CANNABINOID RECEPTORS AS THERAPEUTIC TARGETS

Pyrimidinyl Biphenylureas: Identification of New Lead Compounds as Allosteric Modulators of the Cannabinoid Receptor CB1

The allosteric modulator 1-(4-chlorophenyl)-3-(3-(6-(pyrrolidin-1-yl)pyridin-2-yl)phenyl)urea (PSNCBAM-1, 2) bound the cannabinoid receptor 1 (CB1) and antagonized G protein coupling. This compound demonstrated potent anorectic effects similar to the CB1 antagonist rimonabant that once was marketed for the treatment of obesity, suggesting a new chemical entity for the discovery of antiobesity drugs. To increase structural diversity of this class of CB1 ligands, we designed and synthesized two classes of novel analogues, in which the pyridine ring of 2 was replaced by a pyrimidine ring. These positively modulate the binding of the CB1 orthosteric agonist CP55,940 while exhibiting an antagonism of G-protein coupling activity. Interestingly, compounds 7d and 8d demonstrated ERK1/2 phosphorylation mediated via β-arrestin unlike the orthosteric CP55,940 that does so in a G protein-dependent manner. These can serve as new lead compounds for the future development of CB1 allosteric modulators that show biased agonism and potentially antiobesity behavior via a new mechanism.

Endocannabinoid 2-arachidonoylglycerol protects inflammatory insults from sulfur dioxide inhalation via cannabinoid receptors in the brain

Sulfur dioxide (SO₂) pollution in the atmospheric environment causes brain inflammatory insult and inflammatory-related microvasculature dysfunction. However, there are currently no effective medications targeting the harmful outcomes from chemical inhalation. Endocannabinoids (eCBs) are involved in neuronal protection against inflammation-induced neuronal injury. The 2-arachidonoylglycerol (2-AG), the most abundant eCBs and a full agonist for cannabinoid receptors (CB1 and CB2), is also capable of suppressing proinflammatory stimuli and improving microvasculature dysfunction. Here, we indicated that endogenous 2-AG protected against neuroinflammation in response to SO₂ inhalation by inhibiting the activation of microglia and astrocytes and attenuating the overexpression of inflammatory cytokines, including tumor necrosis factor alpha (TNF-a), interleukin (IL)-1β, and inducible nitric oxide synthase (iNOS). In addition, endogenous 2-AG prevented cerebral vasculature dysfunction following SO₂ inhalation by inhibiting endothelin 1 (ET-1), vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) expression, elevating endothelial nitric oxide synthase (eNOS) level, and restoring the imbalance between thromboxane A2 (TXA2) and prostaglandin I2 (PGI2). In addition, the action of endogenous 2-AG on the suppression of inflammatory insult and inflammatory-related microvasculature dysfunction appeared to be mainly mediated by CB1 and CB2 receptors. Our results provided a mechanistic basis for the development of new therapeutic approaches for protecting brain injuries from SO₂ inhalation.

Allosteric Modulation: An Alternate Approach Targeting the Cannabinoid CB1 Receptor

The cannabinoid CB1 receptor is a G protein coupled receptor and plays an important role in many biological processes and physiological functions. A variety of CB1 receptor agonists and antagonists, including endocannabinoids, phytocannabinoids, and synthetic cannabinoids, have been discovered or developed over the past 20 years. In 2005, it was discovered that the CB1 receptor contains allosteric site(s) that can be recognized by small molecules or allosteric modulators. A number of CB1 receptor allosteric modulators, both positive and negative, have since been reported and importantly, they display pharmacological characteristics that are distinct from those of orthosteric agonists and antagonists. Given the psychoactive effects commonly associated with CB1 receptor agonists and antagonists/inverse agonists, allosteric modulation may offer an alternate approach to attain potential therapeutic benefits while avoiding inherent side effects of orthosteric ligands. This review details the complex pharmacological profiles of these allosteric modulators, their structure-activity relationships, and efforts in elucidating binding modes and mechanisms of actions of reported CB1 allosteric modulators. The ultimate development of CB1 receptor allosteric ligands could potentially lead to improved therapies for CB1-mediated neurological disorders.

Quantitative Analyses of Synergistic Responses between Cannabidiol and DNA-Damaging Agents on the Proliferation and Viability of Glioblastoma and Neural Progenitor Cells in Culture

Evidence suggests that the nonpsychotropic cannabis-derived compound, cannabidiol (CBD), has antineoplastic activity in multiple types of cancers, including glioblastoma multiforme (GBM). DNA-damaging agents remain the main standard of care treatment available for patients diagnosed with GBM. Here we studied the antiproliferative and cell-killing activity of CBD alone and in combination with DNA-damaging agents (temozolomide, carmustine, or cisplatin) in several human GBM cell lines and in mouse primary GBM cells in cultures. This activity was also studied in mouse neural progenitor cells (NPCs) in culture to assess for potential central nervous system toxicity. We found that CBD induced a dose-dependent reduction of both proliferation and viability of all cells with similar potencies, suggesting no preferential activity for cancer cells. Hill plot analysis indicates an allosteric mechanism of action triggered by CBD in all cells. Cotreatment regimens combining CBD and DNA-damaging agents produced synergistic antiproliferating and cell-killing responses over a limited range of concentrations in all human GBM cell lines and mouse GBM cells as well as in mouse NPCs. Remarkably, antagonistic responses occurred at low concentrations in select human GBM cell lines and in mouse GBM cells. Our study suggests limited synergistic activity when combining CBD and DNA-damaging agents in treating GBM cells, along with little to no therapeutic window when considering NPCs.

