Invasion and secondary site colonization as a function of in vitro primary tumor matrix stiffness

Increased breast tissue stiffness is correlated with breast cancer risk and invasive cancer progression. However, its role in promoting bone metastasis, which shares a large burden of breast cancer deaths, has not yet been understood. To better understand the cause-effect relationship of tissue stiffness on breast cancer’s metastatic potential, we fabricated three-dimensional (3D) models to mimic breast and bone tissue in vitro . Based on our previous work, we used alginate-based hydrogels allowing precise control over stiffness and composition of extracellular breast tissue matrix; and 3D printed poly-caprolactone (PCL)-composite scaffolds to mimic the bone. The latter were further modified by promoting bone-ECM deposition using Saos-2 cells. After a decellularization step, PCL scaffolds were assembled with alginate-gelatin hydrogels and a novel breast-to-bone in vitro model was established. It was observed that increased stiffness of hydrogel resulted in higher migration and invasion capacity of MDA-MB 231 cells. Additionally, PTHrP and IL-6 expression, both of which are implicated in bone metastasis, were higher when cells from stiff hydrogels were cultured in bone/PCL scaffolds. These breast-to-bone in vitro models pose as a novel non-animal technology to pave the way for incorporating important tissue microenvironmental factors of the disease physiology (e.g. tissue stiffness) and emerge as promising future platforms for monitoring metastatic disease phenotypes and therapeutic efficacy.