Latest advances in cannabinoid receptor agonists

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 dysbiotic 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.

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.

Targeted delivery of nutraceuticals derived from food for the treatment of obesity and its related complications

Nutraceuticals which are abundant in foods have attracted much attention due to their bioactive activities of anti-obesity, anti-hyperlipidemia and anti-atherosclerosis. Unfortunately, the poor bioavailability severely undermines their envisioned benefits. Therefore, there is an urgent need to develop suitable delivery systems to promote the benefits of their biological activity. Targeted drug delivery system (TDDS) is a novel drug delivery system that can selectively concentrate drugs on targets in the body, improve the bioavailability of agents and reduce side effects. This emerging drug delivery system provides a new strategy for the treatment of obesity with nutraceuticals and would be a promising alternative to be widely used in the food field. This review summarizes the recent studies on the application in the targeted delivery of nutraceuticals for treating obesity and its related complications, especially the available receptors and their corresponding ligands for TDDS and the evaluation methods of the targeting ability.

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.

Cannabinoid type-2 receptors: An emerging target for regulating schizophrenia-relevant brain circuits

Although the cannabinoid type-2 receptor (CB2) is highly expressed in the immune system, emerging evidence points to CB2 playing a key role in regulating neuronal function in the central nervous system. Recent anatomical studies, combined with electrophysiological studies, indicate that CB2 receptors are expressed in specific dopaminergic and glutamatergic brain circuits that are hyperactive in schizophrenia patients. The ability of CB2 receptors to inhibit dopaminergic and hippocampal circuits, combined with the anti-inflammatory effects of CB2 receptor activation, make this receptor an intriguing target for treating schizophrenia, a disease where novel interventions that move beyond dopamine receptor antagonists are desperately needed. The development of new CB2-related pharmacological and genetic tools, including the first small molecule positive allosteric modulator of CB2 receptors, has greatly advanced our understanding of this receptor. While more work is needed to further elucidate the translational value of selectively targeting CB2 receptors with respect to schizophrenia, the studies discussed below could suggest that CB2 receptors are anatomically located in schizophrenia-relevant circuits, where the physiological consequence of CB2 receptor activation could correct circuit-based deficits commonly associated with positive and cognitive deficits.

Enantioselective Organocatalytic Synthesis of Bicyclic Resorcinols via an Intramolecular Friedel-Crafts-Type 1,4-Addition: Access to Cannabidiol Analogues

The organocatalytic transformation of resorcinols is extremely rare. In this article, we report a highly enantioselective, organocatalytic intramolecular cyclization of these systems by a Friedel-Crafts-type 1,4-addition using a Jørgensen-Hayashi-like organocatalyst with a large silyl protecting group, and show that heat improves reaction yield with virtually no detriment to enantioselectivity. A variety of bicyclic resorcinols were obtained with excellent enantioselectivities (up to 94%). To show the utility of these constructs, and as part of a wider project involving the synthesis of cannabinoid-like compounds, the resorcinol formed was used to generate both 'normal' and 'abnormal' cannabidiol (CBD) derivatives which were shown to have anticonvulsant activity.

Cannabinoid receptor type 2 ligands: an analysis of granted patents since 2010

The G-protein-coupled cannabinoid receptor type 2 (CB2R) is a key element of the endocannabinoid (EC) system. EC/CB2R signaling has significant therapeutic potential in major pathologies affecting humans such as allergies, neurodegenerative disorders, inflammation or ocular diseases. CB2R agonism exerts anti-inflammatory and tissue protective effects in preclinical animal models of cardiovascular, gastrointestinal, liver, kidney, lung and neurodegenerative disorders. Existing ligands can be subdivided into endocannabinoids, cannabinoid-like and synthetic CB2R ligands that possess various degrees of potency on and selectivity against the cannabinoid receptor type 1. This review is an account of granted CB2R ligand patents from 2010 up to the present, which were surveyed using Derwent Innovation®.

Clinical Evidence of Magistral Preparations Based on Medicinal Cannabis

Cannabis has been widely used as a medicinal plant for millennia; however, studies related to its main components were first conducted in 1960. Subsequently, laboratories have produced new components and structures related to its active biological properties. Countries that have approved the medicinal use of cannabis impose regulations that govern its clinical and scientific use. One means of administering medicinal cannabis is via a magistral preparation that must have a medical prescription and be prepared in an establishment that meets quality standards to ensure the quantities of its main components, such as tetrahydrocannabinol (THC) and cannabidiol (CBD). Furthermore, suppliers must have a clear indication of its use in the patient before prescription. This review shows the published evidence regarding the clinical use of medicinal cannabis magistral preparations in the management of post-chemotherapy nausea and vomiting, neuropathic pain in multiple sclerosis, and anorexia and cachexia in patients with HIV.

From a Designer Drug to the Discovery of Selective Cannabinoid Type 2 Receptor Agonists with Favorable Pharmacokinetic Profiles for the Treatment of Systemic Sclerosis

Synthetic cannabinoids, as exemplified by SDB-001 (1), bind to both CB1 and CB2 receptors and exert cannabimimetic effects similar to (-)-trans-Δ⁹-tetrahydrocannabinol, the main psychoactive component present in the cannabis plant. As CB1 receptor ligands were found to have severe adverse psychiatric effects, increased attention was turned to exploiting the potential therapeutic value of the CB2 receptor. In our efforts to discover novel and selective CB2 receptor agonists, 1 was selected as a starting point for hit molecule identification and a class of 1H-pyrazole-3-carboxamide derivatives were thus designed, synthesized, and biologically evaluated. Systematic structure-activity relationship investigations resulted in the identification of the most promising compound 66 as a selective CB2 receptor agonist with favorable pharmacokinetic profiles. Especially, 66 treatment significantly attenuated dermal inflammation and fibrosis in a bleomycin-induced mouse model of systemic sclerosis, supporting that CB2 receptor agonists might serve as potential therapeutics for treating systemic sclerosis.

