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

Tigecycline Opposes Bortezomib Effect on Myeloma Cells Decreasing Mitochondrial Reactive Oxygen Species Production

Multiple myeloma is an incurable plasma cell malignancy. Most patients end up relapsing and developing resistance to antineoplastic drugs, like bortezomib. Antibiotic tigecycline has activity against myeloma. This study analyzed tigecycline and bortezomib combination on cell lines and plasma cells from myeloma patients. Apoptosis, autophagic vesicles, mitochondrial mass, mitochondrial superoxide, cell cycle, and hydrogen peroxide were studied by flow cytometry. In addition, mitochondrial antioxidants and electron transport chain complexes were quantified by reverse transcription real-time PCR (RT-qPCR) or western blot. Cell metabolism and mitochondrial activity were characterized by Seahorse and RT-qPCR. We found that the addition of tigecycline to bortezomib reduces apoptosis in proportion to tigecycline concentration. Supporting this, the combination of both drugs counteracts bortezomib in vitro individual effects on the cell cycle, reduces autophagy and mitophagy markers, and reverts bortezomib-induced increase in mitochondrial superoxide. Changes in mitochondrial homeostasis and MYC upregulation may account for some of these findings. These data not only advise to avoid considering tigecycline and bortezomib combination for treating myeloma, but caution on the potential adverse impact of treating infections with this antibiotic in myeloma patients under bortezomib treatment.

Expression of thimet oligopeptidase (THOP) modulated by oxidative stress in human multidrug resistant (MDR) leukemia cells

Thimet oligopeptidase (THOP) is a cytosolic metallopeptidase known to regulate the fate of post-proteasomal peptides, protein turnover and peptide selection in the antigen presentation machinery (APM) system. Oxidative stress influences THOP expression and regulates its proteolytic activity, generating variable cytosolic peptide levels, possibly affecting the immune evasion of tumor cells. In the present work, we examined the association between THOP expression/activity and stress oxidative resistance in human leukemia cells using the K562 cell line, a chronic myeloid leukemia (CML), and the multidrug-resistant (MDR) Lucena 1 (K562-derived MDR cell line) as model. The Lucena 1 phenotype was validated under vincristine treatment and the relative THOP1 mRNA levels and protein expression compared to K562 cell line. Our data demonstrated increased THOP1 gene and protein levels in K562 cells in contrast to the oxidative-resistant Lucena 1, even after H2O2 treatment, suggesting an oxidative stress dependence in THOP regulation. Further, it was observed higher basal levels of reactive oxygen species (ROS) in K562 compared to Lucena 1 cell line using DHE fluorescent probe. Since THOP activity is dependent on its oligomeric state, we also compared its proteolytic activity under reducing agent treatment, which demonstrated that its function modulation with respect to changes in redox state. Finally, the mRNA expression and FACS analyses demonstrated a reduced expression of MHC I only in K562 cell line. In conclusion, our results highlight THOP redox modulation, which could influence antigen presentation in multidrug resistant leukemia cells.

Understanding DNA Damage Response and DNA Repair in Multiple Myeloma

Multiple myeloma (MM) is a plasma cell malignancy characterized by several genetic abnormalities, including chromosomal translocations, genomic deletions and gains, and point mutations. DNA damage response (DDR) and DNA repair mechanisms are altered in MM to allow for tumor development, progression, and resistance to therapies. Damaged DNA rarely induces an apoptotic response, given the presence of ataxia-telangiectasia mutated (ATM) loss-of-function or mutations, as well as deletions, mutations, or downregulation of tumor protein p53 (TP53) and tumor protein p73 (TP73). Moreover, DNA repair mechanisms are either hyperactive or defective to allow for rapid correction of the damage or permissive survival. Medications used to treat patients with MM can induce DNA damage, by either direct effects (mono-adducts induced by melphalan), or as a result of reactive oxygen species (ROS) production by proteasome inhibitors such as bortezomib. In this review, we will describe the mechanisms of DDR and DNA repair in normal tissues, the contribution of these pathways to MM disease progression and other phenotypes, and the potential therapeutic opportunities for patients with MM.

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.

Combined thioredoxin reductase and glutaminase inhibition exerts synergistic anti-tumor activity in MYC-high high-grade serous ovarian carcinoma

Approximately 50%-55% of high-grade serous ovarian carcinoma (HGSOC) patients have MYC oncogenic pathway activation. Because MYC is not directly targetable, we have analyzed molecular pathways enriched in MYC-high HGSOC tumors to identify potential therapeutic targets. Here, we report that MYC-high HGSOC tumors show enrichment in genes controlled by NRF2, an antioxidant signaling pathway, along with increased thioredoxin redox activity. Treatment of MYC-high HGSOC tumors cells with US Food and Drug Administration (FDA)-approved thioredoxin reductase 1 (TrxR1) inhibitor auranofin resulted in significant growth suppression and apoptosis in MYC-high HGSOC cells in vitro and also significantly reduced tumor growth in an MYC-high HGSOC patient-derived tumor xenograft. We found that auranofin treatment inhibited glycolysis in MYC-high cells via oxidation-induced GAPDH inhibition. Interestingly, in response to auranofin-induced glycolysis inhibition, MYC-high HGSOC cells switched to glutamine metabolism for survival. Depletion of glutamine with either glutamine starvation or glutaminase (GLS1) inhibitor CB-839 exerted synergistic anti-tumor activity with auranofin in HGSOC cells and OVCAR-8 cell line xenograft. These findings suggest that applying a combined therapy of GLS1 inhibitor and TrxR1 inhibitor could effectively treat MYC-high HGSOC patients.

PX-12 synergistically enhances the therapeutic efficacy of vorinostat under hypoxic tumor microenvironment in oral squamous cell carcinoma in vitro

Hypoxia is a characteristic feature of solid tumors, including oral squamous cell carcinoma (OSCC), which causes therapeutic resistance. The hypoxia-inducible factor 1-alpha (HIF-1α) is a key regulator of hypoxic tumor microenvironment (TME) and a promising therapeutic target against solid tumors. Among other HIF-1α inhibitors, vorinostat (suberoylanilide hydroxamic acid, SAHA) is a histone deacetylase inhibitor (HDACi) targeting the stability of HIF-1α, and PX-12 (1-methylpropyl 2-imidazolyl disulfide) is a thioredoxin-1 (Trx-1) inhibitor preventing accumulation of HIF-1α. HDACis are effective against cancers; however, they are accompanied by several side effects along with an emerging resistance against it. This can be overcome by using HDACi in a combination regimen with Trx-1 inhibitor, as their inhibitory mechanisms are interconnected. HDACis inhibit Trx-1, leading to an increase in the production of reactive oxygen species (ROS) and inducing apoptosis in cancer cells; thus, the efficacy of HDACi can be elevated by using a Trx-1 inhibitor. In this study, we have tested the EC50 (half maximal effective concentration) doses of vorinostat and PX-12 on CAL-27 (an OSCC cell line) under both normoxic and hypoxic conditions. The combined EC50 dose of vorinostat and PX-12 is significantly reduced under hypoxia, and the interaction of PX-12 with vorinostat was evaluated by combination index (CI). An additive interaction between vorinostat and PX-12 was observed in normoxia, while a synergistic interaction was observed under hypoxia. This study provides the first evidence for vorinostat and PX-12 synergism under hypoxic TME, at the same time highlighting the therapeutically effective combination of vorinostat and PX-12 against OSCC in vitro.

