Cell viability assay

The effects of different compounds on the cell viability of PC9, H1975, PC9-OR2 and PC9-OR4 were studied by use of the colorimetric (MTT). Two thousand (PC9, H1975) or 4000 (PC9-GR4, PC9-OR4) cells were seeded in 100 µL 0.1% FBS media and incubated for 24 hours before treatment; 100 µL of various 2× drug concentration (1× final concentration) were added to the wells, and the cells were incubated for 72 hours.

Cell viability was assessed by the Thiazolyl Blue Tetrazolium Bromide (MTT) (Sigma, St Louis, MO, USA) assay. Cells from each cell line were seeded at 2,000 to 4,000 cells per well in 96-well plates, allowed to attach for 24 h and treated for 72 h (for details of the combination experiments, see below). After treatment, cells were incubated with medium containing MTT (0.75 mg/mL in medium) for 1–2 h at 37 °C. Culture medium with MTT was removed and formazan crystals reabsorbed in 100 µL DMSO (Sigma). Cell numbers were estimated by measuring the absorbance at 495 nm, using a microplate reader (BioWhittaker, Walkersville, MD, USA). The data reported represent the mean ± SD of a minimum of 3 experiments of each drug concentration tested.