BackgroundAngiogenesis is a key process for tumor progression and a target for treatment. However, the regulation of breast cancer angiogenesis and its relevance for clinical resistance to antiangiogenic drugs is still incompletely understood. Recent developments on the contribution of microRNA to tumor angiogenesis and on the oncogenic effects of miR-17-92, a miRNA cluster, point to their potential role on breast cancer angiogenesis. The aim of this work was to establish the contribution of miR-20a, a member of miR-17-92 cluster, to tumor angiogenesis in patients with invasive breast carcinoma.MethodsTube-formation in vitro assays with conditioned medium from MCF7 and MDA-MB-231 breast cancer cell lines were performed after transfection with miR-20a and anti-miR20a. For clinical validation of the experimental findings, we performed a retrospective analysis of a series of consecutive breast cancer patients (n = 108) treated with neoadjuvant chemotherapy and with a full characterization of their vessel pattern and expression of angiogenic markers in pre-treatment biopsies. Expression of members of the cluster miR-17-92 and of angiogenic markers was determined by RT-qPCR after RNA purification from FFPE samples.ResultsIn vitro angiogenesis assays with endothelial cells and conditioned media from breast cancer cell lines showed that transfection with anti-miR20a in MDA-MB-231 significantly decreased mean mesh size and total mesh area, while transfection with miR-20a in MCF7 cells increased mean mesh size. MiR-20a angiogenic effects were abrogated by treatment with aflibercept, a VEGF trap. These results were supported by clinical data showing that mir-20a expression was higher in tumors with no estrogen receptor or with more extensive nodal involvement (cN2-3). A higher miR-20a expression was associated with higher mean vessel size (p = 0.015) and with an angiogenic pattern consisting in larger vessels, higher VEGFA expression and presence of glomeruloid microvascular proliferations (p<0.001). This association was independent of tumor subtype and VEGFA expression.ConclusionsTransfection of breast cancer cells with miR-20a induces vascular changes in endothelial tube-formation assays. Expression of miR-20a in breast invasive carcinomas is associated with a distinctive angiogenic pattern consisting in large vessels, anomalous glomeruloid microvascular proliferations and high VEGFA expression. Our results suggest a role for miR-20a in the regulation of breast cancer angiogenesis, and raise the possibility of its use as an angiogenic biomarker.

Background: microRNAs (miRNAs) are small ribonucleic acids that regulate protein expression through gene silencing mechanisms and show differential expression between cancer subtypes. Several studies have demonstrated that over- or under-expression of miRNA levels in tumors can modulate the expression levels of their gene/protein targets and thus their behavior. In breast cancer, the members of cluster miR-17-92 increase their expression levels as the histological grade increases, behaving like an oncogene, and are preferentially expressed in basal-like carcinomas. Moreover, mature components of this cluster are involved in estrogen receptor pathways and epithelial-mesenchymal transition, which suggest their implication in resistance to chemotherapy. The aim of this study was to determine the prognostic impact of miR-18a expression in the residual (resistant-to-treatment) tumor after neoadjuvant chemotherapy (nQT) in patients with locally advanced breast cancer (BC). Methods: Small RNA was isolated from FFPE samples of post-chemotherapy residual tumor in patients without pathological complete response (pCR). Quantification of miR-18a was performed by RT-qPCR. Expression levels were determined by 2-DDCt method using snRNAU6 as endogenous control. We used the quartiles of expression as cutoff point. Association of miR-18a levels with clinical and pathological characteristics was evaluated with non-parametric tests. Kaplan-Meier curves, log-rank test and Cox proportional hazard regression multivariate models were used for disease free (DFS) and overall (OS) survival analysis. Statistical analysis was performed with SPSS 18.0 software. Results: 121 consecutive women with invasive BC were included, mostly with stages IIB (28%) or IIIA-C (56.4%). Patients were immunohistochemically (IHC) classified as Her2- hormone-sensitive (HS) in 50.4% of cases; other phenotypes: Her2+ HS, 13.2%; Her2+ non-HS, 10.7%; triple negative, 21.5%. Treatment included sequential anthracyclines and taxanes (80.4% docetaxel) and a pCR was obtained in 17.4% of patients. Median overall survival (OS) and disease free survival (DFS) were not reached after a median follow-up of 60 months. High (above the median) expression levels of miR-18a in post-chemotherapy residual tumor were associated with pre-treatment grade 3 (p = 0.008), cN2-3 (p = 0.004), non-HS (p = 0.006) and triple negative phenotype (p = 0.01). No other associations with clinical or pathologic tumor characteristics (stage, HER2NEU overexpression) were found. High expression levels of miR-18a in residual tumors were also associated with reduced DFS and OS (log-rank test; p = 0.004 and p = 0.041 respectively). This negative prognostic impact was also confirmed for DFS in a multivariate analysis that included IHC phenotype and ypN+ (Table 1). Table 1 OR95%CIPPhenotype1.571.11-2.230.010ypN+7.291.67-31.800.008miR-18a high3.091.01-9.410.047 Conclusion: High expression levels of miR-18a in chemotherapy-resistant residual breast cancer associates with pre-treatment aggressive biological characteristics and independently predicts disease recurrence. Our results suggest that post-treatment miR-18a might serve as a marker of treatment resistance and as a new target for BC treatment. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-07-15.