CB1 Receptor Ligands Research Articles

Rational Design, Synthesis, and Evaluation of Fluorescent CB2 Receptor Ligands for Live-Cell Imaging: A Comprehensive Review.

The cannabinoid receptors CB1 and CB2 are class A G protein-coupled receptors (GPCRs) that are activated via endogenous lipids called endocannabinoids. The endocannabinoid system (ECS) plays a critical role in the regulation of several physiological states and a wide range of diseases. In recent years, drug discovery approaches targeting the cannabinoid type 2 receptor (CB2R) have gained prominence. Particular attention has been given to selective agonists targeting the CB2 receptors to circumvent the neuropsychotropic side effects associated with CB1 receptors. The pharmacological modulation of CB2R holds therapeutic promise for various diseases, such as inflammatory disorders and immunological conditions, as well as pain management and cancer treatment. Recently, the utilization of fluorescent probes has emerged as a valuable technique for investigating the interactions between ligands and proteins at an exceptional level of spatial and temporal precision. In this review, we aim to examine the progress made in the development of fluorescent probes targeting CB2 receptors and highlight their significance in facilitating the successful clinical translation of CB2R-based therapies.

NAPE-PLD deletion in stress-TRAPed neurons results in an anxiogenic phenotype

Anandamide (AEA) is an endogenous ligand of the cannabinoid CB1 and CB2 receptors, being a component of the endocannabinoid signaling system, which supports the maintenance or regaining of neural homeostasis upon internal and external challenges. AEA is thought to play a protective role against the development of pathological states after prolonged stress exposure, including depression and generalized anxiety disorder. Here, we used the chronic social defeat (CSD) stress as an ethologically valid model of chronic stress in male mice. We characterized a genetically modified mouse line where AEA signaling was reduced by deletion of the gene encoding the AEA synthesizing enzyme N-acyl-phosphatidylethanolamine-hydrolyzing phospholipase D (NAPE-PLD) specifically in neurons activated at the time of CSD stress. One week after the stress, the phenotype was assessed in behavioral tests and by molecular analyses. We found that NAPE-PLD deficiency in neurons activated during the last three days of CSD stress led to an increased anxiety-like behavior. Investigating the molecular mechanisms underlying this phenotype may suggest three main altered pathways to be affected: (i) desensitization of the negative feedback loop of the hypothalamic-pituitary-adrenal axis, (ii) disinhibition of the amygdala by the prefrontal cortex, and (iii) altered neuroplasticity in the hippocampus and prefrontal cortex.

The Plant Derived 3-3'-Diindolylmethane (DIM) Behaves as CB2 Receptor Agonist in Prostate Cancer Cellular Models.

3-3'-Diindolylmethane (DIM) is a biologically active dimer derived from the endogenous conversion of indole-3-carbinol (I3C), a naturally occurring glucosinolate found in many cruciferous vegetables (i.e., Brassicaceae). DIM was the first pure androgen receptor antagonist isolated from the Brassicaceae family and has been recently investigated for its potential pharmacological use in prostate cancer prevention and treatment. Interestingly, there is evidence that DIM can also interact with cannabinoid receptors. In this context, by considering the well-known involvement of the endocannabinoid system in prostate cancer, we have pharmacologically characterized the properties of DIM on both CB1 and CB2 cannabinoid receptors in two human prostate cancer cell lines: PC3 (androgen-independent/androgen receptor negative) and LNCaP (androgen-dependent). In the PC3 cell line, DIM was able to activate CB2 receptors and potentially associated apoptotic pathways. On the other hand, although DIM was also able to activate CB2 receptors in the LNCaP cell line, no apoptotic effects were observed. Our evidence confirms that DIM is a CB2 receptor ligand and, moreover, it has a potential anti-proliferative effect on androgen-independent/androgen receptor-negative prostate cancer cells.

Docking and Molecular Dynamic Investigations of Phenylspirodrimanes as Cannabinoid Receptor-2 Agonists.

