Analysis of Brain Cancer Metastasis with Microfluidic Models.

Brain cancer metastasis is a global health challenge that is associated with rising incidence rates and a median survival time of 6 months. Despite its severity, the mechanisms that govern brain cancer metastasis are poorly understood. It remains unclear how circulating tumor cells can extravasate across brain microvasculature to infiltrate brain tissue. Additionally, the ability to study tumor cell extravasation into brain tissue is currently limited by a lack of reproducible and physiologically relevant experimental models for brain cancer metastasis.

Here, we developed, characterized, and validated a tissue-on-chip (ToC) model of brain microvasculature to study tumor cell extravasation into brain tissue. The ToC model consists of a hollow channel that is surrounded by a hydrogel that mimics the extracellular matrix. We line the channel with endothelial cells to create a biomimetic model of microvasculature. The channel is connected to two ports, which allows us to introduce tumor cells into the channel. We hypothesized that tumor cells will be able to travel across the endothelial-lined channel and enter the surrounding hydrogel, thereby enabling us to study extravasation events.

We used SolidWorks to design the ToC model and fabricated molds for the model by using 3D printing. We cured polydimethylsiloxane (PDMS) in the molds to generate silicone casings that were bonded to glass coverslips to create the ToC model. We used a fibrin hydrogel within the ToC model to mimic the brain extracellular matrix. We encapsulated astrocytes within the hydrogel and seeded pericytes and brain microvascular endothelial cells within the channel, to create a physiologically relevant model of brain microvasculature. Immunofluorescent staining revealed that our brain microvasculature model expresses ZO1 and occludins, which are two tight junction proteins that are expressed by the blood-brain barrier. Furthermore, by performing a dextran permeability assay, we discovered that the presence of pericytes and astrocytes increases barrier function within the model. Finally, we optimized tumor cell seeding conditions within the model to maximize the extravasation rate of a breast cancer cell line (MDA-MB-231) while minimizing the extravasation of a non-cancer breast epithelial cell line (MCF10A). Collectively, our work has resulted in the development of a biomimetic model of tumor cell extravasation across brain microvasculature, which can be used to study the biological processes that govern extravasation and aid in the identification of therapeutic targets to treat or prevent brain metastasis. Future work is focused on assessing the model’s ability to recapitulate intertumoral differences in incidence rates for brain metastasis, by examining the extravasation tendencies of various cancer types and subtypes.