Brazilian researchers have just proven in dogs the potential of the Zika virus to fight advanced tumors in the central nervous system. The results of the study were published on Tuesday (10) in the journal Molecular Therapy. The article (in English) can be read over the internet.
Three animals of advanced age and spontaneous brain tumors were treated with viral injections by scientists linked to the Human Genome and Stem Cell Research Center (CEGH-CEL), a Research, Innovation and Diffusion Center (CEPID) supported by São Paulo State Research Support Foundation (Fapesp) at USP.
“We observed a surprising reversal of the clinical symptoms of the disease, in addition to tumor reduction and increased survival – and with quality, which is the most important. In addition, the treatment was well tolerated and there were no adverse effects. We are super excited about the results, ”he told Fapesp Agency Mayana Zatz, professor at the Institute of Biosciences (IB) at the University of São Paulo and coordinator of CEGH-CEL.
Zika’s ability to infect and destroy central nervous system tumor cells had already been demonstrated by the group in mice. In this model, the formation of human tumors is induced in the laboratory, which is only possible in immunosuppressed animals. One of the main advantages of the new study, according to the authors, was the possibility of evaluating the effect of therapy on animals with an active immune system.
“The results confirm that the therapy works through two mechanisms. On the one hand, the virus infects tumor cells, begins to replicate and ends up leading them to death. On the other hand, it activates the immune system for the presence of the tumor. The infection triggers an inflammatory reaction and defense cells begin to migrate to the site, ”said Carolini Kaid, a postdoctoral fellow at the foundation and the first author of the article, to Agência Fapesp.
According to Carolini Kaid, tumors of the central nervous system usually do not respond well to immunotherapy. This is because the blood-brain barrier, a structure that aims to protect the brain from potentially toxic substances present in the blood, makes it difficult for the defense cells to migrate to the site.
However, post-mortem (after death) made in the dogs’ brain tissue indicated the presence of T lymphocytes, macrophages and monocytes infiltrated in the tumor mass.
“These assessments also showed the presence of Zika only at the edges of the tumor. No other brain cells were affected. This is a very important finding, as it gives us more confidence that the treatment is safe ”, added Carolini Kaid.
The three dogs treated by the CEGH-CEL team were patients of veterinarian Raquel Azevedo dos Santos Madi, who attends a private hospital in Granja Viana, in the Metropolitan Region of São Paulo. All were diagnosed by means of magnetic resonance imaging when the disease was already in an advanced stage and the clinical signs were more evident. In these cases, the average survival, without treatment, is usually 20 to 30 days.
The virus was inserted into the cerebrospinal fluid of the dogs by means of an injection in the region of the spine just below the skull. A strain isolated from a Brazilian patient (ZIKVBR) was used, purified and given to the group by partners from the Butantan Institute.
The treatment was conducted in the hospital and the animals were only released home after three negative tests for the presence of the virus in the blood and urine. “We follow a very strict protocol to avoid contamination from other people”, emphasized the teacher Mayana Zatz.
The first dog to receive therapy was the 13-year-old, 26-kg (kg) pirate pit bull. “He arrived in a pre-coma state. He no longer stood up and received only parenteral nutrition. Three days after the injection of the virus, he went back to eating, managed to get up and sketch some steps. He remained alive for 14 days, but he was already very weak and had a cardiorespiratory arrest. The owners opted for euthanasia ”, explained the teacher.
The longest survival was observed in the boxer Matheus, eight years old and 32 kg, who remained alive for 150 days after therapy. In this case, through magnetic resonance, it was possible to observe a 35.5% reduction in tumor mass.
Dachshund Nina, 12 years old and 6.4 kg, was the third patient treated. In this case, survival was 80 days and the reduction in tumor mass was 37.92%. “Contrary to what happens in the case of chemotherapy, the animals did not show any negative reaction to the treatment. We started with a very low dose and, as it was well tolerated, we applied a second dose 10 times higher ”, said Mayana Zatz.
The tumor type of each dog was only confirmed in the histopathology analyzes done after death. In the boxer an oligodendroglioma was found and, in the dachshund, an intracranial meningioma. “In the pit bull it was not possible to make the identification, as we did not find any tumor cells. Apparently he was eliminated, as he was small ”, said Carolini Kaid.
In mouse trials, Zika was shown to be able to combat strains of medulloblastoma and atypical rhabdoid tumor (TTRA) – two types of cancer of the central nervous system of embryonic origin that affect children. In the tests in vitro, the researchers had observed the potential of the virus to infect and destroy glioblastoma and ependymoma cells.
In the evaluation of Oswaldo Keith Okamoto, a professor at IB-USP and a member of CEGH-CEL, the data suggest that viral therapy could be applicable to various types of cancer in the central nervous system – both in pediatric patients and in people over 60 years old . “These two groups are the ones that most frequently present aggressive tumors and for which there is no effective treatment today,” he told Agência Fapesp.
The researcher has been investigating strategies for destroying tumor cells that have characteristics similar to those of stem cells for more than 15 years. Although they are not able to transform into any cell type, these “tumor stem cells” make the disease more aggressive and difficult to treat.
In the studies in vitro, the CEGH-CEL group compared how the virus interacts with “tumor stem cells” and healthy neural progenitor cells, a kind of brain stem cell that gives rise to both neurons and astrocytes, oligodendrocytes and other cells nervous.
“When we infect neural progenitor cells, Zika stops proliferation and some of them die. But the spheres [formadas por um agrupamento de células progenitoras em cultura 3D] remain relatively intact. In the case of the tumor stem cell, the destruction is much more prominent. The tests in vitro also showed that the virus does not infect mature nerve cells, such as neurons. Which is a very good result, ”said Carolini Kaid.
According to Oswaldo Keith Okamoto, groups in the United Kingdom and Greece are interested in conducting collaborative projects aimed at better understanding the mechanism of action of Zika on tumor stem cells. In parallel, the CEGH-CEL group is renovating a part of the existing kennel at IB-USP to install an intensive care unit that will be used in the new studies.
“We learned a lot from these three dogs and now we intend to start a new pre-clinical study with a larger number of animals. One of the goals is to find the ideal dose of the virus for treatment. If it works, it will be a hope for treatment for both dogs and us. But for that, we need more funds and we seek partnerships ”, pointed out Mayana Zatz.