Thioredoxin system inhibitors as mediators of apoptosis for cancer therapy

The thioredoxin-1 and glutathione/glutaredoxin-1 systems redundantly fuel murine B-cell development and responses

Antioxidant systems maintain cellular redox homeostasis. The thioredoxin-1 (Trx1) and the glutathione (GSH)/glutaredoxin-1 (Grx1) systems are key players in preserving cytosolic redox balance. In fact, T lymphocytes critically rely on reducing equivalents from the Trx1 system for DNA biosynthesis during metabolic reprogramming upon activation. We here show that the Trx1 system is also indispensable for development and functionality of marginal zone (MZ) B cells and B1 cells in mice. In contrast, development of conventional B cells, follicular B-cell homeostasis, germinal center reactions, and antibody responses are redundantly sustained by both antioxidant pathways. Proliferating B2 cells lacking Txnrd1 have increased glutathione (GSH) levels and upregulated cytosolic Grx1, which is barely detectable in expanding thymocytes. These results suggest that the redox capacity driving proliferation is more robust and flexible in B cells than in T cells, which may have profound implications for the therapy of B and T-cell neoplasms.

Significance of the mitochondrial thioredoxin reductase in cancer cells: An update on role, targets and inhibitors

Thioredoxin reductase 2 (TrxR2) is a key component of the mitochondrial thioredoxin system able to transfer electrons to peroxiredoxin 3 (Prx3) in a reaction mediated by thioredoxin 2 (Trx2). In this way, both the level of hydrogen peroxide and thiol redox state are modulated. TrxR2 is often overexpressed in cancer cells conferring apoptosis resistance. Due to their exposed flexible arm containing selenocysteine, both cytosolic and mitochondrial TrxRs are inhibited by a large number of molecules. The various classes of inhibitors are listed and the molecules acting specifically on TrxR2 are extensively described. Particular emphasis is given to gold(I/III) complexes with phosphine, carbene or other ligands and to tamoxifen-like metallocifens. Also chemically unrelated organic molecules, including natural compounds and their derivatives, are taken into account. An important feature of many TrxR2 inhibitors is provided by their nature of delocalized lipophilic cations that allows their accumulation in mitochondria exploiting the organelle membrane potential. The consequences of TrxR2 inhibition are presented focusing especially on the impact on mitochondrial pathophysiology. Inhibition of TrxR2, by hindering the activity of Trx2 and Prx3, increases the mitochondrial concentration of reactive oxygen species and shifts the thiol redox state toward a more oxidized condition. This is reflected by alterations of specific targets involved in the release of pro-apoptotic factors such as cyclophilin D which acts as a regulator of the mitochondrial permeability transition pore. Therefore, the selective inhibition of TrxR2 could be utilized to induce cancer cell apoptosis.

H2O2 metabolism in liver and heart mitochondria: Low emitting-high scavenging and high emitting-low scavenging systems

Although mitochondria are presumed to emit and consume reactive oxygen species (ROS), the quantitative interplay between the two processes in ROS regulation is not well understood. Here, we probed the role of mitochondrial bioenergetics in H₂O₂ metabolism using rainbow trout liver and heart mitochondria. Both liver and heart mitochondria emitted H₂O₂ at rates that depended on their metabolic state, with the emission rates (free radical leak) constituting 0.8-2.9% and 0.2-2.5% of the respiration rate in liver and heart mitochondria, respectively. When presented with exogenous H₂O₂, liver and heart mitochondria consumed it by first order reactions with half-lives (s) of 117 and 210, and rate constants of 5.96 and 3.37 (× 10^-3 s^-1), respectively. The mitochondrial bioenergetic status greatly affected the rate of H₂O₂ consumption in heart but not liver mitochondria. Moreover, the activities and contribution of H₂O₂ scavenging systems varied between liver and heart mitochondria. The significance of the scavenging systems ranked by the magnitude (%) of inhibition of H₂O₂ removal after correcting for emission were, liver (un-energized and energized): catalase > glutathione (GSH) ≥ thioredoxin reductase (TrxR); un-energized heart mitochondria: catalase > TrxR > GSH and energized heart mitochondria: GSH > TrxR > catalase. Notably, depletion of GSH evoked a massive surge in H₂O₂ emission that grossly masked the contribution of this pathway to H₂O₂ scavenging in heart mitochondria. Irrespective of the organ of their origin, mitochondria behaved as H₂O₂ regulators that emitted or consumed it depending on the ambient H₂O₂ concentration, mitochondrial bioenergetic state and activity of the scavenging enzyme systems. Indeed, manipulation of mitochondrial bioenergetics and H₂O₂ scavenging systems caused mitochondria to switch from being net consumers to net emitters of H₂O₂. Overall, our data suggest that the low levels of H₂O₂ typically present in cells would favor emission of this metabolite but the scavenging systems would prevent its accumulation.

BRCA1 deficiency sensitizes breast cancer cells to bromodomain and extra-terminal domain (BET) inhibition

BRCA1 is a tumor suppressor frequently mutated in breast and ovarian cancer, serving it as a target for therapeutic exploitation. Here, we show that BRCA1 has a synthetic lethality interaction with an epigenetics regulator, bromodomain and extra-terminal domain (BET). BET inhibition led to gene expression changes reversing MYC-dependent transcription repression of a redox regulator, thioredoxin-interacting protein (TXNIP), via switching the promoter occupant from MYC to MondoA:MLX complex. Reversing the MYC-TXNIP axis inhibited thioredoxin activity and elevated cellular oxidative stress, causing DNA damages that are detrimental to BRCA1-deficient breast cancer cells. Tumor xenograft models and breast cancer clinical data analyses further demonstrated an in vivo synthetic lethality interaction and clinical association between BET/TXNIP and BRCA1 deficiency in the survival of breast cancer patients.

The thioredoxin-1 system is essential for fueling DNA synthesis during T-cell metabolic reprogramming and proliferation

The thioredoxin-1 (Trx1) system is an important contributor to cellular redox balance and is a sensor of energy and glucose metabolism. Here we show critical c-Myc-dependent activation of the Trx1 system during thymocyte and peripheral T-cell proliferation, but repression during T-cell quiescence. Deletion of thioredoxin reductase-1 (Txnrd1) prevents expansion the CD4⁻CD8⁻ thymocyte population, whereas Txnrd1 deletion in CD4⁺CD8⁺ thymocytes does not affect further maturation and peripheral homeostasis of αβT cells. However, Txnrd1 is critical for expansion of the activated T-cell population during viral and parasite infection. Metabolomics show that TrxR1 is essential for the last step of nucleotide biosynthesis by donating reducing equivalents to ribonucleotide reductase. Impaired availability of 2′-deoxyribonucleotides induces the DNA damage response and cell cycle arrest of Txnrd1-deficient T cells. These results uncover a pivotal function of the Trx1 system in metabolic reprogramming of thymic and peripheral T cells and provide a rationale for targeting Txnrd1 in T-cell leukemia.

