Abstract 3981: Tamoxifen inhibited cell migration and increased chemosensitivity by reversal of EMT in ER-negative breast cancer cells
Authors: Qu Xiujuan , Wang Qian , Wang Yan , Zhang Ye , Teng Yuee , Liu Yunpeng 
Published: August 2015

BACKGROUND: Tamoxifen (TAM) is the mainstay endocrine drug used as adjuvant therapy for postmenopausal breast cancer (PMBC) patients. Although the efficacy of tamoxifen has been attributed to the induction of cell cycle arrest and apoptosis by inhibition of ER signaling pathway, recent evidence indicates that tamoxifen also possesses ER-independent antitumor activity in breast cancer treatment. However,the mechanism is not clear. Therefore, the present study is aimed to investigate the anti-tumor mechanism of tamoxifen on ER negative breast cancer.

METHODS: The cell morphology changes were observed by using electron microscopy. Proteins expression was tested by western blot. miRNAs expression was examined by Real-Time PCR. And cells migration ability was observed by trans-well assay. Mice experiments were carried by using nude mice. Inhibition of protein expression was done by RNA interfering experiments.

RESULTS: Our results showed an interesting morphology change of ER negative breast cancer cells. After treated with TAM, the morphology ER negative MDA-MB-231 and MCF-7/ADR breast cancer cells were reversed from mesenchymal type to epithelial type accompanied by down regulation of Vimentin and up-regulation of E-cadherin. Meanwhile cells migration ability was also significantly decreased. But ER positive MCF-7 breast cancer cells didn't show any changes after exposure to TAM. Mice experiments demonstrated that TAM significantly suppressed lung metastasis rate of ER negative breast cancer cells. In addition, TAM enhanced adriamycin effect on ER negative but not ER positive breast cancers cells. To explore the mechanisms, we screened miRNAs changes by miRNA array analysis, and found that miR-200c is obviously up-regulated. Through Biological information analysis, CPG island is found exist in the promoter region of miR-200c. The DNA methyltransferase inhibitor 5-aza-2′-deoxycytidine (5Aza-dC) also increased miR-200c expression. Further investigation demonstrated that DNA (cytosine-5)- methyltransferase DNMT 1 and 3A were down-regualted by TAM. And inhibition of DNMT 1 and 3A by RNAi increased miRNA-200c. These results indicated that TAM inhibited cells migration and enhanced adriamycin sensitivity of ER negative breast cancer cells by reversing their EMT-like property. And the EMT reversal effect resulted from up-regulation of miR-200c. Down-regualtion of DNMT 1 and 3A and CPG island demethylation of miRNA-200c contributed to up-regulation of miR-200c.

CONCLUSIONS: Tamoxifen inhibited cells migration and increased chemosensitivity by reversal of EMT in ER negative breast cancer cells. Our findings described a novel mechanism to explain how TAM effect on ER negative breast cancer cells.

Citation Format: Xiujuan Qu, Qian Wang, Yan Wang, Ye Zhang, Yuee Teng, Yunpeng Liu. Tamoxifen inhibited cell migration and increased chemosensitivity by reversal of EMT in ER-negative breast cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3981. doi:10.1158/1538-7445.AM2015-3981