The RBE of 3.4 MeV alpha-particles and 0.565 MeV neutrons relative to 60Co gamma-rays for neoplastic transformation of human hybrid cells and the impact of culture conditions.

The neoplastic transformation of human hybrid CGL1 cells is affected by perturbations from external influences such as serum batch and concentration, the number of medium changes during the 21-day expression period and cell seeding density. Nevertheless, for doses up to 1.5 Gy, published transformation frequencies for low linear energy transfer (LET) radiations (gamma-rays, MeV electrons or photons) are in good agreement, whereas for higher doses larger variations are reported.

Single-strand annealing, conservative homologous recombination, nonhomologous DNA end joining, and the cell cycle-dependent repair of DNA double-strand breaks induced by sparsely or densely ionizing radiation.

The cell cycle-dependent relative contributions of error-prone single-strand annealing (SSA), error-free conservative homologous recombination (HR), and potentially error-prone nonhomologous DNA end joining (NHEJ) to repair simple (induced by 200 kV X rays) or complex (induced by (241)Am alpha particles) DNA double-strand breaks (DSBs) in Chinese hamster ovary cells are reported for the first time. Cells of the parental cell line AA8 and its derivatives UV41 (SSA-deficient), irs1SF (HR-deficient) and V3 (NHEJ-deficient) were synchronized in G(1) or in S phase, and survival responses after exposure to either type of radiation were measured. It is demonstrated for the first time that in G(1)-phase SSA is negligible for the repair of DSBs of various complexities.

The role of nonhomologous DNA end joining, conservative homologous recombination, and single-strand annealing in the cell cycle-dependent repair of DNA double-strand breaks induced by H(2)O(2) in mammalian cells.

The purpose of this study was to investigate the cell cycle-dependent role of nonhomologous DNA end joining (NHEJ), conservative homologous recombination (HR), and single-strand annealing (SSA) for the repair of simple DNA double-strand breaks (DSBs) induced by H(2)O(2)-mediated OH radicals in CHO cells. Cells of the cell lines V3 (NHEJ-deficient), irs1SF (HR-deficient) and UV41 (SSA-deficient) and their parental cell line AA8 were exposed to various concentrations of H(2)O(2) in G(1) or S phase of the cell cycle and their colony-forming ability was assayed. In G(1) phase, NHEJ was the most important-if not the only-mechanism to repair H(2)O(2)-mediated DSBs; this was similar to results obtained in a parallel study of more complex DSBs induced by sparsely or densely ionizing radiation.

Neoplastic transformation of a human hybrid cell line by alpha particles in relation to mammography X rays.

The hybrid cell line CGL1 is the only cell line which allows quantitation of neoplastic transformation in human cells. Hybrid cells were exposed to 3.4 MeV alpha particles or to mammography X rays (29 kV(p)) and both survival and neoplastic cell transformation were assayed.

Mutation induction and neoplastic transformation in human and human-hamster hybrid cells: dependence on photon energy and modulation in the low-dose range.

Mutation induction in the HPRT gene of human fibroblasts after irradiation with mammography-like 29 kVp or 200 kVp x-rays shows radiohypersensitivity for doses smaller than approximately 0.5 Gy. Similarly, mutation induction in the CD 59 gene on human chromosome 11 in A(L) cells shows radiohypersensitivity for doses smaller than approximately 0.