The Radiotoxicity of Iodine-125 in Mammalian Cells: II. A Comparative Study on Cell Survival and Cytogenetic Responses to 125 IUdR, 131 IUdR, and 3 HTdR
3H, 125I or 131I was incorporated into cellular DNA in the form of thymidine or its analogue 5-iodo-2-deoxyuridine. The effects of these radionuclides on cell survival and chromosomes were examined in the V79 Chinese hamster fibroblast cell line. In terms of cell killing, 125I was considerably more effective than 131I and 3H. The mean radioactivity contents at 37% survival were 0.10, 1.16, and 1.64 pCi/cell for 125I, 131I and 3H, respectively. Similarly, 125I was much more effective in inducing chromosome aberrations than 131I or 3H. For example, 0.1 pCi/cell of 125I gave rise to 3 chromosome breaks/cell; it took 1.0 pCi/cell of 131I or 1.7 pCi/cell of 3H to produce the same effect. The cytogenetic consequences of irradiation by these radionuclides, which decay by disparate processes, were directly related to their lethal effects; this strengthens the theory that radiation-induced cell death results from damage in chromatin structures.