Researchers in Alberta have successfully tested a new viral approach to treating prostate cancer in a small number of men.

The study was published in Tuesday's online issue Cancer Research, a journal of the American Association for Cancer Research.

Dr. Don Morris, an oncologist at the Tom Baker Cancer Centre in Calgary and his colleagues used a reovirus — a respiratory virus commonly found in the environment — to kill prostate cancer cells.This illustration shows reovirus particles in a cancer cell. (Oncolytics Biotech/Biodigital Systems)

When people are exposed to the virus, it causes a mild respiratory infection or mild diarrhea at most, Morris said.

The experiment involved injecting the reovirus into six prostate cancer patients, as well as mice models and test-tube studies to check how well the approach worked.

The reovirus naturally responds to mutations in the cancer cells. In normal cells, the virus is neutralized before it can replicate.

When the reovirus enters tumour cells, however, it reproduces itself. This causes the cancer cell to burst and release thousands of viral particles, which go on to kill other cancer cells. The bloodstream also carries particles to adjacent tumours, which may also regress, the researchers found.

Shrinking tumours

"Viruses are very specific in which cells they target," said Matt Coffey of Oncolytics Biotech Inc. in Calgary, which owns the patent on the reovirus and is commercializing the technology. "Basically, the patients feel as though they have a minor cold or malaise while they are being efficaciously treated for cancer."

The six men in the study had the virus injected directly into their tumours three weeks before they had surgery to remove the prostate gland as part of standard treatment.

The tumour cells are targeted by viruses in the experimental treatment, says Dr. Don Morris of the Tom Baker Cancer Centre in Calgary. (CBC)

Signs of cancer-cell death were found in the removed prostate tumour, while the normal parts of the prostate showed minimal toxicity and no viral replication, Morris said.

"It's really a weakness in the tumour cell that has allowed it to be sensitive to viruses but at the same time avoid the immune system," Morris said.

The researchers stressed they don't see reovirus as a cure for cancer, since it was rare that tumours completely vanished. The injections also worked better when given along with chemotherapy.

"I think we are going to make cancer a more treatable disease," Coffey said, noting it will be at least two years before the treatment is approved for regular use in patients if larger human trials testing the IV drug show positive results.

The study is worthy of more clinical trials as a possible way of treating some prostate cancers, said Robert Clarke, a professor of oncology at Lombardi Comprehensive Cancer Center at Georgetown University in Washington, D.C.

"I think this is an interesting approach," said Clarke, who was not involved in the study.

"Clearly, it is an area that is getting increasing attention and we need everything we can get our hands on to make a difference in these patients," he added in a journal release.

"The virus has been shown to be very effective against a variety of cancers, including breast cancer, lung cancer, brain cancer, pancreatic cancer and so on," said Dr. Patrick Lee, who published a paper in the journal Science 12 years ago showing reovirus kills cancer cells in mice. It has taken until now to show it could work humans.

"It targets at least 80 per cent of all human cancers," added Lee, Coffey's former supervisor, who now runs a cancer biology laboratory at Dalhousie University in Halifax.

Reovirus is being tested in other cancers, including a Phase 3 clinical trial for head and neck cancer in the U.S. and Europe. A clinical trial in lung cancer is also in the works.

Other scientists are working with measles, herpes and common cold viruses to try to attack cancer. All of those studies are still in the research phase, and none of them are available outside of clinical trials.

The research was funded by the Alberta Cancer Foundation, Oncolytics Biotech and the Prostate Cancer Research Foundation of Canada.