2-Hydroxyethyl-α-D-glucopyranoside-2,3′,4′-trisphosphate, a novel, metabolically resistant, adenophostin A and myo-inositol-1,4,5-trisphosphate analogue, potently interacts with the myo-inositol-1,4,5-trisphosphate receptor

The novel, synthetic, adenophostin A analogue 2-hydroxyethylα-D-glucopyranoside-2,3′,4′-trisphosphate [Gluc(2,3′,4′)P₃] was synthesized to probe the structure-activity relationship at the D-myo-inositol-1,4,5-trisphosphate [Ins(1,4,5)P₃] receptor [Ins(1,4,5)P₃R]. This study was stimulated by the recent observation that the fungal isolates adenophostins A and B were very potent, metabolically resistant, Ins(1,4,5)P₃R agonists [J. Biol. Chem. 269:369-372 (1994)]. Gluc(2,3′,4′)P₃ can be visualized as a truncated version of adenophostin A, in which the 2′- and 3′-carbons of the ribose ring, with their terminal phosphate groups, are retained and the remainder of the adenosine residue is excised. Gluc(2,3′,4′)P₃ specifically displaced [³H]Ins(1,4,5)P₃ from pig cerebellar Ins(1,4,5)P₃ binding sites, with an affinity (IC₅₀ = 130 nM) only 5-fold weaker than that of Ins(1,4,5)P₃ (IC₅₀ = 27 nM). Gluc(2,3′,4′)P₃ was also a full agonist for Ca²⁺ release, being only 10-12-fold less potent than Ins(1,4,5)P₃ in saponin-permeabilized SH-SY5Y neuroblastoma cells [EC₅₀ = 647 nM; Ins(1,4,5)P₃ EC₅₀ = 52 nM] and Madin-Darby canine kidney cells [EC₅₀ = 2484 nM; Ins(1,4,5)P₃ EC₅₀ = 247 nM]. Gluc(2,3′,4′)P₃ did not significantly interact with recombinant Ins(1,4,5)P₃ 3-kinase and 5-phosphatase enzymes and was also poorly metabolized by saponin-permeabilized SH-SY5Y cells. However, Gluc(2,3′,4′)P₃ was a considerably weaker ligand (∼500-fold) and agonist (∼1000-fold) than adenophostin A, suggesting that the partial excision of the adenosine residue compromised structural motifs that have favorable interactions with the Ins(1,4,5)P₃R. Indeed, molecular dynamics simulations revealed that the potencies of the three compounds show a correlation with the relative distance of the two vicinal ring phosphates from the remaining phosphate. Gluc(2,3′,4′)P₃, with its α-glucoside ring, is the first synthetic Ins(1,4,5)P₃ analogue that is not structurally based on a phosphorylated inositol isomer and that exhibits potent activity at the Ins(1,4,5)P₃R. This, combined with the metabolic resistance of Gluc(2,3′,4′)P₃, thus affords a novel approach for the investigation of the cellular role of Ins(1,4,5)P₃ and its receptor.