Isolation of mammalian cell variants with enhanced endogenous thiol content at low survival levels following irradiation

Approximately half of a group of Chinese hamster V79 cell clones isolated from radiation survivors at low surviving fractions had significantly higher endogenous levels of non-protein and protein thiols than unirradiated cells. A similar group of cell lines cloned from unirradiated cells had thiol levels in the same range as the original unirradiated population. In some cases, clones isolated following irradiation are also more resistant to misonidazole toxicity and to radiation. This phenotype can persist through many cell generations for weeks or months of continuous growth; however, in many clones with altered phenotypes isolated following irradiation, reversion of the population to the same phenotype as that of unirradiated populations has been observed. Induction of elevated thiol levels in tumours by radiotherapy could reduce both the efficacy of the radiation itself and of radiation-modifying or chemotherapeutic drugs given in combination with the radiation.