Tissue-engineered nanoclay-based 3D in vitro breast cancer model for studying breast cancer metastasis to bone.

Breast cancer (BrCa) preferentially spreads to bone and colonises within the bone marrow to cause bone metastases. To improve the outcome of patients with BrCa bone metastasis, we need to understand better the mechanisms underlying bone metastasis. Researchers have relied heavily upon in vivo xenografts due to limited availability of human bone metastasis samples. A significant limitation of these is that they do not have a human bone microenvironment. To address this issue, we have developed a nanoclay-based 3D in vitro model of BrCa bone metastasis using human mesenchymal stem cells (MSCs) and human BrCa cells mimicking late stage of BrCa pathogenesis at the metastatic site. This 3D model can provide a microenvironment suitable for cell-cell and cell-matrix interactions whilst retaining the behaviour of BrCa cells with different metastasis potential (i.e., highly metastatic MDA-MB-231 and low metastatic MCF-7) as shown by the production of alkaline phosphatase and matrix metalloproteinase-9. The sequential culture of MSCs with MCF-7 exhibited 3D tumouroids formation and also occurrence of mesenchymal to epithelial transition of cancer metastasis as evidenced by gene expression and immunocytochemistry. The unique and distinct behaviour of highly metastatic MDA-MB-231 and the low metastatic MCF-7 was observed at the bone metastasis site. The changes to migratory capabilities and invasiveness in MDA-MB-231 in comparison with tumour growth with MCF-7 was observed. Together, a novel bone-mimetic 3D in vitro BrCa model has been developed that could be used to study mechanisms governing the later stage of cancer pathogenesis in bone.