The vascular-targeting fusion toxin VEGF₁₂₁/rGel inhibits the growth of orthotopic human bladder carcinoma tumors

Vascular endothelial growth factor (VEGF) and its receptors (FLT-1 and KDR) are overexpressed by human bladder cancer cells and tumor endothelial cells, respectively. Strategies that target VEGF receptors hold promise as antiangiogenic therapeutic approaches to bladder cancer. A fusion protein of VEGF₁₂₁ and the plant toxin gelonin (rGel) was constructed, expressed in bacteria, and purified to homogeneity. Cytotoxicity experiments of VEGF ₁₂₁/rGel on the highly metastatic 253J B-V human bladder cancer cell line demonstrated that the VEGF₁₂₁/rGel does not specifically target these cells, whereas Western blot analysis showed no detectable expression of KDR. Treatment with VEGF₁₂₁/rGel against orthotopically implanted 253J B-V xenografts in nude mice resulted in a significant suppression of bladder tumor growth (∼60% inhibition; P < .05) compared to controls. Immunohistochemistry studies of orthotopic 253J B-V tumors demonstrated that KDR is highly overexpressed in tumor vasculature. Immunofluorescence staining with antibodies to CD-31 (blood vessel endothelium) and rGel demonstrated a dramatic colocalization of the construct on tumor neovasculature. Treated tumors also displayed an increase in terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling staining compared to controls. Thus, VEGF ₁₂₁/rGel inhibits the growth of human bladder cancer by cytotoxic effects directed against the tumor vascular supply and has significant potential as a novel antiangiogenic therapeutic against human bladder cancer.