Thioredoxin (Trx), Trx reductase, Txnip and NADPH together comprise the Trx system. Here the authors make a T cell-specific thioredoxin reductase-1 knockout mouse to show how this system reprograms cellular metabolism to enable T cell development, proliferation and responses.

Expression of genes and proteins of multidrug resistance in gastric cancer cells treated with resveratrol

Multidrug resistance (MDR) is a notable problem in the use of chemotherapy. Therefore, studies aimed at identifying substances capable of overcoming resistance of cancer cells are required. Examples of these compounds are polyphenols, including resveratrol, that exert a range of various biological activities. The aim of the present study was to demonstrate the effect of 3,5,4'-trihydroxy-trans-stilbene (resveratrol) on the expression of ATP binding cassette subfamily B member 1, Annexin A1 (ANXA1) and thioredoxin (TXN) genes, and the proteins encoded by these genes, which are associated with MDR. The experiments were performed in human gastric cancer cell lines EPG85-257RDB (RDB) and EPG85-257RNOV (RNOV), which are resistant to daunorubicin and mitoxantrone, respectively, in addition to EPG85-257P (control), which is sensitive to cytostatic drugs. Cells were treated with 30 or 50 µM resveratrol for 72 h and changes in the expression levels of the genes were analysed with the use of a reverse transcription-quantitative polymerase chain reaction. The cellular levels of P-glycoprotein (P-gp), ANXA1 and TXN were evaluated using immunofluorescence and western blot analysis. Resveratrol in both concentrations has been shown to have a statistically significant influence on expression of the mentioned genes, compared with untreated cells. In RDB cells, resveratrol reduced the expression level of all analyzed genes, compared with untreated cells. Similar results at the protein level were obtained for P-gp and TXN. In turn, in the RNOV cell line, resveratrol reduced TXN expression at mRNA and protein levels, compared with untreated cells. The results of the present study indicate that resveratrol may reduce the resistance of cancer cells by affecting the expression of a number of the genes and proteins associated with MDR.

Arsenic Induces Thioredoxin 1 and Apoptosis in Human Liver HHL-5 Cells

To further characterize the mechanisms underlying liver toxicity induced by arsenic, we examined in this study the effect of arsenic on thioredoxin (Trx) and the apoptotic signaling pathways in human liver HHL-5 cells. The cells were treated with 0, 2, 5, and 10 μM of sodium arsenite for 24 h, and the changes of Trx1 and thioredoxin reductase (TrxR1) as well as intracellular ROS and apoptosis were examined. A concentration-dependent increase in mRNA and protein levels of Trx1 and TrxR1 was observed in arsenic-treated cells. Intracellular ROS levels and apoptosis were also significantly increased in a concentration-dependent manner. In line with this, protein levels of Bax and cytochrome C were increased and Bcl-2 was decreased by arsenic treatments. Increases in caspase 3 activity were observed. These results indicate that Trx is involved in arsenic-induced liver cell injury, probably through the apoptotic signaling pathway. However, further studies are needed to elucidate on these findings.

A multi-target caffeine derived rhodium(i) N-heterocyclic carbene complex: evaluation of the mechanism of action

A rhodium(i) and a ruthenium(ii) complex with a caffeine derived N-heterocyclic carbene (NHC) ligand were biologically investigated as organometallic conjugates consisting of a metal center and a naturally occurring moiety. While the ruthenium(ii) complex was largely inactive, the rhodium(i) NHC complex displayed selective cytotoxicity and significant anti-metastatic and in vivo anti-vascular activities and acted as both a mammalian and an E. coli thioredoxin reductase inhibitor. In HCT-116 cells it increased the reactive oxygen species level, leading to DNA damage, and it induced cell cycle arrest, decreased the mitochondrial membrane potential, and triggered apoptosis. This rhodium(i) NHC derivative thus represents a multi-target compound with promising anti-cancer potential.

Auranofin, a thioredoxin reductase inhibitor, causes platelet death through calcium overload

Platelets are central to normal hemostasis and must be tightly controlled to prevent thrombosis. However, drug treatments that also affect platelets could lead to unwanted side effects on hemostasis or thrombosis. In this study, the effect of auranofin on platelets was tested. Auranofin, a gold-based thioredoxin reductase (TRXR) inhibitor, has been previously used in arthritis. Recently, auranofin and other inhibitors of the thioredoxin system have been proposed as novel anti-cancer therapies. TRXR is an important part of the antioxidant defenses in many cells that maintain intracellular proteins in their reduced state. TRXR activity in platelets could be completely inhibited by auranofin. Auranofin-treated platelets showed several features of cell death, including the inability to aggregate in response to thrombin, leakage of cytosolic lactate dehydrogenase, and surface exposure of procoagulant phosphatidylserine. Auranofin increased platelet reactive oxygen species production and intracellular calcium concentration. DTT, a sulfydyl reducing agent, and BAPTA-AM, which chelates intracellular calcium, prevented auranofin-induced phosphatidylserine exposure. These data suggest that TRXR is an important part of the platelet antioxidant defense. TRXR inhibition by auranofin triggers oxidative stress and disrupts intracellular calcium homeostasis, leading to platelet necrosis. The use of auranofin or other TRXR inhibitors could therefore lead to unwanted side effects.

Preclinical anti-cancer activity and multiple mechanisms of action of a cationic silver complex bearing N-heterocyclic carbene ligands

Organometallic complexes offer the prospect of targeting multiple pathways that are important in cancer biology. Here, the preclinical activity and mechanism(s) of action of a silver-bis(N-heterocyclic carbine) complex (Ag8) were evaluated. Ag8 induced DNA damage via several mechanisms including topoisomerase I/II and thioredoxin reductase inhibition and induction of reactive oxygen species. DNA damage induction was consistent with cytotoxicity observed against proliferating cells and Ag8 induced cell death by apoptosis. Ag8 also inhibited DNA repair enzyme PARP1, showed preferential activity against cisplatin resistant A2780 cells and potentiated the activity of temozolomide. Ag8 was substantially less active against non-proliferating non-cancer cells and selectively inhibited glycolysis in cancer cells. Ag8 also induced significant anti-tumour effects against cells implanted intraperitoneally in hollow fibres but lacked activity against hollow fibres implanted subcutaneously. Thus, Ag8 targets multiple pathways of importance in cancer biology, is less active against non-cancer cells and shows activity in vivo in a loco-regional setting.

