Background: A gene therapy-mediated approach to the delivery of antiangiogenic agents using adeno-associated virus (AAV) vectors has a number of advantages including the potential for sustained expression. The purpose of this study was to attempt to restrict the growth of disseminated neuroblastoma through delivery of a truncated, soluble form of the vascular endothelial growth factor receptor-2 (VEGFR-2 fetal liver kinase [Flk]-1), a decoy receptor for VEGF.
Study design: Mice underwent portal vein injection of vector, either AAV-CAGG-tsFlk-1 or control vector. Subsequent truncated soluble fetal liver kinase-1 (tsFlk-1) expression was confirmed and quantified by ELISA. After 8 weeks, mice were given human neuroblastoma cells through the tail vein to establish disseminated disease and were sacrificed after 40 days. The weight of liver metastasis was measured. Intrahepatic tumor microvessel density and levels of apoptosis were determined. Survival was assessed in a second cohort of mice.
Results: After intraportal injection of AAV-CAGG-tsFlk-1, high-level, stable transgene expression was generated. Sera from these mice inhibited endothelial cell activation in vitro and Matrigel plug (BD Biosciences) neovascularization in vivo, suggesting that a systemic state of angiogenesis inhibition had been established. After neuroblastoma injection, mice expressing tsFlk-1 had a smaller tumor burden in the liver when sacrificed, as compared with control mice. The decrease in tumor weight in the liver correlated with lower intratumoral microvessel density and higher levels of tumor cell apoptosis in the tsFlk-1-treated tumors, supporting the hypothesis that decreased angiogenesis had occurred. In a second cohort of mice, survival of tsFlk-1-expressing mice after tumor cell challenge was longer than in control mice.
Conclusions: Longterm in vivo expression of a functional VEGF inhibitor was established using an AAV-mediated gene therapy approach, and it demonstrated antiangiogenic and anticancer efficacy in a murine model of disseminated neuroblastoma.