Scientists have developed a new viral therapy that is capable of killing prostate cancer cells, and found it is even more effective when combined with a type of radiotherapy.
The team used a genetically modified strain of the vaccinia virus – the active component of the smallpox vaccine – to infect and multiply inside cancer cells, bursting them from within.
When given in combination with a form of radiotherapy called radioiodide therapy, the treatment was significantly more effective at killing cancer cells and slowing tumour growth than the single treatments alone.
Although at an early stage, the research paves the way for future clinical studies of viral and radiotherapy combinations – with the potential of improving the treatment of prostate cancer.
Scientists at The Institute of Cancer Research, London, in collaboration with other research teams in the UK, US and Australia, used human prostate cancer cell lines and studies in mice to investigate the cancer-killing properties of the modified virus on its own and in combination with different types of radiotherapy.
The study is published in the journal Gene Therapy and was funded by the T&J Meyer Family Foundation and the NIHR Biomedical Research Centre at The Royal Marsden and the ICR.
The vaccinia virus had been modified to selectively infect prostate cancer cells and not normal healthy cells – minimising damage to surrounding cells. In addition, it had been engineered to cause prostate cancer cells to display a channel protein on their surface.
The protein – called the sodium-iodide symporter – allows iodide ions to travel into cells. Using this property, the researchers exposed the prostate cancer cells infected with the virus to a radioactive form of iodine, meaning that radioactive iodine ions were able to enter the cells and kill them.
Radioiodide therapy is already commonly used in the treatment of thyroid cancers – as most of the radioactive iodide is taken up by the thyroid cells that naturally have the channel protein on their surface. This study shows the potential of radioiodide therapy to treat other cancers such as prostate cancer.
The researchers also investigated the modified vaccinia virus in combination with external beam radiotherapy and found that this also increased the rate of prostate cancer cell death. Mice that were treated with viral therapy and radiotherapy survived four times as long as those that were treated with virus alone.
Professor Kevin Harrington, Professor of Biological Cancer Therapies at the ICR, said: “Using viruses to kill cancer cells is an innovative way of treating cancers and an exciting area of research. Our study demonstrates the potential of the vaccinia virus to target cancer cells, and shows how its cancer-killing effects can be enhanced by combining the treatment with radiotherapy.
“Because the virus selectively infects cancer cells, the treatment has the potential to avoid the side-effects caused by damage to healthy tissue. It is therefore an attractive candidate for future clinical trials.”