Cannabinoid CB1 Receptor Inverse Agonist Research Articles

Cannabinoid CP55940 selectively induces apoptosis in Jurkat cells and in ex vivo T-cell acute lymphoblastic leukemia through H2O2 signaling mechanism

T-cell acute lymphoblastic leukemia (T-ALL) is a highly heterogeneous malignant hematological disorder arising from T-cell progenitors. This study was aimed to evaluate the cytotoxic effect of CP55940 on human peripheral blood lymphocytes (PBL) and on T-ALL cells (Jurkat). PBL and Jurkat cells were treated with CP55940 (0−20 μM), and morphological changes in the cell nucleus/ DNA, mitochondrial membrane potential (ΔΨm), and intracellular reactive oxygen species levels were determined by fluorescence microscopy and flow cytometry. Cellular apoptosis markers were also evaluated by western blotting, pharmacological inhibition and immunofluorescence. CP55940 induced apoptotic cell death in Jurkat cells, but not in PBL, in a dose–response manner with increasing fragmentation of DNA, arrest of cell cycle and damage of ΔΨm. CP55940 increased dichlorofluorescein fluorescence (DCF) intensity, increased DJ-1 Cys106- sulfonate, a marker of intracellular stress, induced the up-regulation of p53 and phosphorylation of transcription factor c-JUN. It increased the expression of BAX and PUMA, up-regulated mitochondrial proteins PINK1 and Parkin, and activated CASPASE-3. Antioxidant NAC, pifithrin-α, and SP600125 blocked CP55940 deleterious effect on Jurkat cells. However, the potent and highly specific cannabinoid CB1 and CB2 receptor inverse agonist SR141716 and SR144528 were unable to blunt CP55940-induced apoptosis in Jurkat cells. Conclusively CP55940 provokes cell death in Jurkat through CBR-independent mechanism. Interestingly, CP55940 was also cytotoxic to ex vivo T-ALL cells from chemotherapy-resistant pediatric patients. In conclusion, CP55940 selectively induces apoptosis in Jurkat cells through a H2O2-mediated signaling pathway. Our findings support the use of cannabinoids as a potential treatment for T-ALL cells.

Cannabinoid CB1 receptor inverse agonist MJ08 stimulates glucose production via hepatic sympathetic innervation in rats

As a key insulin target tissue for maintaining systemic glucose homeostasis, the liver plays important roles in improving obesity-associated insulin intolerance via selective cannabinoid CB1 receptor antagonism/inverse agonism. However, it is unclear whether this receptor inverse agonism affects hepatic glucose metabolism. MJ08 is a novel cannabinoid CB1 receptor antagonist/inverse agonist that has superior inverse agonism over the well-known antagonist/inverse agonist, SR141716 (rimonabant). MJ08 remarkably elevates fasting blood glucose independent of inhibition of insulin release in mice. In the current study, MJ08 was used to investigate the mechanism by which liver cannabinoid CB1 receptor inverse activation regulates hepatic glucose metabolism. MJ08 stimulated hepatic glucose production (HGP) in a dose-dependent manner and promoted gluconeogenic gene expression in perfused rat liver. SR141716 exhibited similar but weaker effects. The cannabinoid CB1 receptor agonist (WIN 55,212-2), Gs protein-cyclic AMP (cAMP)-dependent pathway inhibitors (NF449 and H89), β-adrenoceptor antagonist (propranolol), and peripheral sympathetic inhibitor (reserpine) could antagonize MJ08-induced HGP. Furthermore, MJ08 and SR141716 induced monoamine neurotransmitter (noradrenaline) release and increased cAMP content significantly in perfused liver, although only a slight increase was observed in primary cultured hepatocytes. These results indicate that local liver cannabinoid CB1 receptor inverse agonism via hepatic sympathetic innervation is responsible for the HGP induced by MJ08. Thus, high inverse agonistic activity could increase fasting blood glucose levels and should be avoided in the development of peripheral cannabinoid CB1 receptor-targeted weight-loss drugs.

Triazole Ureas Act as Diacylglycerol Lipase Inhibitors and Prevent Fasting-Induced Refeeding.

