Detection and Characterization of Invasive Circulating Tumor Cells Derived from Men with Metastatic Castration- Resistant Prostate Cancer

The Vitatex cell-adhesion matrix (CAM) platform allows for isolation of invasive circulating tumor cells (iCTCs). Here we sought to determine the utility of prostate-specific membrane antigen (PSMA) as a metastatic castration-resistant prostate cancer (mCRPC) iCTC biomarker, to identify solitary cells and clusters of iCTCs expressing either epithelial, mesenchymal, or stem cell markers, and to explore the feasibility of iCTC epigenomic analysis. CTCs were isolated and enumerated simultaneously using the Vitatex and CellSearch platforms in 23 men with mCRPC. CAM-avid iCTCs were identified as nucleated cells capable of CAM uptake, but without detectable expression of hematopoietic lineage (HL) markers including CD45. iCTCs were enumerated immunocytochemically (ICC) and by flow cytometry. Whole-genome methylation status was determined for iCTCs using the Illumina HumanMethylation27 BeadChip. Thirty-four samples were collected for iCTC analysis. A median of 27 (range 0-800) and 23 (range 2-390) iCTCs/mL were detected by ICC and flow, respectively. In a subset of 20 samples, a median of seven CTCs/mL (range 0-85) were detected by the CellSearch platform compared to 26 by the CAM platform. iCTC clusters were observed in 17% of samples. iCTCs expressing PSMA as well as markers of EMT and stemness were detectable. The iCTC methylation profile highly resembled mCRPC. More CTCs were recovered using the CAM platform than the CellSearch platform, and the CAM platform allowed for the detection of iCTC clusters, iCTCs expressing EMT and stem-cell markers, and characterization of the iCTC methylome. Correlation with clinical data in future studies may yield further insight into the functional significance of these findings. What's new? Invasive circulating tumor cells (iCTCs) represent a subpopulation of CTCs with metastatic potential. In this study, blood-derived iCTCs were isolated from patients with metastatic castration-resistant prostate cancer based on their ability to invade into a cell-adhesion matrix (CAM platform). This method was compared to the standard CellSearch platform where cells are isolated based on expression of epithelial cell adhesion molecules. More iCTCs were detected using the CAM platform than using the CellSearch platform, and different iCTC subpopulations were identified expressing markers of epithelial lineage, epithelial-to-mesenchymal transition, stemness, cell-invasion, and the prostate-specific marker PSMA. In addition, the CAM-isolated cells were suitable for DNA methylation array analysis, underscoring the potential benefit for adopting the CAM platform for future analysis.