Enrichment of epithelial exosomes to increase the specificity of circulating microRNAs as biomarkers for colorectal cancer

MT Lowe, GP Young and MZ Michael

Department of Gastroenterology and Hepatology, Flinders Centre for Innovation in Cancer, Flinders University, Flinders Medical Centre, Adelaide

Colorectal cancer (CRC) is a leading cause of cancer related death in Australians but, if detected early, is curable by resection. More sensitive and specific methods are being developed to enhance detection in screening programs. To identify biomarkers, changes in circulating microRNAs (miRNA) between control and CRC were identified. As CRC patients often present with co-morbidities including cardiac disease, hypertension and diabetes, it is notable that some CRC associated miRNA have also been proposed as biomarkers for these other diseases. Epithelial Cell Adhesion Molecule (EpCAM) is a cell surface molecule expressed on epithelia and epithelium-derived exosomes. EpCAM antibody labelled beads were used to capture epithelial tumour exosomes from serum to enrich for CRC associated miRNA miR-17, miR-19b, miR-20b, miR-21, miR-25, miR-186 and miR-486. Relative miRNA levels were determined by real time RT-PCR and were compared to unenriched sera in a cohort of 147 patients comprising 46 non-CRC controls (C), 51 advanced adenoma (AA), 32 stage III (SIII) and 18 stage IV (SIV) CRC patients. Significant differences in miRNA levels were seen in C participants between those with or without co-morbidities. The standout miRNA was miR-21. EpCAM enrichment enhanced specificity for CRC (ANOVA p<0.05) even when co-morbidities were taken into account. Poorer survival occurred in CRC patients with high EpCAM-enriched miR-21 levels (>0.004) encompassing all SIV and 78% SIII patients (p<0.05). Survival was poorest in patients with high miR-21 levels and low miR-186 levels, including 89% SIV patients (p<0.001). Results show promise that simple exosome enrichment may help to increase diagnostic specificity and that co-morbidities can influence miRNA levels in blood.