CXCR4-Positive Subset of Glioma Is Enriched for Cancer Stem Cells

CXC chemokine receptor 4 (CXCR4) is a cell surface molecule expressed in a distinct subset of glioma cells with enhanced tumorigenicity, and it is related to many important biological activities of the tumor. We supposed that this receptor might be a cell surface marker for glioma stem cells. This hypothesis was tested both in vitro and in vivo. The CXCR4(+) and CXCR4(-) subsets were sorted from three human malignant glioma specimens. They were tested for the capability of colony formation in soft agar, generation of tumorosphere, self-renewal, and multipotent differentiation in vitro, and the capability of xenograft tumor in vivo. Drug and radiation resistance and coexpression with CD133 were studied for each subset. CXCR4 glioma cells, but not CXCR4(-) cells, were capable of generating tumorospheres in serum-free medium. In addition, these spheres were able to self-renew after passage, and had multipotent differentiation after being induced in serum-containing medium. In soft agar assay, CXCR4(+) cells generate much more colonies. The animal experiment revealed that CXCR4(+) subpopulation had stronger tumorigenicity than the unsorted parental glioma cells, while the CXCR4(-) cells did not generate xenograft tumor. CXCR4-possitive cells were more resistant to temozolomide and radiation treatment. Both CXCR4(+) and CXCR4- subsets contained very few CD133(+) cells. The CXCR4(+) subsets of glioma cells fulfill the standard of cancer stem cell.