Effects of Antioxidant Gene Overexpression on Stress Resistance and Malignization In Vitro and In Vivo: A Review

Reactive oxygen species (ROS) are normal products of a number of biochemical reactions and are important signaling molecules. However, at the same time, they are toxic to cells and have to be strictly regulated by their antioxidant systems. The etiology and pathogenesis of many diseases are associated with increased ROS levels, and many external stress factors directly or indirectly cause oxidative stress in cells. Within this context, the overexpression of genes encoding the proteins in antioxidant systems seems to have become a viable approach to decrease the oxidative stress caused by pathological conditions and to increase cellular stress resistance. However, such manipulations unavoidably lead to side effects, the most dangerous of which is an increased probability of healthy tissue malignization or increased tumor aggression. The aims of the present review were to collect and systematize the results of studies devoted to the effects resulting from the overexpression of antioxidant system genes on stress resistance and carcinogenesis in vitro and in vivo. In most cases, the overexpression of these genes was shown to increase cell and organism resistances to factors that induce oxidative and genotoxic stress but to also have different effects on cancer initiation and promotion. The last fact greatly limits perspectives of such manipulations in practice. The overexpression of GPX3 and SOD3 encoding secreted proteins seems to be the "safest" among the genes that can increase cell resistance to oxidative stress. High efficiency and safety potential can also be found for SOD2 overexpression in combinations with GPX1 or CAT and for similar combinations that lead to no significant changes in H₂O₂ levels. Accumulation, systematization, and the integral analysis of data on antioxidant gene overexpression effects can help to develop approaches for practical uses in biomedical and agricultural areas. Additionally, a number of factors such as genetic and functional context, cell and tissue type, differences in the function of transcripts of one and the same gene, regulatory interactions, and additional functions should be taken into account.

Thioredoxin System and miR-21, miR-23a/b and let-7a as Potential Biomarkers for Brain Tumor Progression: Preliminary Case Data

BACKGROUND

The thioredoxin system and microRNAs (miRNAs) are potential targets for both cancer progression and treatment. However, the role of miRNAs and their relation with the expression profile of thioredoxin system in brain tumor progression remains unclear.

METHODS

In this study, we aimed to determine the expression profiles of redox components Trx-1, TrxR-1 and PRDX-1, and oncogenic miR-21, miR-23a/b and let-7a and oncosuppressor miR-125 in different brain tumor tissues and their association with increasing tumor grade. We studied Trx-1, TrxR-1, and PRDX-1 messenger RNA expression levels by quantitative real-time polymerase chain reaction and protein levels by Western blot and miR-23a, miR-23b, miR-125a, miR-21, and let-7a miRNA expression levels by quantitative real-time polymerase chain reaction in 16 glioma, 15 meningioma, 5 metastatic, and 2 benign tumor samples. We also examined Trx-1, TrxR-1, and PRDX-1 protein levels in serum samples of 36 patients with brain tumor and 37 healthy volunteers by enzyme-linked immunosorbent assay.

RESULTS

We found that Trx-1, TrxR-1, and PRDX-1 presented high messenger RNA expression but low protein expression in low-grade brain tumor tissues, whereas they showed higher protein expression in sera of patients with low-grade brain tumors. miR-23b, miR-21, miR-23a, and let-7a were highly expressed in low-grade brain tumor tissues and positively correlated with the increase in thioredoxin system activity.

CONCLUSIONS

Our findings showed that Trx-1, TrxR-1, miR-21, miR-23a/b, and let-7a might be used for brain tumor diagnosis in the clinic. Further prospective studies including molecular pathway analyses are required to validate the miRNA/Trx system regulatory axis in brain tumor progression.

The Role of the Thioredoxin Detoxification System in Cancer Progression and Resistance

The intracellular redox homeostasis is a dynamic balancing system between the levels of free radical species and antioxidant enzymes and small molecules at the core of cellular defense mechanisms. The thioredoxin (Trx) system is an important detoxification system regulating the redox milieu. This system is one of the key regulators of cells’ proliferative potential as well, through the reduction of key proteins. Increased oxidative stress characterizes highly proliferative, metabolically hyperactive cancer cells, which are forced to mobilize antioxidant enzymes to balance the increase in free radical concentration and prevent irreversible damage and cell death. Components of the Trx system are involved in high-rate proliferation and activation of pro-survival mechanisms in cancer cells, particularly those facing increased oxidative stress. This review addresses the importance of the targetable redox-regulating Trx system in tumor progression, as well as in detoxification and protection of cancer cells from oxidative stress and drug-induced cytotoxicity. It also discusses the cancer cells’ counteracting mechanisms to the Trx system inhibition and presents several inhibitors of the Trx system as prospective candidates for cytostatics’ adjuvants. This manuscript further emphasizes the importance of developing novel multitarget therapies encompassing the Trx system inhibition to overcome cancer treatment limitations.

Modulation of Cellular Redox Parameters for Improving Therapeutic Responses in Multiple Myeloma

Raised oxidative stress and abnormal redox status are typical features of multiple myeloma cells, and the identification of the intimate mechanisms that regulate the relationships between neoplastic cells and redox homeostasis may reveal possible new anti-myeloma therapeutic targets to increase the effectiveness of anti-myeloma drugs synergistically or to eradicate drug-resistant clones while reducing toxicity toward normal cells. An alteration of the oxidative state is not only responsible for the onset of multiple myeloma and its progression, but it also appears essential for the therapeutic response and for developing any chemoresistance. Our review aimed to evaluate the literature’s current data on the effects of oxidative stress on the response to drugs generally employed in the therapy of multiple myeloma, such as proteasome inhibitors, immunomodulators, and autologous transplantation. In the second part of the review, we analyzed the possibility of using other substances, often of natural origin, to modulate the oxidative stress to interfere with the progression of myelomatous disease.

Ex vivo propagation in a novel 3D high-throughput co-culture system for multiple myeloma

Purpose

Multiple myeloma (MM) remains an incurable hematologic malignancy which ultimately develops drug resistance and evades treatment. Despite substantial therapeutic advances over the past years, the clinical failure rate of preclinically promising anti-MM drugs remains substantial. More realistic in vitro models are thus required to better predict clinical efficacy of a preclinically active compound.

Methods

Here, we report on the establishment of a conical agarose 3D co-culture platform for the preclinical propagation of primary MM cells ex vivo. Cell growth was compared to yet established 2D and liquid overlay systems. MM cell lines (MMCL: RPMI-8226, U266, OPM-2) and primary patient specimens were tested. Drug sensitivity was examined by exploring the cytotoxic effect of bortezomib and the deubiquitinase inhibitor auranofin under various conditions.

Results

In contrast to 2D and liquid overlay, cell proliferation in the 3D array followed a sigmoidal curve characterized by an initial growth delay but more durable proliferation of MMCL over 12 days of culture. Primary MM specimens did not expand in ex vivo monoculture, but required co-culture support by a human stromal cell line (HS-5, MSP-1). HS-5 induced a > fivefold increase in cluster volume and maintained long-term viability of primary MM cells for up to 21 days. Bortezomib and auranofin induced less cytotoxicity under 3D vs. 2D condition and in co- vs. monoculture, respectively.

Conclusions

This study introduces a novel model that is capable of long-term propagation and drug testing of primary MM specimens ex vivo overcoming some of the pitfalls of currently available in vitro models.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00432-021-03854-6.

Upgrade of an old drug: Auranofin in innovative cancer therapies to overcome drug resistance and to increase drug effectiveness

Auranofin is an oral gold(I) compound, initially developed for the treatment of rheumatoid arthritis. Currently, Auranofin is under investigation for oncological application within a drug repurposing plan due to the relevant antineoplastic activity observed both in vitro and in vivo tumor models. In this review, we analysed studies in which Auranofin was used as a single drug or in combination with other molecules to enhance their anticancer activity or to overcome chemoresistance. The analysis of different targets/pathways affected by this drug in different cancer types has allowed us to highlight several interesting targets and effects of Auranofin besides the already well-known inhibition of thioredoxin reductase. Among these targets, inhibitory-κB kinase, deubiquitinates, protein kinase C iota have been frequently suggested. To rationalize the effects of Auranofin by a system biology-like approach, we exploited transcriptomic data obtained from a wide range of cell models, extrapolating the data deposited in the Connectivity Maps website and we attempted to provide a general conclusion and discussed the major points that need further investigation.

