myo-Inositol 1,4,6-Trisphosphorothioate andmyo-Inositol 1,3,6-Trisphosphorothioate: Partial Agonists with Very Low Intrinsic Activity at the Plateletmyo-Inositol 1,4,5-Trisphosphate Receptor

Abstract

Racemic mixtures and enantiomerically pure D-isomers of both myo-inositol 1,3,6-trisphosphorothioate [Ins(1,3,6)PS(3)] and myo-inositol 1,4,6-trisphosphorothioate [Ins(1,4,6)PS(3)], prepared by total synthesis, were examined in Ca(2+) flux and binding assays. Both D-Ins(1,3,6)PS(3) and D-Ins(1,4,6)PS(3) were shown to be low intrinsic activity partial agonists at the platelet myo-inositol 1,4, 5-trisphosphate [Ins(1,4,5)P(3)] receptor, releasing less than 20% of the Ins(1,4,5)P(3)-sensitive Ca(2+) store. D-Ins(1,4,6)PS(3) displaced specifically bound [(3)H]Ins(1,4,5)P(3) from rat cerebellar membranes, although displacement was some 34-fold weaker than by D-Ins(1,4,5)P(3). D-Ins(1,4,6)PS(3) displaced [(3)H]Ins(1,4, 5)P(3) from cerebellar membranes with roughly twice the affinity of DL-Ins(1,4,6)PS(3) (IC(50) value = 1.4 +/- 0.35 microM compared with 2.15 +/- 0.13 microM), whereas D-Ins(1,3,6)PS(3) displaced [(3)H]Ins(1,4,5)P(3) with roughly twice the affinity of DL-Ins(1,3, 6)PS(3) (IC(50) value = 17.5 +/- 5.8 microM compared with 34 +/- 10 microM), confirming that the activity of both these phosphorothioates resides in their D-enantiomers. Increasing concentrations of either D-Ins(1,3,6)PS(3) or D-Ins(1,4,6)PS(3) were able to partially antagonize Ca(2+) release induced by submaximal concentrations of Ins(1,4,5)P(3), an inhibition that could be overcome by increasing the concentration of Ins(1,4,5)P(3), suggesting competition for binding at the Ins(1,4,5)P(3)-R. The only low-efficacy partial agonists at the Ins(1,4,5)P(3)-R discovered to date have been phosphorothioates; the novel D-Ins(1,3,6)PS(3) and D-Ins(1,4,6)PS(3) can now be added to this small group of analogs. However, D-Ins(1,4,6)PS(3) has a relatively high affinity for the Ins(1,4,5)P(3)-R but maintains the lowest efficacy of all the partial agonists thus far identified. As such, it may be a useful tool for pharmacological intervention in the polyphosphoinositide pathway and an important lead compound for the development of further Ins(1,4,5)P(3)-R antagonists.

Nicotinic Acid Adenine Dinucleotide Phosphate (Naadp+) Is an Essential Regulator of T-Lymphocyte Ca2+-Signaling

“…The specific Ins(1,4,5)P 3 antagonist, Ins(1,4,6)PS 3 (Guse et al, 1997;Murphy et al, 2000), was also coinjected with an optimal NAADP ϩ concentration. Surprisingly, there was a partial reduction of the initial Ca 2ϩ -peak, but also a faster decay of this peak as compared with injection of NAADP ϩ alone (Fig.…”

“…cADPR, 8-OCH 3 -cADPR, and D -myo -inositol 1,4,6-trisphosphorothioate (Ins(1,4,6)PS 3 ) were synthesized exactly as described (Ashamu et al, 1995;Murphy et al, 2000), purified by anion-exchange chromatography on Q-Sepharose, and used as their triethylammonium salts. Purity of ligands was assessed by 1 H and 31 P NMR spectroscopy, mass spectroscopy, and, when appropriate, HPLC.…”

Amplification and propagation of pacemaker Ca2+ signals by cyclic ADP-ribose and the type 3 ryanodine receptor in T cells

“…The compounds were quantified by total phosphate assay and then used as their triethylammonium salts. D-Ins(1,4,6)PS3 was evaluated biologically and shown to be a low-efficiency partial agonist at the Ins(1,4,5)P3R (Murphy et al, 2000) and to antagonize Ins(1,4,5)P3-induced Ca 2+ release.…”

Both d- and l-Glucose Polyphosphates Mimic d-myo-Inositol 1,4,5-Trisphosphate: New Synthetic Agonists and Partial Agonists at the Ins(1,4,5)P3 Receptor

“…For decades, analogues of Ins­(1,4,5)­P 3 have been synthesized and investigated in attempts to discover a selective antagonist for Ins­(1,4,5)­P 3 R that could be made, at least temporarily, cell permeable with enzyme-cleavable or photolabile protecting groups. , Very recently, there has also been work carried out by Li et al that describes the delivery of inositol phosphates into cells via lysosomes, rendering phosphate protecting groups unnecessary . To date, however, only a small number of analogues of Ins­(1,4,5)­P 3 with minor structural modifications have been identified as partial agonists or antagonists at Ins­(1,4,5)­P 3 R. Most of these compounds demonstrate that conservative modifications to the phosphates attached to positions 4 and 5 and the hydroxyl group attached to position 3 can lead to degrees of antagonist activity. − However, many analogues of Ins­(1,4,5)­P 3 with modifications to the same regions are inactive . Attaching a bulky substituent to the axial 2-position hydroxyl can also lead to partial agonist activity, and interestingly, even using a simple benzene ring as a surrogate for inositol in a benzene polyphosphate approach, as a dimer or biphenyl, can provide low-affinity antagonists. , …”