Inverse agonist properties of N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide HCl (SR141716A) and 1-(2-chlorophenyl)-4-cyano-5-(4-methoxypheny-1H-pyrazole-3-carboxylic acid phenylamide (CP-272871) for the CB1 cannabinoid receptor

Two subtypes of cannabinoid receptors are currently recognized, CB1, found in brain and neuronal cells, and CB2, found in spleen and immune cells. We have characterized 1-(2-chlorophenyl)-4-cyano-5-(4-methoxyphenyl)-1H-pyrazole-3-carboxylic acid phenylamide (CP-272871) as a novel aryl pyrazole antagonist for the CB1 receptor. CP-272871 competed for binding of the cannabinoid agonist H-3-labeled (-)-3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]-4-[3-hydroxypropyl]cyclohexan-1-ol ([H-3]CP-55940) at the CB1 receptor in rat brain membranes with a K-d value 20-fold greater than that of N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-3-carboxamide HCl (SR141716A). CP-272871 also competed for binding with the aminoalkylindole agonist H-3-labeled (R)-(+)-[2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrrolo[1,2,3-de]1,4-benzoxazin-6-yl] (1-naphthyl)methanone ([H-3]WIN-55212-2), as well as the aryl pyrazole antagonist [H-3]SR141716A. Inverse agonist as well as antagonist properties were observed for both SR141716A and CP-272871 in signal transduction assays in biological preparations in which the CB1 receptor is endogenously expressed. SR141716A augmented secretin-stimulated cyclic AMP (cAMP) accumulation in intact N18TG2 neuroblastoma cells, and this response was reversed by the agonist desacetyllevonantradol. CP-272871 antagonized desacetyllevonantradol-mediated inhibition of adenylyl cyclase in N18TG2 membranes, and increased adenylyl cyclase activity in the absence of agonist. SR141716A and CP-212871 antagonized desacetyllevonantradol-stimulated S-35-labeled guanosine-5'-O-(gamma-thio)-triphosphate ([S-35]GTP gamma S)] binding to brain membrane G-proteins, and decreased basal [S-35]GTP gamma S binding to G-proteins. K+ enhanced CP-272871 and SR141716A inverse agonist activity compared with Na+ or NMDG(+) in the assay. These results demonstrated that the aryl pyrazoles SR141716A and CP-272871 behave as antagonists and as inverse agonists in G-protein-mediated signal transduction in preparations of endogenously expressed CB1 receptors, (C) 2000 Elsevier Science Inc.