Monitoring thioredoxin redox with a genetically encoded red fluorescent biosensor

Thioredoxin (Trx) is one of the two major thiol antioxidants, playing essential roles in redox homeostasis and signaling. Despite its importance, there is a lack of methods for monitoring Trx redox dynamics in live cells, hindering a better understanding of physiological and pathological roles of the Trx redox system. In this work, we developed the first genetically encoded fluorescent biosensor for Trx redox by engineering a redox relay between the active-site cysteines of human Trx1 and rxRFP1, a redox-sensitive red fluorescent protein. We used the resultant biosensor-TrxRFP1-to selectively monitor perturbations of Trx redox in various mammalian cell lines. We subcellularly localized TrxRFP1 to image compartmentalized Trx redox changes. We further combined TrxRFP1 with a green fluorescent Grx1-roGFP2 biosensor to simultaneously monitor Trx and glutathione redox dynamics in live cells in response to chemical and physiologically relevant stimuli.

Targeting the Thioredoxin System for Cancer Therapy

Thioredoxin (Trx) and thioredoxin reductase (TrxR) are essential components of the Trx system which plays pivotal roles in regulating multiple cellular redox signaling pathways. In recent years TrxR/Trx have been increasingly recognized as an important modulator of tumor development, and hence targeting TrxR/Trx is a promising strategy for cancer treatment. In this review we first discuss the structural details of TrxR, the functions of the Trx system, and the rational of targeting TrxR/Trx for cancer treatment. We also highlight small-molecule TrxR/Trx inhibitors that have potential anticancer activity and review their mechanisms of action. Finally, we examine the challenges of developing TrxR/Trx inhibitors as anticancer agents and perspectives for selectively targeting TrxR/Trx.

The Role of NOX4 and TRX2 in Angiogenesis and Their Potential Cross-Talk

The nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) family is the major source of reactive oxygen species (ROS) in the vascular system. In this family, NOX4, a constitutive active form of NOXs, plays an important role in angiogenesis. Thioredoxin 2 (TRX2) is a key mitochondrial redox protein that maintains normal protein function and also provides electrons to peroxiredoxin 3 (PRX3) to scavenge H₂O₂ in mitochondria. Angiogenesis, a process of new blood vessel formation, is involved in a variety of physiological processes and pathological conditions. It seems to be paradoxical for ROS-producing NOX4 and ROS-scavenging TRX2 to have a similar role in promoting angiogenesis. In this review, we will focus on data supporting the role of NOX4 and TRX2 in angiogenesis and their cross-talks and discuss how ROS can positively or negatively regulate angiogenesis, depending on their species, levels and locations. NOX4 and TRX2-mediated ROS signaling could be promising targets for the treatment of angiogenesis-related diseases.

Thioredoxin-1, chemokine (C-X-C motif) ligand-9 and interferon-γ expression in the neoplastic cells and macrophages of Hodgkin lymphoma: clinicopathologic correlations and potential prognostic implications

Expression of thioredoxin-1 (TXN) and CXCL9 is not restricted to THRLBCL macrophages, but may be observed in histiocytes and neoplastic (HRS) cells of EBV + mixed cellularity (MC) classical Hodgkin lymphoma (cHL) and nodular lymphocyte predominant HL. We aimed to validate and extend the above observations in 174 cHL patients evaluating the immunohistochemical expression of TXN, CXCL9 and IFN-γ. HRS-cell CXCL9 expression was higher in latent membrane protein-1 (LMP1)+, MC and Stage IV. TXN and CXCL9 expression by cHL histiocytes was more frequent in LMP1+, MC and older patients (only for CXCL9). TXN expression by HRS cells (≥80%) was independently associated with better failure-free survival. In conclusion, markers of TCHRLBCL histiocytes (TXN, CXCL9), as well as IFN-γ are also expressed by histiocyte subsets and neoplastic cells of cHL. The expression of some of them is more prominent in EBV + MC, but not restricted to this subtype. The prognostic implication of TXN needs further evaluation.

Biological mechanisms of gold nanoparticle radiosensitization

There has been growing interest in the use of nanomaterials for a range of biomedical applications over the last number of years. In particular, gold nanoparticles (GNPs) possess a number of unique properties that make them ideal candidates as radiosensitizers on the basis of their strong photoelectric absorption coefficient and ease of synthesis. However, despite promising preclinical evidence in vitro supported by a limited amount of in vivo experiments, along with advances in mechanistic understanding, GNPs have not yet translated into the clinic. This may be due to disparity between predicted levels of radiosensitization based on physical action, observed biological response and an incomplete mechanistic understanding, alongside current experimental limitations. This paper provides a review of the current state of the field, highlighting the potential underlying biological mechanisms in GNP radiosensitization and examining the barriers to clinical translation.

EM23, a natural sesquiterpene lactone, targets thioredoxin reductase to activate JNK and cell death pathways in human cervical cancer cells

Sesquiterpene lactones (SLs) are the active constituents of a variety of medicinal plants and found to have potential anticancer activities. However, the intracellular molecular targets of SLs and the underlying molecular mechanisms have not been well elucidated. In this study, we observed that EM23, a natural SL, exhibited anti-cancer activity in human cervical cancer cell lines by inducing apoptosis as indicated by caspase 3 activation, XIAP downregulation and mitochondrial dysfunction. Mechanistic studies indicated that EM23-induced apoptosis was mediated by reactive oxygen species (ROS) and the knockdown of thioredoxin (Trx) or thioredoxin reductase (TrxR) resulted in a reduction in apoptosis. EM23 attenuated TrxR activity by alkylation of C-terminal redox-active site Sec498 of TrxR and inhibited the expression levels of Trx/TrxR to facilitate ROS accumulation. Furthermore, inhibition of Trx/TrxR system resulted in the dissociation of ASK1 from Trx and the downstream activation of JNK. Pretreatment with ASK1/JNK inhibitors partially rescued cells from EM23-induced apoptosis. Additionally, EM23 inhibited Akt/mTOR pathway and induced autophagy, which was observed to be proapoptotic and mediated by ROS. Together, these results reveal a potential molecular mechanism for the apoptotic induction observed with SL compound EM23, and emphasize its putative role as a therapeutic agent for human cervical cancer.

Gold nanoparticles for applications in cancer radiotherapy: Mechanisms and recent advancements

Gold nanoparticles (AuNPs) have emerged as novel radiosensitizers owing to their high X-ray absorption, synthetic versatility, and unique chemical, electronic and optical properties. Multi-disciplinary research performed over the past decade has demonstrated the potential of AuNP-based radiosensitizers, and identified possible mechanisms underlying the observed radiation enhancement effects of AuNPs. Despite promising findings from pre-clinical studies, the benefits of AuNP radiosensitization have yet to successfully translate into clinical practice. In this review, we present an overview of the current state of AuNP-based radiosensitization in the context of the physical, chemical and biological modes of radiosensitization. As well, recent advancements that focus on formulation design and enable multi-modality treatment and clinical utilization are discussed, concluding with design considerations to guide the development of next generation AuNPs for clinical applications.

