/rGel binds to both VEGFR-1 and VEGFR-2 but is cytotoxic only to VEGFR-2-expressing endothelial cells. A, Expression of both receptors on their respective cell-lines was confirmed. B, Receptor-specific binding of radiolabeled VEGF121/rGel. Binding was reduced with unlabeled VEGF121/rGel but not by unlabeled gelonin. C, VEGF121/rGel enters PAE/VEGFR-2 cells within one hour of treatment. However, PAE/VEGFR-1 cells did not internalize VEGF121/rGel even after 24 hours of incubation with VEGF121/rGel. D, Effect of exposure time of VEGF121/rGel on PAE/VEGFR-2 cells on cytotoxicity.