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Yong-Tae "Tony" Kim — 2008-09 Fellow

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Cancer progression is a highly complex multistep process involving local cell invasion and destruction of extracellular matrix, intravasation into blood vessels, lymphatics or other channels of transport, survival in circulation, extravasation out of vessels into secondary sites, and growth in the new locations. Invasion requires neoplastic epithelial cells to shed cell-cell adhesions for inducing motility to invade adjacent tissue. During intravasation, tumor cells penetrate through the endothelium of blood or lymphatic vessels to enter into the circulation. While only a small percentage of tumor cells appear to survive the passage into circulation, some of these survivors manage to complete extravasation through the capillary endothelium at distal sites. Finally, in the new host environment, an even smaller subset of these metastasizing cells succeeds in proliferating from micrometastases into malignant, secondary tumors. The consequences though of this subset of cells are debilitating. While there is a diversity of steps involved, the metastatic process has a significant dependence on the process of cell motility.

Cell motility is a fundamental process in early morphogenesis and cancer metastasis that requires sequential cell protrusion, adhesion, and contraction for a cell to move. The leading edge of the cell protrudes as a result of cytoskeletal alteration and adherence to the extracellular matrix, whereas the trailing edge detaches from the matrix. These processes are dynamic and integrated to provide a robust functionality that the cell uses in a diversity of physiological processes including metastasis, wound healing, and angiogenesis. Therefore, a better understanding of the exact role of cell migration in metastasis is critical for the treatment of cancer.

We propose to develop a model experimental system for metastasis that allows precise control of long term chemical stimulations, using the combination of a new high-precision microfluidics and microfabrication approaches. Specifically, we propose a research plan that accomplishes the following.

Objective 1: Develop a novel microfluidic methodology that uses precise pressure regulation to control the flow patter in microfluidic channel to enable long-term spatiotemporal regulation of chemical stimulation

Our proposed experimental system is based on the control of the laminar flow interface in microfluidic channels to precisely control of the cellular chemical environments and to make valuable measurements of cellular responses without destruction of cells for long periods of time. This is critical for investigating cell responses, which are often on the order of hours to days. Closed-loop pressure control for the rapid and precise control of the fluid interface for automatically manipulating a cell's chemical environment has already been demonstrated. However, existing systems have limitations for long-term studies because they use conventional displacement controlled by syringe pumps with relatively small volumes. In this project, we will develop a novel feedback control system for controlling pressure at the inlets of microfluidic channels by modulating the resistance and the capacitance of the fluidic network connecting the microchannels to supply reservoirs. With this approach large fluid reservoirs may be used for long term studies (hours to days) of cellular dynamics.

Objective 2: Investigate the chemotaxis of cancerous cells stimulated by growth factors using the developed microfluidic methodology.

Biochemical studies have generally not had the tools to perform input-output response measurements at high frequencies or at subcellular spatial resolution over a long period of time, which is requisite for many cell functions. However, the results of Objective 1 will allow us to examine the behavior of cells under precisely controlled and potentially varying chemical environments for long periods of time. The time varying environment will serve as the input signal to generate output signals, which may include cell position or distribution of molecules in the cell(s). We will use this system to examine chemotaxis of cancerous cells stimulated by growth factors. We will probe both overall cell behavior and internal molecular signaling, providing us with multiple modalities for developing models of cellular behavior.

With their unique capabilities to integrate chemical parameters to create conditions known to be essential for metastasis, these novel approaches will deliver new information inaccessible by existing technologies and enhance the understanding of metastatic migration. This project will have a far reaching impact on both medical applications and basic biological research by providing new means for investigating the molecular basis of cancer through new methods, techniques, tools, instrumentation, and devices that will facilitate the detection of cancer-related characteristics/alterations at the molecular and cellular levels of organization and function.