Abstract 4891: Molecular and functional analysis of circulating tumor cells in castrate resistant prostate cancer using a geometrically enhanced microfluidic device based on PSMA immunocapture
Authors: Loftus Matthew , Jodari-Karimi Mona , Gakhar Gunjan , Pratt Erica , Santana Steven , Rubin Mark , Bander Neil , Navarro Vincent , Tagawa Scott , Kirby Brian , Nanus David , Giannakakou Paraskevi 
Published: June 2012

Abstract
Prostate cancer (PC) is the most common type of cancer in males and the second leading cause of male cancer deaths in the United States. Circulating tumor cells (CTCs) are commonly found in the blood of metastatic patients and the capture of these cells is important in the study of disease progression. We have developed a geometrically enhanced differential immunocapture (GEDI) microfluidic device coated with the prostate-specific membrane antigen (PSMA) which captures prostate CTCs with high purity and efficiency. This device is designed with a staggered obstacle array in order to maximize the capture efficiency (&gt;80%) and purity (70%) of CTCs. We have used this device to capture, enumerate and molecularly characterize CTCs isolated from 1 ml of blood from patients with castrate resistant prostate cancer (CRPC). First, we compared the capture efficiency from 16 CRPC patients’ blood and subjected it to CTC enumeration by either the GEDI device or the FDA approved CellSearch technology (EpCAM-based immunocapture). Our results showed a 2-350 fold enrichment in CTC counts by the GEDI (range 15-1200 CTCs/ml, median 54). In addition, there was minimal false positive CTC detection in healthy donor blood analyzed by the GEDI. Next we sought to characterize the captured CTCs using multiplex immunofluorescence for proteins specific for PC like androgen receptor (AR), PSMA, TMPRSS2-ERG, EpCAM and other markers involved in epithelial to mesenchymal transition (EMT). We observed low or lack of EpCAM expression in the captured PSMA+/CD45- CTCs, concomitant with high vimentin expression, suggesting that our device may be preferentially capturing CTCs that have undergone EMT. Using the GEDI device, we are able to detect a known single point mutation in the AR using cDNA extracted from approximately 50 C4-2 cells spiked into 1 ml of blood from a healthy donor. Importantly, we have captured CTCs from different CRPC patients and treated them ex vivo with docetaxel to assess effective drug-target engagement by determining the extent of microtubule (MT) stabilization and apoptotic cell death. Our results showed non-uniform CTC response to drug treatment, such that a subset of PSMA+/CD45- CTCs showed MT bundling, indicating tumor heterogeneity and further suggesting that we can potentially use this device to predict patient response to taxane-based chemotherapy. In summary, the GEDI microfluidic device is a novel and specific technology to isolate and characterize PC CTCs at the molecular level. We plan to use this device in prospective clinical studies in order to understand the molecular basis of disease progression and response to taxane-based chemotherapy.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4891. doi:10.1158/1538-7445.AM2011-4891