Activity of ponatinib against AC220 resistance–conferring FLT3-ITD KD mutations. (A) Relative proliferation of Ba/F3 populations stably expressing FLT3-ITD mutant isoforms after 48 hours in various concentrations of ponatinib (error bars represent SD of triplicates from the same experiment). (B) Western blot analysis using anti–phospho-FLT3, anti–phospho-STAT5, anti-FLT3, and anti-STAT5 antibody performed on lysates from IL-3–independent Ba/F3 populations expressing the FLT3-ITD mutant isoforms indicated. Cells were exposed to ponatinib at the indicated concentrations for 90 minutes.