Triazole ureas constitute a versatile class of irreversible inhibitors that target serine hydrolases in both cells and animal models. We have previously reported that triazole ureas can act as selective and CNS-active inhibitors for diacylglycerol lipases (DAGLs), enzymes responsible for the biosynthesis of 2-arachidonoylglycerol (2-AG) that activates cannabinoid CB1 receptor. Here, we report the enantio- and diastereoselective synthesis and structure-activity relationship studies. We found that 2,4-substituted triazole ureas with a biphenylmethanol group provided the most optimal scaffold. Introduction of a chiral ether substituent on the 5-position of the piperidine ring provided ultrapotent inhibitor 38 (DH376) with picomolar activity. Compound 38 temporarily reduces fasting-induced refeeding of mice, thereby emulating the effect of cannabinoid CB1-receptor inverse agonists. This was mirrored by 39 (DO34) but also by the negative control compound 40 (DO53) (which does not inhibit DAGL), which indicates the triazole ureas may affect the energy balance in mice through multiple molecular targets.

Blockade of Nicotine and Cannabinoid Reinforcement and Relapse by a Cannabinoid CB1-Receptor Neutral Antagonist AM4113 and Inverse Agonist Rimonabant in Squirrel Monkeys.

Nicotine, the main psychoactive component of tobacco, and (-)-Δ(9)-tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, play major roles in tobacco and marijuana dependence as reinforcers of drug-seeking and drug-taking behavior. Drugs that act as inverse agonists of cannabinoid CB1 receptors in the brain can attenuate the rewarding and abuse-related effects of nicotine and THC, but their clinical use is hindered by potentially serious side effects. The recently developed CB1-receptor neutral antagonists may provide an alternative therapeutic approach to nicotine and cannabinoid dependence. Here we compare attenuation of nicotine and THC reinforcement and reinstatement in squirrel monkeys by the CB1-receptor inverse agonist rimonabant and by the recently developed CB1-receptor neutral antagonist AM4113. Both rimonabant and AM4113 reduced two effects of nicotine and THC that play major roles in tobacco and marijuana dependence: (1) maintenance of high rates of drug-taking behavior, and (2) priming- or cue-induced reinstatement of drug-seeking behavior in abstinent subjects (models of relapse). In contrast, neither rimonabant nor AM4113 modified cocaine-reinforced or food-reinforced operant behavior under similar experimental conditions. However, both rimonabant and AM4113 reduced cue-induced reinstatement in monkeys trained to self-administer cocaine, suggesting the involvement of a common cannabinoid-mediated mechanism in the cue-induced reinstatement for different drugs of abuse. These findings point to CB1-receptor neutral antagonists as a new class of medications for treatment of both tobacco dependence and cannabis dependence.

Involvement of opioid system in antidepressant-like effect of the cannabinoid CB1 receptor inverse agonist AM-251 after physical stress in mice.

Cannabinoid inverse agonists possess antidepressant-like properties, but the mechanism of this action is unknown. Numerous studies have reported the interaction between opioid and cannabinoid pathways. In this study, acute foot-shock stress was used in mice to investigate the involvement of the opioid pathway in the antidepressant-like effect of the cannabinoid CB1 receptor inverse agonist AM-251. Stress was induced by intermittent foot-shock stimulation for 30 min. Then, using the forced swimming test (FST) and tail suspension test (TST), the immobility time was measured. Results show that the immobility time was significantly prolonged in animals subjected to foot-shock stress, compared with non-stressed controls (P < 0.01). Also, the serum corticosterone level was significantly increased after stress induction (P < 0.001). Administration of AM-251 (0.5 and 0.3 mg/kg, intraperitoneally (i.p.)), significantly decreased the immobility time of stressed mice in the FST (P < 0.001 and P < 0.01, respectively) and TST (P < 0.01 and P < 0.05, respectively). The lowest dose of AM-251 (0.1 mg/kg), naltrexone (0.3 mg/kg), and morphine (1.0 mg/kg) did not show any significant effect on stressed animals (P > 0.05). Co-administration of AM-251 with sub-effective dose of naltrexone decreased the effective dose of this cannabinoid inverse agonist, to 0.1 mg/kg (P < 0.01). On the other hand, administration of the sub-effective dose of morphine reversed the anti-immobility effect of AM-251 (0.5 mg/kg; P < 0.001). In conclusion, the present study for the first time reveals the possible role of opioid signalling in the antidepressant-like properties of AM-251 in a foot-shock stress model.

