Development and characterization of a cell-line model of acquired lapatinib resistance. (A) Schematic depiction of the continuous long-term lapatinib treatment strategy utilized to develop SKBR3-L cells. (B) Effect of lapatinib treatment on SKBR3-par and SKBR3-L cells. (C) Effect of trastuzumab treatment on SKBR3-par and SKBR3-L cells. **denotes p < 0.01. (D) Effect of gefitinib treatment on SKBR3-par and SKBR3-L cells. (E) Immunoblot analysis of total and phosphorylated HER2(Tyr1221/1222), EGFR(Tyr1173), AKT(Ser473) and ERK(Thr202/Tyr204) in cells following 24 hr lapatinib treatment. Error bars represent the mean ± SD (n = 3).