"Study of early radiation-induced cell death using two cell lines with different radiosensitivities in vitro"

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A radiosensitive rat yolk sac tumor cell line, NMT-1, and A radioresistant variant cell line, NMT-1R were used in this study to investigate the difference of radiosensitivity, chemosensitivity and thermosensitivity.1.For NMT-1R,Do for radiation sensitivity was 165 cGy, 1.7 times as large as for NMT-1. The extrapolation number, n, was 1.48 for NMT-1R although that for NMT-1 was 1.8.2.Although a clear G2 delay was observed after irradiation with a dose of 2 Gy for both cell lines, NMT-1R had a shoreter recovery time from G2 block than NMT-1. G1 arrest was observed in NMT-1.3.NMT-1 showed much higher incidence of early morphological changes, especially apoptosis, after irradiation with more than 5 Gy compared with NMT-1R cell.4.Development of apoptosis in NMT-1 was observed as a function of time within 24 h after irradiation with a dose of 5 Gy. The incidence of apoptosis reached a plateau with a single dose of 5 Gy.5.NMT-1 was 4 times as sensitive to cisplatin as NMT-1R based on ID_<50>.6.Cisplatin had a synergistic effect by a factor of 1.30-1.39, which was independent of the time-course and sequence in combination with radiation within 6 h on both cell lines.7.The "TO" for heat sensitivity was 2.5 h at temperature of 42 ﾟC for NMT-1 but that for NMT-1R was 0.7 h. NMT-1R was more sensitive to heat than NMT-1.8.Thermal tolerance ratios for NMT-1 and NMT-1R at 6 hr interval was 8.09 and 6.28 respectively. HSP70 expression was induced predominatly on NMT-1 cells following heating.