Data from Bortezomib-Resistant Nuclear Factor-κB Activity in Multiple Myeloma Cells
Stephanie MarkovinaNatalie S. CallanderShelby L. O’ConnorJihoon KimJae WerndliMartha RaschkoCatherine P. LeithBrad S. KahlKyungMann KimShigeki Miyamoto
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<div>Abstract<p>Bortezomib (Velcade/PS341), a proteasome inhibitor used in the treatment of multiple myeloma (MM), can inhibit activation of nuclear factor-κB (NF-κB), a family of transcription factors often deregulated and constitutively activated in primary MM cells. NF-κB can be activated via several distinct mechanisms, including the proteasome inhibitor–resistant (PIR) pathway. It remains unknown what fraction of primary MM cells harbor constitutive NF-κB activity maintained by proteasome-dependent mechanisms. Here, we report an unexpected finding that constitutive NF-κB activity in 10 of 14 primary MM samples analyzed is refractory to inhibition by bortezomib. Moreover, when MM cells were cocultured with MM patient-derived bone marrow stromal cells (BMSC), microenvironment components critical for MM growth and survival, further increases in NF-κB activity were observed that were also refractory to bortezomib. Similarly, MM-BMSCs caused PIR NF-κB activation in the RPMI8226 MM cell line, leading to increased NF-κB–dependent transcription and resistance to bortezomib-induced apoptosis. Our findings show that primary MM cells frequently harbor PIR NF-κB activity that is further enhanced by the presence of patient-derived BMSCs. They also suggest that this activity is likely relevant to the drug resistance development in some patients. Further elucidation of the mechanism of PIR NF-κB regulation could lead to the identification of novel diagnostic biomarkers and/or therapeutic targets for MM treatment. (Mol Cancer Res 2008;6(8):1356–64)</p></div>Keywords:
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Studies have shown that the 26S proteasome is involved in cell cycle control, transcription, DNA repair, immune response and protein synthesis. In the present study, we investigated the antiproliferative effects of the proteasome inhibitor bortezomib and heat shock protein (Hsp)70 inhibitors on the B16F10 melanoma cell line. The IC50 value of bortezomib was found to be 2.46 nM, while that of the Hsp70 inhibitor quercetin was 45 µM in the B16F10 cells. This indicates that bortezomib is more effective than quercetin in inhibiting cell growth. In response to treatment with 10 nM bortezomib for 24 h, cells underwent rounding, shrinkage and detachment. Unexpectedly, such morphological changes were not observed in cells treated with 20 µM quercetin alone, nor in cells treated with bortezomib + quercetin, indicating that quercetin inhibited the cytotoxic effects of bortezomib. Quantitation of cell viability also indicated that quercetin interfered with the cytotoxic effects of bortezomib. However, the combination of quercetin with another proteasome inhibitor, MG132, caused significant cell death as compared to single-agent treatment. A DNA ladder assay also confirmed the inhibitory effect of quercetin on the apoptosis-inducing effect of bortezomib. However, quercetin did not prevent the induction of apoptosis by MG132; on the contrary, it potentiated the apoptosis-inducing effect of MG132. These results suggest that the combination of quercetin with clinically beneficial proteasome inhibitors (except bortezomib) may have increased efficacy in the treatment of cancer. We also tested the combination of two other Hsp70 inhibitors, KNK-437 and schisandrin-B, in combination with bortezomib. Neither of these combinations was more effective than single-agent treatment.
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Multiple myeloma (MM) is a hematological malignancy caused by the clonal expansion ofbone marrow plasmacytes.It accounts for 10 ％ of all hematological malignancies.The proteasome,an intracellular enzyme complex that degrades ubiquitin-tagged proteins to regulate protein levels within the cell,plays an important role in maintaining cellular homeostasis.Proteasome inhibitors proved to be significantly effective in the clinical treatment of MM.In recent years,the application of the proteasome inhibitor has led to increased survival rates in MM patients.Bortezomib is the first proteasome inhibitor that has been approved by the US Food and Drug Administration due to its ability to reversibly inhibit the 26 s proteasome functions.Despite the fact that Bortezomib improves medical treatment,many patients experience difficulty responding to this drug and some patients who do respond eventually relapse.These results have led researchers to investigate new proteasome inhibitors with mechanisms different from those of Bortezomib.Some drugs that bind to the active site of the proteasome and irreversibly inhibit the complex have recently been developed and are currently being tested in advanced clinical trials.Here,we will elaborate on the proteasome inhibitors targeting MM and focus on newly discovered inhibitors that may overcome the resistance to Bortezomib.