The Multiple Waves of Cannabinoid 1 Receptor Signaling

The cannabinoid 1 receptor (CB1R) is one of the most abundant G protein-coupled receptors (GPCRs) in the central nervous system, with key roles during neurotransmitter release and synaptic plasticity. Upon ligand activation, CB1Rs may signal in three different spatiotemporal waves. The first wave, which is transient (<10 minutes) and initiated by heterotrimeric G proteins, is followed by a second wave (>5 minutes) that is mediated by β-arrestins. The third and final wave occurs at intracellular compartments and could be elicited by G proteins or β-arrestins. This complexity presents multiple challenges, including the correct classification of receptor ligands, the identification of the signaling pathways regulated by each wave, and the underlying molecular mechanisms and physiologic impacts of these waves. Simultaneously, it provides new opportunities to harness the therapeutic potential of the cannabinoid system and other GPCRs. Over the last several years, we have significantly expanded our understanding of the mechanisms and pathways downstream from the CB1R. The identification of receptor mutations that can bias signaling to specific pathways and the use of siRNA technology have been key tools to identifying which signaling cascades are controlled by G proteins or β-arrestins. Here, we review our current knowledge on CB1R signaling, with particular emphasis on the mechanisms and cascades mediated by β-arrestins downstream from the CB1R.

Somatostatin receptor 5 is a prominent regulator of signaling pathways in cells with coexpression of Cannabinoid receptors 1

Endocannabinoids and somatostatin (SST) play critical roles in several pathophysiological conditions via binding to different receptor subtypes. Cannabinoid receptor 1 (CB1R) and somatostatin receptors (SSTRs) are expressed in several brain regions and share overlapping functions. Whether these two prominent members of G-protein-coupled receptor (GPCR) family interact with each other and constitute a functional receptor complex is not known. In the present study, we investigated the colocalization of CB1R and SSTR5 in rat brain, and studied receptor internalization, interaction and signal transduction pathways in HEK-293 cells cotransfected with human cannabinoid receptor 1 (hCB1R) and hSSTR5. Our results showed that CB1R and SSTR5 colocalized in rat brain cortex, striatum, and hippocampus. CB1R was expressed in SSTR5 immunoprecipitate prepared from the brain tissue lysate, indicating their association in a system where these receptors are endogenously expressed. In cotransfected HEK-293 cells, SSTR5 and CB1R existed in a constitutive heteromeric complex under basal condition, which was disrupted upon agonist treatments. Furthermore, concurrent receptor activation led to preferential formation of SSTR5 homodimer and dissociation of CB1R homodimer. We also discovered that second messenger cyclic adenosine monophosphate and downstream signaling pathways were modulated in a SSTR5-dominant and concentration-dependent manner in the presence of receptor-specific agonist. In conclusion, with predominant role of SSTR5, the functional consequences of crosstalk between SSTR5 and CB1R resulting in the regulation of receptor trafficking and signal transduction pathways open new therapeutic avenue in cancer biology and excitotoxicity.

Interaction between Cannabinoid System and Toll-Like Receptors Controls Inflammation

Since the discovery of the endocannabinoid system consisting of cannabinoid receptors, endogenous ligands, and biosynthetic and metabolizing enzymes, interest has been renewed in investigating the promise of cannabinoids as therapeutic agents. Abundant evidence indicates that cannabinoids modulate immune responses. An inflammatory response is triggered when innate immune cells receive a danger signal provided by pathogen- or damage-associated molecular patterns engaging pattern-recognition receptors. Toll-like receptor family members are prominent pattern-recognition receptors expressed on innate immune cells. Cannabinoids suppress Toll-like receptor-mediated inflammatory responses. However, the relationship between the endocannabinoid system and innate immune system may not be one-sided. Innate immune cells express cannabinoid receptors and produce endogenous cannabinoids. Hence, innate immune cells may play a role in regulating endocannabinoid homeostasis, and, in turn, the endocannabinoid system modulates local inflammatory responses. Studies designed to probe the interaction between the innate immune system and the endocannabinoid system may identify new potential molecular targets in developing therapeutic strategies for chronic inflammatory diseases. This review discusses the endocannabinoid system and Toll-like receptor family and evaluates the interaction between them.

Synthesis of (-)-Cannabimovone and Structural Reassignment of Anhydrocannabimovone through Gold(I)-Catalyzed Cycloisomerization

The first total synthesis of cannabimovone from Cannabis sativa and anhydrocannabimovone was achieved by means of a highly stereoselective gold(I)-catalyzed cycloisomerization. The results led to reassignment of the structure of anhydrocannabimovone.

Synthesis and biological evaluation of indole-2-carboxamides bearing photoactivatable functionalities as novel allosteric modulators for the cannabinoid CB1 receptor

5-Chloro-3-ethyl-N-(4-(piperidin-1-yl)phenethyl)-1H-indole-2-carboxamide (ORG27569, 1) is a prototypical allosteric modulator for the cannabinoid CB1 receptor. Based on this indole-2-carboxamide scaffold, we designed and synthesized novel CB1 allosteric modulators that possess photoactivatable functionalities, which include benzophenone, phenyl azide, aliphatic azide and phenyltrifluoromethyldiazrine. To assess their allosteric effects, the dissociation constant (KB) and allosteric binding cooperativity factor (α) were determined and compared to their parent compounds. Within this series, benzophenone-containing compounds 26 and 27, phenylazide-containing compound 28, and the aliphatic azide containing compound 36b showed allosteric binding parameters (KB and α) comparable to their parent compound 1, 7, 8, and 9, respectively. We further assessed these modulators for their impact on G-protein coupling activity. Interestingly, these compounds exhibited negative allosteric modulator properties in a manner similar to their parent compounds, which antagonize agonist-induced G-protein coupling. These novel CB1 allosteric modulators, possessing photoactivatable functionalities, provide valuable tools for future photo-affinity labeling and mapping the CB1 allosteric binding site(s).

