Cell culture and reagents

We used two types of NSCLC cells with respective EGFR mutations for this study: PC9 cells (EGFR^{exon19del E746-A750}) and NCI-H1975 cells (EGFR^L858R/T790M). The PC9 cells were kindly provided by Dr. Pan-Chyr Yang at National Taiwan University, and the NCI-H1975 cells were obtained from the American Type Culture Collection (Manassas, VA). PC9 cells are very sensitive to gefitinib (PC9: IC₅₀ = 60 nM, IC₈₀ = 200 nM), whereas NCI-H1975 cells are sensitive to afatinib (IC₅₀ = 300 nM, IC₈₀ = 500 nM) but not gefitinib, owing to a second mutation on EGFR, i.e., a substitution of methionine for threonine at position 790 (T790M) [23]. Cells were maintained as previously described [34]. All cells were maintained in RPMI 1640 growth medium (Invitrogen, Carlsbad, CA) containing 10% fetal bovine serum (Gibco, Invitrogen), penicillin, and streptomycin (Invitrogen) in humidified 5% CO2 at 37°C. The treatment drugs gefitinib (Ryss Lab, Inc., Union City, CA), afatinib (LC Laboratories, Woburn, MA), dexamethasone, prednisolone, mometasone and mifepristone (Sigma-Aldrich, St. Louis, MO) were commercially obtained. Stock solutions (10 mM) of all chemicals were prepared in DMSO.