/rGel mediates inhibition of tube formation in PAE/VEGFR-2 cells. A, One nM VEGF121/rGel was sufficient to inhibit tube formation by 50%, whereas the same degree of inhibition was seen with rGel only at 100 nM. B, Up to 100 nM VEGF121/rGel was needed to inhibit tube formation in PAE/VEGFR-1 cells, the same concentration as the untargeted gelonin toxin. C, Time-dependent inhibition of tube formation of PAE/VEGFR-2 cells by VEGF121/rGel. Incubation of PAE/VEGFR-2 cells with VEGF121/rGel for as little as 9 h was sufficient to abolish the ability of these cells to form tubes by 50%.