title: Characterization of three diaminopyrimidines as potent and selective antagonists of P2X3 and P2X2/3 receptors with in vivo efficacy in a pain model.
abstract: OBJECTIVE
  P2X3 and P2X2/3 receptors are highly localized on the peripheral and central pathways of nociceptive signal transmission. The discovery of A-317491 allowed their validation as chronic inflammatory and neuropathic pain targets, but this molecule has a very limited oral bioavailability and CNS penetration. Recently, potent P2X3 and P2X2/3 blockers with a diaminopyrimidine core group and better bioavailability were synthesized and represent a new opportunity for the validation of P2X3-containing receptors as targets for pain. Here we present a characterization of three representative diaminopyrimidines.
  
  
  METHODS
  The activity of compounds was evaluated in intracellular calcium flux and electrophysiological recordings from P2X receptors expressed in mammalian cells and in a in vivo model of inflammatory pain (complete Freund's adjuvant (CFA) in rat paws).
  
  
  RESULTS
  Compound A potently blocked P2X3 (pIC(50)= 7.39) and P2X2/3 (pIC(50)=6.68) and showed no detectable activity at P2X1, P2X2, P2X4 and P2X7 receptors (pIC(50)< 4.7). Whole-cell voltage clamp electrophysiology confirmed these results. Compounds showed good selectivities when tested against a panel of different classes of target. In the CFA model, compound B showed significant anti-nociceptive effects (57% reversal at 3mg·kg(-1) ).
  
  
  CONCLUSIONS
  The diaminopyrimidines were potent and selective P2X3 and P2X2/3 receptor antagonists, showing efficacy in vivo and represent useful tools to validate these receptors as targets for inflammatory and neuropathic pain and provide promising progress in the identification of therapeutic tools for the treatment of pain-related disorders.
authors.affiliation: GlaxoSmithKline, Molecular Discovery Research, Verona, Italy. elisa.ballini@aptuit.com
authors.forename: E
authors.initials: E
authors.lastname: Ballini
authors.forename: C
authors.initials: C
authors.lastname: Virginio
authors.forename: S J
authors.initials: SJ
authors.lastname: Medhurst
authors.forename: S G
authors.initials: SG
authors.lastname: Summerfield
authors.forename: L
authors.initials: L
authors.lastname: Aldegheri
authors.forename: A
authors.initials: A
authors.lastname: Buson
authors.forename: C
authors.initials: C
authors.lastname: Carignani
authors.forename: Y H
authors.initials: YH
authors.lastname: Chen
authors.forename: A
authors.initials: A
authors.lastname: Giacometti
authors.forename: I
authors.initials: I
authors.lastname: Lago
authors.forename: A J
authors.initials: AJ
authors.lastname: Powell
authors.forename: W
authors.initials: W
authors.lastname: Jarolimek
mesh_terms: D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007249:Inflammation / Q000139:chemically induced / Q000188:drug therapy; D015394:Molecular Structure; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy*; D058920:Purinergic P2X Receptor Antagonists / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D011743:Pyrimidines / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D051381:Rats
chemical_list: D058920:Purinergic P2X Receptor Antagonists; D011743:Pyrimidines