(20d) 3D Biomimetic Model for Cellular Invasion: A Versatile Platform to Examine 3D Physiological Invasion in Angiogenesis and Pathological Tumor Cell Invasion

Cell invasion is an essential and highly regulated process. Cells invade to vascularize tissues, to form tissues and to respond to inflammation at injured sites. Unfortunately, cell invasion is also involved in numerous pathological conditions such as in invasive tumors. Much of our understanding of cell invasion has been from traditional 2D cell cultures and from cells that are randomly dispersed inside 3D hydrogels. However, such methods also have drawbacks as they often lack tissue architecture, tissue-tissue interfaces, gradient of cytokines, and fluid flow, which may all affect cell invasion [1]. Microfluidic platforms, therefore, offer a possibility to overcome some of these limitations. Microfluidic devices are often fabricated with photolithographic etching to introduce patterned structures and tissue compartments with perfused fluidic chambers. However, because of the photolithographic fabrication, fluidic chambers presented in microfluidic devices sometimes lack the architecture of a tissue compartment. For instance, a widely accepted feature of fluidic chamber is a rectangular fluidic channel with one side exposed to hydrogel, such as collagen to mimic tissue interface while the other three surfaces are either made from glass or PDMS. As a result, cells inhabited inside these channels are constrained to only interact with the microenvironment through one surface interface whereas cells in vivo such as endothelial cells in blood vessels or epithelial cells in ducts are fully surrounded by the extracellular matrices. Additionally, these artificial hard surfaces from glass or PDMS may in turn influence cellular invasion.

To address these limitations, we engineered a microfluidic platform that contain 2 perfusable hollow cylindrical channels that are fully embedded within a 3D extracellular matrix to mimic ductal compartments within a tissue [2]. Soluble factors may be added into one of the channels to generate a gradient across the interstitium matrix between the two channels. Various cell types may also be seeded into these channels to create a basic structure of a ductal compartment. For instance, we utilize this microfluidic platform to model physiological cellular invasion in angiogenesis, a process where new blood vessels form from existing blood vessels. We seeded endothelial cells into one of the channels to form a rudimentary blood vessel. When a gradient of angiogenic factors was administered into the system, endothelial cells began to extend their protrusion and invaded into the interstitium to form 3D angiogenic sprouts. These angiogenic sprouts contain features that resemble in vivo sprouts such as tip and stalk cells, formation of lumen, and formation of branches. The sprouts ultimately develop into perfusable blood vessels. To capture pathological cellular invasion, we seeded pancreatic cancer cells inside one of the channels. Surprisingly, when the pancreatic cancer duct was placed juxtaposed to the rudimentary blood vessel, the pancreatic tumor cells began to invade into the tissue towards the engineered blood vessel. Upon reaching the blood vessel, the pancreatic tumor cells migrated along the blood vessels and invaded into the blood vessel, a phenomenon commonly observed in human pancreatic cancer patients [3]. All together, we demonstrate that our microfluidic platform is a versatile and important platform that enables us to observe and capture multiple processes of cellular invasion in both angiogenesis and tumor cell migration.

[1] Galie, P.A., Nguyen, D.H., Choi, C.K., Cohen, D.M., Janmey, P.A., Chen, C.S. (2014). “Fluid shear stress threshold regulates angiogenic sprouting”. Proceedings of the National Academy of Sciences. 111(22): 7968-7973

[2] 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.

[3] 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.