Abstract LB-128: Annexin a2: A novel molecular mechanism driving aggressive metastasis and angiogenesis
Authors: Chaudhary Pankaj , Maji Sayantan , Gibbs Lee D. , Vishwanatha Jamboor K. 
Published: August 2019

Background: Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype that affects African-American (AA) women three times more frequently than Caucasian (CA) women. TNBC metastasis is mediated by intercellular communication between tumor cells and the stromal microenvironment. These interactions occur via secreted factors such as growth factors, cytokines, nucleic acids, and small vesicles called exosomes. Tumor-derived exosomes mediate both tumorigenesis and tissue-specific metastasis, by stimulating angiogenesis, attracting immune and stromal cells, and by remodeling the extracellular matrix. Thus, a better understanding of the relative contributions of TNBC-derived exosomes has great potential to improve the prevention and treatment of TNBC. In the present studies, we focus on the characterization of one TNBC-derived exosomal protein, called Annexin A2 (AnxA2), which is highly up-regulated in TNBC tumors and implicated in promoting tumorigenesis and angiogenesis.

Methods: Exosomes were isolated from MCF10 progression model, MDA-MB-231 and its organ specific metastatic variants and characterized via Western blotting and particle size analyzer. In vitro endothelial tube formation assay, and in vivo matrigel plug assays were used to explore the role of exo-AnxA2 in angiogenesis. Experimentally induced (intracardiac/tail vein injection) metastasis models were used to examine the function of exo-AnxA2 in metastasis. The function of AnxA2 in exosomes was blocked by either depleting the AnxA2 expression using shRNA in cells or using AnxA2 competitive inhibitory peptide in exosomes.

Results: Our results revealed that exo-AnxA2 expression is significantly higher in malignant cells than normal and pre-metastatic breast cancer cells. Our in vitro (endothelial tube formation assay) and in vivo (matrigel plug assay) angiogenesis studies demonstrated that exo-AnxA2 promotes tPA-dependent angiogenesis in breast cancer. Furthermore, in vivo analysis in nude mice indicated that TNBC cells-derived exosomes create a favorable pre-metastatic microenvironment for aggressive metastasis, and exo-AnxA2 plays an important role in this process, as priming with AnxA2-depleted exosomes reduce brain (∼4-fold) and lung (∼2-fold) metastasis. Upon delineating the mechanism, we found that exo-AnxA2 causes macrophage-mediated activation of the p38MAPK, NF-κB, and STAT3 pathways and increased secretion of IL6 and TNFα. We observed that the concentration of circulating exo-AnxA2 in TNBC patient’s sera were significantly elevated compared to ER+, HER2+ and normal individuals. In addition, our results suggest that the high expression of exo-AnxA2 in AA TNBC patient’s serum correlates with health disparity. Collectively, our data demonstrate an important role of circulating exo-AnxA2 in TNBC pathogenesis.

Conclusion: We found increased expression of exo-AnxA2 in TNBC patient-derived cell lines and sera. Further, we found that exo-AnxA2 is a potent inducer of angiogenesis and metastasis indicating a possible role of exo-AnxA2 in pre-metastatic niche formation and cancer progression.

Funding support: Supported by NIH grant under award number MD006882 and CA220273 to JKV.

Citation Format: Pankaj Chaudhary, Sayantan Maji, Lee D. Gibbs, Jamboor K. Vishwanatha. Annexin a2: A novel molecular mechanism driving aggressive metastasis and angiogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-128.