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.

Dual allosteric and orthosteric pharmacology of synthetic analog cannabidiol-dimethylheptyl, but not cannabidiol, on the cannabinoid CB2 receptor

Cannabinoid CB2 receptor (CB2R) is a class A G protein-coupled receptor (GPCR) involved in a broad spectrum of physiological processes and pathological conditions. For that reason, targeting CB2R might provide therapeutic opportunities in neurodegenerative disorders, neuropathic pain, inflammatory diseases, and cancer. The main components from Cannabis sativa, such as Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), have been therapeutically exploited and synthetically-derived analogs have been generated. One example is cannabidiol-dimethylheptyl (CBD-DMH), which exhibits anti-inflammatory effects. Nevertheless, its pharmacological mechanism of action is not yet fully understood and is hypothesized for multiple targets, including CB2R. The aim of this study was to further investigate the molecular pharmacology of CBD-DMH on CB2R while CBD was taken along as control. These compounds were screened in equilibrium and kinetic radioligand binding studies and various functional assays, including G protein activation, inhibition of cAMP production and ß-arrestin-2 recruitment. In dissociation studies, CBD-DMH allosterically modulated the radioligand binding. Furthermore, CBD-DMH negatively modulated the G protein activation of reference agonists CP55,940, AEA and 2-AG, but not the agonist-induced ß-arrestin-2 recruitment. Nevertheless, CBD-DMH also displayed competitive binding to CB2R and partial agonism on G protein activation, inhibition of cAMP production and ß-arrestin-2 recruitment. CBD did not exhibit such allosteric behavior and only very weakly bound CB2R without activation. This study shows a dual binding mode of CBD-DMH, but not CBD, to CB2R with the suggestion of two different binding sites. Altogether, it encourages further research into this dual mechanism which might provide a new class of molecules targeting CB2R.

The translational value of ligand-receptor binding kinetics in drug discovery

The translation of in vitro potency of a candidate drug, as determined by traditional pharmacology metrics (such as EC50 /IC50 and KD /Ki values), to in vivo efficacy and safety is challenging. Residence time, which represents the duration of drug-target interaction, can be part of a more comprehensive understanding of the dynamic nature of drug-target interactions in vivo, thereby enabling better prediction of drug efficacy and safety. As a consequence, a prolonged residence time may help in achieving sustained pharmacological activity, while transient interactions with shorter residence times may be favourable for targets associated with side effects. Therefore, integration of residence time into the early stages of drug discovery and development has yielded a number of clinical candidates with promising in vivo efficacy and safety profiles. Insights from residence time research thus contribute to the translation of in vitro potency to in vivo efficacy and safety. Further research and advances in measuring and optimizing residence time will bring a much-needed addition to the drug discovery process and the development of safer and more effective drugs. In this review, we summarize recent research progress on residence time, highlighting its importance from a translational perspective.

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.

Structural basis of selective cannabinoid CB2 receptor activation

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

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®.

Modern approaches to the development of synthetic cannabinoid receptor probes

The endocannabinoid system, which spans the central and peripheral nervous systems and regulates many biologic processes, is an important target for probe discovery and medications development. Whereas the earliest endocannabinoid receptor probes were derivatives of the non-selective phytocannabinoids isolated from Cannabis species, modern drug discovery techniques have expanded the definitions of what constitutes a CB1R or CB2R cannabinoid receptor ligand. This review highlights recent advances in synthetic cannabinoid receptor chemistry and pharmacology. We provide examples of new CB1R- and CB2R-selective probes, and discuss rational approaches to the design of peripherally-restricted agents. We also describe structural classes of positive- and negative allosteric modulators (PAMs and NAMs) of CB1R and CB2R. Finally, we introduce new opportunities for cannabinoid receptor probe development that have emerged in recent years, including biased agonists that may lead to medications lacking adverse effects.

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.

