Breast cancer stem cells are contribute to distance metastasis, breast cancer recurrence and drug resistance. SIRT1, a nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase, play significant role in DNA repair, cell survival, stem cells and epigenetic modification. SIRT1 has been related to cancer stem cells in chronic myelogenous leukemia. In this study, we investigate the role of SIRT1 in breast cancer stem cells.

SIRT1 inhibitors cambinol and Ex527 are used for treatment in several breast cancer cell lines, including T47D, TB549, MDA-MB-231 and MDA-MB-468. Stem cell markers, SOX-2 and Nanog, are significantly decreased in SIRT1 inhibitor treated cancer cells by qRT-PCR and western blot in T47D cell line. The ALDH positive cells in MDA-MB-231 cell line are significant reduced from 29% to 3.2% with Adeflour assay, and the CD44 expression is significantly reduced in CD44/CD24 flow cytometry analysis. Using qRT-PCR, SIRT1 inhibitors significantly down regulate vimentin (-3.7 folds), N-cadherin and smooth muscle actin (-2.7 folds) and up regulate the gene of E-cadherin, indicating SIRT1 inhibitors can block the epithelial mesenchymal transformation (EMT) of breast cancer. SIRT1 inhibitors can significantly (40-50%) block the cancer cell invasion and migration in several triple negative breast cancer cell lines. SIRT1 inhibitors can inhibit cell proliferation on all tested breast cancer cell lines, and can induce significant cell apoptosis in T47D cells. In xenograft tumor study, SIRT1 inhibitor cambinol can significantly reduce tumor growth and inhibit tumor metastasis.

The molecular mechanism of SIRT1 inhibitors in blocking EMT and reducing cancer stem cells is likely associated with blocking the Wnt pathway. Several down stream target genes of Wnt pathway, such as cyclin D1, c-Myc and c-Jun, are significantly down regulated after using SIRT1 inhibitor cambinol, and the changes are more significant in TGF-beta stimulated cancer cells. Beta-catenin is significantly reduced including the active beta-catenin, and the decreasing beta-catenin protein may be related to the decreased Dvl proteins.

In summary, our study demonstrated that SIRT1 inhibitors can reduce breast cancer stem cell population in several cancer cell lines, block epithelial mesenchymal transformation, and inhibit breast cancer cell invasion and metastasis. SIRT1 inhibitors appear to inhibit Wnt pathway in cancer cells to block EMT and affect cancer stem cells.

Citation Format: Songlin Zhang, Min Li, Baoxiang Guan, Robert Brown. SIRT1 inhibitors significantly reduce cancer stem cells and block epithelial mesenchymal transformation in breast cancer cells [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-06-08.