Activation and Signaling Mechanism Revealed by Cannabinoid Receptor-Gi Complex Structures

The Interplay between the Immune and the Endocannabinoid Systems in Cancer

The therapeutic potential of Cannabis sativa has been recognized since ancient times. Phytocannabinoids, endocannabinoids and synthetic cannabinoids activate two major G protein-coupled receptors, subtype 1 and 2 (CB1 and CB2). Cannabinoids (CBs) modulate several aspects of cancer cells, such as apoptosis, autophagy, proliferation, migration, epithelial-to-mesenchymal transition and stemness. Moreover, agonists of CB1 and CB2 receptors inhibit angiogenesis and lymphangiogenesis in vitro and in vivo. Low-grade inflammation is a hallmark of cancer in the tumor microenvironment (TME), which contains a plethora of innate and adaptive immune cells. These cells play a central role in tumor initiation and growth and the formation of metastasis. CB2 and, to a lesser extent, CB1 receptors are expressed on a variety of immune cells present in TME (e.g., T cells, macrophages, mast cells, neutrophils, NK cells, dendritic cells, monocytes, eosinophils). The activation of CB receptors modulates a variety of biological effects on cells of the adaptive and innate immune system. The expression of CB2 and CB1 on different subsets of immune cells in TME and hence in tumor development is incompletely characterized. The recent characterization of the human cannabinoid receptor CB2-G_i signaling complex will likely aid to design potent and specific CB2/CB1 ligands with therapeutic potential in cancer.

Biosynthesis of Nature-Inspired Unnatural Cannabinoids

Natural products make up a large proportion of medicine available today. Cannabinoids from the plant Cannabis sativa is one unique class of meroterpenoids that have shown a wide range of bioactivities and recently seen significant developments in their status as therapeutic agents for various indications. Their complex chemical structures make it difficult to chemically synthesize them in efficient yields. Synthetic biology has presented a solution to this through metabolic engineering in heterologous hosts. Through genetic manipulation, rare phytocannabinoids that are produced in low yields in the plant can now be synthesized in larger quantities for therapeutic and commercial use. Additionally, an exciting avenue of exploring new chemical spaces is made available as novel derivatized compounds can be produced and investigated for their bioactivities. In this review, we summarized the biosynthetic pathways of phytocannabinoids and synthetic biology efforts in producing them in heterologous hosts. Detailed mechanistic insights are discussed in each part of the pathway in order to explore strategies for creating novel cannabinoids. Lastly, we discussed studies conducted on biological targets such as CB1, CB2 and orphan receptors along with their affinities to these cannabinoid ligands with a view to inform upstream diversification efforts.

Molecular Dynamics Simulations for the Determination of the Characteristic Structural Differences between Inactive and Active States of Wild Type and Mutants of the Orexin2 Receptor

The orexin2 receptor (OX2R), which is classified as a class A G protein-coupled receptor (GPCR), is the target of our study. We performed over 20 several-microsecond-scale molecular dynamics simulations of the wild type and mutants of OX2R to extract the characteristics of the structural changes taking place in the active state. We introduced mutations that exhibited the stable inactive state and the constitutively active state in class A GPCRs. In these simulations, significant characteristic structural changes were observed in the V309^6.40Y mutant, which corresponded to a constitutively active mutant. These conformational changes include the outward movement of the transmembrane helix 6 (TM6) and the inward movement of TM7, which are common structural changes in the activation of GPCRs. In addition, we extracted a suitable index for the quantitative evaluation of the active and inactive states of GPCRs, namely, the inter-atomic distance of Cα atoms between x(3.46) and Y(7.53). The structures of the inactive and active states solved by X-ray crystallography and cryo-electron microscopy can be classified using the inter-atomic distance. Furthermore, we clarified that the inward movement of TM7 requires the swapping of M305^6.36 on TM6 and L367^7.56 on TM7. Finally, we discussed the structural advantages of TM7 inward movement for GPCR activation.

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®.

Amphipathic environments for determining the structure of membrane proteins by single-particle electron cryo-microscopy

Over the past decade, the structural biology of membrane proteins (MPs) has taken a new turn thanks to epoch-making technical progress in single-particle electron cryo-microscopy (cryo-EM) as well as to improvements in sample preparation. The present analysis provides an overview of the extent and modes of usage of the various types of surfactants for cryo-EM studies. Digitonin, dodecylmaltoside, protein-based nanodiscs, lauryl maltoside-neopentyl glycol, glyco-diosgenin, and amphipols (APols) are the most popular surfactants at the vitrification step. Surfactant exchange is frequently used between MP purification and grid preparation, requiring extensive optimization each time the study of a new MP is undertaken. The variety of both the surfactants and experimental approaches used over the past few years bears witness to the need to continue developing innovative surfactants and optimizing conditions for sample preparation. The possibilities offered by novel APols for EM applications are discussed.

