Redox homeostasis modulates the sensitivity of myeloma cells to bortezomib

In Vitro Low-Bortezomib Doses Induce Apoptosis and Independently Decrease the Activities of Glutathione S-Transferase and Glutathione Peroxidase in Multiple Myeloma, Taking into Account the GSTT1 and GSTM1 Gene Variants

BACKGROUND

Multiple myeloma (MM) is a malignancy derived from plasma cells. Bortezomib affects the concentration of reduced glutathione (GSH) and the activity of glutathione enzymes. The aim of our study was to analyze deletion (null/present) variants of GSTT1 and GSTM1 genes and their association with the levels of glutathione and its enzymes in bortezomib-treated cell cultures derived from MM patients.

MATERIALS AND METHODS

This study included 180 individuals (80 MM patients and 100 healthy blood donors) who were genotyped via multiplex PCR (for the GSTT1/GSTM1 genes). Under in vitro conditions, MM bone marrow cells were treated with bortezomib (1-4 nM) to determine apoptosis (via fluorescence microscopy), GSH concentration, and activity of glutathione enzymes (via ELISA).

RESULTS

Bortezomib increased the number of apoptotic cells and decreased the activity of S-glutathione transferase (GST) and glutathione peroxidase (GPx). We found significant differences in GST activity between 1 nM (GSTT1-null vs. GSTT1-present), 2 nM (GSTT1-null vs. GSTT1-present), and 4 nM (GSTM1-null vs. GSTM1-present) bortezomib: 0.07 vs. 0.12, p = 0.02; 0.06 vs. 0.10, p = 0.02; and 0.03 vs. 0.08, p = 0.01, respectively.

CONCLUSIONS

Bortezomib affects the activities of GST and GPx. GST activity was associated with GSTT1 and GSTM1 variants but only at some bortezomib doses.

Cytotoxic and Apoptotic Effects of Pinostilbene and Bortezomib Combination Treatment on Human Multiple Myeloma Cells

Multiple myeloma (MM) is a cancer of plasma cells in the bone marrow characterized by bone lesions, hypercalcemia, anemia, and renal failure. Bortezomib (BTZ), a common treatment for MM, is a proteasome inhibitor that induces apoptosis in MM cells. However, high doses of BTZ can be very toxic, signifying a need for a synergistic drug combination to improve treatment efficacy. Resveratrol (RES), a phenolic compound found in grapes, has been shown to inhibit MM cell growth. We sought to identify a synergistic combination of BTZ with a RES derivative and analyze the effects on reducing viability and inducing apoptosis in human MM cells. BTZ as well as RES and its derivatives pinostilbene (PIN) and piceatannol (PIC) decreased MM cell viability in a dose- and time-dependent manner and increased expression of cleaved proapoptotic proteins poly(ADP-ribose) polymerase 1 (PARP1) and caspase-3 in a dose-dependent manner. The combination of 5 nM BTZ and 5 μM PIN was identified to have synergistic cytotoxic effects in MM RPMI 8226 cells. MM RPMI 8226 cells treated with this combination for 24 h showed increased cleaved PARP1 and caspase-3 expression and higher percentages of apoptotic cells versus cells treated with the individual compounds alone. The treatment also showed increased apoptosis induction in MM RPMI 8226 cells co-cultured with human bone marrow stromal HS-5 cells in a Transwell model used to mimic the bone marrow microenvironment. Expression of oxidative stress defense proteins (catalase, thioredoxin, and superoxide dismutase) in RPMI 8226 cells were reduced after 24 h treatment, and cytotoxic effects of the treatment were ameliorated by antioxidant N-acetylcysteine (NAC), suggesting the treatment impacts antioxidant levels in RPMI 8226 cells. Our results suggest that this combination of BTZ and PIN decreases MM cell viability synergistically by inducing apoptosis and oxidative stress in MM cells.

Ferroptosis in Haematological Malignancies and Associated Therapeutic Nanotechnologies

Haematological malignancies are heterogeneous groups of cancers of the bone marrow, blood or lymph nodes, and while therapeutic advances have greatly improved the lifespan and quality of life of those afflicted, many of these cancers remain incurable. The iron-dependent, lipid oxidation-mediated form of cell death, ferroptosis, has emerged as a promising pathway to induce cancer cell death, particularly in those malignancies that are resistant to traditional apoptosis-inducing therapies. Although promising findings have been published in several solid and haematological malignancies, the major drawbacks of ferroptosis-inducing therapies are efficient drug delivery and toxicities to healthy tissue. The development of tumour-targeting and precision medicines, particularly when combined with nanotechnologies, holds potential as a way in which to overcome these obstacles and progress ferroptosis-inducing therapies into the clinic. Here, we review the current state-of-play of ferroptosis in haematological malignancies as well as encouraging discoveries in the field of ferroptosis nanotechnologies. While the research into ferroptosis nanotechnologies in haematological malignancies is limited, its pre-clinical success in solid tumours suggests this is a very feasible therapeutic approach to treat blood cancers such as multiple myeloma, lymphoma and leukaemia.

Hypoxia-induced oxidative stress promotes therapy resistance via upregulation of heme oxygenase-1 in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is a hematopoietic malignancy for which proteasome inhibitors have become available in recent years. However, many patients develop resistance to these drugs during treatment. Therefore, it is important to elucidate the mechanisms underlying resistance acquisition by proteasome inhibitors. Side population (SP) cells, which have a high drug efflux capacity and hypoxic responses in the microenvironment have both provided important insights into drug resistance in MM; however, little is known about the characteristics of SP cells in hypoxic microenvironments.

METHODS

We performed cDNA microarray analysis for SP and non-SP obtained from RPMI-8226 and KMS-11 cell lines cultured for 48 h in normoxic and hypoxic conditions (1% O₂ ). Genes specifically upregulated in hypoxic SP were examined.

RESULTS

Our comprehensive gene expression analysis identified HMOX1, BACH2, and DUX4 as protein-coding genes that are specifically highly expressed in SP cells under hypoxic conditions. We have shown that HMOX1/heme oxygenase-1 (HMOX1/HO-1) is induced by hypoxia-inducible reactive oxygen species (ROS) and reduces ROS levels. Furthermore, we found that HMOX1 contributes to hypoxia-induced resistance to proteasome inhibitors in vitro and in vivo. Excessive ROS levels synergistically enhance bortezomib sensitivity. In clinical datasets, HMOX1 had a strong and significantly positive correlation with MAFB but not MAF. Interestingly, hypoxic stimulation increased MAFB/MafB expression in myeloma cells; in addition, the knockdown of MAFB under hypoxic conditions suppressed HMOX1 expression.

CONCLUSION

These results suggest that the hypoxia-ROS-HMOX1 axis and hypoxia-induced MafB may be important mechanisms of proteasome inhibitor resistance in hypoxic microenvironments.

RARγ activation sensitizes human myeloma cells to carfilzomib treatment through the OAS-RNase L innate immune pathway

Proteasome inhibitors (PIs) such as bortezomib (Btz) and carfilzomib (Cfz) are highly efficacious for patients with multiple myeloma (MM). However, relapses are frequent, and acquired resistance to PI treatment emerges in most patients. Here, we performed a high-throughput screen of 1855 Food and Drug Administration (FDA)-approved drugs and identified all-trans retinoic acid (ATRA), which alone has no antimyeloma effect, as a potent drug that enhanced MM sensitivity to Cfz-induced cytotoxicity and resensitized Cfz-resistant MM cells to Cfz in vitro. ATRA activated retinoic acid receptor (RAR)γ and interferon-β response pathway, leading to upregulated expression of IRF1. IRF1 in turn initiated the transcription of OAS1, which synthesized 2-5A upon binding to double-stranded RNA (dsRNA) induced by Cfz and resulted in cellular RNA degradation by RNase L and cell death. Similar to ATRA, BMS961, a selective RARγ agonist, could also (re)sensitize MM cells to Cfz in vitro, and both ATRA and BMS961 significantly enhanced the therapeutic effects of Cfz in established MM in vivo. In support of these findings, analyses of large datasets of patients' gene profiling showed a strong and positive correlation between RARγ and OAS1 expression and patient's response to PI treatment. Thus, this study highlights the potential for RARγ agonists to sensitize and overcome MM resistance to Cfz treatment in patients.

