Increased Yield of Residual γH2AX Foci in p53-Deficient Human Lung Carcinoma Cells Exposed to Subpicosecond Beams of Accelerated Electrons.

We studied quantitative yield of residual (24 h post-irradiation) phosphorylated histone (γH2AX) foci as a marker of DNA double strand breaks in wild-type A549 and p53-deficient H1299 human lung carcinoma cells after exposure to subpicosecond (energy 4 MeV, pulse duration 400 fsec, peak dose rate during the pulse 16 GGy/s) and quasi-continuous (energy 3.6 MeV) beams of accelerated electrons in a dose range of 0.5-10.0 Gy. The efficiency of pulse irradiation in A549 and H1299 cells assessed by the yield of residual foci was higher than the efficiency of quasi-continuous exposure by 1.8 and 5.3 times, respectively. Significant differences in quantitative yield of residual γH2AX foci between wild-type and p53-deficient cell lines were observed only after exposure to subpicosecond, but not quasi-continuous beams of accelerated electrons.

Tightly Focused Femtosecond Laser Radiation Induces DNA Double-Strand Breaks in Human Tumor Cells.

We studied the formation of double-strand DNA breaks (DNA DSB) induced by femtosecond laser radiation in A549 human lung adenocarcinoma cells using immunocytochemical staining of the resulting tracks of a specific DSB marker protein phosphorylated ATM kinase (phospho-ATM). Additionally, colocalization of phospho-ATM tracks with γH2AX protein tracks was studied. The results of immunocytochemical analysis showed that 30 min after irradiation of cells with femtosecond pulses with energies of 1 and 2 nJ (radiation power density 2×1011 and 4×1011 W×cm-2, respectively), the formation of tracks consisting of phospho-ATM and γH2AX proteins located in sites where the laser beam passes through the cell nuclei was observed. The presence of phospho-ATM tracks co-localized with γH2AX allows us to conclude that exposure to focused femtosecond infrared laser radiation with a pulse energy of 1-2 nJ leads to the formation of DNA DSB in irradiated cells.

Colony-Forming Ability and Residual Foci of DNA Repair Proteins in Human Lung Fibroblasts Irradiated with Subpicosecond Beams of Accelerated Electrons.

We performed a comparative study of the colony-forming ability and the number of residual foci of DNA repair proteins in cultured human lung fibroblasts (MRC-5 cell line) after exposure to subpicosecond beams of accelerated electrons with an energy of 3.6 MeV and quasi-continuous radiation (accelerated electrons with an energy of 4 MeV and X-rays). The yield of damages causing reproductive cell death after pulsed subpicosecond radiation exposure was higher by ~1.8 times than after quasi-continuous radiation exposure. The quantitative yield of residual γH2AX foci (phosphorylated H2AX histone, a protein marker of DNA double breaks) in cells irradiated with subpicosecond beams of accelerated electrons was shown to be ~2.0- 2.5-fold higher than in cells irradiated with quasi-continuous beams of accelerated electrons.