Novel Functionalized Cannabinoid Receptor Probes: Development of Exceptionally Potent Agonists

We report the development of novel cannabinergic probes that can stabilize the cannabinoid receptors (CBRs) through tight binding interactions. Ligand design involves the introduction of select groups at a judiciously chosen position within the classical hexahydrocannabinol template (monofunctionalized probes). Such groups include the electrophilic isothiocyanato, the photoactivatable azido, and the polar cyano moieties. These groups can also be combined to produce bifunctionalized probes potentially capable of interacting at two distinct sites within the CBR-binding domains. These novel compounds display remarkably high binding affinities for CBRs and are exceptionally potent agonists. A key ligand (27a, AM11245) exhibits exceptionally high potency in both in vitro and in vivo assays and was designated as "megagonist," a property attributed to its tight binding profile. By acting both centrally and peripherally, 27a distinguishes itself from our previously reported "megagonist" AM841, whose functions are restricted to the periphery.

Endocannabinoid-mediated neuromodulation in the main olfactory bulb at the interface of environmental stimuli and central neural processing

The olfactory system has become an important functional gateway to understand and analyze neuromodulation since olfactory dysfunction and deficits have emerged as prodromal and, at other times, as first symptoms of many of neurodegenerative, neuropsychiatric and communication disorders. Considering olfactory dysfunction as outcome of altered, damaged and/or inefficient olfactory processing, in the current review, we analyze how olfactory processing interacts with the endocannabinoid signaling system. In the human body, endocannabinoid synthesis is a natural and on-demand response to a wide range of physiological and environmental stimuli. Our current understanding of the response dynamics of the endocannabinoid system is based in large part on research advances in limbic system areas, such as the hippocampus and the amygdala. Functional interactions of this signaling system with olfactory processing and associated pathways are just emerging but appear to grow rapidly with multidimensional approaches. Recent work analyzing the crystal structure of endocannabinoid receptors bound to their agonists in a signaling complex has opened avenues for developing specific therapeutic drugs that could help with neuroinflammation, neurodegeneration, and alleviation/reduction of pain. We discuss the role of endocannabinoids as signaling molecules in the olfactory system and the relevance of the endocannabinoid system for synaptic plasticity.

Reprint of "Amorphous nickel titanium alloy film: A new choice for cryo electron microscopy sample preparation"

Cryo-electron microscopy (cryoEM) has become one of the most important approach for structural biology. However, barriers are still there for an increased successful rate, a better resolution and improved efficiency from sample preparation, data collection to image processing. CryoEM sample preparation is one of the bottlenecks with many efforts made recently, including the optimization of supporting substrate (e.g. ultra-thin carbon, graphene, pure gold, 2d crystal of streptavidin, and affinity modification), which was aimed to solve air-water interface problem, or reduce beam induced motion (BIM), or change particle distribution in the grid hole. Here, we report another effort of developing a new supporting substrate, the amorphous nickel-titanium alloy (ANTA) film, for cryoEM sample preparation as a layer of holey supporting film covering on TEM grid. Our investigations showed advantages of ANTA film in comparison with conventional carbon film, including much better electron conductivity and trace non-specific interaction with protein. These advantages yield less BIM and significantly improved particle distribution during cryoEM experiment of human apo-ferritn, thus resulting an improved reconstruction resolution from a reduced number of micrographs and particles. Unlike the pure gold film, the usage of the ANTA film is just same with the carbon film, compatible to conventional automatic cryoEM data collection procedure.

CB1 allosteric modulators and their therapeutic potential in CNS disorders

CB1 is the most abundant GPCR found in the mammalian brain. It has garnered considerable attention as a potential therapeutic drug target. CB1 is involved in a wide range of physiological and psychiatric processes and has the potential to be targeted in a wide range of disease states. However, most of the selective and non-selective synthetic CB1 agonists and antagonists/inverse agonists developed to date are primarily used as research tools. No novel synthetic cannabinoids are currently in the clinic for use in psychiatric illness; synthetic analogues of the phytocannabinoid THC are on the market to treat nausea and vomiting caused by cancer chemotherapy, along with off-label use for pain. Novel strategies are being explored to target CB1, but with emphasis on the elimination or mitigation of the potential psychiatric adverse effects that are observed by central agonism/antagonism of CB1. New pharmacological options are being pursued that may avoid these adverse effects while preserving the potential therapeutic benefits of CB1 modulation. Allosteric modulation of CB1 is one such approach. In this review, we will summarize and critically analyze both the in vitro characterization and in vivo validation of CB1 allosteric modulators developed to date, with a focus on CNS therapeutic effects.

Understanding the complex pharmacology of cannabidiol: Mounting evidence suggests a common binding site with cholesterol

Cannabidiol is claimed to bind to a large number of protein targets based on in vitro assays. This suggests opportunities for a wide range of therapeutic applications. On the other hand, the existence of phytochemical 'nuisance compounds' suggests some measure of caution - these compounds are capable of altering membrane biophysical properties and changing protein function without directly contacting a binding site. Like cannabidiol, cholesterol alters membrane properties, but it also binds directly to membrane proteins through abundant cholesterol recognition sites. We present the evidence that cannabidiol and cholesterol may bind to the same site on some proteins. As a starting point for further research, we also used blind docking to show that cannabidiol binds to a cholesterol binding site on the CB1 receptor. Elucidation of the mechanism(s) of action of cannabidiol will assist the prioritisation of in vitro hits across targets, improve the success rate of medicinal chemistry campaigns, and ultimately benefit patient populations by focusing resources on programs with the most translational potential.

The impact of medical cannabis consumption on the oral flora and saliva

OBJECTIVE

To evaluate the effect of medical cannabis consumption on oral flora and saliva.

