Abstract 1073: Modulation of aromatase inhibitor resistance by miRNAs in breast cancer
Authors: Reiner Hoppe, Ping Fan, Florian Büttner, Stefan Winter, Heather Cunliffe, V. Craig Jordan, Hiltrud B. Brauch
Journal: Cancer Research (2016)

Abstract The blockade of E2 signaling by either tamoxifen or aromatase inhibitors (AI) is the standard treatment of patients with estrogen receptor (ER)-positive breast cancer. However, acquired resistance to antiestrogen therapies remains a big clinical challenge. The in vitro breast cancer models MCF-7:5C and MCF-7:2A mimic clinical AI resistance in that they grow under tamoxifen, but can rapidly regress with E2 due to the reconfiguration of survival signaling known as E2-inducible apoptosis. This principle is currently explored in clinical trials in order to develop strategies to overcome endocrine resistance. To better understand the biology of AI resistance we previously ascertained a wide range of alterations of stress related pathways including the accumulation of endoplasmic reticulum stress, oxidative stress, and inflammatory stress that occur prior to E2-induced apoptosis (Ariazi et al. 2011; Fan et al. 2013, 2015; Sweeney et al. 2014). In this current work we investigated miRNA expression profiles of the 5C and 2A models (both compared to MCF-7:WS8 reference) in order to further elucidate the molecular scenario that characterizes the AI resistance phenotypes and their susceptibility to E2-induced apoptosis. Using Affymetrix GeneChip miRNA2.0 arrays we identified 184 miRNAs differentially expressed between 2A and 5C (FC &amp;gt; 1.5 or &amp;lt; 1/1.5, P &amp;lt; 0.05). Of these, 30 miRNAs were specific for 2A, 99 for 5C, and 55 overlapped. Common miRNAs include upregulated oncogenic miRNAs of the miR-17-92 cluster (Chr. 13q31) and the paralogous 106a-363 cluster (Chr. X), as well as downregulated tumor suppressive miRNAs such as miR-342-5p. Thirty-four miRNAs that cluster at Chr. 14q32 were overexpressed in 5C cells and highly correlate with the downregulated miR-99a and miR-125b (Chr. 21q21). At the clinical level based on data from The Cancer Genome Atlas (miRNA-Seq v. 3.1.17.0), low expression of miR-31 was associated with poor (HR = 3.0, 95% CI: 1.9-4.8; Padj = 8.7E-5), and low miR-222 expression was associated with better outcome (HR = 0.3, 95% CI: 0.1-0.6; Padj. = 4.4E-3). As miR-31 expression is high and miR-222 expression is low in 5C cells compared to the MCF-7:WS8 reference, we suggest protective roles. Functions of miRNAs were deciphered via analyses of their predicted targets (CLIP-confirmed). Using KEGG and GO databases functional enrichment analyses of 5C and 2A specific miRNA sets revealed pathways associated with cell proliferation for both models including insulin, mTOR, and ErbB signaling as well as immune response and metabolism associated pathways. While the 2A specific miRNA set revealed additional metabolic pathways, the 5C specific miRNA set points to pathways involved in apoptosis. Thus, we confirmed the biological processes inherent to AI resistance and provide critical evidence for miRNA profiles as an important regulatory principle in these AI resistance models. Citation Format: Reiner Hoppe, Ping Fan, Florian Büttner, Stefan Winter, Heather Cunliffe, V. Craig Jordan, Hiltrud B. Brauch. Modulation of aromatase inhibitor resistance by miRNAs in breast cancer. [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 1073.