Cannabinoid receptor ligands are renowned as being therapeutically crucial for treating diverse health disorders. Phenylspirodrimanes are meroterpenoids with unique and varied structural scaffolds, which are mainly reported from the Stachybotrys genus and display an array of bioactivities. In this work, 114 phenylspirodrimanes reported from Stachybotrys chartarum were screened for their CB2 agonistic potential using docking and molecular dynamic simulation studies. Compound 56 revealed the highest docking score (-11.222 kcal/mol) compared to E3R_6KPF (native agonist, gscore value -12.12 kcal/mol). The molecular docking and molecular simulation results suggest that compound 56 binds to the putative binding site in the CB2 receptor with good affinity involving key interacting amino acid residues similar to that of the native ligands, E3R. The molecular interactions displayed π-π stacking with Phe183 and hydrogen bond interactions with Thr114, Leu182, and Ser285. These findings identified the structural features of these metabolites that might lead to the design of selective novel ligands for CB2 receptors. Additionally, phenylspirodrimanes should be further investigated for their potential as a CB2 ligand.

Design, Synthesis, and Biological Activity of New CB2 Receptor Ligands: from Orthosteric and Allosteric Modulators to Dualsteric/Bitopic Ligands.

The design of dualsteric/bitopic agents as single chemical entities able to simultaneously interact with both the orthosteric and an allosteric binding site represents a novel approach in medicinal chemistry. Biased dualsteric/bitopic agents could enhance certain signaling pathways while diminishing the others that cause unwanted side effects. We have designed, synthesized, and functionally characterized the first CB2R heterobivalent bitopic ligands. In contrast to the parent orthosteric compound, our bitopic ligands selectively target CB2R versus CB1R and show a functional selectivity for the cAMP signaling pathway versus βarrestin2 recruitment. Moreover, the most promising bitopic ligand FD-22a displayed anti-inflammatory activity in a human microglial cell inflammatory model and antinociceptive activity in vivo in an experimental mouse model of neuropathic pain. Finally, computational studies clarified the binding mode of these compounds inside the CB2R, further confirming their bitopic nature.

The Influence of CB2-Receptor Ligands on the Memory-Related Responses in Connection with Cholinergic Pathways in Mice in the Passive Avoidance Test.

Background: Dysfunction of the cholinergic system is associated with the development of Alzheimer’s disease (AD). One of the new possible strategies for the pharmacological modulation of memory-related problems typical of AD, is connected with the endocannabinoid system (ECS) and the cannabinoid (CB: CB1 and CB2) receptors. Methods: The aim of the study was to determine the influence of the selective CB2 receptor ligands: agonist (JWH 133) and antagonist (AM 630) on different stages of memory and learning in mice, in the context of their interaction with cholinergic pathways. To assess and understand the memory-related effects in mice we used the passive avoidance (PA) test. Results: We revealed that co-administration of non-effective dose of JWH 133 (0.25 mg) or AM 630 (0.25 mg/kg) with the non-effective dose of cholinergic receptor agonist - nicotine (0.05 mg/kg) enhanced cognition in the PA test in mice; however, an acute injection of JWH 133 (0.25 mg/kg) or AM 630 (0.25 mg/kg) had no influence on memory enhancement induced by the effective dose of nicotine (0.1 mg/kg). Co-administration of JWH 133 (0.25 mg) or AM 630 (0.25 mg/kg) with the effective dose of the cholinergic receptor antagonist scopolamine (1 mg/kg) attenuated the scopolamine-induced memory impairment in the PA test in mice. Conclusion: Our experiments have shown that CB2 receptors participate in the modulation of memory-related responses, especially those in which cholinergic pathways are implicated.