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

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

Pharmacological efficacy and safety profile of taranabant in preclinical species

AbstractTaranabant is a highly selective and potent cannabinoid CB1 receptor inverse agonist. We compared the pharmacological properties of taranabant with another inverse agonist, rimonabant, and determined the preclinical safety margins of taranabant. In vitro studies demonstrated that taranabant is ∼10‐fold more potent than rimonabant at the CB1 receptor, and taranabant is more selective based on off‐target in vitro screening. In vivo efficacy studies demonstrated that taranabant is ∼10‐fold more potent than rimonabant in diet‐induced obese rats. In repeat‐dose toxicological studies, taranabant did not cause mortality in rodents and monkeys at exposure margins ≤6478 and 1922 times the estimated human exposure at 0.5 mg/day−1. Taranabant did not produce CNS signs, including seizures, when administered to monkeys for 1 year at 10 mg/kg−1day−1 (highest dose tested chronically), corresponding to an exposure margin of 974 times. In contrast to primates, taranabant produced brief handling‐induced seizure‐like activity in rodents, species predisposed to handling‐induced seizures. Throughout the entire preclinical program, taranabant did not cause histopathological changes in the peripheral or central nervous system. In summary, the highly selective nature of taranabant is consistent with its generally favorable preclinical safety profile. Drug Dev Res 2009. © 2009 Wiley‐Liss, Inc.

Substituted pyrimidines as cannabinoid CB1 receptor ligands

Cannabinoid CB1 receptors have been the avenue of extensive studies since the first clinical results of rimonabant (SR141716) for the treatment of obesity and obesity-related metabolic disorders were reported in 2001. To further evaluate the properties of CB receptors, we have designed and efficiently prepared a series of substituted pyrimidines based on chemical structure of Merck’s taranabant, a cannabinoid CB1 receptor inverse agonist. Noticeably, N4-((2 S,3 S)-3-(3-bromophenyl)-4-(4-chlorophenyl)butan-2-yl)- N6-butylpyrimidine-4,6-diamine ( 13b) demonstrated good binding affinity and decent selectivity for CB1 receptor (IC 50 = 16.3 nM, CB2/CB1 = 181.6).

Cannabinoid CB1 receptor antagonists as potential pharmacotherapies for drug abuse disorders

Since the discovery of the cannabinoid CB1 receptor (CB1R) in 1988, and subsequently of the CB2 receptor (CB2R) in 1993, there has been an exponential growth of research investigating the functions of the endocannabinoid system. The roles of CB1Rs have been of particular interest to psychiatry because of their selective presence within the CNS and because of their association with brain-reward circuits involving mesocorticolimbic dopamine systems. One potential role that has become of considerable focus is the ability of CB1Rs to modulate the effects of the drugs of abuse. Many drugs of abuse elevate dopamine levels, and the ability of CB1R antagonists or inverse agonists to modulate these elevations has suggested their potential application as pharmacotherapies for treating drug abuse disorders. With the identification of the selective CB1R antagonist, rimonabant, in 1994, and subsequently of other CB1R antagonists, there has been a rapid expansion of research investigating their ability to modulate the effects of the drugs of abuse. This review highlights some of the preclinical and clinical studies that have examined the effects of CB1R antagonists under conditions potentially predictive of their therapeutic efficacy as treatments for drug abuse disorders.

The cannabinoid CB1 receptor inverse agonist AM 251 and antagonist AM 4113 produce similar effects on the behavioral satiety sequence in rats

Cannabinoid CB1 inverse agonists such as rimonabant and AM 251 hold therapeutic promise as appetite suppressants, but the extent to which non-motivational factors contribute to their anorectic effects is not fully known. Examination of the behavioral satiety sequence (BSS) in rats, the orderly progression from eating to post-prandial grooming and then resting, has revealed that these compounds preserve the order of events but differ markedly from natural satiation. The most notable difference is that grooming (particularly scratching) is profoundly enhanced at anorectic doses, while eating and resting are diminished, raising the possibility that the anorectic effect is simply secondary to the grooming effect. In the current design, the neutral CB1 antagonist AM 4113, which has been found to lack some of the undesirable effects of AM 251, produced nearly identical effects on the BSS as AM 251. The possibility that competition from enhanced grooming could account for the anorectic effect of AM 4113 was examined by yoking the pattern of disruptions caused by grooming in the AM 4113-treated group to forced locomotion in a different group fed in a modified running wheel. This response competition did not significantly reduce food intake. It was concluded that AM 4113, a CB1 neutral antagonist, produces the same effects on the BSS as AM 251, but that response competition from enhanced grooming may not be a sufficient explanation for the anorectic effects of CB1 antagonists/inverse agonists.

