Response of “type I” FLT3 inhibitor–resistant mutant FLT3-expressing cells to “type II” second-generation FLT3 inhibitors. (A, B) Three-day treatment of FLT3-ITD-Ba/F3 cells with AUZ454, ATH686, or PKC412 (A) and 3-day treatment of PKC412-resistant FLT3-ITD-Ba/F3 cells with AUZ454, ATH686, or PKC412 (B). (C, D) Three-day treatment of FLT3-ITD-Ba/F3 cells with PKC412 or AUZ454 (C) and 3-day treatment of AAE871-resistant FLT3-ITD-Ba/F3 cells with PKC412 or AUZ454 (D).