1,2,3-Triazole derivatives as highly selective cannabinoid receptor type 2 (CB2) agonists

The cannabinoid receptor 2 (CB2 receptor) has attracted considerable interest, mainly due to its potential as a target for therapeutics for treating various diseases that have a neuroinflammatory or neurodegenerative component while avoiding the adverse psychotropic effects that accompany CB1 receptor-based therapies. With the appreciation that CB2-selective ligands show marked functional selectivity, there is a renewed opportunity to explore this promising area of research from both a mechanistic as well as a therapeutic perspective. In this research, we are interested in the discovery of new chemotypes as highly selective CB2 modulators, which may serve as good starting points for further optimization towards the development of CB2 therapeutics. In search of new chemotypes as CB2 selective agents, we screened a series of triazole derivatives with interesting bioactive scaffolds, which led to the discovery of two novel and highly selective ligands for CB2 receptors. Compounds 6 and 11 produced a concentration-dependent inhibition of specific [3H]-CP55,940 (CB2) binding with Ki ± SEM values of 105.3 ± 22.6 and 116.4 ± 19.5 nM, respectively, while no binding affinity towards CB1 receptors or opioid receptors was observed. The CB2 functional activity of 6 and 11, as measured by a GPCR Tango assay (G-protein independent β-arrestin translocation assay), revealed that these compounds act as CB2 agonists with EC50 values ± SEM of 1.83 ± 0.16 and 1.14 ± 0.52 µM, respectively. Molecular modeling results showed that both compounds fit well into the active site of the CB2 receptor and showed strong hydrophobic interactions with key residues. In conclusion, the new triazole derivatives (6 and 11) showed promising activity towards CB2 receptors and have great potential to be developed into therapeutically useful CB2 agonists through hit-to-lead optimization.

Molecular basis for ligand modulation of the cannabinoid CB1 receptor

The cannabinoid CB1 receptor is the most abundant G protein coupled receptor (GPCR) in the central nervous system, which mediates the functional response to endocannabinoids and Cannabis compounds. A variety of ligands for CB1 receptors have been developed as promising drug candidates for the treatment of neurological disorders. New high-resolution structures of CB1 receptor in different functional states have significantly improved our molecular understanding of CB1 ligand interactions, selectivity, receptor activation and allosteric modulation. These advances have paved the way for development of novel ligands for different therapeutic applications. In this review, we describe the structural determinants for modulation of CB1 receptors by different types of ligands, as well as the differences between CB1 and its homologous, the CB2 receptor. LINKED ARTICLES: This article is part of a themed issue on Structure Guided Pharmacology of Membrane Proteins (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.14/issuetoc.

Development of fluorinated and methoxylated benzothiazole derivatives as highly potent and selective cannabinoid CB2 receptor ligands

The upregulation of the CB2 receptors in neuroinflammation and cancer and their potential visualization with PET (positron emission tomography) could provide a valuable diagnostic and therapy-monitoring tool in such disorders. However, the availability of reliable CB2-selective imaging probes is still lacking in clinical practice. We have recently identified a benzothiazole-2-ylidine amide hit (6a) as a highly potent CB2 ligand. With the aim of enhancing its CB2 over CB1 selectivity and introducing structural sites suitable for radiolabeling, we herein describe the development of fluorinated and methoxylated benzothiazole derivatives endowed with extremely high CB2 binding affinity and an exclusive selectivity to the CB2 receptor. Compounds 14, 15, 18, 19, 21, 24 and 25 displayed subnanomolar CB2Ki values (ranging from 0.16 nM to 0.68 nM) and interestingly, all of the synthesized compounds completely lacked affinity at the CB1 receptor (Ki > 10,000 nM for all compounds), indicating their remarkably high CB2 over CB1 selectivity factors. The fluorinated analogs, 15 and 21, were evaluated for their in vitro metabolic stability in mouse and human liver microsomes (MLM and HLM). Both 15 and 21 displayed an exceptionally high stability (98% and 91% intact compounds, respectively) after 60 min incubation with MLM. Contrastingly, a 5- and 2.8-fold lower stability was demonstrated for compounds 15 and 21, respectively, upon incubation with HLM for 60 min. Taken together, our data present extremely potent and selective CB2 ligands as credible leads that can be further exploited for 18F- or 11C-radiolabeling and utilization as PET tracers.

