Effects on immune cells of a new 1,8-naphthyridin-2-one derivative and its analogues as selective CB2 agonists: implications in multiple sclerosis

Activation of CB2R by synthetic CB2R agonist, PM289, improves brain endothelial barrier properties, decreases inflammatory response and enhances endothelial repair

The Cannabinoid 2 Receptor (CB2R) has been found to provide immunological modulation in different cell types. More recently, detection of CB2R in the cerebral endothelium suggests a possible role in the resolution of inflammation at the level of the blood-brain-barrier (BBB). Here, the notion that CB2R upregulation in brain endothelial cells could be exploited to promote vascular protection and BBB integrity was evaluated. Targeting and activation of CB2R was accomplished by a novel and highly specific chromenopyrazole based CB2R agonist, PM289. This study demonstrates that CB2R upregulation is induced as early as 8 h in the cortical vasculature in an experimental mouse model of TBI. Unlike CB2R, CB1R was marginally detected and not significantly induced. In the human brain endothelial cell line, hCMEC/D3 cells, similar induction of CB2R was observed upon stimulation with TNFα. Analysis of transendothelial electrical resistance shows that PM289 markedly prevented the barrier-leakiness induced by TNFα. The BBB is also responsible for maintaining an immunological barrier. The five-fold increase in ICAM1 expression in stimulated endothelial cells was significantly diminished due to CB2R activation. Utilizing wounding assays, results showed that wound repair could be accomplished in nearly half the time when the novel CB2R agonist is present compared to the untreated control. Lastly, mechanistically, the effects of CB2R may be explained by the observed inhibition of the p65 NFκB subunit. Overall, these studies support the notion that targeting and activating CB2R in the brain vasculature could aid in BBB and vascular protection in the context of neuroinflammation.

Cannabinoid CB2 Receptors in Neurodegenerative Proteinopathies: New Insights and Therapeutic Potential

Some of the most prevalent neurodegenerative disorders, including Alzheimer's and Parkinson's disease, are proteinopathies characterized by the accumulation of specific protein aggregates in the brain. Such misfolded protein aggregates can trigger modulation of the innate and adaptive immune systems and subsequently lead to chronic neuroinflammation that drives the onset and progression of neurodegenerative diseases. Since there is still no effective disease-modifying treatment, new therapeutic targets for neurodegenerative proteinopathies have been sought. The endocannabinoid system, and in particular the cannabinoid CB2 receptors, have been extensively studied, due to their important role in neuroinflammation, especially in microglial cells. Several studies have shown promising effects of CB2 receptor activation on reducing protein aggregation-based pathology as well as on attenuating inflammation and several dementia-related symptoms. In this review, we discuss the available data on the role of CB2 receptors in neuroinflammation and the potential benefits and limitations of specific agonists of these receptors in the therapy of neurodegenerative proteinopathies.

Synthesis and In Vitro Characterization of Selective Cannabinoid CB2 Receptor Agonists: Biological Evaluation against Neuroblastoma Cancer Cells

1,8-naphthyridine-3-carboxamide structures were previously identified as a promising scaffold from which to obtain CB2R agonists with anticancer and anti-inflammatory activity. This work describes the synthesis and functional characterization of new 1,8-naphthyridin-2(1H)-one-3-carboxamides with high affinity and selectivity for CB2R. The new compounds were able to pharmacologically modulate the cAMP response without modulating CB2R-dependent β-arrestin2 recruitment. These structures were also evaluated for their anti-cancer activity against SH-SY5Y and SK-N-BE cells. They were able to reduce the cell viability of both neuroblastoma cancer cell lines with micromolar potency (IC50 of FG158a = 11.8 μM and FG160a = 13.2 μM in SH-SY5Y cells) by a CB2R-mediated mechanism. Finally, in SH-SY5Y cells one of the newly synthesized compounds, FG158a, was able to modulate ERK1/2 expression by a CB2R-mediated effect, thus suggesting that this signaling pathway might be involved in its potential anti-cancer effect.

