On the potential of thioredoxin reductase inhibitors for cancer therapy

Discovery of flavopiridol as a noncovalent thioredoxin reductase inhibitor through in silico and in vitro approach

Selenoprotein thioredoxin reductase (TrxR) is critical for regulating several cellular redox signaling pathways and is considered a potential target for anticancer drugs. Most existing TrxR inhibitors directly covalently act on SEC498 of TrxR, which is highly cytotoxic. Therefore, the development of potential noncovalent TrxR inhibitors is a promising cancer treatment strategy. In this study, a virtual screening method based on molecular docking was used to screen out flavopiridol as a noncovalently bound inhibitor of TrxR from the database provided by TargetMol, and 1 μs molecular dynamics (MD) simulations per system were performed. Flavopiridol effectively attenuated the activity of TrxR across a diverse spectrum of cell lines. Furthermore, it demonstrated robust anti-proliferative efficacy against HL60 cells with an IC50 value of 0.28 ± 0.02 μM. Importantly, surface plasmon resonance (SPR) experiments validated the binding interaction between flavopiridol and TrxR. This study offers valuable insights into the identification and investigation of novel TrxR inhibitors, potentially enhancing the application of flavopiridol as a promising TrxR inhibitor.

Roles of selenium-containing glutathione peroxidases and thioredoxin reductases in the regulation of processes associated with glioblastoma progression

Glioblastoma remains the most common and aggressive primary tumor of the central nervous system in adults. Current treatment options include standard surgical resection combined with radiation/chemotherapy, but such protocol most likely only delays the inevitable. Therefore, the problem of finding therapeutic targets to prevent the occurrence and development of this severe oncological disease is currently acute. It is known that the functions of selenoproteins in the regulation of carcinogenesis processes are not unambiguous. Either they exhibit cytotoxic activity on cancer cells, or cytoprotective. A special place in the progression of oncological diseases of various etiologies is occupied by proteins of the thioredoxin and glutathione systems. These are two cellular antioxidant systems that regulate redox homeostasis, counteracting the increased production of reactive oxygen species in cells. The review reflects the latest data on the role of key enzymes of these redox systems in the regulation of processes associated with the progression of glioblastoma. A thorough consideration of these issues will expand fundamental knowledge about the functions of selenium-containing thioredoxin reductases and glutathione peroxidases in the therapy of glioblastomas and provide an understanding of the prospects for the treatment of this aggressive oncological disease.

Current nanocomposite advances for biomedical and environmental application diversity

Nanocomposite materials are emerging as key players in addressing critical challenges in healthcare, energy storage, and environmental remediation. These innovative systems hold great promise in engineering effective solutions for complex problems. Nanocomposites have demonstrated various advantages such as simplicity, versatility, lightweight, and potential cost-effectiveness. By reinforcing synthetic and natural polymers with nanomaterials, a range of nanocomposites have exhibited unique physicochemical properties, biocompatibility, and biodegradability. Current research on nanocomposites has demonstrated promising clinical and translational applications. Over the past decade, the production of nanocomposites has emerged as a critical nano-structuring methodology due to their adaptability and controllable surface structure. This comprehensive review article systematically addresses two principal domains. A comprehensive survey of metallic and nonmetallic nanomaterials (nanofillers), elucidating their efficacy as reinforcing agents in polymeric matrices. Emphasis is placed on the methodical design and engineering principles governing the development of functional nanocomposites. Additionally, the review provides an exhaustive examination of recent noteworthy advancements in industrial, environmental, biomedical, and clinical applications within the realms of nanocomposite materials. Finally, the review concludes by highlighting the ongoing challenges facing nanocomposites in a wide range of applications.

Nanomaterial-based regulation of redox metabolism for enhancing cancer therapy

Altered redox metabolism is one of the hallmarks of tumor cells, which not only contributes to tumor proliferation, metastasis, and immune evasion, but also has great relevance to therapeutic resistance. Therefore, regulation of redox metabolism of tumor cells has been proposed as an attractive therapeutic strategy to inhibit tumor growth and reverse therapeutic resistance. In this respect, nanomedicines have exhibited significant therapeutic advantages as intensively reported in recent studies. In this review, we would like to summarize the latest advances in nanomaterial-assisted strategies for redox metabolic regulation therapy, with a focus on the regulation of redox metabolism-related metabolite levels, enzyme activity, and signaling pathways. In the end, future expectations and challenges of such emerging strategies have been discussed, hoping to enlighten and promote their further development for meeting the various demands of advanced cancer therapies. It is highly expected that these therapeutic strategies based on redox metabolism regulation will play a more important role in the field of nanomedicine.

