Molecular targets for cannabidiol and its synthetic analogues: effect on vanilloid VR1 receptors and on the cellular uptake and enzymatic hydrolysis of anandamide

1. (-)-Cannabidiol (CBD) is a non-psychotropic component of Cannabis with possible therapeutic use as an anti-inflammatory drug. Little is known on the possible molecular targets of this compound. We investigated whether CBD and some of its derivatives interact with vanilloid receptor type 1 (VR1), the receptor for capsaicin, or with proteins that inactivate the endogenous cannabinoid, anandamide (AEA). 2. CBD and its enantiomer, (+)-CBD, together with seven analogues, obtained by exchanging the C-7 methyl group of CBD with a hydroxy-methyl or a carboxyl function and/or the C-5' pentyl group with a di-methyl-heptyl (DMH) group, were tested on: (a) VR1-mediated increase in cytosolic Ca(2+) concentrations in cells over-expressing human VR1; (b) [(14)C]-AEA uptake by RBL-2H3 cells, which is facilitated by a selective membrane transporter; and (c) [(14)C]-AEA hydrolysis by rat brain membranes, which is catalysed by the fatty acid amide hydrolase. 3. Both CBD and (+)-CBD, but not the other analogues, stimulated VR1 with EC(50)=3.2 - 3.5 microM, and with a maximal effect similar in efficacy to that of capsaicin, i.e. 67 - 70% of the effect obtained with ionomycin (4 microM). CBD (10 microM) desensitized VR1 to the action of capsaicin. The effects of maximal doses of the two compounds were not additive. 4. (+)-5'-DMH-CBD and (+)-7-hydroxy-5'-DMH-CBD inhibited [(14)C]-AEA uptake (IC(50)=10.0 and 7.0 microM); the (-)-enantiomers were slightly less active (IC(50)=14.0 and 12.5 microM). 5. CBD and (+)-CBD were also active (IC(50)=22.0 and 17.0 microM). CBD (IC(50)=27.5 microM), (+)-CBD (IC(50)=63.5 microM) and (-)-7-hydroxy-CBD (IC(50)=34 microM), but not the other analogues (IC(50)>100 microM), weakly inhibited [(14)C]-AEA hydrolysis. 6. Only the (+)-isomers exhibited high affinity for CB(1) and/or CB(2) cannabinoid receptors. 7. These findings suggest that VR1 receptors, or increased levels of endogenous AEA, might mediate some of the pharmacological effects of CBD and its analogues. In view of the facile high yield synthesis, and the weak affinity for CB(1) and CB(2) receptors, (-)-5'-DMH-CBD represents a valuable candidate for further investigation as inhibitor of AEA uptake and a possible new therapeutic agent.

The endocannabinoid system and its therapeutic exploitation

The term 'endocannabinoid' - originally coined in the mid-1990s after the discovery of membrane receptors for the psychoactive principle in Cannabis, Delta9-tetrahydrocannabinol and their endogenous ligands - now indicates a whole signalling system that comprises cannabinoid receptors, endogenous ligands and enzymes for ligand biosynthesis and inactivation. This system seems to be involved in an ever-increasing number of pathological conditions. With novel products already being aimed at the pharmaceutical market little more than a decade since the discovery of cannabinoid receptors, the endocannabinoid system seems to hold even more promise for the future development of therapeutic drugs. We explore the conditions under which the potential of targeting the endocannabinoid system might be realized in the years to come.

An endogenous capsaicin-like substance with high potency at recombinant and native vanilloid VR1 receptors

The vanilloid receptor VR1 is a nonselective cation channel that is most abundant in peripheral sensory fibers but also is found in several brain nuclei. VR1 is gated by protons, heat, and the pungent ingredient of "hot" chili peppers, capsaicin. To date, no endogenous compound with potency at this receptor comparable to that of capsaicin has been identified. Here we examined the hypothesis, based on previous structure-activity relationship studies and the availability of biosynthetic precursors, that N-arachidonoyl-dopamine (NADA) is an endogenous "capsaicin-like" substance in mammalian nervous tissues. We found that NADA occurs in nervous tissues, with the highest concentrations being found in the striatum, hippocampus, and cerebellum and the lowest concentrations in the dorsal root ganglion. We also gained evidence for the existence of two possible routes for NADA biosynthesis and mechanisms for its inactivation in rat brain. NADA activates both human and rat VR1 overexpressed in human embryonic kidney (HEK)293 cells, with potency (EC(50) approximately 50 nM) and efficacy similar to those of capsaicin. Furthermore, NADA potently activates native vanilloid receptors in neurons from rat dorsal root ganglion and hippocampus, thereby inducing the release of substance P and calcitonin gene-related peptide (CGRP) from dorsal spinal cord slices and enhancing hippocampal paired-pulse depression, respectively. Intradermal NADA also induces VR1-mediated thermal hyperalgesia (EC(50) = 1.5 +/- 0.3 microg). Our data demonstrate the existence of a brain substance similar to capsaicin not only with respect to its chemical structure but also to its potency at VR1 receptors.

