"Telomerase: The Protein Behind Immortality, Cancer"
"Telomerase: The Protein Behind Immortality, Cancer"
by Aaron Rowe
by Aaron Rowe
"This year’s Nobel Prize in medicine went to a trio of scientists who discovered the enzyme telomerase, which allows cells to divide without any limits, making them effectively immortal. It may be nature’s greatest double-edged sword. Coax cells into producing telomerase, and they will survive indefinitely, but they will also become cancerous. To safeguard against cancer, adult cells keep track of how many times that they have multiplied, and once they have reached a pre-set limit — often around 80 divisions — they die. Telomerase interferes with this record keeping. If you can find a drug or gene therapy that interferes with telomerase, it could fight the unchecked growth of cancer cells, said Mark Muller, a cancer researcher who studies telomeres at the University of Central Florida.
“Ninety percent of all cancer cells are telomerase rich,” Muller said. Several companies, including Geron, have started testing drugs that gum up the telomerase enzyme, so that it can’t extend the lives of cancer cells.
Click image for larger size.Telomerase lengthens telomeres, repetitive DNA sequences that sit at the ends of chromosomes. Each segment of a telomere is like a ticket that gives it permission to divide. When cells run out of those credits, they cease dividing. Geron is developing a modified DNA molecule that gets stuck inside of telomerase, so that it can’t build up the ends of telomeres in cancer cells. The company is also working with a vaccine that trains cancer patients’ immune systems to attack cells that produce telomerase. In adults, almost all of the cells that produce telomerase are cancerous.
Those cancer treatments took shape almost 20 years after academics made a breakthrough discovery. In the early 1980’s Elizabeth Blackburn, Carol Greider and Jack Szostak identified telomerase and learned how it works. Some scientists speculated people could live longer by using the enzyme to buy extra time for their aging cells, but that idea remains risky and unproven. “By itself, lengthening telomeres would probably just increase the rate of tumor formation,” said Chris Patil, a researcher at the Buck Institute for Age Research in Novato, California. “Experiments with mice have shown that lengthening telomeres extends lifespan, but only if you introduce multiple other mutations to block cancer.”
Considering the risks of telomere-extension therapy, he thinks that scientists have bigger fish to fry. “In the absence of a comprehensive understanding, it’s very dangerous,” Muller said. “We have to figure out how to do maintenance on our telomeres.” Muller thinks humans could live for 90 to 210 years once scientists know more about the molecular basis of aging. “If we could figure out how to do maintenance, we could extend our lives,” he said. “But it has to be done very carefully, and we’d have to have a comprehensive understanding of the mechanism.”
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