NGD 94-1

II. Localization and characterization of dopamine D4 binding sites in rat and human brain by use of the novel, D4 receptor-selective ligand [3H]NGD 94-1.[Pubmed:9262371]

J Pharmacol Exp Ther. 1997 Aug;282(2):1020-7.

The dopamine D4 selective ligand, [H]NGD 94-1, was used in these studies to characterize binding sites in rat and human brain tissue by membrane binding and autoradiography techniques. Autoradiographic analysis of rat brain showed that specific [3H]NGD 94-1 binding was greatest in entorhinal cortex, lateral septal nucleus, hippocampus and the medial preoptic area of the hypothalamus. This nonstriatal distribution of [3H]NGD 94-1 binding was distinct from the autoradiographic distribution of dopamine D2 and D3 receptor subtypes. In homogenate preparations from rat brain regions, [3H]NGD 94-1 binding sites were low in density (<30.0 fmol/mg protein). The low density of D4 binding sites was corroborated by autoradiographic comparisons in which binding density for D4 receptors as measured by [3H]NGD 94-1 was only 1/7 of D2 and 1/5 of D3 receptor densities, despite corrections for differing radioligand binding characteristics. Pharmacological evaluation showed high affinity at rat [3H]NGD 94-1 binding sites for compounds with known D4 receptor affinity and little displacement by compounds with affinity for dopamine D1/D2/D3 receptor subtypes. Specific, high-affinity [3H]NGD 94-1 binding was also present in several human brain regions, including hippocampus, hypothalamus, dorsal medial thalamus, entorhinal cortex, prefrontal cortex and lateral septal nucleus. High-affinity [3H]NGD 94-1 binding was not present in any human striatal region examined. The pharmacological profile of [3H]NGD 94-1 binding sites in human brain was consistent with that previously demonstrated for cloned human D4 receptors expressed in mammalian cells. These findings suggest that specific, high-affinity [3H]NGD 94-1 binding exists in rat and human brain and that these sites reflect populations of dopamine D4 receptors with a distribution unique among dopamine receptor subtypes.

Direct determination of dopamine D4 receptors in normal and schizophrenic postmortem brain tissue: a [3H]NGD-94-1 study.[Pubmed:9857979]

Mol Psychiatry. 1998 Nov;3(6):528-33.

Using an indirect subtraction binding technique and human postmortem tissue, several laboratories reported finding increases in dopamine D4 receptors in caudate nuclei of schizophrenic patients, although others have not replicated these findings. NGD-94-1 is a selective D4 antagonist with low affinity for the D2 and D3 receptors. [3H]NGD-94-1 has been used in this study to directly determine the density of D4 receptors in normals (n = 13) and schizophrenic subjects (n = 7) off antipsychotic drugs for at least 3 months prior to death, or on antipsychotic (n = 7) drugs at the time of death. Human postmortem coronal brain sections were incubated with [3H]NGD-94-1 and autoradiograms developed; and binding in pertinent regions was quantified. In normals, the highest density of [3H]NGD-94-1 binding was in the hippocampus (68 fmol mg(-1), temporal (33), insular (30), and entorhinal cortices (24.9). Significant increases in [3H]NGD-94-1 density in schizophrenics (n = 14) vs normals (n = 13) were observed in the entorhinal cortex (46%) at both low and high magnifications. The increases observed in the schizophrenics were found in both schizophrenics off antipsychotic drugs for at least 3 months prior to death and those on antipsychotic drugs at the time of death. Thus, the changes may be disease-related and not a consequence of pharmacological treatment. No significant differences were found between the two schizophrenic groups in any brain area studied.

NGD 94-1 as an agonist at human recombinant dopamine D4.4 receptors expressed in HEK293 cells.[Pubmed:10395031]

Eur J Pharmacol. 1999 May 21;372(3):R9-10.

The atypical antipsychotic, clozapine has some selectivity for dopamine D4 receptors and is a silent antagonist at these receptors. NGD 94-1 (2-phenyl-4(5)-[4-(2-pyrimidinyl)-piperazin-1-yl-methyl]-imidazole ) is a highly selective dopamine D4 receptor ligand recently introduced as a putative antipsychotic mimicking the dopamine D4 receptor antagonist effects of clozapine. We show that NGD 94-1 is not silent. It behaved as an agonist in human embryonic kidney 293 cells expressing human recombinant dopamine D4.4 receptors. This questions the clinical use of NGD 94-1.

I. NGD 94-1: identification of a novel, high-affinity antagonist at the human dopamine D4 receptor.[Pubmed:9262370]

J Pharmacol Exp Ther. 1997 Aug;282(2):1011-9.

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.