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Mosquito virus vs. cancer cells


Mosquito-borne viruses are usually bad news - the cause of such dangerous illnesses as dengue and yellow fevers, eastern equine encephalitis, West Nile fever and others.

But a research team at the New York University School of Medicine has found a mosquito-borne virus that may someday prove to be good news for cancer victims.

The Sindbis virus, named for the town in Egypt where it was identified 50 years ago, has been found to target and kill tumor cells in mice. Better yet, it does not appear to have toxic effects on healthy cells.

These unexpected properties have not been tested in humans. But the researchers hope to launch clinical trials with people in two to three years.

"It's very important for people to understand that lots of things that work in mice don't work in humans. The failure rate is high," said Daniel Meruela, a professor of pathology at the medical school and principal investigator in the study.

Nevertheless, he said, "I'm very optimistic. In the animal experiments we've done, the results are very striking and very promising."

Mosquitoes carry the Sindbis virus in parts of Africa and Asia. Healthy people bitten and infected experience relatively mild symptoms - fever and muscle aches. Its tumor-fighting side effects were discovered recently by Meruela and his co-workers.

In their study, published in the journal Nature Biotechnolgy, Meruela and his team reported that the virus appears to tackle cancerous cells wherever they are found in the mice - in tumors and wherever cancer cells have spread.

Daily injections of the virus, they found, led to the death of 99 percent of the mouse cancer cells in two months or less.

That would be a critical advance in fighting an illness such as ovarian cancer, which frequently goes undiscovered until it has spread too widely for effective treatment. "It's one of the unique properties of this [virus], which is why we're so excited," Meruela said.

Scientists have experimented for years with using genetically engineered viruses as a sort of Trojan horse to carry cancer-killing substances directly to cancer cells. But many of those virus "vectors" are weakened or inactivated in the bloodstream, so they can no longer enter the cells. Some also cause damage to the liver and other tissues.

Because Sindbis evolved to travel through the blood stream, Sindbis stays intact. And it causes no damage except to the tumor cells. "That is rather unique," Meruela said.

A Sindbis shortcoming is that once it has killed the tumor cells, it is no longer effective.

Meruela said his group is working to use Sindbis to carry a substance into tumor cells to stimulate the body's immune system to detect and attack cancer cells that linger, or recur.

The scientists also have attached a gene that creates a glow once it enters the cancer cells. Detection of the glow could tell doctors where invisible cancers might be lurking.

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