Bacterial Protein Can Kill Cancer

New Treatment Causes No Side Effects in Mice

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Oct. 30, 2002 -- A new slant on an age-old approach in using live bacteria to fight cancer may finally be a way to reap the benefits of the bacteria without the nasty infectious side effects. A new study shows that by isolating a cancer-killing protein secreted by bacteria, researchers were able to shrink tumors in mice by as much as 60% -- without any harmful side effects.

The study appears in the Oct. 29 issue of the Proceedings of the National Academy of Sciences.

Researchers say cancer treatments using live bacteria to shrink tumors have been studied for more than 100 years, but the treatment usually ends up causing dangerous infections and possibly even death, which severely limits its viability as a medical therapy.

But rather than using a whole bacteria, the study researchers isolated a protein molecule called azurin that is secreted by a bacteria that normally causes severe respiratory infections in people. The bacteria are often resistant to antibiotics and get their strength from killing infection-fighting cells in the immune system.

This protein molecule derived from the bacteria has already been studied for other uses and is involved in the process that cells use to generate energy, but researchers say this is the first time it's been studied as an anti-cancer agent.

In the study, mice that had implanted human melanomas were injected with a small amount of azurin daily for 22 days. At the end of the study, the tumors in the mice that received the treatment were 60% smaller than those in the untreated mice. None of the treated mice showed signs of illness or weight loss.

Researchers say that azurin seems to work by stabilizing a protein that prevents the formation of cancer. Normally this protein is short-lived, but azurin bonds to this protein and protects it, allowing it to do its cancer-fighting work within the cell.

"These results suggest that azurin could be a useful anticancer agent not just for melanoma but for different kinds of tumors," says study researcher Tapas Das Gupta, MD, head of surgical oncology at the University of Illinois at Chicago, in a news release. But he says more studies are needed to confirm these very preliminary laboratory results.

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