Bridging the Binding Sites 2.0: Photoswitchable Dualsteric Ligands for the Cannabinoid 2 Receptor

The cannabinoid receptor 2 (CB2R) has high, unexploited therapeutic potential in several central nervous system disorders due to its involvement in neuroinflammatory processes and pathologies like neurodegeneration. Dualsteric/bitopic ligands are currently developed to achieve receptor subtype selectivity and biased signaling. To obtain a molecular tool compound with photoswitchable potential dualsteric properties, we applied two different approaches to link a positive allosteric modulator with an orthosteric agonist via a photochromic unit. We characterized the photophysical properties of all compounds and determined efficacy in internalization, calcium mobilization, and BRET studies. We report the first potentially dualsteric photoswitchable ligand for studying molecular mechanisms of CB2R-associated pathologies. Compound 17-para is a submicromolar "cis-on" agonist with >10-fold higher potency compared to its trans photoisomer and allows high spatiotemporal control of CB2R activation.

The Impact of JWH-133 on Articular Cartilage Regeneration in Osteoarthritis Via Metalloproteinase 13-Dependent Mechanism

Objective: Osteoarthritis (OA) is common degenerative joint disease, mostly characterized by gradual cartilage breakdown. Currently there are no disease-modifying drugs available, therefore, there is an increasing need for basic research to focus on cartilage function in OA. Changes in cannabinoid receptor 2 (CB2) expression were observed in the OA-affected joints, although its action on cartilage chondrocytes remain unclear. We studied the action of dimethylbutyl-deoxy-delta-8-THC (JWH-133), selective CB2 agonist, on chondrocytes metabolism using both in vitro and in vivo studies. Design: Intraarticular (i.a.) injection of monoiodoacetate (MIA) was used to induce OA in rats. OA-related pain symptoms were assessed by pressure application measurements (PAMs). Primary human chondrocytes treated with MIA were used to investigate action of JWH-133 on chondrocytes viability, proliferation, and motility. Cannabinoid system components, inflammatory cytokines and metalloproteinases (MMPs) expression was measured on messenger RNA and protein levels in chondrocytes and animal cartilage. Results: Repeated, i.a. administration of JWH-133 showed antinociceptive potential in PAM, as well as decreased levels of MMPs, which suggests that CB2 agonism may modify degradation of cartilage. JWH-133 administration partially reduced toxicity, increased proliferation, and chondrocytes' migration. Moreover, our data suggest that CB2 agonism leads to alleviation of MMPs expression both in vitro and in vivo. Conclusions: In this study, we demonstrate modifying effect of JWH-133 local administration on cartilage metabolism and MMP13 expression that was shown to be involved in cartilage degradation. CB2 receptors' activation may be of benefit for chondrocytes' proliferation, therefore delaying disease progression. Our results propose direction of studies on OA-modifying treatment that can benefit in management of human OA.

Structure-Based Virtual Screening and Molecular Dynamics Simulation Assessments of Depsidones as Possible Selective Cannabinoid Receptor Type 2 Agonists

The discovery of natural drug metabolites is a leading contributor to fulfilling the sustainable development goal of finding solutions to global health challenges. Depsidones are a class of polyketides that have been separated from lichens, fungi, sponges, and plants and possess various bioactivities, including cytotoxic, antimicrobial, antimalarial, antituberculosis, acetylcholinesterase and α-glucosidase inhibition, and anti-inflammatory effects. Endocannabinoid receptors (CB1 and CB2) are G-protein-coupled receptors (GPCRs), and their activation mediates many physiological processes. CB1 is the dominant subtype in the central nervous system, while CB2 is mainly expressed in the immune system. The two receptors exhibit high heterogeneity, making developing selective ligands a great challenge. Attempts to develop CB2 selective agonists for treating inflammatory diseases and neuropathic pain have not been successful due to the high homology of the binding sites of the CB receptors. In this work, 235 depsidones from various sources were investigated for the possibility of identifying CB2-selective agonists by performing multiple docking studies, including induced fit docking and Prime/molecular mechanics-generalized Born surface area (MM-GBSA) calculations to predict the binding mode and free energy. Simplicildone J (10), lobaric acid (110), mollicellin Q (101), garcinisidone E (215), mollicellin P (100), paucinervin Q (149), and boremexin C (161) had the highest binding scores (-12.134 kcal/mol, -11.944 kcal/mol, -11.479 kcal/mol, -11.394 kcal/mol, -11.322 kcal/mol, -11.305 kcal/mol, and -11.254 kcal/mol, respectively) when screened against the CB2 receptor (PDB ID: 6KPF). The molecular dynamic simulation was performed on the compounds with the highest binding scores. The computational outcomes show that garcinisidone E (215) and paucinervin Q (149) could be substantial candidates for CB2 receptor activation and warrant further in vivo and in vitro investigations.

