Author: Meenakshi Kashyap
A drawback of traditional chemotherapy and radiotherapy is the damage done to normal cells surrounding tumours. Scientists are exploring different therapies that can be used to selectively target and kill cancer cells but spare surrounding normal cells. One such treatment modality is light activated therapy also called photodynamic therapy (PDT). Treatment with PDT essentially consists of the administration of a photosensitive drug followed by local illumination of the tumour to activate the drug. Delivery of light into the tumour is controlled through the judicious use of optical fibres. Activation of the drug by light results in the release of a reactive form of oxygen which kills cancer cells.
PDT has several potential advantages. The therapy is relatively non-invasive, it can be accurately targeted to the tumour, repeated doses of therapy can be given, and the healing process results in little or no scarring. PDT has been shown to be effective in the treatment of skin, bladder, endobronchial, esophageal, and head and neck cancers.
PDT is also being investigated in clinical trials for the treatment of aggressive cancers with a poor prognosis, and cancers in organs where other conventional treatments cause high morbidity.
A major challenge in PDT research is the selective targeting of tumour cells alone. Existing PDT drugs accumulate in tumour cells and normal cells which can result in treatment-related toxicity to surrounding normal tissues as well as sunlight-induced skin toxicity.
A major advance in the development of a new PDT drug has been made by scientists, Drs.’ Gang Zheng and Brian Wilson at the Princess Margaret Hospital in Toronto. Their research group has successfully developed a new photosensitizer drug that can only be activated by light once the drug has been localized in the target tumour cells. The photosensitivity of the drug remains masked until its interaction with a specific enzyme, MMP-7, present in the tumour. MMP-7 is abundantly produced by many types of cancers which makes it an attractive anti-cancer target. The enzyme acts upon the drug to unmask the photosensitivity of the drug. Subjecting the tumour cells to laser light then results in the generation of oxygen radicals which kill only the cancer cells and not surrounding normal cells. The researchers tested the efficiency of the drug in cancer cell killing by growing separate cancer cells outside the body in a liquid nutrient system and also in mice that were injected with MMP-7 expressing human cancer cells. Tumour cell death was observed in both instances. Additionally, the tumours in mice completely regressed in 30 days with no signs of regrowth after treatment with PDT. The results of this study have been published in the May 2007 issue of the Proceedings of the National Academy of Sciences (PNAS).
© Copyright, PeopleMenders, 2009. All Rights Reserved.
About the Author
Meenakshi Kashyap has a Ph.D. in applied biology from the Cancer Research Institute, India, and currently works as a biotechnology scientist for an IT and bioinformatics consulting and outsourcing company.
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