Analysis: power of virus can be harnessed for good |

A ubiquitous, harmless virus that is carried by most people at some point in their lives could help to fight cancer, studies suggest.

Some patients with incurable diseases are already benefiting from an experimental virus-based drug in clinical trials in Britain and North America.

Researchers hope that virus therapy could eventually form a third pillar alongside radiotherapy and chemotherapy as life-prolonging treatments for cancer patients, while avoiding some of the debilitating side-effects of those treatments.

The drug, Reolysin, has been developed from the reovirus, a biological agent that is found almost everywhere in the environment, most commonly in stagnant water or sewage.

Up to half of adults have been exposed to the virus by the time they are in their twenties, but because it does not affect normal cells most infections go unnoticed and cause only minor cold-like symptoms, if any.

The virus has the distinctive ability to replicate within cancer cells and destroy them, however, by exploiting a specific pathway that occurs in almost two thirds of all cancers.

At least six virus types are currently being studied or genetically modified to provide potential therapies against cancer, in what scientists believe could provide a radical new way of fighting the disease.

Viral replication within cancer cells causes them to burst open and die, at the same time releasing more of the virus to infect other cancer cells. It is hoped that entire tumours could eventually be eradicated in this way.

Kevin Harrington, team leader in targeted therapies at the Institute of Cancer Research, London, has now treated more than 100 patients with reovirus-based therapy since he started trials four years ago along with colleagues from the University of Leeds.

Encouraging results have so far been seen in patients with head and neck cancers or sarcoma, a disease of the joints or bone, who typically do not live for more than a few months after chemotherapy or radiotherapy stop working.

“Combining viral therapy with chemotherapy or radiotherapy appears to be synergistic, and even when other treatments have failed, patients can see their cancer stabilise or go into remission,” Dr Harrington said. “The typical prognosis for a patient with head or neck cancer is four to six months of life after carboplatin [chemotherapy] has stopped working, but we have had patients go through eight monthly cycles on the trial and are still going,” he added.

A separate trial in the United States, involving 35 patients with sarcomas that had progressed to the lungs, reported that more than a fifth (21 per cent) saw their cancer stabilise or regress for between four to 17 months on the therapy.

“The standard treatment for this type of sarcoma is chemotherapy, but prognosis is poor since there is no cure," Monica Mita who led the trial at the University of Texas Health Science Center, (UTHSC), San Antonio, said. “Patients with only a few months to live face poor quality of life because chemotherapy treatments are so harsh. The goal is to introduce less invasive approaches that help extend life and provide patients with a better quality of life.”

Reolysin, discovered by a Oncolytics Biotech, a company based in Calgary, Canada, is delivered through cycles of daily 40-minute infusions for a week at a time, with gaps of three weeks in between.

Dr Harrington added that it was not yet known whether the viral therapy boosted the effects of chemotherapy or vice versa, but the results were encouraging “hints” before fully randomised phase III trials begin early next year.

“We are effectively using different therapies to attack cancer from different directions and all the signs are that, by complementing each other, they can be very effective in stopping tumours from spreading,” he said. However, it may be some time before viral-based therapies become used as a frontline treatment against cancer, he said.

Professor Peter Johnson, Cancer Research UK’s chief clinician, added: “This is an interesting but preliminary study, which highlights the potential of using genetically modified viruses as a weapon against cancer.

“Finding new treatments that work against disease that has spread is vitally important. This is one of a number of similar approaches for treating cancer that Cancer Research UK is supporting. But it’ll be some years before we’ll find out whether this particular treatment is effective in the long term.”

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