1,8-Naphthyridine Derivatives: A Privileged Scaffold for Versatile Biological Activities

1, 8- Naphthyridine nucleus belongs to significant nitrogen-containing heterocyclic compounds which has garnered the interest of researchers due to its versatile biological activities. It is known to be used as an antimicrobial, anti-psychotic, anti-depressant, anti-convulsant, anti- Alzheimer's, anti-cancer, analgesic, anti-inflammatory, antioxidant, anti-viral, anti-hypertensive, antimalarial, pesticides, anti-platelets, and CB2 receptor agonist, etc. The present review highlights the framework of biological properties of synthesized 1, 8-naphthyridine derivatives developed by various research groups across the globe.

Medicinal Chemistry approach, pharmacology and neuroprotective benefits of CB2R modulators in neurodegenerative diseases

In the last decades, cannabinoid receptor 2 (CB₂R) has continued to receive attention as a key therapeutic target in neuroprotection. Indeed, several findings highlight the neuroprotective effects of CB₂R through suppression of both neuronal excitability and reactive microglia. Additionally, CB₂R seems to be a more promising target than cannabinoid receptor 1 (CB₁R) thanks to the lack of central side effects, its lower expression levels in the central nervous system (CNS), and its inducibility, since its expression enhances quickly in the brain following pathological conditions. This review aims to provide a thorough overview of the main natural and synthetic selective CB₂R modulators, their chemical classification and their potential therapeutic usefulness in neuroprotection, a crucial aspect for the treatment of neurodegenerative diseases.

Cannabinoid Receptors: An Update on Cell Signaling, Pathophysiological Roles and Therapeutic Opportunities in Neurological, Cardiovascular, and Inflammatory Diseases

The identification of the human cannabinoid receptors and their roles in health and disease, has been one of the most significant biochemical and pharmacological advancements to have occurred in the past few decades. In spite of the major strides made in furthering endocannabinoid research, therapeutic exploitation of the endocannabinoid system has often been a challenging task. An impaired endocannabinoid tone often manifests as changes in expression and/or functions of type 1 and/or type 2 cannabinoid receptors. It becomes important to understand how alterations in cannabinoid receptor cellular signaling can lead to disruptions in major physiological and biological functions, as they are often associated with the pathogenesis of several neurological, cardiovascular, metabolic, and inflammatory diseases. This review focusses mostly on the pathophysiological roles of type 1 and type 2 cannabinoid receptors, and it attempts to integrate both cellular and physiological functions of the cannabinoid receptors. Apart from an updated review of pre-clinical and clinical studies, the adequacy/inadequacy of cannabinoid-based therapeutics in various pathological conditions is also highlighted. Finally, alternative strategies to modulate endocannabinoid tone, and future directions are also emphasized.

Synthesis and biological evaluation of 3-(1,3,4-oxadiazol-2-yl)-1,8-naphthyridin-4(1H)-ones as cisplatin sensitizers

A series of novel 3-(1,3,4-oxadiazol-2-yl)-1,8-naphthyridin-4(1H)-one derivatives were synthesized and their anti-cancer as well as cisplatin sensitization activities were evaluated. Among them, compounds 6e and 6h exhibited significant cisplatin sensitization activity against HCT116. Hoechst staining and annexin V-FITC/PI dual-labeling studies demonstrated that the combination of 6e/6h and cisplatin can induce tumour cell apoptosis. Western blot showed that the expression of ATR downstream protein, CHK1, decreased in 6e + cisplatin and 6h + cisplatin groups compared with that in the test compound and cisplatin group. Furthermore, docking of 6e/6h into the ATR structure active site revealed that the N1 and N8 atoms in the naphthyridine ring and the hybrid atom in the oxadiazole ring are involved in hydrogen bonding with Val170, Glu168 and Tyr155. Additionally, the naphthyridine ring is also involved in π-π stacking with Trp169. Accordingly, compounds 6e and 6h can be expected to be potential cisplatin sensitizers that can participate in HCT116 cancer therapy.

