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Strategic Development

Based upon the proven effects in two cellular proliferative disorders attention has turned to developing the use of PDT in other proliferative disorders where there is an established need, an accessibility to laser light for activation and a commercially attractive market. These applications include interventional cardiology, dermatological conditions and auto-immunity, and are areas where PhotoBiotics will shortly become active.

The most frequently used technique in interventional cardiology is angioplasty, which is used to treat coronary and peripheral vascular diseases. Some 1 million procedures are conducted annually in the US and probably 2 million worldwide.

This procedure involves inflating a balloon-catheter to stretch the artery thus opening it up and thereby improving blood flow. Unfortunately in up to 50% of the patients the effects are short lived as the artery closes up again - a phenomenon known as restenosis. Much research has been conducted into products that either could reduce or prevent restenosis, such as stents to hold the artery open or drugs or laser treatments. As yet there is no effective way of preventing restenosis. At least two companies are in phase II clinical trials with PDT, with a laser activating a photoactive agent passed through an intra-arterial catheter.

Dermatology has long used 'light treatment', mainly involving UV light given with or without photosensitisers, to treat severe and widespread eczema and other conditions. Such indications do not suit the current generation of PDT as they involve the treatment of large areas of the skin surface. However, one company - DUSA Pharmaceuticals - has submitted a New Drug Application in the USA for its PDT agent (5-aminolevulinic acid) in a dermatological condition known as actinic keratoses which is a common pre-cancerous skin condition stated to lead to some 4 million patient visits annually in the US alone. The same company has early stage clinical trials with this agent in several other indications such as acne, hair removal and endometrial ablation.

Other attempts to harness the effects of PDT in treating proliferative disorders have focussed upon auto immunity, which in some respects can be considered a proliferative disorder of white blood cells. The hope is that PDT will bring about a damping down of the immune response directed against certain of the body's own cells, which is thought to play a role in a number of chronic systemic diseases such as psoriasis, eczema, rheumatoid arthritis and systemic lupus. All these conditions represent large markets with high degrees of unmet medical need. For example, psoriasis is known to affect some seven million people in the US alone with one third of these patients potentially likely to benefit from PDT. Presently, studies in this area are at a 'proof of concept' stage with products unlikely to be on the market before 2006/7.

Some more speculative applications to have been suggested include:

• Light-activated antimicrobial compounds that even the most antibiotic-resistant bacteria (e.g., methicillin-resistant staphylococcus aureus, or MRSA) cannot withstand: 'photosterilisation' of hospital operating theatres and waiting areas is a real possibility, as are novel approaches to oral hygiene
  
  
• Light-activated antiviral compounds (e.g., treatment of AIDS, blood purification)
  
  
• Non-PDT treatment of transmissible spongiform encephalopathies (TSEs)

PhotoBiotics will target these and other areas in the future.