Assessment of a Size-Based Method for Enriching Circulating Tumour Cells in Colorectal Cancer

SIMPLE SUMMARY: Circulating tumour cells (CTC) are metastatic seeds that arise from solid tumours and drive the metastatic spread of malignancy. A better understanding of the biology of CTCs is critical to enable its clinical application for diagnosis and as a therapeutic target. Currently, CellSearch is the only method approved by the U.S. Food and Drug Administration (FDA) for CTC enrichment. However, it isolates only epithelial CTCs and is resource-intensive, which has led to an interest in developing simpler size-based CTC isolation methods. The MetaCell CTC enrichment kit is a size-based method which has been previously used for enriching and culturing CTCs in vitro from several cancer types. Herein, we evaluate the MetaCell platform on its efficacy for retaining colorectal cancer (CRC) cells spiked into blood and the extent of purity of the enriched CTC fraction, which has not been described in previous studies utilising MetaCell. We subsequently applied this method to colorectal cancer patient blood samples and successfully enriched CTCs. ABSTRACT: Circulating tumour cells (CTC) from solid tumours are a prerequisite for metastasis. Isolating CTCs and understanding their biology is essential for developing new clinical tests and precision oncology. Currently, CellSearch is the only FDA (U.S. Food and Drug Administration)-approved method for CTC enrichment but possesses several drawbacks owing to a reliance on the epithelial cell adhesion molecule (EpCAM) and a resource-intensive nature. Addressing these shortcomings, we optimised an existing size-based method, MetaCell, to enrich CTCs from blood of colorectal cancer (CRC) patients. We evaluated the ability of MetaCell to enrich CTCs by spiking blood with CRC cell lines and assessing the cell recovery rates and WBC depletion via immunostaining and gene expression. We then applied MetaCell to samples from 17 CRC patients and seven controls. Recovery rates were >85% in cell lines, with >95% depletion in WBCs. MetaCell yielded CTCs and CTC clusters in 52.9% and 23.5% of the patients, respectively, without false positives in control patients. CTCs and cluster detection did not correlate with histopathological parameters. Overall, we demonstrated that the MetaCell platform enriched CRC cells with high recovery rates and high purity. Our pilot study also demonstrated the ability of MetaCell to detect CTCs in CRC patients.