Rhodium(I)‐Catalyzed Enantioselective C(sp3)—H Functionalization viaCarbene‐Induced Asymmetric Intermolecular C—H Insertion†

Main observation and conclusionTransition‐metal‐catalyzed C—H insertion of metal‐carbene represents an excellent and powerful approach for C—H functionalization. However, despite remarkable advances in metal‐carbene chemistry, transition metal catalysts that are capable of enantioselective intermolecular carbene C—H insertion are mainly constrained to dirhodium(II) and iridium(III)‐based complexes. Herein, we disclose a new version of asymmetric carbene C—H insertion reaction with rhodium(I) catalyst. A highly enantioselective rhodium(I) complex‐catalyzed C(sp3)—H functionalization of 1,4‐cyclohexadienes with α‐aryl‐α‐diazoacetates was successfully developed. By using chiral bicyclo[2.2.2]‐octadiene as ligand, rhodium(I)‐carbene‐induced asymmetric intermolecular C—H insertion proceeds smoothly at room temperature, allowing access to a diverse variety of α‐aryl‐α‐cyclohexadienyl acetates and gem‐diaryl‐containing acetates in good yields with good to excellent enantioselectivities (up to 99% ee). Furthermore, the synthetic utility of the reaction was highlighted by facile synthesis of a novel cannabinoid CB1 receptor ligand. This method may offer a new opportunity for the development of therapeutically exploitable cannabinoid receptor type ligands in medicinal chemistry.

The endocannabinoid system - current implications for drug development.

In this review, the state of the art for compounds affecting the endocannabinoid (eCB) system is described with a focus on the treatment of pain. Amongst directly acting CB receptor ligands, clinical experience with ∆9‐tetrahydracannabinol and medical cannabis in chronic non‐cancer pain indicates that there are differences between the benefits perceived by patients and the at best modest effect seen in meta‐analyses of randomized controlled trials. The reason for this difference is not known but may involve differences in the type of patients that are recruited, the study conditions that are chosen and the degree to which biases such as reporting bias are operative. Other directly acting CB receptor ligands such as biased agonists and allosteric receptor modulators have not yet reached the clinic. Amongst indirectly acting compounds targeting the enzymes responsible for the synthesis and catabolism of the eCBs anandamide and 2‐arachidonoylglycerol, fatty acid amide hydrolase (FAAH) inhibitors have been investigated clinically but were per se not useful for the treatment of pain, although they may be useful for the treatment of post‐traumatic stress disorder and cannabis use disorder. Dual‐acting compounds targeting this enzyme and other targets such as cyclooxygenase‐2 or transient potential vanilloid receptor 1 may be a way forward for the treatment of pain.

From a Designer Drug to the Discovery of Selective Cannabinoid Type 2 Receptor Agonists with Favorable Pharmacokinetic Profiles for the Treatment of Systemic Sclerosis.

Synthetic cannabinoids, as exemplified by SDB-001 (1), bind to both CB1 and CB2 receptors and exert cannabimimetic effects similar to (-)-trans-Δ9-tetrahydrocannabinol, the main psychoactive component present in the cannabis plant. As CB1 receptor ligands were found to have severe adverse psychiatric effects, increased attention was turned to exploiting the potential therapeutic value of the CB2 receptor. In our efforts to discover novel and selective CB2 receptor agonists, 1 was selected as a starting point for hit molecule identification and a class of 1H-pyrazole-3-carboxamide derivatives were thus designed, synthesized, and biologically evaluated. Systematic structure-activity relationship investigations resulted in the identification of the most promising compound 66 as a selective CB2 receptor agonist with favorable pharmacokinetic profiles. Especially, 66 treatment significantly attenuated dermal inflammation and fibrosis in a bleomycin-induced mouse model of systemic sclerosis, supporting that CB2 receptor agonists might serve as potential therapeutics for treating systemic sclerosis.

