BrdUrd labeling index and tube formation in vitro. (A) In vitro angiogenesis assay showed that HUVEC formed vessel-like structures (tubes) when plated on Matrigel-coated wells. 5-FU treatment did not inhibit tube and network formation. In contrast, IFN-α caused thinner or only weakly-stained tube-like structures. IFN/5-FU also inhibited tube formation compared to the control and caused only weak staining of the tube-like structures, similar to IFN-α alone. (B) 5-FU alone and IFN/5-FU caused significant decreases in BrdUrd labeling index compared with the control and IFN-α alone (p < 0.01). There was no difference in the index between 5-FU alone and IFN/5-FU combination (A, B). There was a significant difference in the number of capillary connections, defined as cross-points consisting of three tubes, among the control, 5-FU alone and IFN-α, IFN/5-FU (p < 0.01).