Differential activation of G protein-mediated signaling by synthetic cannabinoid receptor agonists

Synthetic cannabinoid receptor agonists (SCRAs) are new psychoactive substances associated with acute intoxication and even death. However, the molecular mechanisms through which SCRAs may exert their toxic effects remain unclear-including the potential differential activation of G protein subtypes by cannabinoid receptor type 1 (CB1), a major target of SCRA. We measured CB1-mediated activation of Gαs and Gαi/o proteins by SCRAs by examining stimulation (pertussis toxin, PTX treated) as well as inhibition (non-PTX treated) of forskolin (FSK)-induced cyclic adenosine monophosphate (cAMP) accumulation in human embryonic kidney (HEK) cells stably expressing CB1. Real-time measurements of stimulation and inhibition of cAMP levels were made using a BRET biosensor. We found that the maximum concentration of SCRAs tested (10 µmol L-1 ), increased cAMP levels 12%-45% above that produced by FSK alone, while the phytocannabinoid THC did not significantly alter cAMP levels in PTX-treated HEK-CB1 cells. All SCRAs had greater potency to inhibit FSK-induced cAMP levels than to stimulate cAMP levels. The rank order of potencies for SCRA stimulation of cAMP (Gαs ) was PB-22 > 5F-MDMB-PICA > JWH-018 ≈ AB-FUBINACA > XLR-11. By contrast, the potency of SCRAs for inhibition of cAMP (Gαi/o ) was 5F-MDMB-PICA > AB-FUBINACA > PB-22 > JWH-018 > XLR-11. The different rank order of potency and EMax  of the SCRAs to stimulate Gαs -like signaling compared to Gαi/o signaling suggests differences in G protein preference between SCRAs. Understanding the apparent differences among these drugs may contribute to unravelling their complex effects in humans.

Multiple Binding Sites Contribute to the Mechanism of Mixed Agonistic and Positive Allosteric Modulators of the Cannabinoid CB1 Receptor

The cannabinoid CB1 receptor (CB1R) is an abundant metabotropic G-protein-coupled receptor that has been difficult to address therapeutically because of CNS side effects exerted by orthosteric drug candidates. Recent efforts have focused on developing allosteric modulators that target CB1R. Compounds from the recently discovered class of mixed agonistic and positive allosteric modulators (Ago-PAMs) based on 2-phenylindoles have shown promising functional and binding properties as CB1R ligands. Here, we identify binding modes of both the CP 55,940 agonist and GAT228, a 2-phenylindole allosteric modulator, by using our metadynamics simulation protocol, and quantify their affinity and cooperativity by atomistic simulations. We demonstrate the involvement of multiple adjunct binding sites in the Ago-PAM characteristics of the 2-phenylindole modulators and explain their ability to compete with orthosteric agonists at higher concentrations. We validate these results experimentally by showing the contribution of multiple sites on the allosteric binding of ZCZ011, another homologous member of the class, together with the orthosteric agonist.

The Chemistry and Pharmacology of Synthetic Cannabinoid Receptor Agonists as New Psychoactive Substances: Origins

Synthetic cannabinoid receptor agonists (SCRAs) have proliferated as new psychoactive substances (NPS) over the past decade. Relative to other classes of NPS, SCRAs are structurally heterogeneous; however, most SCRAs act as potent, high-efficacy agonists of cannabinoid type 1 and type 2 receptors (CB₁ and CB₂, respectively). Characterization of the pharmacology and toxicology of these substances is hindered by the dynamic nature of the SCRA marketplace. Beyond basic pharmacological profiling at CB₁ and CB₂ receptors, very little is known about the acute or chronic effects of SCRAs. Many of the effects of SCRAs are qualitatively similar to those of the Δ⁹-tetrahydrocannabinol (Δ⁹-THC) found in cannabis. However, unlike Δ⁹-THC, SCRAs are frequently associated with serious adverse effects, including cardiotoxicity, nephrotoxicity, and death. This chapter will provide an overview of the structure and function of the primary target for SCRAs, the CB₁ receptor, and survey the structure-activity relationships of the historical SCRAs that served as templates for the earliest generations of NPS.

Novel analogs of PSNCBAM-1 as allosteric modulators of cannabinoid CB1 receptor

In this work, we explored the molecular framework of the known CB1R allosteric modulator PSNCBAM-1 with the aim to generate new bioactive analogs and to deepen the structure-activity relationships of this type of compounds. In particular, the introduction of a NH group between the pyridine ring and the phenyl nucleus generated the amino-phenyl-urea derivative SN15b that behaved as a positive allosteric modulator (PAM), increasing the CB1R binding affinity of the orthosteric ligand CP55,940. The functional activity was evaluated using serum response element (SRE) assay, which assesses the CB1R-dependent activation of the MAPK/ERK signaling pathway. SN15b and the biphenyl-urea analog SC4a significantly inhibited the response produced by CP55,940 in the low µM range, thus behaving as negative allosteric modulators (NAMs). The new derivatives presented here provide further insights about the modulation of CB1R binding and functional activity by allosteric ligands.

