Exploring sialyl-Tn expression in microfluidic-isolated circulating tumour cells: A novel biomarker and an analytical...

Circulating tumour cells (CTCs) originating from a primary tumour, lymph nodes and distant metastases hold great potential for liquid biopsies by providing a molecular fingerprint for disease dissemination and its temporal evolution through the course of disease management. CTC enumeration, classically defined on the basis of surface expression of Epithelial Cell Adhesion Molecule (EpCAM) and absence of the pan-leukocyte marker CD45, has been shown to correlate with clinical outcome. However, existing approaches introduce bias into the subsets of captured CTCs, which may exclude biologically and clinically relevant subpopulations. Here we explore the overexpression of the membrane protein O-glycan sialyl-Tn (STn) antigen in advanced bladder and colorectal tumours, but not in blood cells, to propose a novel CTC isolation technology. Using a size-based microfluidic device, we show that the majority (>90%) of CTCs isolated from the blood of patients with metastatic bladder and colorectal cancers express the STn antigen, supporting a link with metastasis. STn⁺ CTC counts were significantly higher than EpCAM-based detection in colorectal cancer, providing a more efficient cell-surface biomarker for CTC isolation. Exploring this concept, we constructed a glycan affinity-based microfluidic device for selective isolation of STn⁺ CTCs and propose an enzyme-based strategy for the recovery of viable cancer cells for downstream investigations. Finally, clinically relevant cancer biomarkers (transcripts and mutations) in bladder and colorectal tumours, were identified in cells isolated by microfluidics, confirming their malignant origin and highlighting the potential of this technology in the context of precision oncology.