ALL cell lines with high-level expression and constitutive phosphorylation of FLT3 are differentially sensitive to FLT3 inhibition. (A) MTT dose-response curves showing mean cytotoxic response to CEP-701 for indicated cell lines, normalized to untreated controls. Error bars represent standard error of the mean (SEM) of triplicate wells. The dotted line indicates mean cytotoxic response of all 8 cell lines at 50 nM CEP-701. (B) FLT3 immunoprecipitation/immunoblotting showing FLT3 phosphorylation status (P-FLT3) and total protein expression (FLT3) for each cell line treated for 1 hour with 50 nM CEP-701 (+) or diluent control (-), grouped by CEP-701 response.