Thursday, November 12, 1998 Published at 22:17 GMT
Reovirus to target cancer
The Calgary research is published in the journal Science
By John Newall, BBC Science
Canadian scientists have discovered a virus that infects and kills cancer cells without affecting normal cells.
The virus, called a reovirus, has been used to kill a human cancer tumour transplanted into a mouse.
About six different viruses that kill cancer cells without affecting normal cells have now been discovered.
Although work on them is still at quite an early stage, they are regarded as a promising approach to therapy because, unlike existing cancer therapy using chemicals or radiation, they appear to have no side effects on normal tissue.
Because the viruses spread naturally from cancer cell to cancer cell, there is also the hope that they might be capable of completely eliminating tumours, whereas some cancer cells often survive conventional cancer treatments and grow to form new tumours.
Reoviruses, the type being used by the team at the University of Calgary in Alberta, Canada, are completely harmless to normal, healthy cells.
"We found that the receptor [for the virus] is very ubiquitous, so the virus attaches itself to all types of cells," virologist Dr Patrick Lee said.
"But we found that not all the cells it binds to are infected by this virus. We found clues that oncogenes, genes that cause cancer, could be important in allowing the virus to cause infection.
"So we introduced oncogenes into cells that are normally resistant to reovirus infection, and lo and behold we found that once the oncogenes had made the cells cancerous, they became susceptible to reovirus infection."
Normally, cells are naturally protected against reovirus. But a reovirus kills cancer cells because an oncogene known as the Ras gene makes a protein that destroys that protection.
Next, Dr Lee tested the reovirus against laboratory cultures of cancer cells from human breast, prostate and pancreatic cancers, with good results. Then he tested it against a human brain tumour transplanted into mice.
"We injected the tumours directly with the virus," he said. "We were able to see tumour regression within three to four weeks. The regression appears to be complete and the mice are still living after five to six months."
The tumour tissue seems to have been completely eliminated. The next step is tests in human patients.
Dr Lee has applied to the Canadian regulatory authorities for permission to carry out human trials, and hopes it will be possible to start the first tests, designed to see if the treatment is safe to use and how best to use it, within a year to 18 months.
If the treatment does prove valuable then it will only be for some cancers - only some have the Ras oncogene that makes them vulnerable to the virus. Some other cancers may also be too inaccessible for the virus to be used.