Project Summary Glioblastoma, the deadliest form of brain cancer, is defined by the invasive nature of its cells. Invasion in the brain follows distinctive routes that correlate with interstitial and bulk flow pathways. In brain cancer, increased interstitial fluid flow develops due to the increase in interstitial pressure in the tumor bulk interfacing with the relatively normal pressure of the surrounding brain tissue, or tumor microenvironment. This differential leads to fluid transport specifically across the invasive edge of the tumor where cells are prone to both interact with the surrounding brain tissue and to evade localized, transport-limited therapies. To examine how interstitial fluid flow affects the invasion of brain cancer cells, we have developed in vitro and in vivo methods to examine fluid flow responses. In vitro, we have found that interstitial flow enhances invasion of brain cancer cells using both cell lines and patient-derived glioma stem cells in tissue-engineered models of the brain-tumor interface via the chemokine/receptor pair CXCL12/CXCR4. In vivo, we have seen interstitial flow and increase invasion of implanted cancer cells through the brain in part through this same mechanism. By conducting in vivo measurements of interstitial flow using MRI we have correlated regions of interstitial fluid flow, glioma invasion, and glial gene expression of the receptor sphingosine-1-phosphate 3. In this proposal, we will examine the role of interstitial fluid flow as a driving factor of glioma invasion. To make a case for the importance of interstitial flow in regulating GBM invasion first, we will elucidate the true nature of interstitial flow in the in vivo GBM microenvironment. We will accomplish this utilizing clinically relevant imaging and computational tools to probe the prevalence of flow as the tumor develops, and determine regions in which flow is the highest. Second, we will determine the contributions of interstitial flow at the level of cancer cell invasion. We will observe invasion patterns of multiple patient-derived glioblastoma stem cells in the specifically interrogating the mechanism of CXCR4/CXCL12-mediated autologous chemotaxis, a novel mechanism of invasion only possible under flow. Finally, we will use our unique ability to tissue engineer the glioblastoma microenvironment to examine the role of glial-expressed S1PR3 under flow on glioma invasion. Altogether, these reports will advance the importance and strategies for mitigating interstitial flow and its effects in GBM and offer modalities by which to study further effects of flow on therapeutic response. Understanding the impact of interstitial flow will ultimately help predict areas of GBM progression and recurrence.