MLN518 variably inhibits the proliferation of Ba/F3 cells stably expressing FLT3-ITD or FLT3 activation loop mutations. (A) MLN518 inhibits the proliferation of Ba/F3 cells expressing FLT3-ITD or FLT3 activation loop mutations by MLN518. Ba/F3 cells stably expressing FLT3-ITD or FLT3 activation loop mutations were incubated with increasing concentrations of MLN518 for 48 hours in the absence of IL-3, as indicated. The number of viable cells at the end of 48 hours was determined using a colorimetric assay based on a vital stain. Results are expressed as a percentage of viable cells after 48 hours of growth in the presence of DMSO without drug. (B) Restoration of cellular proliferation by IL-3 even in the presence of high concentrations of MLN518. The assay described above was repeated, this time in the presence of IL-3. Error bars represent standard error of data derived from 3 independent experiments.