TELOMERASE- THE END OF CANCER?
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
"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
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.