RADIORESISTANT DERIVATIVES OF AN X-RAY-SENSITIVE CHO CELL-LINE EXHIBIT DISTINCT PATTERNS OF SENSITIVITY TO DNA-DAMAGING AGENTS

X-ray-resistant clones of the xrs-5 radiosensitive derivative of the CHO-K1 cell line were generated by transfecting cosmid library DNAs into the X-ray-sensitive cells. Transfectants were selected for both a dominant drug resistance marker present in the vector sequences and return to wild-type survival. Three cell lines were isolated which show X-ray survival characteristics similar to parental K1 cells. These revertant lines were examined for their cross-sensitivity to cis-diamminedichloroplatinum(II) (cisplatin) and bleomycin. Although these cell lines reverted with regard to X-ray sensitivity, they retained their sensitivity to cisplatin. Furthermore, changes in bleomycin and X-ray sensitivity did not correlate. There was a positive correlation between return to wild-type radiosensitivity and an increase In the rate of DNA double-strand break rejoining. © 1990 Oxford University Press.