Effects of cannabinoids and cannabinoid-enriched Cannabis extracts on TRP channels and endocannabinoid metabolic enzymes

BACKGROUND AND PURPOSE

Cannabidiol (CBD) and Δ(9) -tetrahydrocannabinol (THC) interact with transient receptor potential (TRP) channels and enzymes of the endocannabinoid system.

EXPERIMENTAL APPROACH

The effects of 11 pure cannabinoids and botanical extracts [botanical drug substance (BDS)] from Cannabis varieties selected to contain a more abundant cannabinoid, on TRPV1, TRPV2, TRPM8, TRPA1, human recombinant diacylglycerol lipase α (DAGLα), rat brain fatty acid amide hydrolase (FAAH), COS cell monoacylglycerol lipase (MAGL), human recombinant N-acylethanolamine acid amide hydrolase (NAAA) and anandamide cellular uptake (ACU) by RBL-2H3 cells, were studied using fluorescence-based calcium assays in transfected cells and radiolabelled substrate-based enzymatic assays. Cannabinol (CBN), cannabichromene (CBC), the acids (CBDA, CBGA, THCA) and propyl homologues (CBDV, CBGV, THCV) of CBD, cannabigerol (CBG) and THC, and tetrahydrocannabivarin acid (THCVA) were also tested.

KEY RESULTS

CBD, CBG, CBGV and THCV stimulated and desensitized human TRPV1. CBC, CBD and CBN were potent rat TRPA1 agonists and desensitizers, but THCV-BDS was the most potent compound at this target. CBG-BDS and THCV-BDS were the most potent rat TRPM8 antagonists. All non-acid cannabinoids, except CBC and CBN, potently activated and desensitized rat TRPV2. CBDV and all the acids inhibited DAGLα. Some BDS, but not the pure compounds, inhibited MAGL. CBD was the only compound to inhibit FAAH, whereas the BDS of CBC > CBG > CBGV inhibited NAAA. CBC = CBG > CBD inhibited ACU, as did the BDS of THCVA, CBGV, CBDA and THCA, but the latter extracts were more potent inhibitors.

CONCLUSIONS AND IMPLICATIONS

These results are relevant to the analgesic, anti-inflammatory and anti-cancer effects of cannabinoids and Cannabis extracts.

Regulation, function, and dysregulation of endocannabinoids in models of adipose and beta-pancreatic cells and in obesity and hyperglycemia

CONTEXT

Cannabinoid CB(1) receptor blockade decreases weight and hyperinsulinemia in obese animals and humans in a way greatly independent from food intake.

OBJECTIVE

The objective of this study was to investigate the regulation and function of the endocannabinoid system in adipocytes and pancreatic beta-cells.

DESIGN, SETTING, AND PATIENTS

Mouse 3T3-F442A adipocytes and rat insulinoma RIN-m5F beta-cells, pancreas and fat from mice with diet-induced obesity, visceral and sc fat from patients with body mass index equal to or greater than 30 kg/m(2), and serum from normoglycemic and type 2 diabetes patients were studied.

MAIN OUTCOME MEASURE

Endocannabinoid enzyme and adipocyte protein expression, and endocannabinoid and insulin levels were measured.

RESULTS

Endocannabinoids are present in adipocytes with levels peaking before differentiation, and in RIN-m5F beta-cells, where they are under the negative control of insulin. Chronic treatment of adipocytes with insulin is accompanied by permanently elevated endocannabinoid signaling, whereas culturing of RIN-m5F beta-cells in high glucose transforms insulin down-regulation of endocannabinoid levels into up-regulation. Epididymal fat and pancreas from mice with diet-induced obesity contain higher endocannabinoid levels than lean mice. Patients with obesity or hyperglycemia caused by type 2 diabetes exhibit higher concentrations of endocannabinoids in visceral fat or serum, respectively, than the corresponding controls. CB(1) receptor stimulation increases lipid droplets and decreases adiponectin expression in adipocytes, and it increases intracellular calcium and insulin release in RIN-m5F beta-cells kept in high glucose.

CONCLUSIONS

Peripheral endocannabinoid overactivity might explain why CB(1) blockers cause weight-loss independent reduction of lipogenesis, of hypoadiponectinemia, and of hyperinsulinemia in obese animals and humans.

