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Radiotoxicity of 125 I in Mammalian Cells

A. I. Kassis, F. Fayad, B. M. Kinsey, K. S. R. Sastry, R. A. Taube and S. J. Adelstein
Radiation Research
Vol. 111, No. 2 (Aug., 1987), pp. 305-318
DOI: 10.2307/3576987
Stable URL: http://www.jstor.org/stable/3576987
Page Count: 14
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Radiotoxicity of 125 I in Mammalian Cells
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Abstract

The radiotoxicity of 125 I in Chinese hamster V79 lung fibroblasts has been studied following extracellular (${\rm Na}^{125}{\rm I}$), cytoplasmic $[{}^{125}{\rm I}]\text{iododihydrorhodamine}$ (${}^{125}{\rm I}\text{-}{\rm DR}$), and nuclear (125 IUdR) localization of the radionuclide. Exposure of the cells for 18 h to ${\rm Na}^{125}{\rm I}$ (≤7.4 MBq/ml) had no effect on survival. A similar exposure to ${}^{125}{\rm I}\text{-}{\rm DR}$ produced a survival curve with a distinct shoulder and with a mean lethal dose ($D_{37}$) of 4.62 Gy to the nucleus. While this value compares well with the 5.80 Gy X-ray $D_{37}$ dose, it is in contrast to the survival curve obtained with DNA-bound 125 IUdR which is of the high LET type and has a $D_{37}$ of 0.80 Gy to the nucleus. Furthermore, when the uptake of 125 I into DNA is reduced by the addition of nonradioactive IUdR or TdR to the medium and the survival fraction is determined as a function of 125 I contained in the DNA, a corresponding increase in survival is observed. This work demonstrates the relative inefficiency of the Auger electron emitter 125 I when located in the cytoplasm or outside the cell. It indicates that a high dose deposited within the cytoplasm contributes minimally to radiation-induced cell death and that radiotoxicity depends not upon the specific activity of IUdR but upon the absolute amount of 125 I that is associated with nuclear DNA.

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