Most patients who succumb to cancer have metastases to bone that contribute to their death. Cancer cells that metastasize to bone are regularly subjected to mechanical stimuli that may affect their proliferation, growth and protein expression. Understanding why some cancer cells thrive in this environment could provide insight into new approaches to prevent or treat metastasis to bone. We used 4T1 cells as a model of breast cancer cells, and implanted them in gelatin hydrogels with moduli of 1 or 2.7 kPa to mimic the properties of bone marrow. The constructs were subjected to either perfusion of media through the hydrogel or combined perfusion and cyclic mechanical compression for 1 h d−1 for 4 d. Controls were cultured in free-swelling conditions. The cells formed spheroids during the 4 d of culture, with larger spheroids in the statically cultured constructs than in perfusion or compressed constructs. In stiffer gelatin, smaller spheroids formed in compressed constructs than perfusion alone, while compression had no effect compared to perfusion in the softer gelatin. Immunostaining indicated that the spheroids expressed osteopontin, parathyroid hormone-related protein and fibronectin, which are all hallmarks of bone metastasis. The proliferative marker Ki67 was present in all spheroids on day 4. In the 1 kPa gelatin, Ki67 staining intensity was greater in the statically cultured, free-swelling constructs than in bioreactor culture, regardless of dynamic compression. By contrast, proliferation was higher in the compressed gelatins compared to perfusion alone in the 2.7 kPa constructs, although the spheroids were smaller, on average. This suggests the stiffer gelatin may restrict spheroid growth at the same time that it enhances mechanobiological signalling during compression. Taken together, 4T1 breast cancer cells are mechanically sensitive, and mechanical stimuli can alter their proliferation and protein expression within soft materials with mechanical properties similar to bone marrow. As such, both in vivo and in vitro models of cancer metastasis should consider the role of the mechanical environment in the bone.

中文翻译：

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机械刺激和基质特性调节三维明胶培养物中癌球体的生长


大多数死于癌症的患者都有骨转移，这导致了他们的死亡。转移到骨的癌细胞经常受到机械刺激，这可能会影响它们的增殖、生长和蛋白质表达。了解为什么某些癌细胞在这种环境中茁壮成长可以为预防或治疗骨转移的新方法提供见解。我们使用 4T1 细胞作为乳腺癌细胞模型，并将其植入模量为 1 或 2.7 kPa 的明胶水凝胶中，以模拟骨髓的特性。通过水凝胶对构建体进行介质灌注，或者将灌注和循环机械压缩相结合，持续 1 hd−1，持续 4 d。对照在自由膨胀条件下培养。细胞在培养 4 天期间形成球体，静态培养构建体中的球体比灌注或压缩构建体中的球体更大。在较硬的明胶中，与单独灌注相比，压缩结构中形成的球体更小，而与较软的明胶中的灌注相比，压缩没有效果。免疫染色表明，球体表达骨桥蛋白、甲状旁腺激素相关蛋白和纤连蛋白，这些都是骨转移的标志。第 4 天，增殖标记物 Ki67 存在于所有球体中。在 1 kPa 明胶中，无论动态压缩如何，静态培养的自由溶胀构建体中的 Ki67 染色强度均高于生物反应器培养中的染色强度。相比之下，在 2.7 kPa 构建体中，与单独灌注相比，压缩明胶的增殖更高，尽管球体平均较小。 这表明较硬的明胶可能会限制球体生长，同时增强压缩过程中的机械生物学信号。总而言之，4T1乳腺癌细胞对机械敏感，机械刺激可以改变其在机械特性与骨髓相似的软材料内的增殖和蛋白质表达。因此，癌症转移的体内和体外模型都应考虑骨骼中机械环境的作用。