Effects of insulin and pathway inhibitors on the PI3K-Akt-mTOR phosphorylation profile in acute myeloid leukemia cells.

The phosphatidylinositol 3-kinase (PI3K)-Akt-mechanistic target of rapamycin (mTOR) pathway is constitutively activated in human acute myeloid leukemia (AML) cells and is regarded as a possible therapeutic target. Insulin is an agonist of this pathway and a growth factor for AML cells. We characterized the effect of insulin on the phosphorylation of 10 mediators in the main track of the PI3K-Akt-mTOR pathway in AML cells from 76 consecutive patients. The overall results showed that insulin significantly increased the phosphorylation of all investigated mediators. However, insulin effects on the pathway activation profile varied among patients, and increased phosphorylation in all mediators was observed only in a minority of patients; in other patients, insulin had divergent effects. Global gene expression profiling and proteomic/phosphoproteomic comparisons suggested that AML cells from these two patient subsets differed with regard to AML cell differentiation, transcriptional regulation, RNA metabolism, and cellular metabolism. Strong insulin-induced phosphorylation was associated with weakened antiproliferative effects of metabolic inhibitors. PI3K, Akt, and mTOR inhibitors also caused divergent effects on the overall pathway phosphorylation profile in the presence of insulin, although PI3K and Akt inhibition caused a general reduction in Akt pT308 and 4EBP1 pT36/pT45 phosphorylation. For Akt inhibition, the phosphorylation of upstream mediators was generally increased or unaltered. In contrast, mTOR inhibition reduced mTOR pS2448 and S6 pS244 phosphorylation but increased Akt pT308 phosphorylation. In conclusion, the effects of both insulin and PI3K-Akt-mTOR inhibitors differ between AML patient subsets, and differences in insulin responsiveness are associated with differential susceptibility to metabolic targeting.