Apoptosis Induction and Micronucleus Formation after Exposure to the Auger Electron Emitter Zinc-65 in a Human Cell Line

Abstract

Induction of apoptosis and micronucleus formation has been studied in a transformed human squamous cell carcinoma cell line (SCL-II) after exposure to the Auger electron emitter Zinc-65 (⁶⁵Zn) and after external low-LET radiation. Exposure to non-radioactive Zn and unirradiated cells served as controls. Studies on the cellular uptake of ⁶⁵Zn²⁺ have been carried out in vitro and conventional dosimetric models have been applied to derive the absorbed radiation dose. Auger electrons, generated during decay of ⁶⁵Zn²⁺, 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 investigated biological endpoints, depending on which mathematical model for describing the dose-effect curves was used. A non-uniform distribution of intracellular Zn²⁺ was observed, showing a strong signal in the perinuclear region. We conclude that separate radiation weighting factors for Auger electrons should be established depending on the nuclide and its ability to interact with the DNA (e.g. ⁶⁵Zn by Zinc-finger proteins).