Abstract 1062: Overexpression of miRNAs 181a and 222 play a role in triple negative breast cancer, and are targeted by entinostat

Triple-negative breast cancer (TNBC) accounts for 15-20% of all breast cancer in women. Clinically, this subtype is characterized by high recurrence rates, poor prognosis, and lack of targeted therapies. Therefore, there is considerable need to identify TNBC-specific biomarkers that can serve as a diagnositc markers and therapeutic targets. MIcroRNAs (miRNAs), may be such biomarkers. miRNAs are short, non-coding regulatory RNA molecules that modulate the expression of specific proteins by binding to target messenger RNAs (mRNAs) and causing either degradation of the mRNAs or inhibition of their translation to protein. Thus, they play an important role in a variety of normal cellular processes (e.g., differentiation, cell growth, cell death, etc.), and in diseases, such as cancer. MiRNAs have been implicated in breast cancer, but there is not consistent agreement as to which miRNAs are involved in TNBCs, nor have molecular targeting drugs been identified that could treat TNBCs by affecting miRNAs. Previous studies by our lab and others indicate that miRNAs 181a and 222 are involved in estrogen-receptor independence, cancer stem cells, and drug resistance (ex. letrozole resistance). Thus, in this study, the expression of miRNAs 181 and 222 in TNBCs, the effect of inhibiting each miRNA on cell viability and cancer stem cells, and the effect of histone deactylase inhibitor entinostat on miRNA expression are explored. RT-PCR analysis of miRNA expression in both HS578T and BT547 TNBCs and MCF-7 cells (represents the least aggressive subtype), and in representative breast cancer patient biopsy samples indicates that both miRNA 181a and 222 are upregulated by at least 15-fold in TNBCs compared to MCF-7 (least aggressive subtype). Specific inhibition of miRNA 181a via siRNA/miRNA inhibitor in HS578T cells significantly decreased cell viability by at least 80%, as determined by MTT assay, and cancer stem cells by 50%, as determined by mammosphere assays. In addition, inhibition of miRNA 181a produced morphological changes in HS578T cells, in which cells lost their protrusions, became more round, and grew in colonies. Lastly, treatment of HS578T cells or of patient derived xenografts with entinostat, which is currently being explored as a TNBC-targeting drug, decreased miRNA 181a and 222 expression and produced similar results as miRNA inhibition on cell viability, cancer stem cells, and morphology. Overall, these results suggest that miRNAs 181a and 222 are overexpressed in TNBCs and may play a role in regulation of cell viability and cancer stem cells. They also indicate that HDAC inhibitor, entinostat, may be an effective treatment for TNBCs through their action on miRNAs 181a and 222. Citation Format: Armina A. Kazi, Alexa Giammarino, Nicholas Musacchio, Gauri Sabnis, Amanda Schech, Angela Brodie. Overexpression of miRNAs 181a and 222 play a role in triple negative breast cancer, and are targeted by entinostat. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1062.