Citarinostat and Momelotinib co-target HDAC6 and JAK2/STAT3 in lymphoid malignant cell lines: a potential new therapeutic combination

Histone deacetylase (HDAC) inhibitors represent an encouraging class of antitumor drugs. HDAC inhibitors induce a series of molecular and biological responses and minimal toxicity to normal cells. Citarinostat (Acy-241) is a second generation, orally administered, HDAC6-selective inhibitor. Momelotinib (CYT387) is an orally administered inhibitor of Janus kinase/signal transducer of transcription-3 (JAK/STAT3) signaling. Momelotinib showed efficacy in patients with myelofibrosis. We hypothesized that both HDAC and JAK/STAT pathways were important in lymphoproliferative disorders, and that inhibiting JAK/STAT3 and HDAC simultaneously might enhance the efficacy of momelotinib and citarinostat without increasing toxicity. Accordingly, we tested the citarinostat + momelotinib combination in lymphoid cell lines. Citarinostat + momelotinib showed strong cytotoxicity; it significantly reduced mitochondrial membrane potential, down-regulated Bcl-2 and Bcl-xL, and activated caspases 9 and 3. Caspase-8 was upregulated in only two lymphoid cell lines, which indicated activation of the extrinsic apoptotic pathway. We identified a lymphoid cell line that was only slightly sensitive to the combination treatment. We knocked down thioredoxin expression by transfecting with small interfering RNA that targeted thioredoxin. This knockdown increased cell sensitivity to the combination-induced cell death. The combination treatment reduced Bcl-2 expression, activated caspase 3, and significantly inhibited cell viability and clonogenic survival.

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.

Thioredoxin inhibitor PX-12 induces mitochondria-mediated apoptosis in acute lymphoblastic leukemia cells

Imbalances in redox homeostasis have been described to be involved in the development, progression and relapse of leukemia. As the thioredoxin (Trx) system, one of the major cellular antioxidant networks, has been implicated in acute lymphoblastic leukemia (ALL), we investigated the therapeutic potential of Trx inhibition in ALL. Here, we show that the Trx inhibitor PX-12 reduced cell viability and induced cell death in a dose- and time-dependent manner in different ALL cell lines. This antileukemic activity was accompanied by an increase in reactive oxygen species (ROS) levels and enhanced PRDX3 dimerization. Pre-treatment with the thiol-containing ROS scavenger N-acetylcysteine (NAC), but not with non-thiol-containing scavengers α-tocopherol (α-Toc) or Mn(III)tetrakis(4-benzoic acid) porphyrin chloride (MnTBAP), significantly rescued PX-12-induced cell death. Furthermore, PX-12 triggered activation of BAK. Importantly, knockdown of BAK reduced PX-12-stimulated ROS production and cell death. Similarly, silencing of NOXA provided significant protection from PX-12-mediated cell death. The relevance of mitochondria-mediated, caspase-dependent apoptosis was further supported by data showing that PX-12 triggered cleavage of caspase-3 and that addition of the broad-range caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (zVAD.fmk) potently blocked cell death upon PX-12 treatment. This study provides novel insights into the mechanisms of PX-12-induced cell death in ALL and further highlights the therapeutic potential of redox-active compounds in ALL.

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.

Cytotoxic and radiosensitising effects of a novel thioredoxin reductase inhibitor in breast cancer

Radiotherapy is an effective treatment modality for breast cancer but, unfortunately, not all patients respond fully with a significant number experiencing local recurrences. Overexpression of thioredoxin and thioredoxin reductase has been reported to cause multidrug and radiation resistance - their inhibition may therefore improve therapeutic efficacy. Novel indolequinone compounds have been shown, in pancreatic cancer models, to inhibit thioredoxin reductase activity and exhibit potent anticancer activity. The present study evaluates, using in vitro breast cancer models, the efficacy of a novel indolequinone compound (IQ9) as a single agent and in combination with ionising radiation using a variety of endpoint assays including cell proliferation, clonogenic survival, enzyme activity, and western blotting. Three triple-negative breast cancer (MDA-MB-231, MDA-MB-468, and MDA-MB-436) and two luminal (MCF-7 and T47D) breast cancer cell lines were used. Results show that treatment with IQ9 significantly inhibited thioredoxin reductase activity, and inhibited cell growth and colony formation of breast cancer cells with IC₅₀ values in the low micromolar ranges. Enhanced radiosensitivity of triple-negative breast cancer cells was observed, with sensitiser enhancement ratios of 1.20–1.43, but with no evident radiosensitisation of luminal breast cancer cell lines. IQ9 upregulated protein expression of thioredoxin reductase in luminal but not in triple-negative breast cancer cells which may explain the observed differential radiosensitisation. This study provides important evidence of the roles of the thioredoxin system as an exploitable radiobiological target in breast cancer cells and highlights the potential therapeutic value of indolequinones as radiosensitisers.

***This study was not part of a clinical trial. Clinical trial registration number: N/A

The Prognostic Value of Whole-Blood PSMB5, CXCR4, POMP, and RPL5 mRNA Expression in Patients with Multiple Myeloma Treated with Bortezomib

Simple Summary

The mRNA expression of nine previously described genes that may affect resistance to multiple myeloma (MM), viz., ABCB1, CXCR4, MAF, MARCKS, POMP, PSMB5, RPL5, TXN, and XBP1, was compared between bortezomib-refractory and bortezomib-sensitive patients. RPL5 was the only gene to be significantly down-regulated in MM patients compared with non-MM individuals, while POMP was significantly up-regulated in the bortezomib-refractory patients. Multivariate analysis found the best independent predictors of progression-free survival to be high PSMB5 and CXCR expression and autologous stem cell transplantation, and that high expression of POMP and RPL5 were associated with shorter survival.

Abstract

Proteasome inhibitors, like bortezomib, play a key role in the treatment of multiple myeloma (MM); however, most patients eventually relapse and eventually show multiple drug resistance, and the molecular mechanisms of this resistance remain unclear. The aim of our study is to assess the expression of previously described genes that may influence the resistance to bortezomib treatment at the mRNA level (ABCB1, CXCR4, MAF, MARCKS, POMP, PSMB5, RPL5, TXN, and XBP1) and prognosis of MM patients. mRNA expression was determined in 73 MM patients treated with bortezomib-based regimens (30 bortzomib-sensitive and 43 bortezomib-refractory patients) and 11 healthy controls. RPL5 was significantly down-regulated in multiple myeloma patients as compared with healthy controls. Moreover, POMP was significantly up-regulated in MM patients refractory to bortezomib-based treatment. In multivariate analysis, high expression of PSMB5 and CXCR and autologous stem cell transplantation were independent predictors of progression-free survival, and high expression of POMP and RPL5 was associated with shorter overall survival.

Investigating the Thioredoxin and Glutathione Systems' Response in Lymphoma Cells after Treatment with [Au(d2pype)2]CL

Lymphoma is a blood cancer comprising various subtypes. Although effective therapies are available, some patients fail to respond to treatment and can suffer from side effects. Antioxidant systems, especially the thioredoxin (Trx) and glutathione (GSH) systems, are known to enhance cancer cell survival, with thioredoxin reductase (TrxR) recently reported as a potential anticancer target. Since the GSH system can compensate for some Trx system functions, we investigated its response in three lymphoma cell lines after inhibiting TrxR activity with [Au(d2pype)2]Cl, a known TrxR inhibitor. [Au(d2pype)2]Cl increased intracellular reactive oxygen species (ROS) levels and induced caspase-3 activity leading to cell apoptosis through inhibiting both TrxR and glutathione peroxidase (Gpx) activity. Expression of the tumour suppresser gene TXNIP increased, while GPX1 and GPX4 expression, which are related to poor prognosis of lymphoma patients, decreased. Unlike SUDHL2 and SUDHL4 cells, which exhibited a decreased GSH/GSSG ratio after treatment, in KMH2 cells the ratio remained unchanged, while glutathione reductase and glutaredoxin expression increased. Since KMH2 cells were less sensitive to treatment with [Au(d2pype)2]Cl, the GSH system may play a role in protecting cells from apoptosis after TrxR inhibition. Overall, our study demonstrates that inhibition of TrxR represents a valid therapeutic approach for lymphoma.

