DNA double-strand breaks in cancer cells as a function of proton linear energy transfer and its variation in time

Abstract

Purpose

The complex relationship between linear energy transfer (LET) and cellular response to radiation is not yet fully elucidated. To better characterize DNA damage after irradiations with therapeutic protons, we monitored formation and disappearance of DNA double-strand breaks (DNA DSB) as a function of LET and time. Comparisons with conventional γ-rays and high LET carbon ions were also performed.

Materials and Methods

In the present work, we performed immunofluorescence-based assay to determine the amount of DNA DSB induced by different LET values along the 62 MeV therapeutic proton Spread out Bragg peak (SOBP) in three cancer cell lines, i.e. HTB140 melanoma, MCF-7 breast adenocarcinoma and HTB177 non-small lung cancer cells. Time dependence of foci formation was followed as well. To determine irradiation positions, corresponding to the desired LET values, numerical simulations were carried out using Geant4 toolkit. We compared γ-H2AX foci persistence after irradiations with protons to that of γ-rays and carbon ions.

Results

With the rise of LET values along the therapeutic proton SOBP, the increase of γ-H2AX foci number is detected in the three cell lines up to the distal end of the SOBP, while there is a decrease on its distal fall-off part. With the prolonged incubation time, the number of foci gradually drops tending to attain the residual level. For the maximum number of DNA DSB, irradiation with protons attain higher level than that of γ-rays. Carbon ions produce more DNA DSB than protons but not substantially. The number of residual foci produced by γ-rays is significantly lower than that of protons and particularly carbon ions. Carbon ions do not produce considerably higher number of foci than protons, as it could be expected due to their physical properties.

Conclusions

In situ visualization of γ-H2AX foci reveal creation of more lesions in the three cell lines by clinically relevant proton SOBP than γ-rays. The lack of significant differences in the number of γ-H2AX foci between the proton and carbon ion-irradiated samples suggests an increased complexity of DNA lesions and slower repair kinetics after carbon ions compared to protons. For all three irradiation types, there is no major difference between the three cell lines shortly after irradiations, while later on, the formation of residual foci starts to express the inherent nature of tested cells, therefore increasing discrepancy between them.

Keywords:

• Human malignant cells
• γ-rays
• protons
• carbon ions
• DNA double-strand breaks

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was financially supported by the Ministry of Education, Science and Technological Development of Serbia and by Fondo Affari Internazionali (FAI) of the INFN-LNS. The research leading to these results has also received funding from the European Union HORIZIN2020 research and innovation program under [Grant Agreement no 654002 ENSAR2]. The authors wish also to acknowledge financial support from CNRS PICS #8070 France – Serbia Project and MAECI PGR No. 00794 Italy – Serbia Project.

Notes on contributors

Otilija Keta

Otilija Keta received her Ph.D. from the University of Belgrade, Faculty of Biology. Presently she is engaged as Research Assistant Professor at the Vinča Institute of Nuclear Sciences of the University of Belgrade.

Vladana Petković

Vladana Petković received her Master degree from the University of Belgrade, Faculty of Biology. She is a PhD student at the University of Belgrade, Faculty of Biology, working on her thesis at the Vinča Institute of Nuclear Sciences of the University of Belgrade.

Pablo Cirrone

Pablo Cirrone received his PhD in Physics at the University of Catania (I). He is a Senior Researcher at the INFN Italian Institute for Nuclear Physics and Professor of the ‘Medical Physics’ class at the Catania University. He is an expert of Hadrontherapy, laser-driven acceleration and diagnostic, dosimetry of ionization radiation and Monte Carlo simulations.

Giada Petringa

Giada Petringa received her PhD in Physics from the University of Catania (I). She is an expert in diagnostics and dosimetry for clinical and laser-driven proton/ions beams. She has a large experience in Monte Carlo simulations and she is a member of the Geant4 international collaboration.

Giacomo Cuttone

Giacomo Cuttone is Research Director at the INFN Italian Institute for Nuclear Physics and Professor of the ‘Accelerator Physic’ class at the Catania University. He is also the former Director of INFN-LNS. He is expert of accelerator physics, hadrontherapy and dosimetry for ionizing radiation.

Dousatsu Sakata

Dousatsu Sakata received his PhD from University of Tsukuba, Tsukuba, Japan. He is a Research Associate in the National Institute of Radiological Sciences, Japan. He is involved in development of the Geant4 simulation toolkit, in particular, radiobiological modeling.

Wook-Geun Shin

Wook-Geun Shin received his PhD in radiobiological simulation using MC method from Bordeaux University. His research interests are radiobiology, radiation therapy, and comprehensive MC simulation. He is also a member of Geant4 and Geant4-DNA collaboration group.

Sebastien Incerti

Sebastien Incerti received his PhD from Blaise Pascal University, Clermont-Ferrand, France. He is a Research Director in the National Institute of Nuclear and Particle Physics (IN2P3) of the National Center for Scientific Research (CNRS), France. He is involved in development of the Geant4 general purpose and open-source particle-matter simulation toolkit.

Ivan Petrović

Ivan Petrović received his PhD in Nuclear Physics from the Univesity of Paris XI – South (Orsay), France. He is a Research Professor in the Department of Physics at the Vinča Institute of Nuclear Sciences of the University of Belgrade, Serbia, and is actively involved in research and teaching.

Aleksandra Ristić Fira

Aleksandra Ristić Fira received her PhD in Molecular Biology from the University of Belgrade, Faculty of Biology. She is a Research Professor at the University of Belgrade, Vinča Institute of Nuclear Sciences. She is head of Laboratory of radiation biology and is actualy engaged in teaching and research.