Metastatic breast cancer microfluidics: the response of endocrine resistant MCF-7 breast cancer cells to lymphatic flow conditions

The incidence of metastatic breast cancer (BC) mortality remains an urgent issue in need of address. Despite endocrine therapy significantly improving BC mortality rates in recent decades, endocrine resistance continues to limit treatment efficacy and consequently, the probability of metastasis greatly increases. When cancer cells leave the primary tumour and advect through biological microchannels of circulation systems, they are subject to a complex range of flow-induced forces. These microfluidic forces have been shown to influence cancer cell functionality and behaviour, and therefore by extension, metastatic success. As the physiological alterations which cancer cells undergo to become endocrine resistant are unclear, the morphological differences between endocrine sensitive and endocrine resistant MCF?7 BC cells were examined. In addition, the response of endocrine resistant cells to flow-induced forces has yet to be investigated. Both cell lines were thus suspended in a system representative of the lymphatic environment; the primary metastatic route. The circulating cells were exposed to varying levels of laminar flow conditions, following which the properties of cell viability, size and stiffness were quantified for comparative purposes. Firstly, it was observed thatsome endocrine resistant cells were much larger than the endocrine sensitive cells, although on average, this difference was found to be statistically insignificant. Endocrine resistant cells were then found to be predominantly uncompromised following exposure to flows of increasing Reynolds number (2.74–9.13), maintaining ≈ 90% of their size and viability, while endocrine sensitive cells saw corresponding size and viability decreases to ≈ 70% at the lowest flow rate. Finally, it was determined that this flow indifference seen in endocrine resistance cells was most plausibly due to their high deformability (534.7 ± 266.2 Pa) in comparison to their endocrine sensitive counterparts (875.4 ± 504.6 Pa), as deformability-induced lift direct cells with a lower stiffness towards the channel centre where they are protected from detrimental levels of wall shear stress. These properties and behaviour in flow align with those of known metastatic cell types, confirming that endocrine resistant BC cells exhibit a high metastatic potential; a conclusion which worsens the prognosis for patients presenting acquired or inherent endocrine resistance. However, the quantification of cellular stiffness and its identification as a biomarker of metastatic potential in endocrine resistant BC cells will inform the development of novel strategies which exploit or alter this property in an effort to prevent metastasis.