Discriminative stimulus effects of BAY 38-7271, a novel cannabinoid receptor agonist

Structure-Affinity Relationships and Structure-Kinetic Relationships of 1,2-Diarylimidazol-4-carboxamide Derivatives as Human Cannabinoid 1 Receptor Antagonists

We report on the synthesis and biological evaluation of a series of 1,2-diarylimidazol-4-carboxamide derivatives developed as CB₁ receptor antagonists. These were evaluated in a radioligand displacement binding assay, a [³⁵S]GTPγS binding assay, and in a competition association assay that enables the relatively fast kinetic screening of multiple compounds. The compounds show high affinities and a diverse range of kinetic profiles at the CB₁ receptor and their structure–kinetic relationships (SKRs) were established. Using the recently resolved hCB₁ receptor crystal structures, we also performed a modeling study that sheds light on the crucial interactions for both the affinity and dissociation kinetics of this family of ligands. We provide evidence that, next to affinity, additional knowledge of binding kinetics is useful for selecting new hCB₁ receptor antagonists in the early phases of drug discovery.

Differentiation between low- and high-efficacy CB1 receptor agonists using a drug discrimination protocol for rats

RATIONALE

The "subjective high" from marijuana ingestion is likely due to Δ(9)-tetrahydrocannabinol (THC) activating the central cannabinoid receptor type 1 (CB1R) of the endocannabinoid signaling system. THC is a weak partial agonist according to in vitro assays, yet THC mimics the behavioral effects induced by more efficacious cannabinergics. This distinction may be important for understanding similarities and differences in the dose-effect spectra produced by marijuana/THC and designer cannabimimetics ("synthetic marijuana").

OBJECTIVE

We evaluated if drug discrimination is able to functionally detect/differentiate between a full, high-efficacy CB1R agonist [(±)AM5983] and the low-efficacy agonist THC in vivo.

MATERIALS AND METHODS

Rats were trained to discriminate between four different doses of AM5983 (0.10 to 0.56 mg/kg), and vehicle and dose generalization curves were determined for both ligands at all four training doses of AM5983. The high-efficacy WIN55,212-2 and the lower-efficacy (R)-(+)-methanandamide were examined at some AM5983 training conditions. Antagonism tests involved rimonabant and WIN55,212-2 and AM5983. The separate (S)- and (R)-isomers of (±)AM5983 were tested at one AM5983 training dose (0.30 mg/kg). The in vitro cyclic adenosine monophosphate (cAMP) assay examined AM5983 and the known CB1R agonist CP55,940.

RESULTS

Dose generalization ed50 values increased as a function of the training dose of AM5983, but more so for the partial agonists. The order of potency was (R)-isomer > (±)AM5983 > (S)-isomer and AM5983 > WIN55,212-2 ≥ THC > (R)-(+)-methanandamide. Surmountable antagonism of AM5983 and WIN55,212-2 occurred with rimonabant. The cAMP assay confirmed the cannabinergic nature of AM5983 and CP55,940.

CONCLUSIONS

Drug discrimination using different training doses of a high-efficacy, full CB1R agonist differentiated between low- and high-efficacy CB1R agonists.

"Herbal incense": designer drug blends as cannabimimetics and their assessment by drug discrimination and other in vivo bioassays

Recently, synthetic cannabinoids originally designed for testing in the laboratory only have found use recreationally in designer herbal blends, originally called "Spice". The myriad of compounds found are for the most part potent full agonists of the cannabinoid receptor 1, producing effects similar to tetrahydrocannabinol (THC) and marijuana. Drug discrimination of these compounds offers a specific behavioral test that can help determine whether these new synthetic compounds share a similar "subjective high" with the effects of marijuana/THC. By utilization of drug discrimination and other behavioral techniques, a better understanding of these new "designer" cannabinoids may be reached to assist in treating both the acute and chronic effects of these drugs. The paper provides a brief exposé of modern cannabinoid research as a backdrop to the recreational use of designer herbal blend cannabimimetics.

