Biological damage from the Auger effect, possible benefits.

Decay of radioactive isotopes by K-capture leads to the Auger effect and results in the loss of several orbital electrons and the emission of X-rays. Whereas radiation effects are produced from the emitted electrons, the consequences of the Auger effect are strictly localized to the site of the decaying nuclide. The paper reviews the biological consequences of the decay of 125I which produces the Auger effect. Nearly all data were obtained from DNA labeled with 125I-5-iodo-2'-deoxyuridine (IUdR) in bacteria and mammalian cells. Parameters of effects were cell death, DNA strand breaks, and mutation induction. In order to recognize in a cell the contribution from the Auger effect and that of absorbed radiation, experimental data are analysed in terms of the specific energy for the nuclear volume which contains the isotope. The data indicate that decay of 125I is far more toxic than is expected on the basis of absorbed dose to the labeled nucleus. Moreover, it is emphasized that the toxicity of the 125I decay is largely determined by events immediately localized to the site of decay. Because the consequences of the Auger effect are stricly localized to the molecular site of the decay, 125I and perhaps other nuclides decaying by K-capture promise to be interesting tools in cell biology and molecular biology. First data on the Auger effect as a tool are summarized. It appears that recognizable biological damage is only observed when the Auger effect takes place in vitally important molecules, an example of which is DNA.