FLT3 inhibition by CEP-701 and PKC412 in culture medium compared with plasma. TF/ITD cells were incubated with the indicated concentrations of drug for 2 hours, and then FLT3 was immunoprecipitated from cell lysates and resolved by electrophoresis as described in “Patients, materials, and methods,” under “FLT3 phosphorylation.” Immunoblots were probed with antiphosphotyrosine and then stripped and reprobed with anti-FLT3. Densitometry results from the immunoblots were plotted as percent untreated. The calculated IC₅₀ values shown were derived using linear regression analysis. (A) CEP-701, medium versus serum. (B) CEP-701, plasma. (C) PKC412, medium versus serum. (D) PKC412, plasma.