DESIGN OF POTENT AND SELECTIVE INHIBITORS OF MYOINOSITOL 1,4,5-TRISPHOSPHATE 5-PHOSPHATASE

The interactions of synthetic analogues of D-myo-inositol 1,4,5-trisph osphate [Ins(1,4,5)P-3] with the Ins(1,4,5)P-3 receptor in permeabiliz ed SH-SY5Y cells and with two key metabolic enzymes, Ins(1,4,5)P-3 3-k inase from a supernatant preparation of rat brain homogenates and Ins( 1,4,5)P-3 5-phosphatase from human erythrocyte ghosts, have been exami ned. L-chiro-Inositol 2,3,5-trisphosphorothioate [L-chiro-Ins(2,3,5)PS 3], which we have previously identified as a partial agonist at the In s(1,4,5)P-3 receptor [Safrany, S. T., Wilcox, R. A., Liu, C., Dubreuil , D., Potter, B. V. L., & Nahorski S. R. (1993) Mel, Pharmacol. 43, 49 9-503], is identified as the most potent 5-phosphatase inhibitor yet d escribed {inhibiting dephosphorylation of [H-3]Ins(1,4,5)P-3 with K-i = 230nM}. L-chiro-Ins(2,3,5)PS3 was also found to be the most potent s mall-molecule inhibitor of 3-kinase (K-i = 820 nM). The properties of three novel, potent, and selective inhibitors of 5-phosphatase are des cribed. L-myo-Inositol 1,4,5-trisphosphorothioate inhibited 5-phosphat ase with K-i = 430 nM, showing 250-fold selectivity over 3-kinase (K-i = 108 mu M); myo-inositol 1,3,5-trisphosphorothioate inhibited 5-phos phatase with 475-fold selectivity over 3-kinase (K-i = 520 nM and 247 mu M, respectively). The most potent, selective inhibitor of 5-phospha tase was L-chiro-inositol 1,4,6-trisphosphorothioate [L-chiro-Ins(1,4, 6)PS3]. L-chiro-Ins(1,4,6)PS3 inhibited 5-phosphatase with K-i = 300 n M and did not interact with the Ins(1,4,5)P-3 receptor or 3-kinase at doses tested. These studies, therefore, identify a highly potent and s elective inhibitor of 5-phosphatase, which should be considered the to ol of choice when inhibiting this enzyme in a broken cell or cell-free system.