title: Pharmacological characterization of the cannabinoid CB₁ receptor PET ligand ortholog, [³H]MePPEP.
abstract: MePPEP ((3R,5R)-5-(3-methoxy-phenyl)-3-((R)-1-phenyl-ethylamino)-1-(4-trifluoromethyl-phenyl)-pyrrolidin-2-one) is an inverse agonist shown to be an effective PET ligand for labeling cannabinoid CB₁ receptors in vivo. [¹¹C]MePPEP and structurally related analogs have been reported to specifically and reversibly label cannabinoid CB₁ receptors in rat and non-human primate brains, and [¹¹C]MePPEP has been used in human subjects as a PET tracer. We have generated [³H]MePPEP, an ortholog of [¹¹C]MePPEP, to characterize the molecular pharmacology of the cannabinoid CB₁ receptor across preclinical and clinical species. [³H]MePPEP demonstrates saturable, reversible, and single-site high affinity binding to cannabinoid CB₁ receptors. In cerebellar membranes purified from brains of rat, non-human primate and human, and cells ectopically expressing recombinant human cannabinoid CB₁ receptor, [³H]MePPEP binds cannabinoid CB₁ receptors with similar affinity with K(d) values of 0.09 nM, 0.19 nM, 0.14 nM and 0.16 nM, respectively. Both agonist and antagonist cannabinoid ligands compete [³H]MePPEP with predicted rank order potency. No specific binding is present in autoradiographic sections from cannabinoid CB₁ receptor knockout mouse brains, demonstrating that [³H]MePPEP selectively binds cannabinoid CB₁ receptors in native mouse tissue. Furthermore, [³H]MePPEP binding to anatomical sites in mouse and rat brain is comparable to the anatomical profiles of [¹¹C]MePPEP in non-human primate and human brain in vivo, as well as the binding profiles of other previously described cannabinoid CB₁ receptor agonist and antagonist radioligands. Therefore, [³H]MePPEP is a promising tool for translation of preclinical cannabinoid CB₁ receptor pharmacology to clinical PET ligand and cannabinoid CB₁ receptor inverse agonist therapeutic development.
authors.affiliation: Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, Indiana 46285, USA.
authors.forename: Todd M
authors.initials: TM
authors.lastname: Suter
authors.forename: Amy K
authors.initials: AK
authors.lastname: Chesterfield
authors.forename: Chun
authors.initials: C
authors.lastname: Bao
authors.forename: John M
authors.initials: JM
authors.lastname: Schaus
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Krushinski
authors.forename: Michael A
authors.initials: MA
authors.lastname: Statnick
authors.forename: Christian C
authors.initials: CC
authors.lastname: Felder
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002186:Cannabinoids / Q000819:agonists* / Q000037:antagonists & inhibitors; D002531:Cerebellum / Q000033:anatomy & histology / Q000378:metabolism; D054314:Drug Inverse Agonism; D006801:Humans; D008024:Ligands; D008253:Macaca mulatta; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D049268:Positron-Emission Tomography / Q000379:methods; D011760:Pyrrolidinones / Q000378:metabolism* / Q000493:pharmacokinetics; D011849:Radioactive Tracers; D051381:Rats; D043884:Receptor, Cannabinoid, CB1 / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014018:Tissue Distribution; D014316:Tritium
chemical_list: C526255:5-(3-methoxyphenyl)-3-(1-phenylethylamino)-1-(4-trifluoromethylphenyl)pyrrolidin-2-one; D002186:Cannabinoids; D008024:Ligands; D009419:Nerve Tissue Proteins; D011760:Pyrrolidinones; D011849:Radioactive Tracers; D043884:Receptor, Cannabinoid, CB1; D011994:Recombinant Proteins; D014316:Tritium