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An Unlikely Weapon Against Aggressive Brain Cancer: The Zika Virus

Zika, doing something good for humanity for a change.

Jesse Hicks

This article originally appeared on Tonic.

A new study suggests that the Zika virus, known for causing brain defects in fetuses, could eventually be used to treat brain cancer by targeting and killing cancerous cells in the brain.

Glioblastoma is the most common form of brain cancer and it kills most patients within two years of diagnosis. John McCain's cancer is a primary glioblastoma, the more aggressive of two varieties; Senator Edward Kennedy died of a glioblastoma, as did Beau Biden, son of former vice president Joe Biden. It's estimated that nearly 17,000 Americans will die of a brain or central nervous system tumor this year.

That's partly because brain cancers are extremely difficult to treat. Surgery can remove the tumor, but it often still leaves behind the malignant stem cells that grow into tumors. They need to be removed or killed to prevent further growth, but they're often resistant to chemotherapy and radiation.

"It is so frustrating to treat a patient as aggressively as we know how, only to see his or her tumor recur a few months later. We wondered whether nature could provide a weapon to target the cells most likely responsible for this return," Milan Chheda from Washington University School of Medicine in St. Louis, said in a statement.

The Zika virus gained global attention last year, after it spread to Florida from South and Central America. Pregnant women infected with the virus had given birth to babies with abnormally small heads and damaged brains, a condition known as microcephaly. The spike in infection rates was enough for the World Health Organization to declarea global health emergency, only to see the epidemic seemingly peter out months later.

It's still an open question whether Zika is gone for good, but in the meantime scientists are studying how the virus affects developing brains. One method for killing cancer stem cells (the precursors to tumors) uses viruses that target those specific cells. Zika seems to do its damage in unborn brains because the virus targets neural stem and progenitor cells; it has less of an effect on adult brains likely because they contain fewer active stem cells, the researchers said.

That means Zika already targets the cells cancer researchers would like to be able to destroy. To test their theory, the study authors put Zika virus in a petri dish with cells from patients with glioblastoma. The virus "preferentially" infected and killed glioblastoma stem cells compared to other glioblastoma cells and other brain cells.

Zika virus (green) preferentially targets the stem cells (red) in a human glioblastoma. Photo: Zhu et al., 2017

Next they used a mouse-adapted strain of the Zika virus on mice with aggressive brain tumors and found that tumor growth slowed—and the mice lived two to three times longer than mice in the control group. The virus did not spread outside the tumors. They then tested another Zika strain, one more sensitive to the body's immune response as an extra safety precaution, in conjunction with a chemotherapy drug called temozolomide. They found the "attenuated" Zika could still target and kill glioblastoma stem cells, while the previously ineffective chemotherapy drug showed positive results. Pairing the two, researchers suggested, could open up a new avenue for treating brain cancer.

The current optimism is based on testing in petri dishes and on mice, of course, and there's the concern about adapting Zika for medical use. Much more study will be needed, including testing Zika on human glioblastomas transplanted into mice—and another team of doctors in the UK is looking into fighting brain cancer with Zika—but right now it's a glimmer of hope for treating a disease that has long stymied doctors.