Design and Synthesis of Cannabinoid 1 Receptor (CB1R) Allosteric Modulators: Drug Discovery Applications

Also expressed in various peripheral tissues, the type-1 cannabinoid receptor (CB1R) is the predominant G protein-coupled receptor (GPCR) in brain, where it is responsible for retrograde control of neurotransmitter release. Cellular signaling mediated by CB1R is involved in numerous physiological processes, and pharmacological CB1R modulation is considered a tenable therapeutic approach for diseases ranging from substance-use disorders and glaucoma to metabolic syndrome. Despite the design and synthesis of a variety of bioactive small molecules targeted to the CB1R orthosteric ligand-binding site, the potential of CB1R as a therapeutic GPCR has been largely unrealized due to adverse events associated with typical orthosteric CB1R agonists and antagonists/inverse agonists. Modulation of CB1R-mediated signal transmission by targeting alternative allosteric ligand-binding site(s) on the receptor has garnered interest as a potentially safer and more effective therapeutic modality. This chapter highlights the design and synthesis of novel, pharmacologically active CB1R allosteric modulators and emphasizes how their molecular properties and the positive and negative allosteric control they exert can lead to improved CB1R-targeted pharmacotherapeutics, as well as designer covalent probes that can be used to map CB1R allosteric binding domains and inform structure-based drug design.

Enantiospecific Allosteric Modulation of Cannabinoid 1 Receptor

The cannabinoid 1 receptor (CB1R) is one of the most widely expressed metabotropic G protein-coupled receptors in brain, and its participation in various (patho)physiological processes has made CB1R activation a viable therapeutic modality. Adverse psychotropic effects limit the clinical utility of CB1R orthosteric agonists and have promoted the search for CB1R positive allosteric modulators (PAMs) with the promise of improved drug-like pharmacology and enhanced safety over typical CB1R agonists. In this study, we describe the synthesis and in vitro and ex vivo pharmacology of the novel allosteric CB1R modulator GAT211 (racemic) and its resolved enantiomers, GAT228 (R) and GAT229 (S). GAT211 engages CB1R allosteric site(s), enhances the binding of the orthosteric full agonist [³H]CP55,490, and reduces the binding of the orthosteric antagonist/inverse agonist [³H]SR141716A. GAT211 displayed both PAM and agonist activity in HEK293A and Neuro2a cells expressing human recombinant CB1R (hCB1R) and in mouse-brain membranes rich in native CB1R. GAT211 also exhibited a strong PAM effect in isolated vas deferens endogenously expressing CB1R. Each resolved and crystallized GAT211 enantiomer showed a markedly distinctive pharmacology as a CB1R allosteric modulator. In all biological systems examined, GAT211's allosteric agonist activity resided with the R-(+)-enantiomer (GAT228), whereas its PAM activity resided with the S-(-)-enantiomer (GAT229), which lacked intrinsic activity. These results constitute the first demonstration of enantiomer-selective CB1R positive allosteric modulation and set a precedent whereby enantiomeric resolution can decisively define the molecular pharmacology of a CB1R allosteric ligand.

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

The cannabinoid CB2 receptor (CB2R) represents a promising therapeutic target for various forms of tissue injury and inflammatory diseases. Although numerous compounds have been developed and widely used to target CB2R, their selectivity, molecular mode of action and pharmacokinetic properties have been poorly characterized. Here we report the most extensive characterization of the molecular pharmacology of the most widely used CB2R ligands to date. In a collaborative effort between multiple academic and industry laboratories, we identify marked differences in the ability of certain agonists to activate distinct signalling pathways and to cause off-target effects. We reach a consensus that HU910, HU308 and JWH133 are the recommended selective CB2R agonists to study the role of CB2R in biological and disease processes. We believe that our unique approach would be highly suitable for the characterization of other therapeutic targets in drug discovery research.

Mapping Cannabinoid 1 Receptor Allosteric Site(s): Critical Molecular Determinant and Signaling Profile of GAT100, a Novel, Potent, and Irreversibly Binding Probe

