Brussels, 02 Jun 2004
Scientists have used a genetically modified (GM) virus to target cancerous cells while leaving healthy cells uninfected, potentially opening the way for highly selective viral cancer treatments.
The team from Cancer Research UK and the London Queen Mary's school of medicine and dentistry took advantage of a fundamental difference in behaviour between healthy and cancerous cells. If infected, normal cells shut themselves down in order to contain the spread of a virus, whereas cancer cells refuse to stop, allowing a virus to thrive.
Viruses rely on entering cells undetected and destroying them, before replicating themselves and spreading to infect neighbouring cells. The GM virus was created by removing a gene called E1B-19kD, which it and other viruses use to disguise themselves. By revealing the virus, normal cells are able to realise that they have been infected and so self-destruct, while cancer cells are programmed not to shut down, thus allowing the GM virus to spread selectively through the tumour tissue.
'The great thing about this strategy is that the cancer cell does all the hard work,' explains team leader and director of the Cancer Research UK clinical centre Professor Nick Lemoine. 'It makes more and more virus to infect its neighbouring cancer cells. If a normal cell is infected it commits suicide before it can make new virus, its neighbours don't get infected and spread of the virus is contained.'
Professor Lemoine added that the next step for the team will be to introduce a toxic gene into the virus, enabling cancer tumours to be poisoned while leaving healthy tissue unharmed. This task will be made easier by the fact that the GM virus has already had one gene removed, creating room to insert others.
A further advantage of the new virus is that since it thrives in tumours, potentially only a relatively small number of copies of the virus need to come into contact with cancerous cells for the treatment to work. This means that it may be possible to simply inject the GM virus into the bloodstream, rather than directly into the tumour, as with other viral therapies under development.
As to when their research might be applied to treating patients, Professor Lemoine said: 'The virus we are using can replicate in tumour tissue much faster than its predecessors and offers real hope for the future. We plan to test it in clinical trials early next year.'
Cancer Research UK's director of clinical and external affairs, Professor Robert Souhami added: 'In tests so far [the virus] has proven both potent and selective, although only clinical trials will tell us whether the approach can be an effective treatment in people.'
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