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Gene therapy

DNA helixAs cancer is a disease caused by damaged DNA, many researchers have tried to find ways to correct this damage by correcting the DNA itself.

Some gene therapy strategies aim to replace damaged genes with copies that work - like replacing a faulty part of a car that has broken down.

For example, the p53 gene, which normally acts as a brake on cell division, is defective in the majority of human cancers. Many attempts have been made to try to replace the damaged copy of p53 in a tumour with a working one, but, as yet, none has been particularly successful.

Scientists are working on many other gene therapy strategies. Some aim to block the cancer-promoting action of certain proteins made by damaged DNA. Others aim to damage the DNA of cancer cells even more than it is already, causing the cancer cells to commit suicide by apoptosis.

Another strategy, 'Gene-Dependent Enzyme/Pro-drug Therapy' (GDEPT) aims to insert a gene into the cancer cells that causes them to make a new enzyme. Then the patient is given an inactive anti-cancer drug called a 'pro-drug'. When the pro-drug and the enzyme meet in the cancer cell, the pro-drug becomes active.

The hope is that this drug will then kill the cancer cell, but leave other cells unharmed. This may be more effective at killing the cancer cells than conventional treatment, and could cause fewer side effects for the patient. Despite initial promise, none of these strategies has been particularly successful.

Gene therapy often involves using a modified retrovirus to add new genes to a patient's cells. 'Wild' retroviruses infect their hosts by inserting their DNA into their hosts' chromosomes.

For gene therapy, the retrovirus is modified so that it is no longer capable of causing disease, but is able to insert new genes into a patient's chromosomes.

Gene therapy is in its infancy. There are many concerns over the safety of modifying a patients' DNA. To date, no successful gene-based treatment has been approved for routine use on cancer patients, but a huge amount of research is being carried out in this area.

As our understanding of human biology increases, these approaches should eventually yield success. Cancer Research UK is funding a large amount of research in this area.

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Updated: 25 September 2009