VEGF production in K562 cells treated with imatinib mesylate (STI571) in vitro. K562 cells (100 000 cells/mL) were maintained in normal medium supplemented with 10% serum for 48 hours in the absence (control) or in the presence of the indicated imatinib mesylate (STI571). VEGF concentrations in conditioned medium were measured by ELISA (median of 3 independent experiments ± SE). (A) Time course of VEGF production in K562 cells treated with imatinib. (B) VEGF production in K562 cells treated with different concentrations of imatinib during 24 or 48 hours.