DALLAS- A single enzyme, telomerase, appears to be responsible for the unchecked growth of cells seen in human cancers, report researchers from the University of Texas. The finding could offer researchers an entirely new approach to the diagnosis and treatment of cancer.

Telomeres are DNA sequences found at the ends of eukaryotic chromosomes which maintain the fidelity of genetic information during replication. Under normal circumstances the telomeres become shorter and shorter with each cycle of cell division. A sufficiently short telomere is believed to signal the cells to stop dividing. The telomerase enzyme is a ribonucleic protein that synthesizes telomeric DNA on chromosome ends.

After conducting research indicating that telomerase was involved in telomere maintenance, a team of researchers at the University of Texas developed a highly sensitive assay for telomerase. The new assay technique utilizes PCR to increase the sensitivity, speed and efficiency of previous assays.

An evaluation of cell lines from 18 different human tissues revealed the presence of telomerase in 98 of 100 immortal cell lines. Telomerase was not found in any of 22 mortal cell lines. Subsequent assays of tumor biopsies revealed the presence of telomerase in 90 of 101 specimens representing 12 different tumor types. None of 50 normal somatic tissue specimens tested positive for telomerase.

"Telomerase appears to be stringently repressed in normal human somatic tissues but reactivated in cancer, where immortal cells are likely required to maintain tumor growth," the researchers report in a recent issue of Science.

Previous attempts to measure telomerase activity in actual tumor specimens has been limited by insufficient sample sizes and insufficiently sensitive assays. The assay developed by the University of Texas researchers, called TRAP (telomeric repeat amplification protocol), should make analysis of telomerase activity in primary tumor specimens feasible, the researchers believe.

The fact that telomerase appears to be expressed in virtually all advanced malignancies should lead to new diagnostic and therapeutic applications. Assays for telomerase could help clinicians determine the status of suspect tumors, while a drug that block telomerase could have significant anti-cancer effects.

For more details on this study, please see: Kim et al, Science, v.266, pp.2011-2015, 12/23/94.

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