"Most importantly, this study finds that the virus can penetrate into the brain, where it even reaches cells that have migrated away from the main tumour," says Harald Sontheimer, PhD, of the University of Alabama at Birmingham, who was not affiliated with the study. "Assuming that the virus behaves similarly in humans, in the future, it may provide a novel and highly efficacious way to treat resistant tumours."
The study is the culmination of six years of basic research into the fundamental processes of viruses and the cells they target, conducted by senior author Anthony van den Pol, PhD, and his team at Yale University School of Medicine. They set out to test the vesicular stomatis virus, which was selected for its ability to attack brain tumours and leave healthy tissue largely uninfected.
Tumour cells from brain cancers commonly found both in people and in mice were implanted into immune-compromised mice, which then received an injection of the virus in the tail. By viewing fluorescent proteins embedded in both tumour and virus cells in the brains of living mice, van den Pol's team watched as the virus infected multiple sites in the brain, spreading across an entire tumour within three days, killing tumour cells in its wake. The virus did not target normal mouse tissue or non-cancerous human brain cells transplanted into the mouse brain, the team found. They speculated that, unlike those in healthy brain tissue, blood vessels within brain tumours may leak, allowing the virus to cross the usually impenetrable protective barrier around the brain.
The virus was equally effective in destroying tissue from cancers that start in the breast or lung and spread to the brain-the two cancers most likely to metastasize to the brain-and targeted tumours at different sites throughout the body. Each year in the United States, more than 20,000 new cases of brain or nervous system cancers are diagnosed, according to the National Cancer Institute.
Future research will focus on understanding potential safety risks, such as whether the virus could eventually infect normal brain cells, as well exploring potential changes to the virus that could mitigate such risk. "We have some ideas for making the virus safer in the human brain," says van den Pol. "This is important to prevent the virus from potentially infecting normal brain cells after it has targeted the brain tumour."
