Vascular endothelial growth factor-toxin conjugate specifically inhibits KDR/flk-1-positive endothelial cell proliferation in vitro and angiogenesis in vivo

Inhibition of tumor neovascularization has profound effects on the growth of solid tumors. An endothelial cell-specific cytotoxic conjugate was prepared by chemically linking recombinant vascular endothelial growth factor (VEGF165) and a truncated diphtheria toxin molecule (DT385). The treatment of subconfluent cultures of human umbilical vein endothelial cells and human microvascular endothelial cells with the VEGF165-DT385 conjugate resulted in a selective, dose-dependent inhibition of growth. Parallel experiments with either the free toxin or a mixture of VEGF and the toxin polypeptide did not affect proliferation (DNA synthesis) of these cells. The selective cytotoxicity correlated with the appropriate receptor expression (KDR/flk-1 positive) on the target cells. VEGF-toxin conjugate inhibited the growth of a murine hemangioma-derived endothelial cell line (Py-4-1), which was positive for flk-1 expression. Under similar conditions, the conjugate did not affect the proliferation of a receptor-negative ovarian cancer cell line in vitro. In an in vivo model of angiogenesis, the VEGF165-DT385 conjugate blocked basic fibroblast growth factor-induced neovascularization of the chick chorioallantoic membrane. These studies demonstrate the successful targeting of a cytotoxic polypeptide to proliferating vascular endothelial cells (normal and tumorigenic) and the potential utility of such conjugates in blocking tumor neovascularization.