Abstract 4223: Gamma-tocotrienol and simvastatin target TIC and EMT populations in drug-resistant breast cancer

Abstract

Abstract Background and significance: Breast cancer (BC) is the second leading cause of cancer deaths in women. Despite great advances in treatment of early and advanced BC, relapse with drug resistance and metastasis is the biggest impediment to successful remission. Accumulating evidence supports the emerging concept that cancer stem cells (CSCs, also called tumor initiating cells, TICs), a rare tumor cell population that exhibits self-renewal and differentiation properties, are responsible for tumor relapse and metastasis. Hence, identifying molecular mediators responsible for maintenance of TICs and metastasis in drug resistant breast cancer is important to develop better and successful therapeutic strategies. Model system and methods: Acquired tamoxifen resistant (MCF-7/TamR) and doxorubicin resistant (MCF-7/ADR) cell lines as well as their isogenic parental counterparts MCF-7/S and MCF-7/WT, respectively were used in this study. ALDH activity assay was used for characterization and enrichment of TIC population. Immuno-staining/FACS of CD44+/CD24- was used to determine the metastasis potential in-vitro. Western blot analyses were used to detect signal transduction mediators known to be important for maintenance of TIC and EMT populations. Results: Both drug resistant cell lines expressed a higher percentage of TIC population as detected by ALDH activity and elevated EMT population as detected by CD44+/CD24- and increased EMT marker Vimentin and decreased MET marker E-cadherin in comparison with the isogenic sensitive cell lines. Both drug resistant cell lines uniformly expressed higher levels of pStat-3, c-Myc and CyclinD1 in comparison with their respective parental cell lines. Knockdown of Stat-3 using siRNA and Stat-3 inhibitor reduced TIC populations, reduced EMT populations, and decreased c-Myc and CyclinD1, but did not affect Vimentin and E-cadherin protein expression. γT3 and SVA alone and in combination reduced TIC populations as measured by reduced ALDH population and inhibition of mammospheres. Both agents alone and in combination reduced the EMT populations and reduced the levels of p-Stat3, c-Myc and CyclinD1expressed in drug-resistant breast cancer cell lines. Conclusion: These in vitro data demonstrate that drug resistant breast cancer cell lines contain high levels of TIC and EMT sub-populations that are in part controlled by the Stat-3 pathway. Furthermore, αT3 and SVA alone and in combination show the ability to target TIC population and metastasis associated mediators. Supported by the Clayton Foundation for Research. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4223. doi:1538-7445.AM2012-4223