One of the most abundant G-protein coupled receptors (GPCRs) in brain, the cannabinoid 1 receptor (CB1R), is a tractable therapeutic target for treating diverse psychobehavioral and somatic disorders. Adverse on-target effects associated with small-molecule CB1R orthosteric agonists and inverse agonists/antagonists have plagued their translational potential. Allosteric CB1R modulators offer a potentially safer modality through which CB1R signaling may be directed for therapeutic benefit. Rational design of candidate, druglike CB1R allosteric modulators requires greater understanding of the architecture of the CB1R allosteric endodomain(s) and the capacity of CB1R allosteric ligands to tune the receptor's information output. We have recently reported the synthesis of a focused library of rationally designed, covalent analogues of Org27569 and PSNCBAM-1, two prototypic CB1R negative allosteric modulators (NAMs). Among the novel, pharmacologically active CB1R NAMs reported, the isothiocyanate GAT100 emerged as the lead by virtue of its exceptional potency in the [(35)S]GTPγS and β-arrestin signaling assays and its ability to label CB1R as a covalent allosteric probe with significantly reduced inverse agonism in the [(35)S]GTPγS assay as compared to Org27569. We report here a comprehensive functional profiling of GAT100 across an array of important downstream cell-signaling pathways and analysis of its potential orthosteric probe-dependence and signaling bias. The results demonstrate that GAT100 is a NAM of the orthosteric CB1R agonist CP55,940 and the endocannabinoids 2-arachidonoylglycerol and anandamide for β-arrestin1 recruitment, PLCβ3 and ERK1/2 phosphorylation, cAMP accumulation, and CB1R internalization in HEK293A cells overexpressing CB1R and in Neuro2a and STHdh(Q7/Q7) cells endogenously expressing CB1R. Distinctively, GAT100 was a more potent and efficacious CB1R NAM than Org27569 and PSNCBAM-1 in all signaling assays and did not exhibit the inverse agonism associated with Org27569 and PSNCBAM-1. Computational docking studies implicate C7.38(382) as a key feature of GAT100 ligand-binding motif. These data help inform the engineering of newer-generation, druggable CB1R allosteric modulators and demonstrate the utility of GAT100 as a covalent probe for mapping structure-function correlates characteristic of the druggable CB1R allosteric space.

A high efficacy cannabinergic ligand (AM4054) used as a discriminative stimulus: Generalization to other adamantyl analogs and Δ(9)-THC in rats

In addition to endogenous lipids, the two main cloned receptors (CB1R and CB2R) of the endocannabinoid signaling system (ECS) can be activated (and blocked) by various exogenous ligands. A relatively novel template for CB1R activators contains an adamantyl moiety as a key structural subunit, the first being the cannabinergic AM411. Additional chemical optimization efforts using the classical tricyclic scaffold led to AM4054. Here we explored the in vivo consequences of novel adamantyl analogs in rats trained to recognize the effects of the potent adamantyl cannabinergic AM4054. Rats were trained to discriminate between AM4054 (0.1mg/kg) and vehicle. Three AM4054 analogs and Δ(9)-THC were tested for generalization (substitution) and antagonism was assessed with rimonabant. We found that all cannabinergics resulted in response generalization to the target stimulus AM4054. The order of potency was: AM4054≥AM4083≥AM4050>AM4089>Δ(9)-THC. The CB1R antagonist/inverse agonist rimonabant blocked the discriminative stimulus effects of AM4054. Thus the examined structural modifications affected binding affinities but did not markedly change potencies with the exception of AM4089. In vitro (cAMP assay) functional data have suggested that AM4089 behaves as a partial rather than as a full agonist at CB1R which could explain its lower potency compared to AM4054 (Thakur et al., 2013). The 9β-formyl functionality at C-9 position was identified as an important pharmacophore yielding high in vivo potency. Antagonism by rimonabant suggested CB1R mediation.

Computational prediction of formulation strategies for beyond-rule-of-5 compounds

The physicochemical properties of some contemporary drug candidates are moving towards higher molecular weight, and coincidentally also higher lipophilicity in the quest for biological selectivity and specificity. These physicochemical properties move the compounds towards beyond rule-of-5 (B-r-o-5) chemical space and often result in lower water solubility. For such B-r-o-5 compounds non-traditional delivery strategies (i.e. those other than conventional tablet and capsule formulations) typically are required to achieve adequate exposure after oral administration. In this review, we present the current status of computational tools for prediction of intestinal drug absorption, models for prediction of the most suitable formulation strategies for B-r-o-5 compounds and models to obtain an enhanced understanding of the interplay between drug, formulation and physiological environment. In silico models are able to identify the likely molecular basis for low solubility in physiologically relevant fluids such as gastric and intestinal fluids. With this baseline information, a formulation scientist can, at an early stage, evaluate different orally administered, enabling formulation strategies. Recent computational models have emerged that predict glass-forming ability and crystallisation tendency and therefore the potential utility of amorphous solid dispersion formulations. Further, computational models of loading capacity in lipids, and therefore the potential for formulation as a lipid-based formulation, are now available. Whilst such tools are useful for rapid identification of suitable formulation strategies, they do not reveal drug localisation and molecular interaction patterns between drug and excipients. For the latter, Molecular Dynamics simulations provide an insight into the interplay between drug, formulation and intestinal fluid. These different computational approaches are reviewed. Additionally, we analyse the molecular requirements of different targets, since these can provide an early signal that enabling formulation strategies will be required. Based on the analysis we conclude that computational biopharmaceutical profiling can be used to identify where non-conventional gateways, such as prediction of 'formulate-ability' during lead optimisation and early development stages, are important and may ultimately increase the number of orally tractable contemporary targets.

Novel Electrophilic and Photoaffinity Covalent Probes for Mapping the Cannabinoid 1 Receptor Allosteric Site(s)

Undesirable side effects associated with orthosteric agonists/antagonists of cannabinoid 1 receptor (CB1R), a tractable target for treating several pathologies affecting humans, have greatly limited their translational potential. Recent discovery of CB1R negative allosteric modulators (NAMs) has renewed interest in CB1R by offering a potentially safer therapeutic avenue. To elucidate the CB1R allosteric binding motif and thereby facilitate rational drug discovery, we report the synthesis and biochemical characterization of first covalent ligands designed to bind irreversibly to the CB1R allosteric site. Either an electrophilic or a photoactivatable group was introduced at key positions of two classical CB1R NAMs: Org27569 (1) and PSNCBAM-1 (2). Among these, 20 (GAT100) emerged as the most potent NAM in functional assays, did not exhibit inverse agonism, and behaved as a robust positive allosteric modulator of binding of orthosteric agonist CP55,940. This novel covalent probe can serve as a useful tool for characterizing CB1R allosteric ligand-binding motifs.

