Novel CB2 selective cannabinoids and inhibitors of endocannabinoid deactivation

Δ9-Tetrahydrocannabinol (Δ9-THC), a major psychoactive constituent of marijuana is known to exert a variety of pharmacological effects on laboratory animals and humans, through the activation of CB1 and CB2 receptors, which are considered attractive targets in the design of therapeutic agents. However, psychoactive effects and abuse potential have discouraged the therapeutic of use Δ9-THC in modern medicine. The deleterious effects of Δ9-THC have been correlated with direct CB1 activation. There are two possible approaches to eliminate these undesired effects. One approach is to design and synthesize high affinity ligands exhibiting CB2 receptor sub-type selectivity, thus eliminating direct CB1 activation. The second approach is by inhibiting rapid degradation of the major endogenous cannabinoids, N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG) by fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL), respectively, such that CB receptors may be indirectly stimulated through the enhanced levels of the endogenous compounds. Both of these methods have been investigated: (1) by pursuing structure-activity relationship (SAR) studies of bicyclic and tricyclic cannabinoids, biphenyl cannabinoids, and cannabilactones to explore the active site within the CB2 receptor, as well as designing and synthesizing CB2 selective covalent binding probes that may be used to map the receptor-binding site; and, (2) by pursuing the SAR studies of sulfonyl fluorides, biphenyltrifluoromethyl ketones, saccharinyl analogs, and &agr;-ketoheterocycles to explore the active site of the inhibitors of endocannabinoid deactivating proteins. ^ Binding affinities of ligands for rat CB1 and mouse CB2 were determined and selectivity evaluated. Further binding affinity studies on the cloned human CB2 were performed for ligands exhibiting high affinity in the mouse CB2 receptor assay. These studies have led to the development of high affinity ligands and have assisted our understanding the factors that lead to CB2 selectivity. In addition, IC50 values for novel inhibitors of the endocannabinoid deactivating proteins (FAAH and MGL) were determined and selectivity evaluated. This has led to the development FAAH selective inhibitors. These compounds will function as molecular probes to explore cannabiniod receptor action and may find use as therapeutic agents.

C1′-cycloalkyl side chain pharmacophore in tetrahydrocannabinols

In earlier work we have provided evidence for the presence of a subsite within the CB1 and CB2 cannabinoid receptor binding domains of classical cannabinoids. This putative subsite corresponds to substituents on the C1-position of the C3-alkyl side chain, a key pharmacophoric feature in this class of compounds. We have now refined this work through the synthesis of additional C1′-cycloalkyl compounds using newly developed approaches. Our findings indicate that the C1′-cyclopropyl and C1′-cyclopentyl groups are optimal pharmacophores for both receptors while the C1′-cyclobutyl group interacts optimally with CB1 but not with CB2. The C1′-cyclohexyl analogs have reduced affinities for both CB1 and CB2. However, these affinities are significantly improved with the introduction of a C2′-C3′ cis double bond that modifies the available conformational space within the side chain and allows for a better accommodation of a six-membered ring within the side chain subsite. Our SAR results are highlighted by molecular modeling of key analogs. © 2007 American Chemical Society

Effects of fatty acid amide hydrolase (FAAH) inhibitors on working memory in rats.

RationaleManipulations of the endocannabinoid system could potentially produce therapeutic effects with minimal risk of adverse cannabis-like side effects. Inhibitors of fatty acid amide hydrolase (FAAH) increase endogenous levels of the cannabinoid-receptor agonist, anandamide, and show promise for treating a wide range of disorders. However, their effects on learning and memory have not been fully characterized.ObjectivesWe determined the effects of five structurally different FAAH inhibitors in an animal model of working memory known to be sensitive to impairment by delta-9 tetrahydrocannabinol (THC).MethodsA delayed nonmatching-to-position procedure was used in rats. Illuminated nosepoke holes were used to provide sample cues (left versus right) and record responses (correct versus incorrect) after delays ranging from 0 to 28 s. Various test drugs were given acutely up to two times per week before daily sessions.ResultsOne FAAH inhibitor, AM3506 (3 mg/kg), decreased accuracy in the memory task. Four other FAAH inhibitors (URB597, URB694, PF-04457845, and ARN14633) and a monoacylglycerol lipase inhibitor (JZL184, which blocks the degradation of the endocannabinoid 2-arachidonoylglycerol) had no effect. Testing of AM3506 in combination with antagonists for receptors known to be affected by anandamide and other fatty acid amides indicated that the impairment induced by AM3506 was mediated by cannabinoid CB1 receptors, and not by alpha-type peroxisome proliferator-activated receptors (PPAR-alpha) or vanilloid transient receptor potential cation channels (TRPV1).ConclusionsFAAH inhibitors differ with respect to their potential for memory impairment, abuse liability, and probably other cannabis-like effects, and they should be evaluated individually for specific therapeutic and adverse effects

Effects of fatty acid amide hydrolase (FAAH) inhibitors on working memory in rats.

RationaleManipulations of the endocannabinoid system could potentially produce therapeutic effects with minimal risk of adverse cannabis-like side effects. Inhibitors of fatty acid amide hydrolase (FAAH) increase endogenous levels of the cannabinoid-receptor agonist, anandamide, and show promise for treating a wide range of disorders. However, their effects on learning and memory have not been fully characterized.ObjectivesWe determined the effects of five structurally different FAAH inhibitors in an animal model of working memory known to be sensitive to impairment by delta-9 tetrahydrocannabinol (THC).MethodsA delayed nonmatching-to-position procedure was used in rats. Illuminated nosepoke holes were used to provide sample cues (left versus right) and record responses (correct versus incorrect) after delays ranging from 0 to 28 s. Various test drugs were given acutely up to two times per week before daily sessions.ResultsOne FAAH inhibitor, AM3506 (3 mg/kg), decreased accuracy in the memory task. Four other FAAH inhibitors (URB597, URB694, PF-04457845, and ARN14633) and a monoacylglycerol lipase inhibitor (JZL184, which blocks the degradation of the endocannabinoid 2-arachidonoylglycerol) had no effect. Testing of AM3506 in combination with antagonists for receptors known to be affected by anandamide and other fatty acid amides indicated that the impairment induced by AM3506 was mediated by cannabinoid CB1 receptors, and not by alpha-type peroxisome proliferator-activated receptors (PPAR-alpha) or vanilloid transient receptor potential cation channels (TRPV1).ConclusionsFAAH inhibitors differ with respect to their potential for memory impairment, abuse liability, and probably other cannabis-like effects, and they should be evaluated individually for specific therapeutic and adverse effects