A Study On Identification Of The Stemness Properties Of CD44~+Gastric Cancer Cells And Verification Its Invasiveness-related Roles In Gastric Cancer

Objective: Gastric cancer is a highly malignant tumor, mainly due tothe progress of the inspection techniques, some gastric cancers can bediscovered in its early-stage, so that the overall mortality rate of gastriccancer declined. However, gastric cancer patients with advanced diseaseare still a lack of effective treatment, the5-year survival rate is notoptimistic. With the establishment of cancer stem cell theory since1990sand its related research reveals that the vast majority of malignant tumorsare originated from cancer stem cells. Therefore, studies on gastric cancerstem cells are seems to be particularly important for cancer prevention andtreatment; CD44as a cancer stem cell marker had been confirmed in avariety of human cancer cell lines and primary tumors, but whether thismarker is applicable to gastric cancer still unknown. The responses ofCD44+gastric cancer stem-like cells to chemoradiation and the roles theyplay in cancer invasion are not well understood.Methods: In the present study, cell sorting was applied to the poorly differentiated human GC cells to isolate a pure concentration of the CD44+cell populations. The stemness properties of CD44+cell fraction wereconfirmed by two “gold standard” methods; an in vivo tumorigenicityassay and in vitro spheroid colony formation assay. In addition, thetreatment response was evaluated in CD44+and CD44-cell fractions thatunderwent chemoradiation. Furthermore, we conducted the transwellmatrix invasion assay in vitro to compare invasion ability in both cellfractions. Finally, we terminated our experiment by comparison theexpression of cancer invasion-related gene matrix metalloproteinase2(MMP2), Epidermal growth factor receptor (EGFR) in CD44+and CD44-GC cells.Results: Primary GC cells contain a few CD44+cells with stemnessproperties. In general, CD44+stem-like cells tended to respond morepoorly to chemoradiation than their non-stem-like counterparts. Furtherexperimentation revealed that CD44+stem-like cells that recorded positivescores in the migration and invasion assay in vitro formed invasive tumoursin vivo. Therefore, we hypothesized that CD44+stem-like cells maysignificantly express invasion-associated gene. Consistent with thisprediction, increased expression of cancer invasion-associated genes matrixmetalloproteinase-1(MMP1), matrix metalloproteinase-2(MMP2), andepidermal growth factor receptor (EGFR) and cyclooxygenase2(COX-2)were detected in CD44+stem-like cells. Conclusion: CD44+gastric cancer stem cells are likely to be theinitiator of chemoradiotherapy resistance occurred in the treatment ofgastric cancer and may be responsible for cancer invasiveness andmetastasis. By selectively eliminating CD44+stem-like cells, it would belikely to treat patients with aggressive, non-resectable gastric cancers, aswell as preventing the tumour from metastasizing.