Army researchers at Ft. Detrick say cysteine protease inhibitors stop SARS in vitro, in normal doses, and so does interferon, but in doses 10 times higher than are now used -
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The Army lab found that a variety called interferon beta blocks the SARS virus in the lab dish, although it takes 10 times more than would ordinarily be given to a patient. Still, experts say smaller doses might be effective inside the human body.
While interferon appears to have the best chance of quickly becoming a treatment for the disease, Huggins says, extra testing is necessary to make sure it does more good than harm.
Because the respiratory disease is brand new, no one knows exactly why it makes people so sick, in some cases destroying their lungs. Certainly, the virus itself is capable of great damage. But in some infections, the body's own over-the-top counterattack _ including vast production of interferon _ can be as bad as the bug itself.
So before interferon becomes a SARS treatment, doctors will have to be sure patients are not already making more than enough interferon of their own.
However, Dr. Frederick Hayden, a respiratory virus expert at the University of Virginia, notes that when the flu causes pneumonia, the body produces too little interferon to fight back effectively, so the Army lab results "raise the possibility of using interferon either for prevention or for therapy of SARS."
Experts are also encouraged to learn that drugs called cysteine protease inhibitors can stop the virus by jamming one of the enzymes it needs to make new copies of itself. Jahrling says the lab has tested 19 of them, and six work well. "They clearly inhibit replication of the virus and do so at concentrations that are not toxic to the cells."
The drugs were all created by pharmaceutical firms to treat or ward off colds caused by the rhinoviruses, but none of the six have been given to people. Because of similarities between the various respiratory viruses, scientists have hoped from the start that medicines aimed at colds and flu will turn out to be good for the SARS virus, too.
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