RADIOTOXICITY OF I-125 IODODEOXYURIDINE IN PREIMPLANTATION MOUSE EMBRYOS

The radiotoxicity of DNA incorporated I-125 in cultured pre-implantation two-cell mouse embryos was investigated and compared with external gamma-irradiation. The uptake of I-125dU in the two-cell stage embryos was determined as a function of incubation time and concentration of radioactivity (MBq/ml) in the medium. The absorbed dose to the embryos was calculated using conventional procedures. The embryo survival curves show that the dose at 37% survival is only about 15 cGy for I-125dU, whereas for Cs-137-photons it is 175 cGy. The extreme toxicity observed is thought to be due to the localized energy deposition of the numerous low energy Auger electrons emitted in the decay of I-125. These results are consistent with earlier observations in mouse testis and cultured cells and point to the need for assessing the radiation risk from incorporated Auger electron emitting radionuclides based on their subcellular distribution.