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.
Peak
M J
MJ
Biological and Medical Research Division, Argonne National Laboratory, IL 60439.
Wang
L
L
Hill
C K
CK
Peak
J G
JG
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