Protective effects of canolol against hydrogen peroxide-induced oxidative stress in AGS cells

Canolol, a phenolic compound recently isolated from crude canola oil, effectively protected AGS cells against H₂O₂-induced oxidative stress.

The Natural Diterpenoid Isoforretin A Inhibits Thioredoxin-1 and Triggers Potent ROS-Mediated Antitumor Effects

Aberrant expression of thioredoxin 1 (Trx1) plays an important role in cancer initiation and progression and has gained attention as an anticancer drug target. Here we report that the recently discovered natural diterpenoid isoforretin A (IsoA) significantly inhibits Trx1 activity and mediates anticancer effects in multiple preclinical settings. The inhibitory effect of IsoA was antagonized by free radical scavengers polyethylene glycol-catalase, polyethylene glycol superoxide dismutase, thiol-based antioxidants N-acetylcysteine and glutathione. Mass spectrometry analysis revealed that the mechanism of action was based on direct conjugation of IsoA to the Cys32/Cys35 residues of Trx1. This conjugation event attenuated reversible thiol reduction of Trx1, leading to ROS accumulation and a broader degradation of thiol redox homeostasis in cancer cells. Extending these in vitro findings, we documented that IsoA administration inhibited the growth of HepG2 tumors in a murine xenograft model of hepatocellular carcinoma. Taken together, our findings highlight IsoA as a potent bioactive inhibitor of Trx1 and a candidate anticancer natural product. Cancer Res; 77(4); 926-36. ©2016 AACR.

The histone deacetylase inhibitor romidepsin synergizes with lenalidomide and enhances tumor cell death in T-cell lymphoma cell lines

We investigated the cytotoxic interactions of romidepsin, a histone deacetylase inhibitor, and lenalidomide, an immunomodulatory agent, in a T-cell lymphoma preclinical model. Hut-78 and Karpas-299 cells were treated with romidepsin and lenalidomide alone and in combination. The interaction between romidepsin and lenalidomide was evaluated by the Chou-Talalay method, and cell viability and clonogenicity were also evaluated. Apoptosis, reactive oxygen species (ROS) levels, and cell cycle distribution were determined by flow cytometry. ER stress, caspase activation, and the AKT, MAPK/ERK, and STAT-3 pathways were analyzed by Western blot. Combination treatment with romidepsin and lenalidomide had a synergistic effect in Hut-78 cells and an additive effect in Karpas-299 cells at 24 hours and did not decrease the viability of normal peripheral blood mononuclear cells. This drug combination induced apoptosis, increased ROS production, and activated caspase-8, -9, -3 and PARP. Apoptosis was associated with increased hallmarks of ER stress and activation of UPR sensors and was mediated by dephosphorylation of the AKT, MAPK/ERK, and STAT3 pathways.The combination of romidepsin and lenalidomide shows promise as a possible treatment for T-cell lymphoma. This work provides a basis for further studies.

Genistein induces apoptosis by down-regulating thioredoxin-1 in human hepatocellular carcinoma SNU-449 cells

Genistein (GEN), a natural isoflavonoid phytoestrogen, has anti-cancer activity against various types of cancers. However, GEN has not been thoroughly investigated in human hepatocellular carcinoma cells. In this study, we evaluated the anti-cancer effects of GEN on SNU-449 cells. GEN inhibited the proliferation of SNU-449 cells in a concentration-dependent manner. We observed the typical characteristics of apoptosis, such as DNA fragmentation and caspase-3 activation. To identify proteins related to GEN-induced apoptosis, we performed two-dimensional electrophoresis and identified differentially expressed proteins. Proteomic analysis showed that the antioxidant protein thioredoxin-1 was associated with GEN-induced apoptosis. GEN treatment decreased thioredoxin-1 levels and increased intracellular accumulation of reactive oxygen species. In addition, GEN activated apoptosis signal-regulating kinase 1, c-Jun N-terminal kinases (JNK) and p38. We also observed that pretreatment with the JNK and p38 inhibitors (SP600125 and SB203580) decreased GEN-induced cell death. These results indicate that GEN has potential antitumor effects against SNU-449 cells through the down-regulation of thioredoxin-1.

Involvement of genetic factors and lifestyle on the occurrence of colorectal and gastric cancer

Gastrointestinal cancers are diseases due to genetic and environmental factors. In this present work we are interested in the influence of environmental factors on the occurrence of gastrointestinal cancers in Tunisian population. We found that the MTHFR C677T polymorphism was associated with colorectal cancer (P<0.04) but not with gastric cancer. In addition, we have shown that alcohol is associated with an increased risk of colorectal cancer, but the consumption of cheese is protective. Furthermore, we studied tymidylate synthase gene involved in folate metabolism. Indeed, we observed that the 5'UTR repeat polymorphism, is associated with risk of colorectal cancer, and the LL genotype (3R/3R) was significantly frequent in patients with colorectal cancer compared to controls (p=0.002; OR=2.7, 95% CI=1.4-5.2). While we found that SL genotype (2R/3R) was associated with risk of gastric cancer (p=0.015; OR=4.46, 95% CI=1.08-19-64). This polymorphism was also shown to be a predictor of response to chemotherapy based 5'-fluorouracil. However, we are interested in studying the GPX -1 gene involved in phase I metabolism of xenobiotics. We therefore evaluated the risk of TT genotype in GPX-1 C599T polymorphism with the onset of gastric cancer (P=0.0001; OR=5.41, 95% CI 1.98 to 15.58) and colorectal cancer (P=0.00008; OR=4.40, 95% CI 1.93 to 10.27). To clarify the possible relationship between environmental factors and the occurrence of the disease, we studied the additive effect of risk genotype and behavior in order to highlight the interaction of gene-environment factors.

B5, a thioredoxin reductase inhibitor, induces apoptosis in human cervical cancer cells by suppressing the thioredoxin system, disrupting mitochondrion-dependent pathways and triggering autophagy

The synthetic curcumin analog B5 is a potent inhibitor of thioredoxin reductase (TrxR) that has potential anticancer effects. The molecular mechanism underlying B5 as an anticancer agent is not yet fully understood. In this study, we report that B5 induces apoptosis in two human cervical cancer cell lines, CaSki and SiHa, as evidenced by the downregulation of XIAP, activation of caspases and cleavage of PARP. The involvement of the mitochondrial pathway in B5-induced apoptosis was suggested by the dissipation of mitochondrial membrane potential and increased expression of pro-apoptotic Bcl-2 family proteins. In B5-treated cells, TrxR activity was markedly inhibited with concomitant accumulation of oxidized thioredoxin, increased formation of reactive oxygen species (ROS), and activation of ASK1 and its downstream regulatory target p38/JNK. B5-induced apoptosis was significantly inhibited in the presence of N-acetyl-l-cysteine. Microscopic examination of B5-treated cells revealed increased presence of cytoplasmic vacuoles. The ability of B5 to activate autophagy in cells was subsequently confirmed by cell staining with acridine orange, accumulation of LC3-II, and measurement of autophagic flux. Unlike B5-induced apoptosis, autophagy induced by B5 is not ROS-mediated but a role for the AKT and AMPK signaling pathways is implied. In SiHa cells but not CaSki cells, B5-induced apoptosis was promoted by autophagy. These data suggest that the anticarcinogenic effects of B5 is mediated by complex interplay between cellular mechanisms governing redox homeostasis, apoptosis and autophagy.

