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Abstract Bone metastasis is a leading cause of death in patients with breast cancer, but the underlying mechanisms are poorly understood. While much work focuses on the molecular and cellular events that drive breast cancer bone metastasis, it is mostly unclear what role bone extracellular matrix (ECM) properties play in this process. Bone ECM primarily consists of mineralized collagen fibrils, which are composed of non-stoichiometric carbonated apatite (HA) and collagen type I. Reduced bone mineral content is epidemiologically linked with increased risk of bone metastasis. Yet elucidating the potential functional impact of collagen mineralization on breast cancer cells has remained challenging because of a lack of model systems that allow studying tumor cell behavior as a function of physiological, intrafibrillar collagen mineralization. Here, we have developed cell culture substrates composed of mineralized collagen type I fibrils using a polymer-induced liquid-precursor (PILP) process. Intrafibrillar HA decreased breast cancer cell adhesion forces and accordingly reduced collagen fiber alignment relative to cells cultured on control collagen. The resulting mineral-mediated changes in collagen network characteristics and mechanosignaling correlated with increased cell motility, but inhibited directed migration of breast cancer cells. These results suggest that physiological mineralization of collagen fibrils reduces tumor cell adhesion with potential functional consequences on skeletal homing of disseminated tumor cells in early stages of breast cancer metastasis. [ABSTRACT FROM AUTHOR]

Microcalcifications serve as diagnostic markers for breast cancer, yet their formation pathway(s) and role in cancer progression are debated due in part to a lack of relevant 3D culture models that allow studying the extent of cellular regulation over mineralization. Previous studies have suggested processes ranging from dystrophic mineralization associated with cell death to bone-like mineral deposition. Here, we evaluated microcalcification formation in 3D multicellular spheroids, generated from non-malignant, pre-cancer, and invasive cell lines from the MCF10A human breast tumor progression series. The spheroids with greater malignancy potential developed necrotic cores, thus recapitulating spatially distinct viable and non-viable areas known to regulate cellular behavior in tumors in vivo . The spatial distribution of the microcalcifications, as well as their compositions, were characterized using nanoCT, electron-microscopy, and X-ray spectroscopy. Apatite microcalcifications were primarily detected within the viable cell regions and their number and size increased with malignancy potential of the spheroids. Levels of alkaline phosphatase decreased with malignancy potential, whereas levels of osteopontin increased. These findings support a mineralization pathway in which cancer cells induce mineralization in a manner that is linked to their malignancy potential, but that is distinct from physiological osteogenic mineralization. [ABSTRACT FROM AUTHOR]