Almost complete dephosphorylation of FLT3 appears necessary for the achievement of a cytotoxic response to lestaurtinib. (A) MTS assay-derived cytotoxic dose responses of MNCs from 3 FLT3/WT cases exposed to lestaurtinib for 72 hours. (B) Comparative phospho-FLT3 and total FLT3 immunoblots with densitometric dose-response histograms from the same 3 cases following 1-hour exposure to lestaurtinib.