DESIGN

A clinical prospective study, at the rheumatology clinic of the Nazareth Hospital in Nazareth, recruiting consecutively patients approved for medical cannabis, evaluating their saliva flow, pH and microbial load of Streptococcus mutans and Lactobacillus, prior to and under medical cannabis treatment.

METHODS

Patients recently licensed for medical cannabis treatment, were recruited just prior to starting medical cannabis consumption (week 0), 1 and 4 weeks later, patients provided 5-minute time saliva samples, which were measured for their volume and pH, and cultured on a special microbial kit, evaluating the growth of Streptococcus mutans and Lactobacillus.

RESULTS

Out of 16 patients enrolled, 14 were female and had fibromyalgia. The mean age of the patients was 52.8±12.9 years. The mean saliva flow at week 0, week 1 and week 4 were 5.38±3.36 ml/5-minutes, 6 (p = 0.769) and 5.45 (p = 0.391), respectively, and for saliva pH were 6.28, 5.94 (p = 0.51) and 5.5 (p = 0.07) respectively also. The mean Streptococcus mutans growth score at weeks 0, 1 and 4 was1.8±0.75, 1.6±0.83 (p = 0.234), and 2.4±0.84 (p = 0.058), respectively. The mean Lactobacilli growth score at weeks 0, 1 and 4 was 2.59±0.88, 3.1±0.69 (p = 0.033) and 3.3±0.67 (p = 0.025), respectively.

CONCLUSIONS

The results of this study show that medical cannabis consumption has no significant effect on saliva volume or pH, but it may be associated with changes in salivary levels of oral microbes such as Streptococcus mutans and Lactobacilli.

Broadly Neutralizing Synthetic Cannabinoid Vaccines

Synthetic cannabinoids (SCs) constitute a significant portion of psychoactive substances forming a major public health risk. Due to the wide variety of SCs, broadly neutralizing antibodies generated by active immunization present an intriguing pathway to combat cannabinoid use disorder. Here, we probed hapten design for antibody affinity and cross reactivity against two classes of SCs. Of the 10 haptens screened, 3 vaccine groups revealed submicromolar IC₅₀, each targeting 5-6 compounds in our panel of 22 drugs. Moreover, SCs were successfully sequestered when administered by vaping or intraperitoneal injection, which was confirmed within animal models by observing locomotion, body temperature, and pharmacokinetics. We also discovered synergistic effects to simultaneously blunt two drug classes through an admixture vaccine approach. Collectively, our study provides a comprehensive foundation for the development of vaccines against SCs.

Relevance of Peroxisome Proliferator Activated Receptors in Multitarget Paradigm Associated with the Endocannabinoid System

Cannabinoids have shown to exert their therapeutic actions through a variety of targets. These include not only the canonical cannabinoid receptors CB1R and CB2R but also related orphan G protein-coupled receptors (GPCRs), ligand-gated ion channels, transient receptor potential (TRP) channels, metabolic enzymes, and nuclear receptors. In this review, we aim to summarize reported compounds exhibiting their therapeutic effects upon the modulation of CB1R and/or CB2R and the nuclear peroxisome proliferator-activated receptors (PPARs). Concomitant actions at CBRs and PPARα or PPARγ subtypes have shown to mediate antiobesity, analgesic, antitumoral, or neuroprotective properties of a variety of phytogenic, endogenous, and synthetic cannabinoids. The relevance of this multitargeting mechanism of action has been analyzed in the context of diverse pathologies. Synergistic effects triggered by combinatorial treatment with ligands that modulate the aforementioned targets have also been considered. This literature overview provides structural and pharmacological insights for the further development of dual cannabinoids for specific disorders.

The Chemistry of Cannabis and Cannabinoids

The science of cannabis and cannabinoids encompasses a wide variety of scientific disciplines and can appear daunting to newcomers to the field. The encroachment of folklore and ‘cannabis culture’ into scientific discussions can cloud the situation further. This Primer Review is designed to give a succinct overview of the chemistry of cannabis and cannabinoids. It is hoped that it will provide a useful resource for chemistry undergraduates, postgraduates and their instructors, and experienced chemists who require a comprehensive and up to date summary of the field. The Review begins with a brief overview of the history and botany of cannabis, then goes on to detail important aspects of the chemistry of phytocannabinoids, endocannabinoids and synthetic cannabinomimetics. Other natural constituents of the cannabis plant are then described including terpenes and terpenoids, polyphenolics, alkaloids, waxes and triglycerides, and important toxic contaminants. A discussion of key aspects of the pharmacology associated with cannabinoids and the endocannabinoid system then follows, with a focus on the cannabinoid receptors, CB1 and CB2. The medicinal chemistry of cannabis and cannabinoids is covered, highlighting the range of diseases targeted with cannabis and phytocannabinoids, as well as key aspects of phytocannabinoid metabolism, distribution, and delivery. The modulation of endocannabinoid levels through the inhibition of key endocannabinoid-degrading enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) is then discussed. The Review concludes with an assessment of the much touted ‘entourage effect’. References to primary literature and more specialised reviews are provided throughout.