Pharmacological evaluation of synthetic cannabinoids identified as constituents of spice

In recent years, many synthetic cannabinoid (CB) receptor agonists have appeared on the market as constituents of herbal incense mixtures known as "spice". Contrary to the declared use, they are perorally consumed as a replacement for marijuana to get "high". In many cases, detailed information on the physicochemical and pharmacological properties of the synthetic compounds found in spice preparations is lacking. We have now evaluated a large series of heterocyclic compounds, 1,3-disubstituted indole and 2-azaindole derivatives known or assumed to be CB₁ receptor agonists, many of which have previously been identified in forensic samples. The mainly observed structural variations to circumvent restriction by law were bioisosteric exchanges of functional groups in known CB₁ agonists. We analyzed the structure-activity relationships of compounds at human CB₁ and CB₂ receptors based on affinities obtained in radioligand binding studies, and determined their efficacy in cAMP accumulation assays. Moreover, we investigated the activities of the compounds at the orphan G protein-coupled receptors GPR18 and GPR55 both of which are known to interact with cannabinoids. Most of the investigated compounds behaved as potent full agonists of CB₁ and CB₂ receptors with affinities in the low nanomolar to subnanomolar concentration range. Some compounds were moderately potent GPR55 antagonists, while none interacted with GPR18. Most derivatives were predicted to cross the blood-brain barrier as determined by bioinformatics tools. These data are useful for assessing synthetic cannabinoids and will be helpful for predicting pharmacological properties of novel compounds that appear on the illicit drug market.

A critical review of both the synthesis approach and the receptor profile of the 8-chloro-1-(2',4'-dichlorophenyl)-N-piperidin-1-yl-1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide and analogue derivatives

8-Chloro-1-(2',4'-dichlorophenyl)-N-piperidin-1-yl-1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide 9a was discovered as potent and selective CB1 antagonist by part of our group few years ago. In particular it was reported to have an affinity towards the CB1 cannabinoid receptor (CB1R), expressed as Ki, of 0.00035 nM. Nevertheless significantly divergent data were reported for the same compound from other laboratories. To unequivocally define the receptor profile of 9a, we have critically reviewed both its synthesis approach and binding data. Here we report that, in contrast to our previously reported data, 9a showed a Ki value for CB1R in the order of nanomolar rather than of fentomolar range. The new determined receptor profile of 9a was also ascertained for analogue derivatives 9b-i, as well as for 12. Moreover, the structural features of the synthesized compounds necessary for CB1R were investigated. Amongst the novel series, effects on CB1R intrinsic activity was highlighted due to the substituents at the position 3 of the pyrazole ring of the 1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole scaffold. Although the cannabinoid receptor profile of 9a was reviewed in this work, the relevance of this compound in CB1R antagonist based drug discovery is confirmed.

Are the endocannabinoid-like compounds N-acyl aminoacids neuroprotective after traumatic brain injury?

In recent years, a library of approx. 70 N-acyl aminoacids (NAAAs) was discovered in the rat brain. A particular member of this family of compounds is arachidonoyl serine (AraS), which has generated special interest as a potential therapy for traumatic brain injury (TBI). This is due to its structural similarity to the endocannabinoid (eCB) 2-arachidonoyl glycerol (2-AG), which was previously shown to be beneficial in the recovery in a closed head injury model of TBI. Indeed, AraS exerted eCB-mediated neuroprotection, which was evident in numerous aspects related to the secondary damage characterizing TBI. These findings promoted broadening of the research to additional compounds of the NAAA family that share a structural similarity to AraS, namely, palmitoyl serine (PalmS) and oleoyl serine. The latter did not exhibit any improvement in recovery, whereas the former displayed some neuroprotection, albeit inferior to 2-AG and AraS, via unknown mechanisms. Interestingly, when a combined treatment of 2-AG, AraS and PalmS was tested, the overall effect on the severity score was inferior to their individual effects, suggesting not only a lack of direct or indirect synergism, but also possibly some spatial hindrance. Taken together, the complexity of the damage caused by TBI and the many open questions concerning the role of the eCB system in health and disease, the findings so far may serve as a small trace to the understanding of the eCB system, as well as of the mechanisms underlying TBI.

Toxocara canis: Larvicidal activity of fatty acid amides

Considering the therapeutic potential of fatty acid amides, the present study aimed to evaluate their in vitro activity against Toxocara canis larvae and their cytotoxicity for the first time. Linoleylpyrrolidilamide was the most potent, with a minimal larvicidal concentration (MLC) of 0.05 mg/mL and 27% cytotoxicity against murine peritoneal macrophages C57BL/6 mice, as assessed by the MTT assay.