Constitutive Activity of the Cannabinoid CB1 Receptor Regulates the Function of Co-expressed Mu Opioid Receptors

The human mu opioid receptor was expressed stably in Flp-In T-REx HEK293 cells. Occupancy by the agonist DAMGO (Tyr-d-Ala-Gly-N-methyl-Phe-Gly-ol) resulted in phosphorylation of the ERK1/2 MAP kinases, which was blocked by the opioid antagonist naloxone but not the cannabinoid CB1 receptor inverse agonist SR141716A. Expression of the human cannabinoid CB1 receptor in these cells from the inducible Flp-In T-REx locus did not alter expression levels of the mu opioid receptor. This allowed the cannabinoid CB1 agonist WIN55212-2 to stimulate ERK1/2 phosphorylation but resulted in a large reduction in the capacity of DAMGO to activate these kinases. Although lacking affinity for the mu opioid receptor, co-addition of SR141716A caused recovery of the effectiveness of DAMGO. In contrast co-addition of the CB1 receptor neutral antagonist O-2050 did not. Induction of the CB1 receptor also resulted in an increase of basal [(35)S]guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) binding and thereby a greatly reduced capacity of DAMGO to further stimulate [(35)S]GTPgammaS binding. CB1 inverse agonists attenuated basal [(35)S]GTPgammaS binding and restored the capacity of DAMGO to stimulate. Flp-In T-REx HEK293 cells were generated, which express the human mu opioid receptor constitutively and harbor a modified D163N cannabinoid CB1 receptor that lacks constitutive activity. Induction of expression of the modified cannabinoid CB1 receptor did not limit DAMGO-mediated ERK1/2 MAP kinase phosphorylation and did not allow SR141716A to enhance the function of DAMGO. These data indicate that it is the constitutive activity inherent in the cannabinoid CB1 receptor that reduces the capacity of co-expressed mu opioid receptor to function.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamic Properties of Taranabant, a Novel Selective Cannabinoid‐1 Receptor Inverse Agonist, for the Treatment of Obesity: Results From a Double‐Blind, Placebo‐Controlled, Single Oral Dose Study in Healthy Volunteers

Taranabant is a novel cannabinoid CB-1 receptor (CB1R) inverse agonist in clinical development for the treatment of obesity. This double-blind, randomized, placebo-controlled, single oral dose study evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of taranabant (0.5-600 mg) in 24 healthy male volunteers. Single-dose AUC(0-infinity) and C(max) values for taranabant increased approximately linearly with dose up to 200 mg, with slightly less than dose-proportional increases in AUC(0-infinity) and C(max) values for doses >200 mg. Plasma taranabant had a biphasic disposition, with a median t(max) of 1 to 2.5 hours and a terminal elimination t((1/2)) of 38 to 69 hours. Coadministration of taranabant with a high-fat meal led to a 14% increase in C(max) and a 74% increase in AUC(0-infinity). Clinical adverse experiences associated with single doses of taranabant were generally mild and transient. Of the 198 clinical adverse experiences reported, the most common drug-related ones were nausea (36), headache (22), drowsiness (14), abdominal discomfort/abdominal pain/stomachache (14), hiccups (9), dizziness (8), decreased appetite (7), increased bowel movement (7), mood change (6), tiredness (4), vomiting (4), and sweating increased (4). Taranabant has pharmacokinetic characteristics suitable for a once-daily dosing regimen.