Expression of the thioredoxin system in an in vivo-like cancer cell environment upon auranofin treatment

As essential elements of the tumor microenvironment, the variable oxygenation state of the tumor tissue, the extracellular matrix (ECM) and different cell types are important determinants of carcinogenesis. These elements may also influence how tumor cells respond to therapeutic treatments. In the present study, we assessed the anti-cancer activity of auranofin and its effect on the thioredoxin (Trx) system under conditions that closely resemble the in vivo tumor microenvironment with respect to the oxygen levels and tissue architecture. We utilised an oxygen scheme involving growth of cancer cells under normoxia (20%) and hypoxia (0.1%). We also preconditioned cells with intermittent hypoxia (IH) prior to a prolonged hypoxic incubation. This oxygen scheme did not affect the cytotoxicity of auranofin; however, IH preconditioned cells were less sensitive towards the inhibition of thioredoxin reductase (TrxR) specific activity upon treatment with auranofin. IH preconditioning also upregulated Trx protein levels in auranofin treated cells. We also compared the activity of auranofin against cancer cells cultured in 2D monolayer and 3D spheroid-based culture models. Auranofin was less potent against cells grown under a more in vivo-like 3D environment. The results presented in this paper implicate the importance of the tumor oxygen environment and tissue architecture in influencing the response of cancer cells towards auranofin.

The importance of antioxidants which play the role in cellular response against oxidative/nitrosative stress: current state

Remarkable interest has risen in the idea that oxidative/nitrosative stress is mediated in the etiology of numerous human diseases. Oxidative/Nitrosative stress is the result of an disequilibrium in oxidant/antioxidant which reveals from continuous increase of Reactive Oxygen and Reactive Nitrogen Species production. The aim of this review is to emphasize with current information the importance of antioxidants which play the role in cellular responce against oxidative/nitrosative stress, which would be helpful in enhancing the knowledge of any biochemist, pathophysiologist, or medical personnel regarding this important issue. Products of lipid peroxidation have commonly been used as biomarkers of oxidative/nitrosative stress damage. Lipid peroxidation generates a variety of relatively stable decomposition end products, mainly α, β-unsaturated reactive aldehydes, such as malondialdehyde, 4-hydroxy-2-nonenal, 2-propenal (acrolein) and isoprostanes, which can be measured in plasma and urine as an indirect index of oxidative/nitrosative stress. Antioxidants are exogenous or endogenous molecules that mitigate any form of oxidative/nitrosative stress or its consequences. They may act from directly scavenging free radicals to increasing antioxidative defences. Antioxidant deficiencies can develop as a result of decreased antioxidant intake, synthesis of endogenous enzymes or increased antioxidant utilization. Antioxidant supplementation has become an increasingly popular practice to maintain optimal body function. However, antoxidants exhibit pro-oxidant activity depending on the specific set of conditions. Of particular importance are their dosage and redox conditions in the cell.

Expression of thioredoxin-1 (TXN) and its relation with oxidative DNA damage and treatment outcome in adult AML and ALL: A comparative study

OBJECTIVE

Thioredoxin-1 (TXN) is a key element in the elimination of reactive oxygen species as well as activation of tumor suppressor genes and DNA repair enzymes. Several studies showed that TXN was over expressed in solid tumors and this was correlated to poorer prognosis. However, TXN expression has been insufficiently studied, particularly in newly diagnosed adult acute leukemia.

METHODS

This study was designed to evaluate the gene expression of TXN in acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL) adult patients and to investigate its association with oxidative DNA damage. The expression of TXN was analyzed using quantitative reverse transcriptase-polymerase chain reaction while oxidative DNA damage was evaluated by measuring serum 8-hydroxy-2-deoxyguanosine (8-OHdG) by enzyme-linked immunosorbent assay and strand breaks by the comet assay.

RESULTS

We found that TXN was under expressed in both AML and ALL groups (P < 0.001 for both) as compared to the control group. Also TXN expression level was negatively correlated with serum 8-OHdG and tail moment in both AML (P = 0.042 and 0.047, respectively) and ALL (P < 0.001 and P = 0.02, respectively) while it showed no correlation with treatment outcome in either groups.

DISCUSSION

This study suggests that TXN expression is hindered in adult acute leukemia which augments oxidative DNA damage and hence mutagenesis.

CONCLUSION

This study provides a new insight into the pathogenesis of acute leukemia and suggests TXN as a new screening test for the risk for acute leukemia.

Binding of phenothiazines into allosteric hydrophobic pocket of human thioredoxin 1

Thioredoxins are multifunctional oxidoreductase proteins implicated in the antioxidant cellular apparatus and oxidative stress. They are involved in several pathologies and are promising anticancer targets. Identification of noncatalytic binding sites is of great interest for designing new allosteric inhibitors of thioredoxin. In a recent work, we predicted normal mode motions of human thioredoxin 1 and identified two major putative hydrophobic binding sites. In this work we investigated noncovalent interactions of human thioredoxin 1 with three phenotiazinic drugs acting as prooxidant compounds by using molecular docking and circular dichroism spectrometry to probe ligand binding into the previously predicted allosteric hydrophobic pockets. Our in silico and CD spectrometry experiments suggested one preferred allosteric binding site involving helix 3 and adopting the best druggable conformation identified by NMA. The CD spectra showed binding of thioridazine into thioredoxin 1 and suggested partial helix unfolding, which most probably concerns helix 3. Taken together, these data support the strategy to design thioredoxin inhibitors targeting a druggable allosteric binding site.