Cannabinergic aminoalkylindoles, including AM678=JWH018 found in 'Spice', examined using drug (Δ(9)-tetrahydrocannabinol) discrimination for rats

We examined four different cannabinergic aminoalkylindole ligands, including one drug (AM678=JWH018) found in herbal 'Spice' concoctions, for their ability to substitute for Δ(9)-tetrahydrocannabinol (THC), and the ability of the cannabinoid receptor 1-selective antagonist/inverse agonist rimonabant to block the substitution, 30 and 90 min after intraperitoneal injection. Rats trained to discriminate the effects of vehicle from those produced by 3 mg/kg of THC were used. The order of potency was: AM5983≥AM678>AM2233>WIN55212-2 at both test intervals. AM5983 and AM678 appeared eight times more potent than THC, followed by AM2233 (about twice as potent as THC), and WIN55212-2 approximately THC at the 30-min test interval. The aminoalkylindoles showed reduced potency (i.e. an increased ED50 value) at the longer injection-to-test interval of 90 min compared with testing at 30 min. The rightward shifts by coadministration of rimonabant were approximately 8-fold to 12-fold for AM5983 and AM678, compared with an approximately 3-fold rightward shift for the WIN55212-2 curve. AM2233 (1.8 mg/kg) substitution was also blocked by 1 mg/kg of rimonabant. In conclusion, AM5983 and AM678=JWH018 are potent cannabimimetics derived from an aminoalkylindole template. WIN55212-2 seemed to interact differently with rimonabant, compared with either AM5983 or AM678, indicating potential differences in the mechanism(s) of action among cannabinergic aminoalkylindoles.

Conformationally constrained analogs of BAY 59-3074 as novel cannabinoid receptor ligands

To obtain information on the pharmacophoric requirements of the CB1/CB2 partial agonist BAY 59-3074 we have synthesized a series of new conformationally constrained dibenzofuran (4a-d) and dibenzopyran analogs (5). All constrained analogs exhibited reduced binding affinity at both cannabinoid receptor subtypes, suggesting that planar conformations of these ligands are less favored by both receptors. We also found that 4c, 4d, and 5 exhibited 3- to 12-fold selectivity for hCB2 over rCB1 receptors and may serve as new chemotypes for the development of CB2-selective cannabinergics.

Discriminative stimulus functions of methanandamide and delta(9)-THC in rats: tests with aminoalkylindoles (WIN55,212-2 and AM678) and ethanol

OBJECTIVE

The aim of the study was to characterize in vivo the aminoalkylindoles WIN55,212-2 (WIN) and AM678 (naphthalen-1-yl(1-pentyl-1H-indol-3-yl)methanone) as cannabinoid receptor (CB(1)R) ligands using drug discrimination. Tests also involved delta(9)-tetrahydrocannabinol (THC) and R-(+)-methanandamide (mAEA), a metabolically stable analog of the endogenous ligand anandamide, as well as the CB(1)R selective antagonist/inverse agonist rimonabant; tests with ethanol assessed pharmacological specificity. We used two different drug discriminations (mAEA and THC) allowing us to explore potential differences in CB(1)R activation which could be attributed to variations in their respective CB(1)R signaling mechanisms.

METHODS

There were two concurrently trained groups of rats. One group discriminated between i.p. injected vehicle and 10 mg/kg mAEA. The other group was trained to discriminate between vehicle and 1.8 mg/kg THC.

RESULTS

Dose generalization curves for AM678, WIN55,212-2, THC, and mAEA suggested the following rank order of potency: AM678 > WIN55,212-2 > or = THC > mAEA in both drug discrimination groups. Challenge by 1 mg/kg rimonabant resulted in shifts to the right of the generalization curves for the two aminoalkylindoles (4.4-fold for AM678 and 11.3-fold for WIN in the mAEA group, whereas for the THC group, the corresponding values were 13 and 2.6, respectively), suggesting surmountable antagonism. Ethanol did not generalize in either of the two groups, suggesting pharmacological specificity.

CONCLUSION

Data are congruent with the general observation that there is substantial overlap in the discriminative stimulus effects of CB(1)R ligands across different chemical classes. However, the quantitative differences in the interactions between the two aminoalkylindoles and rimonabant in the two discrimination groups suggest subtle variations in the ligand-receptor activation(s).

