Comparison of conventional versus ultra-high dose rate radiotherapy in MCF-7 and MCF-12A human breast cells: analysis of DNA damage response proteins

Radiotherapy (RT) is one of the most important treatment modalities for the cure of cancer.Around 50% of cancer patients are treated with RT alone or in combination with other treatment modalities, such as chemotherapy.However, in the treatment of radioresistant tumors the total radiation dose that can be delivered to the tumor is often limited by the radiation tolerance of neighboring, critical, normal tissues.In such situations, ultra-high dose rate (UHDR-RT) could be of significant interest.Compared with conventional radiotherapy, UHDR-RT can effectively reduce the toxicity in normal tissues and provide similar antitumor effects, which is defined as the FLASH effect.The biological mechanisms responsible for the reduction of normal tissue toxicities with FLASH irradiation compared to CONV are not fully understood.In FLASH, the intrinsic factors "DNA damage" or "clustered DNA damage" is likely involved in the differential response between healthy and tumor tissue.In this paper we show our preliminary study results in which it was planned to investigate the response of selected cell lines MCF-7 and MCF-12A to DNA damage at the protein level, and to doses of ionizing radiation typical for conventional and ultra-high radiotherapy.The cells were exposed to electron beam irradiation at two different dose rates: 0,0833 Gy/s and 10 Gy/s.After irradiation, at various time intervals the cells were lysed and lysates were analyzed by Western blot method with a set of antibodies directed against several important proteins involved in the repair of DNA double-strand breaks and designed to characterize the phosphorylation state of the kinases ATM and DNA-PKcs reacting to DNA damage, and proteins used for assessment of apoptosis induction.Our preliminary results showed some differences in biological response, both between the dose rates used (CONV versus UHDR) and between MCF-7 cancer cells and healthy MCF-12A cells.