Effects of Combined Neutron and Proton Beam Radiation Exposure on the Pool of Breast Cancer Stem Cells In Vitro

The effect is studied of single and combined proton and neutron radiation on the population of cancer stem cells (CSCs), which is the most resistant fraction of tumor cells to damaging factors, and, therefore, plays a key role in metastasis and cancer recurrence after treatment. The purpose of the study is to search for conditions for synergistic interaction of these radiations when irradiating breast cancer cells of two stable lines in vitro. It has been found that the number of CD44⁺CD24^–/low CSCs decreases after combined irradiation at a total equieffective dose of 4.0 Gy compared with the control, in contrast to the effects of γ-radiation, which leads to an increase in the number of CSCs. A synergistic decrease in the CSC pool has been shown for the combined action of neutrons and protons if the contribution of the radiations to the total dose was the same and the time between irradiation sessions did not exceed 4 h. These results are interesting for the further development of radiation therapy concerning the prospects for using new types of radiation to eliminate CSCs.