Comparison of repair of DNA double-strand breaks caused by neutron or gamma radiation in cultured human cells.
The dose-response for the induction of initial double-strand breaks (dsb) in DNA of human epithelioid cells by JANUS 0.85 MeV fission-spectrum neutrons was parabolic as assayed by a calibrated neutral filter elution technique. The relative biological effectiveness (RBE) of these neutrons relative to 60Co gamma-rays was unity. The kinetics of repair after a 60 Gy gamma-ray exposure were biphasic. About 65% of these dsb were rapidly repaired (T 1/2 of approximately 2 min), and the remainder were almost completely removed after 150 min at a slower rate (T 1/2 = 30 min). After the same dose of JANUS neutrons, the rapid repair component was markedly reduced (possibly not a significant repair component), and the bulk of the dsb were sealed more slowly (T 1/2 = 90 min). After 150 min, 25% remained unsealed. Even after a lower neutron dose (20 Gy), a proportion of the dsb were refractory to repair. Thus, unrepaired (or irreparable) dsb induced by high energy neutrons might explain the high RBE of neutrons for cell killing.
Biological and Medical Research Division, Argonne National Laboratory, IL 60439.
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Peak
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Wang
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Hill
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Peak
D002460:Cell Line; D003037:Cobalt Radioisotopes / Q000494:pharmacology; D004247:DNA / Q000187:drug effects / Q000528:radiation effects*; D004260:DNA Repair / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays / Q000009:adverse effects*; D006801:Humans; D007700:Kinetics; D009502:Neutrons / Q000009:adverse effects*; D012062:Relative Biological Effectiveness
D003037:Cobalt Radioisotopes; D004247:DNA