CB2 Agonist GW842166x Protected against 6-OHDA-Induced Anxiogenic- and Depressive-Related Behaviors in Mice

In addition to motor dysfunction, patients with Parkinson's disease (PD) are often affected by neuropsychiatric disorders, such as anxiety and depression. In animal models, activation of the endocannabinoid (eCB) system produces anxiolytic and antidepressant-like behavioral effects. CB2 agonists have demonstrated neuroprotective effects against neurotoxin-induced dopamine neuron loss and deficits in motor function. However, it remains unknown whether CB2 agonism ameliorates anxiogenic- and depressive-like behaviors in PD models. Here, we report that the selective CB2 agonist GW842166x exerted neuroprotective effects against 6-hydroxydopamine (6-OHDA)-induced loss of dopaminergic terminals and dopamine release in the striatum, which were blocked by the CB2 antagonist AM630. We found that 6-OHDA-treated mice exhibited anxiogenic- and depressive-like behaviors in the open-field, sucrose preference, novelty-suppressed feeding, marble burying, and forced swim tests but did not show significant changes in the elevated plus-maze and light-dark box test. GW842166x treatments ameliorated 6-OHDA-induced anxiogenic- and depressive-like behaviors, but the effects were blocked by CB2 antagonism, suggesting a CB2-dependent mechanism. These results suggest that the CB2 agonist GW842166x not only reduces 6-OHDA-induced motor function deficits but also anxiogenic- and depressive-like behaviors in 6-OHDA mouse models of PD.

Tricyclic Pyrazole-Based Compounds as Useful Scaffolds for Cannabinoid CB1/CB2 Receptor Interaction

Cannabinoids comprise different classes of compounds, which aroused interest in recent years because of their several pharmacological properties. Such properties include analgesic activity, bodyweight reduction, the antiemetic effect, the reduction of intraocular pressure and many others, which appear correlated to the affinity of cannabinoids towards CB₁ and/or CB₂ receptors. Within the search aiming to identify novel chemical scaffolds for cannabinoid receptor interaction, the CB₁ antagonist/inverse agonist pyrazole-based derivative rimonabant has been modified, giving rise to several tricyclic pyrazole-based compounds, most of which endowed of high affinity and selectivity for CB₁ or CB₂ receptors. The aim of this review is to present the synthesis and summarize the SAR study of such tricyclic pyrazole-based compounds, evidencing, for some derivatives, their potential in the treatment of neuropathic pain, obesity or in the management of glaucoma.

Effects of cannabinoid receptor 2 synthetic agonist, AM1241, on bleomycin induced pulmonary fibrosis

Bleomycin (BLM) is a chemotherapeutic agent that can cause pulmonary fibrosis. Little is known about the possible protective role of the CB2 receptor agonist, AM1241. We investigated the effects of CB2 receptor activation by AM1241 on BLM induced lung fibrosis in a rat model. BLM was administered via the trachea. Adult female Wistar rats were divided into five groups: saline (control group), BLM (BLM group), CB2 agonist (AM1241) + BLM (BLMA group), CB2 antagonist (AM630) and CB2 agonist (AM1241) + BLM (BLMA + A group), and vehicle (dimethylsulfoxide) + BLM (BLM + vehicle group). Hydroxyproline, collagen type 1, total protein, glutathione (GSH), malondialdehyde (MDA), interleukin (IL)-6 and tumor necrosis factor (TNF)-α levels were measured in lung fibrosis and control tissue using standard methods. We investigated the histopathology of lung tissue to determine the extent of fibrosis. We found significantly higher levels of hydroxyproline, TNF-α, IL-6 and total protein in the BLM group compared to the BLMA group. The level of GSH also was higher in the BLMA group compared to the BLM group. Inflammation and fibrotic changes were significantly reduced in the BLMA group. Our findings suggest that CB2 receptor activation provided protection against BLM induced pulmonary fibrosis by suppressing oxidative stress and increasing cytokines.

Safety, Pharmacokinetics, and Efficacy of Olorinab, a Peripherally Acting, Highly Selective, Full Agonist of the Cannabinoid Receptor 2, in a Phase 2a Study of Patients With Chronic Abdominal Pain Associated With Crohn's Disease

Background

This randomized, open-label phase 2a study investigated the safety/tolerability, pharmacokinetics, and efficacy of olorinab-a highly selective, peripherally acting, full agonist of the cannabinoid receptor 2-in patients with Crohn's disease (CD) experiencing abdominal pain.

