PRELIMINARY INVESTIGATION INTO THE EXTENT OF INCREASED RADIORESISTANCE OR HYPER-RADIOSENSITIVITY IN CELLS OF HAMSTER-CELL LINES KNOWN TO BEDEFICIENT IN DNA-REPAIR

The response to low doses of X rays was assessed in cells of three ham ster cell lines which are defective in DNA repair and was compared wit h their parental lines. Cells of the V79-derived double-strand break r epair-deficient line XR-V15B showed no radioresistance in the 0.5-Gy r ange compared with the V79B wild type, but instead showed an exponenti al response. Cells of the single-strand break repair-deficient line EM 9 showed hyper-radiosensitivity and exhibited increased radioresistanc e. Most interestingly, cells of the UV-20 cell line appeared to respon d exponentially, as a continuation of the hyper-radiosensitive portion of the curve, with no evidence of increased radioresistance. This lin e is defective in an incision step of excision repair and is sensitive to crosslinking agents. Further studies are warranted to address the possible role of single- and double-strand break repair and excision r epair in hyper-radiosensitivity and increased radioresistance,