Development of Chromenopyrazole-Based Selective Cannabinoid 2 Receptor Agonists

The cannabinoid type 2 receptor (CB2R) is an important therapeutic target for pain and inflammatory disorders. G protein-coupled receptors (GPCRs) are conventionally thought to signal exclusively at the plasma membrane; however, recently this has been challenged by the notion of intracellular signalling receptors. Better understanding of GPCR location requires tools that can differentiate cell surface versus subcellular receptors as well as accessing different parts of the body. Herein, we report the synthesis and pharmacological evaluation of polar chromenopyrazole-based CB2R-selective agonists that contain short peptides that could be useful tools for interrogating CB2R.

Positron Emission Tomography Imaging of the Endocannabinoid System: Opportunities and Challenges in Radiotracer Development

The endocannabinoid system (ECS) is involved in a wide range of biological functions and comprises cannabinoid receptors and enzymes responsible for endocannabinoid synthesis and degradation. Over the past 2 decades, significant advances toward developing drugs and positron emission tomography (PET) tracers targeting different components of the ECS have been made. Herein, we summarized the recent development of PET tracers for imaging cannabinoid receptors 1 (CB1R) and 2 (CB2R) as well as the key enzymes monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), particularly focusing on PET neuroimaging applications. State-of-the-art PET tracers for the ECS will be reviewed including their chemical design, pharmacological properties, radiolabeling, as well as preclinical and human PET imaging. In addition, this review addresses the current challenges for ECS PET biomarker development and highlights the important role of PET ligands to study disease pathophysiology as well as to facilitate drug discovery.

Trifluorinated Keto-Enol Tautomeric Switch in Probing Domain Rotation of a G Protein-Coupled Receptor

Conformational dynamics and transitions of biologically active molecules are pivotal for understanding the physiological responses they elicit. In the case of receptor activation, there are major implications elucidating disease mechanisms and drug discovery innovation. Yet, incorporation of these factors into drug screening systems remains challenging in part due to the lack of suitable approaches to include them. Here, we present a novel strategy to probe the GPCR domain rotation by utilizing the ¹⁹fluorine signal variability of a trifluorinated keto-enol (TFKE) chemical equilibrium. The method takes advantage of the high sensitivity of the TFKE tautomerism toward microenvironmental changes resulting from receptor conformational transitions upon ligand binding. We validated the method using the adenosine A_2AR receptor as a model system in which the TFKE was attached to two sites exhibiting opposing motions upon ligand binding, namely, V229C^6.31 on transmembrane domain VI (TM6) and A289C^7.54 on TM7. Our results demonstrated that the TFKE switch was an excellent reporter for the domain rotation and could be used to study the conformational transition and dynamics of relative domain motions. Although further studies are needed in order to establish a quantitative relationship between the rotational angle and the population distribution of different components in a particular system, the research presented here provides a foundation for its application in studying receptor domain rotation and dynamics, which could be useful in drug screening efforts.

Shape matters: The application of activity-based in vitro bioassays and chiral profiling to the pharmacological evaluation of synthetic cannabinoid receptor agonists in drug-infused papers seized in prisons

Synthetic cannabinoid receptor agonists (SCRAs) elicit many of their psychoactive effects via type-1 human cannabinoid (CB₁ ) receptors. Enantiomer pairs of eight tert-leucinate or valinate indole- and indazole-3-carboxamide SCRAs were synthesized and their CB₁ potency and efficacy assessed using an in vitro β-arrestin recruitment assay in a HEK239T stable cell system. A chiral high-performance liquid chromatography method with photodiode array and/or quadrupole time-of-flight-mass spectrometry detection (HPLC-PDA and HPLC-PDA-QToF-MS) was applied to 177 SCRA-infused paper samples seized in Scottish prisons between 2018 and 2020. In most samples, SCRAs were almost enantiopure (S)-enantiomer (>98% of total chromatographic peak area), although in some (n = 18), 2% to 16% of the (R)-enantiomer was detected. (S)-enantiomers are consistently more potent than (R)-enantiomers and often more efficacious. The importance of SCRA-CB₁ receptor interactions in the "head" or "linked group" moiety is demonstrated, with the conformation of the "bulky" tert-leucinate group greatly affecting potency (by up to a factor of 374), significantly greater than the difference observed between valinate SCRA enantiomers. (S)-MDMB-4en-PINACA, (S)-4F-MDMB-BINACA, and (S)-5F-MDMB-PICA are currently the most prevalent SCRAs in Scottish prisons, and all have similar high potency (EC₅₀ , 1-5 nM) and efficacy. Infused paper samples were compared using estimated intrinsic efficacy at the CB₁ receptor (EIE_CB1 ) to evaluate samples with variable SCRA content. Given their similar potency and efficacy, any variation in CB₁ receptor-mediated psychoactive effects are likely to derive from variation in dose, mode of use, pharmacokinetic differences, and individual factors affecting the user, rather than differences in the specific SCRA present.

The discovery of a potent and selective pyrazolo-[2,3-e]-[1,2,4]-triazine cannabinoid type 2 receptor agonist

The development of selective CB₂ receptor agonists is a promising therapeutic approach for the treatment of inflammatory diseases, without CB₁ receptor mediated psychoactive side effects. Preliminary structure-activity relationship studies on pyrazoylidene benzamide agonists revealed the -ylidene benzamide moiety was crucial for functional activity at the CB₂ receptor. A small library of compounds with varying linkage moieties between the pyrazole and substituted phenyl group has culminated in the discovery of a potent and selective pyrazolo-[2,3-e]-[1,2,4]-triazine agonist 19 (CB₂R EC₅₀ = 19 nM, CB₁R EC₅₀ > 10 μM). Docking studies have revealed key structural features of the linkage group that are important for potent functional activity.

