Vascular endothelial growth factor antisense oligonucleotides inhibit leptomeningeal metastasis in vivo

To determine the level of vascular endothelial growth factor (VEGF) protein produced in tumor tissues and to evaluate the effect of antisense oligonucleotides directed against VEGF on tumor growth and animal survival in a rabbit model of leptomeningeal carcinomatosis. New Zealand White (NZW) rabbits were injected with VX2 tumor cells transfected with or without VEGF antisense constructs. The time course of VEGF protein expression in tumor tissues was then examined by immunohistochemistry and western blot analysis. VEGF concentrations in serum and cerebrospinal fluid (CSF) were determined by enzyme-linked immunosorbent assay (ELISA). The efficacy of VEGF antisense therapy was evaluated by calculation of the survival rate and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Immunohistochemical analysis and immunoblotting showed that VEGF protein expression was significantly decreased in tissues from rabbits given VEGF antisense treatment. Serum and CSF VEGF concentrations were also markedly reduced during the first 15 days after tumor inoculation in antisense-treated animals. VEGF antisense therapy resulted in prolonged animal survival. Furthermore, while some meningeal nodular enhancement was evident in almost all of the VX2-inoculated rabbits, meningeal enhancement and thickening was clearly suppressed after VEGF antisense treatment. These results indicate that VEGF antisense oligonucleotides have a potent anti-tumor activity in a rabbit model of VX2 leptomeningeal carcinomatosis. In addition, DCE-MRI provides highly accurate measurements for the detection of experimentally induced leptomeningeal carcinomatosis and could be used as a suitable method for assessing in vivo tumor growth and angiogenesis.