Pharmacological actions of cannabinoids

Mammalian tissues express at least two types of cannabinoid receptor, CB1 and CB2, both G protein coupled. CB1 receptors are expressed predominantly at nerve terminals where they mediate inhibition of transmitter release. CB2 receptors are found mainly on immune cells, one of their roles being to modulate cytokine release. Endogenous ligands for these receptors (endocannabinoids) also exist. These are all eicosanoids; prominent examples include arachidonoylethanolamide (anandamide) and 2-arachidonoyl glycerol. These discoveries have led to the development of CB1- and CB2-selective agonists and antagonists and of bioassays for characterizing such ligands. Cannabinoid receptor antagonists include the CB1-selective SR141716A, AM251, AM281 and LY320135, and the CB2-selective SR144528 and AM630. These all behave as inverse agonists, one indication that CB1 and CB2 receptors can exist in a constitutively active state. Neutral cannabinoid receptor antagonists that seem to lack inverse agonist properties have recently also been developed. As well as acting on CB1 and CB2 receptors, there is convincing evidence that anandamide can activate transient receptor potential vanilloid type 1 (TRPV1) receptors. Certain cannabinoids also appear to have non-CB1, non-CB2, non-TRPV1 targets, for example CB2-like receptors that can mediate antinociception and "abnormal-cannabidiol" receptors that mediate vasorelaxation and promote microglial cell migration. There is evidence too for TRPV1-like receptors on glutamatergic neurons, for alpha2-adrenoceptor-like (imidazoline) receptors at sympathetic nerve terminals, for novel G protein-coupled receptors for R-(+)-WIN55212 and anandamide in the brain and spinal cord, for novel receptors for delta9-tetrahydrocannabinol and cannabinol on perivascular sensory nerves and for novel anandamide receptors in the gastro-intestinal tract. The presence of allosteric sites for cannabinoids on various ion channels and non-cannabinoid receptors has also been proposed. In addition, more information is beginning to emerge about the pharmacological actions of the non-psychoactive plant cannabinoid, cannabidiol. These recent advances in cannabinoid pharmacology are all discussed in this review.

Discriminative stimulus effects of the structurally novel cannabinoid CB1/CB2 receptor partial agonist BAY 59-3074 in the rat

BAY 59-3074 [3-[2-cyano-3-(trifluoromethyl)phenoxy]phenyl-4,4,4-trifluoro-1-butane-sulfonate] is a structurally novel cannabinoid CB1/CB2 receptor partial agonist with analgesic properties. The present study was performed to confirm its receptor binding profile in a highly sensitive in vivo assay. Rats (n=10) learned to discriminate BAY 59-3074 (0.5 mg/kg, p.o., t-1 h) from vehicle in a fixed-ratio: 10, food-reinforced two-lever procedure after a median number of 28 training sessions. BAY 59-3074 generalized dose-dependently (ED(50): 0.081 mg/kg, p.o.) and the cue was detectable between 0.25 and 4 h after administration. The selective cannabinoid CB1 receptor antagonist SR 141716A [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride] blocked the discriminative effects of BAY 59-3074 (ID50: 1.79 mg/kg, i.p.). Complete generalization was also obtained after i.p. administration of BAY 59-3074 (ED50 value: 0.41 mg/kg), and the reference cannabinoids BAY 38-7271 [(-)-(R)-3-(2-hydroxymethylindanyl-4-oxy)phenyl-4,4,4-trifluoro-1-butanesulfonate, 0.011 mg/kg], CP 55,940 [(-)-cis-3-[2-hydroxy-4(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxy-propyl)cyclohexanol, 0.013 mg/kg], HU-210 [(-)-11-OH-Delta8-tetrahydrocannabinol dimethylheptyl, 0.022 mg/kg], WIN 55,212-2 [(R)-4,5-dihydro-2-methyl-4(4-morpholinylmethyl)-1-(1-naphthalenylcarbonyl)-6H-pyrrolo [3,2,1-ij] quinolin-6-one, 0.41 mg/kg] and (-)-Delta9-tetrahydrocannabinol (0.41 mg/kg). Non-cannabinoids with analgesic properties, such as morphine, amitriptyline, carbamazepine, gabapentin and baclofen, did not generalize to the cue. It is concluded that the discriminative stimulus effects of BAY 59-3074 are specifically mediated by cannabinoid CB1 receptor activation.

