Double-strand break induction and repair in V79-4 hamster cells: the role of core ionisations, as probed by ultrasoft X-rays.
OBJECTIVE
To compare the induction of double-strand breaks (DSB) in cells irradiated by 250 and 350 eV ultrasoft X-rays and assess the residual yield of breaks 2 hours post irradiation in order to unravel the correlation between the sharp increase in cell-killing efficiency of ultrasoft X-rays above versus below the carbon-K threshold (284 eV) and the induction of core events in DNA atoms.


METHODS
V79-4 hamster cells were irradiated with synchrotron ultrasoft X-rays at isoattenuating energies of 250 eV and 350 eV. DSB were quantified using pulse field gel electrophoresis.


RESULTS
A significant increase in DSB induction was observed for 350 eV ultrasoft X-rays above the carbon-K threshold, compared to 250 eV below the threshold, per unit dose to the cell. The DSB induced by the 350 eV ultrasoft X-rays were less repaired 2 h after irradiation.


CONCLUSIONS
The increased DSB induction at 350 eV is attributed to the increase in the relative proportion of photon interactions in DNA resulting in significant dose inhomogeneity across the cell with a local increase in dose to DNA. It results from an increase in carbon-K shell interactions and the short range of the electrons produced. Core ionisations in DNA, through core-hole relaxation in conjunction with localised effects of spatially correlated low-energy photo- and Auger-electrons lead to an increase in number and the complexity of DSB.
du Penhoat
Marie-Anne Hervé
MA
Institut de Minéralogie et de Physique des Milieux Condensés, Université Pierre et Marie Curie-Paris6, UMR-CNRS 7590, Paris, France. penhoat@impmc.jussieu.fr
Eschenbrenner
Anne
A
Abel
François
F
Boissiere
Arnaud
A
Guigner
Jean-Michel
JM
Chetioui
Annie
A
Politis
Marie-Françoise
MF
Touati
Alain
A
Sage
Evelyne
E
Jenner
Terry J
TJ
Stevens
David L
DL
Hill
Mark A
MA
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects*; D004260:DNA Repair / Q000502:physiology / Q000528:radiation effects*; D004586:Electrophoresis; D011874:Radiometry; D013997:Time Factors; D014965:X-Rays