AML cells require mTOR for survival of genotoxic stress. (A-C) Primary patient samples were thawed and plated in 96-well plates at 2 × 10⁶ cells/mL in increasing concentrations of etoposide for 48 hours. Relative cell survival was measured using an XTT assay. All values are expressed as a fraction of the untreated controls. Cells were either incubated in increasing concentrations of etoposide alone (□) or increasing concentrations of etoposide with 10 μM rapamycin present (▪). (D) Normal purified CD34⁺ hematopoietic stem cells were thawed, plated at 1 × 10⁶ cells/mL in 96-well dishes, and analyzed as described under “Materials and methods.” Cells were incubated in different concentrations of etoposide in the absence (□) or presence (▪) of rapamycin.