Medicinal chemistry of cannabinoids

The endocannabinoid system comprises the two well characterized G_i/o‐protein coupled receptors (cannabinoid receptor 1 (CB1) and CB2), their endogenous lipid ligands, and the enzymes involved in their biosynthesis and biotransformation. Drug discovery efforts relating to the endocannabinoid system have been focused mainly on the two cannabinoid receptors and the two endocannabinoid deactivating enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL). This review provides an overview of cannabinergic agents used in drug research and those being explored clinically.

N-Bridged 5,6-bicyclic pyridines: Recent applications in central nervous system disorders

The search for novel heterobicyclic compounds within the drug-like chemical space continues to be an area of interest in medicinal chemistry. Unsaturated N-bridgehead heterocycles are well represented in marketed drugs for a variety of therapeutic areas, and continue to play an important role in central nervous system (CNS) drug discovery programs. Examples of medicinal chemistry strategies that make use of N-bridged 5,6-bicyclic pyridines are discussed here in this Minireview, which covers the literature from 2010 up to 2014. B1-class imidazopyridines and B3-class pyrazolopyridines have proven to be at the forefront of molecular prototypes that are capable of interacting with disease relevant targets in neurodegeneration and neuropsychiatry.

β-Caryophyllene, a CB2 receptor agonist produces multiple behavioral changes relevant to anxiety and depression in mice

Recent evidence suggests that the cannabinoid receptor subtype 2 (CB2) is implicated in anxiety and depression disorders, although few systematic studies in laboratory animals have been reported. The aim of the current experiments was to test the effects of the CB2 receptor potent-selective agonist β-caryophyllene (BCP) in animals subjected to models of anxiolytic- and antidepressant-like effects. Therefore effects of BCP (50mg/kg) on anxiety were assessed using the elevated plus maze (EPM), open field (OF), and marble burying test (MBT). However for depression, the novelty-suppressed feeding (NSF), tail suspension test (TST), and forced swim tests (FST) were used. Results indicated that adult mice receiving BCP showed amelioration of all the parameters observed in the EPM test. Also, BCP significantly increased the time spent in the center of the arena without altering the general motor activity in the OF test. This dose was also able to decrease the number of buried marbles and time spent digging in the MBT, suggesting an anti-compulsive-like effect. In addition, the systemic administration of BCP reduced immobility time in the TST and the FST. Finally, BCP treatment decreased feeding latency in the NSF test. Most importantly, pre-administration of the CB2 receptor antagonist AM630, fully abrogated the anxiolytic and the anti-depressant effects of BCP. Taken together, these preclinical results suggest that CB2 receptors may provide alternative therapeutic targets for the treatment of anxiety and depression. The possibility that BCP may ameliorate the symptoms of these mood disorders offers exciting prospects for future studies.

Predicting the molecular interactions of CRIP1a-cannabinoid 1 receptor with integrated molecular modeling approaches

Cannabinoid receptors are a family of G-protein coupled receptors that are involved in a wide variety of physiological processes and diseases. One of the key regulators that are unique to cannabinoid receptors is the cannabinoid receptor interacting proteins (CRIPs). Among them CRIP1a was found to decrease the constitutive activity of the cannabinoid type-1 receptor (CB1R). The aim of this study is to gain an understanding of the interaction between CRIP1a and CB1R through using different computational techniques. The generated model demonstrated several key putative interactions between CRIP1a and CB1R, including the critical involvement of Lys130 in CRIP1a.

Cannabinoids: Do they have the potential to treat the symptoms of multiple sclerosis?

This article reviews the role of cannabinoids in inhibiting neurodegeneration in models of multiple sclerosis (MS). MS is a chronic, debilitating disease of the central nervous system (CNS), induced by autoimmunity-driven inflammation that leads to demyelination and thus disconnection of the normal transmission of nerve impulses. Despite the use of an array of immune modulating drugs that restore blood brain barrier function, disability continues in patients concomitant with the loss of axons in the spinal cord. MS patients therefore suffer neuropathic pain, spasticity and tremor. Anecdotal evidence suggests that MS patients using cannabis, though illegal, achieve symptomatic relief from neuropathic pain and spasticity associated with MS. The discovery of the endogenous cannabinoid (endocannabinoid) system that naturally exists in the body and which responds to cannabinoids to exert their effects has aided research into the therapeutic utility of cannabinoids. The endocannabinoid system consists of two G-protein coupled receptors cannabinoid receptor type-1 (CB₁) and CB₂. CB₁ is mainly expressed in the CNS and CB₂ is predominantly found in leukocytes, while an increasing number of potential ligands and endocannabinoid degradation molecules are being isolated. Several studies have highlighted the involvement of this system in regulating neurotransmission and its ability to prevent excessive neurotransmitter release, consistent with a capacity to provide symptomatic relief. In summary, antagonism of the CB₁ receptor pathway contributes to neuronal damage in chronic relapsing experimental allergic encephalomyelitis (EAE) and suppresses tremor and spasticity. The addition of exogenous CB₁ agonists derived from cannabis also afforded significant neuroprotection from the consequences of inflammatory CNS disease in EAE and experimental allergic uveitis models. Although clear neuroprotective benefits of cannabinoids have been demonstrated, the unwanted psychotropic effects need to be addressed. However, manipulating the endogenous cannabinoid system may be one way of eliciting beneficial effects without some or all of the unwanted side effects.

