OBJECTIVETo observe if ER alpha gene can be induced by 5-aza-CdR in ER alpha negative human breast cancer cell lines (MDA-MB-231 and MDA-MB-435) and the synergistic inhibitory effects of 5-aza-CdR and Tamoxifen on these two cell lines in vitro.

METHODSThe status of 5'CpG island methylation of ER alpha gene in ER alpha negative (MDA-MB-231 and MDA-MB-435) human breast cancer cell lines and 20 cases of breast cancer tissue was studied by MSP, the expression of ER alpha mRNA was inspected by using RT-PCR after these two cell lines were treated with 5-aza-CdR. Cell proliferation was evaluated by MTT assay, distribution of cell cycle and rate of apoptosis were determined by flow cytometry after these two cell lines were treated with 5-aza-CdR or TAM alone, or in combination in vitro.

RESULTSThe 5'CpG island is methylated in the core promotor of ER alpha gene in ER alpha negative (MDA-MB-231 and MDA-MB-435) human breast cancer cell lines and the methylating rate is 25.0%, 66.7%, 83.3%, 100% in 20 cases of breast cancer tissue of stage I, II, III, IV, respectively. The expression of ER alpha mRNA was induced in these two cell lines after treated with 5-aza-CdR, MTT array showed the proliferation activity of these two cell lines was obviously reduced in 5-aza-CdR group and the inhibitory effect on proliferation was enhanced when 5-aza-CdR combined with TAM compared with control group, the induction of apoptosis was 11.20% and 8.71% respectively by 5-aza-CdR, while the rate of apoptosis is 48.8% and 53.1% when these two cells were treated with 5-aza-CdR combined with TAM.

CONCLUSIONS5-aza-CdR can re-express ER alpha by demethylating and sensitive ER alpha negative human breast cancer cell lines to TAM, 5-aza-CdR and TAM synergistically inhibit proliferation and induce apoptosis in ER alpha negative human breast cancer cell lines, thus offer a new way for the treatment of ER alpha negative breast cancer.