The aim of this study was to establish a new paclitaxel (PTX)-resistant human esophageal squamous carcinoma (ESCC) cell line and investigate its biological characteristics. The resistant cell line (EC109/Taxol) was developed in vitro by intermittent exposure of the human ESCC cell line EC109 to a high concentration of PTX with time-stepwise increment over a period of 6 months. The MTT assay was performed to test the drug resistance of EC109 and EC109/Taxol cells. The morphological features were observed using inverted microscopy and apoptosis was measured by flow cytometry (FCM) and Hoechst 33258 fluorescence staining. Cell growth curves and colony formation of EC109 and EC109/Taxol cells were compared. FCM was also used to determine the distribution of the cell cycle. The protein levels of Bcl-2, Bax, Procaspase-3 and P-gp were detected by western blotting. P-gp activity was evaluated by Rh123 accumulation and efflux assay. In vivo resistance characterization was investigated. EC109/Taxol cells were 67.2-fold resistant to PTX in comparison with EC109 cells, and also exhibited cross-resistance to 5-fluorouracil (5-FU), cisplatin (CDDP) and epirubicin (EPI). FCM and Hoechst 33258 fluorescence staining confirmed that EC109 cells treated with PTX showed significantly higher percentage of apoptotic cells compared to EC109/Taxol cells. Simultaneously, EC109/Taxol cells exhibited changes in morphology, proliferation rate, doubling time, cell cycle distribution and colony formation rate were detected as compared with EC109 cells. The resistant cell line overexpressed Bcl-2, Procaspase-3 and P-gp protein, and showed decreased Bax expression. Further, EC109/Taxol cells did not change PTX resistance in vivo. This is the first report on the establishment of an EC109/Taxol cell line with higher resistance. Bcl-2, Bax, Procaspase-3 and P-gp are involved in the resistance of cell lines to PTX, which are invaluable tools to study the resistance of anticancer drugs and to identify the methods to overcome resistance.

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