By Drog, Section News Posted on Tue Jun 01, 2004 at 07:38:03 AM PST
Viruses spread by infiltrating the cells of their host. Their detection causes the cell to commit suicide in a process called apoptosis, which prevents the virus from spreading further. However, viruses can carry genes that allow them to slip past this cell death process in normal cells, thus causing infection. As New Scientist reports, researchers at Cancer Research UK and Queen Mary's School of Medicine and Dentistry, University of London have devised an ingenious new strategy--they deleted one such gene in an adenovirus, causing it to be immediately detected by normal cells and unable to spread. But in cancer cells, which grow uncontrollably and ignore the cell death process, the virus was able to thrive and spread rapidly. It then multiplied so rapidly that it killed the cancer cells by making them explode.
"The great thing about this strategy is that the cancer cell does all the hard work," says Nick Lemoine, director of the Cancer Research UK Clinical Centre at Bart's Medical School, who led the team. "It makes more and more virus to infect its neighbouring cancer cells. But if a normal cell is infected, it commits suicide before it can make new virus and spread of the virus is contained."
Removing the gene, called E1B-19kD, from the adenovirus not only removed its cloak that viruses normally use fo evade detection, but also provided another unexpected benefit. It enabled the viruses to replicate much faster than normal, which in turn helped burst the cancer cells--an effect that previous genetically modified viruses had not shown.
The team examined the effects of the GM virus on pancreatic, lung, ovarian, liver and colorectal cancers in the test tube, as well as on live tumour-bearing mice. They plan to begin clinical trials in people in 2005. "In tests so far it has proven both potent and selective, although only clinical trials will tell us whether the approach can be an effective treatment in people," comments Robert Souhami, Cancer Research UK's director of clinical and external affairs. Lemoine adds that the GM virus could also be armed with additional anti-cancer weapons, in the form of genes producing toxic compounds. "The fact that we have taken a gene out of the viral backbone means we could arm the virus with something that deliberately kills cancer."
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