Modeling the Heterogeneous Brain Tumor Microenvironment to Analyze Mechanisms of Vascular Development and Chemoresistance

Regulation of cancer cell phenotype by the tumor microenvironment has motivated further investigation into how microenvironmental factors could contribute to tumor initiation, development, and therapeutic resistance. Analyzing how the microenvironment drives tumor development and cancer cell heterogeneity is particularly important in cancers such as glioblastoma multiforme (GBM) that have no known risk factors and are characterized by a high degree of heterogeneity. GBM patients have a median survival of 15 months and therefore are in great need of more effective therapeutic options. The goal of this research is to generate in vitro models of the heterogeneous brain tumor microenvironment, with a focus on vascular dynamics, to probe the impact of microenvironmental cues on tumor progression and to integrate the tumor models with highly sensitive analytical tools to characterize the epigenome of discrete phenotypic subpopulations that contribute to intratumoral cellular heterogeneity. As GBM tumors are characterized by a dense vasculature, we delved into microenvironmental factors that may be promoting angiogenesis. The correlations emerging between inflammation and cancer led to analysis of the inflammatory molecule lipopolysaccharide (LPS). We utilized 3D micro-tissue models to simulate vascular exposure to ultra-low chronic inflammatory levels of LPS and observed an increase in vascular formation when brain endothelial cells were exposed to ultra-low doses of LPS. We also utilized our micro-tissue models to analyze histone methylation changes across the epigenome in response to microenvironmental cues, namely culture dimensionality and oxygen status. The H3K4me3 modification we analyzed is associated with increased gene transcription, therefore the alterations we observed in H3K4me3 binding across the genome could be a mechanism by which the tumor microenvironment is regulating cancer cell phenotype. Lastly, we developed a microfluidic platform in which vascular dynamics along with microenvironmental heterogeneities can be modeled in a more physiologically relevant context. We believe the studies presented in this dissertation provide insight into how vasculature primed by chronic inflammation and epigenetic alterations in tumor cells could both contribute to enhanced tumor development. Modeling these biological processes in our advanced microfluidic platform further enables us to better understand microenvironmental regulation of tumor progression, uncovering new potential therapeutic targets.