title: Functional characterization of AT-1001, an α3β4 nicotinic acetylcholine receptor ligand, at human α3β4 and α4β2 nAChR.
abstract: BACKGROUND
  Genome-wide association studies linking the α3, β4, and α5 nicotinic acetylcholine receptor (nAChR) subunits to nicotine dependence suggest that α3β4* nAChR may be targets for smoking cessation pharmacotherapies. We previously reported that AT-1001, a selective α3β4* nAChR ligand binds with high affinity to rat α3β4 and human α3β4α5 nAChR, antagonizes epibatidine-induced activation of rat α3β4 nAChR in HEK cells and potently inhibits nicotine self-administration in rats.
  
  
  METHODS
  Two-electrode voltage clamp was used for functional characterization of AT-1001 at recombinant human α3β4 and α4β2 nAChR expressed in Xenopus oocytes.
  
  
  RESULTS
  Concentration-response curves show that AT-1001 is a partial agonist at human α3β4 nAChR, evoking up to 35% of the maximal acetylcholine (ACh) response (50% effective concentration [EC50] = 0.37 μM). AT-1001 showed very little agonist activity at the α4β2 nAChR, evoking only 6% of the ACh response (EC50 = 1.5 μM). Pre- and co-application of various concentrations of AT-1001 with 50 μM ACh revealed a complex pattern of activation-inhibition by AT-1001 at α3β4 nAChR, which was best fitted by a 2-site equation. At α4β2 nAChR, co-exposure of AT-1001 with ACh only showed inhibition of ACh current with a shallower curve.
  
  
  CONCLUSIONS
  AT-1001 is a partial agonist at the human α3β4 nAChR and causes desensitization at concentrations at which it evokes an inward current, resulting in an overall functional antagonism of α3β4 nAChR. AT-1001 does not significantly activate or desensitize α4β2 nAChR at the same concentrations as at the α3β4 nAChR, but does inhibit ACh responses at α4β2 nAChR at higher concentrations. A combination of these mechanisms may underlie the inhibition of nicotine self-administration by AT-1001, suggesting that AT-1001 and compounds from this class may have clinical potential for smoking cessation pharmacotherapy.
authors.affiliation: Astraea Therapeutics, Mountain View, CA; nurulain@astraeatherapeutics.com.
authors.forename: Nurulain T
authors.initials: NT
authors.lastname: Zaveri
authors.affiliation: HiQ Screen Sarl, Geneva, Switzerland.
authors.forename: Sonia
authors.initials: S
authors.lastname: Bertrand
authors.affiliation: Astraea Therapeutics, Mountain View, CA;
authors.forename: Dennis
authors.initials: D
authors.lastname: Yasuda
authors.affiliation: HiQ Screen Sarl, Geneva, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bertrand
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D054333:Drug Partial Agonism; D005260:Female; D006801:Humans; D008024:Ligands; D009842:Oligopeptides / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D008024:Ligands; D009842:Oligopeptides; D011978:Receptors, Nicotinic; C577191:alpha3beta4alpha5 receptor, human; C403530:nicotinic receptor alpha3beta4; C403531:nicotinic receptor alpha4beta2; C525167:larazotide acetate