CXCL12 does not attract CXCR4+ human metastatic neuroblastoma cells: Clinical implications

Purpose: The role of CXCR4 in bone marrow localization of neuroblastoma cells has been recently proposed. The aim of this study was to investigate the expression and chemotactic functionality of CXCR4 in human metastatic neuroblastoma cells isolated from the bone marrow and, for comparison, in a panel of neuroblastoma cell lines. Experimental Design: CXCR4 expression and chemotactic functionality were investigated in metastatic neuroblastoma cells isolated from patient bone marrow and in neuroblastoma cell lines. The former cells were isolated as CD45^- or GD2⁺ cells by immunomagnetic bead manipulation. Chemotactic assays were done in a transwell system. Regulator of G protein signaling expression was investigated by reverse transcription-PCR. Results: Metastatic neuroblastoma cells consistently expressed CXCR4, which was also detected in 5 of 10 neuroblastoma cell lines. CXCL12 did not stimulate the chemotaxis of primary tumor cells or cell lines in either normoxia or hypoxia, irrespective of CXCR4 up-regulation detected under the latter condition. Accordingly, neuroblastoma cells failed to modulate filamentous actin and to activate mitogen-activated protein kinase upon treatment with CXCL12. RGS16 mRNA was consistently expressed in primary tumor cells and cell lines, but its down-regulation by RNA interference did not restore CXCR4 chemotactic functionality. Conclusions: These results show unambiguously that CXCR4 expressed in human metastatic neuroblastoma cells is not functional and do not support the clinical use of CXCR4 antagonists to prevent neuroblastoma metastasis.