"Zika virus used to treat aggressive brain cancer," BBC News reports. Animal and laboratory research suggests a modified version of the virus could possibly be used to target and destroy cancerous cells.
The Zika virus was first discovered in 1947. It hit the headlines in 2016 when an epidemic of the virus began quickly spreading through parts of South and Central America.
The virus, spread by mosquitoes, rarely causes serious problems in adults. But it can lead to birth defects, specifically microcephaly (a small, not fully developed head), if a woman contracts the virus when pregnant.
The virus has the ability to cross from the blood into the brain, so researchers wanted to see if it could be used to treat a very aggressive type of brain cancer called glioblastoma.
Glioblastoma is hard to eradicate with conventional treatments because the stem cells that drive the growth of the cancer tend to recur after the more developed cancer cells are killed by chemotherapy or removed surgically. Average survival is only two years after diagnosis.
So far, using Zika virus to treat glioblastoma has only been researched in cultured cells and tissue in the laboratory, as well as in mice.
Results have been encouraging, but we don't know if the treatment would work in humans. And more work is needed to find out if the virus can be engineered so it's safe to use.
Where did the story come from?
The work was carried out by researchers from the University of California, Cleveland Clinic, Washington University School of Medicine, and the University of Texas Medical Branch, all in the US.
The research was funded by grants from the US National Institutes of Health and the US National Cancer Institute.
It was published in the peer-reviewed Journal of Experimental Medicine.
BBC News and the Mail Online gave balanced and accurate reports of the study, although their headlines overstated the stage the research is at.
What kind of research was this?
This laboratory-based research involved several phases of experiments using:
- cells grown in the laboratory
- human brain tissue extracted during surgery
- mice
These types of experiments are all useful ways to investigate the action of a potential treatment in the laboratory before it can be tested properly in humans.
Researchers wanted to test the theory that Zika virus would infect and kill glioma stem cells (the cells that primarily drive the cancer) while sparing normal, non-cancerous brain cells.
What did the research involve?
Researchers tested the effect of different strains of Zika virus in several settings on:
- glioma stem cells and more mature glioma tumour cells grown in the laboratory after being removed from patients, and cells in artificially grown "organoids" that mimic the arrangement of cells in the brain
- tissue specimens of glioma tumours taken during surgery
- non-cancerous brain tissue samples
- mice injected with glioma cells that had grown into brain tumours
The researchers also looked at the effects of the West Nile virus, which is related to the Zika virus.
They used two strains of "natural" Zika virus, as well as a strain engineered to infect mice, as mice aren't usually susceptible to Zika.
They also looked at the effect of a strain of Zika engineered to be less likely to spread and cause disease in humans, in combination with an existing chemotherapy (temozolomide) that targets more mature glioma cells.
In the mouse experiments, the researchers randomly selected half the mice for treatment with Zika and half to act as a control group. They measured how much the tumours grew in the week after treatment and how long the mice lived.
What were the basic results?
Zika virus was much more likely to infect and kill glioma stem cells than other types of cells in the brain, including mature glioma cancer cells.
Glioma stem cells reproduced and grew in uninfected cultures, but they didn't reproduce when infected with either type of natural Zika virus. More of the glioma stem cells infected with Zika died.
In newly taken surgical samples, Zika virus infected more of the human glioblastoma tissue than normal brain tissue.
By contrast, West Nile virus infected all types of brain cells, whether cancerous or not, both in cultured cells and tissue samples.
In the mouse experiments, mice injected with adapted Zika virus showed slower tumour growth and lived longer – more than 50 days, compared with between 28 and 35 days for those not treated with Zika virus.
Engineered Zika virus tested alongside conventional chemotherapy on cultured glioma tumour cells also seemed to slow growth of tumour stem cells and improve the effects of the conventional chemotherapy.
How did the researchers interpret the results?
The researchers said the Zika virus "may offer a tailored therapy that could be used in combination with conventional therapies". They say it could help halt the recurrence of glioma stem cells after the mature tumour cells have been removed.
But they warned this research is only the "first step" in developing Zika virus as an anti-cancer therapy, and said "safety remains a paramount concern" with future use of the virus.
Conclusion
This is an interesting piece of research that shows how knowledge in one field of medicine can sometimes be applied to another field with surprising results.
But it's important to be realistic about the stage of research. This is very much a "proof of concept" study, and tests on cells, tissues and mice don't necessarily translate into a safe and effective treatment for humans.
The study has several limitations, but the fact the treatment so far hasn't been tested on humans is the most important. For one thing, Zika virus doesn't naturally infect mice, so researchers had to use a specially engineered virus that's different from the virus that infects humans.
Also, the glioma tumours in mice were taken from mouse models, so they weren't the same as human glioma tumours. The researchers say there are "technical challenges" to overcome before they can test human-derived glioma cells in mice.
They say it may be possible to make the Zika virus safe enough to use in glioma treatment, possibly by injecting it into tumour sites at the same time as surgery to remove tumours. But clinical trials of such a therapy are still some way off.