PSNCBAM‐1, a novel allosteric antagonist at cannabinoid CB1 receptors with hypophagic effects in rats

Rimonabant (Acomplia, SR141716A), a cannabinoid CB1 receptor inverse agonist, has recently been approved for the treatment of obesity. There are, however, concerns regarding its side effect profile. Developing a CB1 antagonist with a different pharmacological mechanism may lead to a safer alternative. To this end we have screened a proprietary small molecule library and have discovered a novel class of allosteric antagonist at CB1 receptors. Herein, we have characterized an optimized prototypical molecule, PSNCBAM-1, and its hypophagic effects in vivo. A CB1 yeast reporter assay was used as a primary screen. PSNCBAM-1 was additionally characterized in [35S]-GTPgammaS, cAMP and radioligand binding assays. An acute rat feeding model was used to evaluate its effects on food intake and body weight in vivo. In CB1 receptor yeast reporter assays, PSNCBAM-1 blocked the effects induced by agonists such as CP55,940, WIN55212-2, anandamide (AEA) or 2-arachidonoyl glycerol (2-AG). The antagonist characteristics of PSNCBAM-1 were confirmed in [35S]-GTPgammaS binding and cAMP assays and was shown to be non-competitive by Schild analyses. PSNCBAM-1 did not affect CB2 receptors. In radioligand binding assays, PSNCBAM-1 increased the binding of [3H]CP55,940 despite its antagonist effects. In an acute rat feeding model, PSNCBAM-1 decreased food intake and body weight. PSNCBAM-1 exerted its effects through selective allosteric modulation of the CB1 receptor. The acute effects on food intake and body weight induced in rats provide a first report of in vivo activity for an allosteric CB1 receptor antagonist.

18F]MK-9470, a positron emission tomography (PET) tracer forin vivohuman PET brain imaging of the cannabinoid-1 receptor

[(18)F]MK-9470 is a selective, high-affinity, inverse agonist (human IC(50), 0.7 nM) for the cannabinoid CB1 receptor (CB1R) that has been developed for use in human brain imaging. Autoradiographic studies in rhesus monkey brain showed that [(18)F]MK-9470 binding is aligned with the reported distribution of CB1 receptors with high specific binding in the cerebral cortex, cerebellum, caudate/putamen, globus pallidus, substantia nigra, and hippocampus. Positron emission tomography (PET) imaging studies in rhesus monkeys showed high brain uptake and a distribution pattern generally consistent with that seen in the autoradiographic studies. Uptake was blocked by pretreatment with a potent CB1 inverse agonist, MK-0364. The ratio of total to nonspecific binding in putamen was 4-5:1, indicative of a strong specific signal that was confirmed to be reversible via displacement studies with MK-0364. Baseline PET imaging studies in human research subject demonstrated behavior of [(18)F]MK-9470 very similar to that seen in monkeys, with very good test-retest variability (7%). Proof of concept studies in healthy young male human subjects showed that MK-0364, given orally, produced a dose-related reduction in [(18)F]MK-9470 binding reflecting CB1R receptor occupancy by the drug. Thus, [(18)F]MK-9470 has the potential to be a valuable, noninvasive research tool for the in vivo study of CB1R biology and pharmacology in a variety of neuropsychiatric disorders in humans. In addition, it allows demonstration of target engagement and noninvasive dose-occupancy studies to aid in dose selection for clinical trials of CB1R inverse agonists.

Current evidence supporting a role of cannabinoid CB1 receptor (CB1R) antagonists as potential pharmacotherapies for drug abuse disorders

Since the discovery of the cannabinoid CB1 receptor (CB1R) in 1988, and subsequently of the CB2 receptor (CB2R) in 1993, there has been an exponential growth of research investigating the functions of the endocannabinoid system. The roles of CB1Rs have been of particular interest to behavioral pharmacologists because of their selective presence within the central nervous system (CNS) and because of their association with brain-reward circuits involving mesocorticolimbic dopamine systems. One potential role that has become of considerable recent focus is the ability of CB1Rs to modulate the effects of drugs of abuse. Many drugs of abuse elevate dopamine levels, and the ability of CB1R antagonists or inverse agonists to attenuate these elevations has suggested their potential application as pharmacotherapies for treating drug abuse disorders. With the identification of the selective CB1R antagonist, SR141716, in 1994, and its subsequent widespread availability, there has been a rapid expansion of research investigating its ability to modulate the effects of drugs of abuse. The preliminary clinical reports of its success in retarding relapse in tobacco users have accelerated this expansion. This report critically reviews preclinical and clinical studies involving the ability of CB1R antagonists to attenuate the effects of drugs of abuse, while providing an overview of the neuroanatomical and neurochemical points of contact between the endocannabinoid system and systems mediating abuse-related effects.

