Sep 29, 2022

NAC Attack: A Phase III clinical trial to test an oral therapy for retinitis pigmentosa

Starting in 2023, a new clinical trial called NAC Attack will be launched to test an oral medication, N-acetylcysteine (NAC), as a potential therapy for patients with retinitis pigmentosa (RP).

NAC Attack is a large, Phase III, multicenter trial, led by Drs. Peter Campochiaro and Xiangrong Kong (Johns Hopkins University). Excitingly, there will be a Canadian site in Montreal led by Dr. Robert Koenekoop (McGill University’s Montreal Children’s Hospital).

About Retinitis Pigmentosa

RP is an inherited retinal disease (IRD) that causes progressive vision loss and in most cases blindness. Over 60 RP genes have been identified. Mutations in these genes lead to the death of light-sensing photoreceptor cells in the eye and vision loss.

There is currently only one approved treatment for RP, the gene therapy Luxturna. This treatment is only for a very small number of individuals who have a mutation in the RPE65 gene. However, for the vast majority of individuals with RP, there are no accepted treatments available.

Like Luxturna, many experimental treatments for RP that are being tested in the laboratory or in human clinical trials are gene-specific, meaning they will only work for individuals with particular gene mutations. While these treatments have shown great promise, it is currently not possible to create a new gene therapy for every different gene for RP. And when you consider other IRDs, which can be caused by mutations in over 300 different genes, it’s clear that developing therapies that are not gene specific could have a large impact for patients.

NAC Attack Clinical Trial

NAC Attack is testing if an oral medication, NAC, can slow or stop vision loss or even increase vision in individuals with RP. NAC is a type of molecule called an antioxidant which protects cells against damage caused by oxidative stress.

Oxidative stress is the result of normal bodily processes, but it can also be triggered by different types of stress or as a result of cellular damage. In the retina of RP patients, the rod photoreceptor cells (that are responsible for night vision) die first. Each eye has 120 million rod photoreceptors, and when they die, the oxygen they used is released into the retina, increasing oxygen levels and causing oxidative stress. This can be toxic to other cells, causing even more cell death including to cone photoreceptor cells (responsible for central and detail vision).

NAC is a plant antioxidant, naturally found in onions. It is already an FDA-approved medication for different conditions including cystic fibrosis and acetaminophen (the active ingredient in medications like Tylenol) overdose. Studies in animal models of RP have shown that NAC treatment can reduce photoreceptor cell loss. NAC has already been tested in small Phase 1 and 2 studies, which showed that it was safe for patients with RP for up to 6 months. While these studies were promising, they did not provide enough evidence to prove that NAC was safe over the long term or would reduce vision loss. That is why a larger Phase 3 study is now being launched, to test NAC in a larger population at clinical trial sites around the world.

“It is very timely and exciting to test an already approved antioxidant drug, NAC, to evaluate its safety and efficacy in protecting or reviving cone function in patients with retinitis pigmentosa, irrespective of their causal gene. It is equally exciting to be the Canadian site in Montreal, at McGill and the Montreal Children’s Hospital, and be part of this multicenter international trial.” Said Dr. Koenekoop.

Why you should avoid self-medicating with NAC supplements

NAC is a supplement, and you may be able to find it in health food stores or pharmacies. However, individuals are warned against self-medicating with NAC supplements. Researchers still don’t know for sure if NAC will truly be helpful and more importantly, they can’t be sure that taking it long-term won’t be harmful. In addition, the NAC available in drug stores or online is supplement grade which is not regulated by the FDA, meaning that the producers do not have to measure exactly what is in it.

Learn more about NAC Attack.

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