Proton Irradiation Increases the Necessity for Homologous Recombination Repair Along with the Indispensability of Non-Homologous End Joining

• Main Authors: Klaudia Szymonowicz, Adam Krysztofiak, Jansje van der Linden, Ajvar Kern, Simon Deycmar, Sebastian Oeck, Anthony Squire, Benjamin Koska, Julian Hlouschek, Melanie Vüllings, Christian Neander, Jens T. Siveke, Johann Matschke, Martin Pruschy, Beate Timmermann, Verena Jendrossek
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Cells
• Subjects: ionizing radiation; DNA damage foci; DNA repair; spread-out Bragg peak (SOBP); relative biological effectiveness (RBE); entrance plateau (EP) protons
• Online Access: https://www.mdpi.com/2073-4409/9/4/889

Technical improvements in clinical radiotherapy for maximizing cytotoxicity to the tumor while limiting negative impact on co-irradiated healthy tissues include the increasing use of particle therapy (e.g., proton therapy) worldwide. Yet potential differences in the biology of DNA damage induction and repair between irradiation with X-ray photons and protons remain elusive. We compared the differences in DNA double strand break (DSB) repair and survival of cells compromised in non-homologous end joining (NHEJ), homologous recombination repair (HRR) or both, after irradiation with an equal dose of X-ray photons, entrance plateau (EP) protons, and mid spread-out Bragg peak (SOBP) protons. We used super-resolution microscopy to investigate potential differences in spatial distribution of DNA damage foci upon irradiation. While DNA damage foci were equally distributed throughout the nucleus after X-ray photon irradiation, we observed more clustered DNA damage foci upon proton irradiation. Furthermore, deficiency in essential NHEJ proteins delayed DNA repair kinetics and sensitized cells to both, X-ray photon and proton irradiation, whereas deficiency in HRR proteins sensitized cells only to proton irradiation. We assume that NHEJ is indispensable for processing DNA DSB independent of the irradiation source, whereas the importance of HRR rises with increasing energy of applied irradiation.