Abstract
Bone is one of the most common sites of cancer metastasis, as its fertile microenvironment attracts tumor cells. The unique mechanical properties of bone extracellular matrix (ECM), mainly composed of hydroxyapatite (HA) affect a number of cellular responses in the tumor microenvironment (TME) such as proliferation, migration, viability, and morphology, as well as angiogenic activity, which is related to bone metastasis. In this study, we engineered a bone-mimetic microenvironment to investigate the interactions between the TME and HA using a microfluidic platform designed for culturing tumor cells in 3D bone-mimetic composite of HA and fibrin. We developed a bone metastasis TME model from colorectal cancer (SW620) and gastric cancer (MKN74) cells, which has very poor prognosis but rarely been investigated. The microfluidic platform enabled straightforward formation of 3D TME composed the hydrogel and multiple cell types. This facilitated monitoring of the effect of HA concentration and culture time on the TME. In 3D bone mimicking culture, we found that HA rich microenvironment affects cell viability, proliferation and cancer cell cytoplasmic volume in a manner dependent on the different metastatic cancer cell types and culture duration indicating the spatial heterogeneity (different origin of metastatic cancer) and temporal heterogeneity (growth time of cancer) of TME. We also found that both SW620 and MKN72 cells exhibited significantly reduced migration at higher HA concentration in our platform indicating inhibitory effect of HA in both cancer cells migration. Next, we quantitatively analyzed angiogenic sprouts induced by paracrine factors that secreted by TME and showed paracrine signals from tumor and stromal cell with a high HA concentration resulted in the formation of fewer sprouts. Finally we reconstituted vascularized TME allowing direct interaction between angiogenic sprouts and tumor-stroma microspheroids in a bone-mimicking microenvironment composing a tunable HA/fibrin composite. Our multifarious approach could be applied to drug screening and mechanistic studies of the metastasis, growth, and progression of bone tumors.
Highlights
Cancer metastasis, a complex phenomenon in which cancer cells spread to new organs, is one of the greatest challenges in cancer research
When the hydroxyapatite [Ca10(PO4)6(OH)2] (HA)/fibrin composite was prepared in six-well plates (Figure S1A), the time required for it to solidify increased with increasing HA concentration (Figure S1B)
We investigated the relationship between the mechanical properties and cellular activities of the bone-mimicking extracellular matrix (ECM)
Summary
A complex phenomenon in which cancer cells spread to new organs, is one of the greatest challenges in cancer research. We analyzed the gel rheology of an HA/fibrin composite to assess the influence of the mechanical properties of the ECM on the TME (Figure 1). We incorporated colorectal cancer (SW620) and gastric cancer (MKN74) cells within a bone-mimicking microfluidic platform consisting of an HA/fibrin composite and investigated their viability, morphology, proliferation, and migration.
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