Enhancement of Sensitivity to Tamoxifen by Berberine in Breast Cancer Cells by Inhibiting ER-α36 Expression

Berberine, an isoquinoline alkaloid purified from Chinese herbs, was verified to have antitumor effects. It has also been reported that berberine can enhance the anticancer effect of tamoxifen (TAM) in estrogen receptor (ER)-positive breast cancer cells; however, the involved underlying mechanism is still unclear. In the present study, the role of one variant of ER-α, ER-α36, in the TAM sensitizing effect of berberine was explored in TAM-resistant breast cancer cells. This study demonstrated that berberine potently sensitized TAM-resistant breast cancer cells, including TAM-resistant MCF7 and BT-474 cells, to TAM treatment. Additionally, this study showed that berberine could simultaneously suppress ER-α36 expression in TAM-resistant cells. However, when ER-α36 was knocked down in TAM-resistant cells, there was no significant TAM-sensitizing effect by berberine. Therefore, this study indicated that ER-α36 is involved in berberine’s TAM-sensitizing effect on ER-positive breast cancer cells, which provided supporting data for the application of berberine in cancer therapy as an adjuvant agent for TAM treatment.