Methods

Eligible subjects 18-80 years of age with quiescent to mildly active CD were randomized to receive olorinab 25 or 100 mg three times daily for 8 weeks. The primary objective was to assess safety/tolerability.

Results

Fourteen subjects received olorinab 25 mg (N = 6) or 100 mg (N = 8). Ten subjects [4 (67%) in the 25-mg group and 6 (75%) in the 100-mg group] reported a total of 34 treatment-emergent adverse events (TEAEs; 32 grade 1/2, not serious events; 2 grade 3, serious, not treatment-related events). No dose reductions or discontinuations due to TEAEs or deaths were reported. Dose-proportional increases in olorinab exposure from 25 to 100 mg were observed, with minimal accumulation at both doses. At week 8, the mean (SD) change from baseline in average abdominal pain score at peak olorinab plasma concentrations was -4.61 (1.77) in the 25-mg group (P = 0.0043) and -4.57 (2.17) in the 100-mg group (P = 0.0036). The change from baseline at week 8 in the mean (SD) number of pain-free days per week was +1.60 (2.61) in the 25-mg group and +2.33 (3.62) in the 100-mg group. No subject required pain medication on study.

Conclusions

Patients with quiescent to mildly active CD receiving olorinab experienced mild-to-moderate adverse events and an improvement in abdominal pain scores in this study.

CB2 Agonist (AM1241) Improving Effect on Ovalbumin-Induced Asthma in Rats

Asthma is a disease characterized by spontaneous contraction of the airways in response to a wide variety of endogenous and exogenous stimuli. Many asthma models are used to mimic the human asthma model in the literature. In order to better understand the role of the cannabinoid (CB) 2 receptor in the ovalbumin (OVA)-induced asthma model, a combination of both selective CB2 agonist (AM1241) and antagonist (AM630) was used to improve inflammatory hypersensitivity and edema in rats. In the present study, it was found that OVA decreased body weight (p < 0.05), increased lung weights (p < 0.05), increased diastolic and systolic blood pressure (p < 0.001), and caused irregularity in pulmonary functions (p < 0.001). Moreover, CB2 agonist was found not to reduce body weight, cause blood pressure and respiratory irregularities (p < 0.05). OVA led to increase in IgE, TNF-α, IL-4, MDA level (p < 0.001), and total WBC count (p < .05). CB2 treatment caused to reduce the number of total WBC and the level of total protein in BALF, to hinder to increase level of MDA, IgE, TNF-α, and IL-4 (p < 0.05) in BALF or serum or lung tissue. But CB2-antagonist treatment prevented the protective effect of CB2 agonist. The aim of this study was to study the role of the CB2 receptor in the OVA induced asthma model, to improve inflammatory hypersensitivity, and edema in the rats. The results suggested that CB2 agonist administration to OVA induced asthmatic rats via anti-asthmatic potential through inhibition of parameters such as IgE, IL-4, TNF-α, microvascular escape, and oxidative stress.

Anti-apoptotic and Immunomodulatory Effect of CB2 Agonist, JWH133, in a Neonatal Rat Model of Hypoxic-Ischemic Encephalopathy

Introduction: Neonatal HIE is associated with high morbidity and mortality. Current research, is focused on developing alternative treatments to therapeutic hypothermia for treatment of HIE. The endocannabinoid system is known to be influential in neuronal protection. Activation of brain CB2 receptors, has been shown to reduce inflammatory markers and decrease infarct volume in adult cerebral ischemic models. Methods: Rat pups were divided into six groups: 1-Placebo; 2-JWH133; 3-HIE + Placebo; 4-HIE + JWH133; 5-HIE + Hypothermia + Placebo; and 6-HIE + Hypothermia + JWH133. HIE was induced in in groups 3-6 by right carotid ligation on postnatal day 7 followed by placement in a hypoxic chamber. Pups in groups 5 and 6 were treated with hypothermia. Western blot analysis was used to analyze brain tissue for acute inflammatory markers (IL-6, TNFα, MIP1α, and RANTES), immunoregulatory cytokines (TGFβ and IL-10), and CB2 receptor expression. DNA fragmentation in the brains of pups was determined via TUNEL staining post HIE. Results: The combination of JWH133 and hypothermia significantly reduced tumor necrosis factor α (TNFα) (-57.7%, P = 0.0072) and macrophage inflammatory protein 1α (MIP1α) (-50.0%, P = 0.0211) as compared to placebo. DNA fragmentation was also significantly reduced, with 6.9 ± 1.4% TUNEL+ cells in HIE+JWH133 and 12.9 ± 2.2% in HIE+Hypothermia + JWH133 vs. 16.6 ± 1.9% in HIE alone. No significant difference was noted between groups for the expression of interleukins 6 and 10, RANTES, or TGFβ. After 8 h, CB2 receptor expression increased nearly 2-fold in the HIE and HIE + JWH133 groups (+214%, P = 0.0102 and +198%, P = 0.0209, respectively) over placebo with no significant change in the hypothermia groups. By 24 h post HIE, CB2 receptor expression was elevated over five times that of placebo in the HIE (P < 0.0001) and HIE + JWH133 (P = 0.0002) groups, whereas hypothermia treatment maintained expression similar to that of placebo animals. Conclusion: These results indicate that the combination of CB2 agonist and hypothermia may be neuroprotective in treating HIE, opening the door for further studies to examine alternative or adjuvant therapies to hypothermia.

