In Vivo: Quizartinib (AC220) inhibits FLT3 activity in vivo, significantly extends survival in a mouse model of FLT3-ITD AML at doses as low as 1 mg/kg when dosed orally once a day, eradicates tumors in a FLT3-dependent mouse xenograft model at 10 mg/kg, and potently inhibits FLT3 activity in primary patient cells. The oral bioavailability of Quizartinib, determined in rats by comparing oral and intravenous pharmacokinetics at 3 mg/kg, is approximately 40%. A single 10 mg/kg dose of Quizartinib is administered by oral gavage, and mice are killed at 2 time points after dosing, using groups of 4 animals each. Quantitation of total FLT3 and phospho-FLT3 in tumor samples revealed time-dependent inhibition of FLT3 autophosphorylation. FLT3 activity is inhibited by 90% at 2 hours, and 40% at 24 hours after administration. The extent of inhibition therefore correlated well with the expected free Quizartinib plasma levels, based on pharmacokinetic experiments[1].