Abstract P4-12-05: Extracellular vesicles from young women's and postpartum breast cancer display unique proteomic content, alter breast cancer aggressive behavior, and influence immune cell function

Abstract

Background: Young women's breast cancer[YWBC] affects 27,000 US women age ≤45 annually. Half of these cancers occur within 5-10 years of a prior childbirth, a postpartum breast cancer[PPBC], incurring a 3 fold increased risk for metastasis and death. Recently, extracellular vesicles[EV] have been identified in human circulation, released from cancer cells, that have paracrine and autocrine effects, alter the tumor microenvironment and establish metastatic niches. EVs isolated from breast cancer lines increase proliferation and invasion of other breast cancer cells in vitro. However, the impact of EVs isolated from primary breast cancer patients on tumor invasion, metastasis and their role in tumor immune suppression is largely unknown. We hypothesized that EVs from YWBC/PPBC patients may contain unique pro-metastatic cargo, influence aggressive breast cancer cell behavior and may demonstrate the ability to alter immune cell function. Method: We isolated EVs using size-exclusion chromatography [SEC] from the plasma of 10 unaffected young women and 20 YWBC patients balanced for parity, age, subtype and stage. We compared the breast cancer-specific EV proteins within various clinical groups of YWBC and PPBC to identify significant proteomic differences by parity, sub-type, stage, and disease recurrence. We determined the functional impact of these EVs on tumor cell motility and proliferation, and analyzed the effect of breast cancer derived EVs on immune cell phenotype, function, and T cell proliferation assays. Results: Of the 582 proteins, 22 proteins are significantly increased in the EVs of YWBC compared to unaffected donors. The protein set includes breast cancer antigens [MUC 1, 2, 5b], transcriptional regulators [Myc target protein], enzymes [catalase, MMP inhibitor 1], and signaling molecules [Annexin 1, latent TGFb binding protein 1], among others. Several identified proteins specifically track with those YWBC cases with subsequent metastases. Furthermore, 8 unique proteins track with PPBC, including cartilage oligomeric matrix protein, a novel breast cancer biomarker that correlates with increased invasiveness, and decreased recurrence-free survival. EVs isolated from the plasma of newly diagnosed YWBC increase breast cancer invasion and EVs derived from breast cancer are engulfed by the majority of monocytic immune cells, including dendritic cells, classical and activated monocytes, but not by lymphocytes. Specifically, CD14+ monocytic myeloid derived suppressor cells engulfed the EVs while the CD15+ granulocytic subset did not. Once engulfed, phenotypic changes occurr in the EV containing monocytes and a significantly reduction in T cell stimulation in standard mixed-lymphocyte reactions is observed. Conclusion: EVs isolated from YWBC & PPBC cases have unique protein content and increase breast cancer invasiveness, which suggests potential mechanistic roles for EVs as increasing metastatic risk and provides novel candidate biomarkers. We identified an immunomodulatory effect of breast cancer EVs on human monocytes that may contribute to immunosuppression in breast cancer and a role for EVs as directly modulating the host and tumor microenvironment. Citation Format: Borges VF, Jordan KR, Hall JK, Schedin T, Hansen K, Schedin P. Extracellular vesicles from young women's and postpartum breast cancer display unique proteomic content, alter breast cancer aggressive behavior, and influence immune cell function [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-12-05.