Potentiation of the antitumor activity of adriamycin against osteosarcoma by cannabinoid WIN-55,212-2

Osteosarcoma is the most frequent primary malignant bone tumor that occurs in children and adolescents. The present study aimed to identify novel therapeutic strategies for osteosarcoma, by assessing the antitumor activity of the cannabinoid WIN-55,212-2 and its combined effect with adriamycin (ADM) against the MG-63 human osteosarcoma cell line. To evaluate the antiproliferative action of these molecules, a Cell Counting kit-8 (CCK-8) assay was used. The ability of cannabinoid to inhibit the migration, invasion and angiogenic activity of MG-63 cells were assessed by scratch, Transwell® chamber and angiogenesis assays, respectively, in vitro. To examine the alterations in expression of targeted genes, quantitative polymerase chain reaction and western blot analysis were used. The administration of cannabinoid combined with ADM was demonstrated to inhibit the growth of MG-63 cells, resulting in a cell viability of 32.12±3.13%, which was significantly lower (P<0.05) compared with the cell viability following treatment with cannabinoid (70.86±7.55%) and ADM (62.87±5.98%) alone. Greater antimetastasis and antiangiogenic activities were also observed following the coadministration of the two agents compared with individual treatments and controls. In addition, the expression levels of Notch-1, matrix metalloproteinase-2 (MMP-2) and vascular endothelial growth factor (VEGF) in MG-63 cells were downregulated following the treatments with cannabinoid alone or in combination with ADM. In conclusion, the present findings demonstrated that cannabinoid WIN-55,212-2 may significantly potentiate the antiproliferative, antimetastasis and antiangiogenic effects of ADM against MG-63 cells via the downregulation of Notch-1, MMP-2 and VEGF. These findings may offer a novel strategy for the treatment of osteosarcoma.

Endocannabinoid regulation of amyloid-induced neuroinflammation

The modulation of endocannabinoid (EC) levels and the activation of cannabinoid receptors are seen as promising therapeutic strategies in a variety of diseases, including Alzheimer's disease (AD). We aimed to evaluate the effect of the pharmacologic and genetic inhibition of anandamide-degrading enzyme in a mouse model of AD (5xFAD). Pharmacologic inhibition of the fatty acid amide hydrolase (FAAH) had little impact on the expression of key enzymes and cytokines and also on the cognitive impairment, plaque deposition, and gliosis in 5xFAD mice. CB1 blockade exacerbated inflammation in this transgenic mouse model of AD. The genetic inactivation of FAAH led to increases in the expression of inflammatory cytokines. At the same time, FAAH-null 5xFAD mice exhibited a behavioral improvement in spatial memory that was independent of the level of anxiety and was not CB1 mediated. Finally, mice lacking FAAH showed diminished soluble amyloid levels, neuritic plaques, and gliosis. These data reinforce the notion of a role for the EC system in neuroinflammation and open new perspectives on the relevance of modulating EC levels in the inflamed brain.

Endogenous 2-Arachidonoylglycerol Alleviates Cyclooxygenases-2 Elevation-Mediated Neuronal Injury From SO2 Inhalation via PPARγ Pathway

Although the health effects of sulfur dioxide (SO2) pollution in the atmospheric environment are not new, epidemiological studies and parallel experimental investigations indicate that acute SO2 exposure causes glutamate-mediated excitotoxicity and even contributes to the outcome of cerebral ischemia. Additionally, the free radical-related inflammatory responses are responsible for neuronal insults and consequent brain disorders. However, few medications are available for preventing the inflammatory responses and relieving the subsequent harmful insults from SO2 inhalation. Here, we show that endocannabinoid 2-arachidonoylglycerol (2-AG) prevents neurotoxicity from SO2 inhalation by suppressing cyclooxygenase-2 (COX-2) overexpression, and this action appears to be mediated via cannabinoid receptor 1 (CB1)-dependent mitogen-activated protein kinase/nuclear factor κB (NF-κB) signaling pathways. Furthermore, CB1-dependent peroxisome proliferator activated receptor γ (PPARγ) expression was an important modulator of the 2-AG-mediated resolution on NF-κB-coupled COX-2 elevation in response to SO2 neuroinflammation. This finding provides evidence of a possible therapeutic effect of endogenous 2-AG regulation for protecting against neurological dysfunction from SO2 inhalation in polluted areas.

CB1 Knockout Mice Unveil Sustained CB2-Mediated Antiallodynic Effects of the Mixed CB1/CB2 Agonist CP55,940 in a Mouse Model of Paclitaxel-Induced Neuropathic Pain

Cannabinoids suppress neuropathic pain through activation of cannabinoid CB1 and/or CB2 receptors; however, unwanted CB1-mediated cannabimimetic effects limit clinical use. We asked whether CP55,940 [(-)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexanol], a potent cannabinoid that binds with similar affinity to CB1 and CB2 in vitro, produces functionally separable CB1- and CB2-mediated pharmacological effects in vivo. We evaluated antiallodynic effects, possible tolerance, and cannabimimetic effects (e.g., hypothermia, catalepsy, CB1-dependent withdrawal signs) after systemic CP55,940 treatment in a mouse model of toxic neuropathy produced by a chemotherapeutic agent, paclitaxel. The contribution of CB1 and CB2 receptors to in vivo actions of CP55,940 was evaluated using CB1 knockout (KO), CB2KO, and wild-type (WT) mice. Low-dose CP55,940 (0.3 mg/kg daily, i.p. ) suppressed paclitaxel-induced allodynia in WT and CB2KO mice, but not CB1KO mice. Low-dose CP55,940 also produced hypothermia and rimonabant-precipitated withdrawal in WT, but not CB1KO, mice. In WT mice, tolerance developed to CB1-mediated hypothermic effects of CP55,940 earlier than to antiallodynic effects. High-dose CP55,940 (10 mg/kg daily, i.p.) produced catalepsy in WT mice, which precluded determination of antiallodynic efficacy but produced sustained CB2-mediated suppression of paclitaxel-induced allodynia in CB1KO mice; these antiallodynic effects were blocked by the CB2 antagonist 6-iodopravadoline (AM630). High-dose CP55,940 did not produce hypothermia or rimonabant-precipitated withdrawal in CB1KO mice. Our results using the mixed CB1/CB2 agonist CP55,940 document that CB1 and CB2 receptor activations produce mechanistically distinct suppression of neuropathic pain. Our study highlights the therapeutic potential of targeting cannabinoid CB2 receptors to bypass unwanted central effects associated with CB1 receptor activation.

