Molecular and genomic characterization of invasive circulating tumor cells (iCTCs) from men with metastatic castration-resistant prostate cancer (mCRPC).

120 Background: Identification, enumeration, and genomic analysis of circulating tumor cells (CTCs) may allow for a better understanding of the mechanisms of resistance to therapies in metastatic castration-resistant prostate cancer (mCRPC). The Vitatex VitaAssay platform captures invasive CTCs (iCTCs) in a cell surface marker-independent fashion based on their ability to invade a fluorescently-labeled cell-adhesion matrix (CAM), allowing for the analysis of multiple CTC subpopulations. Here we sought to estimate epithelial, mesenchymal, and stem-like iCTC subpopulation diversity in men with CRPC starting abiraterone acetate therapy, to compare the genomic profiles of iCTCs to matched metastatic biopsies, and to explore the potential for 2D and 3D CTC culture. Methods: iCTCs were isolated from men with mCRPC using the CAM platform, and paired metastatic biopsies were performed. iCTCs were defined as CAM+/CD45-/CD14-/DAPI+, mesenchymal iCTCs as vimentin+/CAM+/CD45-/CD14-/DAPI+, and stem-like iCTCs as CD44+/CAM+/CD45-/CD14-/DAPI+. iCTCs were enumerated and purified using FACS. Agilent array comparative genomic hybridization (aCGH) of iCTCs and paired biopsies was performed, and to explore the potential for ex-vivo cell expansion and spheroid formation, iCTCs were cultured separately in CAM and in matrigel for up to 10 days. Results: iCTCs were isolated using the CAM platform from 29 men, of whom seven have undergone paired metastatic biopsy. The median pre-FACS purity was 1.06% (range 0.11%-10.16%). Post-FACS purity was increased to greater than 90%, and a median of 60 (range 2 to 1,314) iCTCs/7.5ml were detected by FACS. Both vimentin+ and CD44+ iCTCs are detectable, and compromise between 10 to 50% of total iCTCs. iCTC aCGH profiles resemble paired soft tissue biopsy, in vitro iCTCs culture is feasible, and iCTC spheroids were observed. Conclusions: Multiple CRPC iCTC subpopulations are identifiable from men starting abiraterone therapy, and cell sorting techniques increase iCTC purity. iCTCs resemble metastatic CRPC tissue and can be expanded in culture. Further enumeration, genomic profiling, and clinical correlation of paired iCTCs taken from men with abiraterone-resistant CRPC is underway, and may shed light on mechanisms of abiraterone resistance.