Activity of docetaxel in paclitaxel-resistant ovarian cancer cells

The aim of this study was to determine the behavior of docetaxel (DTX) in ovarian cancer cells resistant to paclitaxel (PTX).

We used human ovarian adenocarcinoma cell lines KF, KFTx (PTX-resistant KF), SK-OV-3, and HAC-2. The sensitivity of the cells to PTX or DTX was determined by the MTT assay. Cellular accumulation of PTX and DTX was measured by high-performance liquid chromatography. mRNA of MDR-1 was detected by RT-PCR. Cell cycle distribution was determined by flow cytometry after exposure to the IC(50) of each drug. Bcl-2 phosphorylation was determined by Western blot analysis. Activity for tubulin polymerization of each drug was examined by a beta-tubulin polymerization assay.

KFTx cells had a 5.5-fold greater resistance to PTX and a 7.3-fold greater resistance to DTX than KF cells, indicating that KFTx cells had acquired cross-resistance to DTX. SK-OV-3 cells were sensitive and HAC-2 cells were resistant to both PTX and DTX. The gene expression of MDR-1 increased after exposure to DTX in KF and KFTx cells. Residual cellular accumulation of PTX and DTX was significantly lower in KFTx cells than in KF cells. In contrast, MDR-1 expression was not detected in SK-OV-3 and HAC-2 cells. Flow cytometric analysis indicated no differences in alterations of cell cycle distribution following exposure to the two drugs. Bcl-2 phosphorylation occurred after exposure to DTX at a concentration equivalent to the clinical dose, but did not occur after exposure to PTX in KFTx cells. In HAC-2 cells, Bcl-2 phosphorylation was not detected after exposure to DTX or PTX at concentrations equivalent to the clinical doses. DTX showed greater tubulin polymerization activity than PTX in KFTx cells. beta-tubulin polymerization did not correlate with the concentration of PTX or DTX, suggesting that alteration in the tubulin reaction might contribute to the resistance in HAC-2 cells.

The present study suggests that the mechanisms involved in cytotoxicity of and resistance to PTX and DTX do not differ, but DTX has a greater cytotoxic potential in PTX-resistant cells with an efflux system.