[3H] A-369508 ([2-[4-(2-cyanophenyl)-1-piperazinyl]-N-(3-methylphenyl) acetamide): an agonist radioligand selective for the dopamine D4 receptor

Eur J Pharmacol. 2004 Aug 23;497(2):147-54. doi: 10.1016/j.ejphar.2004.06.049.


Tritiation of the dopamine D(4) receptor selective agonist A-369508 ([2-[4-(2-cyanophenyl)-1-piperazinyl]-N-(3-methylphenyl) acetamide) has provided a radioligand for the characterization of dopamine D(4) receptors. [(3)H] A-369508 binds with high affinity to the major human dopamine D(4) receptor variants D(4.2), D(4.4) and D(4.7) (K(d)=1.7, 4, and 1.2 nM, respectively). It also binds to the rat dopamine D(4) receptor, (K(d)=4.4 nM), implying similar binding affinity across human and rat receptors. A-369508 shows >400-fold selectivity over D(2L), >350-fold selectivity over 5-HT(1A) and >700-1,000-fold selectivity over all other receptors tested. Agonist activity determined by inhibition of forskolin-induced cAMP in Chinese hamster ovary cells transfected with the human dopamine D(4.4) receptor (EC(50)=7.5 nM, intrinsic activity=0.71) indicates that A-369508 is a potent agonist at the human dopamine D(4) receptor. Similar data was observed in other functional assays. [(3)H] A-369508 binds to a single, high affinity site on membranes containing the human dopamine D(4.4) receptor. When compared to the D(2)-like antagonist [(3)H] spiperone, competition binding for agonists like dopamine and apomorphine were 2-10-fold more potent with [(3)H] A-369508, while the antagonists clozapine, haloperidol and L-745870 bind with similar affinity to both ligands. Binding to rat brain regions demonstrated that the most abundant area was cerebral cortex (51.2 fmol/mg protein) followed by hypothalamus, hippocampus, striatum and cerebellum. [(3)H] A-369508 is a useful tool to define the localization and physiological role of dopamine D(4) receptors in central nervous system and can facilitate measuring accurate affinities (K(i)) for structure/activity relationship studies designed to identify dopamine D(4) receptor selective agonists.

MeSH terms

  • Acetamides / chemistry*
  • Acetamides / metabolism
  • Animals
  • CHO Cells
  • Cell Line
  • Cricetinae
  • Dopamine Agonists / chemistry
  • Dopamine Agonists / metabolism*
  • Dose-Response Relationship, Drug
  • Humans
  • Ligands
  • Piperazines / chemistry*
  • Piperazines / metabolism
  • Radioligand Assay / methods*
  • Rats
  • Receptors, Dopamine D2 / agonists*
  • Receptors, Dopamine D2 / metabolism*
  • Receptors, Dopamine D4
  • Tritium


  • 2-(4-(2-cyanophenyl)-1-piperazinyl)-N-(3-methylphenyl) acetamide
  • Acetamides
  • DRD4 protein, human
  • Dopamine Agonists
  • Drd4 protein, rat
  • Ligands
  • Piperazines
  • Receptors, Dopamine D2
  • Tritium
  • Receptors, Dopamine D4