Regulacja układu zależnego od tioredoksyny jako element farmakoterapii w chorobach z zaburzeniami równowagi redoks

Działanie wielu czynników egzogennych, a także zaburzone procesy metaboliczne komórek przyczyniają się do nasilonego wytwarzania oksydantów, a to zaburza równowagę redoks, wywołując zmiany metaboliczne, w tym śmierci lub transformacji nowotworowej komórek. Jednak każda komórka zawiera antyoksydanty, które mają zapobiegać tego typu sytuacjom. Jednym z układów antyoksydacyjnych, funkcjonujących w komórkach, jest układ zależny od tioredoksyny, w skład którego wchodzą: tioredoksyna (Trx), reduktaza tioredoksyny (TrxR) oraz peroksydaza tioredoksyny (TPx), które mogą redukować utlenione składniki komórek kosztem fosforanu dinukleotydu nikotynoamidoadeninowego (NADPH). Działanie takie wynika z budowy przestrzennej Trx oraz TrxR, która umożliwia wytworzenie wewnątrzcząsteczkowego mostka disulfidowego w obrębie cząsteczki tioredoksyny oraz dwóch międzycząsteczkowych mostków selenosulfidowych w obrębie dimeru reduktazy tioredoksyny. Inną, równie istotną funkcją układu zależnego od tioredoksyny jest regulowanie ekspresji wielu białek za pośrednictwem takich czynników jak czynnik transkrypcyjnego NF-κB oraz kinaza regulująca apoptozę (ASK-1), które uruchamiają kaskady przemian metabolicznych prowadzących ostatecznie do proliferacji lub apoptozy komórek. Wzrost ekspresji/aktywności składników systemu zależnego od Trx obserwuje się w rozwoju wielu nowotworów. Dlatego też poszukiwanie selektywnych inhibitorów tioredoksyny lub reduktazy tioredoksyny jest obecnie jednym z głównych kierunków badań w farmakoterapii nowotworów. Wykazano, że wiele naturalnie występujących związków polifenolowych pochodzenia naturalnego o działaniu antyoksydacyjnym (np. kwercetyna czy kurkumina) powoduje inaktywację układu Trx-TrxR. Jednocześnie wiele syntetycznych związków, w tym związki kompleksowe, które stosowane są w terapii przeciwnowotworowej (np. cisplatyna, auranofina, moteksafina gadolinu), również hamują działanie układu zależnego od Trx.

Thioredoxin-dependent system. Application of inhibitors

One of the systems responsible for maintaining cellular redox homeostasis is the thioredoxin-dependent system. An equally important function of this system is the regulation of the expression of many proteins by the transcription factor NF-κB or the apoptosis regulating kinase (ASK-1). Since it has been shown that the Trx-dependent system can contribute to both the enhancement of tumour angiogenesis and growth as well as apoptosis of neoplastic cells, the search for compounds that inhibit the level/activity of Trx and/or TrxR and thus modulate the course of the neoplastic process is ongoing. It has been shown that many naturally occurring polyphenolic compounds inactivate elements of the thioredoxin system. In addition, the effectiveness of Trx is inhibited by imidazole derivatives, while the activity of TrxR is reduced by transition metal ions complexes, dinitrohalobenzene derivatives, Michael acceptors, nitrosourea and ebselen. In addition, research is ongoing to identify new selective Trx/TrxR inhibitors.

Protein Carbonylation and Lipid Peroxidation in Hematological Malignancies

Among the different mechanisms involved in oxidative stress, protein carbonylation and lipid peroxidation are both important modifications associated with the pathogenesis of several diseases, including cancer. Hematopoietic cells are particularly vulnerable to oxidative damage, as the excessive production of reactive oxygen species and associated lipid peroxidation suppress self-renewal and induce DNA damage and genomic instability, which can trigger malignancy. A richer understanding of the clinical effects of oxidative stress might improve the prognosis of these diseases and inform therapeutic strategies. The most common protein carbonylation and lipid peroxidation compounds, including hydroxynonenal, malondialdehyde, and advanced oxidation protein products, have been investigated for their potential effect on hematopoietic cells in several studies. In this review, we focus on the most important protein carbonylation and lipid peroxidation biomarkers in hematological malignancies, their role in disease development, and potential treatment implications.

On the mechanisms underlying attenuated redox responses to exercise in older individuals: A hypothesis

Responding appropriately to exercise is essential to maintenance of skeletal muscle mass and function at all ages and particularly during aging. Here, a hypothesis is presented that a key component of the inability of skeletal muscle to respond effectively to exercise in aging is a denervation-induced failure of muscle redox signalling. This novel hypothesis proposes that an initial increase in oxidation in muscle mitochondria leads to a paradoxical increase in the reductive state of specific cysteines of signalling proteins in the muscle cytosol that suppresses their ability to respond to normal oxidising redox signals during exercise. The following are presented for consideration:Transient loss of integrity of peripheral motor neurons occurs repeatedly throughout life and is normally rapidly repaired by reinnervation, but this repair process becomes less efficient with aging. Each transient loss of neuromuscular integrity leads to a rapid, large increase in mitochondrial peroxide production in the denervated muscle fibers and in neighbouring muscle fibers. This peroxide may initially act to stimulate axonal sprouting and regeneration, but also stimulates retrograde mitonuclear communication to increase expression of a range of cytoprotective proteins in an attempt to protect the fiber and neighbouring tissues against oxidative damage. The increased peroxide within mitochondria does not lead to an increased cytosolic peroxide, but the increases in adaptive cytoprotective proteins include some located to the muscle cytosol which modify the local cytosol redox environment to induce a more reductive state in key cysteines of specific signalling proteins. Key adaptations of skeletal muscle to exercise involve transient peroxiredoxin oxidation as effectors of redox signalling in the cytosol. This requires sensitive oxidation of key cysteine residues. In aging, the chronic change to a more reductive cytosolic environment prevents the transient oxidation of peroxiredoxin 2 and hence prevents essential adaptations to exercise, thus contributing to loss of muscle mass and function. Experimental approaches suitable for testing the hypothesis are also outlined.

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.

Transcriptional heterogeneity of clonal plasma cells and immune evasion in immunoglobulin light chain amyloidosis

Immunoglobulin light chain amyloidosis (AL amyloidosis) is characterized by the presence of B cells producing amyloidogenic immunoglobulin light chains (LCs). The low frequency of aberrant B cells in AL is often masked by a polyclonal B cell background, making it difficult for treatment. We analyzed the single-cell RNA sequencing data from GEO database to compare the plasma cell (PCs) in four individuals with AL amyloidosis, one AL subject after treatment, and six healthy controls. High interindividual variability in AL-derived PCs in their expression pattern of known overexpressed genes in multiple myeloma and their usage of V regions in LCs was demonstrated. We also found overexpression of MHC class I molecules as one of the common features of clonal PCs in individuals with AL amyloidosis. Significantly reduced frequencies of circulating natural killer (NK) cells were also observed in a small cohort of AL patients when compared to healthy controls. These data demonstrate that aberrant PCs in AL has a highly diverse transcriptome, an upregulation of MHC, and a dampened capability of immunosurveillance by reduction of circulating NK frequencies. The analysis of clonal PCs at single cell level may provide a better approach for precise molecular profiling and diagnosis of AL amyloidosis.