Omega-3 Fatty Acids DHA and EPA Reduce Bortezomib Resistance in Multiple Myeloma Cells by Promoting Glutathione Degradation

Multiple myeloma (MM) is a hematological malignancy that exhibits aberrantly high levels of proteasome activity. While treatment with the proteasome inhibitor bortezomib substantially increases overall survival of MM patients, acquired drug resistance remains the main challenge for MM treatment. Using a combination treatment of docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) and bortezomib, it was demonstrated previously that pretreatment with DHA/EPA significantly increased bortezomib chemosensitivity in MM cells. In the current study, both transcriptome and metabolome analysis were performed to comprehensively evaluate the underlying mechanism. It was demonstrated that pretreating MM cells with DHA/EPA before bortezomib potently decreased the cellular glutathione (GSH) level and altered the expression of the related metabolites and key enzymes in GSH metabolism, whereas simultaneous treatment only showed minor effects on these factors, thereby suggesting the critical role of GSH degradation in overcoming bortezomib resistance in MM cells. Moreover, RNA-seq results revealed that the nuclear factor erythroid 2-related factor 2 (NRF2)-activating transcription factor 3/4 (ATF3/4)-ChaC glutathione specific gamma-glutamylcyclotransferase 1 (CHAC1) signaling pathway may be implicated as the central player in the GSH degradation. Pathways of necroptosis, ferroptosis, p53, NRF2, ATF4, WNT, MAPK, NF-κB, EGFR, and ERK may be connected to the tumor suppressive effect caused by pretreatment of DHA/EPA prior to bortezomib. Collectively, this work implicates GSH degradation as a potential therapeutic target in MM and provides novel mechanistic insights into its significant role in combating bortezomib resistance.

Targeting Reactive Oxygen Species Metabolism to Induce Myeloma Cell Death

Multiple myeloma (MM) is a common hematological disease characterized by the accumulation of clonal malignant plasma cells in the bone marrow. Over the past two decades, new therapeutic strategies have significantly improved the treatment outcome and patients survival. Nevertheless, most MM patients relapse underlying the need of new therapeutic approaches. Plasma cells are prone to produce large amounts of immunoglobulins causing the production of intracellular ROS. Although adapted to high level of ROS, MM cells die when exposed to drugs increasing ROS production either directly or by inhibiting antioxidant enzymes. In this review, we discuss the efficacy of ROS-generating drugs for inducing MM cell death and counteracting acquired drug resistance specifically toward proteasome inhibitors.

Drug and Solute Transporters in Mediating Resistance to Novel Therapeutics in Multiple Myeloma

Multiple myeloma remains an incurable malignancy of plasma cells. Novel therapies, notably proteasome inhibitors and immunomodulatory drugs, have improved the survival of multiple myeloma patients; however, patients either present with, or develop resistance to, these therapies. Resistance to traditional chemotherapeutic agents can be caused by cellular drug efflux via adenosine triphosphate (ATP)-binding cassette (ABC) transporters, but it is still not clear whether these transporters mediate resistance to proteasome inhibitors and immunomodulatory drugs in multiple myeloma. Solute carrier (SLC) transporters also play a role in cancer drug resistance due to changes in cell homeostasis caused by their abnormal expression and changes in the solutes they transport. In this review, we evaluate resistance to novel therapies used to treat multiple myeloma, as mediated by drug and solute transporters.

Crosstalk between endoplasmic reticulum stress and oxidative stress: a dynamic duo in multiple myeloma

Under physiological and pathological conditions, cells activate the unfolded protein response (UPR) to deal with the accumulation of unfolded or misfolded proteins in the endoplasmic reticulum. Multiple myeloma (MM) is a hematological malignancy arising from immunoglobulin-secreting plasma cells. MM cells are subject to continual ER stress and highly dependent on the UPR signaling activation due to overproduction of paraproteins. Mounting evidence suggests the close linkage between ER stress and oxidative stress, demonstrated by overlapping signaling pathways and inter-organelle communication pivotal to cell fate decision. Imbalance of intracellular homeostasis can lead to deranged control of cellular functions and engage apoptosis due to mutual activation between ER stress and reactive oxygen species generation through a self-perpetuating cycle. Here, we present accumulating evidence showing the interactive roles of redox homeostasis and proteostasis in MM pathogenesis and drug resistance, which would be helpful in elucidating the still underdefined molecular pathways linking ER stress and oxidative stress in MM. Lastly, we highlight future research directions in the development of anti-myeloma therapy, focusing particularly on targeting redox signaling and ER stress responses.

Suppression of multiple myeloma by mitochondrial targeting

Treatment of multiple myeloma (MM) aims at inducing cell apoptosis by surpassing the limited capacity of MM cells to cope with oxidative stress. MM cell survival may further be suppressed by limiting cellular cholesterol. Long-chain fatty acid analogs of the MEDICA series promote mitochondrial stress and inhibit cholesterol biosynthesis, thus prompting us to verify their efficacy and mode-of-action in suppressing MM cell survival, in comparison to bortezomib. MEDICA analog is shown here to effectively suppress survival of MM cells, and to inhibit growth of MM xenograft. Suppression of MM cell survival by MEDICA is accompanied by inhibition of the STAT3, MAPK and the mTORC1 transduction pathways due to mitochondrial oxidative stress. MEDICA-induced oxidative stress is abrogated by added exogenous cholesterol. Suppression of MM cell survival by bortezomib is similarly driven by bortezomib-induced oxidative stress, being abrogated by added cholesterol. In line with that, the time-to-best-response of MM patients to bortezomib-based treatment protocols is shown to be positively correlated with their plasma cholesterol level. MEDICA profile may indicate novel therapeutic potential in the management of MM.

DNA Damage Response in Multiple Myeloma: The Role of the Tumor Microenvironment

Multiple myeloma (MM) is an incurable plasma cell malignancy characterized by genomic instability. MM cells present various forms of genetic instability, including chromosomal instability, microsatellite instability, and base-pair alterations, as well as changes in chromosome number. The tumor microenvironment and an abnormal DNA repair function affect genetic instability in this disease. In addition, states of the tumor microenvironment itself, such as inflammation and hypoxia, influence the DNA damage response, which includes DNA repair mechanisms, cell cycle checkpoints, and apoptotic pathways. Unrepaired DNA damage in tumor cells has been shown to exacerbate genomic instability and aberrant features that enable MM progression and drug resistance. This review provides an overview of the DNA repair pathways, with a special focus on their function in MM, and discusses the role of the tumor microenvironment in governing DNA repair mechanisms.

