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Abstract A55: Pancreatic stellate cells promote pancreatic cancer invasion and metastasis by secretion of soluble factors and through contact-mediated mechanisms

Pancreatic ductal adenocarcinoma (PDAC) is rarely detected early, instead presenting in patients as advanced metastatic disease once symptoms are evident. Given the central role of metastasis in pancreatic tumor progression and mortality, there is an urgent need for further investigation of how PDAC metastasizes and for novel treatment strategies targeting PDAC metastasis. A prominent histopathologic feature of PDAC is a desmoplastic, fibrotic stroma consisting of extracellular matrix components, immune cells, and activated fibroblasts termed “pancreatic stellate cells” (PSCs) that often compose a majority of cellular content in many PDAC tumors. Data from recent studies demonstrate multiple phenotypic PSC populations in the stroma (Ohlund et al., 2017); however, the influence of individual PSC populations on metastasis and disease progression is not fully understood. We hypothesized that PSCs promote pancreatic tumor metastasis through secretion of soluble factors and accompany these metastasizing tumor cells to distal sites using collective invasion mechanisms. Tumor spheroids were formed by centrifugation of HPAC cells (a human PDAC cell line) in low adhesion round bottom plates. Spheroids were embedded in both collagen- and Matrigel-based matrices and z-stacks were collected every 24hrs for 72hrs using a Lecia SP8 confocal microscope. Live cell imaging was performed in an incubation chamber for 72hrs using a Leica SP8 confocal microscope. Human pancreatic stellate cells were isolated from surgically resected tumor specimens at Emory University Hospital under IRB-approved protocols and grown to ~70% confluency before supernatants were collected. Utilizing innovative 3D invasion assays, we demonstrate the ability of human PSC conditioned media to initiate and promote invasion of HPAC pancreatic tumor spheroids. HPAC spheroids exposed to 10% PSC supernatants showed significantly decreased roundness in comparison to media alone. Further investigation of possible soluble factors mediating this interaction indicated a protein-based interaction, although alternative mechanisms by which metastasis may be initiated were also identified. Phenotypic analysis of invasion through live cell imaging led to observations of unique invasion mechanisms by which hyperactive cells at the leading edge seemingly guide invasion of large groups of cells. Additionally, we observed co-culture interactions between PSCs and HPAC cells. In comparison to HPAC cells alone, ratios of 10:1 PSCs to HPAC cells increased circularity (less invasive) while inverse ratios decreased circularity of spheroids (more invasive). This study supports the hypothesis that PSCs can promote collective invasion and migration of pancreatic tumor cells through both contact-dependent and -independent means. Further identification of mechanisms mediating this interaction may reveal novel therapeutic targets for the treatment of PDAC and present new strategies for targeting metastasis of this deadly disease. Citation Format: Michael B. Ware, Jerry Yue, Bassel El-Rayes, Shishir K. Maithel, Juan Sarmiento, Gregory B. Lesinski. Pancreatic stellate cells promote pancreatic cancer invasion and metastasis by secretion of soluble factors and through contact-mediated mechanisms [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A55.