I. NGD 94-1: identification of a novel, high-affinity antagonist at the human dopamine D4 receptor.
NGD 94-1 was evaluated for selectivity and in vitro functional activity at the recombinant human D4.2 receptor stably expressed in Chinese hamster ovary cells. NGD 94-1 showed high affinity for the cloned human D4.2 receptor (Ki = 3.6 +/- 0.6 nM) and had greater than 600-fold selectivity for the D4.2 receptor subtype compared with a wide variety of monoamine or other neurotransmitter receptor or modulatory sites except for 5-HT1A and 5-HT3 receptors, in which NGD 94-1 was approximately 50- and 200-fold selective, respectively, for the D4.2 receptor. In measures of in vitro functional activity, NGD 94-1 showed an antagonist profile at the cloned human D4.2 receptor subtype. NGD 94-1 completely reversed the decrease in forskolin-stimulated cAMP levels produced by the dopamine receptor full agonist quinpirole. Furthermore, NGD 94-1 produced a complete reversal of GTPgamma35S binding induced by quinpirole, but was unable on its own to affect GTPgamma35S binding. These data suggest that NGD 94-1 functions as an antagonist rather than a full or partial agonist at the human D4.2 receptor. In addition, NGD 94-1 binding affinity at the D4.2 receptor subtype was unaffected by G-protein activation by GTP, consistent with the binding affinity seen for other antagonists at the D4 receptor. The binding of tritiated NGD 94-1 was saturable and of high affinity at cloned human D4.2 receptors. Furthermore, the binding of [3H]NGD 94-1 to cloned human D4.2 receptors expressed in Chinese hamster ovary cells displayed a pharmacological profile similar to that observed with the nonselective dopamine receptor ligand [3H]YM 09151-2. Saturation and pharmacological analyses of [3H]NGD 94-1 binding at cloned human D4.2, D4.4 and D4.7 receptor variants showed no difference between the three variants. NGD 94-1 is a novel, high-affinity, D4 receptor-selective antagonist. The clinical use of this subtype-specific compound should permit direct evaluation of the role of D4 receptors in psychiatric disorders.
Tallman
J F
JF
Neurogen Corporation, Branford, Connecticut 06405, USA.
Primus
R J
RJ
Brodbeck
R
R
Cornfield
L
L
Meade
R
R
Woodruff
K
K
Ross
P
P
Thurkauf
A
A
Gallager
D W
DW
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D018492:Dopamine Antagonists / Q000378:metabolism / Q000494:pharmacology*; D065127:Dopamine D2 Receptor Antagonists; D019204:GTP-Binding Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000378:metabolism / Q000494:pharmacology*; D011743:Pyrimidines / Q000378:metabolism / Q000494:pharmacology*; D011869:Radioligand Assay; D017448:Receptors, Dopamine D2 / Q000235:genetics; D050638:Receptors, Dopamine D4; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D013045:Species Specificity; D014316:Tritium
C493599:DRD4 protein, human; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D007093:Imidazoles; D011743:Pyrimidines; D017448:Receptors, Dopamine D2; D011994:Recombinant Proteins; D014316:Tritium; D050638:Receptors, Dopamine D4; C107692:NGD 94-1; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins