NGD-94-1 - IDENTIFICATION OF A NOVEL, HIGH-AFFINITY ANTAGONIST AT THEHUMAN DOPAMINE-D-4 RECEPTOR .1.

NGD 94-1 was evaluated for selectivity and in vitro functional activit y at the recombinant human D-4.2 receptor stably expressed in Chinese hamster ovary cells, NGD 94-1 showed high affinity for the cloned huma n D-4.2 receptor (K-i = 3.6 +/- 0.6 nM) and had greater than 600-fold selectivity for the D-4.2 receptor subtype compared with a wide variet y of monoamine or other neurotransmitter receptor or modulatory sites except for 5-HT1A and 5-HT3 receptors, in which NGD 94-1 was approxima tely 50- and 200-fold selective, respectively, for the D-4.2 receptor, In measures of in vitro functional activity, NGD 94-1 showed an antag onist profile at the cloned human D-4.2 receptor subtype, NGD 94-1 com pletely reversed the decrease in forskolin-stimulated cAMP levels prod uced by the dopamine receptor full agonist quinpirole, Furthermore, NG D 94-1 produced a complete reversal of GTP gamma(35)S binding induced by quinpirole, but was unable on its own to affect GTP gamma(35)S bind ing, These data suggest that NGD 94-1 functions as an antagonist rathe r than a full or partial agonist at the human D-4.2 receptor, In addit ion, NGD 94-1 binding affinity at the D-4.2 receptor subtype was unaff ected by G-protein activation by GTP, consistent with the binding affi nity seen for other antagonists at the D-4 receptor, The binding of tr itiated NGD 94-1 was saturable and of high affinity at cloned human D- 4.2 receptors, Furthermore, the binding of [H-3]NGD 94-1 to cloned hum an D-4.2 receptors expressed in Chinese hamster ovary cells displayed a pharmacological profile similar to that observed with the nonselecti ve dopamine receptor ligand [H-3]YM 09151-2, Saturation and pharmacolo gical analyses of [H-3]NGD 94-1 binding at cloned human D-4.2, D-4.4 a nd D-4.7 receptor variants showed no difference between the three vari ants, NGD 94-1 is a novel, high-affinity, D-4 receptor-selective antag onist, The clinical use of this subtype-specific compound should permi t direct evaluation of the role of D-4 receptors in psychiatric disord ers.