The overall goal of this project is to develop a novel gene-based delivery system to treat neovascular age- related macular degeneration (wet AMD), a debilitating ocular disease. AMD is the leading cause of blindness in Americans over 60 years of age, with wet AMD accounting for 90% of all AMD-related blindness. An estimated 2,000,000 people in the United States suffer from wet AMD, and it is expected that the prevalence of wet AMD will grow to 3,000,000 by 2020. Wet AMD is initiated by a thickening and disruption of the membrane underlying the retina. The oxygen supply to the macula is disrupted and the body responds by growing new, abnormal blood vessels. These begin to grow through the breaks of the membrane behind the retina towards the macula, often raising the retina. These abnormal blood vessels tend to be very fragile, and can leak or bleed, causing scarring of the macula. This damage to the macula results in rapid, irreversible central vision loss. The standard of care for wet AMD is repeated intraocular injections of vascular endothelial growth factor (VEGF) inhibitors, including the monoclonal antibody fragment ranibizumab. Optimal control of disease is obtained with monthly injections, which are inconvenient, require frequent office visits, and as is true for any injection into the eye, are associated with morbidity. The proposed therapeutic would be a one-time injection of a gene delivery vehicle, resulting in persistent, stable expression of ranibizumab in the retina. The gene delivery vector belongs to a new family of adeno-associated virus (AAV) serotypes that we identified and which perform substantially better than previously available gene transfer technologies. Recombinant AAV gives stable gene expression in non-dividing tissues without integrating into the genome, and thus avoids potential integration-associated adverse events;furthermore, AAV itself is non-pathogenic. Previously known serotypes of AAV, however, are not very efficient at transducing cells in vivo;the novel AAV serotypes give higher levels of gene expression in the retina, enabling safe and therapeutic gene delivery at lower doses of vector. Gene transfer will be targeted to the RPE and photoreceptors in order to deliver the therapeutic protein directly to the appropriate part of the eye. The immediate goal of this Phase I SBIR application is to identify and develop the optimal clinical candidate. The optimal AAV serotype and promoter for retinal-based gene transfer have been determined. Expression of ranibizumab will be optimized by replacement of the leader sequence and tailoring codon usage for expression in human tissues. Proof of principle studies will be performed by: 1) demonstration of efficacy of the therapeutic in a mouse model of retinal detachment caused by human VEGF expression in the retina, and 2) demonstration and confirmation of previously achieved levels of ranibizumab expression in the non-human primate eye, the species whose retina is closest in structure to the human eye. This will be used for future progression through safety/tox studies and clinical trials.
Age-related macular degeneration (AMD) is one of the leading causes of blindness. The prevalence of neovascular (wet) AMD in the United States is expected to increase to nearly 3 million by 2020. Existing treatments are effective in limiting the progression of the disease but are problematic in both cost of drug and the requirements for frequent administration by intravitreal injection with attendant safety problems. This proposal initiates the clinical development of a new experimental therapy which involves a one-time genetic delivery system using a vector that provides long term expression of the drug which is potentially safer and less burdensome to the patient.
