Rhabdomyosarcoma (RMS) and skeletal muscle-derived tumors frequently infiltrate bone marrow (BM). We have demonstrated that the stromal-derived factor (SDF)-1-CXCR4 receptor (

) and Leukemia Inhibitory Factor (LIF)-LIF- receptor (LIF-R) axes play a pivotal role in RMS metastasis to BM. In this study performed on primary patient material (n=23) and human alveolar and embryonal RMS cell lines, we compared various prometastatic effects of both axes. First, we found that both motomorphogens (LIF and SDF-1) and their corresponding receptors (LIF-R and CXCR4) are upregulated in hypoxic conditions. Second, both functional receptors were expressed on RMS cells; however, the expression of LIF-R in contrast to CXCR4 was PAX3-FKHR-independent and did not correlate with the alveolar rhabdomyosarcoma (ARMS) phenotype. Both ligands stimulated similar signaling pathways (MAPKp42/44 and AKT) in RMS cells and similarly stimulated directional chemotaxis. However, SDF-1 affected the spontaneous motility of RMS cells to a higher degree than LIF and strongly upregulated the secretion of MMPs and VEGF. In contrast, LIF enhanced the resistance of RMS cells to cytostatics (e.g., etoposide). To compare the biological effects of both axes we focused on the ARMS cell line RH30 (highly responsive to SDF-1 and LIF) and selected cells that responded to SDF-1 but not LIF (RH30-S) and to LIF but not SDF-1 (RH30-L) by using repetitive chemotaxis to SDF-1 or LIF. We found that RH30-L cells, as compared to RH30-S cells, responded worse in chemotactic assay to BM-derived conditioned media; however, they adhered much better to BM stroma. When both cell populations (RH30-S and RH30-L), together with the parental RH30 cells, were tested in vivo for their seeding potential in various organs in RAG2 immunodeficient mice, we found that RH30-L cells seeded better to BM, liver and lymph nodes than RH30-S cells. More important, the metastatic potential of RH30 cells was significantly reduced only when the inhibitors of both receptors, (T140 for LIF-R and gp130 blocking antibody for CXCR4) were employed together. Hence, since RMS cells respond to more than one chemoattractant, strategies aimed at targeting a single factor-receptor axis would be ineffective. Targeting of the LIF-LIF-R axis, along with the SDF-1-CXCR4 axis, could thus become a new, more effective antimetastatic strategy to inhibit RMS metastasis.

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