Silencing SARS

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Scientists have developed a potential therapy for severe acute respiratory syndrome (SARS). Harnessing a genetic process called RNA interference, a team of researchers crippled the SARS virus in infected monkeys, preventing the onset of some symptoms and reducing the severity of existing infection. The researchers say it's the first time this technique has been used to block an infectious disease in primates, raising hopes that it can be used to prevent a future SARS outbreak.

RNA interference (RNAi) occurs when small fragments of RNA, called short interfering RNAs (siRNAs), block the expression of genes. So a group of researchers from China and the United States wondered if they could use RNAi to block the genes of the virus that causes SARS--a disease that has killed over 700 people worldwide and for which there is no safe, tested vaccine or treatment.

First, the researchers, led by Patrick Lu, a molecular biologist at Intradigm Corporation in Rockville, Maryland, designed 48 siRNAs, each against a different part of the SARS virus genome. When they injected these siRNAs into cells, they found that 2 worked best at hobbling the virus. The team then infected 20 rhesus macaques with SARS and treated some with the 2 siRNAs. Monkeys treated early did not develop full-blown SARS symptoms, and those treated at later stages of infection had less severe lung damage than those that received no treatment, the researchers report online August 21 in Nature Medicine.

Lu says the therapy appeared to be safe, and he was "very surprised" by how successful it was. The next step, he says, will be to move to safety trials with human volunteers. A similar RNAi-based strategy might work against other respiratory diseases, including avian flu, notes Lu.

"It looks promising," says Andrew Hamilton, an RNAi researcher at Glasgow University in the United Kingdom. But he warns that "one of the concerns of using siRNA as a therapeutic agent" is that you don't want it blocking the body's essential genes. As siRNA therapy advances into clinical testing, the risk of unexpected side effects needs to be studied very carefully, he says.

Related sites
More information on SARS from the CDC
How RNAi works

Posted in Biology