4.5. Analysis of Cell Viability

Cell viability was analyzed by a XTT assay (Roche Diagnostics) according to the manufacturer′s instructions. Cells were seeded in 96-well plates and were treated with the Momundo Artemisia annua extract or compounds for 48 h. For some experiments, cells were pretreated with 5 µM of the MEK inhibitor U0126 (Biomol, Hamburg, Germany) or its inactive analogue U0124 (Bio-Techne, Minneapolis, MN, USA) for 1 h followed by incubation with chrysosplenol d or casticin (each 10 µM) for 48 h. Final DMSO concentrations did not exceed 0.5%. Absorbance of the orange formazan salt formed by mitochondrial reduction of the tetrazolium salt by viable cells was measured using an Tecan Infinite M1000 PRO plate reader (Männedorf, Switzerland) at 450 nm with a 630 nm reference filter.