(69d) 3D Organotypic Cancer Model: Pancreatic Ductal Adenocarcinoma Replaces Endothelium during Tissue Invasion

Although the diagnosis and treatment of cancer in its earliest stages has significantly improved outcomes in many tumors, survival rates in patients with tumors that have spread to distant sites remain dismal. As such, the vast majority of cancer mortalities stem from metastasis and its complications. Metastasis describes the process where tumor cells escape from the tumor primary sites to enter the blood stream, and arrive at other distant organs to form secondary tumors. Among the many metastatic cancers, pancreatic ductal adenocarcinoma (PDAC) over the past decades has remained one of the deadliest metastatic diseases owing to the high incidence of metastasis of pancreatic cancer cells. Remarkably, patients with PDAC exhibits a high degree of vascular invasion and abundant circulating tumor cells in the bloodstream, which suggest that PDAC cells are highly efficient to gain access to the blood stream. Despite this, the interactions between PDAC cells and blood vessels are poorly understood, partly due to the lack of in vitro models to enable close examination of tumor cells and endothelial cells at the blood vessel interface.

Here, we describe an organotypic PDAC-on-a-chip culture model to examine vascular invasion in PDAC. The model features two hollow cylindrical channels embedded within a three-dimensional matrix [1]. One of the channels was lined with endothelial cells to mimic blood vessel while the other was seeded with PDAC cells to mimic a tumorous pancreatic duct [2]. In this model, PDAC cells from the tumorous pancreatic duct invaded through the intervening matrix and into the blood vessel lumen, induced endothelial cell apoptosis, and ultimately replaced the endothelial cells. A phenomenon we termed vascular replacement. We later confirmed the observation of vascular replacement by tumor cells in our organotypic model by using an in vivo model of ectopic PDAC growth. Interestingly, PDAC human patients have also exhibited vascular invasion and tumor-like cells, which populate the lumen side of the blood vessels in previous reports. This confirms the clinically relevant observation of vascular replacement in our 3D organotypic model. Additionally, using small molecule inhibitors and CRISPR technology, we identified the Activin-ALK7 pathway as a critical mediator of vascular replacement by PDAC. This tumor-on-a-chip model thus provides an important in vitro platform for revealing previously unappreciated mechanisms by which tumors interact with vessels.

[1] Nguyen, D.H., Stapleton, S.C., Yang, M.T., Cha, S.S., Choi, C.K., Galie, P.A., Chen, C.S. (2013). Biomimetic model to reconstitute angiogenic sprouting morphogenesis in vitro. Proceedings of the National Academy of Sciences. 110(17): 6712-6717.

[2] Nguyen, D.H., Esak, L., Alimperti, S., Wong, A., Eyckmans, J., Stanger, B.Z., Chen, C.S. (2017). Pancreatic ductal adenocarcinoma replaces endothelium during tissue invasion. Manuscript in revision.