title: In vivo occupancy of the 5-HT1A receptor by a novel pan 5-HT1(A/B/D) receptor antagonist, GSK588045, using positron emission tomography.
abstract: 5-hydroxytryptamine 1 (5-HT1) receptor blockade in combination with serotonin reuptake inhibition may provide a more rapid elevation of synaptic 5-HT compared to serotonin reuptake alone, by blocking the inhibitory effect of 5-HT1 receptor activation on serotonin release. GSK588045 is a novel compound with antagonist activity at 5-HT1A/1B/1D receptors and nanomolar affinity for the serotonin transporter, which was in development for the treatment of depression and anxiety. Here we present the results of an in vivo assessment of the relationship between plasma exposure and 5-HT1A receptor occupancy. Six Cynomolgus monkeys (Macaca fascicularis) were scanned using the PET ligand [(11)C]WAY100635 before and after dosing with GSK588045 (0.03, 0.1 and 0.3 mg/kg 60 min i.v. infusion). Data was quantified using a simplified reference tissue model, with the cerebellar time-activity curve used as an input function. Plasma levels of GSK588045 were measured, and the EC50 of GSK588045 for 5-HT1A receptor occupancy was estimated. An Emax model described the relationship between the GSK588045 plasma concentration and 5-HT1A receptor occupancy data well. EC50 estimates (and 95% confidence intervals) for raphe nuclei and the frontal cortex were 6.99 (2.48 to 11.49) and 7.80 (2.84 to 12.76) ng/ml respectively. GSK588045 dose dependently blocked the signal of the PET ligand [(11)C]WAY100635, confirming its brain entry and occupancy of 5-HT1A receptors in the primate brain. The estimated EC50 at the post-synaptic heteroreceptors and somatodendritic autoreceptors is similar. 5-HT1 receptor blockade by compounds such as GSK588045 may provide a faster alternate mechanism of antidepressant and anxiolytic action than standard SSRI treatment.
authors.affiliation: Clinical Imaging Centre, GlaxoSmithKline, London, United Kingdom.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Comley
authors.affiliation: Clinical Imaging Centre, GlaxoSmithKline, London, United Kingdom.
authors.forename: Jasper
authors.initials: J
authors.lastname: van der Aart
authors.affiliation: Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
authors.forename: Balázs
authors.initials: B
authors.lastname: Gulyás
authors.affiliation: Psychiatry Centre for Excellence in Drug Discovery, GlaxoSmithKline, Verona, Italy.
authors.forename: Martine
authors.initials: M
authors.lastname: Garnier
authors.affiliation: Psychiatry Centre for Excellence in Drug Discovery, GlaxoSmithKline, Verona, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Iavarone
authors.affiliation: Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
authors.forename: Christer
authors.initials: C
authors.lastname: Halldin
authors.affiliation: Clinical Imaging Centre, GlaxoSmithKline, London, United Kingdom. Electronic address: Ilan.Rabiner@imanova.co.uk.
authors.forename: Eugenii A
authors.initials: EA
authors.lastname: Rabiner
mesh_terms: D000818:Animals; D048588:Benzoxazines / Q000097:blood / Q000493:pharmacokinetics*; D001921:Brain / Q000000981:diagnostic imaging* / Q000187:drug effects*; D001931:Brain Mapping; D004305:Dose-Response Relationship, Drug; D005260:Female; D008252:Macaca fascicularis; D010879:Piperazines / Q000493:pharmacokinetics; D049268:Positron-Emission Tomography; D011485:Protein Binding / Q000187:drug effects; D011725:Pyridines / Q000493:pharmacokinetics; D044282:Receptor, Serotonin, 5-HT1A / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000097:blood / Q000493:pharmacokinetics*; D013997:Time Factors; D014316:Tritium / Q000493:pharmacokinetics
chemical_list: C551960:6-(2-(4-(2-methyl-5-quinolinyl)-1-piperazinyl)ethyl)-4H-imidazo(5,1-c)(1,4)benzoxazine-3-carboxamide; D048588:Benzoxazines; D010879:Piperazines; D011725:Pyridines; D012702:Serotonin Antagonists; D014316:Tritium; D044282:Receptor, Serotonin, 5-HT1A; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide
keywords: 5-HT(1) receptors; Anti-anxiety agents; Antidepressive agents; Drug discovery; Positron emission tomography