June 27, 2005

Cancer Drug May Fight Smallpox

WASHINGTON (Reuters) -- A cancer pill noted for its effectiveness in stopping leukemia in some patients can also help delay the deadliest effects of a pox virus in mice -- offering the prospect of using similar drugs to treat or prevent smallpox, scientists said on Monday.

Tests of Gleevec, Swiss drug giant Novartis AG's successful leukemia pill, showed it could save the lives of mice infected with vaccinia -- a close relative of smallpox.

The drug, known generically as imatinib or STI-571, also prevented infection in the mice and slowed the spread of the virus in the body when given after infection.

"We propose the use of STI-571, a drug developed to treat cancer without substantial side effects, as a therapeutic for infections caused by pox viruses," the researchers write in this week's issue of the journal Nature Medicine.

Other drugs being developed in the same class may be even more useful against not only smallpox but other germs that infect cells in similar ways, the researchers, led by Daniel Kalman of Emory University School of Medicine in Atlanta, said.

Smallpox, caused by a virus called variola, was declared eliminated in 1980 after a global vaccination campaign. It no longer exists in nature, but experts fear terrorists or governments could use samples to launch biological attacks.

Once a dreaded disease with a fatality rate of 30 percent, smallpox was wiped out by using the first-ever vaccine -- based on the related vaccinia virus.

With the risk of biological attacks, researchers are working on a better, more modern vaccine and also exploring treatments for both smallpox and the side-effects of the existing smallpox vaccine, which is crude.

Kalman's team discovered that the smallpox virus uses an enzyme called tyrosine kinase to move from cell to cell.

New cancer drugs target this enzyme, which is also used by cancer cells to spread.

So Kalman's team gave the drug or a placebo to mice and then infected them with vaccinia. Only about 30 percent of the mice treated with placebo lived, compared to 100 percent of Gleevec-treated mice.

Pfizer has a drug similar to Gleevec in development. Known only by its experimental name PD-166326, it may be even more potent, experts say.

"Drugs such as PD-166326 may prove useful once the virus has disseminated, a prospect we are currently testing," Kalman's team wrote.

It may also be possible to use Gleevec or similar drugs along with Gilead Sciences Inc's cidofovir, an antiviral drug that has also been shown to work against smallpox.

The approach may work against other viruses and some bacteria, the researchers said.

For instance, when E. coli takes on a dangerous form, it uses tyrosine kinases, as does a virus called polyoma, which has been associated with cancer.

"The approach of fighting disease by targeting drugs to cellular molecules rather than to disease agents themselves may be applicable to a wide variety of pathogenic microorganisms," Kalman said in a statement.


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Emory University School of Medicine