Radiotoxicity of ¹²⁵I-Iododeoxyuridine in Pre-implantation Mouse Embryos

Summary

The radiotoxicity of DNA incorporated ¹²⁵I in cultured pre-implantation two-cell mouse embryos was investigated and compared with external γ-irradiation. The uptake of ¹²⁵IdU 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 ¹²⁵IdU, whereas for ¹³⁷Cs-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 ¹²⁵I. 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.