Characterization of Taxol-resistant cells. A, MDA-435, 435TR1 and 435TRP cells were treated with 20 nM Taxol for 24 hrs and their morphology was observed under fluorescence microscope. The phase image of these cells was shown at the top and the nucleus stained by DAPI was shown at the bottom (200 ×). B, MDA-435, 435TR1 and 435TRP cells were treated with 20 nM Taxol for 48 hrs and apoptosis was examined by flow cytometry using Annexin V/PI staining and by Cell Death Detection ELISA PLUS Kit. Fold induction value was calculated following the formula: mU of the sample (cells treated with Taxol)/mU of the corresponding negative control (cells without Taxol treatment). C, Taxol-resistant cells and their parental cells were treated without or with 20 nM Taxol for 48 hrs, then poly (ADP-ribose) polymerase (PARP) and its cleaved protein (c-PARP) were analyzed by Western blotting with specific antibodies, respectively. β-actin was used as a loading control. D, Cell viability analysis was performed to evaluate cytotoxicity of Taxol to MDA-435 and Taxol-resistant 435TR1 and 435TRP cells under treatment with indicated concentrations of Taxol for 48 hrs.