End of the line for cannabinoid receptor 1 as an anti-obesity target? An opinion

Peripherally restricted CB1 receptor blockers

Antagonists (inverse agonists) of the cannabinoid-1 (CB1) receptor showed promise as new therapies for controlling obesity and related metabolic function/liver disease. These agents, representing diverse chemical series, shared the property of brain penetration due to the initial belief that therapeutic benefit was mainly based on brain receptor interaction. However, undesirable CNS-based side effects of the only marketed agent in this class, rimonabant, led to its removal, and termination of the development of other clinical candidates soon followed. Re-evaluation of this approach has focused on neutral or peripherally restricted (PR) antagonists. Supporting these strategies, pharmacological evidence indicates most if not all of the properties of globally acting agents may be captured by molecules with little brain presence. Methodology that can be used to eliminate BBB penetration and the means (in vitro assays, tissue distribution and receptor occupancy determinations, behavioral paradigms) to identify potential agents with little brain presence is discussed. Focus will be on the pharmacology supporting the contention that reported agents are truly peripherally restricted. Notable examples of these types of compounds are: TM38837 (structure not disclosed); AM6545 (8); JD5037 (15b); RTI-12 (19).

The endocannabinoid signaling system in cancer

Changes in lipid metabolism are intimately related to cancer. Several classes of bioactive lipids play roles in the regulation of signaling pathways involved in neoplastic transformation and tumor growth and progression. The endocannabinoid system, comprising lipid-derived endocannabinoids, their G-protein-coupled receptors (GPCRs), and the enzymes for their metabolism, is emerging as a promising therapeutic target in cancer. This report highlights the main signaling pathways for the antitumor effects of the endocannabinoid system in cancer and its basic role in cancer pathogenesis, and discusses the alternative view of cannabinoid receptors as tumor promoters. We focus on new players in the antitumor action of the endocannabinoid system and on emerging crosstalk among cannabinoid receptors and other membrane or nuclear receptors involved in cancer. We also discuss the enzyme MAGL, a key player in endocannabinoid metabolism that was recently recognized as a marker of tumor lipogenic phenotype.

A novel peripherally restricted cannabinoid receptor antagonist, AM6545, reduces food intake and body weight, but does not cause malaise, in rodents

BACKGROUND AND PURPOSE

Cannabinoid CB(1) receptor antagonists reduce food intake and body weight, but clinical use in humans is limited by effects on the CNS. We have evaluated a novel cannabinoid antagonist (AM6545) designed to have limited CNS penetration, to see if it would inhibit food intake in rodents, without aversive effects.

EXPERIMENTAL APPROACH

Cannabinoid receptor binding studies, cAMP assays, brain penetration studies and gastrointestinal motility studies were carried out to assess the activity profile of AM6545. The potential for AM6545 to induce malaise in rats and the actions of AM6545 on food intake and body weight were also investigated.

KEY RESULTS

AM6545 binds to CB(1) receptors with a K(i) of 1.7 nM and CB(2) receptors with a K(i) of 523 nM. AM6545 is a neutral antagonist, having no effect on cAMP levels in transfected cells and was less centrally penetrant than AM4113, a comparable CB(1) receptor antagonist. AM6545 reversed the effects of WIN55212-2 in an assay of colonic motility. In contrast to AM251, AM6545 did not produce conditioned gaping or conditioned taste avoidance in rats. In rats and mice, AM6545 dose-dependently reduced food intake and induced a sustained reduction in body weight. The effect on food intake was maintained in rats with a complete subdiaphragmatic vagotomy. AM6545 inhibited food intake in CB(1) receptor gene-deficient mice, but not in CB(1)/CB(2) receptor double knockout mice.

CONCLUSIONS AND IMPLICATIONS

Peripherally active, cannabinoid receptor antagonists with limited brain penetration may be useful agents for the treatment of obesity and its complications.

SLV330, a cannabinoid CB(1) receptor antagonist, attenuates ethanol and nicotine seeking and improves inhibitory response control in rats

Cannabinoid CB(1) receptor (CB(1)R) signaling has been shown to play a role in the regulation of addictive behavior. In the present study, our aim was to investigate whether the CB(1)R antagonist SLV330 could reduce ethanol and nicotine self-administration and cue-induced reinstatement of ethanol and nicotine seeking behavior in Wistar rats. In operant chambers, rats were learned to emit a specific response (nose poke) in order to receive an ethanol solution or intravenous injections of nicotine. Discrete light and tone cues were presented during ethanol and nicotine delivery. These cues are particularly important for drug self-administration behavior and, through Pavlovian conditioning, acquire conditioned reinforcing and motivational properties and are therefore able to generate and maintain drug-seeking behavior. Subsequently, the CB(1)R antagonist SLV330 (doses ranging from 1 to 10mg/kg, given orally, p.o.) was administered to investigate the effects on drug self-administration. In addition, responding for ethanol and nicotine was extinguished. Then, the animals were tested for cue-induced reinstatement of ethanol and nicotine seeking and treated with vehicle or SLV330. Finally, the effects of SLV330 were studied on the number of anticipatory responses in the 5-choice serial reaction time task (5-CSRTT) in order to determine whether this compound could also increase impulse control in Wistar rats. The CB(1) antagonist SLV330 was effective in reducing ethanol self-administration at a lowest effective dose (LED) of 10mg/kg (p.o.) and reinstatement of ethanol seeking at a LED of 3mg/kg (p.o.). SLV330 was also effective in reducing nicotine self-administration and reinstatement of nicotine seeking, although at a LED of 10mg/kg (p.o.). Finally, SLV330 decreased time delay-dependent anticipatory responding (LED of 3.0mg/kg, p.o.), indicating an increased inhibitory control. These findings are in agreement with results reported with other CB(1) antagonists. The combined action of reducing the reinforcing and motivational properties of nicotine and alcohol and the improvement of impulse control supports the idea that the cannabinoid system is a promising target for anti-relapse medication.

