoids, but not the more polar LEI-102, APD371, and CP55,940, reach the binding pocket through a membrane channel in TM1-TM7. Favorable physico-chemical properties of LEI-102 enable oral efficacy in a chemotherapy-induced nephropathy model. This study delineates the molecular mechanism of CB₂R activation by selective agonists and highlights the role of lipophilicity in CB₂R engagement. This may have implications for GPCR drug design and sheds light on their activation by endogenous ligands.

Design, synthesis, and structure-activity relationships of diindolylmethane derivatives as cannabinoid CB2 receptor agonists

3,3'-Diindolylmethane (DIM), a natural product-derived compound formed upon ingestion of cruciferous vegetables, was recently described to act as a partial agonist of the anti-inflammatory cannabinoid (CB) receptor subtype CB₂ . In the present study, we synthesized and evaluated a series of DIM derivatives and determined their affinities for human CB receptor subtypes in radioligand binding studies. Potent compounds were additionally evaluated in functional cAMP accumulation and β-arrestin recruitment assays. Small substituents in the 4-position of both indole rings of DIM were beneficial for high CB₂ receptor affinity and efficacy. Di-(4-cyano-1H-indol-3-yl)methane (46, PSB-19837, EC₅₀ : cAMP, 0.0144 µM, 95% efficacy compared to the full standard agonist CP55,940; β-arrestin, 0.0149 µM, 67% efficacy) was the most potent CB₂ receptor agonist of the present series. Di-(4-bromo-1H-indol-3-yl)methane (44, PSB-19571) showed higher potency in β-arrestin (EC₅₀ 0.0450 µM, 61% efficacy) than in cAMP accumulation assays (EC₅₀ 0.509 µM, 85% efficacy) while 3-((1H-indol-3-yl)methyl)-4-methyl-1H-indole (149, PSB-18691) displayed a 19-fold bias for the G protein pathway (EC₅₀ : cAMP, 0.0652 µM; β-arrestin, 1.08 µM). DIM and its analogs act as allosteric CB₂ receptor agonists. These potent CB₂ receptor agonists have potential as novel drugs for the treatment of inflammatory diseases.

The Anti-Tumorigenic Role of Cannabinoid Receptor 2 in Colon Cancer: A Study in Mice and Humans

The endocannabinoid system, particularly cannabinoid receptor 2 (CB2 in mice and CNR2 in humans), has controversial pathophysiological implications in colon cancer. Here, we investigate the role of CB2 in potentiating the immune response in colon cancer in mice and determine the influence of CNR2 variants in humans. Comparing wild-type (WT) mice to CB2 knockout (CB2^-/-) mice, we performed a spontaneous cancer study in aging mice and subsequently used the AOM/DSS model of colitis-associated colorectal cancer and a model for hereditary colon cancer (Apc^Min/+). Additionally, we analyzed genomic data in a large human population to determine the relationship between CNR2 variants and colon cancer incidence. Aging CB2^-/- mice exhibited a higher incidence of spontaneous precancerous lesions in the colon compared to WT controls. The AOM/DSS-treated CB2^-/- and Apc^Min/+CB2^-/- mice experienced aggravated tumorigenesis and enhanced splenic populations of immunosuppressive myeloid-derived suppressor cells along with abated anti-tumor CD8+ T cells. Importantly, corroborative genomic data reveal a significant association between non-synonymous variants of CNR2 and the incidence of colon cancer in humans. Taken together, the results suggest that endogenous CB2 activation suppresses colon tumorigenesis by shifting the balance towards anti-tumor immune cells in mice and thus portray the prognostic value of CNR2 variants for colon cancer patients.

Cannabis Use and Risk of Acute Kidney Injury in Patients with Advanced Chronic Kidney Disease Transitioning to Dialysis

Background: The current social and legal landscape is likely to foster the medicinal and recreational use of cannabis. Synthetic cannabinoid use is associated with acute kidney injury (AKI) in case reports; however, the association between natural cannabis use and AKI risk in patients with advanced chronic kidney disease (CKD) is unknown. Materials and Methods: From a nationally representative cohort of 102,477 U.S. veterans transitioning to dialysis between 2007 and 2015, we identified 2215 patients with advanced CKD who had undergone urine toxicology (UTOX) tests within a year before dialysis initiation and had inpatient serial serum creatinine levels measured within 7 days after their UTOX test. The exposure of interest was cannabis use compared with no use as ascertained by the UTOX test. We examined the association of this exposure with AKI using logistic regression and inverse probability of treatment weighting with extensive adjustment for potential confounders. Results: The mean age of the overall cohort was 61 years; 97% were males, 51% were African Americans, 97% had hypertension, 76% had hyperlipidemia, and 75% were diabetic. AKI occurred in 56% of the cohort, and in multivariable-adjusted analysis, cannabis use (when compared with no substance use) was not associated with significantly higher odds of AKI (odds ratio 0.85, 95% confidence interval 0.38-1.87; p=0.7). These results were robust to various sensitivity analyses. Conclusions: In this observational study examining patients with advanced CKD, cannabis use was not associated with AKI risk. Additional studies are needed to characterize the impact of cannabis use on risk of kidney disease and injury.

