mRNA expression in K 562 cells treated by imatinib mesylate (STI571) in vitro. K562 cells (100 000 cells/mL) were maintained in 10% serum containing medium for 48 hours in the absence (control) or in the presence of the indicated imatinib concentrations. Total RNA (10 μg) isolated for the indicated periods of time were analyzed by Northern blotting. Ribosomal RNAs are shown as a loading control. A representative of 3 independent experiments is shown. (A) Time course of VEGF mRNA concentrations in K562 cells treated with or without 2.5 μM imatinib. (B) VEGF mRNA in K562 cells treated with different concentrations of imatinib for 48 hours.