Comparison of the antiangiogenic activity of modified RGDRGD-endostatin to endostatin delivered by gene transfer in vivo rabbit neovascularization model

PURPOSE Endostatin plays an important role in inhibiting corneal neovascularization (CNV). The aim of this study was to evaluate the antiangiogenic activities of lipid-mediated subconjunctival injection of the modified RGDRGD (arginine- glycin- aspartic- arginine- glycin- aspartic- endostatin gene in a rabbit model of neovascularization in vivo. METHODS A modified human endostatin gene containing an RGDRGD motif was obtained by rapid site-directed mutagenesis. Forty New Zealand white rabbits underwent alkaline burn and developed CNV, which were randomly divided into four groups: an experimental control group, a PCI empty vector group, a PCI-endostatin group, and a PCI-RGDRGD-endostatin group. The vector, endostatin, and RGDRGD-endostatin groups received injections into the superior bulbar conjunctiva after the burn. An injection of 5 μg was given twice at 1-week intervals. Four eyes of two rabbits received neither treatment nor alkaline burn and served as absolute normal controls. The areas of CNV were monitored after 7 and 14 days. Corneas were examined by histology, and VEGF (vascular endothelial growth factor) and CD31 (platelet endothelial cell adhesion molecule-1) expression was detected by immunohistochemistry after 7 and 14 days. Retina, liver, and kidney were examined by histology, and CD38 expression in the inflammatory cells was detected by immunohistochemistry at 90 days. RESULTS Subconjunctival injection of both native endostatin and modified RGDRGD-endostatin genes resulted in a significant suppression of CNV in vivo, with modified RGDRGD-endostatin being more effective than native endostatin. The mean concentration of VEGF in the PCI-RGDRGD-endostatin group significantly decreased compared to the means in the other groups. Upon histological examination, the endostatin-treated and RGDRGD-endostatin-treated eyes showed significantly less neovascular area and fewer vessels than the control and vector-injected groups. Retinal, hepatic, and renal tissue sections were normal, and there was no inflammatory cell infiltration observed. CONCLUSIONS Native and modified endostatin can significantly inhibit CNV by suppressing the expression of VEGF. However, modified endostatin with the RGDRGD motif is far more effective than the endostatin gene in antiangiogenic activity.