Thioredoxin superfamily and its effects on cardiac physiology and pathology

A precise control of oxidation/reduction of protein thiols is essential for intact cardiac physiology. Irreversible oxidative modifications have been proposed to play a role in the pathogenesis of cardiovascular diseases. An imbalance of redox homeostasis with diminution of antioxidant capacities predisposes the heart to oxidant injury. There is growing interest in endoplasmic reticulum (ER) stress in the cardiovascular field, since perturbation of redox homeostasis in the ER is sufficient to cause ER stress. Because a number of human diseases are related to altered redox homeostasis and defects in protein folding, many research efforts have been devoted in recent years to understanding the structure and enzymatic properties of the thioredoxin superfamily. The thioredoxin superfamily has been well documented as thiol oxidoreductases to exert a role in various cell signaling pathways. The redox properties of the thioredoxin motif account for the different functions of several members of the thioredoxin superfamily. While thioredoxin and glutaredoxin primarily act as antioxidants by reducing protein disulfides and mixed disulfide, another member of the superfamily, protein disulfide isomerase (PDI), can act as an oxidant by forming intrachain disulfide bonds that contribute to proper protein folding. Increasing evidence suggests a pivotal role of PDI in the survival pathway that promotes cardiomyocyte survival and leads to more favorable cardiac remodeling. Thus, the thiol redox state is important for cellular redox signaling and survival pathway in the heart. This review summarizes the key features of major members of the thioredoxin superfamily directly involved in cardiac physiology and pathology.

Au(i) N-heterocyclic carbenes from bis-imidazolium amphiphiles: synthesis, cytotoxicity and incorporation onto gold nanoparticles

Bis-imidazolium amphiphiles capable of forming Au(i) N-heterocyclic carbenes and gold nanoparticles for potential cancer therapy.

Down-Regulation of Thioredoxin1 Is Involved in Death of Calu-6 Lung Cancer Cells Treated With Suberoyl Bishydroxamic Acid

Suberoyl bishydroxamic acid (SBHA), a histone deacetylase (HDAC) inhibitor, can show an anticancer effect. In this study, we investigated the effects of SBHA on the growth inhibition and death of Calu-6 and NCI-H1299 cells in relation to reactive oxygen species (ROS) and antioxidant levels. SBHA inhibited the growth of Calu-6 and NCI-H1299 lung cancer cells with an IC50 of 50 µM at 72 h. This agent induced apoptosis in Calu-6 cells and triggered to a G2/M phase arrest in NCI-H1299 cells. Although it also reduced the growth of normal human pulmonary fibroblast (HPF) cells, the susceptibility of Calu-6 cells to SBHA was higher than that of HPF cells. In addition, SBHA did not affect the growth of human small airway epithelial cells (HSAEC). Regarding ROS and antioxidant levels, SBHA increased ROS level and glutathione (GSH) depletion in Calu-6 and NCI-H1299 cells whereas it decreased ROS levels in HPF and HSAEC. SBHA also decreased thioredoxin1 (Trx1) level in Calu-6 cells. Although the down-regulation of Trx1 intensified apoptosis and ROS level in SBHA-treated Calu-6 cells, the overexpression of Trx1 attenuated apoptosis and ROS level in these cells. This down-regulation of Trx1 did not affect apoptosis-signaling regulating kinase1 (ASK1) activation. In conclusion, the down-regulation of Trx1 by SBHA was closely involved in cell death in Calu-6 cells.

Thioredoxin Cross-Linking by Nitrogen Mustard in Lung Epithelial Cells: Formation of Multimeric Thioredoxin/Thioredoxin Reductase Complexes and Inhibition of Disulfide Reduction

The thioredoxin (Trx) system, which consists of Trx and thioredoxin reductase (TrxR), is a major cellular disulfide reduction system important in antioxidant defense. TrxR is a target of mechlorethamine (methylbis(2-chloroethyl)amine; HN2), a bifunctional alkylating agent that covalently binds to selenocysteine/cysteine residues in the redox centers of the enzyme, leading to inactivation and toxicity. Mammalian Trx contains two catalytic cysteines; herein, we determined if HN2 also targets Trx. HN2 caused a time- and concentration-dependent inhibition of purified Trx and Trx in A549 lung epithelial cells. Three Trx cross-linked protein complexes were identified in both cytosolic and nuclear fractions of HN2-treated cells. LC-MS/MS of these complexes identified both Trx and TrxR, indicating that HN2 cross-linked TrxR and Trx. This is supported by our findings of a significant decrease of Trx/TrxR complexes in cytosolic TrxR knockdown cells after HN2 treatment. Using purified recombinant enzymes, the formation of protein cross-links and enzyme inhibition were found to be redox status-dependent; reduced Trx was more sensitive to HN2 inactivation than the oxidized enzyme, and Trx/TrxR cross-links were only observed using reduced enzyme. These data suggest that HN2 directly targets catalytic cysteine residues in Trx resulting in enzyme inactivation and protein complex formation. LC-MS/MS confirmed that HN2 directly alkylated cysteine residues on Trx, including Cys32 and Cys35 in the redox center of the enzyme. Inhibition of the Trx system by HN2 can disrupt cellular thiol-disulfide balance, contributing to vesicant-induced lung toxicity.

TrxR1 as a potent regulator of the Nrf2-Keap1 response system

SIGNIFICANCE

All cells must maintain a balance between oxidants and reductants, while allowing for fluctuations in redox states triggered by signaling, altered metabolic flow, or extracellular stimuli. Furthermore, they must be able to rapidly sense and react to various challenges that would disrupt the redox homeostasis.

RECENT ADVANCES

Many studies have identified Keap1 as a key sensor for oxidative or electrophilic stress, with modification of Keap1 by oxidation or electrophiles triggering Nrf2-mediated transcriptional induction of enzymes supporting reductive and detoxification pathways. However, additional mechanisms for Nrf2 regulation are likely to exist upstream of, or in parallel with, Keap1.

CRITICAL ISSUES

Here, we propose that the mammalian selenoprotein thioredoxin reductase 1 (TrxR1) is a potent regulator of Nrf2. A high chemical reactivity of TrxR1 and its vital role for the thioredoxin (Trx) system distinguishes TrxR1 as a prime target for electrophilic challenges. Chemical modification of the selenocysteine (Sec) in TrxR1 by electrophiles leads to rapid inhibition of thioredoxin disulfide reductase activity, often combined with induction of NADPH oxidase activity of the derivatized enzyme, thereby affecting many downstream redox pathways. The notion of TrxR1 as a regulator of Nrf2 is supported by many publications on effects in human cells of selenium deficiency, oxidative stress or electrophile exposure, as well as the phenotypes of genetic mouse models.

FUTURE DIRECTIONS

Investigation of the role of TrxR1 as a regulator of Nrf2 activation will facilitate further studies of redox control in diverse cells and tissues of mammals, and possibly also in animals of other classes.

