Researchers May Have Key to Cancer Cells’ Immortality

Researchers may have discovered why cancer cells are able to reproduce endlessly, a finding that could lead to drugs that would attack disease cells directly, without harming healthy tissue.

Dr. Calvin B. Harley, who directed the research at McMaster University in Ontario, Canada, said his group has found in cancer cells an enzyme that permits the unlimited replication of new cells. The enzyme is absent in normal body cells.

This suggests, said Harley, that the enzyme, called telomerase, is what allows cancer to become “immortal,” a laboratory term for the ability of a cell line to grow new cells endlessly through the division of old cells.

At a news conference Monday, Harley said that normal cells are able to reproduce only a finite number of times, limited by the condition of the tip end of the chromosomes in a cell. This tip, called the telomere, contains a cap of identical genes that protect the rest of the gene structure. It works rather like the plastic tip on a shoelace that prevents fraying.

When cells divide, some of the telomere genes are lost. Since each cell line started with only about a thousand of the telomere genes, the number of daughter cells that can be produced is limited. When the cell line runs out of telomere genes, the cell line dies, a phenomenon called cell senescence. This is a strong contributing factor to aging and death.

Cancer cell lines, however, seem to be able to replicate endlessly and without control. The researchers, who are publishing their findings in today’s issue of the Proceedings of the National Academy of Sciences, said Monday they might be just two years away from starting tests of a drug that they hope will block the enzyme in human cancer patients. If the hypothetical treatment worked, cancer cells would, theoretically, age quickly and die.

Although the findings are just emerging from the realm of basic science--no animals have been tested--researchers hailed them as major advances. Dr. Huber Warner of the National Institutes of Aging said Harley’s study “gives us a better understanding of the control of cell doubling and its relevance to aging.”