Gene therapy options for AMD
Dr. Simon Clark
Centre for Ophthalmology & Vision Sciences Faculty of Medicine and Human Sciences University of Manchester
When compared to other therapy options, such as traditional drug based treatments, gene therapy is best suited at the early stages of disease, preferably prior to major physical changes. This can be achieved given the genetic nature of AMD and well developed algorithms that take into account a patients genes, diet, age and smoking to predict their level of risk. Other methods are best suited to later stage disease, such as stem cell therapies, that seek to replace the RPE cells already lost because of disease progression.
“Given the localised nature of AMD, gene therapy represents a very real opportunity to deliver therapeutic potential right in the part of the eye we here it is needed. Altering the way the retinal pigment epithelium (RPE) cells contribute to inflammation, lipid synthesis and blood vessel growth means a patient would have a therapy constantly maintained in their eye. This may be delivered by a single sub retinal injection, removing the need for monthly eye clinic appointments currently endured by patients receiving anti-VEGF.
While the anti-VEGF era has seen a tremendous advance in our approach to AMD, the window of opportunity for initiating this therapy is very short. In some senses, anti- VEGF therapy is palliative medicine. Patients are observed until they have the most advanced form of AMD before injecting an eye with drugs that actually fail to target the underlying disease process. Significant tissue damage and visual loss may have already taken place and, further, some patients respond poorly to these treatments.
A note about VEGF: VEGF, or Vascular endothelial growth factor for those in the know, is a small protein that promotes blood vessel growth. Given that excessive blood vessel growth is a major feature of wet AMD it is perhaps not surprising that therapies directed against VEGF were quickly employed. Anti-VEGF is an antibody that perturbs VEGF function, thus stopping blood vessel growth when applied directly to the site of disease. One problem, however, is the transient nature of this treatment and explains why patients are constantly needing injections to keep up the levels of anti-VEGF, or face the consequences of the blood vessels growing again. Herein lies the greatest criticism of anti-VEGF treatments, that it only slows down, or stops the final stages of the disease, and does nothing to address the underlying problem or prevent it in the first place.”
Furthermore, with a new delivery method come new opportunities for therapies and treatment may no longer be the preserve of the wet form of AMD.
However, we still have no treatments in routine use for geographic atrophy, which is thought to affect over 8 million people worldwide. We need to understand that dry AMD is a multi faceted disease, which can only be cured if treated in its very early stages and indeed linked to the underlying disease process and a patient’s specific genotype.
Gene therapy options for AMD