| Summary: | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biological Engineering, 2009. === Vita. Cataloged from PDF version of thesis. === Includes bibliographical references. === Major therapeutic efforts have been devoted to targeting the epidermal growth factor receptor (EGFR), which is aberrantly expressed in many cancers and is correlated with tumor progression and invasiveness. In the current tumor progression paradigm, individual invasive carcinomas arise upon epithelial-mesenchymal transition (EMT) and migrate through a complex tumor microenvironment to successfully metastasize. While the activation of EGFR enhances invasiveness in vivo, it is still unclear which downstream molecular changes caused by EMT contribute to the invasive phenotype and subsequently, how the invasive cell integrates downstream biophysical processes to invade through a three-dimensional (3D) extracellular matrix (ECM). This thesis addresses these questions from a quantitative, engineering perspective, that cell migration in the context of the invasion microenvironment is an inherently multivariate biochemical and biophysical problem. As such, we developed various carefully controlled, but biologically relevant, in vitro experimental systems with an emphasis on the extracellular microenvironment. These systems were combined with quantitative data-driven parameterization of signaling components and subsequent modeling of migration phenotypes via various 2D and 3D single cell tracking assays. By measuring 2D cell migration of immortalized human mammary epithelial cells conferring pre- or post-EMT states, we respectively identified physiologically relevant, EMT-dependent collective and individual migration modes. A comprehensive systems modeling approach identified the novel activation of a downstream kinase, which acts in a switch-like manner to differentially regulate epithelial, EGFR-dependent migration versus mesenchymal migration. Next, the subsequent mesenchymal migration in 3D, as modeled by a human glioblastoma cell line, was assessed via a quantitative biophysical analysis. EGF-enhanced 3D migration arose from a balance between a cell-intrinsic regulation of cell speed and a matrix- and proteolysis-dependent, extrinsic regulation of directional persistence. Lastly, we quantified fibroblast migration in a porous scaffold of varying pore sizes and stiffness to model contact-guided quasi-3D migration. We surprisingly found that the micro-architecture of guidance structures alone influenced cell speed. Therefore, the combination of biologically relevant experimental systems and quantitative models provided novel mechanistic insights pertinent to early stages of tumor metastasis. The experimental approaches and biological mechanisms in this thesis hold potential in guiding therapeutic targeting of the biophysical responses prompted by the extracellular microenvironment. === by Hyung-Do Kim. === Ph.D.
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