D-MYO-INOSITOL 1,4,5-TRISPHOSPHATE ANALOGS MODIFIED AT THE 3-POSITIONINHIBIT PHOSPHATIDYLINOSITOL 3-KINASE

Several natural and unnatural inositol phosphates and analogues were a nalyzed for their ability to inhibit the in vitro phosphatidylinositol 3-kinase (PI 3-kinase) activity immunoprecipitated from a leukemic T cell line by a p85 monoclonal antibody. A 3-position ring-modified ana logue of D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P-3), L-chiro-i nositol 2,3,5-trisphosphate (L-chiro-Ins(2,3,5)P-3) and its phosphorot hioate analogue, L-chiro-inositol 2,3,5-trisphosphorothioate, as well as the analogue benzene 1,2,4-trisphosphate induced reversible inhibit ion of PI 3-kinase activity, which correlated with decreased V-max but unchanged K-m values for PI 3-kinase. Other inositol phosphates, incl uding D- and L-Ins(1,4,5)P-3, D-myo-inositol 1,3,4,5-tetrakisphosphate , the enantiomers of myo-inositol 1,3,4-trisphosphate DL-myo-inositol 1,4,6 trisphosphate (DL-Ins(1,4,6)P-3), and DL-scyllo-inositol 1,2,4-t risphosphate (DL-scyllo-Ins(1,2,4)P-3), did not inhibit PI 3-kinase ac tivity under identical conditions. L-chiro-Ins(2,3,5)P-3 closely resem bles Ins(1,4,5)P-3 and D-Ins(1,4,6)P-3 except for a difference in the orientation of a single hydroxyl group at either the equivalent 3-OH o r 2-OH position of Ins(1,4,5)P-3, respectively. Similarly, L-chiro-Ins (2,3,5)P-3 resembles D-scyllo-Ins(1,2,4)P-3, but has a different orien tation of both the equivalent 3-OH and 2-OH positions. Since Ins(1,4,5 )P-3, DL-Ins(1,4,6)P-3, and DL-scyllo-Ins(1,2,4)P-3 did not inhibit PI 3-kinase activity, this suggests that the orientation of the two hydr oxyl groups at the 2- and 3-positions plays a pivotal role in the inhi bitory action of inositol phosphate analogues on PI 3-kinase activity. Thus, inositol phosphate analogues inter alia are shown for the first time to inhibit PI 3-kinase and may be useful tools for determining t he function of PI 3-kinase and its substrate binding specificities.