Chromatin activation as a unifying principle underlying pathogenic mechanisms in multiple myeloma

Multiple myeloma (MM) is a plasma cell neoplasm associated with a broad variety of genetic lesions. In spite of this genetic heterogeneity, MMs share a characteristic malignant phenotype whose underlying molecular basis remains poorly characterized. In the present study, we examined plasma cells from MM using a multi-epigenomics approach and demonstrated that, when compared to normal B cells, malignant plasma cells showed an extensive activation of regulatory elements, in part affecting coregulated adjacent genes. Among target genes up-regulated by this process, we found members of the NOTCH, NF-kB, MTOR signaling, and TP53 signaling pathways. Other activated genes included sets involved in osteoblast differentiation and response to oxidative stress, all of which have been shown to be associated with the MM phenotype and clinical behavior. We functionally characterized MM-specific active distant enhancers controlling the expression of thioredoxin (TXN), a major regulator of cellular redox status and, in addition, identified PRDM5 as a novel essential gene for MM. Collectively, our data indicate that aberrant chromatin activation is a unifying feature underlying the malignant plasma cell phenotype.

Selenoproteins and their emerging roles in signaling pathways

The functional activity of selenoproteins has a wide range of effects on complex pathogenetic processes, including teratogenesis, immuno-inflammatory, neurodegenerative. Being active participants and promoters of many signaling pathways, selenoproteins support the lively interest of a wide scientific community. This review is devoted to the analysis of recent data describing the participation of selenoproteins in various molecular interactions mediating important signaling pathways. Data processing was carried out by the method of complex analysis. For convenience, all selenoproteins were divided into groups depending on their location and function. Among the group of selenoproteins of the ER membrane, selenoprotein N affects the absorption of Ca2+ by the endoplasmic reticulum mediated by oxidoreductin (ERO1), a key player in the CHOP/ERO1 branch, a pathogenic mechanism that causes myopathy. Another selenoprotein of the ER membrane selenoprotein K binding to the DHHC6 protein affects the IP3R receptor that regulates Ca2+ flux. Selenoprotein K is able to affect another protein of the endoplasmic reticulum CHERP, also appearing in Ca2+ transport. Selenoprotein S, associated with the lumen of ER, is able to influence the VCP protein, which ensures the incorporation of selenoprotein K into the ER membrane. Selenoprotein M, as an ER lumen protein, affects the phosphorylation of STAT3 by leptin, which confirms that Sel M is a positive regulator of leptin signaling. Selenoprotein S also related to luminal selenoproteins ER is a modulator of the IRE1α-sXBP1 signaling pathway. Nuclear selenoprotein H will directly affect the suppressor of malignant tumours, p53 protein, the activation of which increases with Sel H deficiency. The same selenoprotein is involved in redox regulation. Among the cytoplasmic selenoproteins, abundant investigations are devoted to SelP, which affects the PI3K/Akt/Erk signaling pathway during ischemia/reperfusion, is transported into the myoblasts through the plasmalemma after binding to the apoER2 receptor, and into the neurons to the megaline receptor and in general, selenoprotein P plays the role of a pool that stores the necessary trace element and releases it, if necessary, for vital selenoproteins. The thioredoxin reductase family plays a key role in the invasion and metastasis of salivary adenoid cystic carcinoma through the influence on the TGF-β-Akt/GSK-3β pathway during epithelial-mesenchymal transition. The deletion of thioredoxin reductase 1 affects the levels of messengers of the Wnt/β-catenin signaling pathway. No less studied is the glutathione peroxidase group, of which GPX3 is able to inhibit signaling in the Wnt/β-catenin pathway and thereby inhibit thyroid metastasis, as well as suppress protein levels in the PI3K/Akt/c-fos pathway. A key observation is that in cases of carcinogenesis, a decrease in GPX3 and its hypermethylation are almost always found. Among deiodinases, deiodinase 3 acts as a promoter of the oncogenes BRAF, MEK or p38, while stimulating a decrease in the expression of cyclin D1. The dependence of the level of deiodinase 3 on the Hedgehog (SHH) signaling pathway is also noted. Methionine sulfoxide reductase A can compete for the uptake of ubiquitin, reduce p38, JNK and ERK promoters of the MAPK signaling pathway; methionine sulfoxide reductase B1 suppresses MAPK signaling messengers, and also increases PARP and caspase 3.

Hydrogen Sulfide Mediates Tumor Cell Resistance to Thioredoxin Inhibitor

Thioredoxin (Trx) is a pro-oncogenic molecule that underlies tumor initiation, progression and chemo-resistance. PX-12, a Trx inhibitor, has been used to treat certain tumors. Currently, factors predicting tumor sensitivity to PX-12 are unclear. Given that hydrogen sulfide (H₂S), a gaseous bio-mediator, promotes Trx activity, we speculated that it might affect tumor response to PX-12. Here, we tested this possibility. Exposure of several different types of tumor cells to PX-12 caused cell death, which was reversely correlated with the levels of H₂S-synthesizing enzyme CSE and endogenous H₂S. Inhibition of CSE sensitized tumor cells to PX-12, whereas addition of exogenous H₂S elevated PX-12 resistance. Further experiments showed that H₂S abolished PX-12-mediated inhibition on Trx. Mechanistic analyses revealed that H₂S stimulated Trx activity. It promoted Trx from the oxidized to the reduced state. In addition, H₂S directly cleaved the disulfide bond in PX-12, causing PX-12 deactivation. Additional studies found that, besides Trx, PX-12 also interacted with the thiol residues of other proteins. Intriguingly, H₂S-mediated cell resistance to PX-12 could also be achieved through promotion of the thiol activity of these proteins. Addition of H₂S-modified protein into culture significantly enhanced cell resistance to PX-12, whereas blockade of extracellular sulfhydryl residues sensitized cells to PX-12. Collectively, our study revealed that H₂S mediated tumor cell resistance to PX-12 through multiple mechanisms involving induction of thiol activity in multiple proteins and direct inactivation of PX-12. H₂S could be used to predict tumor response to PX-12 and could be targeted to enhance the therapeutic efficacy of PX-12.

The role of deubiquitinating enzymes in cancer drug resistance

Drug resistance is a well-known phenomenon leading to a reduction in the effectiveness of pharmaceutical treatments. Resistance to chemotherapeutic agents can involve various intrinsic cellular processes including drug efflux, increased resistance to apoptosis, increased DNA damage repair capabilities in response to platinum salts or other DNA-damaging drugs, drug inactivation, drug target alteration, epithelial-mesenchymal transition (EMT), inherent cell heterogeneity, epigenetic effects, or any combination of these mechanisms. Deubiquitinating enzymes (DUBs) reverse ubiquitination of target proteins, maintaining a balance between ubiquitination and deubiquitination of proteins to maintain cell homeostasis. Increasing evidence supports an association of altered DUB activity with development of several cancers. Thus, DUBs are promising candidates for targeted drug development. In this review, we outline the involvement of DUBs, particularly ubiquitin-specific proteases, and their roles in drug resistance in different types of cancer. We also review potential small molecule DUB inhibitors that can be used as drugs for cancer treatment.

Cross-talk between Bcr-abl and the Thioredoxin System in Chronic Myeloid Leukaemia: Implications for CML Treatment

Chronic myeloid leukaemia (CML) is currently treated with inhibitors of the CML specific oncoprotein, bcr-abl. While this strategy is initially successful, drug resistance can become a problem. Therefore, new targets need to be identified to ensure the disease can be appropriately managed. The thioredoxin (Trx) system, comprised of Trx, thioredoxin reductase (TrxR), and NADPH, is an antioxidant system previously identified as a target for therapies aimed at overcoming drug resistance in other cancers. We assessed the effectiveness of TrxR inhibitors on drug resistant CML cells and examined links between TrxR and the bcr-abl cell-signalling pathway. Two TrxR inhibitors, auranofin and [Au(d2pype)₂]Cl, increased intracellular ROS levels and elicited apoptosis in both sensitive and imatinib resistant CML cells. Inhibition of TrxR activity by these pharmacological inhibitors, or by specific siRNA, also resulted in decreased bcr-abl mRNA and protein levels, and lower bcr-abl downstream signalling activity, potentially enhancing the effectiveness of TrxR inhibitors as CML therapies. In addition, imatinib resistant CML cell lines showed upregulated expression of the Trx system. Furthermore, analysis of datasets showed that CML patients who did not respond to imatinib had higher Trx mRNA levels than patients who responded to treatment. Our study demonstrates a link between the Trx system and the bcr-abl protein and highlights the therapeutic potential of targeting the Trx system to improve CML patients’ outcomes.

