Introduction. Radioresistance of cancer cells leads to the failure of radiotherapy and poor prognosis in tumor patients.

Aim: The work aims to investigate the sensitivity of human myelogenous leukemia K562 cells to the action of ionizing radiation.

Materials and methods: K562 cells were cultured in the RPMI 1640 medium with 10% FBS and 50 μg/ml of gentamycin (complete medium). We evaluated the growth of cell culture by counting the number of cells in the cytometric chamber at 24, 48, 72, and 96 h of cell cultivation. The cytostatic effect of the genotoxic factor was defined as the ratio of the total number of cells in the irradiated sample to the total number of cells in the control (non-irradiated) one. Staining with 0.1% trypan blue solution was used for the determination of dead cells. Fixed cell staining with fluorescent dye 4,6-diamidino-2phenylindole (DAPI) was performed to identify apoptotic cells. 

Results: Inhibition of cell growth of the K562 line after ionizing radiation exposure at a dose of 2 Gy was established. This effect was more pronounced with increasing duration of cell cultivation after cessation of genotoxic factor exposure. At 24 h following irradiation, there was no statistically significant difference in the number of irradiated cells compared with the control non-irradiated ones (р>0.05). A cell number decrease was revealed by 26.5±2.5% (р<0.001) at 48 h, by 34.6±1.1% (р<0.001) at 72 h and by 37.8±1.6% (р<0.001) at 96 h following irradiation. Identification of apoptotic cells was performed based on analysis of morphological features: chromatin condensation, nucleus fragmentation, and brightness of staining of fixed cells with fluorescent dye DAPI. We found that the number of apoptotic cells for 24 h after exposure to radiation at a dose of 2 Gy has not exceeded 4%. No statistically significant differences were revealed in the number of dead cells between irradiated (2 Gy) and non-irradiated cells at each identical time-point (р>0.05).

Conclusions: In response to the action of ionizing radiation (2 Gy), many metabolic and regulatory pathways are triggered in K562 cells, causing cell cycle arrest and DNA repair rather than induction of cell death by apoptosis or necrosis.