Investigating the Impact of Confinement on Collectively Migrating Cancer Cells

Cancer metastasis is responsible for over 90% of all cancer-related deaths. The metastatic cascade is a multifaceted and complex biological process in which tumor cells acquire phenotypic changes enabling them to migrate from a primary tumor and traverse diverse physiological hurdles to form new metastases in distant tissues and organs. Classical depictions of the metastatic cascade portray single tumor cells departing from a primary tumor and embarking on an arduous journey to form new metastatic colonies. While this depiction is partly true, it fails to consider the contribution of collectively migrating circulating tumor cell (CTC) clusters in tumor invasion, progression, and metastasis. Collectively migrating CTC clusters have been detected in the blood of lung cancer patients, have demonstrated increased resistance to chemotherapeutics, and exhibit a high correlation to poor patient prognosis, thereby suggesting the critical contribution of collective migration in tumor cell dissemination and metastatic spread. In vivo, metastatic cancer cells must travel through 3-dimensional (3D) fiber-, pore-, and channel-like tracks to form metastases, and these 3D tracks can range from a highly confining 3 m in width to a less confining 30 m in width, and between 100 m and 600 m in length. To recapitulate this environment for in vitro studies, we utilized bioengineering principles and a novel polydimethylsiloxane (PDMS) microfluidic system equipped with an array of confining microchannel through which cells migrate. Using this system, we can directly observe and probe the mechanisms by which cancer cells migrate collectively in confining spaces. Our findings suggest a mechanism whereby confinement of collectively migrating tumor cells leads to elevated RhoA activity and myosin IIA (MIIA) contractility resulting in leader cell dissociations from collectively migrating tumor cell strands. Furthermore, our studies indicate that nuclear dynamics are tightly implicated in this process. Collective cell migration into confining microchannels promotes linker of nucleoskeleton and cytoskeleton (LINC) complex-facilitated leader cell nuclear area expansion. This increase in leader cell nuclear area triggers the cPLA2 signaling pathway promoting downstream RhoA activity, myosin II contractility, and leader cell dissociations from collective strands