C-phycocyanin, being a component of the photosynthetic apparatus of cyanobacteria, is an effective antioxidant and anti-inflammatory agent and is often used in medical studies. The intracellular effect of C-phycocyanin isolated from cyanobacteria Arthrospira platensis on the levels of the prooxidant-induced oxidative stress and cell death of the aerobic yeast Yarrowia lipolytica is considered. We show that C-phycocyanin accumulated in the yeast cells and had a direct antioxidant effect on the yeast suspension within the concentration range of 10–100 μg/mL and a cytotoxic effect with a further increase in concentration. The effect of C-phycocyanin in the most effective concentration is comparable to the antioxidant effect of the mitochondria-targeted cation SkQ1.

Cancer stem cells (CSCs) are highly resistant to chemo- and radiotherapy. The aim of this work was to study the effect of metformin on the radiosensitivity of MCF-7 cells cultivated as mammospheres enriched with CSCs. One hour after the addition of metformin at a nontoxic concentration of 0.25 mmol/L, cells of mammospheres were exposed to γ-radiation at a dose of 2 Gy or reactor γ,n-radiation at a dose of 1 Gy. After 24 hours of cultivation, the drug was removed. Six days after irradiation, the total number of cells was calculated by a hemocytometer, then the percentage of CSCs with the CD44+/CD24–/low phenotype was determined, and the number of CSCs in the samples was calculated. The exposure to γ,n-radiation led to a significant decrease in both the total number of cells and CSCs compared with γ-radiation. The combined exposure to metformin and γ- or γ,n-radiation led to a significant decrease in both the total number of cells and CSCs compared with the exposure to γ-or γ,n-radiation only (p < 0.05). Thus, γ,n-radiation is more effective with respect to eliminating the MCF-7 CSCs than γ-radiation. Metformin increases the sensitivity of the MCF-7 CSCs to γ-and γ,n-radiation.