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Abstract Objective Multiple myeloma is a haematological malignancy characterized by proliferation of monoclonal plasma cells in the bone marrow. Development of resistance and minimal residual disease remain challenging in the treatment of multiple myeloma. Transforming growth factor-β activated kinase 1 (TAK1) has recently gained attention as a potential drug target in multiple myeloma. This study aimed at determining the in vivo effects of TAK1-inhibitors in a Vκ*MYC multiple myeloma mouse model. Results We treated mice carrying Vκ*MYC multiple myeloma cells with the TAK1-inhibitors 5Z-7-oxozeaenol and NG25. There were tendencies towards increased survival for both inhibitors, but only NG25 prolonged survival significantly. However, this effect was limited, and no differences in disease burden were observed for any of the treatments. In conclusion, although TAK1-inhibitors might prolong survival somewhat, they do not prevent disease in the Vκ*MYC mouse model of multiple myeloma.

Abstract Elevated activity of bone-degrading osteoclasts (OC) contributes to pathological bone degradation in diseases such as multiple myeloma. Several proinflammatory cytokines, including TNF, contribute to osteoclastogenesis. The receptor-interacting protein kinase 1 (RIPK1) regulates inflammation and cell death. It is recruited to the TNF-receptor complex, where it is ubiquitinated, and activates transcription factor NF-κB and mitogen-activated protein kinases (MAPK). Smac-mimetics (SM) is a group of drugs that block RIPK1 ubiquitination and shifts RIPK1 to activation of apoptosis or necroptosis. In this manuscript, we show that the two SM birinapant and LCL-161 reduced the number and viability of primary human OC, and induced TNF-dependent cell death in OC precursors (pre-OC). Birinapant was more cytotoxic than LCL-161 and induced predominantly apoptosis and to some degree necroptosis. Both inhibitors restrained osteoclastogenesis induced by myeloma patient bone-marrow aspirates. SM has gained attention as novel treatment strategies both for cancer and chronic inflammatory pathologies, but limited information has been available on interactions with primary human immune cells. As LCL-161 is in phase 2 clinical studies for multiple myeloma, we propose that SM might possess additional benefits in reducing bone degradation in myeloma patients. Taken together, we show that SM reduces human osteoclastogenesis, and that these compounds may represent promising drug candidates for pathological bone degradation.