The DNA in our cells is under continuous attack. DNA can be damaged by many factors, including highly reactive chemical by-products generated during respiration, mistakes made by polymerases during DNA replication and even cosmic radiation. Since DNA contains the instructions for producing all the proteins essential for life, selective pressure has produced cells with effective processes for detecting and repairing DNA damage. The aim of many cancer therapies is to cause high levels of DNA damage to prevent cancer cells from dividing successfully. However, the ability of cells to repair DNA damage often counteracts these treatments, leading to reduced effectiveness.
During radiotherapy beams of high-energy X-rays are focused on the tumour from outside the body, causing DNA damage in the cancer cells. However well targeted these X-rays are, they still need to pass through healthy tissue to reach the tumour. This can cause side-effects. When treating brain tumours, even localised side effects can have serious consequences, since the brain controls so many critical functions. Doctors often have to limit the radiation dose to avoid causing collateral damage that would severely affect quality of life. This means that brain tumours frequently regrow. This problem has led researchers to develop drugs that make the cancer cells more responsive to radiotherapy, for example by blocking their DNA repair mechanisms. In addition to knowing about the effects on the tumour, it is essential to test what potential side-effects these new drugs have on normal brain tissue.
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