Anti-Proliferative Properties and Proapoptotic Function of New CB2 Selective Cannabinoid Receptor Agonist in Jurkat Leukemia Cells

Several studies demonstrated that cannabinoids reduce tumor growth, inhibit angiogenesis, and decrease cancer cell migration. As these molecules are well tolerated, it would be interesting to investigate the potential benefit of newly synthesized compounds, binding cannabinoid receptors (CBRs). In this study, we describe the synthesis and biological effect of 2-oxo-1,8-naphthyridine-3-carboxamide derivative LV50, a new compound with high CB2 receptor (CB2R) affinity. We demonstrated that it decreases viability of Jurkat leukemia cells, evaluated by Trypan Blue and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), but mainly induces a proapoptotic effect. We observed an increase of a hypodiploid peak by propidium iodide staining and changes in nuclear morphology by Hoechst 33258. These data were confirmed by a significant increase of Annexin V staining, cleavage of the nuclear enzyme poly(ADP-ribose)-polymerase (PARP), and caspases activation. In addition, in order to exclude that LV50 non-specifically triggers death of all normal leukocytes, we tested the new compound on normal peripheral blood lymphocytes, excluding the idea of general cytotoxicity. To characterize the involvement of CB2R in the anti-proliferative and proapoptotic effect of LV50, cells were pretreated with a specific CB2R antagonist and the obtained data showed reverse results. Thus, we suggest a link between inhibition of cell survival and proapoptotic activity of the new compound that elicits this effect as selective CB2R agonist.

Bioactive products from singlet oxygen photooxygenation of cannabinoids

Photooxygenation of Δ⁸ tetrahydrocannabinol (Δ⁸-THC), Δ⁹ tetrahydrocannabinol (Δ⁹-THC), Δ⁹ tetrahydrocannabinolic acid (Δ⁹-THCA) and some derivatives (acetate, tosylate and methyl ether) yielded 24 oxygenated derivatives, 18 of which were new and 6 were previously reported, including allyl alcohols, ethers, quinones, hydroperoxides, and epoxides. Testing these compounds for their modulatory effect on cannabinoid receptors CB₁ and CB₂ led to the identification of 7 and 21 as CB₁ partial agonists with Ki values of 0.043 μM and 0.048 μM, respectively and 23 as a cannabinoid with high binding affinity for CB₂ with Ki value of 0.0095 μM, but much less affinity towards CB₁ (Ki 0.467 μM). The synthesized compounds showed cytotoxic activity against cancer cell lines (SK-MEL, KB, BT-549, and SK-OV-3) with IC₅₀ values ranging from 4.2 to 8.5 μg/mL. Several of those compounds showed antimicrobial, antimalarial and antileishmanial activities, with compound 14 being the most potent against various pathogens.

Sativex® effects on promoter methylation and on CNR1/CNR2 expression in peripheral blood mononuclear cells of progressive multiple sclerosis patients

Multiple sclerosis (MS) is a chronic demyelinating central nervous system (CNS) disease that involve oligodendrocyte loss and failure to remyelinate damaged brain areas causing a progressive neurological disability. Studies in MS mouse model suggest that cannabinoids ameliorate symptoms as spasticity, tremor and pain reducing inflammation via cannabinoid-mediated system. The aim of our study is to investigate the changes in cannabinoid type 1 (CNR1) and 2 (CNR2) receptors mRNA expression levels and promoter methylation in peripheral blood mononuclear cells (PBMCs) of MS secondary progressive (MSS-SP) patients treated with Sativex®. Our cohort included MSS-SP patients, that at the time of Sativex® treatment, are treated (n=7), not treated (n=11) or that had terminated interferon-β-1b (IFN-β-1b) therapy (n=12). By Methylation Sensitive High Resolution Melting (MS-HRM), we characterized the methylation profile of CNR1 and CNR2 promoter region, while the relative mRNA transcript levels of these two genes were evaluated in the same samples by Quantitative Real-Time PCR (qRT-PCR) analysis. We did not find different pattern of cytosine-phosphate-guanine (CpG) methylation in the CNR1/CNR2 promoter region of all MSS-SP patients treated with Sativex®. In addition, CNR1 and CNR2 expression did not significantly differ in MSS-SP patients not treated with IFN-β-1b vs. them that have suspended, while in MSS-SP patients treated with IFN-β-1b during Sativex® therapy we found a specific decrease of the CNR2 expression levels. These results suggest that the different expression of cannabinoid receptors by Sativex® treatment in leukocytes might be regulated through a molecular mechanism that involve interferon modulation.

