CXCR4 Is a Regulator Of Disease Involvement Of Extramedullary Myeloma Confirmed By a Novel Mouse Model For Extramedullary Disease

Extramedullary disease (EMD) in patients with multiple myeloma occurs mostly in advanced disease or relapse. EMD seems to have a different pathogenesis from medullary myeloma and is often characterized by a more aggressive clinical course. To date molecular mechanisms of development of EMD have not been fully understood. Methods: Human MM cell lines, IM-9 and MM1S were serially selected in immune-deficient mice. IM-9 and MM1S cells were inoculated intravenously and harvested from the tumors developed in the bone marrow (BM) and liver (site of extramedullary disease), aiming to establish BM-prone and liver-prone clones. Tumor progression was periodically checked by bioluminescence (BLI) and in vivo live confocal imaging. After three rounds of in vivo selections, the cells of both BM- and liver-prone were characterized by gene and protein expression and cellular functional assays. Results: We obtained three liver-prone sub-clones in both IM-9 and MM1S after serial in vivo selections. These cells had equal proliferation rates in vitro compared to the original or BM-prone cells, but exhibited more aggressive phenotype in vivo. Liver-prone clones had significantly higher migration ability than BM-prone clones (11.6% vs 6.1% migration, respectively p=0.018). Gene and protein expression analysis revealed that each liver-prone clone had a higher expression of sets of chemokine receptors specifically CXCR4. Using thein vivo metastatic model CXCR4-over expressing myeloma cells exhibited higher metastatic property to the extramedullary organs whereas CXCR4-knockdown cells has less tumor metastasis to the liver. Discussion: We established EMD-prone human multiple myeloma cell lines that reproducibly developed liverinvolvement consistent with human extramedullary disease. These cells exhibited higher migratory ability and increased expression of several chemokine receptors, specifically CXCR4. We validated the effect of CXCR4 on developing extramedullary myeloma using our established in vivo mode. Further studies to determine the role of CXCR4 for therapeutic targeting of extramedullary disease in MM are ongoing.

Ghobrial:Sanofi: Research Funding; Noxxon: Research Funding; BMS: Advisory board, Advisory board Other, Research Funding; Onyx: Advisoryboard Other.