STUDIES ON THE MECHANISM OF PHOSPHATIDYLINOSITOL 3-KINASE INHIBITION BY WORTMANNIN AND RELATED ANALOGS

Wortmannin, a fungal metabolite, was identified as a potent inhibitor (IC50 = 4.2 nM) of phosphatidylinositol 3-kinase (PI 3-kinase). Due to the importance of PI 3-kinase in several intracellular signaling path ways, structure-activity studies on wortmannin analogs were performed in an effort to understand the structural requirements necessary for P I 3-kinase inhibition. Since wortmannin is an irreversible inhibitor o f PI 3-kinase, it was postulated that covalent attachment at the elect rophilic C-21 site was a possible mode of action for PI 3-kinase inhib ition. We have prepared various wortmannin analogs which address the p ossibility of this mechanism. Of particular interest are compounds whi ch affect the C-21 position of wortmannin either sterically or electro nically. Our results support the conclusion that nucleophilic addition by the kinase onto the 0-21 position of wortmannin is required for in hibition of PI 3-kinase by wortmannin analogs. Additionally, we have p repared several D-ring analogs of wortmannin, and their activities are reported herein. We conclude that the wortmannin D ring is an importa nt recognition site since modifications have such a dramatic effect on inhibitor potency. Finally, the identification of 17 beta-hydroxywort mannin represents the first reported subnanomolar inhibitor of PI 3-ki nase. These studies, along with in vivo antitumor experiments, suggest that the mechanism of PI 3-kinase inhibition correlates to the associ ated toxicity observed with wortmannin-based inhibitors of PI 3-kinase .