Effects of rimonabant on the development of single dose-induced behavioral sensitization to ethanol, morphine and cocaine in mice

RATIONALE

The endocannabinoid system has been implicated in the neurobiological mechanism underlying drug addiction, especially the primary rewarding dopamine-dependent processes. Therefore, endocannabinoid receptor antagonists, such as the CB1 cannabinoid antagonist rimonabant, have been proposed as candidates for preventive addiction therapies.

OBJECTIVES

Investigate the possible involvement of CB1 receptors in the development of behavioral sensitization to ethanol, morphine and cocaine in mice.

METHODS

We compared the effects of different doses of rimonabant (0.3, 1, 3 and 10mg/kg) on spontaneous locomotor activity in the open-field, hyperlocomotion induced by acute administration of ethanol (1.8g/kg), morphine (20mg/kg) or cocaine (10mg/kg) and on subsequent drug-induced locomotor sensitization using a two-injection protocol in mice. We also investigated a possible depressive-like effect of an acute rimonabant challenge at the highest dose and its potential anxiogenic property.

RESULTS

At the highest dose, rimonabant abolished ethanol- and cocaine-induced hyperlocomotion and behavioral sensitization without modifying spontaneous and central locomotor activity or inducing depressive-like behavior on the forced swim test in mice. The other doses of rimonabant also selectively blocked acute ethanol-induced central hyperlocomotion. Although rimonabant at 0.3 and 1mg/kg potentiated the central hyperlocomotion induced by acute morphine injection, it was effective in attenuating morphine-induced behavioral sensitization at all doses.

CONCLUSIONS

Because the neural basis of behavioral sensitization has been proposed to correspond to some components of addiction, our findings indicate that the endocannabinoid system might be involved in ethanol, cocaine and morphine abuse.

Minocycline Attenuates Neonatal Germinal-Matrix-Hemorrhage-Induced Neuroinflammation and Brain Edema by Activating Cannabinoid Receptor 2

Germinal matrix hemorrhage (GMH) is the most common neurological disease of premature newborns leading to detrimental neurological sequelae. Minocycline has been reported to play a key role in neurological inflammatory diseases by controlling some mechanisms that involve cannabinoid receptor 2 (CB2R). The current study investigated whether minocycline reduces neuroinflammation and protects the brain from injury in a rat model of collagenase-induced GMH by regulating CB2R activity. To test this hypothesis, the effects of minocycline and a CB2R antagonist (AM630) were evaluated in male rat pups that were post-natal day 7 (P7) after GMH. We found that minocycline can lead to increased CB2R mRNA expression and protein expression in microglia. Minocycline significantly reduced GMH-induced brain edema, microglial activation, and lateral ventricular volume. Additionally, minocycline enhanced cortical thickness after injury. All of these neuroprotective effects of minocycline were prevented by AM630. A cannabinoid CB2 agonist (JWH133) was used to strengthen the hypothesis, which showed the identical neuroprotective effects of minocycline. Our study demonstrates, for the first time, that minocycline attenuates neuroinflammation and brain injury in a rat model of GMH, and activation of CBR2 was partially involved in these processes.

Structure-activity relationships of substituted 1H-indole-2-carboxamides as CB1 receptor allosteric modulators

A series of substituted 1H-indole-2-carboxamides structurally related to compounds Org27569 (1), Org29647 (2) and Org27759 (3) were synthesized and evaluated for CB1 allosteric modulating activity in calcium mobilization assays. Structure-activity relationship studies showed that the modulation potency of this series at the CB1 receptor was enhanced by the presence of a diethylamino group at the 4-position of the phenyl ring, a chloro or fluoro group at the C5 position and short alkyl groups at the C3 position on the indole ring. The most potent compound (45) had an IC₅₀ value of 79 nM which is ∼2.5 and 10 fold more potent than the parent compounds 3 and 1, respectively. These compounds appeared to be negative allosteric modulators at the CB1 receptor and dose-dependently reduced the Emax of agonist CP55,940. These analogs may provide the basis for further optimization and use of CB1 allosteric modulators.

Exposure of Adolescent Mice to Delta-9-Tetrahydrocannabinol Induces Long-Lasting Modulation of Pro- and Anti-Inflammatory Cytokines in Hypothalamus and Hippocampus Similar to that Observed for Peripheral Macrophages

Cannabis use is frequent among adolescents. Its main component, delta-9-tetrahydrocannabinol (THC), affects the immune system. We recently demonstrated that chronic exposure of adolescent mice to THC suppressed immunity immediately after treatment but that after a washout period THC induced a long-lasting opposite modulation towards a proinflammatory and T-helper-1 phenotype in adulthood. The main objective of this study was to investigate whether the same effect was also present in brain regions such as the hypothalamus and hippocampus. Thirty-three-day-old adolescent and 80-day-old adult male mice were used. Acute THC administration induced a similar reduction of macrophage proinflammatory cytokines and an IL-10 increase in adult and adolescent mice. THC did not affect brain cytokines in adult mice, but a proinflammatory cytokine decrease was evident in the adolescent brain. A similar effect was present in the hypothalamus and hippocampus after 10 days' THC administration. In contrast, when brain cytokines were measured 47 days after the final THC administration, we observed an inverted effect in adult mice treated as adolescents, i.e., IL-1β and TNF-α increased and IL-10 decreased, indicating a shift toward neuroinflammation. These data suggest that THC exposure in adolescence has long-lasting effects on brain cytokines that parallel those present in the periphery. This modulation may affect vulnerability to immune and behavioural diseases in adulthood.

