DTX-resistant cells (SPC-A1/DTX) were derived from lung adenocarcinoma cell lines (SPC-A1). (A) Morphologies of SPC-A1 and SPC-A1/DTX cells. Cells were grown to 80% confluency and then photographed under 40x magnification. (B) The doubling time of SPC-A1 and SPC-A1/DTX cell lines was 34.0 h and 26.5 h, respectively. (C) The IC50 values of DTX or paclitaxel in SPC-A1 and SPC-A1/DTX cells were determined. (D) The colony formation of SPC-A1 and SPC-A1/DTX cells treated with various concentrations of DTX (0.5, 1.0 and 1.5 µg/L). Results represent the average of three independent experiments (mean ± SD). *p < 0.05 and **p < 0.01 compared with parental SPC-A1.