BC cell lines MCF-7 (ER+, PR+, HER2−) and MDA-MB-231 (ER−, PR−, HER2−) (both lines: American Type Culture Collection, ATCC; Manassas, VA, USA) were used in all in vitro experiments. In addition, a non-cancerous MCF-10A (human mammary gland epithelial cells) were used as a normal breast epithelial model. MCF-7 cells were maintained in DMEM medium (GE Healthcare, Piscataway, NJ, USA), MDA-MB-231 in RPM1 1640 medium (Biosera, Kansas City, MO, USA), and MCF-10A in DMEM F12 medium (Biosera, Kansas City, MO, USA) + suppl. insulin, EGF- epithelial growth factor and HC-hydrocortisone (all Sigma, Steinheim, Germany). The 10% FBS (Fetal bovine serum, Gibco) and antibiotic/antimycotic solution (1× HyClone™; GE Healthcare, Chicago, IL, USA) were used to supplement culture media. Basic cultivation conditions were a 5% CO2-containing atmosphere, humidified air, and 37°C temperature. A trypan blue exclusion test was used to estimate the viability of used cells (≥95%). For the flow cytometry experiments, the MCF-7 (3 × 105) and MDA-MB-231 (1 × 105) cells were seeded in Petri dishes. After 24 h seeding and initial colony growth in a complete cultivation medium, the cells were treated with the SPGE (Calendula, Nová Ľubovňa, Slovakia) for 24, 48, and 72 h before analysis (Kubatka et al., 2019 (link); Kubatka et al., 2020a (link); Kubatka et al., 2020b (link)).
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