CI-1007, a dopamine partial agonist and potential antipsychotic agent. I. Neurochemical effects

T. A. Pugsley, M. D. Davis, H. C. Akunne, L. W. Cooke, S. Z. Whetzel, R. G. Mackenzie, Y. H. Shih, D. H. Van Leeuwen, S. B. Demattos, L. M. Georgic, B. W. Caprathe, J. C. Wright, J. C. Jaen, L. D. Wise, T. G. Heffner

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Abstract

The receptor binding and biochemical effects of the putative dopamine (DA) partial agonist CI-1007 ([R(+)-1,2,3,6-tetrahydro-4-phenyl-1-[(3-phenyl-3- cyclohexen-1-yl)methyl]pyridine] maleate) and potential antipsychotic were evaluated with a variety of biochemical methods. In receptor binding studies, CI-1007 bound to rat striatal DA receptors exhibiting a K(i) of 3 nM as assessed by inhibition of [3H]N-propylnorapomorphine binding. CI-1007 also exhibited high affinity for cloned human D2L (K(i) = 25.5 nM) and D3 (K(i) = 16.6 nM) receptors with less affinity for D4.2 receptors (K(i) = 90.9 nM). The affinity for serotonin-1A (5-HT-1A), alpha-2 adrenergic and 5-HT-2 receptors was moderate (submicromolar range) and slight or negligible for alpha-1, DA D1 and various other receptors. Unlike dopamine, the inhibition of [3H]spiperone binding was monophasic for CI-1007 and only slightly affected by the addition of Gpp-(NH)p. In vitro CI-1007 antagonized the forskolin-induced increases in cyclic AMP levels in GH4C1 cells expressing the human D2L receptor, having an intrinsic activity of 53% of that seen with the full agonist quinpirole. In vivo CI-1007 antagonized the γ-butyrolactone (GBL)-induced accumulation of L-3,4-dihydroxyphenylalanine in striatum and mesolimbic regions of rat brain, causing a maximal 64% reversal in striatum, consistent with a partial agonist profile. In microdialysis studies it decreased DA overflow in both striatum and nucleus accumbens, indicating decreased release of DA. CI-1007 also reduced brain DA synthesis (DOPA accumulation), metabolism (DOPAC and HVA) and utilization (after tyrosine hydroxylase inhibition with α-methyl-p-tyrosine). CI-1007 did not affect striatal acetylcholine levels indicating lack of potent postsynaptic DA actions. CI-1007 seemed to be selective for DA neurons as it did not alter rat brain norepinephrine (NE) synthesis in the NE-enriched brainstem or NE utilization in the mesolimbic region. In addition, it did not affect in general 5-HT synthesis and metabolism in striatum and mesolimbic regions. These neurochemical results demonstrate that CI-1007 is a selective potent brain dopamine partial agonist with limited agonist activity at postsynaptic DA receptors.

Original languageEnglish (US)
Pages (from-to)898-911
Number of pages14
JournalJournal of Pharmacology and Experimental Therapeutics
Volume274
Issue number2
StatePublished - Jan 1 1995

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ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

Cite this

Pugsley, T. A., Davis, M. D., Akunne, H. C., Cooke, L. W., Whetzel, S. Z., Mackenzie, R. G., Shih, Y. H., Van Leeuwen, D. H., Demattos, S. B., Georgic, L. M., Caprathe, B. W., Wright, J. C., Jaen, J. C., Wise, L. D., & Heffner, T. G. (1995). CI-1007, a dopamine partial agonist and potential antipsychotic agent. I. Neurochemical effects. Journal of Pharmacology and Experimental Therapeutics, 274(2), 898-911.