Biomimetic tumor microenvironments based on collagen matrices.

The extracellular matrix (ECM) establishes the basis for the cell's microenvironment providing structural and mechanical support to cells and tissues, and regulating multiple cell functions including gene expression, cell cycle, apoptosis, morphogenesis, and migration. Tumor development can be considered as a process where the cells are subjected to mutations. However, changes in the microenvironment of tumor cells can strongly impact the growth, invasion and survival of tumor cells. This specialized microenvironment is known to have an abundance of inflammatory cells and activated fibroblasts both expressing ECM components and growth factors that support the survival and proliferation of tumor cells in a paracrine fashion. Growing evidence points towards a key role of the ECM in the modulation of tumor progression and metastasis, even influencing therapeutic pharmacosensitivity. Accordingly, to better understand the mechanisms of tumor cell behavior, e.g. proliferation, invasion and survival, in dependence on microenvironmental cues as well as the cell-microenvironment interaction, it is necessary to engineer well-defined 3D matrices to closely mimic in vivo like microenvironments in a controlled in vitro setting. In that way the full repertoire of high-resolution, in-depth analytical technologies available for in vitro settings can be applied to reveal the underlying molecular mechanisms in an in vivo like ECM microenvironment. This review provides an overview of the current bioengineering techniques of defined biomimetic 3D models with a focus on naturally derived biopolymer components for the investigation of tumor cell behavior in vitro.