OBJECTIVETo investigate the synergistical killing effect of docetaxel combined with ABT-737 on human prostate cancer cell line PC-3 by inducing apoptosis and further to determine the mechanism underlying such effect.

METHODSPC-3 cells were treated with various concentrations of docetaxel or (and) ABT-737. Cell viability was determined using MTT assay. Apoptosis was assessed by fluorescence microscopy analysis of cells with condensed and segmented nuclei following staining with 4',6-diamidino-2-phenylindole (DAPI). Cellular DNA was stained with propidium iodide and flow cytometric analysis was performed to analyze the cell cycle distribution. Bcl-2, Bax, Bcl-xL and Mcl-1 protein changes were detected by Western blot. The activity of caspase-3 was measured using a colorimetric assay.

RESULTSDocetaxel (20 nmol/L) combination with ABT-737 (400 nmol/L) for 48 hours, the cell viability was decreased to 19.7% ± 3.2% to compare with 44.2% ± 4.4% (t = 4.45) of docetaxel and 93.2% ± 1.8% of ABT-737 separately and there was a synergistic effect between the two drugs (CI = 0.8). Apoptosis rate of the combination group was higher than other two drugs. Docetaxel increased the cell number arrested in G(2)/M phase compared with control group (P < 0.05), but the combination treatment resulted in a significant arrest in the G(0)/G(1) phase. The combination treatment could significantly reduced the Bcl-2, Bcl-xL and Mcl-1 expression (F = 369.53, 57.89 and 32.77, all P < 0.05) and enhanced the activity of caspase-3 (419.7% ± 15.6%) (F = 207.33, P < 0.05).

CONCLUSIONSThe combination of ABT-737 with docetaxel can synergistically inhibit the proliferation of PC-3 cells through inducing apoptosis, which may be associated with cell cycle arrest, down-regulation of Bcl-2, Bcl-xL and Mcl-1 expression and activation of caspase-3.