Figure 1. Development of gefitinib-resistant PC-9-GR cells.

(A). ARMS assay showing the emergency of EGFR T790M mutation in PC-9 cells exposed to chronic treatments of gefitinib. (B). Effects of gefitinib on cell growths of PC-9 and PC-9-GR cells. Cells were treated with different concentrations of gefitinib for 72 hours, and cell viabilities were determined by MTS assay. (C). Persistence of EGFR T790M in established PC-9-GR cells. ARMS assays were used to determine the T790M mutation and the 15 bp deletion of EGFR in cell samples with DNA extracted from PC-9-GR cells. ddH₂O was used as negative control, and a DNA template with T790M mutation or 15bp deletion was included as positive control in these assays.