Examine opens up prospects for the usage of virotherapy for the remedy of tumors of the central nervous system
In a study conducted at the Human Genome and Stem Cell Research Center (HUG-CELL) at the University of São Paulo, Brazil, serial systemic injections of the Zika virus in mice with brain tumors destroyed the cancer without causing neurological damage or otherwise Injuring organs and increasing the survival rate of the animals.
Scientists also injected Zika into cerebral organoids, brain-like organs made from stem cells in vitro. The virus not only prevented the tumors from progressing, but actually reduced their size.
In both the mice and the organoids, cytokines (proteins that regulate the immune response) suppressed tumor growth after the treatment, and defense cells migrated into the brain region affected by the tumor and made the immune system aware of its existence.
These results, published in an article published in a special issue of the journal Viruses, confirm the efficacy and safety of treatment with Zika in both models and open prospects for the use of virotherapy to treat tumors of the central nervous system.
According to the National Cancer Institute (INCA), around 11,000 new cases of brain cancer were registered in Brazil in 2020, around 5,200 of them in women.
One of the key points that confirmed previous research was immune system recruitment, which ensured a good response to treatment. Both viral pathways are very important as they allow the virus to act on a larger number of tumors than we originally expected. “
Mayana Zatz, Professor at the Institute of Biosciences (IB-USP) and Principal Investigator for HUG-CELL, one of FAPESP’s. Funded Research, Innovation and Dissemination Center (RIDC)
Zatz is the final author of the article, having led the project with co-authors Carolini Kaid, a researcher on a postdoctoral fellowship from FAPESP, and Oswaldo Keith Okamoto, also a professor at IB-USP.
Scientists from HUG-CELL had already shown in a study with mice published in 2018 and a study with dogs published in 2020 that the Zika virus can infect and destroy tumor cells of the central nervous system (more at: agencia.fapesp.br/27677 and agencia. fapesp.br/32733). They were the first to discover that Brazilian zika can be an effective agent in treating aggressive forms of embryonic tumors of the central nervous system, including medulloblastoma. The therapies available for these tumors, which mostly manifest in children, are rarely effective and have severe side effects that affect patients’ quality of life.
This latest study confirms that the approach is safe and effective. “You need to know the dosage and route of administration for any treatment attempt. In our study, three doses of systemic intraperitoneal injections of Zika at seven-day intervals produced promising results in the models,” said Raiane Ferreira, lead author of the articles. Ferreira has a PhD scholarship from FAPESP.
FAPESP also supported the research through a grant to Rodolfo Sanches Ferreira.
An epidemic of Zika fever began in Brazil and affected other American countries from April 2015 to November 2016. Most of the cases have occurred in Brazil, in part due to the widespread presence of the Aedes aegypti mosquito, which transmits both Zika and dengue.
Although Zika is usually asymptomatic, research has shown a link between the disease and the development of neurological complications such as Guillain-Barré syndrome and meningitis in adults, and congenital malformations such as microcephaly in newborns.
A significant number of women infected with Zika gave birth to babies with congenital Zika syndrome, mainly in the northeast region. According to the Brazilian Ministry of Health, 3,423 babies were born with the syndrome between 2015 and 2020.
Zatz was collecting genetic material on a visit to the northeast when the group began their research. “Neural progenitor cells contribute to the formation of the brain and the central nervous system. We collected samples from divided twins, only one of whom had microcephaly. We used these precursors to cultivate cell lines in the laboratory. We then infected them with Zika to find out how the virus behaved. That led to the idea of testing it on brain tumors that are rich in this type of cell, ”recalls Zatz.
The researchers worked with BALB / c nude mice, a type of laboratory animal that is hairless, lacks a normal thymus, and has a defective immune system due to a genetic mutation. Naked mice in particular are deficient in T lymphocytes and are often used in cancer research because they do not reject tumor cells.
The viral load per vaccination was 2,000 plaque forming units (PFU) from Zika. The first step was to analyze the safety of the treatment by applying the virus directly to the brains of the tumor-bearing animals. The effect was positive, but tumor growth started again after 21 days.
The researchers then tested serial intracerebroventricular (ICV) injections in mice infected with the same viral load that were high in virulence and viraemia, lost a significant amount of weight, and only survived four weeks. The control group remained alive and well with no clinical changes.
They next injected three doses of the virus intraperitoneally with the same intervals between doses. The effects were positive: the mice continued to feed and did not lose weight, while good clinical conditions were maintained.
In an experiment to analyze the tropism of the Zika virus, that is, its preference for infection of a particular tissue, determined in part by its interaction with receptors in the brain or tumor, the scientists injected tumor cells into the flanks of each mouse and found that the virus did not interact with them. No tumor remission was observed, suggesting that Zika preferentially interacts with the central nervous system.
“After we confirmed that the treatment was safe and the viral tropism was focused on the brain, we started the three intraperitoneal injections seven days apart and observed the results,” said Ferreira.
In the case of brain tumors, the serial injections efficiently destroyed them without neurological damage or injuries to other organs, while at the same time extending survival time.
The organoids of the brain were in the early stages (26 days) and were infected with Zika seven days after the addition of the tumor cells with 2,000 PFU. The tumor cells quickly attached themselves and began to spread in the organoids. The result was that viral infection of the tumor cells stopped the progression of the disease, confirming the potent oncolytic effects of Zika. An oncolytic virus infects and breaks down cancer cells, but not normal cells.
Similar positive results have been obtained with embryonic tumor cells of the central nervous system, but the authors of the article indicate that further research is needed to confirm the selectivity of the virus in these cases.
According to Zatz, a new phase of research has now begun in which dogs with brain tumors are being recruited. The suggestion is to work with animals of different breeds and sizes. “Dogs are extremely important models before we even think about testing human patients,” she said. “They have tumors very similar to human tumors and a preserved immune system. It will be possible to analyze different types of tumors. “
São Paulo Research Foundation (FAPESP)
Ferreira, RA, et al. (2021) Effect of serial systemic and intratumoral injections of oncolytic ZIKVBR in mice with embryonic CNS tumors. Viruses. doi.org/10.3390/v13102103.