The scientists took their cues from the epidemic itself. Knowing how Zika attacked the developing brain, they wondered if the virus could have the same impact on brain tumors. “There’s a major effort to study viruses for their potential in treating illness,” Oswaldo K. Okamoto, a biologist and cancer researcher at USP’s department of genetics and evolutionary biology, told me. “At first we assumed that other institutions were already on this.”
As it happened, Zika was still a research frontier. So to test their hunch Okamoto and his colleagues devised a laboratory experiment to introduce the virus to cancerous cells of the central nervous system.
To their surprise, the lab tests showed that Zika mostly skipped normal tissue and went straight at the cancer cells, first in test tubes and later in mice carrying human tumor cells.
While virus-free mice died of cancer within a few weeks, animals infected with Zika lived longer, developed smaller tumors, suffered fewer cases of metastasis, and in some cases went into full remission. “At each phase of the study we had new surprises,” said Okamoto. “Just a small dose of the virus inoculated into the mice proved to be enough to eliminate tumors and stop the disease from spreading.”
The researchers also studied Zika’s effect on other tumors, such as prostate, breast and colorectal cancers, but found repeatedly that the virus had a predilection for cancer of the brain.
What’s especially encouraging is that Zika’s preferred targets include some of the most harrowing tumors of the central nervous system in children: medulloblastoma and the rarer but deadly ATRT. Young children diagnosed with such cancers respond poorly to conventional therapies such as chemotherapy, radiation and surgery, and survivors often are left with neurological damage, Okamoto told me.
The Brazilians were not the only ones chasing Zika’s secrets. Simultaneously, a team at Washington University School of Medicine in St. Louis came up with similar findings after injecting the virus into mice carrying glioblastoma, another aggressive brain tumor that resists conventional treatment and can kill in just 12 to 14 months. There, too, the results were promising.
Treating disease with disease has a long track record. Many vaccines are developed from trace elements of pathogens that trigger the body’s immune response. And consider the recent study that suggested how failing to expose infants to germs can leave them susceptible to leukemia.
The study of viruses has raised the quest for hair-of-the-dog therapy to a new level. Known for their resilience and stealth, viruses are capable of stealing unscathed inside cells to unleash destruction. Today scientists are looking to harness that same surreptitiousness to deliver potentially cancer-beating drugs and chemicals, or trigger the body’s own immune response.
Medical experts call these oncolytic viruses, or viruses that combat cancer naturally or through retooling in the laboratory. Scores of experiments and trials with viruses like polio, measles and herpes are already in train, although to date only one has been approved by the the U.S. Food and Drug Administration. Research into the evolving Zika epidemic could push oncolytics even further.
“Research tells us that cancer stem cells are especially resistant. They can repopulate a tumor even after aggressive treatment. So the dream has been to find, target and kill these cells,” neuro-oncology specialist Milan Chheda, who is part of a team studying Zika at the Washington University School of Medicine, said in an interview. “Zika naturally hones in on cancer stem cells. We’re leveraging natural properties of the virus.”
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