CB1 cannabinoid receptors promote oxidative/nitrosative stress, inflammation and cell death in a murine nephropathy model

BACKGROUND AND PURPOSE

Accumulating recent evidence suggests that cannabinoid-1 (CB(1)) receptor activation may promote inflammation and cell death and its pharmacological inhibition is associated with anti-inflammatory and tissue-protective effects in various preclinical disease models, as well as in humans.

EXPERIMENTAL APPROACH

In this study, using molecular biology and biochemistry methods, we have investigated the effects of genetic deletion or pharmacological inhibition of CB(1) receptors on inflammation, oxidative/nitrosative stress and cell death pathways associated with a clinically relevant model of nephropathy, induced by an important chemotherapeutic drug cisplatin.

RESULTS

Cisplatin significantly increased endocannabinoid anandamide content, activation of p38 and JNK mitogen-activated protein kinases (MAPKs), apoptotic and poly (ADP-ribose)polymerase-dependent cell death, enhanced inflammation (leucocyte infiltration, tumour necrosis factor-alpha and interleukin-1beta) and promoted oxidative/nitrosative stress [increased expressions of superoxide-generating enzymes (NOX2(gp91phox), NOX4), inducible nitric oxide synthase and tissue 4-hydroxynonenal and nitrotyrosine levels] in the kidneys of mice, accompanied by marked histopathological damage and impaired renal function (elevated creatinine and serum blood urea nitrogen) 3 days following its administration. Both genetic deletion and pharmacological inhibition of CB(1) receptors with AM281 or SR141716 markedly attenuated the cisplatin-induced renal dysfunction and interrelated oxidative/nitrosative stress, p38 and JNK MAPK activation, cell death and inflammatory response in the kidney.

CONCLUSIONS AND IMPLICATIONS

The endocannabinoid system through CB(1) receptors promotes cisplatin-induced tissue injury by amplifying MAPK activation, cell death and interrelated inflammation and oxidative/nitrosative stress. These results also suggest that inhibition of CB(1) receptors may exert beneficial effects in renal (and most likely other) diseases associated with enhanced inflammation, oxidative/nitrosative stress and cell death.

Probing the cannabinoid CB1/CB2 receptor subtype selectivity limits of 1,2-diarylimidazole-4-carboxamides by fine-tuning their 5-substitution pattern

The cannabinoid CB(1)/CB(2) receptor subtype selectivity in the 1,2-diarylimidazole-4-carboxamide series was boosted by fine-tuning its 5-substitution pattern. The presence of the 5-methylsulfonyl group in 11 led to a greater than approximately 840-fold CB(1)/CB(2) subtype selectivity. The compounds 10, 18 and 19 were found more active than rimonabant (1) in a CB(1)-mediated rodent hypotension model after oral administration. Our findings suggest a limited brain exposure of the P-glycoprotein substrates 11, 12 and 21.

SLV330, a cannabinoid CB1 receptor antagonist, ameliorates deficits in the T-maze, object recognition and Social Recognition Tasks in rodents

Cannabinoid CB(1) receptor (CB(1)R) signaling has been suggested to play an important role in the regulation of memory and cognition. In the present study, our aim was to investigate whether the CB(1)R antagonist SLV330 (doses ranging from 0.3 to 10mg/kg, given orally, p.o.) could ameliorate impairments in distinct aspects of cognition using different disruption models in both mice and rats. Effects of SLV330 were tested on working memory deficits in the T-maze Continuous Alternation Task (T-CAT) in mice; episodic memory deficits in the Object Recognition Task (ORT) and Social Recognition Task (SRT) in rats. The acetylcholinesterase inhibitor (AChEI) donepezil (Aricept, approved for symptomatic treatment of Alzheimer's disease) and nicotine were used as reference compounds. SLV330 markedly improved aging and scopolamine-induced memory deficits in the T-CAT in mice with a lowest effective dose (LED) of 1mg/kg p.o., while reversing the cognitive dysfunction induced by the N-methyl-D-aspartate (NMDA) antagonist dizocilpine (MK-801) only at the middle dose of 3mg/kg. In the ORT, we have found that combined administration of subthreshold doses of SLV330 (1mg/kg, p.o.) and the AChEI donepezil (0.1mg/kg, p.o.), that had no discernable effects on performance when given alone, enhanced memory performance in Wistar rats with deficits induced by the muscarinic antagonist scopolamine, suggestive of additive synergistic effects of SLV330 and donepezil on cognitive impairment. Finally, SLV330 was found to have cognition enhancing properties in a time delay paradigm in the SRT at a LED dose of 3mg/kg (p.o.). In conclusion, the CB(1)R antagonist SLV330 was found to clearly improve memory in several preclinical models for cognitive impairment.