Abstract B166: MicroRNAs downstream of ADAM8 as therapeutic targets and non-invasive biomarkers for triple-negative breast cancer.

Triple-negative breast cancer (TNBC) represents ∼20% of breast cancers, is highly aggressive and lacks targeted therapies due to the absence of hormone and HER2 receptors. TNBCs respond only poorly to chemotherapy and recur more frequently than other breast cancers. Their recurrence often involves distant metastasis, especially to the brain and lungs with a poor prognosis, which lead to approximately 25% of the half million yearly deaths worldwide from breast cancer. Thus, there is a critical unmet need for early detection and new therapeutic targets for TNBC treatment, which was the focus of our current study. Recently, our lab has shown that the transmembrane protein ADAM8 (A Disintegrin And Metalloproteinase 8) plays a key role in invasion and metastasis of TNBCs and high ADAM8 levels correlate with a poor prognosis in breast cancer patients. MicroRNAs (miRNAs) play important functions in both normal and disease development. It is estimated that more than 60% of the protein-coding genes in the human genome are regulated by miRNAs. Furthermore, circulating tumor cell-associated miRNAs and free circulating miRNAs have been identified in whole blood, plasma and serum in various cancer subtypes. Here we tested two related hypotheses, that: (1) miRNAs regulated by the ADAM8 pathway are important mediators promoting invasion and migration of TNBC cells; and (2) these miRNAs represent potential therapeutic targets and/or noninvasive biomarkers for detection of TNBC recurrence. A microarray analysis was performed using TaqMan microRNA cards on RNA isolated from MDA-MB-231 cells after 72 h of transient siRNA-mediated knockdown of ADAM8. We identified 68 miRNAs that were differentially regulated upon ADAM8 knockdown. Thus far we have confirmed 13 miRNAs using real-time PCR. Of the miRNAs confirmed, miR-720 was selected as the initial candidate of study, since it has been previously identified as an oncomiR and also detected in blood from breast cancer patients. Transient ectopic ADAM8 overexpression in MDA-MB-231 and SUM149 TNBC cell lines induced levels of miR-720 whereas ADAM8 siRNA reduced them. Furthermore, knockdown of miR-720 using an antagomiR led to a significant decrease of the migratory and invasive phenotype of TNBC cells as judged by Boyden chamber and 3D Matrigel outgrowth assays, respectively. Consistently, we used a miRNA mimic to overexpress miR-720 activity and observed increased migration and invasion of TNBC cells. Importantly, a profound increase in levels of miR-720 was detected in the plasma of mice bearing orthotopic mammary tumors derived from control shRNA-MDA-MB-231 cells in contrast to shADAM8-MDA-MB-231 cells and non-tumor bearing mice, which suggests that miR-720 levels in blood correlate with ADAM8 expression in tumors. Taken together our data indicates that the miR-720 is induced by ADAM8 and miRNAs regulated downstream of ADAM8 have a strong potential as both biomarkers and therapeutic targets for the treatment of TNBC. Research was funded by grants from the DOD (W81XWH-11-1-0814) and the NIH (R01 CA129129) Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B166. Citation Format: Sonia G. Das, Mathilde Romagnoli, Nora D. Mineva, Gail E. Sonenshein. MicroRNAs downstream of ADAM8 as therapeutic targets and non-invasive biomarkers for triple-negative breast cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B166.