Thioredoxin System in Insects: Uncovering the Roles of Thioredoxins and Thioredoxin Reductase beyond the Antioxidant Defences

Increased levels of reactive oxygen species (ROS) produced during aerobic metabolism in animals can negatively affect the intracellular redox status, cause oxidative stress and interfere with physiological processes in the cells. The antioxidant defence regulates ROS levels by interplaying diverse enzymes and non-enzymatic metabolites. The thioredoxin system, consisting of the enzyme thioredoxin reductase (TrxR), the redox-active protein thioredoxin (Trx) and NADPH, represent a crucial component of antioxidant defence. It is involved in the signalling and regulation of multiple developmental processes, such as cell proliferation or apoptotic death. Insects have evolved unique variations of TrxR, which resemble mammalian enzymes in overall structure and catalytic mechanisms, but the selenocysteine-cysteine pair in the active site is replaced by a cysteine-cysteine pair typical of bacteria. Moreover, the role of the thioredoxin system in insects is indispensable due to the absence of glutathione reductase, an essential enzyme of the glutathione system. However, the functions of the Trx system in insects are still poorly characterised. In the present review, we provide a critical overview of the current knowledge on the insect Trx system, focusing mainly on TrxR's role in the antioxidant and immune system of model insect species.

Melanoma redox biology and the emergence of drug resistance

Melanoma is the deadliest form of skin cancer, with the loss of approximately 60,000 lives world-wide each year. Despite the development of targeted therapeutics, including compounds that have selectivity for mutant oncoproteins expressed only in cancer cells, many patients are either unresponsive to initial therapy or their tumors acquire resistance. This results in five-year survival rates of below 25%. New strategies that either kill drug-resistant melanoma cells or prevent their emergence would be extremely valuable. Melanoma, like other cancers, has long been described as being under increased oxidative stress, resulting in an increased reliance on antioxidant defense systems. Changes in redox homeostasis are most apparent during metastasis and during the metabolic reprogramming associated with the development of treatment resistance. This review discusses oxidative stress in melanoma, with a particular focus on targeting antioxidant pathways to limit the emergence of drug resistant cells.

Recent advances in c-Met-based dual inhibitors in the treatment of cancers

The cellular-mesenchymal epithelial transition factor (c-Met) is a receptor tyrosine kinase (RTK) located on the 7q31 locus encoding the Met proto-oncogene and plays a critical role in regulating cell proliferation, metastasis, differentiation, and apoptosis through various signaling pathways. However, its aberrant activation and overexpression have been implicated in many human cancers. Therefore, c-Met is a promising target for cancer treatment. However, the anticancer effect of selective single-targeted drugs is limited due to the complexity of the signaling system and the involvement of different proteins and enzymes. After inhibiting one pathway, signal molecules can be transmitted through other pathways, resulting in poor efficacy of single-targeted drug therapy. Dual inhibitors that simultaneously block c-Met and another factor can significantly improve efficacy and overcome some of the shortcomings of single-target inhibitors, including drug resistance. In this review, We introduced c-Met kinase and the synergism between c-Met and other anti-tumor targets, then dual-target inhibitors based on c-Met for the treatment of cancers were summarized and their design concepts and structure-activity relationships (SARs) were discussed elaborately, providing a valuable insight for the further development of novel c-Met-based dual inhibitors.

Unresolved questions regarding cellular cysteine sources and their possible relationships to ferroptosis

Cysteine is required for synthesis of glutathione (GSH), coenzyme A, other sulfur-containing metabolites, and most proteins. In most cells, cysteine comes from extracellular disulfide sources including cystine, glutathione-disulfide, and peptides. The thioredoxin reductase-1 (TrxR1)- or glutathione-disulfide reductase (GSR)-driven enzymatic systems can fuel cystine reduction via thioredoxins, glutaredoxins, or other thioredoxin-fold proteins. Free cystine enters cells thorough the cystine-glutamate antiporter, xCT, but systemically, plasma glutathione-disulfide might predominate as a cystine source. Erastin, inhibiting both xCT and voltage-dependent anion channels, induces ferroptotic cell death, so named because this type of cell death is antagonized by iron-chelators. Many cancer cells seem to be predisposed to ferroptosis, which has been proposed as a targetable cancer liability. Ferroptosis is associated with lipid peroxidation and loss of either glutathione peroxidase-4 (GPX4) or ferroptosis suppressor protein-1 (FSP1), which each prevent accumulation of lipid peroxides. It has been suggested that an xCT inhibition-induced cellular cysteine-deficiency lowers GSH levels, starving GPX4 for reducing power and allowing membrane lipid peroxides to accumulate, thereby causing ferroptosis. Aspects of ferroptosis are however not fully understood and need to be further scrutinized, for example that neither disruption of GSH synthesis, loss of GSH, nor disruption of glutathione disulfide reductase (GSR), triggers ferroptosis in animal models. Here we reevaluate the relationships between Erastin, xCT, GPX4, cellular cysteine and GSH, RSL3 or ML162, and ferroptosis. We conclude that, whereas both Cys and ferroptosis are potential liabilities in cancer, their relationship to each other remains insufficiently understood.

