New therapy proven to be effective in the treatment of MRS

Apr 6 2006

Cosmetic considerations and a perceived lack of patent opportunities could be stopping the pharmaceutical and healthcare industries from investing in the development of a new therapy proven to be effective in the treatment of MRSA.

According to a leading scientist based at Liverpool John Moores University (LJMU) photodynamic or dye therapy could be an effective alternative therapy for the hospital superbug.

Around 5000 people die and many thousands more suffer long term complications in the UK every year as a result of infections caused by superbugs such as MRSA. These fatal bacterial infections are increasing because of drug resistance, most worryingly to vancomycin, the drug of last resort. Common disinfectant drugs, like mupirocin, are also becoming less and less effective.

Dr Mark Wainwright, a senior LJMU lecturer in medicinal chemistry, who has been researching the therapy for nearly 20 years, explained: “After decades of wonder drugs, man’s supremacy over the microbe is over. Over-prescription and misuse of antibacterial drugs are to blame for this rise in resistance and we urgently need to change the way in which we employ such valuable drugs.”

He continued: “Photodynamic therapy could be an effective alternative treatment. If antibiotics use a sniper’s approach to killing infections, dye therapy is like a hand grenade. Bacteria and viruses have no defence against the active oxygen it releases. The Darwinian argument of ‘survival of the fittest’ doesn’t apply because all of the bacterial cells are destroyed so they can’t develop resistance to the therapy. Its low human toxicity and the local/topical application of the drugs also mean that patients have fewer side effects.”

Photodynamic therapy (PDT) is a relatively straightforward and cheap therapy. It works by the topical application of light sensitive compounds (related to dyes) onto the infected area and then shining light onto it.

The light causes the dye to produce a highly reactive form of oxygen in situ, which if released close enough to a bacteria or virus, kills them, halting the infection.

The therapy doesn’t even require expensive lasers as the right wavelength can be provided by ordinary light sources.

At the moment, the therapy is limited to areas of the body accessible to light sources but this would still allow for the treatment of a wide range of bacterial diseases, skin infections, burns and wounds.

“An enormous amount of money is currently spent by the NHS every year on treating such conditions, many of which end up being colonised with MRSA,” said Dr Wainwright.

“These infections could be treated effectively using PDT out in the local community, helping prevent the introduction of potentially lethal infections into the hospital environment.”

Many of PDT’s light sensitive dyes – or photosensitisers – have been used clinically for a long time; many before the discovery of penicillin. One of the lead compounds, methylene blue, for example, was first used therapeutically in 1891 against malaria.

Photodynamic (dye) therapy has been successfully used to treat certain cancers for around 25 years, but so far the UK’s pharmaceutical and healthcare industries have been reluctant to investigate further uses.

Dr Wainwright believes that this is partly because photosensitisers are the poor relations in the pharmaceutical industry, often classified as textile dyes rather than drugs.

Potential profits are also limited because the dyes currently in use are already established, but novel compounds with new patent opportunities are available.

In addition, the effectiveness of photosensitisers as disinfectants has already been proved to great effect by the National Blood Service, who use photodisinfection to ensure the safety of blood plasma products.

Overseas, Russian scientists are using photosensitisers to treat multi-drug-resistant forms of TB, while dye therapy using another old dye, gentian violet, has been successful in the treatment of MRSA-infected patients in Japan.

So why hasn’t the UK’s pharmaceutical industry been more receptive?

Dr Wainwright believes cosmetic concerns may also be to blame. He explained: “There’s a general dislike of coloured staining medication and it’s true in the past patients were often heavily stained. But the stains are only temporary and as the number of life-threatening pathogens, such as MRSA, increases, surely this is a price worth paying if it saves lives?”

Dr Wainwright is now in pursuit of new funding to support clinical trials to test the efficacy of photobactericidal agents in the treatment of bacterial infections.