Influence of the endocannabinoid system on the antidepressant activity of bupropion and moclobemide in the behavioural tests in mice

BackgroundThough there are several classes of antidepressant drugs available on the pharmaceutical market, depression that affects globally over 320 million people is still undertreated. Scientists have made attempts to develop novel therapeutical strategies to maximize effectiveness of therapy and minimize undesired reactions. One of the ideas is use of either dual-action agents or combined administration of two substances that affect diverse neurotransmissions. Thus, we investigated whether the selected CB receptor ligands (oleamide, AM251, JWH133, and AM630) can have an impact on the activity of bupropion and moclobemide. Bupropion belongs to the dual acting drugs, whereas moclobemide is an inhibitor of monoamine oxidase.MethodsThe mice forced swim test and the tail suspension test were applied in order to determine the potential antidepressant-like activity, whereas the HPLC method was used in order to assess the brain concentrations of the tested antidepressants.ResultsAn intraperitoneal injection of sub-effective doses of oleamide (5 mg/kg), AM251 (0.25 mg/kg), and AM630 (0.25 mg/kg) increased activity of bupropion (10 mg/kg) in both behavioural tests. Effects of moclobemide (1.5 mg/kg) were potentiated only by AM251. These results were not influenced by the hypo- or hyperlocomotion of animals.ConclusionThe outcomes of the present study revealed that particularly activation or inhibition of the CB1 receptor function may augment the antidepressant activity of bupropion, whereas only inhibition of the CB1 receptor function manages to increase activity of moclobemide. Most probably, an interplay between CB receptor ligands and bupropion or moclobemide takes place at the cellular level.

PYRAZOLE BEARING MOLECULES AS BIOACTIVE SCAFFOLDS: A REVIEW

Pyrazole being a heterocyclic motif has secured an eccentric status in the field of medicinal chemistry. Pyrazole and its derivatives have tremendous biological applications like anti-cancer, anti-microbial, antiviral, antifungal, anti-inflammatory, analgesic, insecticidal etc. In this review, some recent developments have been reported for the synthesis of biologically active pyrazole based molecules having biological potential such as anti-SIRT1 and SIRT2, anti-FAAH, anti-NOSs, as liver X receptor partial agonist, CB2 receptor ligand and glucagon receptor antagonists.

Abstract P3-05-11: Cannabidiol increases potency of tamoxifen in inhibiting breast cancer cell viability

Abstract Background: Breast cancer (BC) is a very heterogeneous disease. Currently, decision-making regarding treatment of individual patients is based on several factors, most important of them are expression of estrogen receptors (ER), progesterone receptors and receptor for epidermal growth factor 2 (HER2). Common endocrine therapies include selective estrogen receptor modulator tamoxifen (TAM), aromatase inhibitors (AIs) and selective estrogen receptor degrader fulvestrant. Inhibitors of cyclin dependent kinases 4/6 (iCDK 4/6) in combination with AIs or fulvestrant, are recently being used in treatment of metastatic BC. Trastuzumab, an anti-HER2 monoclonal antibody, is a cornerstone treatment in HER2 positive disease. Next to other chemotherapeutic drugs, cisplatin is commonly used in triple-negative BC. Cannabinoids, a therapeutic option in the palliative treatment of cancer patients, have recently been demonstrated to induce anti-tumor response in certain cancer types, including BC. Reportedly, cannabinoids have been shown to exert antiproliferative and antimetastatic activities against BC cells. The effects of cannabinoids on signaling pathways in cancer cells are conferred via G-protein coupled cannabinoid receptors (CBRs) type 1 (CB1) and type 2 (CB2), other receptors (e.g. GPR55, TRPV2) or in a receptor-independent way. Cannabidiol (CBD) is a ligand of CB1 and CB2 receptors and is not psychoactive. Recent studies have shown that TAM acts as inverse agonist on CBRs but the significance of this interaction is unknown. Objectives: The aim of the study was to evaluate the effect of CBD on cell viability of selected BC cell lines of different subtypes (ER+, HER2+, triple-negative) alone and in combination with different BC therapies (TAM, fulvestrant, fulvestrant + iCDK 4/6, trastuzumab and cisplatin). Methods: The expression of CBRs in BC cell lines (MCF7, MDA-MB-231, MDA-MB-361, T-47D, SK-BR-3) was confirmed using western blot (WB). We used polyclonal antibodies against CB1 and CB2 receptors (ab23703 and ab45942, Abcam), and were among the first to test the monoclonal antibodies (sc-518035 and sc-293188, Santa Cruz Biotechnology) that exhibit lower levels of the requested specificity. All tested cell lines (T-47D, MDA-MB-231, SK-BR-3) were exposed to different concentrations of CBD. In addition, T47D cell line (ER+) was exposed to combination of CBD and endocrine therapy (TAM, fulvestrant), as well as combination of fulvestrant and palbociclib. Triple-negative MB-231 cell line was exposed to combination of CBD and cisplatin and SK-BR-3 cell line (HER2+) to CBD and trastuzumab. Results and Conclusions: CB1 and CB2 receptors are expressed in all tested BC cell lines. CBD decreased cell viability of all tested cell lines, however in MB-MDA-231 and SK-BR-3 cell lines only in above 25 µM concentrations. We are first to demonstrate that CBD increases the potency of TAM in inhibiting T-47D cell line viability. So far we could not confirm similar effect of CBD in combination with cisplatin, trastuzumab, fulvestrant alone or the combination of fulvestrant and iCDK 4/6. Citation Format: Luka Dobovišek, Metka Novak, Fran Krstanović, Polonca Ferk, Simona Borštnar, Tamara Lah Turnšek, Nataša Debeljak. Cannabidiol increases potency of tamoxifen in inhibiting breast cancer cell viability [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-05-11.

