An integrative alginate-based 3D in vitro model to explore epithelial-stromal cell dynamics in the breast tumor microenvironment.

The tumor microenvironment (TME) orchestrates cellular and extracellular matrix (ECM) interactions, playing a key role in tumorigenesis, tumor growth, and metastization. Investigating the interplay between stromal-epithelial cells within the TME is paramount for understanding cancer mechanisms but demands reliable biological models. 3D-models have emerged as powerful in vitro tools, but many fall short in replicating cell-cell/cell-matrix interactions. This study introduces a novel hybrid 3D-model of the breast TME, combining epithelial cells, cancer-associated fibroblasts (CAFs), and their ECM. To build the stromal compartment, porous 3D-printed alginate scaffolds were seeded with CAFs, which proliferated and produced ECM. The pores were infused with oxidized peptide-modified alginate hydrogel laden with MCF10A cells, forming the parenchymal compartment. The hybrid system supported epithelial morphogenesis into acini surrounded by fibroblasts and ECM, and could be readily solubilized to recover cells, their matrix, and sequestered soluble factors. Proteome profiling of the retrieved ECM showed upregulation of proteins associated with matrix assembly/remodeling, epithelial-to-mesenchymal transition (EMT), and cancer. The TME-like microenvironment induced a partial EMT in MCF10A cells, generating a hybrid population with epithelial and mesenchymal features, characteristic of aggressive phenotypes. Our model provided new insights into epithelial-stromal interactions within the TME, offering a valuable tool for cancer research in a physiologically-relevant 3D setting.