PKs and plasma inhibitory activity (PIA). (A) Dose proportionality in the steady-state plasma exposures of PLX3397 (pexidartinib) in AML patients. (B-C) In part 1 of the study, plasma samples from 29 patients across 8 dosing cohorts were collected and evaluated for PIA in the FLT3-ITD–containing human AML cell line Molm14. Predose samples were collected on day 1, day 2, and at steady state (day 15 or 29). (B) Inhibition of pFLT3 by PIA is concentration dependent with an EC95 of 6530 ng/mL. (C) Inhibition of phosphorylated (phospho) FLT3 by PIA increases with dose and is ≥95% at ≥3000 mg for both day 2 and steady-state samples.