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Infections May Fight Cancer Growth

Study says inflammation be a medical ally, not an enemy

MONDAY, May 7 (HealthScout) -- Serious infections may stop the growth of cancer cells, says a new study.

For decades scientists believed that immune-system cells mobilize to destroy both life-threatening infections and tumors.

But it seems that infection, not the immune system, prohibits tumor growth, says lead study author Andrei Thomas-Tikhonenko, assistant professor of pathology at the University of Pennsylvania's School of Veterinary Medicine.

"What we see is that you don't need the immune response to block tumor growth. In fact, tumor growth can be stunted even in immunodeficient animals," says Thomas-Tikhonenko.

The clue "came from our discovery that during infection there is a suppression of angiogenesis," says Thomas-Tikhonenko.

Angiogenesis is the growth of new blood vessels. In normal tissue, unwanted growth is controlled by inhibitors, but when angiogenic growth factors are produced in excess of angiogenesis inhibitors, as with tumors, the new blood vessels can grow and feed diseased tissues.

"Since tumors need blood vessels, and since in infected mice angiogenesis is suppressed, infection and tumor growth should be incompatible," Thomas-Tikhonenko says.

The researchers used mice with severely weakened immune systems. They infected them the parasite Toxoplasma gondii, then injected melanoma cells, the deadliest form of skin cancer, which usually produce tumors in 10 to 12 days.

However, tumor growth in the infected mice was suppressed, and so was angiogenesis, suggesting that inhibitors of angiogenesis, not the immune system, keep infected animals tumor-free, researchers say.

"Such inhibitors are the holy grail of cancer research," Thomas-Tikhonenko says. "But the main question is where to find them. No one has ever shown that you can infect mice with a parasite and get inhibition of angiogenesis. We're obviously very excited."

Thomas-Tikhonenko says the next step is to identify those tumor-inhibiting molecules that are pressed into service by the infections. That process could take months, even years, he says.

Dawn Willis, scientific program director for the American Cancer Society, says she's surprised by the findings. "It does challenge the accepted dogma. For years we've been using (substances) to get the immune system going, but they've never been so good that they've been accepted" as therapy.

"Assuming this is true, it's still going to be a major undertaking" to find the magic molecules, Willis says. "And the idea of just using infected animals to produce it isn't very practical. It would be very expensive, and you'd need large animals, horses, cows, something big -- mice will not do -- and then it would have to be isolated, purified … and cloned."

But, she says, "It opens up a search" for new ways to inhibit tumor growth and may be useful when used with the approximate 40 other angiogenics which already exist. "I don't know if it will be different, better or not."

The study will appear in the May 15 issue of the Journal of Immunology.

What To Do

Get a primer on angiogenesis from the Angiogenesis Foundation.

Find out about available cancer treatments from the American Cancer Society

Read other HealthScout articles about cancer treatments.

SOURCES: Interviews with Andrei Thomas-Tikhonenko, Ph.D., assistant professor of pathology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, and Dawn Willis, Ph.D., scientific program director, American Cancer Society, New York City; May 15 Journal of Immunology
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