Antitumor activity of plant cannabinoids with emphasis on the effect of cannabidiol on human breast carcinoma

Delta(9)-Tetrahydrocannabinol (THC) exhibits antitumor effects on various cancer cell types, but its use in chemotherapy is limited by its psychotropic activity. We investigated the antitumor activities of other plant cannabinoids, i.e., cannabidiol, cannabigerol, cannabichromene, cannabidiol acid and THC acid, and assessed whether there is any advantage in using Cannabis extracts (enriched in either cannabidiol or THC) over pure cannabinoids. Results obtained in a panel of tumor cell lines clearly indicate that, of the five natural compounds tested, cannabidiol is the most potent inhibitor of cancer cell growth (IC(50) between 6.0 and 10.6 microM), with significantly lower potency in noncancer cells. The cannabidiol-rich extract was equipotent to cannabidiol, whereas cannabigerol and cannabichromene followed in the rank of potency. Both cannabidiol and the cannabidiol-rich extract inhibited the growth of xenograft tumors obtained by s.c. injection into athymic mice of human MDA-MB-231 breast carcinoma or rat v-K-ras-transformed thyroid epithelial cells and reduced lung metastases deriving from intrapaw injection of MDA-MB-231 cells. Judging from several experiments on its possible cellular and molecular mechanisms of action, we propose that cannabidiol lacks a unique mode of action in the cell lines investigated. At least for MDA-MB-231 cells, however, our experiments indicate that cannabidiol effect is due to its capability of inducing apoptosis via: direct or indirect activation of cannabinoid CB(2) and vanilloid transient receptor potential vanilloid type-1 receptors and cannabinoid/vanilloid receptor-independent elevation of intracellular Ca(2+) and reactive oxygen species. Our data support the further testing of cannabidiol and cannabidiol-rich extracts for the potential treatment of cancer.

The endocannabinoid system: a general view and latest additions

After the discovery, in the early 1990s, of specific G-protein-coupled receptors for marijuana's psychoactive principle Delta(9)-tetrahydrocannabinol, the cannabinoid receptors, and of their endogenous agonists, the endocannabinoids, a decade of investigations has greatly enlarged our understanding of this altogether new signalling system. Yet, while the finding of the endocannabinoids resulted in a new effort to reveal the mechanisms regulating their levels in the brain and peripheral organs under physiological and pathological conditions, more endogenous substances with a similar action, and more molecular targets for the previously discovered endogenous ligands, anandamide and 2-arachidonoylglycerol, or for some of their metabolites, were being proposed. As the scenario becomes subsequently more complicated, and the experimental tasks to be accomplished correspondingly more numerous, we briefly review in this article the latest 'additions' to the endocannabinoid system together with earlier breakthroughs that have contributed to our present knowledge of the biochemistry and pharmacology of the endocannabinoids.

N-oleoyldopamine, a novel endogenous capsaicin-like lipid that produces hyperalgesia

N-Arachidonoyldopamine (NADA) was recently identified as an endogenous ligand for the vanilloid type 1 receptor (VR1). Further analysis of the bovine striatal extract from which NADA was isolated indicated the existence of substances corresponding in molecular mass to N-oleoyldopamine (OLDA), N-palmitoyldopamine (PALDA), and N-stearoyldopamine (STEARDA). Quadrupole time-of-flight mass spectrometric analysis of bovine striatal extracts revealed the existence of OLDA, PALDA, and STEARDA as endogenous compounds in the mammalian brain. PALDA and STEARDA failed to affect calcium influx in VR1-transfected human embryonic kidney (HEK) 293 cells or paw withdrawal latencies from a radiant heat source, and there was no evidence of spontaneous pain behavior. By contrast, OLDA induced calcium influx (EC(50) = 36 nm), reduced the latency of paw withdrawal from a radiant heat source in a dose-dependent manner (EC(50) = 0.72 microg), and produced nocifensive behavior. These effects were blocked by co-administration of the VR1 antagonist iodo-resiniferatoxin (10 nm for HEK cells and 1 microg/50 micro;l for pain behavior). These findings demonstrate the existence of an endogenous compound in the brain that is similar to capsaicin and NADA in its chemical structure and activity on VR1. Unlike NADA, OLDA was only a weak ligand for rat CB1 receptors; but like NADA, it was recognized by the anandamide membrane transporter while being a poor substrate for fatty-acid amide hydrolase. Analysis of the activity of six additional synthetic and potentially endogenous N-acyldopamine indicated the requirement of a long unsaturated fatty acid chain for an optimal functional interaction with VR1 receptors.