Presynaptic cannabinoid CB2 receptors modulate [3 H]-Glutamate release at subthalamo-nigral terminals of the rat

Recent studies suggested the expression of CB2 receptors in neurons of the CNS, however, most of these studies have only explored one aspect of the receptors, i.e., expression of protein, messenger RNA, or functional response, and more complete studies appear to be needed to establish adequately their role in the neuronal function. Electron microscopy studies showed the presence of CB2r in asymmetric terminals of the substantia nigra pars reticulata (SNr), and its mRNA appeared is expressed in the subthalamic nucleus. Here, we explore the expression, source, and functional effects of such receptors by different experimental approaches. Through PCR and immunochemistry, we showed mRNA and protein for CB2rs in slices and primary neuronal cultures from subthalamus. GW833972A, GW405833, and JHW 133, three CB2r agonists dose-dependent inhibited K⁺ -induced [³ H]-Glutamate release in slices of SNr, and the two antagonist/inverse agonists, JTE-907 and AM630, but not AM281, a CB1r antagonist, prevented GW833972A effect. Subthalamus lesions with kainic acid prevented GW833972A inhibition on release and decreased CB2r protein in nigral synaptosomes, thus nigral CB2rs originate in subthalamus. Inhibition of [³ H]-Glutamate release was PTX- and gallein-sensitive, suggesting a Gi_βγ -mediated effect. P/Q Ca²⁺ -type channel blocker, ω-Agatoxin-TK, also inhibited the [³ H]-Glutamate release, this effect was occluded with GW833972A inhibition, indicating that the βγ subunit effect is exerted on Ca²⁺ channel activity. Finally, microinjections of GW833972A in SNr induced contralateral turning. Our data showed that presynaptic CB2rs inhibit [³ H]-Glutamate release in subthalamo-nigral terminals by P/Q-channels modulation through the Gi_βγ subunit and suggested their participation in motor behavior.

Development of Quinazoline/Pyrimidine-2,4(1H,3H)-diones as Agonists of Cannabinoid Receptor Type 2

Starting from a prototypical structure 1, we describe our efforts to design and obtain novel quinazoline/pyrimidine-2,4(1H,3H)-diones with high CB2 agonist potency and selectivity as well as improved physicochemical characteristics, mainly hydrophilicity. The most potent and selective CB2 agonists, 8 and 36, in this series were also endowed with lower logP values than that of GW842166X and lead compound 1. These derivatives appear to be promising lead compounds for the development of future CB2 agonists.

Discovery of novel Tetrahydrobenzo[b]thiophene and pyrrole based scaffolds as potent and selective CB2 receptor ligands: The structural elements controlling binding affinity, selectivity and functionality

CB2-based therapeutics show strong potential in the treatment of diverse diseases such as inflammation, multiple sclerosis, pain, immune-related disorders, osteoporosis and cancer, without eliciting the typical neurobehavioral side effects of CB1 ligands. For this reason, research activities are currently directed towards the development of CB2 selective ligands. Herein, the synthesis of novel heterocyclic-based CB2 selective compounds is reported. A set of 2,5-dialkyl-1-phenyl-1H-pyrrole-3-carboxamides, 5-subtituted-2-(acylamino)/(2-sulphonylamino)-thiophene-3-carboxylates and 2-(acylamino)/(2-sulphonylamino)-tetrahydrobenzo[b]thiophene-3-carboxylates were synthesized. Biological results revealed compounds with remarkably high CB2 binding affinity and CB2/CB1 subtype selectivity. Compound 19a and 19b from the pyrrole series exhibited the highest CB2 receptor affinity (Ki = 7.59 and 6.15 nM, respectively), as well as the highest CB2/CB1 subtype selectivity (∼70 and ∼200-fold, respectively). In addition, compound 6b from the tetrahydrobenzo[b]thiophene series presented the most potent and selective CB2 ligand in this series (Ki = 2.15 nM and CB2 subtype selectivity of almost 500-fold over CB1). Compound 6b showed a full agonism, while compounds 19a and 19b acted as inverse agonists when tested in an adenylate cyclase assay. The present findings thus pave the way to the design and optimization of heterocyclic-based scaffolds with lipophilic carboxamide and/or retroamide substituent that can be exploited as potential CB2 receptor activity modulators.

