Figure 1.
Establishment of an erlotinib‐resistant lung cancer cell line. (A) Overview of the strategy to establish erlotinib‐resistant cells from PC‐9 cells. (B) A light microscopic (×100) image of PC‐9 and PC‐9/ER3 cells. Cells were exposed to erlotinib (1 μM) for 72 h. (C) Relative cell numbers of PC‐9 and PC‐9/ER3 are shown in the culture medium for 72 h. PC‐9 and PC‐9/ER3 cells were seeded on 6‐cm dishes (4 × 105 per dish) in the absence of erlotinib. Cells were trypsinized and counted in triplicate. DT, doubling time. Data are presented as the mean ± SD. (D) Cells (3 × 103 per well) were seeded onto 96‐well plates in quadruplicate and grown in the absence or presence of the indicated concentration of erlotinib. After 96 h, the cells were subjected to MTT assays. PC‐9/ER3 cells were maintained in culture medium without erlotinib for 5 (5W), 10 (10W) or 20 (20W) weeks. EGFR, epidermal growth factor receptor; NSCLC, non‐small cell lung cancer.