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Stem cells track and destroy brain tumors

LOS ANGELES, Oct. 15 (UPI) -- Using embryonic neural stem cells from mouse brains as genetically engineered, microscopic bloodhounds, researchers said Tuesday they have developed a technique that sniffs out and destroys cancer cells on contact.

The bloodhound cells are so persistent they can track down and eliminate even tiny elusive pockets of malignant tumor.

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"We've shown that we can use these cells to deliver tumor-toxic cytokines to disseminated tumor pockets, lead researcher Moneeb Ehtesham, a neuroscientist at the Maxine Dunitz Neurosurgical Institute at Cedars-Sinai Hospital, told United Press International. Cytokines are proteins that help control immune responses. "There is no other realistic way to identify and target all of these microscopic tumor reservoirs. Here we now have a powerful tool that can do this on our behalf."

Stem cells have the ability to become many different types of cells, but they also exhibit the unique quality of tracking down cancer cells in the brain. Nobody knows exactly why. Experts guess one reason might be stem cells inherently home in on chemicals the malignant cells secrete.

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"This is a very exciting observation that I think has promise, as we translate these findings into clinical studies," said co-investigator Keith L. Black, neurosurgeon and director of the Maxine Dunitz institute.

The most common form of cancerous brain tumors are called gliomas. They are very difficult to treat because the cancer sends microscopic pockets of tumor cells throughout normal brain tissue, making it impossible to remove the tumor entirely by surgery.

As reported in the Oct. 15 issue of the journal Cancer Research, Ehtesham, Black and colleagues created mouse gliomas by injecting cancerous cells into the brains of mice. They obtained stem cells from mouse embryos and inserted a gene that enables them to produce interleukin-12, a substance that recruits the immune system to attack and kill tumor cells. They then injected gene-carrying stem cells into the main tumor masses.

The tumors disappeared in 30 percent of the mice. Those animals are still alive and even show resistance to re-injection with glioma tumors. On average, mice that received stem cells lived about twice as long as those who did not -- about six weeks as opposed to three weeks.

Although the researchers think this technique someday might lead to human cancer treatment, using embryonic stem cells from humans remains a roadblock because it is controversial for ethical reasons. The researchers are studying stem cells derived from adult bone marrow, but that alternative seems much less promising.

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"This is too big of a jump to make at this point. No one has shown that bone marrow stem cells integrate into brain and follow tumor cells," said Jim Olson, a stem cell and brain tumor researcher at the Fred Hutchinson Cancer Research Center in Seattle. It also is probable human glioma cells will be harder to target than the laboratory grown glioma cells were in the experimental mouse model, Olson said.

One expert also raised a safety issue.

"One has to wonder, what would be the fate of these cells that you inject in the brain?" asked Viviane Tabar, assistant professor of neurosurgery and stem cell researcher at Memorial Sloan-Kettering Cancer Center in New York. "They might continue to divide. Uncontrolled division in the brain gets you worried about forming a new mass," she said.

(Reported by Joe Grossman, UPI Science News, in Santa Cruz, Calif.)

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