Abstract PO4-28-03: Investigating the role of extracellular vesicles in tumor-stromal cell interactions in early-stage breast cancer invasion

Abstract Ductal carcinoma in situ (DCIS) is the most common form of early-stage breast cancer. Anywhere from 10%–30% of DCIS cases progress to invasive ductal carcinoma (IDC), resulting in poor prognosis and clinical challenges. Still, the cellular basis of this DCIS transition remains poorly understood. To escape the primary site during local invasion, DCIS cells navigate through the extracellular matrix and a diverse collection of stromal cells in the surrounding microenvironment. Cancer associated fibroblasts (CAFs) are a stromal cell population that can facilitate tumor invasion in part through extracellular matrix remodeling. CAFs at the primary tumor are largely derived from fibroblasts that have been reprogrammed to an activated state. In addition, several physical, cellular and metabolic changes within the tumor microenvironment (TME) are known to alter the breast cancer invasive capacity. Here we report that forced inhibition of cell invasion, by blocking the activity of known regulators of cell invasion in the ductal epithelial cell line, MCF10ADCIS.com, (herein referred to as DCIS.com), is accompanied by a marked reduction in extracellular vesicle (EV) secretion. Moreover, we show that DCIS.com cells conditioned with secreted EVs exhibit significantly enhanced invasive capacity relative to naïve DCIS.com cells. It is now well documented that breast and other tumor cells release heterogenous populations of EVs that can function as mediators of intercellular communication in the tumor microenvironment. EVs contain a host of bioactive cargo, such as membrane and cytosolic proteins, various RNA species including microRNAs, as well as dsDNA. These shed vesicles may deposit paracrine information and can also be taken up by stromal cells such as fibroblasts causing the recipient cells to undergo phenotypic changes that profoundly impact various facets of tumor progression. Conversely, EVs shed from stromal cells also affect tumor cell behavior. This unique form of intercellular crosstalk helps condition the TME and promotes both invasive and metastatic activity. In this regard, we found that incubation of human fibroblast cells with EVs shed from tumor cells leads to a loss of SMAD-7 expression (previously implicated in CAF reprogramming), and this loss is abrogated when shedding cells are depleted of miR-21 or regulators of miRNA trafficking to surface-derived EVs. Further, using spheroid invasion assays we demonstrate that fibroblast-derived EVs facilitate directed and leader-follower modes of migration, suggesting the possibility that CAFs likely deposit chemotactic cues to promote directional movement in DCIS. While the regulation of this behavior is still being explored, our observations suggest that EVs, in addition to facilitating distal proteolysis, may also support both autocrine and paracrine signaling during cell invasion. Finally, we are investigating how these pathways may also contribute to the ‘field effect’ of breast cancerization, a poorly understood process that introduces genetic and phenotypic changes in normal epithelia, potentially contributing to disease onset and/or recurrence. Citation Format: Madison Schmidtmann, Grace Richmond, Shireen Jayman, James Clancy, Crislyn D'Souza-Schorey. Investigating the role of extracellular vesicles in tumor-stromal cell interactions in early-stage breast cancer invasion abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-28-03.