London: Viruses which often cause dangerous infections could soon be the latest weapon in the war against cancer, scientists have claimed.
A team of researchers in the US have claimed that they are creating viruses that would be weak to damage healthy cells but strong enough to destroy cancer cells.
Scientists have already known that viruses can weaken cancer since the turn of the century.
However, early efforts to use this knowledge to cure patients largely failed as recovery was only temporary and sometimes sufferers died of the infection. Research into cures
then shifted to other treatments.
But, now following new understanding about genetics and how viruses and cancers work together, doctors have realised that specially tailored viruses might be the answer.
At the moment several potential cancer-fighting viruses are in trials, Dr Robert Martuza, chief neurosurgeon at the Massachusetts General Hospital and professor of neuroscience at Harvard Medical School, said.
"It`s a very exciting time. I think it will work out in some tumour with some virus," the Daily Mail quoted Dr Martuza as telling the New York Times.
According to the scientists, a form of the herpes virus is being tested on skin cancer, and vaccinia -- the virus used to protect against smallpox -- is currently being tested on liver cancer, which is the third cause of cancer deaths across the world. Other viruses are being tested against bladder, head and neck cancers, they noted.
In one trial the survival time for some patients doubled, they claimed. There are flu-like side effects to the viruses, however, doctors say these are much easier to manage than the effects of chemotherapy.
Dr Martuza began looking at how the herpes virus could fight cancer in 1991. He injected the a weakened form of the virus into mice with brain cancer and the disease in the rodents went into remission.
However, they died of encephalitis.
In 1990, Bernard Roizman, a virologist at the University of Chicago, discovered that when a particular gene in herpes was removed it slowed the growth of cancer cells.
Six years later, Dr Ian Mohr, a virologist at New York University, stumbled on a way of further altering Dr Roizman`s crippled virus.
He exposed it repeatedly to cancer cells until a new viral mutant evolved with the ability to replicate in those cells.
Unlike chemotherapy, which can diminish in effectiveness over time, oncolytic viruses multiply in the body and gain strength as the infection becomes established.
In addition to attacking cancer cells directly, some also produce an immune response that targets tumors, the scientists added.