Objective: To investigate the changes of drug sensitivity of spindle poison-induced polyploid tumor cells to chemotherapeutic agents and its possible mechanism.
Methods: Nocodazole in a dose of 100 ng/ml was used to induce polyploidization in a breast cancer cell line MDA-MB-231 cells. The polyploid cells (T-MDA-MB-231) were sorted by flow cytometry. The morphological changes and proliferation of T-MDA-MB-231 cells were compared with that of MDA-MB-231 cells. The cell growth inhibition was assessed by MTT assay. The cells were treated with paclitaxel, docetaxel, vincristine, epirubicin, 5-Fu, VP16 and oxaliplatin, respectively. Those cells were labeled with annexin V-FITC/PI and analyzed by flow cytometry. Bcl-2 was knocked down in T-MDA-MB-231 cells using SiRNA and their growth inhibition was evaluated by MTT assay to evaluate the reversing effect of Bcl-2-silencing on drug resistance.
Results: The polyploid T-MDA-MB-231 cells grew in vitro continuously and maintained constant DNA content. They had a larger cell size, and grew more slowly than MDA-MB-231 cells. The IC(50(s)) of T-MDA-MB-231 cells were significantly higher than that of the MDA-MB-231 cells: paclitaxel: (6.37 ± 0.07) vs. (2.05 ± 0.83) µmol/L; docetaxel: (32.98 ± 1.48) vs. (11.95 ± 0.98) µmol/L; vincristine: (35.28 ± 1.66) vs. (14.58 ± 0.94) µmol/L; oxaliplatin: (19.07 ± 0.45) vs. (9.75 ± 1.05) µmol/L; 5-Fu: (85.49 ± 3.21) vs. (31.35 ± 1.51) µmol/L; and epirubicin: (0.53 ± 0.06) vs. (0.15 ± 0.01) µmol/L, (all P < 0.05). The IC(50(s)) of VP16 in T-MDA-MB-231 cells was (2.85 ± 0.50)µmol/L, significantly lower than the (12.20 ± 1.55) µmol/L in MDA-MB-231 cells (P < 0.05), and that of T-MDA-MB-231 cells after Bcl-2-knocked down by siRNA was (19.59 ± 0.48) µmol/L, significantly higher than the (12.20 ± 1.55) µmol/L in the MDA-MB-231 cells (P < 0.05). The IC(50(s)) of docetaxel of T-MDA-MB-231 cells after Bcl-2-knocked down by siRNA was (21.52 ± 0.68) µmol/L, significantly decreased and lower than that before Bcl-2 silencing (32.98 ± 1.48) µmol/L.
Conclusions: Our results indicate that polyploid tumor cells induced by spindle poison Nocodazole are more resistant to most of chemotherapeutic drugs. Downregulation of Bcl-2 increases the sensitivity of polyploid cells to docetaxel. The high expression of Bcl-2 may be one of the drug resistance mechanisms of polyploid tumor cells. The polyploid tumor cells are relatively sensitive to VP16, suggesting that VP16 might be an effective candidate drug for treatment of chemoresistant polyploid tumors.