Identification of a highly potent and selective CB2 agonist, RQ-00202730, for the treatment of irritable bowel syndrome

Herein we report the identification of a highly potent and selective CB2 agonist, RQ-00202730 (40), obtained by lead optimization of the benzimidazole scaffold. Compound 40 showed strong agonistic activity with an EC50 of 19nM and excellent selectivity (>1300-fold) over the CB1 receptor. Compound 40 displayed a dose dependent analgesic effect on TNBS-induced visceral hypersensitivity in rats by oral administration (ED50 0.66mg/kg at 2.5h after oral administration). In addition, 40 did not show a significant effect on body temperature in rats after oral administration at 300mg/kg. These findings suggest that highly selective CB2 agonists will be effective agents for IBS therapy.

Discovery of 1a,2,5,5a-tetrahydro-1H-2,3-diaza-cyclopropa[a]pentalen-4-carboxamides as potent and selective CB2 receptor agonists

The design and synthesis of novel 1a,2,5,5a-tetrahydro-1H-2,3-diaza-cyclopropa[a]pentalen-4-carboxamide CB2 selective ligands for the potential treatment of pain is described. Compound (R,R)-25 has good balance between CB2 agonist potency and selectivity over CB1, and possesses overall favorable pharmaceutical properties. It also demonstrated robust in vivo efficacy mediated via CB2 activation in the rodent models of inflammatory and osteoarthritis pain after oral administration.

The SAR development of substituted purine derivatives as selective CB2 agonists for the treatment of chronic pain

Osteoarthritis (OA) and the associated joint pain are highly prevalent and a leading cause of disability. We have previously reported the identification of a series of purines as selective CB2 agonists and the identification of compound 1 as a clinical candidate for the treatment of joint pain. In this article we describe the further SAR development of the purine scaffold leading to the discovery of compound 6 as a potent, CNS penetrating CB2 agonist with high selectivity for CB2 over CB1 and oral efficacy in animal models of chronic OA pain.

The cannabinoid CB₂ receptor agonist AM1241 enhances neurogenesis in GFAP/Gp120 transgenic mice displaying deficits in neurogenesis

BACKGROUND AND PURPOSE

HIV-1 glycoprotein Gp120 induces apoptosis in rodent and human neurons in vitro and in vivo. HIV-1/Gp120 is involved in the pathogenesis of HIV-associated dementia (HAD) and inhibits proliferation of adult neural progenitor cells (NPCs) in glial fibrillary acidic protein (GFAP)/Gp120 transgenic (Tg) mice. As cannabinoids exert neuroprotective effects in several model systems, we examined the protective effects of the CB₂ receptor agonist AM1241 on Gp120-mediated insults on neurogenesis.

EXPERIMENTAL APPROACH

We assessed the effects of AM1241 on survival and apoptosis in cultures of human and murine NPCs with immunohistochemical and TUNEL techniques. Neurogenesis in the hippocampus of GFAP/Gp120 transgenic mice in vivo was also assessed by immunohistochemistry.

KEY RESULTS

AM1241 inhibited in vitro Gp120-mediated neurotoxicity and apoptosis of primary human and murine NPCs and increased their survival. AM1241 also promoted differentiation of NPCs to neuronal cells. While GFAP/Gp120 Tg mice exhibited impaired neurogenesis, as indicated by reduction in BrdU⁺ cells and doublecortin⁺ (DCX⁺) cells, and a decrease in cells with proliferating cell nuclear antigen (PCNA), administration of AM1241 to GFAP/Gp120 Tg mice resulted in enhanced in vivo neurogenesis in the hippocampus as indicated by increase in neuroblasts, neuronal cells, BrdU⁺ cells and PCNA⁺ cells. Astrogliosis and gliogenesis were decreased in GFAP/Gp120 Tg mice treated with AM1241, compared with those treated with vehicle.

CONCLUSIONS AND IMPLICATIONS

The CB₂ receptor agonist rescued impaired neurogenesis caused by HIV-1/Gp120 insult. Thus, CB₂ receptor agonists may act as neuroprotective agents, restoring impaired neurogenesis in patients with HAD.