Apoptosis induction and micronucleus formation after exposure to the Augerelectron emitter Zinc-65 in a human cell line

Induction of apoptosis and micronucleus formation has been studied in a tra nsformed human squamous cell carcinoma cell line (SCL-II) after exposure to the Auger electron emitter Zinc-65 (Zn-65) and after external low-LET radi ation. Exposure to non-radioactive Zn and unirradiated cells served as cont rols. Studies on the cellular uptake of Zn-65(2+) have been carried out in vitro and conventional dosimetric models have been applied to derive the ab sorbed radiation dose. Auger electrons, generated during decay of Zn-65(2+) , are strong inducers of micronuclei as well as of apoptosis, in comparison to external low-LET irradiation. The relative biological effectiveness has been determined and was found to be in the range of 1.2-2.7 for the two in vestigated biological endpoints, depending on which mathematical model for describing the dose-effect curves was used. A non-uniform distribution of i ntracellular Zn2+ was observed, showing a strong signal in the perinuclear region. We conclude that separate radiation weighting factors for Auger ele ctrons should be established depending on the nuclide and its ability to in teract with the DNA (e.g. Zn-65 by Zinc-finger proteins).