Resistance of Ba/F3 cells ectopically expressing mutant or wild-type ERBB2 to the reversible EGFR TKI erlotinib. (a) ERBB2 expression levels of cells transformed with various NSCLC-derived mutants of ERBB2 as well as wild-type ERBB2. Total cell lysates of cells harboring the indicated retroviral constructs were analysed for the expression of mutant or wild-type ERBB2 by immunoblotting using an antibody recognizing total ERBB2 (upper panel). Actin protein levels are shown as a loading control (lower panel). (b) 10 000 cells per well of a 96-well plate of each transformed cell line carrying the indicated retroviruses were treated with the indicated dose of erlotinib (x-axis) for 72 h. Viability was determined colorimetrically by the WST assay (Roche). Viability (y-axis) is shown as percentage of the untreated control following subtraction of the background values (media only). Ba/F3 cells carrying the L858R or the L858R/T790M double mutant of EGFR were used as controls.