ROS Overproduction Sensitises Myeloma Cells to Bortezomib-Induced Apoptosis and Alleviates Tumour Microenvironment-Mediated Cell Resistance

Multiple myeloma (MM) is a plasma cell neoplasm that remains incurable due to innate or acquired resistance. Although MM cells produce high intracellular levels of reactive oxygen species (ROS), we hypothesised that they could remain sensitive to ROS unbalance. We tested if the inhibition of ROS, on one hand, or the overproduction of ROS, on the other, could (re)sensitise cells to bortezomib (BTZ). Two drugs were used in a panel of MM cell lines with various responses to BTZ: VAS3947 (VAS), an inhibitor of NADPH oxidase and auranofin (AUR), an inhibitor of thioredoxin reductase (TXNRD1), an antioxidant enzyme overexpressed in MM cells. We used several culture models: in suspension, on a fibronectin layer, in coculture with HS-5 mesenchymal cells, and/or in 3-D culture (or spheroids) to study the response of MM primary cells and cell lines. Several MM cell lines were sensitive to VAS but the combination with BTZ showed antagonistic or additive effects at best. By contrast, in all culture systems studied, the combined AUR/BTZ treatment showed synergistic effects on cell lines, including those less sensitive to BTZ and primary cells. MM cell death is due to the activation of apoptosis and autophagy. Modulating the redox balance of MM cells could be an effective therapy for refractory or relapse post-BTZ patients.

Increased glutathione utilization augments tumor cell proliferation in Waldenstrom Macroglobulinemia

Metabolic reprogramming is a hallmark of cancer cells. In Waldenstrom Macroglobulinemia (WM), the infiltration of IgM-secreting lymphoplamacytic cells into the bone marrow (BM) could shift the homeostasis of proteins and metabolites towards a permissive niche for tumor growth. Here, we investigated whether alerted metabolic pathways contribute to the pathobiology of WM and whether the cytokine composition of the BM promotes such changes. Metabolomics analysis on WM patients and normal donors' serum samples revealed a total of 75 metabolites that were significantly altered between two groups. While these metabolites belonged to amino acids, glucose, glutathione and lipid metabolism pathways, the highest number of the differentially expressed metabolites belonged to glutathione metabolism. Proteomics analysis and immunohistochemical staining both confirmed the increased protein levels mediating glutathione metabolism, including GCLC, MT1X, QPCT and GPX3. Moreover, treatment with IL-6 and IL-21, cytokines that induce WM cell proliferation and IgM secretion, increased gene expression of the amino acid transporters mediating glutathione metabolism, including ASCT2, SLC7A11 and 4F2HC, indicating that cytokines in the WM BM could modulate glutathione metabolism. Glutathione synthesis inhibition using Buthionine sulphoximine (BSO) significantly reduced WM cells proliferation in vitro, accompanied with decreased NFκB-p65 and MAPK-p38 phosphorylation. Moreover, BSO treatment significantly reduced the tumor growth rate in a WM xenograft model, further highlighting the role of glutathione metabolism in promoting tumor growth and proliferation. In summary, our data highlight a central role for glutathione metabolism in WM pathobiology and indicate that intervening with the metabolic processes could be a potential therapy for WM patients.

Proteomic analysis identifies mechanism(s) of overcoming bortezomib resistance via targeting ubiquitin receptor Rpn13

Our prior study showed that inhibition of 19S proteasome-associated ubiquitin receptor Rpn13 can overcome bortezomib resistance in MM cells. Here, we performed proteomic analysis of Rpn13 inhibitor (RA190)-treated MM cells and identified an antioxidant enzyme superoxide dismutase (SOD1) as a mediator of Rpn13 signaling. SOD1 levels are higher in MM patient cells versus normal PBMCs; and importantly, SOD1 expression correlates with the progression of disease and shorter survival. Functional validation studies show that RA190-induced cytotoxicity in bortezomib-sensitive and -resistant MM cells is associated with decrease in SOD1 levels; conversely, forced expression of SOD1 inhibits RA190-induced cell death. Genetic knockdown and biochemical blockade of SOD1 with LCS-1 sensitizes bortezomib-resistant MM cells to bortezomib. SOD1 inhibitor LCS-1 decreases viability in MM cell lines and patient cells. LCS-1-induced cell death is associated with: (1) increase in superoxide and ROS levels; (2) activation of caspases, and p53/p21 signaling; (3) decrease in MCL-1, BCL_xL, CDC2, cyclin-B1, and c-Myc; (4) ER stress response; and (5) inhibition of proteasome function. In animal model studies, LCS-1 inhibits xenografted bortezomib-resistant human MM cell growth and prolongs host survival. Our studies therefore show that targeting Rpn13 overcomes bortezomib resistance by decreasing cellular SOD1 levels, and provide the rationale for novel therapeutics targeting SOD1 to improve patient outcome in MM.

Racial disparities, cancer and response to oxidative stress

At the intersection of genetics, biochemistry and behavioral sciences, there is a largely untapped opportunity to consider how ethnic and racial disparities contribute to individual sensitivity to reactive oxygen species and how these might influence susceptibility to various cancers and/or response to classical cancer treatment regimens that pervasively result in the formation of such chemical species. This chapter begins to explore these connections and builds a platform from which to consider how the disciplines can be strengthened further.

Synthesis and mechanistic studies of quinolin-chlorobenzothioate derivatives with proteasome inhibitory activity in pancreatic cancer cell lines

Inhibition of proteasome activity blocks the degradation of dysfunctional proteins and induces cancer cell death due to cellular stress. Thus, proteasome inhibitors represent an attractive class of anticancer agents, and bortezomib, carfilzomib and ixazomib have been FDA-approved to treat multiple myeloma. However, cancer cells acquire resistance to these inhibitors through point mutations in the proteasome catalytic subunit or induction of alternative compensatory mechanisms. In this study, we identified a quinolin-chlorobenzothioate, QCBT7, as a new proteasome inhibitor showing cytotoxicity in a panel of cancer cell lines. QCBT7 is a more stable derivative of quinoline-8-thiol that targets the regulatory subunit instead of the catalytic subunit of the proteasome. QCBT7 caused the accumulation of ubiquitylated proteins in the cancer cells, indicating its proteasome inhibitory activity. Additionally, QCBT7 increased the expression of a set of genes (PFKFB4, CHOP, HMOX1 and SLC7A11) at both nascent RNA and protein levels, similarly to the known proteasome inhibitors MG132 and ixazomib. Together, QCBT7 induces proteasome inhibition, hypoxic response, endoplasmic reticulum stress and glycolysis, finally leading to cell death. Importantly, we have identified PFKFB4 as a potential biomarker of proteasome inhibitors that can be used to monitor treatment response.

Resveratrol Sensitizes Carfilzomib-Induced Apoptosis via Promoting Oxidative Stress in Multiple Myeloma Cells

The proteasome inhibitor is a target therapy for multiple myeloma (MM) patients, which has increased the overall survival rate of multiple myeloma in clinic. However, relapse and toxicity are major challenges for almost all MM patients. Thus, there is an urgent need for an effective and less toxic combination therapy. Here, we demonstrated that a natural compound, resveratrol (RSV) displayed anti-proliferative activity in a dose- and time-dependent manner in a panel of MM cell lines. More importantly, a low concentration of RSV was synergistic with a low dose of the proteasome inhibitor carfilzomib (CFZ) to induce apoptosis in myeloma cells. Further studies showed that mitochondria was a key regulatory site after RSV/CFZ combination treatment. RSV induced the release of second mitochondria-derived activator of caspase (Smac) in a dose-dependent manner and kept the Smac in a high level after combination with CFZ. Also, RSV was additive with CFZ to increase reactive oxygen species (ROS) production. Moreover, a stress sensor SIRT1, with deacetylase enzyme activity, was remarkably downregulated after RSV/CFZ combination, thereby significantly decreasing its target protein, survivin in MM cells. Simultaneously, autophagy was invoked after RSV/CFZ combination treatment in myeloma cells. Further inhibition of autophagy could increase more ROS production and apoptosis, indicating a close linkage between autophagy and proteasome to modulate the oxidative stress. Together, these findings suggest that induction of multiple stress responses after RSV/CFZ combination is a major mechanism to synergistically inhibit MM cell growth and reduce the toxicity of CFZ in MM cells. This study also provides an important rationale for the clinic to consider an autophagy inhibitor for the combination therapy in MM patients.