Cryo-EM Structure of the Prostaglandin E Receptor EP4 Coupled to G Protein

Prostaglandin E receptor EP4, a class A G protein-coupled receptor (GPCR), is a common drug target in various disorders, such as acute decompensated heart failure and ulcerative colitis. Here, we report the cryoelectron microscopy (cryo-EM) structure of the EP4-heterotrimeric G protein (Gs) complex with the endogenous ligand at a global resolution of 3.3 Å. In this structure, compared with that in the inactive EP4 structure, the sixth transmembrane domain is shifted outward on the intracellular side, although the shift is smaller than that in other class A GPCRs bound to Gs. Instead, the C-terminal helix of Gs is inserted toward TM2 of EP4, and the conserved C-terminal hook structure formsthe extended state. These structural features are formed by the conserved residues in prostanoid receptors (Phe54^2.39 and Trp327^7.51). These findings may be important for the thorough understanding of the G protein-binding mechanism of EP4 and other prostanoid receptors.

Biased agonism at the cannabinoid receptors - Evidence from synthetic cannabinoid receptor agonists

The type 1 and type 2 cannabinoid receptors are G protein-coupled receptors implicated in a variety of physiological processes and diseases. Synthetic cannabinoid receptor agonists (SCRAs) were originally developed to explore the therapeutic benefits of cannabinoid receptor activation, although more recently, these compounds have been diverted to the recreational drug market and are increasingly associated with incidences of toxicity. A prominent concept in contemporary pharmacology is functional selectivity or biased agonism, which describes the ability of ligands to elicit differential activation of signalling pathways through stabilisation of distinct receptor conformations. Biased agonists may maximise drug effectiveness by reducing on-target adverse effects if they are mediated by signalling pathways distinct from those that drive the therapeutic effects. For the cannabinoid receptors, it remains unclear as to which signalling pathways mediate desirable and adverse effects. However, given their structural diversity and potential to induce a plethora of signalling effects, SCRAs provide the most promising prospect for detecting and studying bias at the cannabinoid receptors. This review summarises the emerging evidence of SCRA bias at the cannabinoid receptors.

The Potential of 19F NMR Application in GPCR Biased Drug Discovery

Although structure-based virtual drug discovery is revolutionizing the conventional high-throughput cell-based screening system, its limitation is obvious, together with other critical challenges. In particular, the resolved static snapshots fail to represent a full free-energy landscape due to homogenization in structural determination processing. The loss of conformational heterogeneity and related functional diversity emphasize the necessity of developing an approach that can fill this space. In this regard, NMR holds undeniable potential. However, outstanding questions regarding the NMR application remain. This review summarizes the limitations of current drug discovery and explores the potential of ¹⁹F NMR in establishing a conformation-guided drug screening system, advancing the cell- and structure-based discovery strategy for G protein-coupled receptor (GPCR) biased drug screening.

Current challenges in the pathophysiology, diagnosis, and treatment of paroxysmal movement disorders

INTRODUCTION

Paroxysmal movement disorders mostly comprise paroxysmal dyskinesia and episodic ataxia, and can be the consequence of a genetic disorder or symptomatic of an acquired disease.

AREAS COVERED

In this review, the authors focused on certain hot-topic issues in the field: the respective contribution of the cerebellum and striatum to the generation of paroxysmal dyskinesia, the importance of striatal cAMP turnover in the pathogenesis of paroxysmal dyskinesia, the treatable causes of paroxysmal movement disorders not to be missed, with a special emphasis on the treatment strategy to bypass the glucose transport defect in paroxysmal movement disorders due to GLUT1 deficiency, and functional paroxysmal movement disorders.

EXPERT OPINION

Treatment of genetic causes of paroxysmal movement disorders is evolving towards precision medicine with targeted gene-specific therapy. Alteration of the cerebellar output and modulation of the striatal cAMP turnover offer new perspectives for experimental therapeutics, at least for paroxysmal movement disorders due to selected causes. Further characterization of cell-specific molecular pathways or network dysfunctions that are critically involved in the pathogenesis of paroxysmal movement disorders will likely result in the identification of new biomarkers and testing of innovative-targeted therapeutics.

Lysolipid Chain Length Switches Agonistic to Antagonistic G Protein-Coupled Receptor Modulation

Activation of lysolipid-sensitive G protein-coupled receptors (GPCR) depends not only on lysolipid class but also on the length and degree of saturation of their respective hydrophobic tails. Positive regulation of these signaling networks caused by the lipid chain length specificity of upstream phospholipases is firmly established. Nonagonistic lysolipid homologues, featuring incompatible lipid tails, have been suggested to indirectly modulate GPCR signaling by delaying agonist catabolism. Nonetheless, recent results seem inconsistent with this hypothesis. Utilizing a simplified lysolipid-GPCR signaling assay based on the established lysophosphatidylglucoside-GPR55 signaling axis in primary sensory neurons, we demonstrate that short-chain ligand homologues directly modulate receptor activation via a potent competitive antagonistic activity. Considering the well-documented tissue-specific concentration of lysolipid homologues, we propose that endogenous lysolipids with insufficient chain length for stable receptor activation exert an antagonistic activity, effectively representing a negative control mechanism for GPCR-associated lysolipid signaling.