Partial agonist-like profile of the cannabinoid receptor antagonist SR141716A in a food-reinforced operant paradigm

Both cannabinoid CB1 receptor agonists, such as delta-tetrahydrocannabinol (delta-THC), CP 55,940 and WIN 55,212-2, and the antagonist/inverse agonist SR141716A, dose-dependently suppress operant behavior. The present study investigated to what extent combined i.p. application of SR141716A with these cannabinoids resulted in mutually antagonistic effects, in additive effects, or in no interactive effects on operant responding in rats trained in a fixed-ratio 10, food-reinforced 10-min procedure. Pretreatment with SR141716A either had no effect on (at 0.3-1mg/kg), or partially blocked (at 3 mg/kg), the inhibitory effects on responding induced by delta-THC (3-5 mg/kg) and CP 55,940 (0.03-0.2 mg/kg). Interestingly, while 3 mg/kg SR141716A induced moderate inhibitory effects on operant responding, its combination with either agonist resulted in the same level of inhibitory activity on responding as that obtained by SR141716A when tested alone. Pretreatment with a low dose of CP 55,940 (0.01 mg/kg) or WIN 55,212-2 (0.3 mg/kg) did not affect response inhibition induced by SR141716A. Combination of SR141716A (0.5 and 1mg/kg) with delta-THC (3 mg/kg) resulted in the same level of response inhibition, independently of whether SR141716A was given 5 min before or 15 min after delta-THC. Although alternative explanations are conceivable, the data may indicate that SR141716A is a partial agonist at those cannabinoid receptors mediating the response-rate suppressive effects of cannabinoids.

3-[2-Cyano-3-(trifluoromethyl)phenoxy]phenyl-4,4,4-trifluoro-1-butanesulfonate (BAY 59-3074): A Novel Cannabinoid CB1/CB2 Receptor Partial Agonist with Antihyperalgesic and Antiallodynic Effects

3-[2-Cyano-3-(trifluoromethyl)phenoxy]phenyl-4,4,4-trifluoro-1-butanesulfonate (BAY 59-3074) is a novel, selective cannabinoid CB(1)/CB(2) receptor ligand (K(i) = 55.4, 48.3, and 45.5 nM at rat and human cannabinoid CB(1) and human CB(2) receptors, respectively), with partial agonist properties at these receptors in guanosine 5-[gamma(35)S]-thiophosphate triethyl-ammonium salt ([(35)S]GTPgammaS) binding assays. In rats, generalization of BAY 59-3074 to the cue induced by the cannabinoid CB(1) receptor agonist (-)-(R)-3-(2-hydroxymethylindanyl-4-oxy)phenyl-4,4,4-trifluoro-1-butanesulfonate (BAY 38-7271) in a drug discrimination procedure, as well as its hypothermic and analgesic effects in a hot plate assay, were blocked by the cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR 141716A). BAY 59-3074 (0.3-3 mg/kg, p.o.) induced antihyperalgesic and antiallodynic effects against thermal or mechanical stimuli in rat models of chronic neuropathic (chronic constriction injury, spared nerve injury, tibial nerve injury, and spinal nerve ligation models) and inflammatory pain (carrageenan and complete Freund's adjuvant models). Antiallodynic efficacy of BAY 59-3074 (1 mg/kg, p.o.) in the spared nerve injury model was maintained after 2 weeks of daily administration. However, tolerance developed rapidly (within 5 days) for cannabinoid-related side effects, which occur at doses above 1 mg/kg (e.g., hypothermia). Uptitration from 1 to 32 mg/kg p.o. (doubling of daily dose every 4th day) prevented the occurrence of such side effects, whereas antihyperalgesic and antiallodynic efficacy was maintained/increased. No withdrawal symptoms were seen after abrupt withdrawal following 14 daily applications of 1 to 10 mg/kg p.o. It is concluded that BAY 59-3074 may offer a valuable therapeutic approach to treat diverse chronic pain conditions.