Insights into the importance for designing curcumin-inspired anticancer agents by a prooxidant strategy: The case of diarylpentanoids

Developing anticancer agents by a prooxidant strategy has attracted increasing attention in recent years, although it is not conventional in medicinal chemistry and is completely opposite to antioxidant therapy. In this work, a panel of diarylpentanoids as the curcumin mono-carbonyl analogs were designed and synthesized, and their cytotoxic and proapoptotic mechanisms against human lung cancer A549 cells were investigated at the frontiers of chemistry and biology. It was found that compared with curcumin, the compounds (A1, B1, and C1) bearing two ortho substituents on the aromatic rings, especially A1, exhibit significantly increased cytotoxic and proapoptotic activities through a Michael acceptor unit-dependent prooxidant-mediated mechanism. The prooxidative ability is governed not only by their electrophilicity but also by their geometry, cellular uptake and metabolic stability, and TrxR-inhibitory activity. Mechanistic investigation reveals that the compound A1 could effectively and irreversibly modify the TrxR by virtue of the above optimal biochemical parameters, and convert this antioxidant enzyme into a reactive oxygen species (ROS) promoter, resulting in a burst of the intracellular ROS including H2O2 and O2(-)•. The ROS generation is associated with falling apart in the redox buffering system, and subsequently induces increases in Ca(2+) influx and oxidative stress, collapse of mitochondrial membrane potential, and activation of caspase-9 and caspase-3, ultimately leading to cell apoptosis. This work highlights the feasibility in designing curcumin-inspired anticancer agents by a prooxidant strategy, and gives us useful information on how to design them.

Cyclophilin A regulates JNK/p38-MAPK signaling through its physical interaction with ASK1

Cyclophilin A (CypA), a member of the immunophilin family, is predominantly localized in the cytoplasm. The peptidylprolyl isomerase (PPIase) activity of CypA has been demonstrated to be involved in diverse cellular processes, including intracellular protein trafficking, mitochondrial function, pre-mRNA processing, and maintenance of multiprotein complex stability. In this study, we have demonstrated that CypA regulates apoptosis signaling-regulating kinase 1 (ASK1) through its direct binding. ASK1 is a member of MAPK kinase kinase (MAP3K) family, and selectively activates both JNK and p38 MAPK pathways. Here, we also report that CypA negatively regulates phosphorylation of ASK1 at Ser966, and that CypA reduces ASK1 and its downstream kinases of the JNK and p38 signaling. ASK1 is known to induce caspase-3 activation and apoptosis, and CypA inhibited ASK1-mediated apoptosis by decrease in caspase-3 activity under cellular stress conditions. Overall, we conclude that CypA negatively regulates ASK1 functions by its physical interaction with ASK1.

Thioredoxin/thioredoxin reductase system involvement in cerebellar granule cell apoptosis

The involvement of thioredoxin/thioredoxin reductase system has been investigated in cerebellar granule cells (CGCs), a cellular system in which neurons are induced in apoptosis by the physiological stimulus of lowering extracellular potassium. Clarifying the sequence of events that occur during apoptosis is a critical issue as it can lead to the identification of those key events that, if blocked, can slow down or reverse the death process. The results reported in this work show that TrxR is involved in the early phase of CGC apoptosis with an increase in activity that coincides with the increased expression of the TrxR1 isoform and guarantees the maintenance of adequate level of Trx in its reduced, active form. However, in late apoptosis, when about 50 % of cells are dead, partial proteolysis of TrxR1 by calpain occurs and the reduction of TrxR1 mRNA, together with the overall decrease in TrxR activity, contribute to increase the levels of the oxidized form of Trx. When the reduced form of Trx is externally added to apoptotic cultures, a significant reduction in cell death is achieved confirming that a well-functioning thioredoxin/thioredoxin reductase system is required for survival of CGCs.

Selenium-containing chrysin and quercetin derivatives: attractive scaffolds for cancer therapy

Selenium-containing chrysin (SeChry) and 3,7,3',4'-tetramethylquercetin (SePQue) derivatives were synthesized by a microwave-based methodology. In addition to their improvement in terms of DPPH scavenging and potential GPx-like activities, when tested in a panel of cancer cell lines both selenium-derivatives revealed consistently to be more cytotoxic when compared with their oxo and thio-analogues, evidencing the key role of selenocabonyl moiety for these activities. In particular, SeChry elicited a noteworthy cytotoxic activity with mean IC50 values 18- and 3-fold lower than those observed for chrysin and cisplatin, respectively. Additionally, these seleno-derivatives evidenced an ability to overcome cisplatin and multidrug resistance. Notably, a differential behavior toward malignant and nonmalignant cells was observed for SeChry and SePQue, exhibiting higher selectivity indexes when compared with the chalcogen-derivatives and cisplatin. Our preliminary investigation on the mechanism of cytotoxicity of SeChry and SePQue in MCF-7 human mammary cancer cells demonstrated their capacity to efficiently suppress the clonal expansion along with their ability to hamper TrxR activity leading to apoptotic cell death.

The overexpression and nuclear translocation of Trx-1 during hypoxia confers on HepG2 cells resistance to DDP, and GL-V9 reverses the resistance by suppressing the Trx-1/Ref-1 axis

Microenvironmental hypoxia gives many tumor cells the capacity for drug resistance. Thioredoxin family members play critical roles in the regulation of cellular redox homeostasis in a stressed environment. In this study, we established a hypoxia-drug resistance (hypoxia-DR) model using HepG2 cells and discovered that the overexpression and nuclear translocation of thioredoxin-1 (Trx-1) are closely associated with this resistance through the regulation of the metabolism by the oxidative stress response to glycolysis. Intranuclear Trx-1 enhances the DNA-binding activity of HIF-1α via its interaction with and reducing action on Ref-1, resulting in increased expression of glycolysis-related proteins (PDHK1, HKII, and LDHA), glucose uptake, and lactate generation under hypoxia. Meanwhile, we found that GL-V9, a newly synthesized flavonoid derivative, shows an ability to reverse the hypoxia-DR and has low toxicity both in vivo and in vitro. GL-V9 could inhibit the expression and nuclear translocation of Trx-1 and then suppress HIF-1α DNA-binding activity by inhibiting the Trx-1/Ref-1 axis. As a result, glycolysis is weakened and oxidative phosphorylation is enhanced. Thus, GL-V9 leads to an increment in intracellular ROS generation and consequently intensified apoptosis induced by DDP.

Thioredoxin reductase inhibitor auranofin prevents membrane transport of diphtheria toxin into the cytosol and protects human cells from intoxication

During cellular uptake, diphtheria toxin delivers its catalytic domain DTA from acidified endosomes into the cytosol, which requires reduction of the disulfide linking DTA to the transport domain. In vitro, thioredoxin reduces this disulfide and thioredoxin reductase (TrxR) is part of a cytosolic complex facilitating DTA-translocation. We found that the TrxR-specific inhibitor auranofin prevented DTA delivery into the cytosol and intoxication of HeLa cells with diphtheria toxin, offering perspectives for novel pharmacological strategies against diphtheria.