Structural Insights into β-arrestin/CB1 Receptor Interaction: NMR and CD Studies on Model Peptides

Activation of the cannabinoid CB1 receptor induces different cellular signaling cascades through coupling to different effector proteins (G-proteins and β-arrestins), triggering numerous therapeutic effects. Conformational changes and rearrangements at the intracellular domain of this GPCR receptor that accompany ligand binding dictate the signaling pathways. The GPCR-binding interface for G proteins has been extensively studied, whereas β-arrestin/GPCR complexes are still poorly understood. To gain knowledge in this direction, we designed peptides that mimic the motifs involved in the putative interacting region: β-arrestin1 finger loop and the transmembrane helix 7-helix 8 (TMH7-H8) elbow located at the intracellular side of the CB1 receptor. According to circular dichroism and NMR data, these peptides form a native-like, helical conformation and interact with each other in aqueous solution, in the presence of trifluoroethanol, and using zwitterionic detergent micelles as membrane mimics. These results increase our understanding of the binding mode of β-arrestin and CB1 receptor and validate minimalist approaches to structurally comprehend complex protein systems.

Cannabinoid Receptor Subtype 2 (CB2R) in a Multitarget Approach: Perspective of an Innovative Strategy in Cancer and Neurodegeneration

The cannabinoid receptor subtype 2 (CB2R) represents an interesting and new therapeutic target for its involvement in the first steps of neurodegeneration as well as in cancer onset and progression. Several studies, focused on different types of tumors, report a promising anticancer activity induced by CB2R agonists due to their ability to reduce inflammation and cell proliferation. Moreover, in neuroinflammation, the stimulation of CB2R, overexpressed in microglial cells, exerts beneficial effects in neurodegenerative disorders. With the aim to overcome current treatment limitations, new drugs can be developed by specifically modulating, together with CB2R, other targets involved in such multifactorial disorders. Building on successful case studies of already developed multitarget strategies involving CB2R, in this Perspective we aim at prompting the scientific community to consider new promising target associations involving HDACs (histone deacetylases) and σ receptors by employing modern approaches based on molecular hybridization, computational polypharmacology, and machine learning algorithms.

Binding Modes and Selectivity of Cannabinoid 1 (CB1) and Cannabinoid 2 (CB2) Receptor Ligands

The cannabinoid (CB) receptors (CB₁R and CB₂R) represent a promising therapeutic target for several indications such as nociception and obesity. The ligands with nonselectivity can be traced to the high similarity in the binding sites of both cannabinoid receptors. Therefore, the need for selectivity, potency, and G-protein coupling bias has further complicated the design of desired compounds. The bias of currently studied cannabinoid agonists is seldom investigated, and agonists that do exhibit bias are typically nonselective. However, certain long-chain endocannabinoids represent a class of selective and potent CB₁R agonists. The binding mode for this class of compounds has remained elusive, limiting the implementation of its binding features to currently studied agonists. Hence, in the present study, the binding poses for these long-chain cannabinoids, along with other interesting ligands, with the receptors have been determined, by using a combination of molecular docking and molecular dynamics (MD) simulations along with molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) binding free energy calculations. The binding poses for the long-chain cannabinoids implicate that a site surrounded by the transmembrane (TM)2, TM7, and extracellular loop (ECL)2 is vital for providing the long-chain ligands with the selectivity for CB₁R, especially I267 of CB₁R (corresponding to L182 of CB₂R). Based on the obtained binding modes, the calculated relative binding free energies and selectivity are all in good agreement with the corresponding experimental data, suggesting that the determined binding poses are reasonable. The computational strategy used in this study may also prove fruitful in applications with other GPCRs or membrane-bound proteins.

Structure of the human gonadotropin-releasing hormone receptor GnRH1R reveals an unusual ligand binding mode

Gonadotrophin-releasing hormone (GnRH), also known as luteinizing hormone-releasing hormone, is the main regulator of the reproductive system, acting on gonadotropic cells by binding to the GnRH1 receptor (GnRH1R). The GnRH-GnRH1R system is a promising therapeutic target for maintaining reproductive function; to date, a number of ligands targeting GnRH1R for disease treatment are available on the market. Here, we report the crystal structure of GnRH1R bound to the small-molecule drug elagolix at 2.8 Å resolution. The structure reveals an interesting N-terminus that could co-occupy the enlarged orthosteric binding site together with elagolix. The unusual ligand binding mode was further investigated by structural analyses, functional assays and molecular docking studies. On the other hand, because of the unique characteristic of lacking a cytoplasmic C-terminal helix, GnRH1R exhibits different microswitch structural features from other class A GPCRs. In summary, this study provides insight into the ligand binding mode of GnRH1R and offers an atomic framework for rational drug design.

