CD73 as a therapeutic target of pancreatic neuroendocrine tumor stem cells

Background: Identification and purification of cancer stem cells (CSCs) lead to new therapeutic targets; however, there has been no study to identify and isolated pancreatic neuroendocrine tumor (pNET) CSC. Therefore the clinical significance and its target remain unknown. This study aimed to identify pNET CSCs and characterize therapeutic candidate for pNET CSCs. Methods: We isolated CSCs sorting by ALDH activity in pNET surgical section and cell lines. We verified whether these cells have the property of stemness in vivo and in vitro. Additionally in order to acquire CSC gene profile, genome-wide gene expression profiles were investigated using a microarray technique. Results: ALDHhigh cells, but not control bulk cells, formed spheres, proliferated in hypoxia as well as normoxia and promoted cell motility, which are features of CSCs. Injection of as few as 10 ALDHhigh cells led to subcutaneous tumor formation, and 105 ALDHhigh cells established metastases but not control bulk cells in mice. Comprehensive gene expression analysis revealed that genes associated with mesenchymal stem cell, including CD73, and epithelial-mesenchymal transition (EMT) were overexpressed in ALDHhigh cells. APCP, which is CD73 inhibitor, inhibited sphere formation and cell motility in ALDHhigh cells in vitro, and tumor growth inhibition were observed in ALDHhigh cells in vivo. Conclusions: We identified ALDHhigh cells of pNET and elucidated that they have stemness property. Furthermore we identified CD73 as a target of ALDHhigh cells. CD73 is a promising novel target of pNET CSCs. Human pNET cell line QGP1 was obtained from Health Science Research Resources Bank (Osaka, Japan). Comprehensive gene expression analysis in ALDHhigh pNET cells was performed to acquire the CSC gene profile. The gene expression changes in 185 probe sets were found by microarray analysis (fold-change value > 2 between ALDHhigh pNET and control cells). Genes associated with mesenchymal stem cell, including CD73 (5'-nucleotidase, ecto) and CD109, and epithelial-mesenchymal transition (EMT), including caveolin1 (CAV1) and SLUG (SNAI2) were overexpressed in ALDHhigh cells.