TrxR1 inhibition overcomes both hypoxia-induced and acquired bortezomib resistance in multiple myeloma through NF-kβ inhibition

Multiple myeloma (MM) is a B-cell malignancy characterized by an accumulation of abnormal clonal plasma cells in the bone marrow. Introduction of the proteasome-inhibitor bortezomib has improved MM prognosis and survival; however hypoxia-induced or acquired bortezomib resistance remains a clinical problem. This study highlighted the role of thioredoxin reductase 1 (TrxR1) in the hypoxia-induced and acquired bortezomib resistance in MM. Higher TrxR1 gene expression correlated with high-risk disease, adverse overall survival, and poor prognosis in myeloma patients. We demonstrated that hypoxia induced bortezomib resistance in myeloma cells and increased TrxR1 protein levels. Inhibition of TrxR1 using auranofin overcame hypoxia-induced bortezomib resistance and restored the sensitivity of hypoxic-myeloma cells to bortezomib. Hypoxia increased NF-k beta subunit p65 nuclear protein levels and TrxR1 inhibition decreased hypoxia-induced NF-k beta p65 protein levels in the nucleus and reduced the expression of NF-k beta-regulated genes. In addition, higher TrxR1 protein levels were observed in bortezomib-resistant myeloma cells compared to the naive cells, and its inhibition using either auranofin or TrxR1-specific siRNAs reversed bortezomib resistance. TrxR1 inhibition reduced p65 mRNA and protein expression in bortezomib-resistant myeloma cells, and also decreased the expression of NF-k beta-regulated anti-apoptotic and proliferative genes. Thus, TrxR1 inhibition overcomes both hypoxia-induced and acquired bortezomib resistance by inhibiting the NF-k beta signaling pathway. Our findings demonstrate that elevated TrxR1 levels correlate with the acquisition of bortezomib resistance in MM. We propose considering TrxR1-inhibiting drugs, such as auranofin, either for single agent or combination therapy to circumvent bortezomib-resistance and improve survival outcomes of MM patients.