The Multifaceted Roles of DJ-1 as an Antioxidant

The DJ-1 protein was originally linked with Parkinson's disease and is now known to have antioxidant functions. The protein has three redox-sensitive cysteine residues, which are involved in its dimerisation and functional properties. A mildly oxidised form of DJ-1 is the most active form and protects cells from oxidative stress conditions. DJ-1 functions as an antioxidant through a variety of mechanisms, including a weak direct antioxidant activity by scavenging reactive oxygen species. DJ-1 also regulates a number of signalling pathways, including the inhibition of apoptosis signal-regulating kinase 1 (ASK1)-induced apoptosis under oxidative stress conditions. Other proteins regulated by DJ-1 include enzymes, chaperones, the 20S proteasome and transcription factors, including Nrf2. Once activated by oxidative stress, Nrf2 upregulates antioxidant gene expression including members of the thioredoxin and glutathione pathways, which in turn mediate an antioxidant protective function. Crosstalk between DJ-1 and both the thioredoxin and glutathione systems has also been identified. Thioredoxin reduces a cysteine residue on DJ-1 to modulate its activity, while glutaredoxin1 de-glutathionylates DJ-1, preventing degradation of DJ-1 and resulting in its accumulation. DJ-1 also regulates the activity of glutamate cysteine ligase, which is the rate-limiting step for glutathione synthesis. These antioxidant functions of DJ-1 are key to its role in protecting neurons from oxidative stress and are hypothesised to protect the brain from the development of neurodegenerative diseases such as Parkinson's disease (PD) and to protect cardiac tissues from ischaemic-reperfusion injury. However, DJ-1, as an antioxidant, also protects cancer cells from undergoing oxidative stress-induced apoptosis.

Cyclin D1 unbalances the redox status controlling cell adhesion, migration, and drug resistance in myeloma cells

The interactions of multiple myeloma (MM) cells with their microenvironment are crucial for pathogenesis. MM cells could interact differentially with their microenvironment depending on the type of cyclin D they express. We established several clones that constitutively express cyclin D1 from the parental RPMI8226 MM cell line and analyzed the impact of cyclin D1 expression on cell behavior. We performed a gene expression profiling study on cyclin D1-expressing vs. control cells and validated the results by semi-quantitative RT-PCR. The expression of cyclin D1 altered the transcription of genes that control adhesion and migration. We confirmed that cyclin D1 increases cell adhesion to stromal cells and fibronectin, stabilizes F-actin fibers, and enhances chemotaxis and inflammatory chemokine secretion. Both control and cyclin D1-expressing cells were more resistant to acute carfilzomib treatment when cultured on stromal cells than in suspension. However, this resistance was specifically reduced in cyclin D1-expressing cells after pomalidomide pre-treatment that modifies tumor cell/microenvironment interactions. Transcriptomic analysis revealed that cyclin D1 expression was also associated with changes in the expression of genes controlling metabolism. We also found that cyclin D1 expression disrupted the redox balance by producing reactive oxygen species. The resulting oxidative stress activated the p44/42 mitogen-activated protein kinase (or ERK1/2) signaling pathway, increased cell adhesion to fibronectin or stromal cells, and controlled drug sensitivity.

Our results have uncovered a new function for cyclin D1 in the control of redox metabolism and interactions of cyclin D1-expressing MM cells with their bone marrow microenvironment.

Modeling multiple myeloma-bone marrow interactions and response to drugs in a 3D surrogate microenvironment

Multiple myeloma develops primarily inside the bone marrow microenvironment, that confers pro-survival signals and drug resistance. 3D cultures that reproduce multiple myeloma-bone marrow interactions are needed to fully investigate multiple myeloma pathogenesis and response to drugs. To this purpose, we exploited the 3D Rotary Cell Culture System bioreactor technology for myeloma-bone marrow co-cultures in gelatin scaffolds. The model was validated with myeloma cell lines that, as assessed by histochemical and electron-microscopic analyses, engaged contacts with stromal cells and endothelial cells. Consistently, pro-survival signaling and also cell adhesion-mediated drug resistance were significantly higher in 3D than in 2D parallel co-cultures. The contribution of the VLA-4/VCAM1 pathway to resistance to bortezomib was modeled by the use of VCAM1 transfectants. Soluble factor-mediated drug resistance could be also demonstrated in both 2D and 3D co-cultures. The system was then successfully applied to co-cultures of primary myeloma cells-primary myeloma bone marrow stromal cells from patients and endothelial cells, allowing the development of functional myeloma-stroma interactions and MM cell long-term survival. Significantly, genomic analysis performed in a high-risk myeloma patient demonstrated that culture in bioreactor paralleled the expansion of the clone that ultimately dominated in vivo. Finally, the impact of bortezomib on myeloma cells and on specialized functions of the microenvironment could be evaluated. Our findings indicate that 3D dynamic culture of reconstructed human multiple myeloma microenvironments in bioreactor may represent a useful platform for drug testing and for studying tumor-stroma molecular interactions.

Repurposing of the CDK inhibitor PHA-767491 as a NRF2 inhibitor drug candidate for cancer therapy via redox modulation

Oxidative stress and cellular response mechanisms such as NRF2-mediated antioxidant responses play differential roles in healthy and diseased cells. Constant generation and elimination of high levels of reactive oxygen species is a hallmark of many cancer cell types; this phenomenon is not observed during steady state of healthy cells. Manipulation of NRF2 transcriptional activity and the cellular redox homeostasis therefore has potential to be therapeutically exploitable for cancer therapy by preferentially targeting cancer cells for induction of oxidative stress. We found that the NRF2 inhibitor brusatol triggered increased oxidative stress while compromising viability and proliferation of multiple myeloma cells. Using a repurposing approach we discovered that the Cdc7/CDK9 inhibitor PHA-767491 is also a potent inhibitor of NRF2 transcriptional activity. The molecule was identified by high throughput screening of a library of about 5900 drug-like molecules. Screening assays included two cell-based assays using HepG2 hepatocellular carcinoma cells: a) A NRF2 nuclear translocation assay, and b) A NRF2 luciferase reporter assay. Validation assays were performed in multiple myeloma cells and included detection of mitochondrial superoxide levels and MTS assays. We found that PHA-767491 treatment of multiple myeloma cells was associated with inhibition of nuclear translocation of NRF2, increased mitochondrial superoxide levels and inhibition of cell growth. Our findings suggest that PHA-767491 is a promising drug candidate for cancer therapy with NRF2 inhibitory potency contributing to its anti-cancer properties.

High NRF2 expression controls endoplasmic reticulum stress induced apoptosis in multiple myeloma

Multiple myeloma (MM) is an incurable disease characterized by clonal plasma cell proliferation. The stress response transcription factor Nuclear factor erythroid 2 [NF-E2]-related factor 2 (NRF2) is known to be activated in MM in response to proteasome inhibitors (PI). Here, we hypothesize that the transcription factor NRF2 whose physiological role is to protect cells from reactive oxygen species via the regulation of drug metabolism and antioxidant gene plays an important role in MM cells survival and proliferation. We report for the first time that NRF2 is constitutively activated in circa 50% of MM primary samples and all MM cell lines. Moreover, genetic inhibition of constitutively expressed NRF2 reduced MM cell viability. We confirm that PI induced further expression of NRF2 in MM cell lines and primary MM. Furthermore, genetic inhibition of NRF2 of PI treated MM cells increased ER-stress through the regulation of CCAAT-enhancer-binding protein homologous protein (CHOP). Finally, inhibition of NRF2 in combination with PI treatment significantly increased apoptosis in MM cells. Here we identify NRF2 as a key regulator of MM survival in treatment naive and PI treated cells.

