Isolation of cancer progenitor cells from cancer stem cells in gastric cancer.

The success of cancer treatment may depend on the complete elimination of cancer stem cells (CSCs). However, data regarding the current characterization of CSCs in different types of tumor are inconsistent, possibly due to the mixture of CSCs with cancer progenitor cells (CPCs). Therefore, it is important to exclude CPCs for the characterization of CSCs. The present study aimed to characterize gastric cancer stem cells (GCSC) by separating GCPC from gastric progenitor cells (GCSC) with flow cytometry. In total, 615 murine gastric cancer (GC) cells were divided into aldehyde dehydrogenase (ALDH)(high), ALDH(low) and ALDH(neg) groups by flow cytometry according to their ALDH activity. With decreased ALDH activity, the expression levels of stemness-associated markers, CD133(+), octamer-binding transcription factory-4 and sex determining region Y-box 2 decreased. The ALDH(high) and ALDH(low) cells proliferated and formed tumor spheres in ultra-low adhesion medium without serum, however, the latter formed larger tumor spheres. In mice transplanted with 5,000 cells, the rate of tumor formation in the ALDH(low) group was significantly higher, compared with that in the ALDH(high) group. Of note, an increased number of mice developed tumors in the ALDH(high) group 16 weeks following the injection of 500 cells, whereas tumors appeared at 8 weeks in the ALDH(low) group. The mice in the ALDH(neg) group exhibited less tumor formation under these conditions. These results demonstrated that ALDH(high) cells had characteristics of GCSCs with a high level of self-renewal ability, but were in a relative resting stage. The ALDH(low) cells had characteristics of GCPCs with limited self-renewal ability, but were in a rapid proliferation stage. These findings suggested that the separation of GCPCs from GCSCs is important for elucidating the biology of GCSCs and identifying strategies to eliminate GCSCs in GC.