Both compounds potently inhibited FLT3-ITD–expressing cells with a half maximal inhibitory concentration (IC50) of 13 nM for PKC412 and 2.5 nM for AC220, respectively. FLT3 N676K-expressing cells were also sensitive to FLT3 inhibitors with an IC50 of 7.5 nM for PKC412 and 3 nM for AC220. FLT3-ITD-N676K double mutants showed a strong resistance to both inhibitors (IC50 greater than 80 nM for PKC412 and greater than 16 nM for AC220).