The researchers also tested the ability of the virus to work against cancer in living animals by injecting it into brain tumors of 18 mice. (For control, 15 additional mice with brain tumors were injected with placebo.) After 2 weeks, the mice injected with the Zika virus had significantly smaller tumors and a longer survival rate than the mice injected with placebo. Additional studies that used brain tissue collected from epilepsy patients also revealed that noncancerous brain cells were not infected by the virus.
To be able to use the treatment in humans, the Zika virus would need to be injected directly into the brain, “most likely during surgery to remove the primary tumor,” according to the press release. If the virus were introduced “through another part of the body, the person's immune system would sweep it away before it could reach the brain.”
Although the act of injecting the Zika virus directly into the brain would seem to be counterintuitive, given the virus’ ability to cause brain damage in infants, neuroprogenitor cells—the virus’ primary target—are more abundant in the fetal brain than the adult brain. This makes the virus potentially safer to use in adults, in whom the virus causes usually only mild symptoms.
To make the virus safer, 2 mutations were introduced that weakened its ability to fight cell’s defense systems. This mutation still allowed the virus to grow inside of the tumor cells, but rendered it weak enough that healthy cells would quickly be able to destroy it. Although weaker, the (safer) mutated virus was found to still be able to kill the cancer cells.
Michael S. Diamond, MD, PhD, from the Herbert S. Gasser Professor of Medicine at Washington University School of Medicine, and senior co-author on the study remarked on these changes to the virus in the press release, stating, “We're going to introduce additional mutations to sensitize the virus even more to the innate immune response and prevent the infection from spreading. Once we add a few more changes, I think it's going to be impossible for the virus to overcome them and cause disease.”
These cancer-killing capabilities seem to be unique to the Zika virus; for example, the researchers “found that West Nile virus indiscriminately killed both tumor and normal neural cells.” Thus, as an oncolytic virus, Zika has the potential to be modified and used as a complimentary therapy against glioblastoma in adults, in the future.
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