From Phytocannabinoids to Cannabinoid Receptors and Endocannabinoids: Pleiotropic Physiological and Pathological Roles Through Complex Pharmacology

Apart from having been used and misused for at least four millennia for, among others, recreational and medicinal purposes, the cannabis plant and its most peculiar chemical components, the plant cannabinoids (phytocannabinoids), have the merit to have led humanity to discover one of the most intriguing and pleiotropic endogenous signaling systems, the endocannabinoid system (ECS). This review article aims to describe and critically discuss, in the most comprehensive possible manner, the multifaceted aspects of 1) the pharmacology and potential impact on mammalian physiology of all major phytocannabinoids, and not only of the most famous one Δ9-tetrahydrocannabinol, and 2) the adaptive pro-homeostatic physiological, or maladaptive pathological, roles of the ECS in mammalian cells, tissues, and organs. In doing so, we have respected the chronological order of the milestones of the millennial route from medicinal/recreational cannabis to the ECS and beyond, as it is now clear that some of the early steps in this long path, which were originally neglected, are becoming important again. The emerging picture is rather complex, but still supports the belief that more important discoveries on human physiology, and new therapies, might come in the future from new knowledge in this field.

Plant-derived cannabinoids modulate the activity of transient receptor potential channels of ankyrin type-1 and melastatin type-8

The plant cannabinoids (phytocannabinoids), cannabidiol (CBD), and Delta(9)-tetrahydrocannabinol (THC) were previously shown to activate transient receptor potential channels of both vanilloid type 1 (TRPV1) and ankyrin type 1 (TRPA1), respectively. Furthermore, the endocannabinoid anandamide is known to activate TRPV1 and was recently found to antagonize the menthol- and icilin-sensitive transient receptor potential channels of melastatin type 8 (TRPM8). In this study, we investigated the effects of six phytocannabinoids [i.e., CBD, THC, CBD acid, THC acid, cannabichromene (CBC), and cannabigerol (CBG)] on TRPA1- and TRPM8-mediated increase in intracellular Ca2+ in either HEK-293 cells overexpressing the two channels or rat dorsal root ganglia (DRG) sensory neurons. All of the compounds tested induced TRPA1-mediated Ca2+ elevation in HEK-293 cells with efficacy comparable with that of mustard oil isothiocyanates (MO), the most potent being CBC (EC(50) = 60 nM) and the least potent being CBG and CBD acid (EC(50) = 3.4-12.0 microM). CBC also activated MO-sensitive DRG neurons, although with lower potency (EC(50) = 34.3 microM). Furthermore, although none of the compounds tested activated TRPM8-mediated Ca2+ elevation in HEK-293 cells, they all, with the exception of CBC, antagonized this response when it was induced by either menthol or icilin. CBD, CBG, THC, and THC acid were equipotent (IC(50) = 70-160 nM), whereas CBD acid was the least potent compound (IC(50) = 0.9-1.6 microM). CBG inhibited Ca2+ elevation also in icilin-sensitive DRG neurons with potency (IC(50) = 4.5 microM) similar to that of anandamide (IC(50) = 10 microM). Our findings suggest that phytocannabinoids and cannabis extracts exert some of their pharmacological actions also by interacting with TRPA1 and TRPM8 channels, with potential implications for the treatment of pain and cancer.

Activity-based protein profiling reveals off-target proteins of the FAAH inhibitor BIA 10-2474

A recent phase 1 trial of the fatty acid amide hydrolase (FAAH) inhibitor BIA 10-2474 led to the death of one volunteer and produced mild-to-severe neurological symptoms in four others. Although the cause of the clinical neurotoxicity is unknown, it has been postulated, given the clinical safety profile of other tested FAAH inhibitors, that off-target activities of BIA 10-2474 may have played a role. Here we use activity-based proteomic methods to determine the protein interaction landscape of BIA 10-2474 in human cells and tissues. This analysis revealed that the drug inhibits several lipases that are not targeted by PF04457845, a highly selective and clinically tested FAAH inhibitor. BIA 10-2474, but not PF04457845, produced substantial alterations in lipid networks in human cortical neurons, suggesting that promiscuous lipase inhibitors have the potential to cause metabolic dysregulation in the nervous system.

Why do cannabinoid receptors have more than one endogenous ligand?

The endocannabinoid system was revealed following the understanding of the mechanism of action of marijuana's major psychotropic principle, Δ(9)-tetrahydrocannabinol, and includes two G-protein-coupled receptors (GPCRs; the cannabinoid CB1 and CB2 receptors), their endogenous ligands (the endocannabinoids, the best studied of which are anandamide and 2-arachidonoylglycerol (2-AG)), and the proteins that regulate the levels and activity of these receptors and ligands. However, other minor lipid metabolites different from, but chemically similar to, anandamide and 2-AG have also been suggested to act as endocannabinoids. Thus, unlike most other GPCRs, cannabinoid receptors appear to have more than one endogenous agonist, and it has been often wondered what could be the physiological meaning of this peculiarity. In 1999, it was proposed that anandamide might also activate other targets, and in particular the transient receptor potential of vanilloid type-1 (TRPV1) channels. Over the last decade, this interaction has been shown to occur both in peripheral tissues and brain, during both physiological and pathological conditions. TRPV1 channels can be activated also by another less abundant endocannabinoid, N-arachidonoyldopamine, but not by 2-AG, and have been proposed by some authors to act as ionotropic endocannabinoid receptors. This article will discuss the latest discoveries on this subject, and discuss, among others, how anandamide and 2-AG differential actions at TRPV1 and cannabinoid receptors contribute to making this signalling system a versatile tool available to organisms to fine-tune homeostasis.