S-Se oxidative addition to auranofin derivatives: a DFT study

Oxidative addition of the S-Se bond to Au(I) complexes is discussed for a series of 26 auranofin (AF) derivatives. AF and its analogues are Au(I) complexes with recognized anticancer activity that act by binding and inhibiting the thioredoxin reductase (TrxR) enzyme. Generally, the oxidative addition to Au(I) is a sluggish reaction under mild conditions (i.e., a high activation barrier - ΔH‡), which is also verified here for AF, ΔH‡ = 33.0 kcal mol-1. However, we predicted that subtle changes in the AF ligands can make the process feasible under standard conditions. For instance, the exchange of -PEt3 by -P(Et2)(OEt), which is a weaker electron σ-donor, reduced the activation barrier to 17.1 kcal mol-1. Furthermore, substitution of the -SAtg ligand by -Cl- leads to a ΔH‡ value of 22.5 kcal mol-1. Overall, the reaction is driven by the nucleophilic attack of the S-Se bond on the Au(I) center, attributed mainly to the charge transfer (4p)Se → (6p)Au, which characterizes the addition step. At the transition state (TS) point, the (5d)Au → σ*(S-Se) charge transfer becomes relevant, facilitating the S-Se bond breakage and the oxidation step. In addition to the electron transfers, the strain energy to deform the linear Au(I) geometry to the tetracoordinated Au(III) arrangement in the TS structure plays a primary role in explaining the trends in the activation barriers. Finally, the activation barrier (ΔH‡) and reaction energy (ΔH°) were correlated for most of the complexes studied, which suggests that the reaction passes through a late or product-like TS and, therefore, the steric and electronic factors affecting ΔH‡ also act on ΔH°. Overall, the results presented here might open up a new field of investigation for interactions between AF derivatives and TrxR, which contributes to a full understanding of the biological mechanism of action of these species.

Cytotoxic auranofin analogues bearing phosphine, arsine and stibine ligands: A study on the possible role of the ligand on the biological activity

Three gold(I) linear compounds, sharing the general formula [AuI(LPh3)], have been synthesized and characterized. The nature of the ligand has been modified by moving down among some of the elements of group 15, i.e. phosphorus, arsenic and antimony. The structures of derived compounds have been solved through XRD and the reactivity behaviour towards selected biomolecules has been investigated through a multi-technique approach involving NMR, high-resolution mass spectrometry and IR. Moreover, the biological activity of the investigated compounds has been comparatively analyzed through classical methodologies and the disclosed differences are discussed in detail.

Biosynthesis, Engineering, and Delivery of Selenoproteins

Selenocysteine (Sec) was discovered as the 21st genetically encoded amino acid. In nature, site-directed incorporation of Sec into proteins requires specialized biosynthesis and recoding machinery that evolved distinctly in bacteria compared to archaea and eukaryotes. Many organisms, including higher plants and most fungi, lack the Sec-decoding trait. We review the discovery of Sec and its role in redox enzymes that are essential to human health and important targets in disease. We highlight recent genetic code expansion efforts to engineer site-directed incorporation of Sec in bacteria and yeast. We also review methods to produce selenoproteins with 21 or more amino acids and approaches to delivering recombinant selenoproteins to mammalian cells as new applications for selenoproteins in synthetic biology.

Effects of Arbutin on Potassium Bromate-Induced Erythrocyte Toxicity in Rats: Biochemical Evaluation of Some Metabolic Enzyme Activities In Vivo and In Vitro

In the present study, the inhibitory effect of potassium bromate on the pentose phosphate pathway and intracellular antioxidant systems enzymes (glucose 6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), glutathione reductase (GR), glutathione S-transferase (GST), and thioredoxin reductase (TrxR)) and the role of arbutin in ameliorating this inhibition were investigated. In the in vivo phase of the study, Wistar Albino rats (28 male adults) were randomly divided into four groups. Control (n = 7): isotonic serum (0.5 mL, i.p), potassium bromate group (n = 7): potassium bromate (100 mg/kg), arbutin group (n = 7): arbutin (i.p.) (50 mg/kg/day), potassium bromate + arbutin, and Group (n = 7): potassium bromate (100 mg/kg) + arbutin (50 mg/kg/day) (i.p). The results of in vivo study showed that the activities of G6PD, 6PGD, GR, and TrxR enzymes were strongly inhibited in potassium bromate groups (p < 0.05). It was determined that GST enzyme activity decreased in the potassium bromate group, but this decrease was not statistically significant compared to the control group (p ⩾ 0.05). A statistically significant increase was found in G6PD, 6PGD, GST, and TrxR enzyme activities in the arbutin group compared to the control group (p < 0.05). The increase in GR enzyme activity was not statistically significant (p ⩾ 0.05). The potassium bromate + arbutin group's enzyme activity increased in comparison to the potassium bromate group and was discovered to be closer to the control group. It was found that potassium bromate inhibited the 6PGD enzyme obtained from rat erythrocyte tissues with IC50 = 346 μM value and Ki = 434.4 μM ± 6.1 value, and the inhibition was noncompetitive.

