Quizartinib, Free Base, is an fms-related tyrosine kinase 3 (FLT3) receptor tyrosine kinase inhibitor. In binding assays, quizartinib has demonstrated a high affinity for FLT3 (Kd = 1.6 nM). in vitro assays examining FLT3 internal tandem duplicate mutations and wild-type FLT3 demonstrate the ability of quizartinib to inhibit FLT3 autophosphorylation (IC50 = 1.1 nM for FLT3-ITD and 4.2 nM for wt FLT3). Quizartinib, Free Base, has also been shown to inhibit the growth of human leukemia cell line MV4-11 (IC50 = 0.56 nM) and A375 cells (IC50 > 10,000 nM).