The selective 5-HT2A receptor agonist 25CN-NBOH: Structure-activity relationship, in vivo pharmacology, and in vitro and ex vivo binding characteristics of [3H]25CN-NBOH

The remarkable effects exhibited by classical psychedelics in recent clinical trials have spawned considerable interest in 5-HT_2A receptor (5-HT_2AR) activation as a treatment strategy for several psychiatric/cognitive disorders. In this study we have continued our development of 25CN-NBOH, one of the most 5-HT_2AR-selective agonists reported to date, as a pharmacological tool for exploration of 5-HT_2AR expression and functions. The importance of the 2' and 3' positions in 25CN-NBOH as structural hotspots for its 5-HT_2AR activity was investigated by synthesis and pharmacological characterization of six novel analogs at 5-HT_2AR and 5-HT_2CR in binding and functional assays. While the 5-HT_2AR activity of 25CN-NBOH was retained in 3'-methyl, 2',3'-chroman, 2',3'-dihydrofuran and 2',3'-furan analogs, the 3'-methoxy and 3'-ethyl analogs displayed substantially lower binding affinities and agonist potencies than 25CN-NBOH. Interestingly, the 2',3'-substitution pattern was also a key determinant of agonist efficacy, as all six analogs exhibited low-efficacy partial agonism or de facto antagonism at the 5-HT_2AR in the functional assays. Systemic administration of 25CN-NBOH and its close structural analog 25CN-NBMD induced robust head-twitch response in mice, a well-established behavioural effect of 5-HT_2AR activation in vivo, and 25CN-NBOH mediated robust reductions in the activity of mice in an anxiety-related marble burying assay, which supports the proposed beneficial effects of 5-HT_2AR activation on disorders characterized by cognitive rigidity. Finally, tritiated 25CN-NBOH exhibited high 5-HT_2AR binding affinity (K_D ~1 nM) and selectivity against 5-HT_2BR and 5-HT_2CR in equilibrium and kinetic binding studies of the recombinant receptors, and in concordance [³H]25CN-NBOH displayed substantial specific, ketanserin-sensitive binding to cortex and small levels of binding to choroid plexus in rat brain slices in autoradiography studies. In conclusion, this work delineates the subtle molecular determinants of the 5-HT_2AR activity in 25CN-NBOH, substantiates the potential in this compound and its analogs as tools for in vivo studies of the 5-HT_2AR, and introduces a novel selective agonist radioligand as another potentially valuable tool for future explorations of this receptor.

Perspective: Implications of Ligand-Receptor Binding Kinetics for Therapeutic Targeting of G Protein-Coupled Receptors

The concept of ligand-receptor binding kinetics has been broadly applied in drug development pipelines focusing on G protein-coupled receptors (GPCRs). The ligand residence time (RT) for a receptor describes how long a ligand-receptor complex exists, and is defined as the reciprocal of the dissociation rate constant (k _off). RT has turned out to be a valuable parameter for GPCR researchers focusing on drug development as a good predictor of in vivo efficacy. The positive correlation between RT and in vivo efficacy has been established for several drugs targeting class A GPCRs (e.g., the neurokinin-1 receptor (NK₁R), the β₂ adrenergic receptor (β₂AR), and the muscarinic 3 receptor (M₃R)) and for drugs targeting class B1 (e.g., the glucagon-like peptide 1 receptor (GLP-1R)). Recently, the association rate constant (k _on) has gained similar attention as another parameter affecting in vivo efficacy. In the current perspective, we address the importance of studying ligand-receptor binding kinetics for therapeutic targeting of GPCRs, with an emphasis on how binding kinetics can be altered by subtle molecular changes in the ligands and/or the receptors and how such changes affect treatment outcome. Moreover, we speculate on the impact of binding kinetic parameters for functional selectivity and sustained receptor signaling from endosomal compartments; phenomena that have gained increasing interest in attempts to improve therapeutic targeting of GPCRs.

Structure-Activity Relationship Studies of Pyridine-Based Ligands and Identification of a Fluorinated Derivative for Positron Emission Tomography Imaging of Cannabinoid Type 2 Receptors

The cannabinoid type 2 (CB2) receptor has emerged as a valuable target for therapy and imaging of immune-mediated pathologies. With the aim to find a suitable radiofluorinated analogue of the previously reported CB2 positron emission tomography (PET) radioligand [¹¹C]RSR-056, 38 fluorinated derivatives were synthesized and tested by in vitro binding assays. With a K_i (hCB2) of 6 nM and a selectivity factor of nearly 700 over cannabinoid type 1 receptors, target compound 3 exhibited optimal in vitro properties and was selected for evaluation as a PET radioligand. [¹⁸F]3 was obtained in an average radiochemical yield of 11 ± 4% and molar activities between 33 and 114 GBq/μmol. Specific binding of [¹⁸F]3 to CB2 was demonstrated by in vitro autoradiography and in vivo PET experiments using the CB2 ligand GW-405 833. Metabolite analysis revealed only intact [¹⁸F]3 in the rat brain. [¹⁸F]3 detected CB2 upregulation in human amyotrophic lateral sclerosis spinal cord tissue and may thus become a candidate for diagnostic use in humans.