The thioredoxin redox potential and redox charge are surrogate measures for flux in the thioredoxin system

The thioredoxin system plays a central role in intracellular redox regulation and its dysregulation is associated with a number of pathologies. However, the connectivity within this system poses a significant challenge for quantification and consequently several disparate measures have been used to characterize the system. For in vitro studies, the thioredoxin system flux has been measured by NADPH oxidation while the thioredoxin redox state has been used to estimate the activity of the system in vivo. The connection between these measures has been obscure although substrate saturation in the thioredoxin system results from the saturation of the thioredoxin redox cycle. We used computational modeling and in vitro kinetic assays to clarify the relationship between flux and the current in vivo measures of the thioredoxin system together with a novel measure, the thioredoxin redox charge (reduced thioredoxin/total thioredoxin). Our results revealed that the thioredoxin redox potential and redox charge closely tracked flux perturbations showing that these indices could be used as surrogate measures of the flux in vivo and, provide a mechanistic explanation for the previously observed correlations between thioredoxin oxidation and certain pathologies. While we found no significant difference in the linear correlations obtained for the thioredoxin redox potential and redox charge with the flux, the redox charge may be preferred because it is bounded between zero and one and can be determined over a wider range of conditions allowing for quantitative flux comparisons between cell types and conditions.

Inhibition of the Nrf2-TrxR Axis Sensitizes the Drug-Resistant Chronic Myelogenous Leukemia Cell Line K562/G01 to Imatinib Treatments

Nuclear factor erythroid 2-related factor 2 (Nrf2) is involved in tumor drug resistance, but its role in imatinib resistance of chronic myeloid leukemia (CML) remains elusive. We aimed to investigate the effects of Nrf2 on drug sensitivity, thioredoxin reductase (TrxR) expression, reactive oxygen species (ROS) production, and apoptosis induction in imatinib-resistant CML K562/G01 cells and explored their potential mechanisms. Stable K562/G01 cells with knockdown of Nrf2 were established by infection of siRNA-expressing lentivirus. The mRNA and protein expression levels of Nrf2 and TrxR were determined by real-time quantitative polymerase chain reaction and western blot, respectively. ROS generation and apoptosis were assayed by flow cytometry, while drug sensitivity was measured by the Cell Counting Kit-8 assay. Imatinib-resistant K562/G01 cells had higher levels of Nrf2 expression than the parental K562 cells at both mRNA and protein levels. Expression levels of Nrf2 and TrxR were positively correlated in K562/G01 cells. Knockdown of Nrf2 in K562/G01 cells enhanced the intracellular ROS level, suppressed cell proliferation, and increased apoptosis in response to imatinib treatments. Nrf2 expression contributes to the imatinib resistance of K562/G01 cells and is positively correlated with TrxR expression. Targeted inhibition of the Nrf2-TrxR axis represents a potential therapeutic approach for imatinib-resistant CML.

Expression of thioredoxin 1 and peroxiredoxins in squamous cervical carcinoma and its predictive role in NACT

Background

This study aims to investigate the expression of thioredoxin 1, peroxiredoxin 1 and peroxiredoxin 2 in bulky cervical squamous carcinoma and its predictive role in cisplatin-based neoadjuvant chemotherapy.

Methods

Initially, the expression of thioredoxin 1, peroxiredoxin 1 and peroxiredoxin 2 protein was analyzed in 13 human cervical squamous cancer tissues and their paired adjacent non-cancerous tissues by western-blotting and immunohistochemistry. Then, correlation between the expression of thioredoxin 1, peroxiredoxin 1, peroxiredoxin 2 and responses to cisplatin-based neoadjuvant chemotherapy was analyzed in 35 paired tumor samples (pre- and post-chemotherapy) from bulky cervical squamous cancer patients by immunohistochemistry.

Results

A clinical response occurred in 48.6% (17/35) of patients, including 14.3% (5/35) with a complete response and 34.3% (12/35) with a partial response. The expression of thioredoxin 1, peroxiredoxin 1 and peroxiredoxin 2 was much higher in cervical squamous cancer tissues compared with paired adjacent non-cancerous tissues by western-blotting and immunohistochemistry. Additionally, the expression of thioredoxin 1, peroxiredoxin 1 and peroxiredoxin 2 was significantly up-regulated in post-chemotherapy tissues compared to pre-chemotherapy cervical cancer tissues. High levels of thioredoxin 1, peroxiredoxin 1 and peroxiredoxin 2 were associated with a poor chemotherapy response in cervical squamous cancer patients.

Conclusions

Thioredoxin 1, peroxiredoxin 1 and peroxiredoxin 2 are frequently over-expressed in cervical squamous cancer. High expression levels of these proteins were related to a poor response to cisplatin-based neoadjuvant chemotherapy. The present study is the first report that thioredoxin peroxidase system may serve as a prediction of the responses to neoadjuvant chemotherapy in cervical squamous cancer.

Anticancer activity of a Gold(I) phosphine thioredoxin reductase inhibitor in multiple myeloma

Multiple myeloma (MM), the second most common haematological malignancy, is a clonal plasma B-cell neoplasm that forms within the bone marrow. Despite recent advancements in treatment, MM remains an incurable disease. Auranofin, a linear gold(I) phosphine compound, has previously been shown to exert a significant anti-myeloma activity by inhibiting thioredoxin reductase (TrxR) activity. A bis-chelated tetrahedral gold(I) phosphine complex [Au(d2pype)₂]Cl (where d2pype is 1,2-bis(di-2-pyridylphosphino)ethane) was previously designed to improve the gold(I) compound selectivity towards selenol- and thiol-containing proteins, such as TrxR. In this study, we show that [Au(d2pype)₂]Cl significantly inhibited TrxR activity in both bortezomib-sensitive and resistant myeloma cells, which led to a significant reduction in cell proliferation and induction of apoptosis, both of which were dependent on ROS. In clonogenic assays, treatment with [Au(d2pype)₂]Cl completely abrogated the tumourigenic capacity of MM cells, whereas auranofin was less effective. We also show that [Au(d2pype)₂]Cl exerted a significant anti-myeloma activity in vivo in human RPMI8226 xenograft model in immunocompromised NOD/SCID mice. The MYC oncogene, known to drive myeloma progression, was downregulated in both in vitro and in vivo models when treated with [Au(d2pype)₂]Cl. This study highlights the "proof of concept" that improved gold(I)-based compounds could potentially be used to not only treat MM but as an alternative tool to understand the role of the Trx system in the pathogenesis of this blood disease.

Hypoxia-Inducible Factors as an Alternative Source of Treatment Strategy for Cancer

Hypoxia-inducible factors (HIFs) are transcription factors that activate the transcription of genes necessary to circumvent to hypoxic (low oxygen level) environments. In carcinogenesis, HIFs play a critical role. Indeed, HIF-1α has been validated as a promising target for novel cancer therapeutics, even as clinical investigations have linked increased levels of HIF-1α with aggressive cancer progression as well as poor patient prognosis. More so, inhibiting HIF-1 activity restricted cancer progression. Therefore, HIF-1 is a viable target for cancer therapy. This may be expected considering the fact that cancer cells are known to be hypoxic. In order to survive the hypoxic microenvironment, cancer cells activate several biochemical pathways via the HIF-1α. Additionally, cellular and molecular insights have proved prospects of the HIF-1α pathway for the development of novel anticancer treatment strategies. The biochemical importance of hypoxia-inducible factors (HIFs) cannot be overemphasized as carcinogenesis, cancer progression, and HIFs are intricately linked. Therefore, this review highlights the significance of these linkages and also the prospects of HIFs as an alternative source of cancer therapies.