New synthesis of N1- and N2-substituted pyrazolo[4,3-b]pyridine-5-one derivatives as CB2 receptor ligands

This synthesis of pyrazolo[4,3-b]pyridine-5-one derivatives, recently described as potent and selective agonists/inverse agonists of the cannabinoid type-2 receptor (CB2R), allows for a wider exploration of the structure-activity relationship.

Influence of the CB1 and CB2 cannabinoid receptor ligands on the activity of atypical antidepressant drugs in the behavioural tests in mice

Available data support the notion that cannabinoids, whose therapeutic value is limited due to severe adverse reactions, could be beneficial as adjunctive agents in the management of mood disorders. Polytherapy, which is superior to monotherapy in the terms of effectiveness, usually requires lower doses of the individual components. Therefore, the main objective of our study was to determine whether administration of cannabinoid (CB) receptor ligands would enhance the antidepressant activity of atypical antidepressant drugs, i.e. agomelatine and tianeptine. To evaluate the antidepressant-like potential of the tested combinations, the mouse forced swim test (FST) and the tail suspension test (TST) were used. The HPLC method was applied to assess the brain levels of agomelatine and tianeptine. Both behavioural tests demonstrated that per se an ineffective intraperitoneal dose of oleamide (CB1 receptor agonist, 5 mg/kg) potentiated the anti-immobility activity of tianeptine (15 mg/kg), whereas AM251 (CB1 receptor inverse agonist/antagonist, 0.25 mg/kg) enhanced the antidepressant effects of tianeptine and agomelatine (20 mg/kg). Intraperitoneal co-administration of per se inactive doses of AM630 (CB2 receptor inverse agonist/antagonist) and agomelatine or tianeptine significantly reduced the immobility time of animals only in the FST. CB receptor ligands did not affect the brain levels of the tested atypical antidepressants. In summary, the outcomes of the present study showed that activation and inhibition of CB1 receptors as well as inhibition of CB2 receptors may increase the antidepressant activity of tianeptine, whereas only inhibition of CB1 and CB2 receptors has a potential to augment the antidepressant activity of agomelatine.

