3.2. Resazurin Viability Assay

The viability of A549, HepG2, and PANC-1 cells was determined by the fluorescent resazurin assay as described previously [34]. Briefly, cells (6 × 10³) were seeded into 96-well plates (Corning Life Sciences, Tewksbury, MA, USA) in media. Cells were cultured overnight before treatment. Viability was determined after a 72 h incubation in treated and non-treated cells. Resazurin reagent (Sigma-Aldrich) was dissolved in phosphate buffered saline (PBS, pH 7.4) at 0.15 mg/mL concentration, sterile filtered (0.22 µm, Merck Millipore) and aliquoted at −20 °C. Samples were treated in 120 µL volume with a final concentration of 25 µg/mL resazurin. After 2 hours incubation at 37 °C 5% CO₂, fluorescence (530 nm excitation/580 nm emission) was recorded on a multimode microplate reader (Cytofluor4000, PerSeptive Biosytems, Framingham, MA, USA). Viability was calculated in relation to untreated control cells and blank wells containing media without cells. The presented IC₅₀ values (half maximal inhibitory concentration) were determined based on dose-response curves plotted in GraphPad Prism^® 5 (La Jolla, CA, USA).