Silencing a Gene in the Eye

Medical Authors and Editors: Barbara K. Hecht, Ph.D. and Frederick Hecht, M.D.

Macular degeneration is an eye disease that destroys the central vision. The disease occurs most commonly in people over 60 and is called age-related macular degeneration (AMD). AMD can occur in two forms -- dry and wet. Wet AMD is a leading cause of blindness and affects more than a million people in the US.

Wet AMD occurs when new blood vessels behind the retina start to grow toward the macula, the spot where vision is keenest. Because these new blood vessels are very fragile, they often leak blood and fluid under the macula. This damages the macula in such a way that loss of central vision can occur in a short period of time.

There have been reports that taking supplements of zinc and antioxidants vitamin C, vitamin E and beta-carotene may slow the progression of wet AMD. In some cases, wet AMD can be treated with laser surgery. The treatment involves aiming a high energy beam of light directly onto the leaking blood vessels to seal them.

A New treatment

Acuity Pharmaceuticals has filed an Investigational New Drug application with the FDA. The company plans to begin Phase I clinical trials of their product designed to treat wet AMD. The product is currently being called by the uninformative name Cand5 (apparently because it is candidate drug #5).

Cand5 is a small interfering RNA (siRNA) which uses the mechanism of RNA interference (RNAi) to shut down a gene. Cand5 specifically shuts down the production of VEGF (vascular endothelial growth factor), a major stimulus in the development of wet AMD (as well as diabetic retinopathy).

The efficacy of Cand5 in reducing the new blood vessel growth and leakage that causes AMD has already been demonstrated in primates and rodents. Acuity Pharmaceuticals feels that the product is now ready to be tested in humans for the first time. About half a dozen people at risk of blindness will receive injections of Cand5 through the whites of their eyes into the vitreous fluid behind the lens. This early stage clinical trial is characterized primarily as a safety review.


This is exciting new technology. If it proves successful, we would predict that it will be used to treat a number of other diseases as well. And that this will not be the last MedicineNet news story about RNAi.

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