Exploring the need for more biologically relevant models to assess migration across the Blood-Brain Barrier

Introduction
In vitro Blood-brain barrier (BBB) models are difficult to recapitulate due to the difficulty in representing the diverse BBB environment. The BBB consists of different cell types such as endothelial cells, astrocytes and pericytes, each of which play a crucial role in maintaining the BBB, however, this can be problematic in management of disorders such as Glioblastoma (GBM), due to low permeability. Advanced BBB models are therefore required for enhanced drug delivery with minimal disruption.

Methods
As proof of concept to highlight three-dimensional (3D) in vitro modelling as a more truthful representation of cancer cell migration/invasion, a comparison between two-dimensional (2D) and 3D models was conducted using in-house engineered GBM U251 knockdown cells to promote/target cell migration. Initial in vitro migration/invasion assays including 2D scratch assays and collagen embedded 3D spheroids to characterise cell migration/invasion.

Results
The MTT assay provided the relevant information to determine the concentration of T60A and TMZ treatments to use for both assays. Data gathered from scratch and collagen invasion assays both indicated cellular migration, with the 3D assay providing a more accurate insight of how the cells would move through a structure in vivo and whether the treatments impacted this.

Conclusion
Despite current 2D in vitro models demonstrating cellular migration, they do not accurately reflect effects of drug delivery across the BBB to reach invading cancer cells. Here we highlighted differences in cancer cell migration to consider when developing a biologically relevant BBB GBM model with integrated barrier and targetable migrating brain tumour cells. A biologically accurate model using advanced technologies such as 3D bioprinting to form interactions between different cells, mimicking the barrier and incorporating migrating/invading cancer cells is the next step.