UK scientists are preparing to begin trials to develop a new way of fighting cancer using viruses that cause colds.
Adenoviruses cause cold-like symptoms but could fight cancer
The new therapy would kill tumours while avoiding harming healthy cells by using viruses specially coated to stop detection by the immune system.
Initial trials expected this year will test the ability of viruses to kill liver cancer cells in humans.
The work is led by scientists at Oxford University and supported by Cancer Research UK.
Previous research has shown that viruses can be used to kill cancer cells, but these studies have concentrated mainly on injecting the viruses directly into tumours.
This method cannot be used if the cancer is inaccessible or has spread throughout the body.
Professor Leonard Seymour, leading the new research, plans to overcome this problem and allow the virus to travel through the blood to tumours throughout the body.
He said chemical modifications had been made to the virus to put a polymer coat around it, making it a "stealth virus" not detected by the body's immune system.
Because cancer cells suppress the body's local immune system in order to survive, they then provide a good environment for these viruses to live and replicate in, making the tumours susceptible to attack from the viruses.
Professor Seymour described the new method as "a way to turn the strength of a tumour into the weakness."
In the new therapy, only small amounts of virus are needed to initially treat patients, because the virus replicates in cancer cells until the cells burst and infect adjacent tumour cells.
This is different to many previous studies which have used replication-deficient viruses to deliver genes to the tumours to kill them.
Adenoviruses (small red dots) can infect cancer cells and replicate
Preliminary research on mice shows the new treatment works well on tumours resistant to cancer drugs, and trials on liver tumours later this year will test uncoated adenovirus, which normally causes cold-like symptoms, and vaccinia, used in the vaccine against smallpox .
The viruses will be disabled and delivered locally to the tumours to establish whether the treatment is in principle safe in humans, and what dose is needed.
Several more trials will be needed before the therapy can be used widely for treatment, but Professor Seymour said if these go well the therapy might be "a powerful and selective anti-cancer agent that could be potentially very useful."
He said it could even in principle be many times more effective than regular chemotherapy.
Dr Richard Sullivan, Cancer Research UK's director of clinical programmes, said: "Whilst this approach is still at an early stage of development it has exciting potential, particularly for the treatment of cancer which has spread - a notoriously difficult stage of the disease to treat."