Impact of Gold Nanoparticles and Ionizing Radiation on Whole Chromatin Organization as Detected by Single-Molecule Localization Microscopy

In radiation tumor therapy, irradiation, on one hand, should cause cell death to the tumor. On the other hand, the surrounding non-tumor tissue should be maintained unaffected. Therefore, methods of local dose enhancements are highly interesting. Gold nanoparticles, which are preferentially uptaken by very-fast-proliferating tumor cells, may enhance damaging. However, the results in the literature obtained from cell culture and animal tissue experiments are very contradictory, i.e., only some experiments reveal increased cell killing but others do not. Thus, a better understanding of cellular mechanisms is required. Using the breast cancer cell model SkBr3, the effects of gold nanoparticles in combination with ionizing radiation on chromatin network organization were investigated by Single-Molecule Localization Microscopy (SMLM) and applications of mathematical topology calculations (e.g., Persistent Homology, Principal Component Analysis, etc.). The data reveal a dose and nanoparticle dependent re-organization of chromatin, although colony forming assays do not show a significant reduction of cell survival after the application of gold nanoparticles to the cells. In addition, the spatial organization of γH2AX clusters was elucidated, and characteristic changes were obtained depending on dose and gold nanoparticle application. The results indicate a complex response of ALU-related chromatin and heterochromatin organization correlating to ionizing radiation and gold nanoparticle incorporation. Such complex whole chromatin re-organization is usually associated with changes in genome function and supports the hypothesis that, with the application of gold nanoparticles, not only is DNA damage increasing but also the efficiency of DNA repair may be increased. The understanding of complex chromatin responses might help to improve the gold nanoparticle efficiency in radiation treatment.