Cancer stem-like cells of nasopharyngeal carcinoma express CXCR4 and display highly invasive activity

Abstract: Background: Nasopharyngeal carcinoma (NPC) patients with distant metastasis have a poor response to conventional first-line chemoradiotherapy and a poor prognosis. Growing evidence suggests that a subpopulation of cancer stem cells (CSCs) with certain markers is essential for cancer metastasis. However, the unique subset of CSCs that drives NPC metastasis is still unclear. Methods: Immunohistochemistry was used to analyze the expression characteristics, distribution and relationship of CXCR4 with clinical parameters in nasopharyngeal carcinoma. The expression characteristics of CD133 and CXCR4 in nasopharyngeal carcinoma tumorspheres were analyzed by flow cytometry. Through a magnetic activated cell sorting system, CXCR4-positive and CXCR4-negative tumorsphere cells were obtained, and then, the differences in invasion (in vitro and in vivo), metastatic tumor formation, stemness and EMT characteristics of the two cell types were compared. SDF-1 and its inhibitor were used to explore the roles of stromal-cell derived factor-1 (SDF-1) in the metastatic process. Results: In 71 cases of human nasopharyngeal carcinoma, CXCR4 expression was correlated with T stage and N stage. The CXCR4-positive rate of the tumor cells in the T3-4 group was higher than that in the T1-2 group (60.6% vs 28.9%, P =0.009), and that in the N2-3 group was higher than that in the N0-1 group (76.5% vs 13.5%, P=0.000). The CXCR4 expression level was higher in cells with high metastasis or low differentiation. The culture of tumor spheres enriched CD133-positive and CXCR4-positive cells, and most CD133-positive cells also expressed CXCR4 in NPC. The secondary tumorsphere-forming rate of the CXCR4-positive tumorsphere cells was higher than that of the CXCR4-negative tumorsphere cells, and most of the CXCR4-positive tumorsphere cells had a spindle morphology. The CXCR4-positive tumorsphere cells had stronger migration and invasion ability in vitro and metastatic tumor formation ability in mice, which depends on the SDF-1/CXCR4 axis, than the CXCR4-negative tumorsphere cells.Compared with those of the CXCR4-negative tumorsphere cells, the mRNA expression levels of Oct4, Nanog, Sox2, Snail, Twist, Vimentin and N-cadherin in the CXCR4-positive tumor tumorsphere cells were increased, while E-cadherin decreased, and the protein expression levels of Vimentin and N-cadherin increased, while that of E-cadherin decreased. Conclusion: Therefore, CXCR4 may be a marker of nasopharyngeal metastatic tumor stem cells, and CXCR4 may be involved in tumor stem cell migration and invasion by regulating the EMT process. These results suggest that targeting the SDF1/CXCR4 axis may interfere with nasopharyngeal carcinoma tumor stem cell migration and invasion and provide new treatment strategies.