The amyloidogenic light chain is a stressor that sensitizes plasma cells to proteasome inhibitor toxicity

Amyloidogenic PCs show unique PI susceptibility and altered organelle homeostasis, consistent with defective autophagy. Amyloidogenic LC production is an intrinsic cellular stressor that sensitizes to PI toxicity.

TrxR1 inhibition overcomes both hypoxia-induced and acquired bortezomib resistance in multiple myeloma through NF-кβ 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-кβ subunit p65 nuclear protein levels and TrxR1 inhibition decreased hypoxia-induced NF-кβ p65 protein levels in the nucleus and reduced the expression of NF-кβ-regulated genes. In addition, higher TrxR1 protein levels were observed in bortezomib-resistant myeloma cells compared to the naïve 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-кβ-regulated anti-apoptotic and proliferative genes. Thus, TrxR1 inhibition overcomes both hypoxia-induced and acquired bortezomib resistance by inhibiting the NF-кβ 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.

Sabotaging of the oxidative stress response by an oncogenic noncoding RNA

Overexpression of the multiple myeloma set domain (MMSET) Wolf-Hirschhorn syndrome candidate 1 gene, which contains an orphan box H/ACA class small nucleolar RNA, ACA11, in an intron, is associated with several cancer types, including multiple myeloma (MM). ACA11 and MMSET are overexpressed cotranscriptionally as a result of the t(4;14) chromosomal translocation in a subset of patients with MM. RNA sequencing of CD138⁺ tumor cells from t(4;14)-positive and -negative MM patient bone marrow samples revealed an enhanced oxidative phosphorylation mRNA signature. Supporting these data, ACA11 overexpression in a t(4;14)-negative MM cell line, MM1.S, demonstrated enhanced reactive oxygen species (ROS) levels. In addition, an enhancement of cell proliferation, increased soft agar colony size, and elevated ERK1/2 phosphorylation were observed. This ACA11-driven hyperproliferative phenotype depended on increased ROS levels as exogenously added antioxidants attenuate the increased proliferation. A major transcriptional regulator of the cellular antioxidant response, nuclear factor (erythroid-derived 2)-like 2 (NRF2), shuttled to the nucleus, as expected, in response to ACA11-driven increases in ROS; however, transcriptional up-regulation of some of NRF2's antioxidant target genes was abrogated in the presence of ACA11 overexpression. These data show for the first time that ACA11 promotes proliferation through inhibition of NRF2 function resulting in sustained ROS levels driving cancer cell proliferation.-Mahajan, N., Wu, H.-J., Bennett, R. L., Troche, C., Licht, J. D., Weber, J. D., Maggi, L. B., Jr., Tomasson, M. H. Sabotaging of the oxidative stress response by an oncogenic noncoding RNA.

Intracellular glutathione determines bortezomib cytotoxicity in multiple myeloma cells

Multiple myeloma (myeloma in short) is an incurable cancer of antibody-producing plasma cells that comprise 13% of all hematological malignancies. The proteasome inhibitor bortezomib has improved treatment significantly, but inherent and acquired resistance to the drug remains a problem. We here show that bortezomib-induced cytotoxicity was completely dampened when cells were supplemented with cysteine or its derivative, glutathione (GSH) in ANBL-6 and INA-6 myeloma cell lines. GSH is a major component of the antioxidative defense in eukaryotic cells. Increasing intracellular GSH levels fully abolished bortezomib-induced cytotoxicity and transcriptional changes. Elevated intracellular GSH levels blocked bortezomib-induced nuclear factor erythroid 2-related factor 2 (NFE2L2, NRF2)-associated stress responses, including upregulation of the xCT subunit of the Xc- cystine-glutamate antiporter. INA-6 cells conditioned to increasing bortezomib doses displayed reduced bortezomib sensitivity and elevated xCT levels. Inhibiting Xc- activity potentiated bortezomib-induced cytotoxicity in myeloma cell lines and primary cells, and re-established sensitivity to bortezomib in bortezomib-conditioned cells. We propose that intracellular GSH level is the main determinant of bortezomib-induced cytotoxicity in a subset of myeloma cells, and that combined targeting of the proteasome and the Xc- cystine-glutamate antiporter can circumvent bortezomib resistance.

Stress Regulates Aquaporin-8 Permeability to Impact Cell Growth and Survival

Aquaporin-8 (AQP8) allows the bidirectional transport of water and hydrogen peroxide across biological membranes. Depending on its concentration, H2O2 exerts opposite roles, amplifying growth factor signaling in physiological conditions, but causing severe cell damage when in excess. Thus, H2O2 permeability is likely to be tightly controlled in living cells.

AIMS

In this study, we investigated whether and how the transport of H2O2 through plasma membrane AQP8 is regulated, particularly during cell stress.

RESULTS

We show that diverse cellular stress conditions, including heat, hypoxia, and ER stress, reversibly inhibit the permeability of AQP8 to H2O2 and water. Preventing the accumulation of intracellular reactive oxygen species (ROS) during stress counteracts AQP8 blockade. Once inhibition is established, AQP8-dependent transport can be rescued by reducing agents. Neither H2O2 nor water transport is impaired in stressed cells expressing a mutant AQP8, in which cysteine 53 had been replaced by serine. Cells expressing this mutant are more resistant to stress-, drug-, and radiation-induced growth arrest and death.

INNOVATION AND CONCLUSION

The control of AQP8-mediated H2O2 transport provides a novel mechanism to regulate cell signaling and survival during stress. Antioxid. Redox Signal. 24, 1031-1044.

Drug metabolism and clearance system in tumor cells of patients with multiple myeloma

Resistance to chemotherapy is a major limitation of cancer treatments with several molecular mechanisms involved, in particular altered local drug metabolism and detoxification process. The role of drug metabolism and clearance system has not been satisfactorily investigated in Multiple Myeloma (MM), a malignant plasma cell cancer for which a majority of patients escapes treatment. The expression of 350 genes encoding for uptake carriers, xenobiotic receptors, phase I and II Drug Metabolizing Enzymes (DMEs) and efflux transporters was interrogated in MM cells (MMCs) of newly-diagnosed patients in relation to their event free survival. MMCs of patients with a favourable outcome have an increased expression of genes coding for xenobiotic receptors (RXRα, LXR, CAR and FXR) and accordingly of their gene targets, influx transporters and phase I/II DMEs. On the contrary, MMCs of patients with unfavourable outcome displayed a global down regulation of genes coding for xenobiotic receptors and the downstream detoxification genes but had a high expression of genes coding for ARNT and Nrf2 pathways and ABC transporters. Altogether, these data suggests ARNT and Nrf2 pathways could be involved in MM primary resistance and that targeting RXRα, PXR, LXR and FXR through agonists could open new perspectives to alleviate or reverse MM drug resistance.

Inhibition of thioredoxin 1 leads to apoptosis in drug-resistant multiple myeloma

Multiple myeloma (MM) is a hematological malignancy characterized by the aberrant accumulation of clonal plasma cells in the bone marrow. Despite recent advancement in anti-myeloma treatment, MM remains an incurable disease. This study showed higher intrinsic oxidative stress and higher Trx1 and TrxR1 protein levels in MM cells compared to normal cells. Drug-induced Trx1 (PX-12) and TrxR1 (Auranofin) inhibition disrupted redox homeostasis resulting in ROS-induced apoptosis in MM cells and a reduction in clonogenic activity. Knockdown of either Trx1 or TrxR1 reduced MM cell viability. Trx1 inhibition by PX-12 sensitized MM cells to undergo apoptosis in response to the NF-κβ inhibitors, BAY 11-7082 and curcumin. PX-12 treatment decreased the expression of the NF-κβ subunit p65 in MM cells. Bortezomib-resistant MM cells contained higher Trx1 protein levels compared to the parental cells and PX-12 treatment resulted in apoptosis. Thus, increased Trx1 enhances MM cell growth and survival and exerts resistance to NF-κβ inhibitors. Therefore inhibiting the thioredoxin system may be an effective therapeutic strategy to treat newly diagnosed as well as relapsed/refractory MM.

