Turnover of the FLT3 receptor. (A) Molm14 and MV411 cells (each harboring a FLT3-ITD mutation) and primary AML samples (2 from patients with FLT3-ITD mutations, 1 from a patient with wild-type FLT3) were cultured in the presence or absence of 50 μg/mL cycloheximide. At designated time points, cells were harvested and analyzed for total FLT3 expression by immunoblotting. Densitometric results were analyzed by regression analysis after linear conversion to estimate a t_1/2. (B) Whole blood was collected at designated time points after dosing from a participant receiving 100 mg per day FF-10101 who had circulating blasts at enrollment. For each time point, half of the sample was used to directly isolate and analyze P-FLT3 from the circulating blasts whereas the other half was used to isolate plasma for the PIA assay using Molm14 cells.