VARYING LEVELS OF RADIOPROTECTION FROM THE EFFECTS OF JANUS NEUTRONS IN REPAIR-DEFICIENT XRS-5 HAMSTER-CELLS TREATED WITH AZACYTIDINE

A series of cell lines have been generated from the radiation-sensitiv e Chinese hamster ovary line xrs-5 by treatment with azacytidine. Seve ral of these lines have been shown to be resistant to gamma radiation. Survival curves have been generated for several of these lines and th e parental lines after exposure to 0 to 5 Gy of JANUS neutrons in the presence or absence of a 30-min pretreatment with the aminothiol radio protector WR-1065. These studies were performed to determine whether t he parental xrs-5 cell line was radioresistant to exposure to JANUS ne utrons and whether reversion to a neutron-resistant phenotype correlat ed with recovery of aminothiol radioprotection. Exposure to 4 mM WR-10 65 enhanced survival after exposure to neutron radiation for most ''re vertant'' lines, although the increase in survival varied. The xrs-5 c ell line was sensitive to JANUS neutrons and showed no protection by W R-1065. These data indicate that xrs-5 cells are also sensitive to neu tron radiation, that azacytidine-induced revertants for gamma-ray surv ival demonstrate the wildtype phenotype for survival after neutron exp osure, and that the gene product that is defective is responsible for repairing only a small portion of neutron-induced damage.