[Increase in the number of cancer stem cells after exposure to low-LET radiation].

Radioresistance of cancer stem cells (CSCs) is regarded as one of the possible causes of cancer recurrence after radiotherapy. Since the regularities and mechanisms of radiation effects on this population of cells have not been sufficiently studied, the aim of this work is to elucidate the changes in the CSC number after γ-irradiation in stable cultures of tumor cells in vitro and tumor tissue in vivo (in the course of radiation therapy of patients with cancers of the upper respiratory tract). CSCs were identified in the cell lines B16, MCF-7, HeLa by the ability to exclude the fluorescent dye Hoechst 33342 (SP method) 48-72 h after irradiation at the doses of 1-20 Gy and in biopsy material by immunophenotype CD44+CD24(-/low) before and 24 h after irradiation at the total dose of 10 Gy. The essential differences in the response of CSCs and other cancer cells were found after exposure to low-LET radiation. The absolute number of CSCs increased after a single exposure at the doses ranging from 1 to 5-10 Gy in different cell cultures, but a further dose increase maintained the current number of CSCs or decreased it. At the same time, the number of non CSCs significantly decreased with increasing doses of radiation exposure, as expected. Fractionated irradiation in vivo at a total dose of 10 Gy increased the relative amount of CSCs in most patients. The registered changes are an integral indicator of cell death, cell division delay immediately after irradiation, proliferation at a later time, possible dedifferentiation of non CSCs, etc. The exact contribution of each of them to the radiation-induced increase of the CSCs number is of considerable interest and requires further research.