Improved ovarian cancer EMT-CTC isolation by immunomagnetic targeting of epithelial EpCAM and mesenchymal N-cadherin

Epithelial cell adhesion molecule (EpCAM)-targeted capture remains the most common isolation strategy for circulating tumor cells (CTCs). However, epithelial-to-mesenchymal transition (EMT) leads to decreased epithelial EpCAM expression affecting the optimal CTC capture. In this study, we tested a cohort of ovarian cancer cell lines using flow cytometry to identify N-cadherin as the additional immunomagnetic cell surface target for ovarian cancer cell isolation. Combined immunomagnetic targeting of mesenchymal N-cadherin and epithelial EpCAM enriched CTCs from advanced ovarian cancer patient blood approximately three times more efficiently than targeting of EpCAM alone. We also show that more EMT-phenotype CTCs are captured by including N-cadherin targeting into CTC isolation protocols. However, after N-cadherin-based CTC isolation, in some blood samples of healthy individuals, we also observed the presence of cells expressing markers common to CTCs. Our data show that these "false positives" can be largely distinguished from CTCs as circulating endothelial cells (CECs) by vascular endothelial-cadherin co-staining. CEC counts are highly variable in patients and healthy controls. Our data demonstrate that a combination of EpCAM with N-cadherin-targeted isolation can improve CTC detection and widen the EMT-phenotype spectrum of captured CTCs.