Cell proliferation assay

Generation of Ba/F3 stable lines expressing various EGFR mutants was described in Supplementary Materials and Methods. For MTS assay, Ba/F3 cells were prepared in RPMI1640 with 10% FBS and 10 ng/ml EGF, seeded in 96-well plates at 30,000 cells per well, and incubated overnight. The next day, compounds at different concentrations were added to the assay plates, and cells were incubated for additional 72 hours. Following compound treatment, 20 μl/well of CellTiter 96^® AQueous One Solution Reagent (Promega, Madison, WI, USA) was added, incubated at room temperature for 2 hours, then 25 μl/well of 10% SDS was added to stop the reaction. The absorbance was measured at 490 nm wavelength using 650 nm as reference on Tecan Spark 20M (Tecan Group Ltd., Zurich, Switzerland). The data was processed and plotted using GraphPad Prism 6 (GraphPad Software Inc., San Diego, CA, USA).