Lethal effects and DNA break rejoining in two L5178Y cell lines irradiated with fast neutrons and X-rays

Two strains of murine lymphoma L5178Y cells differ with respect to X-ray sensitivity, L5178Y-R being more resistant than L5178Y-S. Parameters of their survival curves (D0, Dsub(q), n) are 1.10, 0.19, 1.19 and 0.54, 0.00, 1.00 for L5178Y-R and L5178-S cells, resp., where D0 and Dsub(q) are given in Gy. Both cell lines respond almost equally to 6.2 MeV neutrons, appropriate parameters being 0.42, 0.10, 1.25 and 0.42, 0.09, 1.04 for the R- and S-cell strain, resp. Rejoining of DNA breaks differed for L5178Y-R and L5178Y-S cells after X-ray irradiation but not after neutron irradiation. During 90 min incubation at 37 0C after irradiation with 100 Gy of X-rays L5178Y-R cells rejoined 92%, and L5178Y-S cells only 64% of single-strand breaks. Within 90 min after irradiation by 140 Gy of neutrons, both cell lines rejoined only 70% of breaks. Our data suggest a relation between the radiosensitivity of L5178Y cells and capacity to rejoin DNA breaks. (author)