Abstract P2-02-13: EpCAM-independent enrichment approach for isolation of circulating tumor cells (CTCs) in breast cancer - What can be found in the EpCAM-depleted fraction?

Circulating tumor cells (CTCs) are the potential precursors of metastatic disease. Many assays have been established for the enumeration of CTCs. However, major limitations include the reliance on the expression of the cell surface marker epithelial cell adhesion molecule (EpCAM). These approaches may not detect CTCs that either express no/low levels of EpCAM or undergo epithelial-to-mesenchymal transition (EMT). We present an enrichment strategy combining different antibodies specific for surface proteins and extracellular matrix (ECM) components to capture EpCAMneg cell lines and EpCAMneg CTCs from EpCAM-depleted breast cancer blood samples. Expression of proteins (Trop2, CD49f, cMet, CK8, CD44, ADAM8, CD146, TEM8, CD47) was verified by immunofluorescence on EpCAM-positive (e.g. MCF7, SKBR3) and -negative (MDA-MB-231) breast cancer cell lines; antibodies and ECM proteins (e.g. hyaluronic acid (HA), collagen I, laminin) were further spotted in a single- and multi-arrayed format onto glass slides (Schott, NEXTERION® AL) and coupled to immunomagnetic beads (Dynabeads/Adembeads). Tumor cell adhesion of EpCAMpos/neg cell lines was visualized by Coomassie/MitoTracker; EpCAMneg CTCs enriched via functionalized Adem-/Dynabeads were identified by immunofluorescence staining for anti-pan-Cytokeratin(CK)-FITC/anti-CD45 AF647/DAPI and quantified manually by microscopy. Regarding cell lines, marginal binding of EpCAMneg MDA-MB-231 cells to EpCAM-antibodies could be observed. Efficient adhesion/capturing of EpCAMneg cells could be achieved via HA and immobilized antibodies against CD49f and Trop2. By analyzing 29 EpCAM-depleted fractions from 25 metastatic breast cancer patients, we were able to identify EpCAMneg CTCs in 69% of the samples [range 1-24] applying Trop2, CD49f, cMet, CK8 and/or HA magnetic enrichment. Accessorily, EpCAMneg dual-positive (CKpos/CD45pos) cells could be traced in 28 out of 29 samples [range 1-480]. Herein, we demonstrate an enhanced enrichment strategy to optimize capturing of EpCAMneg CTCs by targeting various cell surface antigens with antibody mixtures and ECM components. Thereby, potential relevant CTCs can be gathered and subjected to subsequent molecular analysis. Citation Format: Fehm T, Schneck H, Gierke B, Pawlak M, Templin M, Niederacher D, Neubauer H. EpCAM-independent enrichment approach for isolation of circulating tumor cells (CTCs) in breast cancer - What can be found in the EpCAM-depleted fraction?. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-02-13.