INTRODUCTION

The goal of our research program is to develop genetic therapies for retinal degenerations that lead to blindness.  Specifically, we are interested in developing therapies for age related macular degeneration (AMD) and retinitis pigmentosa (RP).  In order to deliver these genetic therapies to the human retina, we are developing viral and non viral vectors that are safe and efficient at delivering genes to human ocular tissues.
On the Cover: Adenovirus transduced retina (IOVS 2006; 47, 6: 3496-3504)

OUR MOST RECENT STUDIES

Purpose: Choroidal neovascularization (CNV) is the leading cause of blindness in age related macular degeneration (AMD).  Several lines of evidence implicate increased levels of Vascular Endothelial Growth Factor (VEGF) in retinal pigment epithelium (RPE) from AMD patients.  Current approaches to attenuate VEGF or its receptors, including the use of small interfering RNA (siRNA) show significant promise but still have limited efficacy and require repeat administrations using procedures associated with multiple complications. The goal of this study was to develop an approach for long-term endogenous expression of short hairpin RNA (shRNA) that would significantly attenuate VEGF and hence act as a potential therapy for AMD.

Methods: We developed several shRNAs expressed from recombinant adenovirus.  These shRNAs were expressed in human RPE cells in the presence of adenovirus vectors over-expressing VEGF and the amount of VEGF attenuation evaluated.  Adenovirus vectors expressing VEGF were subsequently injected into the subretinal space of mice and induction of CNV measured in the presence of adenovirus vectors expressing shRNA targeting VEGF.

Results: We identified potent shRNA sequences able to silence VEGF in human RPE cells.  When expressed from adenovirus backbones, these shRNA constructs silenced VEGF by 94% at a 1:5 (VEGF:shRNA) molar ratio and 64% at 1:0.05 molar ratio.  Adenovirus vectors expressing high levels of VEGF could induce CNV in mice within 5 days.  Co injection of VEGF-expressing viruses into mice with shRNA targeting VEGF led to a substantial (84%) reduction in CNV.

Conclusions: shRNA targeting VEGF from adenovirus vectors allows potent attenuation of VEGF and prevents CNV.  This approach shows promise as a therapy for AMD.

(IOVS 2006; 47, 6: 3496-3504)