Relationship between radiosensitivity of human squamous carcinoma cell lines and changes in telomerase activity and telomere length

Objective: To investigate the changes in radiosensitivity, telomerase activity, telomere length in a radiation-induced radioresistant cell line of human squamous carcinoma and its parent cell line. Methods: A radioresistant cell line, Hep-2R, was isolated from a radiosensitive human laryngeal squamous carcinoma cell line Hep-2 by repeated γ-irradiation. The radiobiological characteristics, in the presence or absence of telomerase inhibitor AZT, of both cell lines were analyzed by means of clonogenic assay. Radiosensitivity coefficients were calculated. The telomerase activity was examined by the PCR-based telomeric repeat amplification protocol (TRAP) and the telomere length (mean length for telomere restriction fragments, TRF) by Southern blotting. Results: A radioresistant cell line, Hep-2R, was obtained after prolonged exposure to γ-rays for 7 months and has been already maintained for more than 30 generations. The radioresistance of Hep-2R cell line was proved to be stable in long-term subculturing as well as in frozen samples. The SF2, D0, telomerase activity, TRF for Hep-2R cell line were 0.6798, 3.24, 0.982 ± 0.0005, 11.12, respectively and were 0.4148, 2.06, 0.604 ±0.015, 3.76 for Hep-2 cell line. After treated with AZT, the SF2, D0, telomerase activity, TRF for Hep-2R cell line were turned to be 0.4892, 2.51, 0.708 ±0.011, 10.18, respectively and were 0.3843, 1.81, 0.364 ± 0.0003, 2.76 for Hep-2. Conclusion: Hep-2R cell line is stably radioresistant. The telomerase activity is increased and telomere length is lengthened in the radiation-induced radioresistant Hep-2R cell line. Telomerase inhibitor AZT could increase the susceptibility of the cell line to radiation by down-regulating telomerase activity and shortening telomere length. (authors)