Endostatin, a proteolytic fragment of collagen XVIII, is an endogenous inhibitor of tumor angiogenesis that also inhibits choroidal neovascularization. In this study, we assessed the effects of increased intraocular expression of endostatin on vascular endothelial growth factor (VEGF)-induced changes in the retina. After subretinal injection of a pair of gutless adenoviral vectors (AGV) designed to provide tamoxifen-inducible expression of endostatin, diffuse endostatin immunoreactivity was induced thoroughout the retina by administration of tamoxifen. Induction of endostatin in double transgenic mice with doxycycline-induced expression of VEGF in the retina resulted in significant suppression of leakage of intravascular [3H]mannitol into the retina. The ability of endostatin to reduce VEGF-induced retinal vascular permeability was confirmed by using [3H]mannitol leakage and two other parameters, fluorescein leakage and retinal thickness, after subretinal injection of a bovine immunodeficiency lentiviral vector coding for endostatin (BIV-vectored endostatin, or BIVendostatin). Subretinal injection of BIVendostatin resulted in more discrete, less intense staining for endostatin in the retina than that seen with the inducible AGV system, which suggested lower levels and allowed visualization of sites where endostatin was concentrated. Endostatin staining outlined retinal blood vessels, which suggested endostatin binding to a component of vessel walls. More prolonged or higher level expression of VEGF in the retina resulted in neovascularization and retinal detachment, both of which were also significantly reduced by BIVendostatin. These data suggest that endostatin may be an endogenous inhibitor of vasopermeability as well as neovascularization. In patients with diabetic retinopathy, endostatin gene transfer may provide a way to decrease the risk of three causes of visual loss: macular edema, neovascularization, and retinal detachment.

Sustained local delivery of PKC412 provides a promising approach for treatment of CNV.

Gene transfer provides a potential way to achieve sustained delivery of therapeutic proteins to the eye. Studies in rodents have suggested that periocular injection of adenoviral vectors containing expression cassettes for antiangiogenic proteins results in high intraocular levels of the proteins and suppression of choroidal neovascularization (CNV). However, the differences in size and scleral thickness between mouse and human eyes make it difficult to ascertain if periocular gene transfer is a feasible approach for treating human choroidal diseases. To address this issue, we tested the effect of periocular injection of an expression cassette for pigment epithelium-derived factor (PEDF) packaged in adenoviral vector (AdPEDF.11) in a CNV model in pigs, which have eyes that are very similar to humans in size and scleral thickness. Periocular injection of beta-galactosidase (AdLacZ.11) resulted in prominent transduction of periocular tissues, as was seen in mice. Periocular injection of AdPEDF.11 caused increased levels of PEDF in the choroid and significantly reduced the amount of CNV at rupture sites in Bruch's membrane. These data suggest that periocular gene transfer may be feasible for treatment of human choroidal diseases.