A class of 30-year-old HIV drugs could in future be used to prevent a common cause of incurable blindness, scientists believe.
Nucleoside Reverse Transcriptase Inhibitors (NRTIs) were originally developed to treat cancer but later harnessed to combat HIV and Aids.
New research shows that they block an inflammatory pathway closely linked to age-related macular degeneration (AMD), a disease that leads to progressive loss of vision and affects up to 600,000 people in the UK.
There are two forms of AMD, wet and dry, classified by the presence or absence of blood vessels invading the retina. Although several therapies exist for the wet form, there is no approved treatment for dry AMD.
Dr Mark Young, from the Cardiff University School of Biosciences, said: "Our work presents the first evidence for a potential therapy for the untreatable dry form of AMD, a condition which affects millions of people worldwide, with a drug that is already approved for use in humans.
"It also paves the way for repurposing of the NRTI drug family for treatment of a wide variety of inflammatory diseases."
The drugs target a cell-surface protein called P2X7 that is known to play a role in a number of inflammatory disorders. In the study a number of different NRTIs were found to prevent retinal degeneration in mice affected by AMD.
"So far the efficacy of the NRTIs in combatting AMD has only been proven in mouse models, but given that the drug is already licensed for use in humans, we hope that clinical trials can begin as soon as possible," said Dr Young.
The research, led by a US team from the University of Kentucky, was reported in an online edition of the journal Science.
NRTIs are the most widely used class of anti-HIV drugs. They act on the enzyme reverse transcriptase which is necessary for the replication of HIV.
Previous research has shown that a toxic molecule called Alu RNA that accumulates in the retina in patients with dry AMD also depends on reverse transcriptase.
Dr Maria Dawson, from the blind people's charity RNIB, said: "This research is exciting but it is still at a very early stage. It offers hope for finding an effective therapy for dry AMD, for which there is currently no treatment, but extensive clinical trials are needed to establish whether this treatment is safe and effective for use in the eye.
"AMD is the most common cause of blindness in the over-50s, so an effective treatment for dry AMD would make a huge difference to the lives of many people.
"The more sight someone has, the more they are able to live safe, independent lives - this could mean not having to give up driving, remaining in employment, being able to cook safely and read medication instructions.
"The research adds to our understanding of how dry AMD develops and how it could be treated in the future."