Possible endocannabinoid control of colorectal cancer growth

BACKGROUND & AIMS

The endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) inhibit cancer cell proliferation by acting at cannabinoid receptors (CBRs). We studied (1). the levels of endocannabinoids, cannabinoid CB(1) and CB(2) receptors, and fatty acid amide hydrolase (FAAH, which catalyzes endocannabinoid hydrolysis) in colorectal carcinomas (CRC), adenomatous polyps, and neighboring healthy mucosa; and (2). the effects of endocannabinoids, and of inhibitors of their inactivation, on human CRC cell proliferation.

METHODS

Tissues were obtained from 21 patients by biopsy during colonoscopy. Endocannabinoids were measured by liquid chromatography-mass spectrometry (LC-MS). CB(1), CB(2), and FAAH expression were analyzed by RT-PCR and Western immunoblotting. CRC cell lines (CaCo-2 and DLD-1) were used to test antiproliferative effects.

RESULTS

All tissues and cells analyzed contain anandamide, 2-AG, CBRs, and FAAH. The levels of the endocannabinoids are 3- and 2-fold higher in adenomas and CRCs than normal mucosa. Anandamide, 2-AG, and the CBR agonist HU-210 potently inhibit CaCo-2 cell proliferation. This effect is blocked by the CB(1) antagonist SR141716A, but not by the CB(2) antagonist SR144528, and is mimicked by CB(1)-selective, but not CB(2)-selective, agonists. In DLD-1 cells, both CB(1) and CB(2) receptors mediate inhibition of proliferation. Inhibitors of endocannabinoid inactivation enhance CaCo-2 cell endocannabinoid levels and block cell proliferation, this effect being antagonized by SR141716A. CaCo-2 cell differentiation into noninvasive cells results in increased FAAH expression, lower endocannabinoid levels, and no responsiveness to cannabinoids.

CONCLUSIONS

Endocannabinoid levels are enhanced in transformed colon mucosa cells possibly to counteract proliferation via CBRs. Inhibitors of endocannabinoid inactivation may prove useful anticancer agents.

Endocannabinoid signalling in the blood of patients with schizophrenia

AIM

To test the hypothesis that schizophrenia might be associated with alterations of the endogenous cannabinoid system in human blood.

RESULTS

Blood from 20 healthy volunteers and 12 patients with schizophrenia, 5 of which both before and after a successful antipsychotic treatment, was analysed for: 1) the amounts of the endocannabinoid anandamide; 2) the levels of cannabinoid CB1 and CB2 receptor mRNAs, and 3) the levels of the mRNA encoding the enzyme fatty acid amide hydrolase (FAAH), responsible for anandamide degradation. The amounts of anandamide were significantly higher in the blood of patients with acute schizophrenia than in healthy volunteers (7.79 +/- 0.50 vs. 2.58 +/- 0.28 pmol/ml). Clinical remission was accompanied by a significant decrease of the levels of anandamide (3.88 +/- 0.72 pmol/ml) and of the mRNA transcripts for CB2 receptors and FAAH.

CONCLUSION

These findings indicate that endocannabinoid signalling might be altered during the acute phase of schizophrenia not only in the central nervous system but also in the blood. These changes might be related to the several immunological alterations described in schizophrenia.

Anandamide acts as an intracellular messenger amplifying Ca2+ influx via TRPV1 channels

The endocannabinoid anandamide is able to interact with the transient receptor potential vanilloid 1 (TRPV1) channels at a molecular level. As yet, endogenously produced anandamide has not been shown to activate TRPV1, but this is of importance to understand the physiological function of this interaction. Here, we show that intracellular Ca2+ mobilization via the purinergic receptor agonist ATP, the muscarinic receptor agonist carbachol or the Ca(2+)-ATPase inhibitor thapsigargin leads to formation of anandamide, and subsequent TRPV1-dependent Ca2+ influx in transfected cells and sensory neurons of rat dorsal root ganglia (DRG). Anandamide metabolism and efflux from the cell tonically limit TRPV1-mediated Ca2+ entry. In DRG neurons, this mechanism was found to lead to TRPV1-mediated currents that were enhanced by selective blockade of anandamide cellular efflux. Thus, endogenous anandamide is formed on stimulation of metabotropic receptors coupled to the phospholipase C/inositol 1,4,5-triphosphate pathway and then signals to TRPV1 channels. This novel intracellular function of anandamide may precede its action at cannabinoid receptors, and might be relevant to its control over neurotransmitter release.

