Detection and genomic interrogation of circulating tumor cells (CTCs) and circulating tumor stem cells (CTSCs) from men with metastatic castration-resistant prostate cancer (mCRPC).

Abstract

144 Background: Isolation, enumeration, and genomic profiling of CRPC CTCs offers the potential to discover genetic changes that occur in advanced disease. The Vitatex VitaCap platform captures CTCs based on their ability to invade collagenous matrices (CAM), allows for CTC and CTSC capture independent of EpCAM status, and yields viable cells suitable for comprehensive genomic analysis. In this study we sought to compare CTC yields between the VitaCap and the Veridex CellSearch platforms, to determine the utility of prostate-specific membrane antigen (PSMA) as a mCRPC CTC biomarker, to identify CTSCs and CTC clusters, and to explore the feasibility of CTC epigenomic analysis. Methods: CTCs were isolated and enumerated simultaneously using the CellSearch and VitaCap platforms in 23 men. CAM isolated CTCs and CTSCs were defined as EpCAM+PSMA+ and CD44+DPPA5+ respectively, and were enumerated immunocytochemically (ICC) and by flow cytometry. CTC clusters were enumerated by ICC. The Illumina HumanMethylation27 BeadChip was used to determine whole genome methylation status for CAM isolated cells. Results: 35 samples were collected for CAM analysis. A median of 27 (range 0-800) and 23 (range 2-390) CAM+ CTCs/ml were detected by ICC and flow respectively. In a subset of 20 samples, a median of 7 CTCs/ml (range 0-85) were detected by the CellSearch platform. CTCs were detectable by either CAM or CellSearch in >95% of samples. CAM isolated CTC clusters were observed in 23% of samples with a median 7 clusters/ml (range 1-200). CTSCs were detected in 70% and 97% of samples by ICC and flow respectively, with a median of 9 CTSCs/ml (range 1-264) by flow. The CTC methylation profile highly resembled mCRPC with hypermethylation occurring more frequently in pathways associated with apoptosis (p<0.006), angiogenesis (p<0.007), and VEGF signaling (p<0.003). Conclusions: CAM and CellSearch platforms yield comparable CTC counts. CTSCs and CTC clusters are detectable using the CAM platform, and the CTC methylome closely resembles that of mCRPC. Correlation with clinical data may yield further insight into the functional significance of these findings.