3D in vitro bioengineered tumors based on collagen I hydrogels.

Cells cultured within a three-dimensional (3D) in vitro environment have the ability to acquire phenotypes and respond to stimuli analogous to in vivo biological systems. This approach has been utilized in tissue engineering and can also be applied to the development of a physiologically relevant in vitro tumor model. In this study, collagen I hydrogels cultured with MDA-MB-231 human breast cancer cells were bioengineered as a platform for in vitro solid tumor development. The cell-cell and cell-matrix interactions present during in vivo tissue progression were encouraged within the 3D hydrogel architecture, and the biocompatibility of collagen I supported unconfined cellular proliferation. The development of necrosis beyond a depth of ~150-200 μm and the expression of hypoxia-inducible factor (HIF)-1α were demonstrated in the in vitro bioengineered tumors. Oxygen and nutrient diffusion limitations through the collagen I matrix as well as competition for available nutrients resulted in growing levels of intra-cellular hypoxia, quantified by a statistically significant (p < 0.01) upregulation of HIF-1α gene expression. The bioengineered tumors also demonstrated promising angiogenic potential with a statistically significant (p < 0.001) upregulation of vascular endothelial growth factor (VEGF)-A gene expression. In addition, comparable gene expression analysis demonstrated a statistically significant increase of HIF-1α (p < 0.05) and VEGF-A (p < 0.001) by MDA-MB-231 cells cultured in the 3D collagen I hydrogels compared to cells cultured in a monolayer on two-dimensional tissue culture polystyrene. The results presented in this study demonstrate the capacity of collagen I hydrogels to facilitate the development of 3D in vitro bioengineered tumors that are representative of the pre-vascularized stages of in vivo solid tumor progression.