Trial Watch: Proteasomal inhibitors for anticancer therapy

The so-called "ubiquitin-proteasome system" (UPS) is a multicomponent molecular apparatus that catalyzes the covalent attachment of several copies of the small protein ubiquitin to other proteins that are generally (but not always) destined to proteasomal degradation. This enzymatic cascade is crucial for the maintenance of intracellular protein homeostasis (both in physiological conditions and in the course of adaptive stress responses), and regulates a wide array of signaling pathways. In line with this notion, defects in the UPS have been associated with aging as well as with several pathological conditions including cardiac, neurodegenerative, and neoplastic disorders. As transformed cells often experience a constant state of stress (as a result of the hyperactivation of oncogenic signaling pathways and/or adverse microenvironmental conditions), their survival and proliferation are highly dependent on the integrity of the UPS. This rationale has driven an intense wave of preclinical and clinical investigation culminating in 2003 with the approval of the proteasomal inhibitor bortezomib by the US Food and Drug Administration for use in multiple myeloma patients. Another proteasomal inhibitor, carfilzomib, is now licensed by international regulatory agencies for use in multiple myeloma patients, and the approved indications for bortezomib have been extended to mantle cell lymphoma. This said, the clinical activity of bortezomib and carfilzomib is often limited by off-target effects, innate/acquired resistance, and the absence of validated predictive biomarkers. Moreover, the antineoplastic activity of proteasome inhibitors against solid tumors is poor. In this Trial Watch we discuss the contribution of the UPS to oncogenesis and tumor progression and summarize the design and/or results of recent clinical studies evaluating the therapeutic profile of proteasome inhibitors in cancer patients.

Emerging Therapeutic Strategies for Overcoming Proteasome Inhibitor Resistance

The debut of the proteasome inhibitor bortezomib (Btz; Velcade®) radically and immediately improved the treatment of multiple myeloma (MM), an incurable malignancy of the plasma cell. Therapeutic resistance is unavoidable, however, and represents a major obstacle to maximizing the clinical potential of the drug. To address this challenge, studies have been conducted to uncover the molecular mechanisms driving Btz resistance and to discover new targeted therapeutic strategies and combinations that restore Btz activity. This review discusses the literature describing molecular adaptations that confer Btz resistance with a primary disease focus on MM. Also discussed are the most recent advances in therapeutic strategies that overcome resistance, approaches that include redox-modulating agents, murine double minute 2 inhibitors, therapeutic monoclonal antibodies, and new epigenetic-targeted drugs like bromodomain and extra terminal domain inhibitors.

Toward understanding induction of oxidative stress and apoptosis by proteasome inhibitors

SIGNIFICANCE

Proteasome inhibitors (PIs) are used in the clinic for the treatment of hematopoietic malignancies. PI inhibitors induce endoplasmatic reticulum (ER) stress and oxidative stress, disruption of signaling pathways, mitochondrial dysfunction, and, eventually, cell death by apoptosis. PIs designated as clinical candidates include natural product derivatives and compounds developed by rational design and feature a wide diversity of structural elements. The vast amount of literature on this topic underscores PIs significance in driving basic research alongside therapeutic benefit.

RECENT ADVANCES

Research in recent years has brought an in-depth insight into the molecular mechanisms of PI-induced apoptosis. However, there are some paradoxes and controversies in the literature. In this review, the advances and uncertainties, in particular on the time course events that make cells commit to apoptosis, are discussed. In addition, some mechanisms of evolved PI resistance are presented, and speculations on the difference in sensitivity between cell or tumor types are brought forward. The review concludes by giving an outlook of recent methods that may be employed to describe the system biology of how PIs impact cell survival decisions.

CRITICAL ISSUES

The biology of ER stress, reactive oxygen species (ROS) production, and apoptosis as induced by PIs is not well understood. Absorbed by the strong focus on PIs, one might overlook the importance of proteasome activity activators or modulators and the study of enzymatic pathways that lie up- or downstream from the proteasome function.

FUTURE DIRECTIONS

An increased understanding of the systems biology at mRNA and protein levels and the kinetics behind the interaction between PIs and cells is imperative. The design and synthesis of subunit specific inhibitors for each of the seven known proteasome activities and for the enzymes associated to proteasomes will aid in unraveling biology of the ubiquitin-proteasome system in relation to ER stress, ROS production, and apoptosis and will generate leads for therapeutic intervention.

Copper-zinc superoxide dismutase-mediated redox regulation of bortezomib resistance in multiple myeloma

Multiple myeloma (MM) is an incurable B-cell malignancy. The proteasome inhibitor bortezomib (BTZ) is a frontline MM drug; however, intrinsic or acquired resistance to BTZ remains a clinical hurdle. As BTZ induces oxidative stress in MM cells, we queried if altered redox homeostasis promotes BTZ resistance. In primary human MM samples, increased gene expression of copper–zinc superoxide dismutase (CuZnSOD or SOD1) correlated with cancer progression, high-risk disease, and adverse overall and event-free survival outcomes. As an in vitro model, human MM cell lines (MM.1S, 8226, U266) and the BTZ-resistant (BR) lines (MM.1SBR, 8226BR) were utilized to determine the role of antioxidants in intrinsic or acquired BTZ-resistance. An up-regulation of CuZnSOD, glutathione peroxidase-1 (GPx-1), and glutathione (GSH) were associated with BTZ resistance and attenuated prooxidant production by BTZ. Enforced overexpression of SOD1 induced BTZ resistance and pharmacological inhibition of CuZnSOD with disulfiram (DSF) augmented BTZ cytotoxicity in both BTZ-sensitive and BTZ-resistant cell lines. Our data validates CuZnSOD as a novel therapeutic target in MM. We propose DSF as an adjuvant to BTZ in MM that is expected to overcome intrinsic and acquired BTZ resistance as well as augment BTZ cytotoxicity.

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Multiple myeloma (MM) displays intrinsic/adaptive resistance to bortezomib (BTZ).

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An up-regulation of antioxidant levels is observed in BTZ-resistant MM cell lines.

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Inhibition of CuZnSOD increases BTZ cytotoxicity in BTZ naïve/resistant cells.

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We propose disulfiram as a combination chemotherapy drug to inhibit relapse in MM.

Angiopoietin-2 in Bone Marrow milieu promotes Multiple Myeloma-associated angiogenesis

Angiopoietin-2 (Ang-2) is involved in angiogenesis in both solid and hematological malignancies. In Multiple Myeloma (MM), serum Ang-2 correlates with disease progression and response to therapy. To address the patho-physiologic role of Ang-2 in MM associated angiogenesis, we used sera from patients with active MM, which contained significantly higher levels of the molecule, compared to those from patients with smoldering MM and Monoclonal Gammopathy of Undetermined Significance. MM Bone Marrow (BM) sera with high Ang-2 concentration specifically contributed to endothelial cell (EC) activation, while Ang-1 containing sera maintained EC stabilization. The functional dichotomy of Ang-1 and Ang-2 was confirmed by the triggering of distinctive signaling pathways down-stream the common Tie-2 receptor, i.e., the Akt or the ERK- phosphorylation pathway. Notably, Ang-2 but not VEGF serum levels correlated with BM micro-vessel density, further underscoring the key role of Ang-2 in angiogenesis. Western Blot, RT-PCR and immunocytochemistry identified MMEC as the major source of Ang-2, at variance with MM cells and CD14(+) BM monocytes. These data suggest that Ang-2 produced in the BM milieu may contribute to MM angiogenesis and suggest that the molecule can be further exploited both as angiogenesis biomarker and as a potential therapeutic target.

