- Appearing forever young like Dick Clark
is everybody's dream. But, biologists wonder, what good is immortality
if all those extra years are accompanied by cancer?
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- That's the quandary posed by the discovery
earlier this year that a body substance called telomerase is an ``immortality
enzyme'' that encourages cells to keep dividing indefinitely instead of
dying with age. Scientists theorized that telomerase could be used to
slow the aging process. At the same time, some feared that the enzyme could
cause cancer by allowing cell division to run amok.
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- Now, new experiments by the same University
of Texas team of researchers have concluded that such fears are groundless.
The researchers watched human cells divide hundreds of times in test tubes
and concluded that telomerase does not by itself turn healthy cells into
malignant ones. In fact, they said the enzyme may offer promising new ways
to treat cancer.
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- ``Telomerase does not cause cancer progression,''
said Woodring Wright of the UT Southwestern Medical Center in Dallas, a
co-author of the study, published Tuesday in the January issue of the journal
Nature Genetics. ``The abnormalities seen in cancer are due to other mutations.''
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- Other researchers said the experiment
is too limited to exonerate telomerase. They said that while telomerase
may not cause cancer by itself, it appears to play a fundamental role in
the growth of cancerous cells, even if the cancer itself is triggered by,
say, radiation or a virus. ``There is no simple statement that telomerase
is irrelevant to cancer,'' said Ronald DiPinho of the Dana Farber Cancer
Institute of Harvard University. ``It's a very complex subject.''
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- Thomas Cech, a 1989 Nobel laureate and
biochemistry professor at the University of Colorado, said the Texas researchers
looked only at the effects of adding telomerase to a normal cell, not what
happens when telomerase is blocked in a cancer cell.
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- A year ago, Wright and colleague Jerry
Shay published research demonstrating that telomerase enables cells to
keep on dividing and avoid the normal process of aging and death.
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- Normally, human cells divide about 75
times over a lifetime. But each time a cell divides, the telomere, or the
protective end of a chromosome, erodes. Eventually, the telomere becomes
too short to protect the chromosome. When that happens, the cell can no
longer divide and eventually dies. By the time a person is an adult, most
of their healthy cells no longer contain any telomerase. But 90 percent
of cancer cells have been found to have telomerase, raising suspicions
that telomerase is linked to cancer.
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- In test-tube experiments, Wright and
Shay showed that normal cell death can be avoided by inserting a gene that
instructs the cell to produce telomerase.
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- As of late December, the cells had divided
as many as 220 times beyond their typical lifespan, and none exhibited
cancerous traits such as abnormalities in chromosomes, the researchers
said.
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- At least a dozen pharmaceutical companies
are in the early stages of developing drugs that would shut down telomerase
and starve cancer of the tumor growth substance critical to its survival.
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- Telomerase also is being considered for
use in unclogging blood vessels, restoring circulation involved in some
forms of blindness, and accelerating the healing of skin grafts.
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