Investigators at the University of Leeds and the Institute of Cancer Research (ICR) say that they have recently figured out how a two-step approach to targeting cancer cells using viruses works. The group was able to determine how the viral agents escape the actions of the immune system.
Usually, whenever a foreign cell or contaminant enters the blood stream, our body's natural defenses kick in, and immediately disintegrate and degrade the intruder. If scientists want to use viruses to attack tumors, they need to stop this from happening.
One approach is to suppress the activity of the entire immune system, as doctors do in patients who've just received organs from donors. This is undesirable because it exposes the body to other infections.
Another approach is to hide the viruses from the immune system. If this is made possible, then cancer cells would become blind to the approaching viruses as well. In the new study, experts have managed to show how the viruses are shielded from antibodies in the bloodstream.
The new data appear to suggest that this type of therapies could from now on be applied to people in an outpatient setting, similar to the one used to administer standard chemotherapy drugs. In addition, the viruses could turn out to be effective against a large number of cancer types.
The active agent in the therapy the team tested is called the reovirus. It attacks tumor cells on two fronts simultaneously. First, it kills cancer cells directly, by infiltrating them. Secondly, it triggers a type of immune response that is tremendously effective at cleaning up residual cells.
Several clinical trials using the reovirus are currently being performed at a number of sites around the world. The preliminary results are expected to be published soon.
“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 bloodstream,” Dr. Kevin Harrington explains.
The investigator holds an appointment with the Institute of Cancer Research, as well as with the Royal Marsden NHS Foundation Trust. Details of the new study were presented in the latest issue of the esteemed journal Science Translational Medicine.
“It would have been a significant barrier to their widespread use if they could only have been injected into the tumor, but the finding that they can hitch a ride on blood cells will potentially make them relevant to a broad range of cancers,” says Harrington, one of the researchers who led the study.
“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,” he concludes.