DNA damage produced in V79 cells by DNA-incorporated iodine-123: a comparison with iodine-125

The neutral elution technique (pH 9.6) has been used to compare the damage produced in the DNA of V79 cells following the decay of the Auger-electron emitters 123I and 125I incorporated into DNA in the form of 5-[123I/125I]iodo-2'-deoxyuridine (123IdU, 125IdU) or after 60Co gamma irradiation. Elution profiles of retained radioactivity versus eluted volume were generally found to be nonlinear and partially dependent on the cell treatment prior to elution. Plots of a suitable function of radioactivity retention on the filters versus total decays for 123I or 125I and dose (Gy) for gamma radiation were linear. Assuming that each 125I decay produces one double-strand break (DSB), the 60Co efficiency in DSB production was found to be 53.4 DSBs/Gy/cell (or 17.8 DSBs/Gy/10(12) Da), in agreement with values reported previously. The decay of 123I led to 0.74 DSB/decay/cell if decays occurring only during nonrepair conditions were counted. This DSB production efficiency is in agreement with Monte Carlo semiempirical models of the action of radiation on DNA.