Development of High-Specificity Fluorescent Probes to Enable Cannabinoid Type 2 Receptor Studies in Living Cells

Pharmacological modulation of cannabinoid type 2 receptor (CB₂R) holds promise for the treatment of numerous conditions, including inflammatory diseases, autoimmune disorders, pain, and cancer. Despite the significance of this receptor, researchers lack reliable tools to address questions concerning the expression and complex mechanism of CB₂R signaling, especially in cell-type and tissue-dependent contexts. Herein, we report for the first time a versatile ligand platform for the modular design of a collection of highly specific CB₂R fluorescent probes, used successfully across applications, species, and cell types. These include flow cytometry of endogenously expressing cells, real-time confocal microscopy of mouse splenocytes and human macrophages, as well as FRET-based kinetic and equilibrium binding assays. High CB₂R specificity was demonstrated by competition experiments in living cells expressing CB₂R at native levels. The probes were effectively applied to FACS analysis of microglial cells derived from a mouse model relevant to Alzheimer's disease.

Therapeutic Exploitation of GPR18: Beyond the Cannabinoids?

GPR18 is a G-protein-coupled receptor that belongs to the orphan class A family. Even though it shares low sequence homology with the cannabinoid receptors CB₁R and CB₂R, a growing body of research suggests its relationship with the endocannabinoid system, not only because it is able to recognize cannabinoid ligands but also because of its expression and ability to heteromerize with CBRs. In this review, we aim to analyze the biological relevance, reported modulators, and structural features of GPR18. In order to guide future drug design in this field, highlights from molecular modeling of GPR18 will be provided.

The Nucleotide-Free State of the Cannabinoid CB2/Gi Complex

In this issue of Cell, two papers report agonist-bound cryo-EM structures of the cannabinoid receptor, CB2, in complex with Gi. Importantly, beyond providing information that could help distinguish CB2 ligand binding from CB1, these structures support the existence of a nucleotide-free state during G-protein signaling.

Amorphous nickel titanium alloy film: A new choice for cryo electron microscopy sample preparation

Cryo-electron microscopy (cryoEM) has become one of the most important approach for structural biology. However, barriers are still there for an increased successful rate, a better resolution and improved efficiency from sample preparation, data collection to image processing. CryoEM sample preparation is one of the bottlenecks with many efforts made recently, including the optimization of supporting substrate (e.g. ultra-thin carbon, graphene, pure gold, 2d crystal of streptavidin, and affinity modification), which was aimed to solve air-water interface problem, or reduce beam induced motion (BIM), or change particle distribution in the grid hole. Here, we report another effort of developing a new supporting substrate, the amorphous nickel-titanium alloy (ANTA) film, for cryoEM sample preparation as a layer of holey supporting film covering on TEM grid. Our investigations showed advantages of ANTA film in comparison with conventional carbon film, including much better electron conductivity and trace non-specific interaction with protein. These advantages yield less BIM and significantly improved particle distribution during cryoEM experiment of human apo-ferritn, thus resulting an improved reconstruction resolution from a reduced number of micrographs and particles. Unlike the pure gold film, the usage of the ANTA film is just same with the carbon film, compatible to conventional automatic cryoEM data collection procedure.

Novel approaches and current challenges with targeting the endocannabinoid system

INTRODUCTION

The pathophysiological relevance of the endocannabinoid system has been widely demonstrated in a variety of diseases including cancer, neurological disorders, and metabolic issues. Therefore, targeting the receptors and the endogenous machinery involved in this system can provide a successful therapeutic outcome. Ligands targeting the canonical cannabinoid receptors, CB1 and CB2, along with inhibitors of the endocannabinoid enzymes have been thoroughly studied in diverse disease models. In fact, phytocannabinoids such as cannabidiol or Δ9-tetrahydrocannabinol are currently on the market for the management of neuropathic pain due to spasticity in multiple sclerosis or seizures in children epilepsy amongst others.

AREAS COVERED

Challenges in the pharmacology of cannabinoids arise from its pharmacokinetics, off-target effects, and psychoactive effects. In this context, the current review outlines the novel molecular approaches emerging in the field discussing their clinical potential.

EXPERT OPINION

Even if orthosteric CB1 and CB2 ligands are on the forefront in cannabinoid clinical research, emerging strategies such as allosteric or biased modulation of these receptors along with controlled off-targets effects may increase the therapeutic potential of cannabinoids.

Structural and Functional Insights into Cannabinoid Receptors

Cannabinoid receptors type 1 (CB1) and 2 (CB2) are widely expressed in the human body, and are attractive drug targets in the prevention and management of central nervous system (CNS) and immune system dysfunction, respectively. Recent breakthroughs in the structural elucidation of cannabinoid receptors and their signaling complexes with G proteins, provide the important molecular basis of ligand-receptor interactions, activation and signaling mechanism, which will facilitate the next-generation drug design and the precise modulation of the endocannabinoid system. Here, we provide an overview on the structural features of cannabinoid receptors in different functional states and the diverse ligand binding modes. The major challenges and new strategies for future therapeutic applications targeting the endocannabinoid system (ECS) are also discussed.