The spinal anti-inflammatory mechanism of motor cortex stimulation: cause of success and refractoriness in neuropathic pain?

Background

Motor cortex stimulation (MCS) is an effective treatment in neuropathic pain refractory to pharmacological management. However, analgesia is not satisfactorily obtained in one third of patients. Given the importance of understanding the mechanisms to overcome therapeutic limitations, we addressed the question: what mechanisms can explain both MCS effectiveness and refractoriness? Considering the crucial role of spinal neuroimmune activation in neuropathic pain pathophysiology, we hypothesized that modulation of spinal astrocyte and microglia activity is one of the mechanisms of action of MCS.

Methods

Rats with peripheral neuropathy (chronic nerve injury model) underwent MCS and were evaluated with a nociceptive test. Following the test, these animals were divided into two groups: MCS-responsive and MCS-refractory. We also evaluated a group of neuropathic rats not stimulated and a group of sham-operated rats. Some assays included rats with peripheral neuropathy that were treated with AM251 (a cannabinoid antagonist/inverse agonist) or saline before MCS. Finally, we performed immunohistochemical analyses of glial cells (microglia and astrocytes), cytokines (TNF-α and IL-1β), cannabinoid type 2 (CB2), μ-opioid (MOR), and purinergic P2X4 receptors in the dorsal horn of the spinal cord (DHSC).

Findings

MCS reversed mechanical hyperalgesia, inhibited astrocyte and microglial activity, decreased proinflammatory cytokine staining, enhanced CB2 staining, and downregulated P2X4 receptors in the DHSC ipsilateral to sciatic injury. Spinal MOR staining was also inhibited upon MCS. Pre-treatment with AM251 blocked the effects of MCS, including the inhibitory mechanism on cells. Finally, MCS-refractory animals showed similar CB2, but higher P2X4 and MOR staining intensity in the DHSC in comparison to MCS-responsive rats.

Conclusions

These results indicate that MCS induces analgesia through a spinal anti-neuroinflammatory effect and the activation of the cannabinoid and opioid systems via descending inhibitory pathways. As a possible explanation for MCS refractoriness, we propose that CB2 activation is compromised, leading to cannabinoid resistance and consequently to the perpetuation of neuroinflammation and opioid inefficacy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-014-0216-1) contains supplementary material, which is available to authorized users.

Thiazole: a promising heterocycle for the development of potent CNS active agents

Thiazole is a valuable scaffold in the field of medicinal chemistry and has accounted to display a variety of biological activities. Thiazole and its derivatives have attracted continuing interest to design various novel CNS active agents. In the past few decades, thiazoles have been widely used to develop a variety of therapeutic agents against numerous CNS targets. Thiazole containing drug molecules are currently being used in treatment of various CNS disorders and a number of thiazole derivatives are also presently in clinical trials. A lot of research has been carried out on thiazole and their analogues, which has proved their efficacy to overcome several CNS disorders in rodent as well as primate models. The aim of present review is to highlights diverse CNS activities displayed by thiazole and their derivatives. SAR of this nucleus has also been well discussed. This review covers the recent updates present in literature and will surely provide a greater insight for the designing and development of potent thiazole based CNS active agents in future.

Rising stars: modulation of brain functions by astroglial type-1 cannabinoid receptors

The type-1-cannabinoid (CB1 ) receptor is amongst the most widely expressed G protein-coupled receptors in the brain. In few decades, CB1 receptors have been shown to regulate a large array of functions from brain cell development and survival to complex cognitive processes. Understanding the cellular mechanisms underlying these functions of CB1 is complex due to the heterogeneity of the brain cell types on which the receptor is expressed. Although the large majority of CB1 receptors act on neurons, early studies pointed to a direct control of CB1 receptors over astroglial functions including brain energy supply and neuroprotection. In line with the growing concept of the tripartite synapse highlighting astrocytes as direct players in synaptic plasticity, astroglial CB1 receptor signaling recently emerged as the mediator of several forms of synaptic plasticity associated to important cognitive functions. Here, we shortly review the current knowledge on CB1 receptor-mediated astroglial functions. This functional spectrum is large and most of the mechanisms by which CB1 receptors control astrocytes, as well as their consequences in vivo, are still unknown, requiring innovative approaches to improve this new cannabinoid research field.

(4-(Bis(4-fluorophenyl)methyl)piperazin-1-yl)(cyclohexyl)methanone hydrochloride (LDK1229): a new cannabinoid CB1 receptor inverse agonist from the class of benzhydryl piperazine analogs

