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Dawn of a new era

Recent advances in the treatment of the chronic eye disease wet age-related macular degeneration bring the possibility of using combination therapies.

DawnAge-related macular degeneration (AMD) is a chronic eye disease that occurs when the macula, a specialised area in the centre of the retina, responsible for central vision, deteriorates. This can result in blurred vision but rarely ends in total blindness because peripheral vision is not affected.

However, the loss of central vision severely affects the quality of life of the patient and, depending on the severity of the disease, patients can be classified as legally blind.

There are two types of AMD, commonly known as dry and wet. The wet form of AMD causes choroidal neovascularisation (CNV) - the growth of abnormal blood vessels in the macula. These blood vessels are poorly formed and leak fluid, or blood, that cause damage to the macula.

The wet form of the disease affects just 10-15 per cent of patients suffering from AMD. However, it is the most severe form of the disease and accounts for 90 per cent of the blindness caused by AMD.

What are the options?
Photodynamic therapy (PDT) is a fairly recent treatment for wet AMD. It involves injection of a photosensitive drug into the bloodstream followed by the application of a laser. The drug localises in the CNV and, once activated by the laser, closes off the new blood vessels.

The first, and currently only available, light-activated therapy for wet AMD is Visudyne (verteporfin). This was launched in 2000 and was a major advance in the treatment of wet AMD. It was the first drug approved for the disease, albeit for a particular subgroup of patients.

New contender
Despite being a major advance, Visudyne has its drawbacks. While it leads to a slower rate of vision decline and reduces the risk of vision loss, it doesn't stop or restore the vision already lost. Consequently, the pharma industry was on the look out for improvements. It hasn't found exactly what it is looking for in Macugen (pegaptanib) but it's a major step forward.

Macugen is the first targeted anti-VEGF therapy. VEGF is an essential signal in the pathological processes underlying AMD. Macugen, a pegylated modified oligo-nucleotide, binds with high affinity and selectivity to the major pathological isoform of VEGF.

Macugen doesn't restore vision but it does target the underlying biology of wet AMD and slows vision loss. Eyetech Pharmaceuticals is co-promoting the drug in the US with Pfizer Ophthalmics. It was launched in the US as monotherapy for all subtypes of wet AMD in January 2005. It is awaiting approval in Europe and Canada and is in clinical trials in Japan.

Data from Macugen pivotal studies, reported in the New England Journal of Medicine said the treatment was not dramatically better than photodynamic therapy. However, there is a great deal of enthusiasm about the drug and it does mark 'the start of a new era'. With the advent of an alternative treatment for wet AMD, comes the possibility of combination therapy.

Possible rival
Not surprisingly, other companies are jumping on the VEGF bandwagon and many other anti-VEGF therapies are in development. These include Lucentis (ranibizumab), which is a fragment of an anti-VEGF antibody that non-selectively blocks all forms of VEGF.

It is likely to be the second anti-VEGF compound to reach the market. It was initially developed by Genentech, which licensed the drug to Novartis Ophthalmics. Currently in phase III clinical trials, it is expected to be filed for approval in the US in 2006.

Eyetech believes Macugen will have the advantage over the Novartis drug as moderate to severe inflammation has been observed in patients treated with LucentisTM. However, supporters of Lucentis are excited about the product and it remains to be seen how it will fare against Macugen should it pass the necessary regulatory hurdles.

On the horizon
AMD is the leading cause of legal blindness in adults aged 50 or over in the Western world. Over 500,000 people worldwide lose their sight annually from the disease. Macugen will hopefully pave the way for improved treatment strategies either in terms of better compounds or, more likely, in terms of combinations of therapies.

For more information on Adis services contact: Darren Gillgrass, tel: 01829 772773 or e-mail: darren.gillgrass@uk.adis.com

2nd September 2008

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