Therapeutic cooperation between auranofin, a thioredoxin reductase inhibitor and anti-PD-L1 antibody for treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBCs) is a very aggressive and lethal form of breast cancer with no effective targeted therapy. Neoadjuvant chemotherapies and radiotherapy remains a mainstay of treatment with only 25-30% of TNBC patients responding. Thus, there is an unmet clinical need to develop novel therapeutic strategies for TNBCs. TNBC cells have increased intracellular oxidative stress and suppressed glutathione, a major antioxidant system, but still, are protected against higher oxidative stress. We screened a panel of antioxidant genes using the TCGA and METABRIC databases and found that expression of the thioredoxin pathway genes is significantly upregulated in TNBC patients compared to non-TNBC patients and is correlated with adverse survival outcomes. Treatment with auranofin (AF), an FDA-approved thioredoxin reductase inhibitor caused specific cell death and impaired the growth of TNBC cells grown as spheroids. Furthermore, AF treatment exerted a significant in vivo antitumor activity in multiple TNBC models including the syngeneic 4T1.2 model, MDA-MB-231 xenograft and patient-derived tumor xenograft by inhibiting thioredoxin redox activity. We, for the first time, showed that AF increased CD8^+Ve T-cell tumor infiltration in vivo and upregulated immune checkpoint PD-L1 expression in an ERK1/2-MYC-dependent manner. Moreover, combination of AF with anti-PD-L1 antibody synergistically impaired the growth of 4T1.2 primary tumors. Our data provide a novel therapeutic strategy using AF in combination with anti-PD-L1 antibody that warrants further clinical investigation for TNBC patients.

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.

Manipulation of Glucose and Hydroperoxide Metabolism to Improve Radiation Response

Dysregulated glucose and redox metabolism are near universal features of cancers. They therefore represent potential selectively toxic metabolic targets. This review outlines the preclinical and clinical data for targeting glucose and hydroperoxide metabolism in cancer, with a focus on drug strategies that have the most available evidence. In particular, inhibition of glycolysis using 2-deoxyglucose, and inhibition of redox metabolism using the glutathione pathway inhibitor buthionine sulfoximine and the thioredoxin pathway inhibitor auranofin, have shown promise in preclinical studies to increase sensitivity to chemotherapy and radiation by increasing intracellular oxidative stress. Combined inhibition of glycolysis, glutathione, and thioredoxin pathways sensitizes highly glycolytic, radioresistant cancer models in vitro and in vivo. Although the preclinical data support this approach, clinical data are limited to exploratory trials using a single drug in combination with either chemotherapy or radiation. Open research questions include optimizing drug strategies for targeting glycolysis and redox metabolism, determining the appropriate timing for administering this therapy with concurrent chemotherapy and radiation, and identifying biomarkers to determine the cancers that would benefit most from this approach. Given the quality of preclinical evidence, dual targeting of glycolysis and redox metabolism in combination with chemotherapy and radiation should be further evaluated in clinical trials.

The future of myeloma precision medicine: integrating the compendium of known drug resistance mechanisms with emerging tumor profiling technologies

Multiple myeloma (MM) is a hematologic malignancy that is considered mostly incurable in large part due to the inability of standard of care therapies to overcome refractory disease and inevitable drug-resistant relapse. The post-genomic era has been a productive period of discovery where modern sequencing methods have been applied to large MM patient cohorts to modernize our current perception of myeloma pathobiology and establish an appreciation for the vast heterogeneity that exists between and within MM patients. Numerous pre-clinical studies conducted in the last two decades have unveiled a compendium of mechanisms by which malignant plasma cells can escape standard therapies, many of which have potentially quantifiable biomarkers. Exhaustive pre-clinical efforts have evaluated countless putative anti-MM therapeutic agents and many of these have begun to enter clinical trial evaluation. While the palette of available anti-MM therapies is continuing to expand it is also clear that malignant plasma cells still have mechanistic avenues by which they can evade even the most promising new therapies. It is therefore becoming increasingly clear that there is an outstanding need to develop and employ precision medicine strategies in MM management that harness emerging tumor profiling technologies to identify biomarkers that predict efficacy or resistance within an individual's sub-clonally heterogeneous tumor. In this review we present an updated overview of broad classes of therapeutic resistance mechanisms and describe selected examples of putative biomarkers. We also outline several emerging tumor profiling technologies that have the potential to accurately quantify biomarkers for therapeutic sensitivity and resistance at genomic, transcriptomic and proteomic levels. Finally, we comment on the future of implementation for precision medicine strategies in MM and the clear need for a paradigm shift in clinical trial design and disease management.

Thioredoxin Confers Intrinsic Resistance to Cytostatic Drugs in Human Glioma Cells

Thioredoxin (Trx) overexpression is known to be a cause of chemotherapy resistance in various tumor entities. However, Trx effects on resistance are complex and depend strictly on tissue type. In the present study, we analyzed the impact of the Trx system on intrinsic chemoresistance of human glioblastoma multiforme (GBM) cells to cytostatic drugs. Resistance of GBM cell lines and primary cells to drugs and signaling inhibitors was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Impact of Trx inhibition on apoptosis was investigated by proteome profiling of a subset of proteins and annexin V apoptosis assays. Trx-interacting protein (TXNIP) was overexpressed by transfection and protein expression was determined by immunoblotting. Pharmacological inhibition of Trx by 1-methyl-2-imidazolyl-disulfide (PX-12) reduced viability of three GBM cell lines, induced expression of active caspase-3, and reduced phosphorylation of AKT-kinase and expression of β-catenin. Sensitivity to cisplatin could be restored by both PX-12 and recombinant expression of the upstream Trx inhibitor TXNIP, respectively. In addition, PX-12 also sensitized primary human GBM cells to temozolomide. Combined inhibition of Trx and the phosphatidylinositide 3-kinase (PI3K) pathway resulted in massive cell death. We conclude that the Trx system and the PI3K pathway act as a sequential cascade and could potentially present a new drug target.

Mutant p53 tunes the NRF2-dependent antioxidant response to support survival of cancer cells

NRF2 (NFE2L2) is one of the main regulators of the antioxidant response of the cell. Here we show that in cancer cells NRF2 targets are selectively upregulated or repressed through a mutant p53-dependent mechanism. Mechanistically, mutant p53 interacts with NRF2, increases its nuclear presence and resides with NRF2 on selected ARE containing gene promoters activating the transcription of a specific set of genes while leading to the transcriptional repression of others. We show that thioredoxin (TXN) is a mutant p53-activated NRF2 target with pro-survival and pro-migratory functions in breast cancer cells under oxidative stress, while heme oxygenase 1 (HMOX1) is a mutant p53-repressed target displaying opposite effects. A gene signature of NRF2 targets activated by mutant p53 shows a significant association with bad overall prognosis and with mutant p53 status in breast cancer patients. Concomitant inhibition of thioredoxin system with Auranofin and of mutant p53 with APR-246 synergizes in killing cancer cells expressing p53 gain-of-function mutants.

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.