Virtual Screening of C. Sativa Constituents for the Identification of Selective Ligands for Cannabinoid Receptor 2

The selective targeting of the cannabinoid receptor 2 (CB2) is crucial for the development of peripheral system-acting cannabinoid analgesics. This work aimed at computer-assisted identification of prospective CB2-selective compounds among the constituents of Cannabis Sativa. The molecular structures and corresponding binding affinities to CB1 and CB2 receptors were collected from ChEMBL. The molecular structures of Cannabis Sativa constituents were collected from a phytochemical database. The collected records were curated and applied for the development of quantitative structure-activity relationship (QSAR) models with a machine learning approach. The validated models predicted the affinities of Cannabis Sativa constituents. Four structures of CB2 were acquired from the Protein Data Bank (PDB) and the discriminatory ability of CB2-selective ligands and two sets of decoys were tested. We succeeded in developing the QSAR model by achieving Q² 5-CV > 0.62. The QSAR models helped to identify three prospective CB2-selective molecules that are dissimilar to already tested compounds. In a complementary structure-based virtual screening study that used available PDB structures of CB2, the agonist-bound, Cryogenic Electron Microscopy structure of CB2 showed the best statistical performance in discriminating between CB2-active and non-active ligands. The same structure also performed best in discriminating between CB2-selective ligands from non-selective ligands.

Targeting Cannabinoid Receptors: Current Status and Prospects of Natural Products

Cannabinoid receptors (CB1 and CB2), as part of the endocannabinoid system, play a critical role in numerous human physiological and pathological conditions. Thus, considerable efforts have been made to develop ligands for CB1 and CB2, resulting in hundreds of phyto- and synthetic cannabinoids which have shown varying affinities relevant for the treatment of various diseases. However, only a few of these ligands are clinically used. Recently, more detailed structural information for cannabinoid receptors was revealed thanks to the powerfulness of cryo-electron microscopy, which now can accelerate structure-based drug discovery. At the same time, novel peptide-type cannabinoids from animal sources have arrived at the scene, with their potential in vivo therapeutic effects in relation to cannabinoid receptors. From a natural products perspective, it is expected that more novel cannabinoids will be discovered and forecasted as promising drug leads from diverse natural sources and species, such as animal venoms which constitute a true pharmacopeia of toxins modulating diverse targets, including voltage- and ligand-gated ion channels, G protein-coupled receptors such as CB1 and CB2, with astonishing affinity and selectivity. Therefore, it is believed that discovering novel cannabinoids starting from studying the biodiversity of the species living on planet earth is an uncharted territory.

Structural basis of CXC chemokine receptor 2 activation and signalling

Chemokines and their receptors mediate cell migration, which influences multiple fundamental biological processes and disease conditions such as inflammation and cancer¹. Although ample effort has been invested into the structural investigation of the chemokine receptors and receptor-chemokine recognition^2-4, less is known about endogenous chemokine-induced receptor activation and G-protein coupling. Here we present the cryo-electron microscopy structures of interleukin-8 (IL-8, also known as CXCL8)-activated human CXC chemokine receptor 2 (CXCR2) in complex with G_i protein, along with a crystal structure of CXCR2 bound to a designed allosteric antagonist. Our results reveal a unique shallow mode of binding between CXCL8 and CXCR2, and also show the interactions between CXCR2 and G_i protein. Further structural analysis of the inactive and active states of CXCR2 reveals a distinct activation process and the competitive small-molecule antagonism of chemokine receptors. In addition, our results provide insights into how a G-protein-coupled receptor is activated by an endogenous protein molecule, which will assist in the rational development of therapeutics that target the chemokine system for better pharmacological profiles.

Cannabinoids and Cannabinoid Receptors: The Story so Far

Like most modern molecular biology and natural product chemistry, understanding cannabinoid pharmacology centers around molecular interactions, in this case, between the cannabinoids and their putative targets, the G-protein coupled receptors (GPCRs) cannabinoid receptor 1 (CB₁) and cannabinoid receptor 2 (CB₂). Understanding the complex structure and interplay between the partners in this molecular dance is required to understand the mechanism of action of synthetic, endogenous, and phytochemical cannabinoids. This review, with 91 references, surveys our understanding of the structural biology of the cannabinoids and their target receptors including both a critical comparison of the extant crystal structures and the computationally derived homology models, as well as an in-depth discussion about the binding modes of the major cannabinoids. The aim is to assist in situating structural biochemists, synthetic chemists, and molecular biologists who are new to the field of cannabis research.

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Cannabinoid research has greatly expanded

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Structural biology and computational chemistry jointly provide mechanistic insight

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Structural data are being generated at an exponentially increasing rate

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Phytocannabinoid targeting of other GPCR receptors deserves investigation

Structural features of activated GPCR signaling complexes

G protein-coupled receptors (GPCRs) couple to diverse heterotrimeric G protein subtypes and then activate downstream signaling pathways in classical GPCR activation. It has also been found that GPCRs transduce signals through different regulatory proteins, such as arrestins. Recently, owing to the breakthroughs in cryo-electron macroscopy (Cryo-EM), numerous structures of GPCR-G protein or GPCR-arrestin complexes have been deciphered. In this review, we summarize most of reported GPCR signaling complex structures, with an emphasis on the structural features of rhodopsin-like GPCR activation and G protein-binding/arrestin-binding modes, to illustrate the activation and signaling mechanism of rhodopsin-like GPCRs.

Synthesis of Functionalized Cannabilactones

A new approach to synthesize cannabilactones using Suzuki cross-coupling reaction followed by one-step demethylation-cyclization is presented. The two key cannabilactone prototypes AM1710 and AM1714 were obtained selectively in high overall yields and in a lesser number of synthetic steps when compared to our earlier synthesis. The new approach expedited the synthesis of cannabilactone analogs with structural modifications at the four potential pharmacophoric regions.