title: In-vivo rat striatal 5-HT4 receptor occupancy using non-radiolabelled SB207145.
abstract: OBJECTIVE
  The objective of the current investigation was to develop a simple, rapid method for determining in-vivo 5-hydroxytryptamine type 4 receptor (5-HT4 R) occupancy in rat brain using non-radiolabelled SB207145 as a tracer for accelerating the drug discovery process.
  
  
  METHODS
  In-vivo tracer optimization studies for tracer dose, survival intervals and brain distribution profile were carried out in rats. The tracer was pharmacologically validated using potent well-characterized 5-HT4 R ligands. The brain regional concentrations of tracer (SB207145); plasma and brain concentrations of 5-HT4 R ligands were quantified using high-performance liquid chromatography coupled with a tandem mass spectrometric detector (LC-MS/MS).
  
  
  RESULTS
  SB207145 showed a higher specific binding in striatum (1.96 ng/g) and lower binding in cerebellum (0.66 ng/g), which is consistent with findings of other published 5-HT4 R expression studies. Pretreatment with potent 5-HT4 ligands dose-dependently reduced striatal SB207145 concentration and the effective dose to achieve 50% receptor occupancy (ED50 ) values were 4.8, 2.0, 7.4, 9.9, 3.8 and 0.02 mg/kg for GR113808, piboserod, prucalopride, RS67333, TD8954 and PF04995274, respectively.
  
  
  CONCLUSIONS
  Results from the mass spectrometry approach to determine 5-HT4 R occupancy in rat brain are comparable with those reported using radiolabelled scintillation spectroscopy methods. In conclusion, the LC-MS/MS characterization permits use of tracer at a preclinical stage in high-throughput fashion as well as characterization of target expression.
authors.affiliation: Pharmacokinetics and Drug Metabolism, Suven Life Sciences Ltd, Hyderabad, India. nvsrk@suven.com
authors.forename: Ramakrishna
authors.initials: R
authors.lastname: Nirogi
authors.forename: Vishwottam
authors.initials: V
authors.lastname: Kandikere
authors.forename: Gopinadh
authors.initials: G
authors.lastname: Bhyrapuneni
authors.forename: Ramanatha
authors.initials: R
authors.lastname: Saralaya
authors.forename: Devender Reddy
authors.initials: DR
authors.lastname: Ajjala
authors.forename: Raghupathi Reddy
authors.initials: RR
authors.lastname: Aleti
authors.forename: Mohammed Abdul
authors.initials: MA
authors.lastname: Rasheed
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D001572:Benzofurans / Q000737:chemistry / Q000494:pharmacology; D001667:Binding, Competitive; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D055808:Drug Discovery / Q000379:methods*; D007211:Indoles / Q000737:chemistry / Q000494:pharmacology; D008024:Ligands; D008297:Male; D010078:Oxazines / Q000737:chemistry / Q000494:pharmacology; D010880:Piperidines / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044422:Receptors, Serotonin, 5-HT4 / Q000378:metabolism*; D017366:Serotonin Receptor Agonists / Q000737:chemistry* / Q000494:pharmacology; D013449:Sulfonamides / Q000737:chemistry / Q000494:pharmacology; D053719:Tandem Mass Spectrometry; D014018:Tissue Distribution
chemical_list: D000814:Aniline Compounds; D001572:Benzofurans; D007211:Indoles; D008024:Ligands; D010078:Oxazines; D010880:Piperidines; C534709:SB 207145; D017366:Serotonin Receptor Agonists; D013449:Sulfonamides; C406662:prucalopride; D044422:Receptors, Serotonin, 5-HT4; C107826:RS 67333; C479132:piboserod; C082871:GR 113808