Some inverse agonists of cannabinoid receptor type 1 (CB1) have been demonstrated to be anorectic antiobesity drug candidates. However, the first generation of CB1 inverse agonists, represented by rimonabant (SR141716A), otenabant, and taranabant, are centrally active, with a high level of psychiatric side effects. Hence, the discovery of CB1 inverse agonists with a chemical scaffold distinct from these holds promise for developing peripherally active CB1 inverse agonists with fewer side effects. We generated a new CB1 inverse agonist, (4-(bis(4-fluorophenyl)methyl)piperazin-1-yl)(cyclohexyl)methanone hydrochloride (LDK1229), from the class of benzhydryl piperazine analogs. This compound binds to CB1 more selectively than cannabinoid receptor type 2, with a Ki value of 220 nM. Comparable CB1 binding was also observed by analogs 1-[bis(4-fluorophenyl)methyl]-4-cinnamylpiperazine dihydrochloride (LDK1203) and 1-[bis(4-fluorophenyl)methyl]-4-tosylpiperazine hydrochloride (LDK1222), which differed by the substitution on the piperazine ring where the piperazine of LDK1203 and LDK1222 are substituted by an alkyl group and a tosyl group, respectively. LDK1229 exhibits efficacy comparable with SR141716A in antagonizing the basal G protein coupling activity of CB1, as indicated by a reduction in guanosine 5'-O-(3-thio)triphosphate binding. Consistent with inverse agonist behavior, increased cell surface localization of CB1 upon treatment with LDK1229 was also observed. Although docking and mutational analysis showed that LDK1229 forms similar interactions with the receptor as SR141716A does, the benzhydryl piperazine scaffold is structurally distinct from the first-generation CB1 inverse agonists. It offers new opportunities for developing novel CB1 inverse agonists through the optimization of molecular properties, such as the polar surface area and hydrophilicity, to reduce the central activity observed with SR141716A.

Toxicology and Management of Novel Psychoactive Drugs

Health care providers are seeing an increased number of patients under the influence of several new psychoactive drug classes. Synthetic cannabinoids, cathinones, and piperazines are sought by users for their psychoactive effects, perceived safety profile, minimal legal regulations, and lack of detection on routine urine drug screening. However, these drugs are beginning to be recognized by the medical community for their toxic effects. The neuropsychiatric and cardiovascular toxicities are among the most common reasons for emergency medical treatment, which in some cases, can be severe and even life-threatening. Management strategies are often limited to supportive and symptomatic care due to the limited published data on alternative treatment approaches. The purpose of this article is to offer health care providers, emergency medical personnel in particular, an awareness and understanding of the dangers related to some of the new psychoactive drugs of abuse. The background, pharmacology, toxicity, management, detection, and legal status of each class will be discussed.

Diarylureas as allosteric modulators of the cannabinoid CB1 receptor: structure-activity relationship studies on 1-(4-chlorophenyl)-3-{3-[6-(pyrrolidin-1-yl)pyridin-2-yl]phenyl}urea (PSNCBAM-1)

The recent discovery of allosteric modulators of the CB1 receptor including PSNCBAM-1 (4) has generated significant interest in CB1 receptor allosteric modulation. Here in the first SAR study on 4, we have designed and synthesized a series of analogs focusing on modifications at two positions. Pharmacological evaluation in calcium mobilization and binding assays revealed the importance of alkyl substitution at the 2-aminopyridine moiety and electron deficient aromatic groups at the 4-chlorophenyl position for activity at the CB1 receptor, resulting in several analogs with comparable potency to 4. These compounds increased the specific binding of [(3)H]CP55,940, in agreement with previous reports. Importantly, 4 and two analogs dose-dependently reduced the Emax of the agonist curve in the CB1 calcium mobilization assays, confirming their negative allosteric modulator characteristics. Given the side effects associated with CB1 receptor orthosteric antagonists, negative allosteric modulators provide an alternative approach to modulate the pharmacologically important CB1 receptor.

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

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

CB2 receptor activation ameliorates the proinflammatory activity in acute lung injury induced by paraquat

Paraquat, a widely used herbicide, is well known to exhibit oxidative stress and lung injury. In the present study, we investigated the possible underlying mechanisms of cannabinoid receptor-2 (CB2) activation to ameliorate the proinflammatory activity induced by PQ in rats. JWH133, a CB2 agonist, was administered by intraperitoneal injection 1 h prior to PQ exposure. After PQ exposure for 4, 8, 24, and 72 h, the bronchoalveolar lavage fluid was collected to determine levels of TNF-α and IL-1β, and the arterial blood samples were collected for detection of PaO₂ level. At 72 h after PQ exposure, lung tissues were collected to determine the lung wet-to-dry weight ratios, myeloperoxidase activity, lung histopathology, the protein expression level of CB2, MAPKs (ERK1/2, p38MAPK, and JNK1/2), and NF-κBp65. After rats were pretreated with JWH133, PQ-induced lung edema and lung histopathological changes were significantly attenuated. PQ-induced TNF-α and IL-1β secretion in BALF, increases of PaO₂ in arterial blood, and MPO levels in the lung tissue were significantly reduced. JWH133 could efficiently activate CB2, while inhibiting MAPKs and NF-κB activation. The results suggested that activating CB2 receptor exerted protective activity against PQ-induced ALI, and it potentially contributed to the suppression of the activation of MAPKs and NF-κB pathways.

Δ⁹-Tetrahydrocannabinol-induced anti-inflammatory responses in adolescent mice switch to proinflammatory in adulthood

Marijuana abuse is prominent among adolescents. Although Δ(9)-THC, one of its main components, has been demonstrated to modulate immunity in adults, little is known about its impact during adolescence on the immune system and the long-lasting effects in adulthood. We demonstrate that 10 days of Δ(9)-THC treatment induced a similar alteration of macrophage and splenocyte cytokines in adolescent and adult mice. Immediately at the end of chronic Δ(9)-THC, a decrease of proinflammatory cytokines IL- 1β and TNF-α and an increase of anti-inflammatory cytokine IL-10 production by macrophages were present as protein and mRNA in adolescent and adult mice. In splenocytes, Δ(9)-THC modulated Th1/Th2 cytokines skewing toward Th2: IFN-γ was reduced, and IL-4 and IL-10 increased. These effects were lost in adult animals, 47 days after the last administration. In contrast, in adult animals treated as adolescents, a perturbation of immune responses, although in an opposite direction, was present. In adults treated as adolescents, a proinflammatory macrophage phenotype was observed (IL-1β and TNF-α were elevated; IL-10 decreased), and the production of Th cytokines was blunted. IgM titers were also reduced. Corticosterone concentrations indicate a long-lasting dysregulation of HPA in adolescent mice. We measured blood concentrations of Δ(9)-THC and its metabolites, showing that Δ(9)-THC plasma levels in our mice are in the order of those achieved in human heavy smokers. Our data demonstrate that Δ(9)-THC in adolescent mice triggers immune dysfunctions that last long after the end of abuse, switching the murine immune system to proinflammatory status in adulthood.

