A 3Rs approach to tumour metastasis: investigating the role of cancer stem cells in metastasis using an in vitro microfluidic model

Tumour metastasis, which seeds secondary tumours in distant organs, causes the majority of cancer deaths. However, despite many decades of research into primary tumours, much less is known about the processes underlying metastasis. Cancer stem cells (CSCs) are the long-lived sub-population of cells within a tumour; they maintain long-term tumour growth, and have the special ability to adopt diverse characteristics that enable resistance to cancer therapy and are required for tumour invasion and metastasis. Epithelial-to-mesenchymal transition (EMT), a developmental process that causes cells to stop proliferating and become motile, is re-activated in CSCs to drive tumour invasion and migration to secondary sites. Mesenchymal-to-epithelial transition (MET), where migratory CSCs revert back to a stationary and proliferative identity, enables new metastatic tumour growth at secondary sites. These findings are based on mouse models and 2D cell culture models, both of which have yielded important results but now present significant barriers to further progress in metastasis research. Importantly, they do not allow the study of metastasis in a human context, and do not allow the simple imaging of key steps (EMT and MET) that would enable scientists to gain deeper insight into the factors driving metastatic processes. There is therefore an urgent requirement for new 3D cell culture models that accurately model the metastatic process, in order that metastatic mechanisms can be identified and targeted with new therapies, and to enable the replacement of mouse models for studies of human metastasis.

To address these issues, we aim to develop a human-relevant 3D metastasis-on-a-chip cell culture model that incorporates all the stages of metastasis and can replace mouse assays for investigating the role of CSCs in tumour metastasis. An important advantage over mouse models is that the chip can be viewed directly under a microscope, enabling tracking of cells through the metastatic process in a way that is particularly difficult in animal models. We predominantly focus on oral squamous cell carcinoma (OSCC); OSCC is one of the top ten cancers worldwide, with over 300,000 cases annually, and incidence is increasing both worldwide and in the UK. OSCC is a disease with an important role for metastasis, and it is also an exceptionally good model for studies of tumour behaviour due to highly reproducible characteristics between individual tumours. We will incorporate both established OSCC cell lines and cells from fresh human tumour specimens into this model - efficient incorporation of fresh human tumour material will enable utilization of our chip model in the development of personalised anti-metastatic medicine. We will also assess human tumour specimens for expression of metastatic CSC markers and correlate this with clinical outcome as an important direct human validation of the findings from our chip model. In this way, we aim to develop a human-relevant metastasis-on-a-chip model that could be widely used for the replacement of animal models, and use this model to answer some of the most pressing questions in the CSC field which would otherwise be investigated using mouse models. Identification of metastatic CSCs and their associated protein markers will enable determination of new therapeutic targets for anti-metastatic therapies, and we will test the activity of anti-metastatic therapies in this model.

• Early Career Engagement Award: Inaugural award scheme supports NC3Rs-funded junior researchers