Radiofluorination and biological evaluation of N-aryl-oxadiazolyl-propionamides as potential radioligands for PET imaging of cannabinoid CB2 receptors

Background

The level of expression of cannabinoid receptor type 2 (CB₂R) in healthy and diseased brain has not been fully elucidated. Therefore, there is a growing interest to assess the regional expression of CB₂R in the brain. Positron emission tomography (PET) is an imaging technique, which allows quantitative monitoring of very low amounts of radiolabelled compounds in living organisms at high temporal and spatial resolution and, thus, has been widely used as a diagnostic tool in nuclear medicine. Here, we report on the radiofluorination of N-aryl-oxadiazolyl-propionamides at two different positions in the lead structure and on the biological evaluation of the potential of the two tracers [¹⁸F]1 and [¹⁸F]2 as CB₂ receptor PET imaging agents.

Results

High binding affinity and specificity towards CB₂ receptors of the lead structure remained unaffected by the structural changes such as the insertion of the aliphatic and aromatic fluorine in the selected labelling sites of 1 and 2. Aliphatic and aromatic radiofluorinations were optimized, and [¹⁸F]1 and [¹⁸F]2 were achieved in radiochemical yields of ≥30% with radiochemical purities of ≥98% and specific activities of 250 to 450 GBq/μmol. Organ distribution studies in female CD1 mice revealed that both radiotracers cross the blood–brain barrier (BBB) but undergo strong peripheral metabolism. At 30 min after injection, unmetabolized [¹⁸F]1 and [¹⁸F]2 accounted for 60% and 2% as well as 68% and 88% of the total activity in the plasma and brain, respectively. The main radiometabolite of [¹⁸F]2 could be identified as the free acid [¹⁸F]10, which has no affinity towards the CB₁ and CB₂ receptors but can cross the BBB.

Conclusions

N-aryl-oxadiazolyl-propionamides can successfully be radiolabelled with ¹⁸F at different positions. Fluorine substitution at these positions did not affect affinity and specificity towards CB₂R. Despite a promising in vitro behavior, a rather rapid peripheral metabolism of [¹⁸F]1 and [¹⁸F]2 in mice and the generation of brain permeable radiometabolites hamper the application of these radiotracers in vivo. However, it is expected that future synthetic modification aiming at a replacement of metabolically susceptible structural elements of [¹⁸F]1 and [¹⁸F]2 will help to elucidate the potential of this class of compounds for CB₂R PET studies.

Selective cannabinoid receptor type 2 (CB2) agonists: optimization of a series of purines leading to the identification of a clinical candidate for the treatment of osteoarthritic pain

A focused screening strategy identified thienopyrimidine 12 as a cannabinoid receptor type 2 agonist (hCB2) with moderate selectivity over the hCB1 receptor. This initial hit suffered from poor in vitro metabolic stability and high in vivo clearance. Structure-activity relationships describe the optimization and modification to a new more polar series of purine CB2 agonists. Examples from this novel scaffold were found to be highly potent and fully efficacious agonists of the human CB2 receptor with excellent selectivity against CB1, often having no CB1 agonist activity at the highest concentration measured (>100 μM). Compound 26 is a centrally penetrant molecule which possesses good biopharmaceutical properties, is highly water-soluble, and demonstrates robust oral activity in rodent models of joint pain. In addition, the peripherally restricted molecule 22 also demonstrated significant efficacy in the same analgesic model of rodent inflammatory pain.

Novel adamantyl cannabinoids as CB1 receptor probes

In previous studies, compound 1 (AM411), a 3-(1-adamantyl) analogue of the phytocannabinoid (-)-Δ(8)-tetrahydrocannabinol (Δ(8)-THC), was shown to have improved affinity and selectivity for the CB1 receptor. In this work, we further explored the role of the 1-adamantyl group at the C-3 position in a series of tricyclic cannabinoid analogues modified at the 9-northern aliphatic hydroxyl (NAH) position. Of these, 9-hydroxymethyl hexahydrocannabinol 11 (AM4054) exhibited high CB1 affinity and full agonist profile. In the cAMP assay, the 9-hydroxymethyl cannabinol analogue 24 (AM4089) had a partial agonist profile, with high affinity and moderate selectivity for rCB1 over hCB2. In vivo results in rat models of hypothermia and analgesia were congruent with in vitro data. Our in vivo data indicate that 3-(1-adamantyl) substitution, within NAH cannabinergics, imparts improved pharmacological profiles when compared to the corresponding, traditionally used 3-dimethylheptyl analogues and identifies 11 and 24 as potentially useful in vivo CB1 cannabinergic probes.

Design, synthesis, and binding mode prediction of 2-pyridone-based selective CB2 receptor agonists

Selective CB2 agonists have the potential for treating pain without central CB1-mediated adverse effects. Screening efforts identified 1,2-dihydro-3-isoquinolone 1; however, this compound has the drawbacks of being difficult to synthesize with two asymmetric carbons on an isoquinolone scaffold and of having a highly lipophilic physicochemical property. To address these two major problems, we designed the 2-pyridone-based lead 15a, which showed moderate affinity for CB2. Optimization of 15a led to identification of 39f with high affinity for CB2 and selectivity over CB1. Prediction of the binding mode of 39f in complex with an active-state CB2 homology model provided structural insights into its high affinity for CB2.