Blood levels of the endocannabinoid anandamide are increased in anorexia nervosa and in binge-eating disorder, but not in bulimia nervosa

The endocannabinoid system, consisting of two cannabinoid receptors (CB1 and CB2) and the endogenous ligands anandamide (arachidonoylethanolamide (AEA)) and 2-arachidonoylglycerol (2-AG), has been shown to control food intake in both animals and humans, modulating either rewarding or quantitative aspects of the eating behavior. Moreover, hypothalamic endocannabinoids seem to be part of neural circuitry involved in the modulating effects of leptin on energy homeostasis. Therefore, alterations of the endocannabinoid system could be involved in the pathophysiology of eating disorders, where a deranged leptin signalling has been also reported. In order to verify this hypothesis, we measured plasma levels of AEA, 2-AG, and leptin in 15 women with anorexia nervosa (AN), 12 women with bulimia nervosa (BN), 11 women with binge-eating disorder (BED), and 15 healthy women. Plasma levels of AEA resulted significantly enhanced in both anorexic and BED women, but not in bulimic patients. No significant change occurred in the plasma levels of 2-AG in all the patients' groups. Moreover, circulating AEA levels were significantly and inversely correlated with plasma leptin concentrations in both healthy controls and anorexic women. These findings show for the first time a derangement in the production of the endogenous cannabinoid AEA in drug-free symptomatic women with AN or with BED. Although the pathophysiological significance of this alteration awaits further studies to be clarified, it suggests a possible involvement of AEA in the mediation of the rewarding aspects of the aberrant eating behaviors occurring in AN and BED.

An introduction to the endocannabinoid system: from the early to the latest concepts

A rather complex and pleiotropic endogenous signalling system was discovered in the late 1990s, starting from studies on the mechanism of action of Delta(9)-tetrahydrocannabinol, the major psychoactive principle of the hemp plant Cannabis sativa. This system includes: (1) at least two G-protein-coupled receptors, known as the cannabinoid CB(1) and CB(2) receptors; (2) the endogenous agonists at these receptors, known as endocannabinoids, of which anandamide and 2-arachidonoylglycerol are the best known; and (3) proteins and enzymes for the regulation of endocannabinoid levels and action at receptors. The number of the members of this endocannabinoid signalling system seems to be ever increasing as new non-CB(1) non-CB(2) receptors for endocannabinoids, endocannabinoid-related molecules with little activity at CB(1) and CB(2) receptors, and new enzymes for endocannabinoid biosynthesis and degradation are being identified every year. The complexity of the endocannabinoid system and of its physiological and pathological function is outlined in this introductory chapter, for a better understanding of the subsequent chapters in this special issue.

Non-THC cannabinoids inhibit prostate carcinoma growth in vitro and in vivo: pro-apoptotic effects and underlying mechanisms

BACKGROUND AND PURPOSE

Cannabinoid receptor activation induces prostate carcinoma cell (PCC) apoptosis, but cannabinoids other than Δ(9) -tetrahydrocannabinol (THC), which lack potency at cannabinoid receptors, have not been investigated. Some of these compounds antagonize transient receptor potential melastatin type-8 (TRPM8) channels, the expression of which is necessary for androgen receptor (AR)-dependent PCC survival.

EXPERIMENTAL APPROACH

We tested pure cannabinoids and extracts from Cannabis strains enriched in particular cannabinoids (BDS), on AR-positive (LNCaP and 22RV1) and -negative (DU-145 and PC-3) cells, by evaluating cell viability (MTT test), cell cycle arrest and apoptosis induction, by FACS scans, caspase 3/7 assays, DNA fragmentation and TUNEL, and size of xenograft tumours induced by LNCaP and DU-145 cells.

KEY RESULTS

Cannabidiol (CBD) significantly inhibited cell viability. Other compounds became effective in cells deprived of serum for 24 h. Several BDS were more potent than the pure compounds in the presence of serum. CBD-BDS (i.p.) potentiated the effects of bicalutamide and docetaxel against LNCaP and DU-145 xenograft tumours and, given alone, reduced LNCaP xenograft size. CBD (1-10 µM) induced apoptosis and induced markers of intrinsic apoptotic pathways (PUMA and CHOP expression and intracellular Ca(2+)). In LNCaP cells, the pro-apoptotic effect of CBD was only partly due to TRPM8 antagonism and was accompanied by down-regulation of AR, p53 activation and elevation of reactive oxygen species. LNCaP cells differentiated to androgen-insensitive neuroendocrine-like cells were more sensitive to CBD-induced apoptosis.

