Scientists at John Hopkins successfully delivered gene therapy using nanoparticles to treat blinding retinal disease in rodents. The study is published online in the journal Science Advances.
The team developed a new approach of gene delivery using a biodegradable polymer that surrounds and compacts long stretches of DNA, creating nanoparticles that can enter the cells. This technology allows the researchers to convert the cells of the eye into mini-factories for a therapeutic protein, notes the authors.
Many gene therapy approaches depend on viral vectors, which use a virus’s natural ability to carry genetic material into cells. However, viruses create an immune response, which prevents repeat dosing, and the most commonly used one for ocular gene therapy cannot carry large genes.
“Some of the most prevalent inherited retinal degenerations are due to mutations in large genes that simply cannot fit into the most commonly used viral vector,” says Peter Campochiaro, MD, the Eccles Professor of Ophthalmology at the Johns Hopkins University School of Medicine, and a member of the Johns Hopkins Medicine Wilmer Eye Institute.
The therapy was used to treat wet macular degeneration as well as rarer case of inherited blinding diseases of the retina. Wet macular degeneration is an eye disease characterized by abnormal blood vessel growth that damages the light-sensitive tissue in the back of the eye.
The nanoparticles were tested by loading a gene for fluorescent protein. The molecule allowed the researchers to determine the target location, amount and duration of gene expression achievable with the nanoparticles.
They found that even eight months after treatment, the majority of the light-sensitive cells in the rats’ eyes glowed, showing that the nanoparticles effectively deposited the fluorescent gene into the cells.
The team then used the nanoparticles to target a biologically relevant gene into the eye that caused the disease. They loaded the nanoparticles with a gene for a vascular endothelial growth factor (VEGF), which is responsible for the growth of abnormal blood vessels in people with wet macular degeneration.
The researchers injected the eyes of 30 rats with the nanoparticles carrying the VEGF gene and determined the effects in the retina one, two and five months after injection. One month after injection, each rat tested had developed abnormal blood vessels under and within the retina, like those seen in patients with wet macular degeneration. The abnormal blood vessels were more extensive at two and five months after injection, and there was associated scarring under the retina similar to that seen in chronic untreated wet macular degeneration.
“These results show that the genes delivered by nanoparticles stayed active within the cells for several months,” says Campochiaro, where current treatment requires physicians to inject anti- VEGF proteins into the eyes of people with macular degeneration, a treatment that helps control the overgrowth of abnormal, leaky blood vessels. But this procedure must be repeated frequently and is burdensome for patients and their caretakers, say the researchers.
The nanoparticles were then used to deliver the therapeutic gene for the disease in genetically engineered mice that developed a form of wet macular degeneration similar to that in humans. The researchers loaded nanoparticles with a gene that produces a protein that neutralises or blocks VEGF.
Three weeks after injecting nanoparticles containing the gene for the anti-VEGF protein, the mice had a 60% reduction in abnormal blood vessels when compared to control mice. The same effect was seen 35 days later.
The nanoparticle-based treatment thus could pave way for a sustained therapy to treat cells most significantly affected by degenerative eye disease, according to researchers.