Combined inhibition of mTOR and Mnk activity results in enhanced antileukemic effects. (A) U937 cells were incubated for 2 hours with rapamycin, in the presence or absence of cercosporamide, as indicated. Cell lysates were resolved by SDS-PAGE and immunoblotted with an antibody against the phosphorylated form of eIF4E on serine 209 or with an antibody against total eIF4E, as indicated. (B) U937 cells were plated in methylcellulose culture assay system with rapamycin (20 nM) and/or cercosporamide (10 µM), as indicated, and CFU-L leukemic colony formation was assessed. Data are expressed as a percentage control of CFU-L for untreated cells. Means ± SE of the values from 4 independent experiments are shown. Paired t test analysis for the combination of rapamycin plus cercosporamide showed P = .00087 compared with cercosporamide alone and P = .00024 compared with rapamycin alone.