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Cyclic Cholecystokinin Analogues with High Selectivity for Central Receptors

Bruno Charpentier, Didier Pelaprat, Christiane Durieux, Adeline Dor, Michel Reibaud, Jean-Charles Blanchard and Bernard P. Roques
Proceedings of the National Academy of Sciences of the United States of America
Vol. 85, No. 6 (Mar. 15, 1988), pp. 1968-1972
Stable URL: http://www.jstor.org/stable/31429
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Cyclic Cholecystokinin Analogues with High Selectivity for Central Receptors
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Abstract

Taking as a model the N-terminal folding of the cholecystokinin tyrosine-sulfated octapeptide [CCK-8; Asp-Tyr-(SO3H)-Met-Gly-Trp-Met-Asp-Phe-NH$_{2}$] deduced from conformational studies, two cyclic cholecystokinin (CCK) analogues were synthesized by conventional peptide synthesis: Boc-D-A$\overline{\text{sp-Tyr-(SO}_{3}\text{H)-Ahx-D-Ly}}$s -Trp-Ahx-Asp-Phe-NH2 [compound I (Ahx, 2-aminohexanoic acid)] and Boc-γ -D-G$\overline{\text{lu-Tyr(SO}_{3}\text{H)-Ahx-D-Ly}}$s-Trp-Ahx-Asp-Phe-NH2 (compound II). The binding characteristics of these peptides were investigated on brain cortex membranes and pancreatic acini of guinea pig. Compounds I and II were competitive inhibitors of [3H]Boc[Ahx28,31]CCK-(27-33) binding to central CCK receptors and showed a high degree of selectivity for these binding sites (compound I: Ki for pancreas/Ki for brain, 179; compound II: Ki for pancreas/Ki for brain, 1979). This high selectivity was associated with a high affinity for central CCK receptors (compound I: Ki, 5.1 nM; compound II: Ki, 0.49 nM). Similar affinities and selectivities were found when 125I Bolton-Hunter-labeled CCK-8 was used as a ligand. Moreover, these compounds were only weakly active in the stimulation of amylase release from guinea pig pancreatic acini (EC50 > 10,000 nM) and were unable to induce contractions in the guinea pig ileum (to 10-6 M). The two cyclic CCK analogues, therefore, appear to be synthetic ligands exhibiting both high affinity and high selectivity for central CCK binding sites. These compounds could help clarify the respective role of central and peripheral receptors for various CCK-8-induced pharmacological effects.

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