High cholesterol increases myeloma tumour burden and promotes resistance to bortezomib

Multiple myeloma (MM) is an incurable hematologic cancer where malignant plasma cells accumulate in the bone marrow (BM), with disease progression highly dependent on cellular interactions. Obesity is a major risk factor for myeloma, however the underlying mechanisms are unclear. Here we used a murine myeloma model to show that a high cholesterol diet increases local and circulating levels of low density lipoprotein cholesterol (LDL), increasing bone marrow tumour burden in vivo. Exogenous LDL induced bortezomib-specific drug resistance in metabolically stressed myeloma cells in vitro and ex vivo. RNA-seq analysis revealed bortezomib-induced changes in the cholesterol biosynthesis/homeostasis pathway that were completely reverted with LDL pretreatment. In silico analysis of patient data supported a role for cholesterol in response to bortezomib-based therapies. Targeted proteome profiling revealed changes in expression of the adipokine resistin in the bone marrow of cholesterol-treated or myeloma-bearing mice, with elevated resistin expression observed in MGUS patients. Bone marrow adipocytes were found to be a major source of resistin, which was further increased in response to LDL. In summary, we demonstrate that high cholesterol promotes both myeloma development and bortezomib resistance, identifying resistin as a potential mediator so revealing new mechanisms underlying myeloma pathogenesis.