Epithelial and mesenchymal pancreatic cancer cells exhibit different stem cell phenotypes being associated with different metastatic propensity
Pancreatic ductal adenocarcinoma (PDAC) is the most common malignant pancreatic tumor in western countries, characterized by a low 5-year survival rate of only 11 %. Owing to a lack of early and specific symptoms, most patients are diagnosed at advanced or even me-tastasized stages essentially impairing treatment efficacy. Metastatic outgrowth requires a high plasticity of tumor cells implying phenotypic switching in response to changing envi-ronments. One important process leading to phenotypic switching is the Epithelial-Mesenchymal-Transition (EMT) and its reversion, the Mesenchymal-Epithelial-Transition (MET). This process has been associated with the gain of cancer stem cell (CSC) properties being regarded as drivers of tumor initiation at primary and secondary sites. Still, it is poorly understood whether different CSC phenotypes exist along the EMT/MET axis and how these impact malignancy associated properties. Thus, this study aimed to characterize CSC popula-tions of epithelial and mesenchymal PDAC cells and how these relate to functional pheno-types.  Methods: For this purpose, single-cell-cloning of the two PDAC cell lines Panc1 and Panc89 was performed to isolate and expand CSC- (Holoclone cells) and non-CSC (Paraclone cells) clones. Cell variants were characterized regarding cell growth, migration, invasion, cell ad-hesion and tumorigenicity. Results: Panc1 Holoclone cells showed a mesenchymal phenotype dominated by high ex-pression of the stemness marker Nestin, while Panc89 Holoclone cells exhibited an epitheli-al phenotype with elevated expression of the stemness marker SOX2. Moreover, Panc89 Holoclone cells showed enhanced cell growth and colony formation ability compared to Panc1 Holoclone cells. In contrast, slowly proliferating Panc1 Holoclone cells were highly invasive, while Panc89 Holoclone cells showed a slow cluster-like invasion. In line with these findings, a higher number of metastases was formed by Panc1 Holoclone cells in vivo. How-ever, Panc89 Holoclone cells led to formation of larger tumors limiting survival of inoculated mice. Moreover, epithelial and mesenchymal CSC-clones showed clear differences with re-spect to organ manifestation. Conclusion: Overall, these data support the view of different CSC phenotypes in PDAC cells that are linked to distinct EMT/MET phenotypes and that manifest in a different metastatic propensity. Overall design: Single-cell-cloning of the two PDAC cell lines Panc1 and Panc89 was performed to isolate and expand CSC- (Holoclone cells) and non-CSC (Paraclone cells) clones. Gene expression of the parental, holocone and paraclone cell lines were quantified by RNA-seq in triplicates.