CONCLUSIONS AND IMPLICATIONS

These data support the clinical testing of CBD against prostate carcinoma.

Colon carcinogenesis is inhibited by the TRPM8 antagonist cannabigerol, a Cannabis-derived non-psychotropic cannabinoid

Cannabigerol (CBG) is a safe non-psychotropic Cannabis-derived cannabinoid (CB), which interacts with specific targets involved in carcinogenesis. Specifically, CBG potently blocks transient receptor potential (TRP) M8 (TRPM8), activates TRPA1, TRPV1 and TRPV2 channels, blocks 5-hydroxytryptamine receptor 1A (5-HT1A) receptors and inhibits the reuptake of endocannabinoids. Here, we investigated whether CBG protects against colon tumourigenesis. Cell growth was evaluated in colorectal cancer (CRC) cells using the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide and 3-amino-7-dimethylamino-2-methylphenazine hydrochloride assays; apoptosis was examined by histology and by assessing caspase 3/7 activity; reactive oxygen species (ROS) production by a fluorescent probe; CB receptors, TRP and CCAAT/enhancer-binding protein homologous protein (CHOP) messenger RNA (mRNA) expression were quantified by reverse transcription-polymerase chain reaction; small hairpin RNA-vector silencing of TRPM8 was performed by electroporation. The in vivo antineoplastic effect of CBG was assessed using mouse models of colon cancer. CRC cells expressed TRPM8, CB1, CB2, 5-HT1A receptors, TRPA1, TRPV1 and TRPV2 mRNA. CBG promoted apoptosis, stimulated ROS production, upregulated CHOP mRNA and reduced cell growth in CRC cells. CBG effect on cell growth was independent from TRPA1, TRPV1 and TRPV2 channels activation, was further increased by a CB2 receptor antagonist, and mimicked by other TRPM8 channel blockers but not by a 5-HT1A antagonist. Furthermore, the effect of CBG on cell growth and on CHOP mRNA expression was reduced in TRPM8 silenced cells. In vivo, CBG inhibited the growth of xenograft tumours as well as chemically induced colon carcinogenesis. CBG hampers colon cancer progression in vivo and selectively inhibits the growth of CRC cells, an effect shared by other TRPM8 antagonists. CBG should be considered translationally in CRC prevention and cure.

Inhibitory effects of cannabinoid CB1 receptor stimulation on tumor growth and metastatic spreading: actions on signals involved in angiogenesis and metastasis

Stimulation of cannabinoid CB1 receptors by 2-methyl-arachidonyl-2'-fluoro-ethylamide (Met-F-AEA) inhibits the growth of a rat thyroid cancer cell-derived tumor in athymic mice by inhibiting the activity of the oncogene product p21ras. Here we report that Met-F-AEA also blocks the growth of tumors previously induced in nude mice by the s.c. injection of the same rat thyroid carcinoma cells. Met-F-AEA significantly inhibited, in tumors as well as transformed cells, the expression of the vascular endothelial growth factor, an angiogenetic factor known to be up-regulated by p21ras, as well as of one of its receptors, flt-1/VEGFR-1. The levels of the cyclin-dependent kinase inhibitor p27(kip1), which is down-regulated by p21ras, were instead increased by Met-F-AEA. All these effects were antagonized by the selective CB1 receptor antagonist SR141716A. Met-F-AEA inhibited in vitro the growth of a metastasis-derived thyroid cancer cell line more potently than a primary cancer cell line. Therefore, the hypothesis that CB1 receptor stimulation interferes not only with angiogenesis but also with metastatic processes was tested in a widely used model of metastatic infiltration in vivo, the Lewis lung carcinoma (3LL) in C57Bl/6 mice. Three weeks from the paw injection of 3LL cells, Met-F-AEA reduced significantly the number of metastatic nodes, in a way antagonized by SR141716A. Our findings indicate that CB1 receptor agonists might be used therapeutically to retard tumor growth in vivo by inhibiting at once tumor growth, angiogenesis, and metastasis.