Microglial Cannabinoid CB2 Receptors in Pain Modulation

Pain, especially chronic pain, can strongly affect patients' quality of life. Cannabinoids ponhave been reported to produce potent analgesic effects in different preclinical pain models, where they primarily function as agonists of G_i/o protein-coupled cannabinoid CB₁ and CB₂ receptors. The CB₁ receptors are abundantly expressed in both the peripheral and central nervous systems. The central activation of CB₁ receptors is strongly associated with psychotropic adverse effects, thus largely limiting its therapeutic potential. However, the CB₂ receptors are promising targets for pain treatment without psychotropic adverse effects, as they are primarily expressed in immune cells. Additionally, as the resident immune cells in the central nervous system, microglia are increasingly recognized as critical players in chronic pain. Accumulating evidence has demonstrated that the expression of CB₂ receptors is significantly increased in activated microglia in the spinal cord, which exerts protective consequences within the surrounding neural circuitry by regulating the activity and function of microglia. In this review, we focused on recent advances in understanding the role of microglial CB₂ receptors in spinal nociceptive circuitry, highlighting the mechanism of CB₂ receptors in modulating microglia function and its implications for CB₂ receptor- selective agonist-mediated analgesia.

Identification of Novel CB2 Ligands through Virtual Screening and In Vitro Evaluation

Cannabinoid receptor type 2 (CB2) is a very promising therapeutic target for a variety of potential indications. However, despite the existence of multiple high affinity CB2 ligands, none have yet been approved as a drug. Therefore, it would be beneficial to explore new chemotypes of CB2 ligands. The recent elucidation of CB2 tertiary structure allows for rational hit identification with structure-based (SB) methods. In this study, we established a virtual screening workflow based on SB techniques augmented with ligand-based ones, including molecular docking, MM-GBSA binding energy calculations, pharmacophore screening, and QSAR. We screened nearly 7 million drug-like, commercially available compounds. We selected 16 molecules for in vitro evaluation and identified two novel, selective CB2 antagonists with K_i values of 65 and 210 nM. Both compounds are structurally diverse from CB2 ligands known to date. The established virtual screening protocol may prove useful for hit identification for CB2 and similar molecular targets. The two novel CB2 ligands provide a desired starting point for future optimization and development of potential drugs.

Utilizing PET and MALDI Imaging for Discovery of a Targeted Probe for Brain Endocannabinoid α/β-Hydrolase Domain 6 (ABHD6)

Multimodal imaging provides rich biological information, which can be exploited to study drug activity, disease associated phenotypes, and pharmacological responses. Here we show discovery and validation of a new probe targeting the endocannabinoid α/β-hydrolase domain 6 (ABHD6) enzyme by utilizing positron emission tomography (PET) and matrix-assisted laser desorption/ionization (MALDI) imaging. [¹⁸F]JZP-MA-11 as the first PET ligand for in vivo imaging of the ABHD6 is reported and specific uptake in ABHD6-rich peripheral tissues and major brain regions was demonstrated using PET. A proof-of-concept study in nonhuman primate confirmed brain uptake. In vivo pharmacological response upon ABHD6 inhibition was observed by MALDI imaging. These synergistic imaging efforts used to identify biological information cannot be obtained by a single imaging modality and hold promise for improving the understanding of ABHD6-mediated endocannabinoid metabolism in peripheral and central nervous system disorders.

