An anti-malaria drug could help radiotherapy to destroy tumours, according to a new study.

The Cancer Research UK-funded study, published in Nature Communications, looked at the effect of the drug atovaquone on tumours with low oxygen levels in mice to see if it could be repurposed to treat cancer. The research showed that the drug slows down the rate at which cancer cells use oxygen by targeting the mitochondria, the powerhouses of the cell that make energy, a process that uses oxygen.

As radiotherapy works by damaging the DNA in cells, and a good supply of oxygen reduces the ability of cancer cells to repair broken DNA, tumours with low oxygen levels are more difficult to treat successfully with radiotherapy. By slowing down the use of oxygen, atovaquone therefore reverses the low-oxygen levels in nearly all of the tumours. The fully-oxygenated tumours are more easily destroyed by radiotherapy.

The drug was shown to be effective in a wide range of cancers, including lung, bowel, brain, and head and neck cancer. This older medicine is no longer patented and is readily and cheaply available as a generic.

Lead author, Professor Gillies McKenna, at the Cancer Research UK/Medical Research Council Institute for Radiation Oncology in Oxford, said: "This is an exciting result. We have now started a clinical trial in Oxford to see if we can show the same results in cancer patients. We hope that this existing low cost drug will mean that resistant tumours can be re-sensitised to radiotherapy. And we're using a drug that we already know is safe."

Dr Emma Smith, Cancer Research UK's science information manager, added: "The types of cancer that tend to have oxygen deprived regions are often more difficult to treat – such as lung, bowel, brain and head and neck cancer. Looking at the cancer-fighting properties of existing medicines is a very important area of research where medical charities can make a big impact and is a priority for Cancer Research UK. Clinical trials will tell us whether this drug could help improve treatment options for patients with these types of tumour."