Potent immunomodulatory activity of a highly selective cannabinoid CB2 agonist on immune cells from healthy subjects and patients with multiple sclerosis

COR167, a novel CB2-selective high affinity agonist, was found to significantly inhibit, in a dose-dependent manner, the proliferation of both peripheral blood mononuclear cells and myelin basic protein-reactive T cell lines from normal healthy subjects and patients with relapsing-remitting multiple sclerosis (MS). In MS, a significantly higher inhibition was observed in patients on treatment with disease modifying drugs compared to those naive to treatment. The inhibitory activity of COR167 was exerted through a mixed mechanism involving atypical and incomplete shift of Th1 phenotype towards Th2 phenotype associated with slight reduction of IL-4 and IL-5 as well as strongly reduced levels of Th17-related cytokines. COR167 was also able to reduce in vitro migration of stimulated immunocompetent cells through human brain endothelium associated with a significant reduction of levels of several chemokines. These findings demonstrate that COR167 exerts potent immunomodulatory effects and confirm the cannabinoid CB2 receptor as a novel pharmacological target to counteract neuroinflammation.

Pharmacological Preventions of Brain Injury Following Experimental Germinal Matrix Hemorrhage: an Up-to-Date Review

Germinal matrix hemorrhage (GMH) is defined as the rupture of immature blood vessels in the subependymal zone of premature infants with significant mortality and morbidity. Considering the notable social and ecological stress brought by GMH-induced brain injury and sequelae, safe and efficient pharmacological preventions are badly needed. Currently, several appropriate animal models are available to mimic the clinical outcomes of GMH in human patients. In the long run, hemorrhagic strokes are the research target. Previously, we found that minocycline was efficient to alleviate GMH-induced brain edema and posthemorrhagic hydrocephalus (PHH) in rats, which may be closely related to the activation of cannabinoid receptor 2 (CB2R). However, how the two molecules correlate and the underlined molecular pathway remain unknown. To extensively understand current experimental GMH treatment, this literature review critically evaluates existing therapeutic strategies, potential treatments, and potentially involved molecular mechanisms. Each strategy has its own advantages and disadvantages. Some of the mechanisms are still controversial, requiring an increasing number of animal experiments before the therapeutic strategy would be widely accepted.

Regulation of cannabinoid receptor gene expression and endocannabinoid levels in lymphocyte subsets by interferon-β: a longitudinal study in multiple sclerosis patients

Evidence suggests the involvement of the cannabinoid system in the pathogenesis of multiple sclerosis (MS). We studied cannabinoid receptor (CB)1 and CB2 receptor gene expression in B, natural killer (NK) and T cells from MS patients before and after 1 year of interferon beta therapy, and compared these levels to those of healthy controls. We also measured the production of the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) and the gene expression of the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH) in these cells. Prior to interferon therapy, MS patients showed significantly elevated CB2 expression in B cells, but not in T or NK cells. These levels decreased gradually within 6 months to 1 year of interferon treatment. CB1 expression was elevated in all cell subsets, but only reached statistical significance in T cells; all levels decreased progressively over time. Before treatment, AEA but not 2-AG levels were significantly elevated in the three cell populations; after 1 year of treatment, all values decreased to control levels. The expression of FAAH was unchanged. The different expression of cannabinoid receptor genes and the increased level of AEA in lymphocytes point to a possible role of the cannabinoid system in MS immune response and its modulation by interferon.