Phase 2 study of imexon, a prooxidant molecule, in relapsed and refractory B-cell non-Hodgkin lymphoma

Lymphoma cells are subject to higher levels of oxidative stress compared with their normal counterparts and may be vulnerable to manipulations of the cellular redox balance. We therefore designed a phase 2 study of imexon (Amplimexon/NSC-714597), a prooxidant molecule, in patients with relapsed/refractory B-cell non-Hodgkin lymphoma (NHL). Imexon was administered at 1000 mg/m(2) IV daily for 5 days in 21-day cycles. Gene expression analysis performed on pretreatment tumor specimens included 13 transcripts used to generate a redox signature score, previously demonstrated to correlate with lymphoma prognosis. Twenty-two patients were enrolled having follicular (n = 9), diffuse large B-cell (DLBCL) (n = 5), mantle cell (n = 3), transformed follicular (n = 2), small lymphocytic (n = 2), and Burkitt (n = 1) lymphoma. The most common grade 3/4 adverse events were anemia (14%) and neutropenia (9%). The overall response rate was 30%, including responses in follicular lymphoma (4 of 9) and DLBCL (2 of 5). Gene expression analyses revealed CD68 and the redox-related genes, GPX1 and SOD2, as well as a higher redox score to correlate with clinical responses. Therefore, pretreatment markers of oxidative stress may identify patients likely to respond to this therapeutic approach. This trial was registered at www.clinicaltrials.gov as #NCT01314014.

Targeting MUC1-C is synergistic with bortezomib in downregulating TIGAR and inducing ROS-mediated myeloma cell death

The proteosome inhibitor bortezomib (BTZ) induces endoplasmic reticulum and oxidative stress in multiple myeloma (MM) cells. The mucin 1 C-terminal subunit (MUC1-C) oncoprotein is aberrantly expressed in most MM cells, and targeting MUC1-C with GO-203, a cell-penetrating peptide inhibitor of MUC1-C homodimerization, is effective in inducing reactive oxygen species (ROS)-mediated MM cell death. The present results demonstrate that GO-203 and BTZ synergistically downregulate expression of the p53-inducible regulator of glycolysis and apoptosis (TIGAR), which promotes shunting of glucose-6-phosphate into the pentose phosphate pathway to generate reduced glutathione (GSH). In turn, GO-203 blocks BTZ-induced increases in GSH and results in synergistic increases in ROS and MM cell death. The results also demonstrate that GO-203 is effective against BTZ-resistant MM cells. We show that BTZ resistance is associated with BTZ-induced increases in TIGAR and GSH levels, and that GO-203 resensitizes BTZ-resistant cells to BTZ treatment by synergistically downregulating TIGAR and GSH. The GO-203/BTZ combination is thus highly effective in killing BTZ-resistant MM cells. These findings support a model in which targeting MUC1-C is synergistic with BTZ in suppressing TIGAR-mediated regulation of ROS levels and provide an experimental rationale for combining GO-203 with BTZ in certain settings of BTZ resistance.

Ex-vivo dynamic 3-D culture of human tissues in the RCCS™ bioreactor allows the study of Multiple Myeloma biology and response to therapy

Three-dimensional (3-D) culture models are emerging as invaluable tools in tumor biology, since they reproduce tissue-specific structural features and cell-cell interactions more accurately than conventional 2-D cultures. Multiple Myeloma, which depends on myeloma cell-Bone Marrow microenvironment interactions for development and response to drugs, may particularly benefit from such an approach. An innovative 3-D dynamic culture model based on the use of the RCCS™ Bioreactor was developed to allow long-term culture of myeloma tissue explants. This model was first validated with normal and pathological explants, then applied to tissues from myeloma patients. In all cases, histological examination demonstrated maintenance of viable myeloma cells inside their native microenvironment, with an overall well preserved histo-architecture including bone lamellae and vessels. This system was then successfully applied to evaluate the cytotoxic effects exerted by the proteasome inhibitor Bortezomib not only on myeloma cells but also on angiogenic vessels. Moreover, as surrogate markers of specialized functions expressed by myeloma cells and microenvironment, β2 microglobulin, VEGF and Angiopoietin-2 levels, as well as Matrix Metalloproteases activity, were evaluated in supernatants from 3D cultures and their levels reflected the effects of Bortezomib treatment. Notably, determination of β2 microglobulin levels in supernatants from Bortezomib-treated samples and in patients'sera following Bortezomib-based therapies disclosed an overall concordance in the response to the drug ex vivo and in vivo.

Our findings indicate, as a proof of principle, that 3-D, RCCS™ bioreactor-based culture of tissue explants can be exploited for studying myeloma biology and for a pre-clinical approach to patient-targeted therapy.

Iron increases the susceptibility of multiple myeloma cells to bortezomib

Multiple myeloma is a malignant still incurable plasma cell disorder. Pharmacological treatment based on proteasome inhibition has improved patient outcome; however, bortezomib-resistance remains a major clinical problem. Inhibition of proteasome functionality affects cellular iron homeostasis and iron is a potent inducer of reactive oxygen species and cell death, unless safely stored in ferritin. We explored the potential role of iron in bortezomib-resistance. We analyzed iron proteins, oxidative status and cell viability in 7 multiple myeloma cell lines and in plasma cells from 5 patients. Cells were treated with increasing bortezomib concentrations with or without iron supplementation. We reduced ferritin levels by both shRNA technology and by drug-induced iron starvation. Multiple myeloma cell lines are characterized by distinct ferritin levels, which directly correlate with bortezomib resistance. We observed that iron supplementation upon bortezomib promotes protein oxidation and cell death, and that iron toxicity inversely correlates with basal ferritin levels. Bortezomib prevents ferritin upregulation in response to iron, thus limiting the ability to buffer reactive oxygen species. Consequently, reduction of basal ferritin levels increases both bortezomib sensitivity and iron toxicity. In patients' cells, we confirmed that bortezomib prevents ferritin increase, that iron supplementation upon bortezomib increases cell death and that ferritin reduction overcomes bortezomib resistance. Bortezomib affects iron homeostasis, sensitizing cells to oxidative damage. Modulation of iron status is a strategy worth exploring to improve the efficacy of proteasome inhibition therapies.

On the redox control of B lymphocyte differentiation and function

SIGNIFICANCE

On the one hand, redox emerges as a key mechanism in regulating intra- and intercellular signaling and homeostatic systems. On the other hand, cells of the B lineage provide powerful systems to unravel the intra- and intercellular mechanisms that coordinate the processes of development and terminal differentiation.

RECENT ADVANCES

This essay summarizes a few paradigmatic examples of redox regulation and signal modulation that emerged from, or were confirmed by, studies on the development, differentiation and function of B cells.

CRITICAL ISSUES

While a role for intra- and intercellular redox signaling has been firmly established for differentiating B cells, many fundamental questions remain open, including the cellular sources of reactive oxygen species (ROS), the spatial and temporal constraints of ROS signaling, and the functional role of the antioxidant response.

FUTURE DIRECTIONS

Given their robustness and biotechnological and clinical interest, cells of the B lineage continue to be fruitful goldmines from which redox biologists can dig novel mechanistic knowledge of general relevance.

