Malignant brain tumors completely regress after treatment with parvoviruses, according to researchers from the German Cancer Research Center.

For the study, rats received brain tumors by implantation and were treated with parvoviruses once the brain tumors reached a specific size. According to the press release announcing the findings, the researchers realized early on that parvovirus H-1 had important advantages over other viruses.

Researchers reported that in the mice in which the viruses had been injected directly into the tumor, the tumors shrank after 3 days and completely disappeared in 8 of 12 mice treated. The mice survived without any symptoms compared to untreated controls, which suffered from severe disease symptoms within 3 weeks following implantation of their brain tumor. In addition, 6 out of 9 mice treated with the parvovirus intravenously showed complete tumor regression.

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More significantly, the researchers found no infection-related damage in the nervous tissue surrounding the tumor, and the viruses did not spread to the whole organism. The viruses reproduced in the tumor tissue, and viral protein production was found only in those cells.

The authors explained that parvoviruses kill tumors using natural properties, so their genetic material does not need to be genetically manipulated—as with herpes viruses, polio viruses, or adenoviruses, which have been used in other studies.

“Parvoviruses pass the blood-brain barrier, so that they can be administered via the bloodstream. In addition, they reproduce in cancer cells, which is particularly important for successfully treatment of glioblastoma, with its diffuse growth,” added Jorg Schlehofer, one of the study’s researchers. “Thus, the second-generation viruses reach and eliminate even those cancer cells that have already settled at some distance from the primary tumor.”

The findings were published in Neuro-Oncology (2010 Mar 18 [Epub ahead of print]).