Analysis of circulatory extracellular vesicle–associated cytokines as candidate disease-associated markers in ER-positive breast cancer

Abstract Introduction Cytokines are signaling molecules produced by various cell types, including immune cells, and play important roles in tumor development and progression. Extracellular vesicles (EVs) are small membrane-bound particles secreted by all cell types, including cancer cells. EVs mediate intercellular communication through the transfer of proteins, lipids and nucleic acids, affecting many cellular processes. EV-associated cytokines may therefore represent a novel source of circulatory biomarkers in cancer. In this study, we investigated EV-associated cytokines obtained from estrogen receptor-positive (ER+) breast cancer (BC) patients and healthy individuals and evaluated treatment-associated changes during neoadjuvant endocrine therapy (NET). Materials and methods EVs were isolated from plasma samples of BC patients, healthy individuals, and from breast cell lines through ultracentrifugation. EVs were characterized by transmission electron microscopy, flow cytometry, nanoparticle tracking analysis and western blotting. EV-associated cytokines were profiled using Luminex multiplex assay in plasma samples of ER + BC patients ( n = 46) enrolled in the Neoletexe clinical trial. EV-associated cytokine levels were analyzed at three timepoints, before (T0) and after NET (T1 and T2), and in healthy individuals ( n = 13). EV-associated cytokine levels were compared with free-circulating cytokines in blood and with cytokine gene expression in tumor tissue from a subset of the same patients from the Neoletexe cohort. Results Three EV-associated cytokines, interleukin 10 (IL-10), interleukin 12 (IL-12) and interferon gamma inducible protein 10 (IP-10), were significantly elevated in ER + BC patients compared to healthy individuals. CXCL10 (IP-10) gene expression was also found to be overexpressed in breast cancer tissue relative to normal and benign tissue, supporting the EV-associated IP-10 findings. Levels of EV-associated IL-10 and IL-12 decreased significantly during NET, but only eotaxin was associated with Ki-67 treatment response. Treatment-associated changes were more pronounced in EV-associated cytokines than for corresponding free-circulating cytokines and tumor gene expression. Conclusion EV-associated cytokines differ between ER + BC patients and healthy individuals and change during NET in ER+ LABC patients. These findings suggest that EV-associated cytokines may reflect disease and treatment related changes and provide complementary information to free-circulating cytokines and tumor gene expression. Further studies are required to determine their potential clinical relevance as biomarkers. Trial registration The Neoletexe study was approved on March 19th, 2015, by the Regional Ethics Committee (REC) of Southeast Norway in Oslo (national registration number: 2015/84).