Background & objective: Loss or decreased expression of estrogen receptor (ER) and decreased growth rate regularly occur in drug-resistant breast cancer cells. This study was designed to investigate the effect of estrogen receptor status on the drug resistance to droloxifene (Dro) and Adriamycin (Adr) of drug-resistant MCF-7/Adr human breast cancer cells.
Methods: The expression of ER in MCF-7 and MCF-7/Adr cells was determined using Western blot analysis. ER expression plasmid was constructed and introduced into MCF-7/Adr cells using LipofectAMINE. After G418 screening, the positive clone (MTER/Adr) was obtained. The integration and expression of ER gene were analyzed by polymerase chain reaction (PCR) and Western blot. The cell cycle distribution was investigated by flow cytometry. The effects of droloxifene and Adriamycin on the growth of cells were investigated by MTT assay.
Results: Western blot analysis showed that ER was positive in MCF-7 cells, but was negative in MCF-7/Adr cells. The ER expression plasmid was constructed and introduced into MCF-7/Adr cells. The integration and expression of ER gene were successful in positive clone -MTER/Adr cells. Droloxifene inhibited the growth of MCF-7 at the concentration of 10-20 micromol/L and the MCF-7/Adr only at concentration of 20 micromol/L. Droloxifene inhibited the growth of MTER/Adr at the concentration of 15 micromol/L, and the percentage of MTER/Adr cells increased in G0/G1 phase. The sensitivity of MTER/Adr cells to Adriamycin increased.
Conclusion: The insensitivity of MCF-7/Adr human breast cancer cells to droloxifene was associated with the loss of ER. MTER/Adr cells partially restore the sensitivity to droloxifene and Adriamycin.