SUPPRESSION OF RETINAL NEOVASCULARIZATION IN-VIVO BY INHIBITION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR (VEGF) USING SOLUBLE VEGF-RECEPTOR CHIMERIC PROTEINS

The majority of severe visual loss in the United States results from c omplications associated with retinal neovascularization in patients wi th ischemic ocular diseases such as diabetic retinopathy, retinal vein occlusion, and retinopathy of prematurity. Intraocular expression of the angiogenic protein vascular endothelial growth factor (VEGF) is cl osely correlated with neovascularization in these human disorders and with ischemia-induced retinal neovascularization in mice. In this stud y, we evaluated whether in vivo inhibition of VEGF action could suppre ss retinal neovascularization in a murine model of ischemic retinopath y. VEGF-neutralizing chimeric proteins were constructed by joining the extracellular domain of either human (Flt) or mouse (Flk) high-affini ty VEGF receptors with IgG. Control chimeric proteins that did not bin d VEGF were also used. VEGF-receptor chimeric proteins eliminated in v itro retinal endothelial cell growth stimulation by either VEGF (P < 0 .006) or hypoxic conditioned medium (P < 0.005) without affecting grow th under nonstimulated conditions. Control proteins had no effect. To assess in vivo response, animals with bilateral retinal ischemia recei ved intravitreal injections of VEGF antagonist in one eye and control protein in the contralateral eye. Retinal neovascularization was quant itated histologically by a masked protocol. Retinal neovascularization in the eye injected with human Flt or murine Flk chimeric protein was reduced in 100% (25/25; P < 0.0001) and 95% (21/22; P < 0.0001) of an imals, respectively, compared to the control treated eye. This respons e was evident after only a single intravitreal injection and was dose dependent with suppression of neovascularization noted after total del ivery of 200 ng of protein (P < 0.002). Reduction of histologically ev ident neovascular nuclei per 6-mu m section averaged 47% +/- 4% (P < 0 .001) and 37% +/- 2% (P < 0.001) for Flt and Flk chimeric proteins wit h maximal inhibitory effects of 77% and 66%, respectively. No retinal toxicity was observed by light microscopy. These data demonstrate VEGF 's causal role in retinal angiogenesis and prove the potential of VEGF inhibition as a specific therapy for ischemic retinal disease.