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* Center for Radiological Research, Columbia University, New York, New York 10032, USA;
Radiation Oncology Department, St.-Luc University Hospital, Belgium; and
Johns Hopkins Oncology Center, Baltimore, Maryland 21205, USA
1Correspondence: Center for Radiological Research, VC11–213 College of Physicians and Surgeons, Columbia University, 630 West, 168th St., New York, NY 10032, USA. E-mail: tkp1{at}columbia.edu
Radiotherapy plays a key role in the treatment of many tumors. It is difficult to determine what fraction of tumor cells survives after treatment with ionizing radiation. A convenient and sensitive biochemical assay could be efficacious in determining the potential success of radiotherapy. Since telomerase activity is frequently associated with the malignant phenotype, we sought to determine whether a correlation existed between ionizing radiation-induced cell killing and telomerase activity. We evaluated telomerase activity in two telomerase-positive and one telomerase-negative human cell line exposed to ionizing radiation. Telomerase activity was determined using a PCR-based telomeric repeat amplification protocol coupled with ELISA. We found ionizing radiation treatment to decrease the telomerase activity (in plateau phase cells of RKO, HeLa; and growing cells of RKO) in a dose-dependent manner, which correlated with cell death in in vitro tests as well as during tumor regression in nude mice. In contrast, growing HeLa cells after 24 h postradiation treatment showed an increase in telomerase activity, but there was no increase in the levels of mRNA of hTERT. To assess the sensitivity of the telomerase activity assay, we performed mixing experiments of HeLa and AG1522 cell extracts. These studies showed that telomerase activity could be detected in lysate equal to a single HeLa cell when mixed with 10,000 AG1522 cells. Our results indicate that even a few surviving neoplastic cells can be detected by telomerase activity assay. Therefore, detection of telomerase activity may be a useful monitor of radiotherapeutic efficacy and an early predictor of outcome.—Sawant, S. G., Gregoire, V., Dhar, S., Umbricht, C. B., Cvilic, S., Sukumar, S., Pandita, T. K. Telomerase activity as a measure for monitoring radiocurability of tumor cells.
Key Words: cell kill • ionizing radiation • tumor growth
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