Synergistic effects of cannabinoid inverse agonist AM251 and opioid antagonist nalmefene on food intake in mice

Oral administration of the opioid antagonist nalmefene alone (up to 20 mg/kg) failed to show a significant effect on acute food intake in mice. However, combined oral dosing of nalmefene and subthreshold doses of AM251, a cannabinoid CB1 receptor inverse agonist, led to a significant reduction in food intake in both lean and diet-induced obese (DIO) mice. Furthermore, the anorectic effect of a high dose of AM251 was further enhanced when co-administered with nalmefene. The results support a synergistic interaction between opioid and cannabinoid systems in regulating feeding behavior.

Voluntary exercise augments acute effects of CB1-receptor inverse agonist on body weight loss in obese and lean mice

Cannabinoid CB1 receptor (CB1R) inverse agonists reduce appetite and body weight (BW) gain in various species. Exercise is thought to be a natural reward process and the cannabinoid system is also believed to influence reward. We tested the hypothesis that voluntary exercise would augment the effects of AM251, a CB1R inverse agonist, on food intake (FI) and BW loss in murine genetic models of obesity. ob/ob, agouti yellow (A y), and lean C57BL/6J mice were treated via oral gavage with vehicle or AM251 (1, 3, or 10 mg/kg) 1 h before the dark cycle. The suppressive effects of 3 and 10 mg/kg AM251 on overnight FI, BW gain, and water intake (WI) were significant in ob/ob mice. In contrast, in A y mice, 10 mg/kg AM251 decreased FI and BW gain while it did not influence WI. Food consumption of ob/ob and A y mice, as evidenced by feeding frequency (FF) and feeding duration (FD), was reduced by AM251 for 4–6 h. AM251 at these doses had no impact on the appetitive behavior or BW gain of lean mice. After a 1-week wash-out period, mice were given running wheels in their home cages. With running wheel exercise, lean and obese mice exhibited increased sensitivity to AM251. Low voluntary wheel running activity of ob/ob mice precluded detection of combined effects of AM251 and exercise in this genetic model of obesity. Lean and agouti mice given AM251 combined with exercise lost a greater amount of BW than with AM251 alone. Our data suggest that voluntary exercise can enhance CB1R inverse agonist effects on appetite and BW loss in both lean and agouti obese mice.

Antidepressant-like and anorectic effects of the cannabinoid CB1 receptor inverse agonist AM251 in mice.

Psychopathological disorders, and depression in particular, are strongly linked to eating attitude in obese patients. The identification of cannabinoid CB1 receptors (CB1Rs) in areas of the central nervous system (CNS) that have been implicated in regulation of mood and food intake suggests that these receptors may mediate such a behavioral link. The goal of this study was to evaluate CB1R modulation of antidepressant-like effects and food intake. For this purpose, 129/SVE and C57BL/6 male mice were acutely dosed intraperitoneally (i.p.) with the CB1R inverse agonist AM251 (3-30 mg/kg) and tested, respectively, in the tail-suspension test (TST) and in the forced-swim test (FST), which have been used widely as tests sensitive to antidepressant compounds. Like the antidepressant desipramine (DMI, 16 mg/kg), AM251 significantly reduced immobility at 10 mg/kg in the TST and at 1 and 10 mg/kg in the FST. Such a decrease of immobility was not accompanied by an increase in motor activity in the open field, suggesting that occupancy of CB1R by AM251 induced antidepressant-like effects. This was supported by two additional experiments. First, the co-administration of the CB1R agonist CP55940, at a dose that did not induce motor impairment or profound hypothermia (0.01 mg/kg), reversed effects of AM251 in the TST. Secondly, effects of AM251 in the FST were absent in CB1R knockout (KO) mice. In addition to an antidepressant-like effect, AM251 reduced fasting-induced hyperphagia over a comparable dose range. Taken together, these data suggest that regulation of mood and food intake might be obtained through inverse agonism of CB1R.