Development of a 3D in vitro model of cancer progression

The hallmark of cancer is the ability of cancer cells to disseminate and invade to distant organs. Metastasis accounts for over 90% of cancer related deaths and therefore requires a better understanding of the metastatic cascade to develop better therapeutic regimens. The metastatic process is heavily influenced by the extracellular matrix (ECM) density and composition of the surrounding tumour microenvironment. These microenvironmental cues also regulate the angiogenic processes within a tumour, facilitating the spread of cancer cells. The aim of this thesis was to develop a biomimetic 3D in vitro model of colorectal cancer with controllable matrix parameters that regulate cancer invasion, the formation of a primitive vascular network and response to targeted drug treatment. A novel 3D in vitro cancer model was established based on the removal of interstitial fluid in collagen type I hydrogels. Colorectal cancer cells cultured in dense collagen gels formed well-defined cellular aggregates mimicking avascular micrometastases observed in vivo. Cancer cells invaded from the artificial cancer mass (ACM) into the stromal surround in cell specific patterns, either as spherical aggregates or cell sheets. Invasion into a denser collagen matrix altered the migration pattern predominantly to cell sheets. Laminin was found to enhance the invasion profile of colorectal cancer cells independent of stromal matrix density. The pro-invasive and epithelial-mesenchymal transition (EMT) markers MMP7 and vimentin were upregulated in 3D cultures in comparison to 2D monolayers. Stromal cultures containing fibroblasts and endothelial cells formed highly branched end-to-end vascular networks in the presence of laminin. The addition of cancer cells produces significantly longer but substantially less interconnected vascular networks mimicking in vivo ‘leaky’ tumour vasculature. The loss of CK20 by invading cancer cells significantly correlated with the overall distance of invasion into the stromal surround. Although the expression of the biomarker EGFR was upregulated in 3D, targeted treatment using cetuximab lead to a greater inhibition profile in 2D monolayers than in 3D cultures. Drug resistance in 3D cultures corresponded with the presence of cancer stem cells. These findings signify the importance of 3D in vitro cancer models as important tools to study the effect of microenvironmental conditions on tumour malignancy