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MOLECULAR PHARMACOLOGY 52:741-748 (1997).

Structural Analogues of D-myo-Inositol-1,4,5-trisphosphate and Adenophostin A: Recognition by Cerebellar and Platelet Inositol-1,4,5-trisphosphate Receptors

C. T. Murphy, A. M. Riley, C. J. Lindley, D. J. Jenkins, J. Westwick, and B. V. L. Potter

Departments of Pharmacology (C.T.M., C.J.L., J.W.) and Medicinal Chemistry (A.M.R., D.J.J., B.V.L.P.), School of Pharmacy and Pharmacology, University of Bath, Bath, Avon, BA2 7AY, UK

Adenophostins A and B, which are metabolic products of the fungus Penicillium brevicompactum, are potent agonists at the D-myo-inositol-1,4,5-trisphosphate [Ins(1,4,5)P₃] receptor. In the current study, adenophostin A was ~50-fold more potent than Ins(1,4,5)P₃ at both releasing Ca²⁺ from the intracellular stores of permeabilized platelets and displacing [³H]Ins(1,4,5)P₃ from its receptor on rat cerebellar membranes. Various analogues bearing structural features found in the adenophostins and/or Ins(1,4,5)P₃ were examined to elucidate the molecular basis for the observed enhanced potency. 2-AMP did not induce Ca²⁺ release from permeabilized platelets or have any effect on Ins(1,4,5)P₃-induced Ca²⁺ release. Two carbohydrate-based analogues, (2-hydroxyethyl)--D-glucopyranoside-2,3,4-trisphosphate and ,-trehalose-3,4,3,4-tetrakisphosphate, could induce release of Ca²⁺ and displace [³H]Ins(1,4,5)P₃ from its binding site on rat cerebellar membranes, although both were less potent than Ins(1,4,5)P₃. In common with adenophostin A, release of Ca²⁺ from the intracellular stores could be inhibited by heparin, and both analogues were metabolically resistant. This study is the first to demonstrate the activity of a synthetic disaccharide at the Ins(1,4,5)P₃ receptor and that the Ins(1,4,5)P₃ receptor is capable of accommodating an increased steric bulk. The minimal importance of the 2-hydroxyl group of Ins(1,4,5)P₃ (occupied by the pyranoside oxygen in adenophostin) was confirmed by comparing the activity of DL-scyllo-Ins(1,2,4)P₃ [which differs from Ins(1,4,5)P₃ solely by the orientation of this hydroxyl group] with that of Ins(1,4,5)P₃. An analogue of this compound, namely, DL-6-CH₂OH-scyllo-Ins(1,2,4)P₃, which possesses an equatorial hydroxymethyl group analogous to the 5-hydroxymethyl group of adenophostin, was found to be equipotent to Ins(1,4,5)P₃, demonstrating the tolerance of the Ins(1,4,5)P₃ receptor to additional steric bulk at this position.