Thioredoxin reductase and its inhibitors

Thioredoxin plays a crucial role in a wide number of physiological processes, which span from reduction of nucleotides to deoxyriboucleotides to the detoxification from xenobiotics, oxidants and radicals. The redox function of Thioredoxin is critically dependent on the enzyme Thioredoxin NADPH Reductase (TrxR). In view of its indirect involvement in the above mentioned physio/pathological processes, inhibition of TrxR is an important clinical goal. As a general rule, the affinities and mechanisms of binding of TrxR inhibitors to the target enzyme are known with scarce precision and conflicting results abound in the literature. A relevant analysis of published results as well as the experimental procedures is therefore needed, also in view of the critical interest of TrxR inhibitors. We review the inhibitors of TrxR and related flavoreductases and the classical treatment of reversible, competitive, non competitive and uncompetitive inhibition with respect to TrxR, and in some cases we are able to reconcile contradictory results generated by oversimplified data analysis.

Detailed analysis of pro-apoptotic signaling and metabolic adaptation triggered by a N-heterocyclic carbene-gold(I) complex

Due to their broad spectrum of biological activity and antiproliferative effect on different human cancer cell lines, gold compounds have been in the focus of drug research for many years. Gold(I)-N-heterocyclic carbene complexes are of particular interest, because of their stability, ease of derivatization and clear cytotoxicity in cancer cells. To obtain a more detailed view of the molecular mechanisms underlying their cellular activity, we used a novel gold(I)-N-heterocyclic carbene complex, [triphenylphosphane-(1,3-diethyl-5-methoxy-benzylimidazol-2-ylidene)]gold(I) iodide and investigated changes in cellular signaling pathways using quantitative signal transduction protein microarray analysis. We also analyzed changes in cell metabolism in a time-dependent manner by on-line metabolic measurements and used isolated mitochondria to elucidate the direct effects on this cell organelle. We found strong cytotoxic effects in cancer cells, accompanied by an immediate and irreversible loss of mitochondrial respiration as well as by a crucial imbalance of the intracellular redox state, resulting in apoptotic cell death. ELISA microarray analysis of signal transduction pathways revealed a time-dependent up-regulation of pro-apoptotic signaling proteins, e.g. p38 and JNK, whereas pro-survival signals that are directly linked to the thioredoxin system were down-regulated, which pinpoints to thioredoxin reductase as a central target of the compound. Further results suggest that DNA is an indirect target of the compound. Based on our findings, we outline a signaling model for the molecular mechanism underlying the antiproliferative activity of the gold(I)-N-heterocyclic carbene complex investigated, which provides a good general model for the known pattern of cell death induced by this class of substances.

Ruthenium polypyridyl complexes as inducer of ROS-mediated apoptosis in cancer cells by targeting thioredoxin reductase

TrxR is an NADPH-dependent selenoenzyme upregulated in a number of cancers. It plays a pivotal role in cancer progression and represents an increasingly attractive target for anticancer drugs. The limitations of cisplatin in cancer treatment have motivated the extensive investigation to other metal complexes, especially ruthenium (Ru) complexes. In this study, we present the in vitro biological evaluation of four Ru(II) polypridyl complexes with diimine ligands, namely, [Ru(bpy)3](2+) (1), [Ru(phen)3](2+) (2), [Ru(ip)3](2+) (3), [Ru(pip)3](2+) (4) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, ip = imidazole[4,5-f][1,10]phenanthroline, pip = 2-phenylimidazo[4,5-f][1,10]phenanthroline), and demonstrate that they exhibit antiproliferative activities against A375 human melanoma cells through inhibition of TrxR. As the planarity of the structure increases, their TrxR-inhibitory effects and in vitro anticancer activities were enhanced. Among them, complex 4 exhibited higher antiproliferative activity than cisplatin, and the TrxR-inhibitory potency of 4 was more effective than auranofin, a positive TrxR inhibitor. Complex 4 suppressed the cancer cell growth through induction of apoptosis as evidenced by accumulation of sub-G1 cell population, DNA fragmentation and nuclear condensation. Moreover, complex 4 was able to localize in mitochondria and therein induced ROS-dependent apoptosis by inhibition of TrxR activity. Activation of MAPKs, AKT, DNA damage-mediated p53 phosphorylation and inhibition of VEGFR signaling were also triggered in cells exposed to complex 4. On the basis of this evidence, we suggest that Ru polypyridyl complexes could be developed as TrxR-targeted agents that demonstrate application potentials for treatment of cancers.

Design, synthesis, and biological evaluation of benzoselenazole-stilbene hybrids as multi-target-directed anti-cancer agents

To identify novel multi-target-directed drug candidates for the treatment of cancer, a series of benzoselenazole-stilbene hybrids were synthesised by combining the pharmacophores of resveratrol and ebselen. The biological assay indicated that all of the hybrids exhibited antiproliferative activities against four human cancer cell lines and demonstrated good TrxR inhibitory activities. The mechanism of cell apoptosis was investigated in G2/M cell cycle arrest induced by compound 6e and the apoptosis of the human liver carcinoma Bel-7402 cell line. The significant increase in intracellular ROS confirmed that compound 6e was capable of causing oxidative stress-induced apoptosis in cancer cells. Our results support the potential of compound 6e as a candidate for further studies examining the development of novel drugs for cancer treatment.

Increased reactive oxygen species production during reductive stress: The roles of mitochondrial glutathione and thioredoxin reductases

Both extremes of redox balance are known to cause cardiac injury, with mounting evidence revealing that the injury induced by both oxidative and reductive stress is oxidative in nature. During reductive stress, when electron acceptors are expected to be mostly reduced, some redox proteins can donate electrons to O2 instead, which increases reactive oxygen species (ROS) production. However, the high level of reducing equivalents also concomitantly enhances ROS scavenging systems involving redox couples such as NADPH/NADP+ and GSH/GSSG. Here our objective was to explore how reductive stress paradoxically increases net mitochondrial ROS production despite the concomitant enhancement of ROS scavenging systems. Using recombinant enzymes and isolated permeabilized cardiac mitochondria, we show that two normally antioxidant matrix NADPH reductases, glutathione reductase and thioredoxin reductase, generate H2O2 by leaking electrons from their reduced flavoprotein to O2 when electron flow is impaired by inhibitors or because of limited availability of their natural electron acceptors, GSSG and oxidized thioredoxin. The spillover of H2O2 under these conditions depends on H2O2 reduction by peroxiredoxin activity, which may regulate redox signaling in response to endogenous or exogenous factors. These findings may explain how ROS production during reductive stress overwhelms ROS scavenging capability, generating the net mitochondrial ROS spillover causing oxidative injury. These enzymes could potentially be targeted to increase cancer cell death or modulate H2O2-induced redox signaling to protect the heart against ischemia/reperfusion damage.