title: Pre-clinical validation of a novel alpha-7 nicotinic receptor radiotracer, [(3)H]AZ11637326: target localization, biodistribution and ligand occupancy in the rat brain.
abstract: The alpha-7 neuronal nicotinic receptor is a novel pharmacological target for psychiatric and cognitive disorders. Selective radiotracer tools for pre-clinical receptor occupancy can facilitate the interpretation of the biological actions of small molecules at a target receptor. We discovered a high affinity nicotinic alpha-7 subtype-selective ligand, AZ11637326, with physical-chemical and pharmacokinetic properties suitable for an in vivo radioligand tool. [(3)H]AZ11637326 synthesis by tritiodehalogenation of the corresponding tribromide precursor yielded a high specific activity radiotracer with high affinity alpha-7 receptor binding in the rat hippocampus determined by autoradiography (Kd = 0.2 nM). When [(3)H]AZ11637326 was administered to rats by intravenous bolus, rapid uptake was measured in the brain followed by a 3-4 fold greater specific binding in regions containing the alpha-7 receptor (frontal cortex, hippocampus, hypothalamus and midbrain) when compared to non-target regions (striatum and cerebellum). Systemic administration of the high affinity alpha-7 receptor antagonist, methyllycaconitine (MLA), or pretreatment with alpha-7 selective agonists (AR-R17779, PyrQTC, DBCO-4-POM, and DBCO-3-POM) significantly blocked the alpha-7 specific binding of [(3)H]AZ11637326 in the rat brain. The rank order of ligand ED(50) values for in vivo alpha-7 receptor occupancy in rat hippocampus was: DBCO-4-POM > DBCO-3-POM ∼ MLA > PyrQTC > AR-R17779. The occupancy affinity shift was consistent with in vitro binding affinity in autoradiography. Our studies established the optimal conditions for [(3)H]AZ11637326 in vivo specific binding in the rat brain and support the use of [(3)H]AZ11637326 as a pre-clinical tool for assessment of novel alpha-7 compounds in drug discovery.
authors.affiliation: Department of Neuroscience, CNS Discovery, AstraZeneca Pharmaceuticals, Wilmington, DE 19850, USA. dmaier5285@aol.com
authors.forename: Donna L
authors.initials: DL
authors.lastname: Maier
authors.forename: Geraldine
authors.initials: G
authors.lastname: Hill
authors.forename: Min
authors.initials: M
authors.lastname: Ding
authors.forename: David
authors.initials: D
authors.lastname: Tuke
authors.forename: Emily
authors.initials: E
authors.lastname: Einstein
authors.forename: David
authors.initials: D
authors.lastname: Gurley
authors.forename: John C
authors.initials: JC
authors.lastname: Gordon
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Bock
authors.forename: Jeff S
authors.initials: JS
authors.lastname: Smith
authors.forename: Russell
authors.initials: R
authors.lastname: Bialecki
authors.forename: Mark
authors.initials: M
authors.lastname: Eisman
authors.forename: Charles S
authors.initials: CS
authors.lastname: Elmore
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Werkheiser
mesh_terms: D000818:Animals; D053961:Azabicyclo Compounds / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism*; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D016503:Drug Delivery Systems / Q000379:methods*; D004353:Drug Evaluation, Preclinical / Q000379:methods; D008024:Ligands; D008297:Male; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013141:Spiro Compounds / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism*; D014018:Tissue Distribution / Q000187:drug effects / Q000502:physiology; D014316:Tritium / Q000008:administration & dosage / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C555067:5'-(2-fluorophenyl)-spiro(1-azabicyclo(2.2.2)octane-3,2'(3'H)-furo(2,3-b)pyridine); D053961:Azabicyclo Compounds; C579165:Chrna7 protein, rat; D008024:Ligands; D011978:Receptors, Nicotinic; D013141:Spiro Compounds; D064569:alpha7 Nicotinic Acetylcholine Receptor; D014316:Tritium