Oxygen availability plays a critical role in cancer progression and is correlated with poor prognosis. Despite this connection, the independent effects of oxygen gradients on tumor tissues have not been measured. To address this, we developed an oxygen delivery device that uses microelectrodes to generate oxygen directly underneath three-dimensional tumor cylindroids composed of colon carcinoma cells. The extent of cell death was measured using fluorescence staining. Supplying oxygen for 60 h eliminated the necrotic region typically found in the center of cylindroids despite the continued presence of other nutrient gradients. A mathematical model of cylindroid growth showed that the rate of cell death was more sensitive to oxygen than the growth rate. After oxygenation, a ring of dead cells was observed at the outside edge of cylindroids, and dead cells were observed moving outward from cylindroid centers. This movement suggests that dead cells were pushed by viable cells migrating in response to oxygen gradients, a mechanism that may connect transient oxygen gradients to metastasis formation. These measurements show that oxygen gradients are a primary factor governing cell viability and rearrange cells in tumors. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012
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