Analysis of the Factors in Determining Radiosensitivity in Mammalian Cells by Using Radio-Sensitive and -Resistant Clones Isolated from HeLa S3 Cells in Vitro

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Abstract
The factors in determining radiosensitivity of cultured mammalian cells were analysed by using two clones each having different radiosensitivities. The radiosensitive clones were isolated from HeLa S3 cells by the N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-treatment, X-irradiation (200R) and 5-bromodeoxyuridine (BUdR)-visible light method. On the other hand, the radioresistant clone was isolated by single X-irradiation (2000R) from MNNG-treated HeLa S3 cell population. The radiosensitivities expressed in Do and Dq values were 110 and 140 R in radiosensitive SM-1a clone and 180 and 230 R in radioresistant RM-1b clone respectively. The biological and biochemical characteristics of both clones such as the distribution of chromosome numbers, formation and rejoining of single strand breaks in DNA caused by X-irradiation, non-protein sulfhydryl (NPSH) and apparent total sulfhydryl (APSH) contents were measured. Among the characteristics analysed, different contents of NPSH in the cells were well correlated to their radiosensitivities among the original HeLa S3 cells, SM-1a and RM-1b clones. Additionally, it was found that the radioresistant L·P3 Co-3 cells isolated by Tsuboi et al. from the original mouse L·P3 cells by means of serial irradiation with 60Co γ-rays have more abundant NPSH than the original L·P3 cells. From these results, it can be concluded that the amount of NPSH play the main role in determining radiosensitivity in cultured mammalian cells.

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