- LOS ANGELES (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.
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- 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."
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- One expert also raised a safety issue.
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- "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.
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