Pancreatic Ductal Adenocarcinoma (PDAC) is a devastating disease which is in part driven, and supported by changes in its microenvironment, or stroma. These changes occur early, yet PDAC is usually undetected until the disease has metastasized, causing survival rates to drop dramatically. Therefore, there exists an urgency to detect this disease as early as possible and understand its progression. This project dissects the intercellular communication that exists between the primary stromal component, cancer-associated fibroblasts (CAFs), and PDAC cells. Specifically, we focus on how CAF-secreted extracellular vesicles (EVs) promote PDAC progression, with an additional goal to identify biomarkers suitable to generate a non-invasive “liquid biopsy” test for early PDAC detection and prognosis. PDAC communicates with its microenvironment, in part, through the exchange of specific types of EVs, which include exosomes and recently characterized “ectosomes.”
We observe distinct types of CAF-derived EVs containing unique surface receptors. One novel surface protein, NetrinG1, is expressed on the plasma membrane of pancreatic CAFs, but not their normal/healthy counterparts. Further, PDAC cells, but not healthy pancreatic epithelial cells, upregulate NetrinG1's lone binding partner, suggesting a role for these factors in PDAC-selective EV uptake. Functional assays designed to test PDAC viability in nutrient deprivation show that CAF-EVs are capable of protecting PDAC cells from the induction of programmed cell death. Further, we show NetrinG1's expression in CAFs is necessary for this EV-mediated survival effect. We also determine that NetrinG1 localizes to the novel “ectosome” EV sub-population, suggesting it possesses unique cargo and is packaged into EVs and secreted through a yet-unknown mechanism separate from canonical exosome trafficking. We also determine, that sub-populations of EVs can be “filtered” locally by the extracellular matrix, based on various EV surface markers. This suggests that the extracellular matrix can play an important role in determining the fate of secreted EVs; which has significant implications for what sub-populations maybe be found circulating systemically in blood, or acting locally in the tumor microenvironment.
Pursuing our biomarker goal, we confirm stromal NetrinG1 expression precedes tumorigenesis and are currently seeking to validate the prognostic potential of NetrinG1(+)EVs in blood of PDAC patients. Altogether, this research shines light on a novel mechanism of tumor-stroma communication, and introduces EV biomarkers potentially capable of identifying both early PDAC occurrences and predicted efficacy of certain adjuvant interventions.
Citation Format: Kristopher Raghavan, Debora Vendramini, Ralph Francescone, Janusz Franco-Barraza, Edna Cukierman. NetrinG1's pro-tumor role on stroma-derived extracellular vesicles in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3173.