(A and C) Western blot analyses of total HER2, AKT, ERK and S6 as well as phospho-Tyrosine, phospho AKT (Ser473), phospho ERK (Thr202/Tyr204) and phospho S6 (Ser235/236) in whole-cell extracts from Sk-Br-3 (A) and BT-474 (C) cells expressing empty-vector, wild-type (WT) HER2, or HER2 L755S and cultured in various concentrations of neratinib for 4 hours. (p, phosphorylated). (B and D) Cell viability by CTG assay of the cells described in (A) and (C), respectively after incubation with increasing concentrations of lapatinib (ranging from 0.05 to 25nM). Data are means ± SD from three independent experiments. P value obtained by two-tailed Student’s t-test.