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e21041 Background: microRNAs are small endogenous non-coding RNAs, which posttranscriptionally regulate gene expression. In breast cancer, overexpression of the transmembrane heparan sulfate proteoglycan syndecan-1, a predicted target of the oncomiR miR-10b, correlates with poor clinical outcome. Here, we investigatet the potential functional relationship of miR-10b and syndecan-1 in an in vitro study. Methods: MDA-MB-231 and MCF-7 breast cancer cells were transiently transfected with pre-miR-10b, syndecan-1 siRNA or control reagents, respectively. Altered cell behaviour was monitored by proliferation, migration and invasion chamber assays, and time-lapse video microscopy. Results: miR-10b overexpression induced posttranscriptional downregulation of syndecan-1, as demonstrated by qPCR, flow cytometry, and 3’UTR luciferase assays, resulting in increased cancer cell migration and matrigel invasiveness. Syndecan-1 silencing generated a copy of this phenotype. Adhesion to fibronectin and laminin and basal cell proliferation were increased. Syndecan-1 co-immunoprecipitated with focal adhesion kinase, which showed increased activation upon syndecan-1 depletion. Affymetrix screening and confirmatory qPCR and Western blotting analysis of syndecan-1 deficient cells revealed upregulation of ATF-2, COX- 2, cadherin-11, vinculin, ACTG2, MYL9, transgelin-1, RhoA/C, MMP2 and heparanase, and downregulation of AML1/RUNX1, E-cadherin, CLDN1, p21WAF/CIP, Cdk6, TLR-4, PAI1/2, Collagen1alpha1, JHDM1D, Mpp4, MMP9, matrilin-2 and ANXA3/A10. Video microscopy demonstrated massively increased Rho kinase-dependent motility of syndecan-1-depleted cells, which displayed increased filopodia formation. Conclusions: We conclude that syndecan-1 is a novel target of the oncomiR miR-10b. Rho-GTPase dependent modulation of cytoskeletal function and downregulation of E-cadherin expression are identified as relevant effectors of the miR-10b-syndecan-1 axis, which emerges as a promising target for the development of new therapeutic approaches for breast cancer.

10627 Background: Based on its potential use as a therapeutic target through PARP inhibitors expression of Poly-A-Ribose-Polymerase-1 (PARP-1) has come into scientific focus. Furthermore, it could be demonstrated that cytoplasmic PARP-1 expression varies depending on molecular breast cancer subtypes and that it correlates with an increased response to neoadjuvant taxane-anthrazykline containing chemotherapy (von Minckwitz et al., J Clin Oncol 2011). In-vitro-chemotherapy sensitivity and resistance assays (CSRAs) are a means to directly measure chemotherapy sensitivity in a given tumor uninfluenced by host factors. Methods: We conducted a systematic immunohistochemical tissue-microarray (TMA)-based analysis of 550 samples of invasive breast cancers to evaluate the expression of a set of molecular markers including estrogen receptor (ER), progesterone receptor (PR) and HER2 as well as PARP-1. Triple negative breast cancers (TNBC) were identified through lack of (over-)expression of ER, PR and HER2. All carcinomas were analyzed in an in vitro CSRA protocol for epirubicin/docetaxel (ED) and epirubicin/cyclophosphamide (EC). In-vitro-chemotherapy sensitivity was analyzed using an adenosine triphosphate (ATP) bioluminescence assay. Results: Moderate/high expression of PARP-1 was found in 48 and 33% of cases with TNBC and non-TNBC, respectively (p=0.015). No correlation between TNBC phenotype and cytoplasmic expression was observed. However, increased expression of both cytoplasmic and nuclear PARP-1 was correlated with an increased in-vitro sensitivity against ED (p=0.012 and 0.025, respectively) but not EC (p=0.27 and 0.62, respectively). Conclusions: Our results support previous observations demonstrating a significant correlation between expression of PARP-1 and an increased sensitivity against taxane-anthracycline chemotherapy independent of tumor phenotype.

e11534 Background: Triple negative breast cancer (TNBC) is defined by the lack of estrogen-receptor alpha (ERα) and progesterone receptor (PGR) expression as well as absence of human epidermal growth factor receptor2 (HER2/neu) overexpression. This type of breast cancer is characterized by a poor prognosis and significantly reduced survival rate compared to other BC subtypes. This is mostly due to the lack of targeted agents like endocrine or anti HER2 targets. Breast cancers which overexpress HER2 are usually treated by chemicals targeting HER2; either by blocking the extracellular domain through trastuzumab or the intracellular domain through the small molecule lapatinib. Both therapeutics lead to inhibition of downstream pathways like MAPK and PI3K, resulting in increased apoptosis as well as reduced proliferation. Methods: We hypothesize that downstream effects might be induced in TNBC cells when HER2 is artificially overexpressed and cells get treated as HER2 positive cells. Therefore, triple negative breast cancer cell lines were transfected with HER2. These cells were treated with anti-HER2 agents. Molecular analyses will demonstrate whether transfection with HER2 will yield a HER2 positive breast cancer phenotype in that all downstream signaling mechanisms act similarly to a priori HER2 positive cells. Results: Preliminary experiments suggest that proliferation of TNBC cells transfected with HER2 does not change significantly. Treatment with HER2-blocking antibody trastuzumab leads to significant decrease of proliferation in HER2 transfected, initially triple negative MDA-MB-231 breast cancer cells. Only a moderate decrease in proliferation was observed when lapatinib, a molecule directed against both EGFR and HER2, was used in both MDA-MB-231 wildtype and HER2-transfected cell lines. Conclusions: We surmise that firstly, conversion of cancer might become a clinical tool to treat cancer of poor prognosis and secondly that our results might shed light on future therapeutic approaches e.g. small molecule compound screening for endogenous HER2 reactivation / overexpression and subsequent targeted treatment of triple negative breast cancers.

597 Background: Triple-negative breast cancer (TNBC) is characterized by lack of expression of estrogen and progesterone receptor as well as lack of overexpression/amplification of HER2/neu. Patien...

9625 Background: Clinical studies have demonstrated that amplification and overexpression of c-erbB2 in breast carcinomas indicates poor clinical outcome. Previously, we reported the detection of c...