Endocannabinoid signaling in the central nervous system

It is hard to overestimate the influence of the endocannabinoid signaling (ECS) system on central nervous system (CNS) function. In the 40 years since cannabinoids were found to trigger specific cell signaling cascades, studies of the ECS system continue to cause amazement, surprise, and confusion! CB1 cannabinoid receptors are expressed widely in the CNS and regulate cell-cell communication via effects on the release of both neurotransmitters and gliotransmitters. CB2 cannabinoid receptors are difficult to detect in the CNS but seem to "punch above their weight" as compounds targeting these receptors have significant effects on inflammatory state and behavior. Positive and negative allosteric modulators for both receptors have been identified and examined in preclinical studies. Concentrations of the endocannabinoid ligands, N-arachidonoylethanolamine and 2-arachidonoylglycerol (2-AG), are regulated by a combination of enzymatic synthesis and degradation and inhibitors of these processes are available and making their way into clinical trials. Importantly, ECS regulates many essential brain functions, including regulation of reward, anxiety, inflammation, motor control, and cellular development. While the field is on the cusp of preclinical discoveries providing impactful clinical and therapeutic insights into many CNS disorders, there is still much to be learned about this remarkable and versatile modulatory system.

Cellular Assay to Study β-Arrestin Recruitment by the Cannabinoid Receptors 1 and 2

Cannabinoid receptor 1 (CB₁R) and cannabinoid receptor 2 (CB₂R) are G protein-coupled receptors (GPCRs) that activate a variety of pathways upon activation by (partial) agonists including the G protein pathway and the recruitment of β-arrestins. Differences in the activation level of these pathways lead to biased signaling. Here, we describe a detailed protocol to characterize the potency and efficacy of ligands to induce or inhibit β-arrestin recruitment to the human CB₁R and CB₂R using the PathHunter^® assay. This is a cellular assay that uses a β-galactosidase complementation system which has a chemiluminescent read-out and can be performed in 384-well plates. We have successfully used this assay to characterize a set of reference ligands (both agonists, antagonists, and an inverse agonist) on human CB₁R and CB₂R, of which some examples will be presented here.

Role of integrating cannabinoids and the endocannabinoid system in neonatal hypoxic-ischaemic encephalopathy

Neonatal hypoxic-ischaemic events, which can result in long-term neurological impairments or even cell death, are among the most significant causes of brain injury during neurodevelopment. The complexity of neonatal hypoxic-ischaemic pathophysiology and cellular pathways make it difficult to treat brain damage; hence, the development of new neuroprotective medicines is of great interest. Recently, numerous neuroprotective medicines have been developed to treat brain injuries and improve long-term outcomes based on comprehensive knowledge of the mechanisms that underlie neuronal plasticity following hypoxic-ischaemic brain injury. In this context, understanding of the medicinal potential of cannabinoids and the endocannabinoid system has recently increased. The endocannabinoid system plays a vital neuromodulatory role in numerous brain regions, ensuring appropriate control of neuronal activity. Its natural neuroprotection against adult brain injury or acute brain injury also clearly demonstrate the role of endocannabinoid signalling in modulating neuronal activity in the adult brain. The goal of this review is to examine how cannabinoid-derived compounds can be used to treat neonatal hypoxic-ischaemic brain injury and to assess the critical function of the endocannabinoid system and its potential for use as a new neuroprotective treatment for neonatal hypoxic-ischaemic brain injury.

Anandamide and other N-acylethanolamines: A class of signaling lipids with therapeutic opportunities

N-acylethanolamines (NAEs), including N-palmitoylethanolamine (PEA), N-oleoylethanolamine (OEA), N-arachidonoylethanolamine (AEA, anandamide), N-docosahexaenoylethanolamine (DHEA, synaptamide) and their oxygenated metabolites are a lipid messenger family with numerous functions in health and disease, including inflammation, anxiety and energy metabolism. The NAEs exert their signaling role through activation of various G protein-coupled receptors (cannabinoid CB₁ and CB₂ receptors, GPR55, GPR110, GPR119), ion channels (TRPV1) and nuclear receptors (PPAR-α and PPAR-γ) in the brain and periphery. The biological role of the oxygenated NAEs, such as prostamides, hydroxylated anandamide and DHEA derivatives, are less studied. Evidence is accumulating that NAEs and their oxidative metabolites may be aberrantly regulated or are associated with disease severity in obesity, metabolic syndrome, cancer, neuroinflammation and liver cirrhosis. Here, we comprehensively review NAE biosynthesis and degradation, their metabolism by lipoxygenases, cyclooxygenases and cytochrome P450s and the biological functions of these signaling lipids. We discuss the latest findings and therapeutic potential of modulating endogenous NAE levels by inhibition of their degradation, which is currently under clinical evaluation for neuropsychiatric disorders. We also highlight NAE biosynthesis inhibition as an emerging topic with therapeutic opportunities in endocannabinoid and NAE signaling.