A multiple classifier system identifies novel cannabinoid CB2 receptor ligands

Drugs have become an essential part of our lives due to their ability to improve people’s health and quality of life. However, for many diseases, approved drugs are not yet available or existing drugs have undesirable side effects, making the pharmaceutical industry strive to discover new drugs and active compounds. The development of drugs is an expensive process, which typically starts with the detection of candidate molecules (screening) after a protein target has been identified. To this end, the use of high-performance screening techniques has become a critical issue in order to palliate the high costs. Therefore, the popularity of computer-based screening (often called virtual screening or in silico screening) has rapidly increased during the last decade. A wide variety of Machine Learning (ML) techniques has been used in conjunction with chemical structure and physicochemical properties for screening purposes including (i) simple classifiers, (ii) ensemble methods, and more recently (iii) Multiple Classifier Systems (MCS). Here, we apply an MCS for virtual screening (D2-MCS) using circular fingerprints. We applied our technique to a dataset of cannabinoid CB2 ligands obtained from the ChEMBL database. The HTS collection of Enamine (1,834,362 compounds), was virtually screened to identify 48,232 potential active molecules using D2-MCS. Identified molecules were ranked to select 21 promising novel compounds for in vitro evaluation. Experimental validation confirmed six highly active hits (> 50% displacement at 10 µM and subsequent Ki determination) and an additional five medium active hits (> 25% displacement at 10 µM). Hence, D2-MCS provided a hit rate of 29% for highly active compounds and an overall hit rate of 52%.

Ligands of the CB2 cannabinoid receptors augment activity of the conventional antidepressant drugs in the behavioural tests in mice

Although a lot of information can be found on the specific dual role of the endocannabinoid system in the emotional-related responses, little is known whether stimulation or inhibition of the cannabinoid (CB) receptors may affect the activity of the frequently prescribed antidepressant drugs. Our interests have been particularly focused on the potential influence of the CB2 receptors, as the ones whose central effects are relatively poorly documented when compared to the central effects of the CB1 receptors. Therefore, we evaluated the potential interaction between the CB2 receptor ligands (i.e., JWH133 – CB2 receptor agonist and AM630 – CB2 receptor inverse agonist) and several common antidepressant drugs that influence the monoaminergic system (i.e., imipramine, escitalopram, reboxetine). In order to assess the antidepressant-like effects we used two widely recognized behavioural tests, the mouse forced swim test (FST) and the tail suspension test (TST). Brain concentrations of the tested antidepressants were evaluated by the HPLC method. Intraperitoneal co-administration of per se ineffective doses of JWH133 (0.25 mg/kg) or AM630 (0.25 mg/kg) with imipramine (15 mg/kg), escitalopram (2 mg/kg), and reboxetine (2.5 mg/kg) significantly shortened the immobility time of mice in the FST and the TST, whereas it did not disturb their spontaneous locomotor activity. Furthermore, the brain levels of antidepressants were not changed. Summarizing, the results of the present study revealed that both activation and inhibition of the CB2 receptor function have a potential to strengthen the antidepressant activity of drugs targeting the monoaminergic system. Most probably, the described interaction has a pharmacodynamic background.

Influence of the CB1 cannabinoid receptors on the activity of the monoaminergic system in the behavioural tests in mice

Antidepressants that target the monoaminergic system are prescribed most frequently in the psychiatric practice. However, not all patients benefit from their use. It is generally known that co-administration of agents aiming distinct targets may increase the therapeutic effect and at the same time permit dose reduction. A number of studies have suggested a CB1 receptor-mediated interplay between the endocannabinoid system and the monoaminergic signalling in the brain. Therefore, we wanted to determine whether the CB1 receptor ligands (oleamide and AM251) affect the activity of the common antidepressant drugs that influence the monoaminergic system. In order to determine the antidepressant‐like activity, the forced swim test and the tail suspension test in mice were used. Additionally, brain concentrations of the tested antidepressants were evaluated by the HPLC method. Concurrent intraperitoneal administration of per se inactive doses of oleamide (5 mg/kg) or AM251 (0.25 mg/kg) and imipramine (15 mg/kg), escitalopram (2 mg/kg), and reboxetine (2.5 mg/kg) reduced the immobility time of animals in the forced swim test and the tail suspension test. The observed effect was not associated with hyperlocomotion of animals. Summarizing, the outcomes of the present study demonstrated that modulation (i.e., activation or inhibition) of the CB1 receptor function potentiates the antidepressant activity of common drugs that influence the monoaminergic (serotonergic and noradrenergic) system. This effect is most probably predominantly pharmacodynamic in nature instead of pharmacokinetic.