The CXCR4-CXCL12 axis in Ewing sarcoma: promotion of tumor growth rather than metastatic disease

To gain insight into the role of the CXCR4-CXCL12 axis in Ewing sarcoma, CXCR4, CXCL12 and hypoxia-inducible factor-1α protein expression was studied in therapy-na？ve and metastatic tumors by immunohistochemistry. CXCR4 function was assessed in vitro, by flow cytometry and proliferation/ cell viability assays, in the presence of recombinant CXCL12 and/or CXCR4-antagonist AMD3100 or under hypoxic conditions.Whereas CXCR4 was predominantly expressed by tumor cells, CXCL12 was observed in both tumor and stromal areas. Survival analysis revealed an (expression level-dependent) negative impact of CXCR4 expression (p？<？0.04). A role for the CXCR4-CXCL12 axis in Ewing sarcoma growth was suggested by our observations that i) CXCR4 expression correlated positively with tumor volume at diagnosis (p？=？0.013), ii) CXCL12 was present within the microenvironment of virtually all cases, iii) CXCL12 induced proliferation of CXCR4-positive Ewing sarcoma cell lines, which could be abrogated by AMD3100. CXCR4 expression was not correlated with occurrence of metastatic disease. Also, therapy-na？ve tumors demonstrated higher CXCR4 expression as compared to metastases (p？=？0.027). Evaluation of in vivo hypoxia-inducible factor-1α expression and culture of cells under hypoxic conditions revealed no role for hypoxia in CXCR4 expression.Together, our results imply a crucial role for the CXCR4-CXCL12 axis in auto- and/or paracrine growth stimulation. Integration of CXCR4-targeting strategies into first- and/or second-line treatment regimens may represent a promising treatment option for Ewing sarcoma.The chemokine network, initially described as an essential mediator of directional cell migration in inflammation and immune cell homing, has become increasingly recognized as contributing to a broad spectrum of other physiological and pathological processes, including cancer [1]. Although cancers of different histological origin express different chemokine receptors and/or (corresponding) ligan