Epithelial-to-mesenchymal transition leads to disease-stage differences in circulating tumor cell detection and metastasis in pre-clinical models of prostate cancer
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Lori E. Lowes1, David Goodale3, Ying Xia3, Carl Postenka3, Matthew M. Piaseczny1, Freeman Paczkowski3, Alison L. Allan1,2,3,4
1Department of Anatomy & Cell Biology, Schulich School of Medicine and Dentistry, Western University, London ON, Canada
2Department of Oncology, Schulich School of Medicine and Dentistry, Western University, London ON, Canada
3London Regional Cancer Program, London Health Sciences Centre, London ON, Canada
4Lawson Health Research Institute, London ON, Canada
Alison L. Allan, email: [email protected]
Keywords: prostate cancer, circulating tumor cells, epithelial-to-mesenchymal transition, metastasis, pre-clinical models
Received: July 14, 2016 Accepted: September 29, 2016 Published: October 15, 2016
Metastasis is the cause of most prostate cancer (PCa) deaths and has been associated with circulating tumor cells (CTCs). The presence of ≥5 CTCs/7.5mL of blood is a poor prognosis indicator in metastatic PCa when assessed by the CellSearch® system, the “gold standard” clinical platform. However, ~35% of metastatic PCa patients assessed by CellSearch® have undetectable CTCs. We hypothesize that this is due to epithelial-to-mesenchymal transition (EMT) and subsequent loss of necessary CTC detection markers, with important implications for PCa metastasis. Two pre-clinical assays were developed to assess human CTCs in xenograft models; one comparable to CellSearch® (EpCAM-based) and one detecting CTCs semi-independent of EMT status via combined staining with EpCAM/HLA (human leukocyte antigen). In vivo differences in CTC generation, kinetics, metastasis and EMT status were determined using 4 PCa models with progressive epithelial (LNCaP, LNCaP-C42B) to mesenchymal (PC-3, PC-3M) phenotypes. Assay validation demonstrated that the CellSearch®-based assay failed to detect a significant number (~40-50%) of mesenchymal CTCs. In vivo, PCa with an increasingly mesenchymal phenotype shed greater numbers of CTCs more quickly and with greater metastatic capacity than PCa with an epithelial phenotype. Notably, the CellSearch®-based assay captured the majority of CTCs shed during early-stage disease in vivo, and only after establishment of metastases were a significant number of undetectable CTCs present. This study provides important insight into the influence of EMT on CTC generation and subsequent metastasis, and highlights that novel technologies aimed at capturing mesenchymal CTCs may only be useful in the setting of advanced metastatic disease.
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