7-Alkyl-3-benzylcoumarins: a versatile scaffold for the development of potent and selective cannabinoid receptor agonists and antagonists

A series of 7-alkyl-3-benzylcoumarins was designed, synthesized, and tested at cannabinoid CB(1) and CB(2) receptors in radioligand binding and cAMP accumulation studies. 7-Alkyl-3-benzylcoumarins were found to constitute a versatile scaffold for obtaining potent CB receptor ligands with high potency at either CB(1) or CB(2) and a broad spectrum of efficacies. Fine-tuning of compound properties was achieved by small modifications of the substitution pattern. The most potent compounds of the present series include 5-methoxy-3-(2-methylbenzyl)-7-pentyl-2H-chromen-2-one (19a, PSB-SB-1201), a selective CB(1)antagonist (K(i) CB(1) 0.022 μM), 5-methoxy-3-(2-methoxybenzyl)-7-pentyl-2H-chromen-2-one (21a, PSB-SB-1202), a dual CB(1)/CB(2)agonist (CB(1)K(i) 0.032 μM, EC(50) 0.056 μM; CB(2)K(i) 0.049 μM, EC(50) 0.014 μM), 5-hydroxy-3-(2-hydroxybenzyl)-7-(2-methyloct-2-yl)-2H-chromen-2-one (25b, PSB-SB-1203), a dual CB(1)/CB(2) ligand that blocks CB(1) but activates CB(2) receptors (CB(1)K(i) 0.244 μM; CB(2)K(i) 0.210 μM, EC(50) 0.054 μM), and 7-(1-butylcyclopentyl)-5-hydroxy-3-(2-hydroxybenzyl)-2H-chromen-2-one (27b, PSB-SB-1204), a selective CB(2) receptor agonist (CB(1)K(i) 1.59 μM; CB(2)K(i) 0.068 μM, EC(50) 0.048 μM).

Use of SPME-HS-GC-MS for the analysis of herbal products containing synthetic cannabinoids

The increasing prevalence and use of herbal mixtures containing synthetic cannabinoids presents a growing public health concern and legal challenge for society. In contrast to the plant-derived cannabinoids in medical marijuana and other cannabinoid-based therapeutics, the commonly encountered synthetic cannabinoids in these mendaciously labeled products constitute a structurally diverse set of compounds of relatively unknown pharmacology and toxicology. Indeed, the use of these substances has been associated with an alarming number of hospitalizations and emergency room visits. Moreover, there are already several hundred known cannabinoid agonist compounds that could potentially be used for illicit purposes, posing an additional challenge for public health professionals and law enforcement efforts, which often require the detection and identification of the active ingredients for effective treatment or prosecution. A solid-phase microextraction headspace gas chromatography-mass spectrometry method is shown here to allow for rapid and reliable detection and structural identification of many of the synthetic cannabinoid compounds that are currently or could potentially be used in herbal smoking mixtures. This approach provides accelerated analysis and results that distinguish between structural analogs within several classes of cannabinoid compounds, including positional isomers. The analytical results confirm the continued manufacture and distribution of herbal materials with synthetic cannabinoids and provide insight into the manipulation of these products to avoid legal constraints and prosecution.

Recent Advances in Selective CB2 Agonists for the Treatment of Pain

The cannabinoid CB2 receptor is one of a family of GPCRs that mediate the effects of endocannabinoids. Several agonists of this receptor are currently in clinical trials for the treatment of pain and inflammation, indications that have been validated by pre-clinical studies on agonists and in receptor knockout mice. Key to the clinical advancement of CB2 agonists is achieving selectivity over the related CB1 receptor, whose activation results in undesirable CNS effects, limiting therapeutic utility. A variety of CB2 receptor agonist chemotypes are reviewed including mono-, bi- and tricyclic cores and bi- and triaryl cores. Pharmacology, with a focus on selectivity requirements and a variety of pre-clinical animal models to assess activity and selectivity, is presented.

CB₂: therapeutic target-in-waiting

CB₂ cannabinoid receptor agonists hold promise as a new class of therapeutics for indications as diverse as pain, neuroinflammation, immune suppression and osteoporosis. These potential indications are supported by strong preliminary data from multiple investigators using diverse preclinical models. However, clinical trials for CB₂ agonists, when they have been reported have generally been disappointing. This review considers possible explanations for the mismatch between promising preclinical data and disappointing clinical data. We propose that a more careful consideration of CB₂ receptor pharmacology may help move CB₂ agonists from "promising" to "effective" therapeutics.

Selective cannabinoid receptor 2 modulators: a patent review 2009--present

INTRODUCTION

The activation of the cannabinoid receptor 2 (CB2) affects a myriad of immune responses from inflammation to neuroprotection, demonstrates analgesic effects and suppresses responses in many animal models of pain. Questions around the involvement of CB1 activation in these effects remain, but efforts have been directed toward the discovery of highly selective CB2 modulators lacking the psychotropic effects of cannabinoids, which are mediated by the CB1 receptor.

