Industry Cooperation

Sponsored by: STEP Sensor Technology and Electronics Pockau GmbH

Duration: 2007 until 2014

Responsible project manager: Dr. R. Kriehuber

Objectives

The project focuses on the question to what extent the radiation effect on cells can be significantly increased by so-called "seeds", i.e. small, rice grain-sized, encapsulated radioactive sources, as they are usually used in brachytherapy, and thus their range of application in medicine can be extended. The idea pursued in the project here is to use the so-called Auger effect.

Background

Radionuclides that decay via electron capture emit a shower of low-energy, and thus short-range Auger electrons, which induce high-LET-like cell damage, provided that the emitter is localized at or in the hereditary molecule DNA. The damage caused primarily to the DNA is far more toxic than that observed with low-LET radiation, so that Auger electrons are considered to be extremely biologically effective (Kriehuber & Simkó 2000, Kriehuber et al. 2004a and b). The emission of Auger electrons can also be initiated in stable atoms. For this purpose, photons of suitable energy are irradiated, which ionize an inner electron shell via the photoelectric effect. In this project, DNA-seeking and DNA-binding molecules, so-called DNA triplex-forming oluigonucleotides, are used for the labeling. Cell death (cell death) and DNA damage ("genotoxic" damage) are mainly considered as indicators of radiation effects. Selection of DNA-binding molecules Short, single-stranded DNA molecules of specific sequence are able to attach permanently to the DNA double helix via "reverse Hoogsteen" hydrogen bonds under physiological conditions (Fig. 1). These stable structures are referred to as "triplex DNA." The short DNA molecules, also called "triplex-forming oligonucleotides" (TFOs), thereby reach extreme spatial proximity to the "target" DNA (Fig. 2). Studies on TFOs in our own laboratory have already shown (Kadenbach et al. 2004 and 2005) that:

TFOs form stable "triplex DNA" in vitro with certain sequences of genomic DNA TFOs can be easily introduced into cells TFOs themselves do not have any cyto- or genotoxic effectTFOs are stable in cells for a sufficiently long time (> 48 h)TFOs are preferentially detectable in the cell nucleus (which harbors the genomic DNA) after cell divisions have occurred.

Due to these properties, TFOs are very well suited as "DNA-seeking" molecules. The fact that TFOs are more frequently detectable in cell nuclei, especially after cell division has occurred, is of particular interest for the intended application, since tumor cells in particular are characterized by their high proliferative capacity. This could mean that, in this context, it is mainly in tumor cells that "triplex DNA" is formed and thus, after photon activation has occurred, it is exclusively in these cells that the cyto- and genotoxic effects of the Auger effect can be observed.

Sources

Dagle JM, Weeks DL. Oligonucleotide-based strategies to reduce gene expression. Differentiation 2001, 69: 75-82

Kadenbach K, Gniech B, Lee JS, Kriehuber R. Triplex-forming oligonucleotides as a tool to target specific DNA structures. Proceedings of the 8th Wolfsberg meeting on Molecular Radiation Biology/Oncology 2004, edited by M. Baumann, S. Bodis, E. Dikomey, HP Rodemann: 2004, p 94

Kadenbach K, Gniech B, Lee JS, Kriehuber R. Triplex-forming oligonucleotides as a tool to regulate gene expression. European J Cell Biol. 2005, 84, 55: 67-68

Kriehuber R and Simkó M. Apoptosis induction and micronucleus formation after exposure to the Auger-electron emitter Zinc-65 in a human cell line. Acta Oncologica 2000 39, 6: 699-706.

Kriehuber R, Riedling M, Simkó M, Weiss DG. Cytotoxicity, genotoxicity and intracellular distribution of the Auger electron emitter 65Zn in two human cell lines. Radiat Environ Biophys. 2004a 43(1):15-22.

Kriehuber R, Kadenbach K, Schultz F, Weiss DG. Study on cell survival, induction of apoptosis and micronucleus formation in SCL-II cells after exposure to the Auger electron emitter Tc-99m. Int J Radiat Biol. 2004b, 11-12, 80: 875-880.