Quantification of tumor/stroma interactions using an embedded spheroid model
Tevis, Kristie Mercedes
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A monolayer differs significantly from the multicellular nature and three- dimensional growth of a tumor. Tumors are often modeled with a multicellular aggregate of cancer cells referred to as a spheroid embedded in a collagen gel. Although embedded spheroids in research are widespread, the scope of experiments performed is often limited to observations of growth. Therefore in this thesis, we developed methods to use an embedded spheroid model to study drug response, secondary cell types, and injury. Tumor associated macrophages are critical as stromal components intimately involved with the progression, invasion, and metastasis of cancer. To mimic clinically observed TAM localizations, two tumor cell/macrophage models are described. Macrophages are incorporated as a heterospheroid, a spheroid containing tumor cells and macrophages or diffusely seeded in the collagen surrounding a spheroid. The inclusion of macrophages as a heterospheroid changes the metabolic profile, indicative of synergistic growth, which is not observed in the diffuse model. The macrophages in the heterospheroid secrete cytokines that promote tumor cell growth and indicate Tam-like differentiation. In summary, macrophages incorporated in a heterospheroid are exposed to increased tumor cell contact, hypoxia and metabolic gradients, which promote TAM- like characteristics. To investigate the effect of spheroid culture on chemotherapeutic efficacy, we evaluated the response of our spheroid model compared to cells diffusely seeded in collagen or a traditional monolayer. The spheroid model contains two populations, a core, a dense aggregate of cells, and a periphery, cells that have grown into the surrounding collagen. The core demonstrates chemoresistance, compared to cells in the spheroid periphery, diffusely seeded in collagen and monolayer. Preliminary research indicates that the core is associated with a higher percentage of chemoresistant cancer stem cells Cancer is described as a wound that does not heal due to the presence of inflammation. To study the effect of a wound on a growing tumor, we developed a model for removing half of the spheroid and monitoring subsequent growth. Invasion into the collagen indicates increased growth and a microarray was performed to investigate relative changes in expression. In conclusion, we have demonstrated the utility of embedded spheroids in several cancer research applications.