Optimization of chemical functionalities of indole-2-carboxamides to improve allosteric parameters for the cannabinoid receptor 1 (CB1)

5-Chloro-3-ethyl-N-(4-(piperidin-1-yl)phenethyl)-1H-indole-2-carboxamide (1; ORG27569) is a prototypical allosteric modulator for the cannabinoid type 1 receptor (CB1). Here, we reveal key structural requirements of indole-2-carboxamides for allosteric modulation of CB1: a critical chain length at the C3-position, an electron withdrawing group at the C5-position, the length of the linker between the amide bond and the phenyl ring B, and the amino substituent on the phenyl ring B. These significantly impact the binding affinity (K_B) and the binding cooperativity (α). A potent CB1 allosteric modulator 5-chloro-N-(4-(dimethylamino)phenethyl)-3-propyl-1H-indole-2-carboxamide (12d) was identified. It exhibited a K_B of 259.3 nM with a strikingly high binding α of 24.5. We also identified 5-chloro-N-(4-(dimethylamino)phenethyl)-3-hexyl-1H-indole-2-carboxamide (12f) with a K_B of 89.1 nM, which is among the lowest K_B values obtained for any allosteric modulator of CB1. These positive allosteric modulators of orthosteric agonist binding nonetheless antagonized the agonist-induced G-protein coupling to the CB1 receptor, yet induced β-arrestin mediated ERK1/2 phosphorylation.

3D-QSAR/CoMFA-based structure-affinity/selectivity relationships of aminoalkylindoles in the cannabinoid CB1 and CB2 receptors

A 3D-QSAR (CoMFA) study was performed in an extensive series of aminoalkylindoles derivatives with affinity for the cannabinoid receptors CB1 and CB2. The aim of the present work was to obtain structure-activity relationships of the aminoalkylindole family in order to explain the affinity and selectivity of the molecules for these receptors. Major differences in both, steric and electrostatic fields were found in the CB1 and CB2 CoMFA models. The steric field accounts for the principal contribution to biological activity. These results provide a foundation for the future development of new heterocyclic compounds with high affinity and selectivity for the cannabinoid receptors with applications in several pathological conditions such as pain treatment, cancer, obesity and immune disorders, among others.

Long-term consequences of perinatal fatty acid amino hydrolase inhibition

BACKGROUND AND PURPOSE

Fatty acid amide hydrolase inhibitors show promise as a treatment for anxiety, depression and pain. Here we investigated whether perinatal exposure to URB597, a fatty acid amide hydrolase inhibitor, alters brain development and affects behaviour in adult mice.

EXPERIMENTAL APPROACH

Mouse dams were treated daily from gestational day 10.5 to 16.5 with 1, 3 or 10 mg kg−1 URB597. MS was used to measure a panel of endocannabinoids and related lipid compounds and brain development was assessed at embryonic day 16.5. Separate cohorts of mouse dams were treated with 10 mg kg−1 URB597, from gestational day 10.5 to postnatal day 7, and the adult offspring were assessed with a battery of behavioural tests.

KEY RESULTS

Perinatal URB597 exposure elevated anandamide and related N-acyl amides. URB597 did not induce signs of toxicity or affect dam weight gain, neurogenesis or axonal development at embryonic day 16.5. It did lead to subtle behavioural deficits in adult offspring, manifested by reduced cocaine-conditioned preference, increased depressive behaviours and impaired working memory. Anxiety levels, motor function and sensory-motor gating were not significantly altered.

CONCLUSIONS AND IMPLICATIONS

Taken together, the present results highlight how exposure to elevated levels of anandamide and related N-acyl amides during brain development can lead to subtle alterations in behaviour in adulthood.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6

Bicyclic imidazole-4-one derivatives: a new class of antagonists for the orphan G protein-coupled receptors GPR18 and GPR55

GPR18 and GPR55 are orphan G protein-coupled receptors (GPCRs) that interact with certain cannabinoid (CB) receptor ligands.

Identification of CB1/CB2 ligands from Zanthoxylum bungeanum

In order to study cannabinoid receptor ligands, a novel plate-based assay was developed previously to measure internalization of CB1/CB2 receptors by determining the change in the intracellular levels of the radiolabeled agonists. This plate-based assay was also used for screening against complex matrices, specifically, in the present study screening for CB1/CB2 receptor activity of extracts for several species of the plant genus Zanthoxylum. The objective of this screen was to identify novel antagonists of the CB1 receptor, which simultaneously displayed agonist activity against the CB2 receptor, since compounds matching this criterion could be potential candidates for the treatment of type-1 diabetes. As a result, two Z. bungeanum extracts were deemed active, leading to the identification of eight compounds, of which compound 7 [(2E,4E,8E,10E,12E)-N-isobutyl-2,4,8,10,12-tetradecapentaenamide, γ-sanshool] was obtained as a promising lead compound.