Manipulation of cellular redox parameters for improving therapeutic responses in B-cell lymphoma and multiple myeloma

Developing novel combined-modality therapeutic approaches based on understanding of the involvement of redox biology in apoptosis of malignant cells is a promising approach for improving clinical responses in B-cell lymphoma and multiple myeloma. Therapeutic modalities that generate reactive oxygen species (i.e., radiation, photodynamic therapy, and specific chemotherapeutic drugs) have been shown to be selectively cytotoxic to malignant B-cells. In this review, we will discuss agents that induce apoptosis in B-cell tumors by oxidative stress. Subsequently, a novel biochemical rationale (based on fundamental differences in cancer vs. normal cell oxidative metabolism) for combining oxidative stressors with radiotherapy and chemotherapy, that may lead to designing of more effective treatment strategies for B-cell malignancies, will be discussed. Besides providing potential curative benefit, such novel therapies could also selectively target and inhibit the emergence of drug-resistance in tumor cells, which is a major determinant of treatment failure in many B-cell malignancies.

Protein kinase CK2 protects multiple myeloma cells from ER stress-induced apoptosis and from the cytotoxic effect of HSP90 inhibition through regulation of the unfolded protein response

PURPOSE

Protein kinase CK2 promotes multiple myeloma cell growth by regulating critical signaling pathways. CK2 also modulates proper HSP90-dependent client protein folding and maturation by phosphorylating its co-chaperone CDC37. Because the endoplasmic reticulum (ER) stress/unfolded protein response (UPR) is central in myeloma pathogenesis, we tested the hypothesis that the CK2/CDC37/HSP90 axis could be involved in UPR in myeloma cells.

EXPERIMENTAL DESIGN

We analyzed CK2 activity upon ER stress, the effects of its inactivation on the UPR pathways and on ER stress-induced apoptosis. The consequences of CK2 plus HSP90 inhibition on myeloma cell growth in vitro and in vivo and CK2 regulation of HSP90-triggered UPR were determined.

RESULTS

CK2 partly localized to the ER and ER stress triggered its kinase activity. CK2 inhibition reduced the levels of the ER stress sensors IRE1α and BIP/GRP78, increased phosphorylation of PERK and EIF2α, and enhanced ER stress-induced apoptosis. Simultaneous inactivation of CK2 and HSP90 resulted in a synergic anti-myeloma effect (combination index = 0.291) and in much stronger alterations of the UPR pathways as compared with the single inhibition of the two molecules. Cytotoxicity from HSP90 and CK2 targeting was present in a myeloma microenvironment model, on plasma cells from patients with myeloma and in an in vivo mouse xenograft model. Mechanistically, CK2 inhibition led to a reduction of IRE1α/HSP90/CDC37 complexes in multiple myeloma cells.

CONCLUSIONS

Our results place CK2 as a novel regulator of the ER stress/UPR cascades and HSP90 function in myeloma cells and offer the groundwork to design novel combination treatments for this disease.

Redox control of the ubiquitin-proteasome system: from molecular mechanisms to functional significance

In their natural environments, cells are regularly exposed to oxidizing conditions that may lead to protein misfolding. If such misfolded proteins are allowed to linger, they may form insoluble aggregates and pose a serious threat to the cell. Accumulation of misfolded, oxidatively damaged proteins is characteristic of many diseases and during aging. To counter the adverse effects of oxidative stress, cells can initiate an antioxidative response in an attempt to repair the damage, or rapidly channel the damaged proteins for degradation by the ubiquitin-proteasome system (UPS). Recent studies have shown that elements of the oxidative stress response and the UPS are linked on many levels. To manage the extra burden of misfolded proteins, the UPS is induced by oxidative stress, and special proteasome subtypes protect cells against oxidative damage. In addition, the proteasome is directly associated with a thioredoxin and other cofactors that may adjust the particle's response during an oxidative challenge. Here, we give an overview of the UPS and a detailed description of the degradation of oxidized proteins and of the crosstalk between oxidative stress and protein degradation in health and disease.

Treatment-induced oxidative stress and cellular antioxidant capacity determine response to bortezomib in mantle cell lymphoma

PURPOSE

Proteasome inhibition disrupts protein homeostasis and induces apoptosis. Up to 50% of patients with relapsed mantle cell lymphoma (MCL) respond to bortezomib. We used gene expression profiling to investigate the connection between proteasome inhibition, cellular response, and clinical efficacy.

EXPERIMENTAL DESIGN

We assessed transcriptional changes in primary tumor cells from five patients during treatment with bortezomib in vivo, and in 10 MCL cell lines exposed to bortezomib in vitro, on Affymetrix microarrays. Key findings were confirmed by western blotting.

RESULTS

MCL cell lines exposed to bortezomib in vitro showed upregulation of endoplasmic reticulum and oxidative stress response pathways. Gene expression changes were strongest in bortezomib-sensitive cells and these cells were also more sensitive to oxidative stress induced by H2O2. Purified tumor cells obtained at several timepoints during bortezomib treatment in 5 previously untreated patients with leukemic MCL showed strong activation of the antioxidant response controlled by NRF2. Unexpectedly, activation of this homeostatic program was significantly stronger in tumors with the best clinical response. Consistent with its proapoptotic function, we found upregulation of NOXA in circulating tumor cells of responding patients. In resistant cells, gene expression changes in response to bortezomib were limited and upregulation of NOXA was absent. Interestingly, at baseline, bortezomib-resistant cells displayed a relatively higher expression of the NRF2 gene-expression signature than sensitive cells (P < 0.001).

CONCLUSION

Bortezomib triggers an oxidative stress response in vitro and in vivo. High cellular antioxidant capacity contributes to bortezomib resistance.

Antioxidant protection: A promising therapeutic intervention in neurodegenerative disease

Oxidative stress has been consistently linked to ageing-related neurodegenerative diseases. Neurodegenerative diseases are characterized by progressive dysfunction and death of neurons. Oxidative stress is associated with dysfunction of the mitochondria and endoplasmic reticulum, inducing apoptosis and protein misfolding in neurons. Decreased activities of antioxidant enzymes like SOD, catalase, glutathione, glutathione peroxidase in neurodegenerative states signifies role of reduced antioxidant potential in neurodegeneration. Among the cellular pathways conferring protection against oxidative stress, a key role is played by vitagenes, which include Hsp70, heme oxygenase-1, thioredoxin and sirtuins. Cellular signalling pathways and molecular mechanisms that mediate hormetic responses typically involve antioxidant enzymes and transcription factors such as Nrf-2 and NFκB. Vitagenes, either individually or by acting in concert, contribute to counteract the ROS mediated damage. In this review the importance of oxidative stress and the potential use of antioxidants in the prevention and treatment of neurodegenerative disorders are discussed.

Bortezomib induces autophagic death in proliferating human endothelial cells

The proteasome inhibitor Bortezomib has been approved for the treatment of relapsed/refractory multiple myeloma (MM), thanks to its ability to induce MM cell apoptosis. Moreover, Bortezomib has antiangiogenic properties. We report that endothelial cells (EC) exposed to Bortezomib undergo death to an extent that depends strictly on their activation state. Indeed, while quiescent EC are resistant to Bortezomib, the drug results maximally toxic in EC switched toward angiogenesis with FGF, and exerts a moderate effect on subconfluent HUVEC. Moreover, EC activation state deeply influences the death pathway elicited by Bortezomib: after treatment, angiogenesis-triggered EC display typical features of apoptosis. Conversely, death of subconfluent EC is preceded by ROS generation and signs typical of autophagy, including intense cytoplasmic vacuolization with evidence of autophagosomes at electron microscopy, and conversion of the cytosolic MAP LC3 I form toward the autophagosome-associated LC3 II form. Treatment with the specific autophagy inhibitor 3-MA prevents both LC3 I/LC3 II conversion and HUVEC cell death. Finally, early removal of Bortezomib is accompanied by the recovery of cell shape and viability. These findings strongly suggest that Bortezomib induces either apoptosis or autophagy in EC; interfering with the autophagic response may potentiate the antiangiogenic effect of the drug.