Browsing by Author "Stine, Caleb A."

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    Autologous Gradient Formation under Differential Interstitial Fluid Flow Environments
    Stine, Caleb A.; Munson, Jennifer M. (MDPI, 2022-01-04)
    Fluid flow and chemokine gradients play a large part in not only regulating homeostatic processes in the brain, but also in pathologic conditions by directing cell migration. Tumor cells in particular are superior at invading into the brain resulting in tumor recurrence. One mechanism that governs cellular invasion is autologous chemotaxis, whereby pericellular chemokine gradients form due to interstitial fluid flow (IFF) leading cells to migrate up the gradient. Glioma cells have been shown to specifically use CXCL12 to increase their invasion under heightened interstitial flow. Computational modeling of this gradient offers better insight into the extent of its development around single cells, yet very few conditions have been modelled. In this paper, a computational model is developed to investigate how a CXCL12 gradient may form around a tumor cell and what conditions are necessary to affect its formation. Through finite element analysis using COMSOL and coupled convection-diffusion/mass transport equations, we show that velocity (IFF magnitude) has the largest parametric effect on gradient formation, multidirectional fluid flow causes gradient formation in the direction of the resultant which is governed by IFF magnitude, common treatments and flow patterns have a spatiotemporal effect on pericellular gradients, exogenous background concentrations can abrogate the autologous effect depending on how close the cell is to the source, that there is a minimum distance away from the tumor border required for a single cell to establish an autologous gradient, and finally that the development of a gradient formation is highly dependent on specific cell morphology.
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    Convection-Enhanced Delivery: Connection to and Impact of Interstitial Fluid Flow
    Stine, Caleb A.; Munson, Jennifer M. (Frontiers, 2019-10-02)
    Convection-enhanced delivery (CED) is a method used to increase transport of therapeutics in and around brain tumors. CED works through locally applying a pressure differential to drive fluid flow throughout the tumor, such that convective forces dominate over diffusive transport. This allows therapies to bypass the blood brain barrier that would otherwise be too large or solely rely on passive diffusion. However, this also drives fluid flow out through the tumor bulk into surrounding brain parenchyma, which results in increased interstitial fluid (IF) flow, or fluid flow within extracellular spaces in the tissue. IF flow has been associated with altered transport of molecules, extracellular matrix rearrangement, and triggering of cellularmotility through a number ofmechanisms. Thus, the results of a simple method to increase drug delivery may have unintended consequences on tissue morphology. Clinically, prediction of dispersal of agents via CED is important to catheter design, placement, and implementation to optimize contact of tumor cells with therapeutic agent. Prediction software can aid in this problem, yet we wonder if there is a better way to predict therapeutic distribution based simply on IF flow pathways as determined from pre-intervention imaging. Overall, CED based therapy has seen limited success and we posit that integration and appreciation of altered IF flow may enhance outcomes. Thus, in this manuscript we both review the current state of the art in CED and IF flow mechanistic understanding and relate these two elements to each other in a clinical context.
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    Interstitial Fluid Flow Magnitude and Its Effects on Glioblastoma Invasion
    Stine, Caleb A. (Virginia Tech, 2022-06-13)
    Fluid flow is a complex and dynamic process in the brain, taking place at the macro- and microscopic level. Interstitial fluid in particular flows throughout the interstitial spaces within the tissue, interacting with cells and the extracellular matrix. We are coming to find that this interstitial fluid flow plays an important role in both homeostatic and pathologic conditions. It helps to transport chemokines and other molecules such as extracellular vesicles within the environment, clear waste from the brain, and provide biophysical cues to cells. When this flow is disrupted however, such as in glioblastoma or Alzheimer's disease, profound events can occur, for example the build-up of plaques or an increase in tumor cell invasion. While there has recently been an up-tick in interstitial fluid flow research, there is surprisingly little known about its exact nature within the interstitial space and its effects on brain pathology such as glioblastoma. In particular, ways to manipulate and measure brain IFF magnitude at the cellular level are lacking. In this dissertation, a set of tools is created and used to explore the role that interstitial fluid flow magnitude plays in the brain through the lens of glioma invasion. We developed and implemented a flow device that is used in conjunction with an established in vitro tissue culture insert assay to manipulate fluid flow rates through a 3D matrix of tumor cells. We showed that this flow device is biocompatible and accurately recreates flow rates that have been measured previously through the use of MRI. We quantified tumor cell invasion from several glioma cell lines using this device to show a nonlinear trend of invasion in response to increasing fluid flow magnitudes. In addition, we developed a computational model to explore one potential mechanism that fluid flow magnitude might be modulating: autologous chemotaxis. Through this model we showed that increased flow magnitudes such as those seen in gliomas cause an increase in the distribution of the chemokine gradient around a cell of interest, that the morphology of the cell is important to this gradient formation, that temporal effects should not be overlooked, and that within the tumor environment, a minimum distance is required for the invading cell to develop this gradient. Finally, we developed a novel in vivo surgical technique that allows for the manipulation and measurement of interstitial fluid flow within the brain through simultaneous multiphoton imaging. We showed that this technique can be used to modulate interstitial fluid flow, as a mechanism by which to label cells of interest, and as a means to implant and monitor glioma progression. Through these means we further characterize interstitial fluid flow in the brain, allowing for its manipulation and measurement, and examine the ability of increased interstitial fluid flow magnitudes to impact glioma invasion.
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    A patient-designed tissue-engineered model of the infiltrative glioblastoma microenvironment
    Cornelison, R. Chase; Yuan, J. X.; Tate, Kinsley M.; Petrosky, A.; Beeghly, G. F.; Bloomfield, Mathew; Schwager, S. C.; Berr, A. L.; Stine, Caleb A.; Cimini, Daniela; Bafakih, F. F.; Mandell, J. W.; Purow, B. W.; Horton, B. J.; Munson, Jennifer M. (Nature Portfolio, 2022-07-29)
    Glioblastoma is an aggressive brain cancer characterized by diffuse infiltration. Infiltrated glioma cells persist in the brain post-resection where they interact with glial cells and experience interstitial fluid flow. We use patient-derived glioma stem cells and human glial cells (i.e., astrocytes and microglia) to create a four-component 3D model of this environment informed by resected patient tumors. We examine metrics for invasion, proliferation, and putative stemness in the context of glial cells, fluid forces, and chemotherapies. While the responses are heterogeneous across seven patient-derived lines, interstitial flow significantly increases glioma cell proliferation and stemness while glial cells affect invasion and stemness, potentially related to CCL2 expression and differential activation. In a screen of six drugs, we find in vitro expression of putative stemness marker CD71, but not viability at drug IC50, to predict murine xenograft survival. We posit this patient-informed, infiltrative tumor model as a novel advance toward precision medicine in glioblastoma treatment.