title: Methyllycaconitine: a non-radiolabeled ligand for mapping α7 neuronal nicotinic acetylcholine receptors - in vivo target localization and biodistribution in rat brain.
abstract: BACKGROUND
  Reduction of cerebral cortical and hippocampal α7 neuronal nicotinic acetylcholine receptor (nAChR) density was observed in the Alzheimer's disease (AD) and other neurodegenerative diseases. Mapping the subtypes of nAChRs with selective ligand by viable, quick and consistent method in preclinical drug discovery may lead to rapid development of more effective therapeutic agents. The objective of this study was to evaluate the use of methyllycaconitine (MLA) in non-radiolabeled form for mapping α7 nAChRs in rat brain.
  
  
  METHODS
  MLA pharmacokinetic and brain penetration properties were assessed in male Wistar rats. The tracer properties of MLA were evaluated in rat brain by dose and time dependent differential regional distribution studies. Target specificity was validated after blocking with potent α7 nAChR agonists ABBF, PNU282987 and nicotine. High performance liquid chromatography combined with triple quad mass spectral detector (LC-MS/MS) was used to measure the plasma and brain tissue concentrations of MLA.
  
  
  RESULTS
  MLA has shown rapid brain uptake followed by a 3-5 fold higher specific binding in regions containing the α7 nAChRs (hypothalamus - 1.60 ng/g), when compared to non-specific regions (striatum - 0.53 ng/g, hippocampus - 0.46 ng/g, midbrain - 0.37 ng/g, frontal cortex - 0.35 ng/g and cerebellum - 0.30 ng/g). Pretreatment with potent α7 nAChR agonists significantly blocked the MLA uptake in hypothalamus. The non-radiolabeled MLA binding to brain region was comparable with the α7 mRNA localization and receptor distribution reported for [(3)H] MLA in rat brain.
  
  
  CONCLUSIONS
  The rat pharmacokinetic, brain penetration and differential brain regional distribution features favor that MLA is suitable to use in preclinical stage for mapping α7 nAChRs. Hence, this approach can be employed as an essential tool for quicker development of novel selective ligand to map variation in the α7 receptor densities, as well as to evaluate potential new chemical entities targeting neurodegenerative diseases.
authors.affiliation: Pharmacokinetics and Drug Metabolism, Discovery Research, Suven Life Sciences Ltd, Serene Chambers, Banjara Hills, Hyderabad 500034, 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: Nageswararao
authors.initials: N
authors.lastname: Muddana
authors.forename: Prashanth
authors.initials: P
authors.lastname: Komarneni
mesh_terms: D000157:Aconitine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D001572:Benzofurans / Q000494:pharmacology; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D001643:Bridged Bicyclo Compounds / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008024:Ligands; D008297:Male; D018733:Nicotinic Antagonists / Q000493:pharmacokinetics*; D011812:Quinuclidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011978:Receptors, Nicotinic / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: D001549:Benzamides; D001572:Benzofurans; D001643:Bridged Bicyclo Compounds; C579165:Chrna7 protein, rat; D008024:Ligands; C520027:N-(1-azabicyclo(2.2.2)oct-3-yl)-7-(2-(methoxy)phenyl)-1-benzofuran-2-carboxamide; D018733:Nicotinic Antagonists; C498513:PNU-282987; D011812:Quinuclidines; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C054634:methyllycaconitine; D000157:Aconitine