AREAS COVERED

This review covers the patent literature which was published since April 2009 on CB2 selective modulators. It provides a general summary of the CB2 biology supporting the interest in CB2 as a drug target, new potential therapeutic indications and the development status of selective CB2 agonists.

EXPERT OPINION

There is a continuous interest in the CB2 receptor as a drug target. Many highly selective compounds of various chemotypes have been identified and their analgesic effects in animal models further support the potential of this mechanism in pain therapy. Several companies have initiated clinical trials. While some of these have been terminated for various reasons, one can anticipate the emergence of new drugs from CB2 modulation once a better understanding around the cannabinoid receptors is gained.

Immunofluorescent spectral analysis reveals the intrathecal cannabinoid agonist, AM1241, produces spinal anti-inflammatory cytokine responses in neuropathic rats exhibiting relief from allodynia

During pathological pain, the actions of the endocannabinoid system, including the cannabinoid 2 receptor (CB(2)R), leads to effective anti-allodynia and modifies a variety of spinal microglial and astrocyte responses. Here, following spinal administration of the CB(2)R compound, AM1241, we examined immunoreactive alterations in markers for activated p38 mitogen-activated protein kinase, interleukin-1β (IL-1β), the anti-inflammatory cytokine, interleukin-10 (IL-10) as well as degradative endocannabinoid enzymes, and markers for altered glial responses in neuropathic rats. In these studies, the dorsal horn of the spinal cord and dorsal root ganglia were examined. AM1241 produced profound anti-allodynia with corresponding immunoreactive levels of p38 mitogen-activated kinase, IL-1β, IL-10, the endocannabinoid enzyme monoacylglycerol lipase, and astrocyte activation markers that were similar to nonneuropathic controls. In contrast, spinal AM1241 did not suppress the increased microglial responses observed in neuropathic rats. The differences in fluorescent markers were determined within discrete anatomical regions by applying spectral analysis methods, which virtually eliminated nonspecific signal during the quantification of specific immunofluorescent intensity. These data reveal expression profiles that support the actions of intrathecal AM1241 control pathological pain through anti-inflammatory mechanisms by modulating critical glial factors, and additionally decrease expression levels of endocannabinoid degradative enzymes.

γ-Carbolines: a novel class of cannabinoid agonists with high aqueous solubility and restricted CNS penetration

An oral, peripherally restricted CB1/CB2 agonist could provide an interesting approach to treat chronic pain by harnessing the analgesic properties of cannabinoids but without the well-known central side effects. γ-Carbolines are a novel class of potent mixed CB1/CB2 agonists characterized by attractive physicochemical properties including high aqueous solubility. Optimization of the series has led to the discovery of 29, which has oral activity in a rat inflammatory pain model and limited brain exposure at analgesic doses, consistent with a lower risk of CNS-mediated tolerability issues.

Central and peripheral cannabinoid receptors as therapeutic targets in the control of food intake and body weight

The endocannabinoid system consists of lipid-derived agonists that activate cannabinoid (CB) receptors. CB receptor agonists, namely, the phytocannabinoid Δ(9)-THC and the endocannabinoid anandamide, increase hunger sensation and food intake. These discoveries led to the clinical use of Δ(9)-THC derivatives for the treatment of cancer and HIV-related nausea and cachexia. Animal studies clarified the important role of CB1 receptors in the hypothalamus and in the limbic system in mediating orexigenic effects. In parallel, data on CB1-specific blockade either by drugs or by genetic ablation further demonstrated that CB1 inhibition protects against weight gain induced by high-fat feeding and reduces body weight in obese animals and humans. The mechanisms of weight reduction by CB1 blockade are complex: they comprise interactions with several orexigenic and anorexigenic neuropeptides and hormones, regulation of sympathetic activity, influences on mitochondrial function, and on lipogenesis. Although these mechanisms appear to be mainly mediated by the CNS, weight loss also occurs when drugs that do not reach CNS concentrations sufficient to inhibit CB1 signaling are used. The development of peripherally restricted CB1 inverse agonists and antagonists opened new routes in CB1 pharmacology because centrally acting CB1 inverse agonists, e.g., rimonabant and taranabant, exerted unacceptable side effects that precluded their further development and application as weight loss drugs. Tissue and circulating endocannabinoid concentrations are often increased in animal models of obesity and in obese humans, especially those with visceral fat accumulation. Thus, further research on CB1 inhibition is still promising to treat human obesity.

The Central Role of Glia in Pathological Pain and the Potential of Targeting the Cannabinoid 2 Receptor for Pain Relief

Under normal conditions, acute pain processing consists of well-characterized neuronal signaling events. When dysfunctional pain signaling occurs, pathological pain ensues. Glial activation and their released factors participate in the mediation of pathological pain. The use of cannabinoid compounds for pain relief is currently an area of great interest for both basic scientists and physicians. These compounds, bind mainly either the cannabinoid receptor subtype 1 (CB(1)R) or cannabinoid receptor subtype 2 (CB(2)R) and are able to modulate pain. Although cannabinoids were initially only thought to modulate pain via neuronal mechanisms within the central nervous system, strong evidence now supports that CB(2)R cannabinoid compounds are capable of modulating glia, (e.g. astrocytes and microglia) for pain relief. However, the mechanisms underlying cannabinoid receptor-mediated pain relief remain largely unknown. An emerging body of evidence supports that CB(2)R agonist compounds may prove to be powerful novel therapeutic candidates for the treatment of chronic pain.