In a significant step forward for the development of a potential new cancer treatment, scientists have found how a common cold virus can kill tumors and trigger an immune response, like a vaccine, when injected into the blood stream.
Researchers from Britain's Leeds University and the Institute of Cancer Research (ICR) said by hitching a ride on blood cells, the virus was protected from antibodies in the blood stream that might otherwise neutralize its cancer-fighting abilities.
The findings suggest viral therapies like this, called reovirus, could be injected into the blood stream at routine outpatient appointments - like standard chemotherapy - making them potentially suitable for treating a range of cancers.
The study, part-funded by the charity Cancer Research UK and conducted on 10 patients with advanced bowel cancer, confirmed that reovirus attacks on two fronts - killing cancer cells directly and triggering an immune response that helps eliminate leftover cancer cells.
"Viral treatments like reovirus are showing real promise in patient trials. This study gives us the very good news that it should be possible to deliver these treatments with a simple injection into the blood stream," said Kevin Harrington from ICR, who co-led the study and published it in the journal Science Translational Medicine on Wednesday.
Harrington said if viral treatments had been found only to work when injected directly into tumors, that would have been a significant barrier to their widespread use.
"But the finding that they can hitch a ride on blood cells will potentially make them relevant to a broad range of cancers," he said.
Reovirus is being investigated by several research teams around the world - including scientists at Canada's Oncolytics Biotech Inc - because it has shown an ability to infect and kill cancer cells without affecting normal tissue.
"We also confirmed that reovirus was specifically targeting cancer cells and leaving normal cells alone, which we hope should mean fewer side-effects for patients," Harrington said.
Cancer killed 7.6 million people worldwide in 2008, the most recent year for which the World Health Organisation has full data. The number of cancer cases is expected to surge by more than 75 percent across the world by 2030.
The 10 patients in the study were all due to have surgery on tumors that had spread to their livers. During outpatient appointments in the weeks before their surgery, they were given up to five doses of the experimental reovirus treatment.
When researchers looked at pieces of tissue removed during surgery up to four weeks later, they found what they described as "viral factories" of active virus in the tumor - but not in the normal liver tissue.
This confirmed the reovirus had been delivered specifically to the cancer cells after being injected into the blood stream.
"It seems that reovirus is even cleverer than we had thought," said University of Leeds' researcher Alan Melcher.
"By piggybacking on blood cells, the virus is managing to hide from the body's natural immune response and reach its target intact. This could be hugely significant for the uptake of viral therapies like this in clinical practice."