Plant, Synthetic, and Endogenous Cannabinoids in Medicine

Although used for more than 4000 years for recreational and medicinal purposes, Cannabis and its best-known pharmacologically active constituents, the cannabinoids, became a protagonist in medical research only recently. This revival of interest is explained by the finding in the 1990s of the mechanism of action of the main psychotropic cannabinoid, Delta9-tetrahydrocannabinol (THC), which acts through specific membrane receptors, the cannabinoid receptors. The molecular characterization of these receptors allowed the development of synthetic molecules with cannabinoid and noncannabinoid structure and with higher selectivity, metabolic stability, and efficacy than THC, as well as the development of antagonists that have already found pharmaceutical application. The finding of endogenous agonists at these receptors, the endocannabinoids, opened new therapeutic possibilities through the modulation of the activity of cannabinoid receptors by targeting the biochemical mechanisms controlling endocannabinoid tissue levels.

Non-psychoactive cannabinoids modulate the descending pathway of antinociception in anaesthetized rats through several mechanisms of action

BACKGROUND AND PURPOSE

Two non-psychoactive cannabinoids, cannabidiol (CBD) and cannabichromene (CBC), are known to modulate in vitro the activity of proteins involved in nociceptive mechanisms, including transient receptor potential (TRP) channels of vanilloid type-1 (TRPV1) and of ankyrin type-1 (TRPA1), the equilibrative nucleoside transporter and proteins facilitating endocannabinoid inactivation. Here we have tested these two cannabinoids on the activity of the descending pathway of antinociception.

EXPERIMENTAL APPROACH

Electrical activity of ON and OFF neurons of the rostral ventromedial medulla in anaesthetized rats was recorded extracellularly and tail flick latencies to thermal stimuli were measured. CBD or CBC along with various antagonists were injected into the ventrolateral periaqueductal grey.

KEY RESULTS

Cannabidiol and CBC dose-dependently reduced the ongoing activity of ON and OFF neurons in anaesthetized rats, whilst inducing antinociceptive responses in the tail flick-test. These effects were maximal with 3 nmol CBD and 6 nmol CBC, and were antagonized by selective antagonists of cannabinoid CB(1) adenosine A(1) and TRPA1, but not of TRPV1, receptors. Both CBC and CBD also significantly elevated endocannabinoid levels in the ventrolateral periaqueductal grey. A specific agonist at TRPA1 channels and a synthetic inhibitor of endocannabinoid cellular reuptake exerted effects similar to those of CBC and CBD.

CONCLUSIONS AND IMPLICATIONS

CBD and CBC stimulated descending pathways of antinociception and caused analgesia by interacting with several target proteins involved in nociceptive control. These compounds might represent useful therapeutic agents with multiple mechanisms of action.

Novel selective and metabolically stable inhibitors of anandamide cellular uptake

Novel aromatic analogues of N-oleoylethanolamine and N-arachidonoylethanolamine (anandamide, AEA) were synthesized and, based on the capability of similar compounds to interact with proteins of the endocannabinoid and endovanilloid signaling systems, were tested on: (i) cannabinoid CB(1) and CB(2) receptors; (ii) vanilloid VR1 receptors; (iii) anandamide cellular uptake (ACU); and (iv) the fatty acid amide hydrolase (FAAH). The (R)- and, particularly, the (S)-1'-(4-hydroxybenzyl) derivatives of N-oleoylethanolamine and AEA (OMDM-1, OMDM-2, OMDM-3, and OMDM-4) inhibited to a varied extent ACU in RBL-2H3 cells (K(i) ranging between 2.4 and 17.7 micro M), the oleoyl analogues (OMDM-1 and OMDM-2, K(i) 2.4 and 3.0 micro M, respectively) being 6- to 7-fold more potent than the arachidonoyl analogues (OMDM-3 and OMDM-4). These four compounds exhibited: (i) poor affinity for either CB(1) (K(i)> or = 5 micro M) or CB(2) (K(i)>10 micro M) receptors in rat brain and spleen membranes, respectively; (ii) almost no activity at vanilloid receptors in the intracellular calcium assay carried out with intact cells over-expressing the human VR1 (EC(50)> or = 10 micro M); and (iii) no activity as inhibitors of FAAH in N18TG2 cell membranes (K(i)>50 micro M). The oleoyl- and arachidonoyl-N'-(4-hydroxy-3-methoxybenzyl)hydrazines (OMDM-5 and OMDM-6), inhibited ACU (K(i) 4.8 and 7.0 micro M, respectively), and were more potent as VR1 agonists (EC(50) 75 and 50nM, respectively), weakly active as CB(1) receptor ligands (K(i) 4.9 and 3.2 micro M, respectively), and inactive as CB(2) ligands (K(i)>5 micro M) as well as on FAAH (K(i)> or = 40 micro M). In conclusion, we report two novel potent and selective inhibitors of ACU (OMDM-1 and OMDM-2) and one "hybrid" agonist of CB(1) and VR1 receptors (OMDM-6). Unlike other compounds of the same type, OMDM-1, OMDM-2, and OMDM-6 were very stable to enzymatic hydrolysis by rat brain homogenates.