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Mutiple myeloma; Proteasome inhibitor; Drug resistance
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The 26S proteasome is a multicatalytic enzyme responsible for degradation of a large fraction of intracellular proteins. Targeting the proteasome activity is a rational and novel strategy for cancer therapy that can lead to cell death for transformed cells. Today, bortezomib, a first-in-class proteasome inhibitor, has established clinical efficacy and an approved clinical indication for the treatment of relapsed and refractory multiple myeloma. Since bortezomib has also shown to induce chemosensitization, the drug is utilized for combination with a variety of chemotherapeutics. In this review, we provide an overview of the current state of the use of bortezomib and second generation proteasome inhibitors.
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The ubiquitin-proteasome pathway is one of important pathways during selective protein degradation,which participates in many intracellular physiological and biochemical processes.Bortezomib,a kind of proteasome inhibitor,can inhibit cell growth and proliferation,induce cell apoptosis and overcome drug resistance in chemotherapy.The mechanisms of bortezomib on the therapy of multiple myeloma are reviewed in this paper.
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Multiple myeloma; Proteasome inhibitor, Bortezomib; Therapy
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Bortezomib is a proteasome inhibitor with remarkable clinical antitumor activity in multiple myeloma (MM) and is under evaluation in clinical trials in various types of cancer including breast cancer. Although the initial rationale for its use in cancer treatment was the inhibition of NF-κB activity by blocking proteasomal degradation of IκBα, direct evidence indicating inhibition of constitutive NF-κB activity by bortezomib in tumor cells in patients has not yet been reported. Moreover, recent studies have shown that bortezomib activates constitutive NF-κB activity via stimulating the canonical pathway in MM cells. In this study, we first examined protein expression of IκBα after bortezomib treatment. We observed that bortezomib upregulated the phosphorylation and downregulated IκBα protein expression in a dose- and time-dependent manner in MCF7 and T47D cells, associated with phosphorylation of IKKβ. Since IκBα is an inhibitor of nuclear translocation of NF-κB, we further examined alteration of NF-κB activity by bortezomib. Importantly, bortezomib significantly upregulates NF-κB activity in both MCF7 and T47D in a dose-dependent fashion, demonstrated by electrophoretic mobility shift analysis (EMSA). Furthermore, immunocytochemical analysis confirmed enhanced nuclear translocation of p65 NF-κB (RelA) by bortezomib treatment. Supershift assay showed supershifted bands by anti-p65 and -p50 antibodies. Taken together, these results indicate that bortezomib activates the canonical NF-κB pathway in both cell lines. Finally, we demonstrated that IKKβ inhibitor enhanced cytotoxicity, associated with inhibition of NF-κB activity induced by bortezomib in MCF7 and T47D breast cancer cells.
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Probing the Specificity and Activity Profiles of the Proteasome Inhibitors Bortezomib and Delanzomib
The ubiquitin proteasome system is an attractive pharmacological target for the treatment of cancer. The proteasome inhibitor bortezomib has been approved for the treatment of multiple myeloma and mantle cell lymphoma but is associated with substantial adverse effects and the occurrence of resistance, underscoring the continued need for novel proteasome inhibitors. In this study, bortezomib and the novel proteasome inhibitor delanzomib were compared for their ability to inhibit proteasome activity using both fluorogenic substrates and a recently developed fluorescent proteasome activity probe. Bortezomib and delanzomib were equipotent in inhibiting distinct subunits of the proteasome in a panel of cell lines in vitro. In a preclinical multiple myeloma model, both inhibitors inhibited the proteasome in normal tissues to a similar extent. Tumor proteasome activity was inhibited to a significantly higher extent by delanzomib (60%) compared to bortezomib (32%). In addition, delanzomib was able to overcome bortezomib resistance in vitro. The present findings demonstrate that proteasome activity probes can accurately monitor the effects of proteasome inhibitors on both normal and tumor tissues in preclinical models and can be used as a diagnostic approach to predict resistance against treatment with proteasome inhibitors. Furthermore, the data presented here provide rationale for further clinical development of delanzomib.
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The anti-diabetic drug metformin is currently tested for the treatment of hematological and solid cancers. Proteasome inhibitors, e.g., Bortezomib, are approved for the treatment of multiple myeloma and mantle cell lymphoma but are also studied for lung cancer therapy. We here analyzed the interaction of the two drugs in two cell lines, namely the mantle cell lymphoma Jeko-1 and the non-small-cell lung cancer (NSCLC) H1299 cells, using proliferation and survival assays, native-gel analysis for proteasome activity and assembly, and expression analysis of proteasome assembly factors. Our results demonstrate that metformin treatment induces resistance of cancer cells to the proteasome inhibitor Bortezomib by impairing the activity and assembly of the 26S proteasome complexes. These effects of metformin on proteasome inhibitor sensitivity in cancer cells are of potential relevance for patients that receive proteasome inhibitor therapy.
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The proteasome inhibitor bortezomib is clinically approved for the treatment of multiple myeloma. Recently, we demonstrated that bortezomib eliminates autoreactive plasma cells in SLE mice, thereby representing a promising novel treatment for antibody-mediated diseases. Here, we investigated the effect …
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