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Light-activated anti-cancer drugs on target

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Combining light-activated cancer drugs with tumour-targeting proteins could provide a more effective way of treating many cancers, according to new research published on-line at the end of October in the International Journal of Cancer.

The study describes how Imperial College London scientists successfully attached over 10 light-activated drug molecules to an antibody fragment which recognises and homes in on cancerous cells. This delivers these highly potent drug molecules precisely to cancer targets much more effectively than if they are not attached to the antibody.

The techniques of using light-activated drugs to treat cancer, is known as photodynamic therapy (PDT). This treatment involves ensuring the drugs are located in diseased tissues, and then illuminating them with cold laser light. A chain reaction is set off which converts oxygen into a highly toxic bleach-like form that destroys any cells in its close proximity. PDT has been successfully used to treat head and neck, prostate and skin cancers.

However, current PDT is limited by the inefficiency with which the light-activated drugs specifically target tumours. This means they circulate in the body for some time after PDT treatment, leaving patients prone to acute light-sensitised skin damage. The study's Imperial research team think their results show how to solve this problem, by ensuring the drugs go specifically to cancerous cells, and then leave the body long before they can damage the skin.
Dr Mahendra Deonarain, from Imperial College London's Department of Life Sciences and lead author on the paper, explains: "PDT is a very promising way to treat cancer because compared to current surgical techniques, it leaves patients with very little cosmetic scarring and the chances of drug resistance are minimal. We have shown that it's possible to use tumour-seeking antibodies, like the ones used in the drugs Herceptin and Rituxan, to deliver these highly potent drugs safely and accurately to the site of the cancer, minimising the risk of healthy tissue getting accidentally damaged in the treatment process, and maximising the number of cancer cells that are destroyed."

The research team, led by scientists from Imperial and the Imperial spin-out company PhotoBiotics, has shown that their antibody-carrying light-sensitive drugs have effected complete tumour regression in an animal model. Dr Deonarain explains that the next step is to take the study forward into clinical trials: "Quite counter-intuitively, we've managed to show that it's possible to attach more of these drug molecules to antibody fragments than it is to whole antibodies, and without destroying the useful targeting properties of the fragment itself. Our initial results are extremely promising and we're hoping to take this forward into clinical trials in the near future. Our work is expanding the applications of PDT for many cancers and we're excited about moving towards making targeted PDT a clinical reality."
PhotoBiotics has filed four patents protecting this new technology and is currently completing further pre-clinical studies with a view to moving into clinical trials within the next three years.

For more information please contact:

Dr Lionel R Milgrom, PhotoBiotics Ltd Press Office,
Tel: +44 (0)208 450 8760
Mob: +44 (0)7970 852156
Email: lionel.milgrom@hotmail.com

Notes to Editors:

The research paper is available here:-

1. Targeted photodynamic therapy with multiply-loaded recombinant antibody fragments
   The International Journal of Cancer, published online 31 October 2007.