Immune system: a possible nexus between cannabinoids and psychosis

BACKGROUND

Endocannabinoid system is involved in the regulation of the brain-immune axis. Cannabis consumption is related with the development, course, and severity of psychosis. The epidemiological evidence for increased occurrence of immunological alterations in patients with psychosis has not been sufficiently addressed. The aim of this review is to establish whether there is any scientific evidence of the influence of cannabinoids on aspects of immunity that affect susceptibility to psychotic disorder induction.

METHODS

A comprehensive search of PubMed/MEDLINE, EMBASE and ISI Web of Knowledge was performed using combinations of key terms distributed into three blocks: "immune", "cannabinoid", and "endocannabinoid receptor". Studies were considered to be eligible for the review if they were original articles, they reported a quantitative or qualitative relation between cannabinoid ligands, their receptors, and immune system, and they were carried out in vitro or in mammals, included humans. All the information was systematically extracted and evaluated.

RESULTS

We identified 122 articles from 446 references. Overall, endocannabinoids enhanced immune response, whereas exogenous cannabinoids had immunosuppressant effects. A general change in the immune response from Th1 to Th2 was also demonstrated for cannabinoid action. Endogenous and synthetic cannabinoids also modulated microglia function and neurotransmitter secretion.

CONCLUSION

The actions of cannabinoids through the immune system are quite regular and predictable in the peripheral but remain fuzzy in the central nervous system. Despite this uncertainty, it may be hypothesized that exposure to exocannabinoids, in particular during adolescence might prompt immunological dysfunctions that potentially cause a latent vulnerability to psychosis. Further investigations are warranted to clarify the relationship between the immunological effects of cannabis and psychosis.

What we know and do not know about the cannabinoid receptor 2 (CB2)

It has been well appreciated that the endocannabinoid system can regulate immune responses via the cannabinoid receptor 2 (CB2), which is primarily expressed by cells of the hematopoietic system. The endocannabinoid system is composed of receptors, ligands and enzymes controlling the synthesis and degradation of endocannabinoids. Along with endocannabinoids, both plant-derived and synthetic cannabinoids have been shown to bind to and signal through CB2 via G proteins leading to both inhibitory and stimulatory signals depending on the biological process. Because no cannabinoid ligand has been identified that only binds to CB2, the generation of mice deficient in CB2 has greatly expanded our knowledge of how CB2 contributes to immune cell development and function in health and disease. In regards to humans, genetic studies have associated CB2 with a variety of human diseases. Here, we review the endocannabinoid system with an emphasis on CB2 and its role in the immune system.

Immune-modulation and properties of absorption and blood brain barrier permeability of 1,8-naphthyridine derivatives

Considering the high selectivity at the cannabinoid CB2 receptor of recently designed 1,8-naphthyridine derivatives and the protective role of this receptor in neurological disorders, in this study we investigated the immune-modulatory and anti-inflammatory effects of these compounds as well as their potential properties of intestinal absorption and blood-brain barrier (BBB) permeability. We used peripheral blood mononuclear cells (PBMC) known to express the CB2 receptor. We observed that test compounds, CB13, CB82 and CB91 reduced PBMC proliferation. The anti-proliferative effect of CB13 and CB91 was partially mediated by the CB2 receptor. These compounds blocked the cells cycle and CB91 reduced T cell activation. CB82 and CB91 down-regulated the expression of phosphorylated proteins like NF-κB, ERK, Akt and the enzyme Cox-2, CB91 blocked the expression of the CB2 receptor and its inhibitory effect was CB2 receptor mediated. We also investigated CB91 properties of intestinal absorption and BBB permeability in order to suggest its potential efficacy on the infiltrating auto-reactive lymphocytes at the level of the central nervous system. For this purpose, CB91 was tested in drug-permeability assays on Caco-2 cells to evaluate its oral bioavailability and on MDCKII-hMDR1 cells to estimate its BBB permeability. The results indicated that this compound possesses medium level of intestinal absorption and BBB permeability. Our data suggest that CB91, modulating the immune response by CB2 receptor mediated mechanism and showing medium level of intestinal absorption and BBB permeability, might be developed as a potential orally delivered drug and might find potential application in pathologies like multiple sclerosis.