Fig 1. BT.Her^R and SK.Her^R cells demonstrate different sensitivities to EGFR inhibitors in the absence of trastuzumab.

Cell proliferation in AG1478 (left), gefitinib (middle) and erlotinib (right) was measured by SRB assay after exposure to 0.1% DMSO or increasing concentrations of the respective drugs. IC₅₀ values were obtained using CalcuSyn and normalized to the average IC₅₀ for the appropriate parental cell line. Each bar represents the mean of three independent experiments ±SD. (A) Relative sensitivity for BT474 parental and two BT.Her^R clones (1.0C and 1.0E) treated with DMSO or drugs for 7 days. (B) Relative sensitivity for SK-Br-3 parental and SK.Her^R cells treated with DMSO or drugs for 5 days. *, p<0.05; **, p<0.01; ***, p<0.001 compared to parental cells.