Arsenic trioxide re-sensitizes ERalpha-negative breast cancer cells to endocrine therapy by restoring ERalpha expression in vitro and in vivo.

摘要

Approximately one-third of breast cancers lack estrogen receptor alpha (ERalpha) because of the hypermethylation of the CpG island in the receptor's promoter. These tumors are associated with poorer histological differentiation, a higher growth fraction, are rarely responsive to endocrine therapy and have a worse clinical outcome. Thus, re-expression of ERalpha in ERalpha-negative breast cancers may restore the sensitivity of antiestrogen therapy. The ERalpha-negative breast cancer cell line MDA-MB-435s was treated with different concentrations of arsenic trioxide (As2O3). MS-PCR was used to detect the change in the methylation status of ERalpha. RT-PCR, immunohistochemistry and Western blot analyses were used to detect changes in the mRNA and protein expression of DNA methyl-transferase-1 (DNMT1) and ERalpha. Cell proliferation was examined using the MTT assay. A xenograft model in nude mice was used to further examine the results we observed in vitro. The ERalpha gene was demethylated after As2O3 treatment of MDA-MB-435s cells. RT-PCR, immunohistochemistry and Western blot analyses revealed that DNMT1 expression was inhibited and ERalpha was re-expressed in a concentration-dependent manner after As2O3 treatment. The MTT assay showed that cell proliferation was significantly suppressed after exposure to different concentrations of As2O3. Addition of tamoxifen (TAM) further suppressed levels of cell proliferation. In vivo, the xenograft tumor volumes of As2O3-treated mice were smaller than those observed in untreated and TAM-treated mice. Treatment with a combination of As2O3+TAM resulted in further suppression. As2O3 can act as a demethylation agent to restore ERalpha expression in ERalpha-negative breast cancer cells and re-sensitize these cells to endocrine therapy in vitro and in vivo.