New trials in the UK could see virus therapy become a regular part of cancer treatment, helping to avoid some of the side effects of chemotherapy and radiotherapy. Alok Jhareports
British scientists are preparing to launch trials of a radical new way to fight cancer, which kills tumours by infecting them with viruses such as the common cold.
If successful, virus therapy could eventually form a third pillar alongside radiotherapy and chemotherapy in the standard arsenal against cancer, while avoiding some of the debilitating side effects.
Leonard Seymour, a professor of gene therapy at Oxford University, who has been working on the virus therapy with colleagues in London and the US, will lead the trials later this year.
Cancer Research UK says it is excited by the potential of Seymour's pioneering techniques.
Seymour, one of the leading geneticists in the UK, has been working with viruses that kill cancer cells directly, while avoiding harm to healthy tissue.
"In principle, you've got something which could be many times more effective than regular chemotherapy," he says.
Cancer-killing viruses exploit the fact that cancer cells suppress the body's local immune system.
"If a cancer doesn't do that, the immune system wipes it out. If you can get a virus into a tumour, viruses find them a very good place to be because there's no immune system to stop them replicating. You can regard it as the cancer's Achilles' heel."
Only a small amount of the virus needs to get to the cancer. "They replicate, you get a million copies in each cell and the cell bursts and they infect the tumour cells adjacent and repeat the process," according to Seymour.
Preliminary research on mice shows that the viruses work well on tumours resistant to standard cancer drugs.
"It's an interesting possibility that they may have an advantage in killing drug-resistant tumours, which could be quite different to anything we've had before."
Researchers have known for some time that viruses can kill tumour cells and some aspects of the work have already been published in scientific journals.
American scientists have previously injected viruses directly into tumours but this technique will not work if the cancer is inaccessible or has spread throughout the body.
Seymour's innovative solution is to mask the virus from the body's immune system, effectively allowing the viruses to do what chemotherapy drugs do - spread through the blood and reach tumours wherever they are.
The big hurdle has always been to find a way to deliver viruses to tumours via the bloodstream without the body's immune system destroying them on the way.
"What we've done is make chemical modifications to the virus to put a polymer coat around it - it's a stealth virus when you inject it," he says.
After the stealth virus infects the tumour, it replicates, but the copies do not have the chemical modifications. If they escape from the tumour, the copies will be quickly recognised and mopped up by the body's immune system.
The therapy would be especially useful for secondary cancers, called metastases, which sometimes spread around the body after the first tumour appears.
"There's an awful statistic of patients in the West . . . with malignant cancers; 75 per cent of them go on to die from metastases," says Seymour.
Two viruses are likely to be examined in the first clinical trials: adenovirus, which normally causes a cold-like illness, and vaccinia, which causes cowpox and is also used in the vaccine against smallpox.
For safety reasons, both will be disabled to make them less pathogenic in the trial, but Seymour says he eventually hopes to use natural viruses.
The first trials will use uncoated adenovirus and vaccinia and will be delivered locally to liver tumours, to establish whether the treatment is safe in humans and what dose of virus will be needed.
Several more years of trials will be needed, eventually also on the polymer-coated viruses, before the therapy can be considered for use in the NHS in the UK.
Though the approach will be examined at first for cancers that do not respond to conventional treatments, Seymour hopes that one day it might be applied to all cancers.
Richard Sullivan, Cancer Research UK's director of clinical programmes, says the research shows interesting potential.
"We are pleased to be supporting this new and important research.
"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."