Cannabinoid Type 2 Receptor Activation Reduces the Progression of Kidney Fibrosis Using a Mouse Model of Unilateral Ureteral Obstruction

Background: Kidney fibrosis is a hallmark consequence of all forms of chronic kidney disease with few available treatment modalities. Material and Methods: In this study, we performed the unilateral ureteral obstruction (UUO) procedure to investigate the effects of a selective cannabinoid type 2 (CB2) agonist receptor, SMM-295, as a nephroprotective therapy. Results: SMM-295 was demonstrated to exhibit 50-fold selectivity over the cannabinoid type 1 (CB1) receptor with an EC₅₀ ∼2 nM. Four other off-targets were identified in the safety panel, but only at the highest concentration (5 mM) tested in the assay demonstrating the relative selectivity and safety of our compound. Administration of SMM-295 (12 mg/kg IP daily) in UUO mice led to a significant decrease of 33% in tubular damage compared to the vehicle-treated UUO mice after 7 days. Consistent with these findings, there was a significant decrease in α-smooth muscle actin and fibronectin, which are markers of tubulointerstitial fibrosis, as determined by Western blot analysis. DNA damage as detected by a classic marker, γ-H2AX, was significantly reduced by 50% in the SMM-295 treatment group compared to vehicle treatment. Genetic knockout of CB2 or administration of a CB2 inverse agonist did not exhibit any beneficial effect on tubulointerstitial fibrosis or kidney tubule injury. Conclusions: In conclusion, our study provides new evidence that SMM-295 can therapeutically target the CB2 receptor with few, if any, physiological off-target sites to reduce kidney tissue damage and slow the fibrotic progression in a mouse model of kidney fibrosis.

Cannabinoids as Immune System Modulators: Cannabidiol Potential Therapeutic Approaches and Limitations

Introduction: Cannabidiol (CBD) is the second most abundant Phytocannabinoid in Cannabis extracts. CBD has a binding affinity for several cannabinoid and cannabinoid-associated receptors. Epidiolex (oral CBD solution) has been lately licensed by the Food and Drug Administration (FDA) for the treatment of pediatric epileptic seizures. Methods: In this review, we discussed the most promising applications of CBD for chronic inflammatory conditions, namely CBD's anti-inflammatory effects during inflammatory bowel disease, coronavirus disease (antiviral effect), brain pathologies (neuroprotective and anti-inflammatory properties), as well as CBD immunomodulatory and antitumoral activities in the tumor microenvironment. Special focus was shed on the main therapeutic mechanisms of action of CBD, particularly in the control of the immune system and the endocannabinoid system. Results: Findings suggest that CBD is a potent immunomodulatory drug as it has manifested immunosuppressive properties in the context of sterile inflammation (e.g., inflammatory bowel disease, rheumatoid arthritis, and neurodegenerative diseases), and immunoprotective effects during viral infections (e.g. COVID-19) Similarly, CBD has exhibited a selective response toward cancer types by engaging different targets and signaling pathways. These results are in favor of the primary function of the endocannabinoid system which is homeostatic maintenance. Conclusion: The presented evidence suggests that the endocannabinoid system is a prominent target for the treatment of inflammatory and autoimmune diseases, rheumatoid diseases, viral infections, neurological and psychological pathologies, and cancer. Moreover, the antitumoral activities of CBD have been suggested to be potentially used in combination with chemo- or immunotherapy during cancer. However, clinical results are still lacking, which raises a challenge to apply translational cannabis research to the human immune system.

The Role of Cannabinoid Type 2 Receptors in Parkinson's Disease

Parkinson's disease (PD) is the second most frequent neurodegenerative disease and currently represents a clear unmet medical need. Therefore, novel preventive and therapeutic strategies are needed. Cannabinoid type 2 (CB2) receptors, one of the components of the endocannabinoid system, can regulate neuroinflammation in PD. Here, we review the current preclinical and clinical studies investigating the CB2 receptors in PD with the aim to clarify if these receptors could have a role in PD. Preclinical data show that CB2 receptors could have a neuroprotective action in PD and that the therapeutic targeting of CB2 receptors could be promising. Indeed, it has been shown that different CB2 receptor-selective agonists exert protective effects in different PD models. Moreover, the alterations in the expression of CB2 receptors observed in brain tissues from PD animal models and PD patients suggest the potential value of CB2 receptors as possible novel biomarkers for PD. However, to date, there is no direct evidence of the role of CB2 receptors in PD. Further studies are strongly needed in order to fully clarify the role of CB2 receptors in PD and thus pave the way to novel possible diagnostic and therapeutic opportunities for PD.