Auranofin radiosensitizes tumor cells through targeting thioredoxin reductase and resulting overproduction of reactive oxygen species

Auranofin (AF) is an anti-arthritic drug considered for combined chemotherapy due to its ability to impair the redox homeostasis in tumor cells. In this study, we asked whether AF may in addition radiosensitize tumor cells by targeting thioredoxin reductase (TrxR), a critical enzyme in the antioxidant defense system operating through the reductive protein thioredoxin. Our principal findings in murine 4T1 and EMT6 tumor cells are that AF at 3-10 μM is a potent radiosensitizer in vitro, and that at least two mechanisms are involved in TrxR-mediated radiosensitization. The first one is linked to an oxidative stress, as scavenging of reactive oxygen species (ROS) by N-acetyl cysteine counteracted radiosensitization. We also observed a decrease in mitochondrial oxygen consumption with spared oxygen acting as a radiosensitizer under hypoxic conditions. Overall, radiosensitization was accompanied by ROS overproduction, mitochondrial dysfunction, DNA damage and apoptosis, a common mechanism underlying both cytotoxic and antitumor effects of AF. In tumor-bearing mice, a simultaneous disruption of the thioredoxin and glutathione systems by the combination of AF and buthionine sulfoximine was shown to significantly improve tumor radioresponse. In conclusion, our findings illuminate TrxR in cancer cells as an exploitable radiobiological target and warrant further validation of AF in combination with radiotherapy.

Peroxiredoxin Involvement in the Initiation and Progression of Human Cancer

SIGNIFICANCE

It has been proposed that cancer cells are heavily dependent on their antioxidant defenses for survival and growth. Peroxiredoxins are a family of abundant thiol-dependent peroxidases that break down hydrogen peroxide, and they have a central role in the maintenance and response of cells to alterations in redox homeostasis. As such, they are potential targets for disrupting tumor growth. Recent Advances: Genetic disruption of peroxiredoxin expression in mice leads to an increased incidence of neoplastic disease, consistent with a role for peroxiredoxins in protecting genomic integrity. In contrast, many human tumors display increased levels of peroxiredoxin expression, suggesting that strengthened antioxidant defenses provide a survival advantage for tumor progression. Peroxiredoxin inhibitors are being developed and explored as therapeutic agents in different cancer models.

CRITICAL ISSUES

It is important to complement peroxiredoxin knockout and expression studies with an improved understanding of the biological function of the peroxiredoxins. Although current results can be interpreted within the context that peroxiredoxins scavenge hydroperoxides, some peroxiredoxin family members appear to have more complex roles in regulating the response of cells to oxidative stress through protein interactions with constituents of other signaling pathways.

FUTURE DIRECTIONS

Further mechanistic information is required for understanding the role of oxidative stress in cancer, the function of peroxiredoxins in normal versus cancer cells, and for the design and testing of specific peroxiredoxin inhibitors that display selectivity to malignant cells. Antioxid. Redox Signal. 28, 591-608.

Inhibition of thioredoxin activates mitophagy and overcomes adaptive bortezomib resistance in multiple myeloma

Background

Although current chemotherapy using bortezomib (Velcade) against multiple myeloma in adults has achieved significant responses and even remission, a majority of patients will develop acquired resistance to bortezomib. Increased thioredoxin level has been reported to be associated with carcinogenesis; however, the role of thioredoxin in bortezomib drug resistance of myeloma remains unclear.

Methods

We generated several bortezomib-resistant myeloma cell lines by serially passaging with increased concentrations of bortezomib over a period of 1.5 years. Thioredoxin expression was measured by real-time PCR and western blot.

Results

The role of thioredoxin in the survival of bortezomib-resistant myeloma cells was determined by specific shRNA knockdown in vitro and in vivo. Thioredoxin inhibitor (PX12) was used to determine the effectiveness of thioredoxin inhibition in the treatment of bortezomib-resistant myeloma cells. The effect of thioredoxin inhibition on mitophagy induction was examined. The correlation of thioredoxin expression with patient overall survival was interrogated. Thioredoxin expression was significantly upregulated in bortezomib-resistant myeloma cells and the change correlated with the increase of bortezomib concentration. Thioredoxin gene knockdown using specific shRNA sensitized bortezomib-resistant myeloma cells to bortezomib efficiency in vitro and in vivo. Similarly, pharmacological inhibition with PX12 inhibited the growth of bortezomib-resistant myeloma cells and overcame bortezomib resistance in vitro and in vivo. Furthermore, inhibition of thioredoxin resulted in the activation of mitophagy and blockage of mitophagy prevented the effects of PX12 on bortezomib-resistant myeloma cells, indicating that mitophagy is the important molecular mechanism for the induction of cell death in bortezomib-resistant myeloma cells by PX12. Moreover, inhibition of thioredoxin resulted in downregulation of phosphorylated mTOR and ERK1/2. Finally, thioredoxin was overexpressed in primary myeloma cells isolated from bortezomib-resistant myeloma patients and overexpression of thioredoxin correlated with poor overall survival in patients with multiple myeloma.

Conclusions

Our findings demonstrated that increased thioredoxin plays a critical role in bortezomib resistance in multiple myeloma through mitophagy inactivation and increased mTOR and ERK1/2 phosphorylation. Thioredoxin provides a potential target for clinical therapeutics against multiple myeloma, particularly for bortezomib-resistant/refractory myeloma patients.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0575-7) contains supplementary material, which is available to authorized users.

Comparative proteomic profiling of refractory/relapsed multiple myeloma reveals biomarkers involved in resistance to bortezomib-based therapy

Identifying biomarkers of the resistance in multiple myeloma (MM) is a key research challenge. We aimed to identify proteins that differentiate plasma cells in patients with refractory/relapsed MM (RRMM) who achieved at least very good partial response (VGPR) and in those with reduced response to PAD chemotherapy (bortezomib, doxorubicin and dexamethasone). Comparative proteomic analysis was conducted on pretreatment plasma cells from 77 proteasome inhibitor naïve patients treated subsequently with PAD due to RRMM. To increase data confidence we used two independent proteomic platforms: isobaric Tags for Relative and Absolute Quantitation (iTRAQ) and label free (LF). Proteins were considered as differentially expressed when their accumulation between groups differed by at least 50% in iTRAQ and LF. The proteomic signature revealed 118 proteins (35 up-regulated and 83 down-regulated in ≥ VGPR group). Proteins were classified into four classes: (1) involved in proteasome function; (2) involved in the response to oxidative stress; (3) related to defense response; and (4) regulating the apoptotic process. We confirmed the differential expression of proteasome activator complex subunit 1 (PSME1) by enzyme-linked immunosorbent assay. Increased expression of proteasomes and proteins involved in protection from oxidative stress (eg., TXN, TXNDC5) plays a major role in bortezomib resistance.

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.

Thioredoxin promotes survival signaling events under nitrosative/oxidative stress associated with cancer development

Accumulating mutations may drive cells into the acquisition of abnormal phenotypes that are characteristic of cancer cells. Cancer cells feature profound alterations in proliferation programs that result in a new population of cells that overrides normal tissue construction and maintenance programs. To achieve this goal, cancer cells are endowed with up regulated survival signaling pathways. They also must counteract the cytotoxic effects of high levels of nitric oxide (NO) and of reactive oxygen species (ROS), which are by products of cancer cell growth. Accumulating experimental evidence associates cancer cell survival with their capacity to up-regulate antioxidant systems. Elevated expression of the antioxidant protein thioredoxin-1 (Trx1) has been correlated with cancer development. Trx1 has been characterized as a multifunctional protein, playing different roles in different cell compartments. Trx1 migrates to the nucleus in cells exposed to nitrosative/oxidative stress conditions. Trx1 nuclear migration has been related to the activation of transcription factors associated with cell survival and cell proliferation. There is a direct association between the p21Ras-ERK1/2 MAP Kinases survival signaling pathway and Trx1 nuclear migration under nitrosative stress. The expression of the cytoplasmic protein, the thioredoxin-interacting protein (Txnip), determines the change in Trx1 cellular compartmentalization. The anti-apoptotic actions of Trx1 and its denitrosylase activity occur in the cytoplasm and serve as important regulators of cell survival. Within this context, this review focuses on the participation of Trx1 in cells under nitrosative/oxidative stress in survival signaling pathways associated with cancer development.