title: CB(1) receptor allosteric modulators display both agonist and signaling pathway specificity.
abstract: We have previously identified allosteric modulators of the cannabinoid CB(1) receptor (Org 27569, PSNCBAM-1) that display a contradictory pharmacological profile: increasing the specific binding of the CB(1) receptor agonist [(3)H]CP55940 but producing a decrease in CB(1) receptor agonist efficacy. Here we investigated the effect one or both compounds in a broad range of signaling endpoints linked to CB(1) receptor activation. We assessed the effect of these compounds on CB(1) receptor agonist-induced [(35)S]GTPγS binding, inhibition, and stimulation of forskolin-stimulated cAMP production, phosphorylation of extracellular signal-regulated kinases (ERK), and β-arrestin recruitment. We also investigated the effect of these allosteric modulators on CB(1) agonist binding kinetics. Both compounds display ligand dependence, being significantly more potent as modulators of CP55940 signaling as compared with WIN55212 and having little effect on [(3)H]WIN55212 binding. Org 27569 displays biased antagonism whereby it inhibits: agonist-induced guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPγS) binding, simulation (Gα(s)-mediated), and inhibition (Gα(i)-mediated) of cAMP production and β-arrestin recruitment. In contrast, it acts as an enhancer of agonist-induced ERK phosphorylation. Alone, the compound can act also as an allosteric agonist, increasing cAMP production and ERK phosphorylation. We find that in both saturation and kinetic-binding experiments, the Org 27569 and PSNCBAM-1 appeared to influence only orthosteric ligand maximum occupancy rather than affinity. The data indicate that the allosteric modulators share a common mechanism whereby they increase available high-affinity CB(1) agonist binding sites. The receptor conformation stabilized by the allosterics appears to induce signaling and also selectively traffics orthosteric agonist signaling via the ERK phosphorylation pathway.
authors.affiliation: School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom.
authors.forename: Gemma L
authors.initials: GL
authors.lastname: Baillie
authors.forename: James G
authors.initials: JG
authors.lastname: Horswill
authors.forename: Sharon
authors.initials: S
authors.lastname: Anavi-Goffer
authors.forename: Patricia H
authors.initials: PH
authors.lastname: Reggio
authors.forename: Daniele
authors.initials: D
authors.lastname: Bolognini
authors.forename: Mary E
authors.initials: ME
authors.lastname: Abood
authors.forename: Sean
authors.initials: S
authors.lastname: McAllister
authors.forename: Phillip G
authors.initials: PG
authors.lastname: Strange
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Stephens
authors.forename: Roger G
authors.initials: RG
authors.lastname: Pertwee
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Ross
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects*; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D048588:Benzoxazines / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D016466:CHO Cells; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D003511:Cyclohexanols / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D010880:Piperidines / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists* / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D000071557:beta-Arrestins
chemical_list: C572504:5-chloro-3-ethyl-1H-indole-2-carboxylic acid (2-(4-piperidin-1-yl-phenyl)ethyl)amide; D019390:Arrestins; D048588:Benzoxazines; D003511:Cyclohexanols; D007211:Indoles; D008024:Ligands; D009025:Morpholines; D009281:Naphthalenes; D010880:Piperidines; D043884:Receptor, Cannabinoid, CB1; D000071557:beta-Arrestins; D005576:Colforsin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; C054649:3-(2-hydroxy-4-(1,1-dimethylheptyl)phenyl)-4-(3-hydroxypropyl)cyclohexanol; D000242:Cyclic AMP