Gefitinib and erlotinib do not reverse lapatinib resistance. (A) Cell growth of rBT474 and rSKBR3 cells after treatment with 5 μM gefitinib or erlotinib or 1 μM or 5 μM neratinib for 72 hours. Resistant cells were maintained in the presence of 1 μM lapatinib. Results represent the mean ± standard error of triplicate samples, and are representative of three independent experiments. P < 0.0025 (rBT474) and P < 0.0008 (rSKBR3). (B) Western blot analysis showing steady-state pEGFRY992, pHER3Y1197, pAktY308 phosphoprotein and cleaved PARP product expression in rBT474 and rSKBR3 cells after 72 hours of treatment with 5 μM gefitinib, erlotinib, or neratinib (1 and 5 μM), or vehicle (0.01% DMSO) alone. Steady-state actin protein levels served as a control for equal loading of protein. The results are representative of three independent experiments.