The PI3K/AKT pathway is frequently activated in human cancers. Activation occurs through many mechanisms including mutation of receptor tyrosine kinases, point mutations in PIK3CA, deletion/silencing of PTEN and amplifications in PI3 kinase and AKT. This makes the pathway a target for therapeutic intervention. We have used cellular assays to determine the impact of intervention at various nodes along the pathway. Using high throughput phospho- assays we have demonstrated different mode of action of small molecule inhibitors of PI3K, PI3K/TOR, TOR and rapamycin. PI3K/TOR compounds inhibit phosphorylation of AKT on both Ser473 & Thr 308 with equal potency; TOR kinase inhibitors inhibit Ser 473 more potently than Thr 308, whereas Rapamycin does not inhibit AKT phosphorylation & in some cell types increases pAKT Ser473. Differential inhibition of AKT phosphorylation sites affects inhibition of downstream AKT substrates in a cell type specific manner. In contrast, all compounds inhibit phosphorylation of p70S6K and S6 on Ser 235/236. We have used a panel of > 70 cell lines to investigate the relationship between mutation status and activity of compounds on the PI3K pathway and contrasted this to activity of MEK pathway compounds. We demonstrate that compounds active at different nodes in the PI3K pathway have distinct patterns of activity in the cell panel which is related to the mutational status of the cell lines. There is an anti-correlation between the activity of PI3K and MEK compounds in the cell panel and inhibition of both pathways simultaneously is synergistic.

99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA