Hybrid cancer stem cells utilise vascular tracks for collective streaming invasion in a metastasis-on-a-chip device

Cancer stem cells (CSCs) drive cancer metastatic dissemination. They do not do so in a vacuum, and the important influence of the tumour microenvironment (TME) on metastatic dissemination is becoming increasingly recognised. Therapeutic targeting of CSC-TME interactions may be a promising route to suppression of tumour metastasis. However, we must first understand how interactions with the TME influence CSC metastatic dissemination. To achieve this understanding, there is a need for experimental models that enable the analysis of dynamic interactions at single cell resolution within a complex environment. To this end, we utilise a metastasis-on-a-chip device to produce a 3D in vitro model of CSC interaction with a developing microvasculature, that is amenable to precise imaging and real time studies at single cell resolution. We show that the invasive phenotype of oral squamous cell carcinoma (OSCC) cells is markedly altered when in proximity to a microvasculature, with a switch to a hybrid CSC phenotype that undergoes collective streaming invasion. Mechanistically, ECM compression by the developing vasculature creates an environment that is refractory to cancer invasion, whilst leaving abandoned vascular tracks that can be utilised by hybrid CSCs for collective streaming invasion. Human tissue studies identify streaming invasion in association with vascularised regions in OSCC specimens. These findings elucidate the influence of the vasculature on CSC metastatic dissemination in OSCC, and the role of hybrid CSC invasion plasticity in overcoming this TME constraint.