Behavioral effects of cannabinoids show differential sensitivity to cannabinoid receptor blockade and tolerance development

This study compared the potency and efficacy of the cannabinoids delta-tetrahydrocannabinol (delta-THC), HU-210, WIN 55,212-2 and CP 55,940 in suppressing food-reinforced operant behavior, increasing reaction latency in a hot-plate test and inducing hypothermia, and tested whether these behavioral effects induced by CP 55,940 showed differential sensitivity to the cannabinoid CB1 receptor antagonist SR141716A, and to tolerance development. After acute i.p. administration to rats, operant behavior was more potently affected than reaction latency and body temperature, but the order of potency of the different drugs was similar across the tests: HU-210<CP 55,940<WIN 55,212-2=delta-THC. SR141716A blocked the hypothermic and analgesic effects more potently/efficiently than the response-rate suppressive effect of CP 55,940. After repeated administration of CP 55,940, the extent and speed of tolerance development was most pronounced in the hypothermia test, and least pronounced in the operant test. It is concluded that the more the behavioral effect induced by a cannabinoid receptor agonist is situated at the left-hand side of the dose-spectrum, the more the effect is resistant to blockade by a cannabinoid receptor antagonist and to the development of tolerance. The possible consequence of this observation for the therapeutic use of cannabinoids is discussed.

BAY 38-7271: a novel highly selective and highly potent cannabinoid receptor agonist for the treatment of traumatic brain injury

Traumatic brain injury (TBI) is the most common cause of mortality and morbidity in adults under 40 years of age in industrialized countries. Worldwide the incidence is increasing, about 9.5 million people are hospitalized per year due to TBI, and the death rate is estimated to be more than one million people per year. Recently BAY 38-7271 has been characterized as a structurally novel, selective and highly potent cannabinoid CB1/CB2 receptor agonist in vitro and in vivo with pronounced neuroprotective efficacy in a rat traumatic brain injury model, showing a therapeutic window of at least 5 h. Furthermore, neuroprotective efficacy was also found in models of transient and permanent occlusion of the middle cerebral artery and brain edema models as well. In this article we review the in vitro and in vivo pharmacology of BAY 38-7271, the results from acute and subacute toxicity studies, pharmacokinetics and drug metabolism in animals and healthy male volunteers. In phase I studies BAY 38-7271 was safe and well tolerated when administered by i.v. infusion for either 1 or 24 h. As the doses of BAY 38-7271 in animals needed for maximal neuroprotective efficacy were significantly lower than those inducing typical cannabinoid-like side effects, it is to be expected that the compound will offer a novel therapeutic approach with a favorable therapeutic window for the treatment of TBI or cerebral ischemia.

Neuroprotective and brain edema-reducing efficacy of the novel cannabinoid receptor agonist BAY 38-7271

BAY 38-7271 is a new high-affinity cannabinoid receptor agonist with strong neuroprotective efficacy in a rat model of traumatic brain injury (acute subdural hematoma, SDH). In the present study we investigated CB1 receptor signal transduction by [35S]GTPgammaS binding in situ and in vitro to assess changes in receptor functionality after SDH. Further, we continued to investigate the neuroprotective properties of BAY 38-7271 in the rat SDH and transient middle cerebral artery occlusion (tMCA-O) model as well as the efficacy with respect to SDH-induced brain edema. [35S]GTPgammaS binding revealed minor attenuation of CB1 receptor functionality on brain membranes from injured hemispheres when compared to non-injured hemispheres or controls. In the rat SDH model, BAY 38-7271 displayed strong neuroprotective efficacy when administered immediately after SDH either as a 1 h (65% infarct volume reduction at 0.1 microg/kg) or short-duration (15 min) infusion (53% at 10 microg/kg). When administered as a 4 h infusion with a 5 h delay after injury, significant neuroprotection was observed (49% at 1.0 microg/kg/h). This was also observed when BAY 38-7271 was administered as a 5 h delayed 15 min short-duration infusion (64% at 3 microg/kg). In addition, the neuroprotective potential of BAY 38-7271 was demonstrated in the rat tMCA-O model, displaying pronounced neuroprotective efficacy in the cerebral cortex (91% at 1 ng/kg/h) and striatum (53% at 10 ng/kg/h). BAY 38-7271 also reduced intracranial pressure (28% at 250 ng/kg/h) and brain water content (20% at 250 ng/kg/h) when determined 24 h post-SDH. Based on these data it is concluded that the neuroprotective efficacy of BAY 38-7271 is mediated by multiple mechanisms triggered by cannabinoid receptors.