MTT growth inhibitory assay. 5-FU alone inhibited HUVEC cells growth (A). IFN-α alone slightly inhibited HUVEC cell growth, even when used at a high concentration (10,000 units/ml) (B). Significant synergistic effects for IFN-α and 5-FU were observed at 0.05 μg/ml of 5-FU and 500 or 5,000 units/ml of IFN-α (p < 0.05), but not at 0.5 or 5 μg/ml of 5-FU plus 500 units/ml of IFN-α (C). A significant difference was observed in cell numbers on day 7 between the IFN/5-FU combination group and the other groups (D).