Comparative testing of various pancreatic cancer stem cells results in a novel class of pancreatic-cancer-initiating cells

No systemic therapy is effective against pancreatic cancer (PC). Pancreatic cancer stem cells (PCSC) are hypothesized to account for therapeutic resistance. Several PCSC subpopulations were reported, each characterized by different markers. To be able to target PCSC, we sought to better define this putative heterogeneity. Therefore, we tested most of the known putative PCSC markers in established and fresh tumor cell lines. CD20, CD24, CD44, CD133, CD184 (CXCR4), CD326 (EpCam, ESA), Sox-2, OCT 3/4, and the side-population (SP) were tested in five PC cell lines, and the effects of confluency, hypoxia, radiation, and gemcitabine on the SP. The testing phase suggested several putative PCSC populations that were further tested and validated for their tumor-initiating capacity against known PCSC in 3 established and 1 fresh PC cell lines. Cell surface and intracellular markers showed significant variability among cell lines. SP was the only common marker in all cell lines and consistently less than 1%. SP response to confluence, hypoxia, radiation, and gemcitabine was inconsistent between cell lines. The initial testing phase suggested that SP/CD44-CD24-CD326+ cells might be a novel PCSC subpopulation. Tumor initiation capacity tests in nude mice confirmed their increased tumorigenicity over previously reported PCSC. Our data better define the heterogeneity of reported PCSC in cell lines tested in this study. We propose that prior to targeting PC via PCSC, one will need to gain more insight into this heterogeneity. Finally, we show that SP/CD44-CD24-CD326+ cells are a novel subpopulation of pancreatic cancer tumor initiating cells. Further mechanistic studies may lead to better targeting of PC via targeting this novel PCSC.