Most cancer deaths are caused by metastases, which are the end-results of circulating tumor cells (CTC) that detach from the cancer primary and succeed to survive in distant organs. The aim of the present study was to develop a gene signature of CTC and to assess its prognostic relevance after surgery for pancreatic ductaladenocarcinoma (PDAC).
A negative depletion fluorescence activated cell sorting (FACS) procedure was developed and validated with spiking experiments using cancer cell lines in whole human blood samples. This FACS-based method was used to enrich for CTC from the blood of 10 patients who underwent surgery for PDAC. Total RNA was isolated from 4 subgroup samples, i.e. CTC, haematological cells (G), original tumor (T), and non-tumoral pancreatic control tissue (P). After RNA quality control, samples of 6 patients were eligible for further analysis. Whole genome microarray analysis was performed after double linear amplification of RNA. The ‘Ingenuity Pathway Analysis’ software and AmiGO were used for functional data analyses. A CTC gene signature was developed and validated with the nCounter system on expression data of 78 primary PDAC using Cox regression analysis for disease-free (DFS) and overall survival (OS).
Using stringent statistical analysis, we finally retained 8,152 genes to compare expression profiles of CTC vs. other subgroups, and found 1,059 genes to be differentially expressed. The pathway with the highest expression ratio in CTC was p38 mitogen-activated protein kinase (p38 MAPK) signaling, known to be involved in cancer cell migration. In the p38 MAPK pathway TGF-β1, cPLA2, and MAX were significantly upregulated. In addition, 9 other genes associated with both p38 MAPK signaling and cell motility were over-expressed in CTC. High co-expression of TGF-1 and our cell motility panel (≥ 4 out of 9 genes for DFS and ≥ 4 out of 9 genes for OS) in primary PDAC was identified as an independent predictor of DFS (p=0.041, HR (95% CI) = 1.885 (1.025 – 3.559)) and OS (p=0.047, HR (95% CI) = 1.366 (1.004 – 1.861)).
Pancreatic CTC isolated from blood samples using a FACS-based negative depletion method,express a cell motility gene signature. The expression of this newly defined cell motility gene signature in the primary tumor is able to predict survival of patients who undergo surgical resection for pancreatic cancer.
Overall design: Total RNA was isolated from circulation tumor samples (CTC), haematological cells (G), original tumor (T), and non-tumor pancreatic control tissue (P) of patients with pancreatic ductal adenocarcinoma (PDAC). Gene expression profiles of CTC were compared to G, T, and P. The aim of the current study was to develop a ‘negative depletion strategy’ to isolate CTC without the exclusion of any particular subset of CTC, and to study their gene-expression profiles in order to find novel therapeutic targets and prognostic markers in patients with pancreatic cancer.
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