A genetically engineered polio virus, stripped of its ability to infect brain cells, has now been turned on a deadly form of brain cancer in a promising new treatment that’s now in its early stages. The weakened virus destroyed brain cancer cells and stimulated the immune system to clear out more distant tumor cells.
Researchers at the Duke University School of Medicine reported that 21 percent of those who received the treatment survived for 36 months. That compares with a survival rate of only 4 percent for a comparable group whose cancer was treated in other ways. Their study was published June 26 in the New England Journal of Medicine.
In adapting the polio virus as a cancer weapon, scientists overcame two major challenges, said Dr. Herbert Newton, FAAN, a neuro-oncologist at the Florida Hospital Cancer Institute who specializes in chemotherapy and molecular therapeutics.
First, the polio virus was long thought to be too dangerous, especially for people with brain cancer. To make it work, researchers had to defang the virus. They did it by replacing a key component of the virus — the part that allows it to enter a brain cell — with the matching part of a common cold virus, which can’t infect brain cells. This preserved the polio virus’ ability to kill tumor cells while removing its ability to attack healthy brain tissue.
“It’s brilliant to be able to modify something as dangerous as a polio virus,” Dr. Newton said. “These viruses have evolved the ability to kill and divide in human cells and now we’re using that evolution to attack tumors.”
The second difficulty involved delivering the virus to its target and getting past the body’s own defense mechanisms, such as the blood-brain barrier. “One difficult part of viral therapy is getting the virus into the tumor in a high enough concentration to make a difference,” Dr. Newton said. In this case, doctors used a surgical procedure to inject the virus directly into the tumor for six and a half hours.
Though it is far too early to say that patients in this trial were cured, its success in keeping many of them alive for more than two years is noteworthy, Dr. Newton says, “There is no magic bullet right now, but this success in a Phase 1 study is promising.”
A big part of the researchers’ success was realized not through the direct action of the viruses, but through the response of the patients’ immune system. The presence of the polio virus “leads the immune system to attack the tumor more vigorously,” Dr. Newton said. Targeting faraway cells is especially important in glioblastomas, which send tendrils away from a tumor to regrow elsewhere. The next step for this research will involve more patients, though it will likely not appear in most hospitals anytime soon. “They’re working with an extremely dangerous modified virus that many hospitals won’t have the capacity to handle,” Dr. Newton said.
Florida Hospital Cancer Institute is investigating a number of potential clinical trials involving immunotherapy. Patients who would like to learn more about the institute or schedule a one-on-one consultation should visit our website or call 407-303-1700.