Drug-Target Residence Time Affects in Vivo Target Occupancy through Multiple Pathways

The drug discovery and development process is greatly hampered by difficulties in translating in vitro potency to in vivo efficacy. Recent studies suggest that the long-neglected drug-target residence time parameter complements classical drug affinity parameters (K _I, K _d, IC₅₀, or EC₅₀) and is a better predictor of in vivo efficacy. Compounds with a long drug-target residence time are often more efficacious in vivo. The impact, however, of the drug-target residence time on in vivo efficacy remains controversial due to difficulties in experimentally determining the in vivo target occupancy during drug treatment. To tackle this problem, an in vivo displacement assay was developed using soluble epoxide hydrolase as a biological model. In this report, we experimentally demonstrated that drug-target residence time affects the duration of in vivo drug-target binding. In addition, the drug-target residence time plays an important role in modulating the rate of drug metabolism which also affects the efficacy of the drug.

Investigating the Influence of Tracer Kinetics on Competition-Kinetic Association Binding Assays: Identifying the Optimal Conditions for Assessing the Kinetics of Low-Affinity Compounds

An increased appreciation of the importance of optimizing drug-binding kinetics has lead to the development of various techniques for measuring the kinetics of unlabeled compounds. One approach is the competition-association kinetic binding method first described in the 1980s. The kinetic characteristics of the tracer employed greatly affects the reliability of estimated kinetic parameters, a barrier to successfully introducing these kinetic assays earlier in the drug discovery process. Using a modeling and Monte Carlo simulation approach, we identify the optimal tracer characteristics for determining the kinetics of the range of unlabeled ligands typically encountered during the different stages of a drug discovery program (i.e., rapidly dissociating, e.g., k _off = 10 minute^-1 low-affinity "hits" through to slowly dissociating e.g., k _off = 0.01 minute^-1 high-affinity "candidates"). For more rapidly dissociating ligands (e.g., k _off = 10 minute^-1), the key to obtaining accurate kinetic parameters was to employ a tracer with a relatively fast off-rate (e.g., k _off = 1 minute^-1) or, alternatively, to increase the tracer concentration. Reductions in assay start-time ≤1second and read frequency ≤5 seconds significantly improved the reliability of curve fitting. Timing constraints are largely dictated by the method of detection, its inherent sensitivity (e.g., TR-FRET versus radiometric detection), and the ability to inject samples online. Furthermore, we include data from TR-FRET experiments that validate this simulation approach, confirming its practical utility. These insights into the optimal experimental parameters for development of competition-association assays provide a framework for identifying and testing novel tracers necessary for profiling unlabeled competitors, particularly rapidly dissociating low-affinity competitors.

Chromenopyrazole-based High Affinity, Selective Fluorescent Ligands for Cannabinoid Type 2 Receptor

Cannabinoid type 2 receptor (CB₂R) is an attractive target for the treatment of pain and inflammatory disorders. Availability of a selective CB₂R fluorescent ligand to study CB₂R expression and localization in healthy and disease conditions would greatly contribute to improving our understanding of this receptor. Herein, we report a series of chromenopyrazole-based CB₂R fluorescent ligands. The highest affinity fluorescent ligand was Cy5-containing 24 (hCB₂R pK _i = 7.38 ± 0.05), which had 131-fold selectivity over CB₁R. In a cAMP BRET assay, 24 behaved as a potent CB₂R inverse agonist. Widefield imaging experiments showed that 24 binds to CB₂R in live cells with good selectivity and low levels of nonspecific fluorescence. The high affinity, selectivity, and suitable imaging properties of fluorescent ligand 24 make it a valuable tool for studying CB₂R.