Thioredoxin Reductase and Organometallic Complexes: A Pivotal System to Tackle Multidrug Resistant Tumors?

Cancers classified as multidrug-resistant (MDR) are a family of diseases with poor prognosis despite access to increasingly sophisticated treatments. Several mechanisms explain these resistances involving both tumor cells and their microenvironment. It is now recognized that a multi-targeting approach offers a promising strategy to treat these MDR tumors. Inhibition of thioredoxin reductase (TrxR), a key enzyme in maintaining redox balance in cells, is a well-identified target for this approach. Auranofin was the first inorganic gold complex to be described as a powerful inhibitor of TrxR. In this review, we will first recall the main results obtained with this metallodrug. Then, we will focus on organometallic complexes reported as TrxR inhibitors. These include gold(I), gold(III) complexes and metallocifens, i.e., organometallic complexes of Fe and Os derived from tamoxifen. In these families of complexes, similarities and differences in the molecular mechanisms of TrxR inhibition will be highlighted. Finally, the possible relationship between TrxR inhibition and cytotoxicity will be discussed and put into perspective with their mode of action.

Enzymatic Redox Properties and Cytotoxicity of Irreversible Nitroaromatic Thioredoxin Reductase Inhibitors in Mammalian Cells

NADPH:thioredoxin reductase (TrxR) is considered a potential target for anticancer agents. Several nitroheterocyclic sulfones, such as Stattic and Tri-1, irreversibly inhibit TrxR, which presumably accounts for their antitumor activity. However, it is necessary to distinguish the roles of enzymatic redox cycling, an inherent property of nitroaromatics (ArNO2), and the inhibition of TrxR in their cytotoxicity. In this study, we calculated the previously unavailable values of single-electron reduction potentials of known inhibitors of TrxR (Stattic, Tri-1, and 1-chloro-2,4-dinitrobenzene (CDNB)) and inhibitors identified (nitrofuran NSC697923 and nitrobenzene BTB06584). These calculations were according to the rates of their enzymatic single-electron reduction (PMID: 34098820). This enabled us to compare their cytotoxicity with that of model redox cycling ArNO2. In MH22a and HCT-116 cells, Tri-1, Stattic, CDNB, and NSC697023 possessed at least 10-fold greater cytotoxicity than can be expected from their redox cycling activity. This may be related to TrxR inhibition. The absence of enhanced cytotoxicity in BTB06548 may be attributed to its instability. Another known inhibitor of TrxR, tetryl, also did not possess enhanced cytotoxicity, probably because of its detoxification by DT-diaphorase (NQO1). Apart from the reactions with NQO1, the additional mechanisms influencing the cytotoxicity of the examined inhibitors of TrxR are their reactions with cytochromes P-450. Furthermore, some inhibitors, such as Stattic and NSC697923, may also inhibit glutathione reductase. We suggest that these data may be instrumental in the search for TrxR inhibitors with enhanced cytotoxic/anticancer activity.

NFATc1-mediated expression of SLC7A11 drives sensitivity to TXNRD1 inhibitors in osteoclast precursors

Excess osteoclast activity is found in many bone metabolic diseases, and inhibiting osteoclast differentiation has proven to be an effective strategy. Here, we revealed that osteoclast precursors (pre-OCs) were more susceptible to thioredoxin reductase 1 (TXNRD1) inhibitors than bone marrow-derived monocytes (BMDMs) during receptor activator of nuclear factor kappa B ligand (RANKL)-mediated osteoclastogenesis. Mechanistically, we found that nuclear factor of activated T-cells 1 (NFATc1) upregulated solute carrier family 7 member 11 (SLC7A11) expression through transcriptional regulation during RANKL-induced osteoclastogenesis. During TXNRD1 inhibition, the rate of intracellular disulfide reduction is significantly reduced. Increased cystine transport leads to increased cystine accumulation, which leads to increased cellular disulfide stress and disulfidptosis. We further demonstrated that SLC7A11 inhibitors and treatments that prevent disulphide accumulation could rescue this type of cell death, but not the ferroptosis inhibitors (DFO, Ferro-1), the ROS scavengers (Trolox, Tempol), the apoptosis inhibitor (Z-VAD), the necroptosis inhibitor (Nec-1), or the autophagy inhibitor (CQ). An in vivo study indicated that TXNRD1 inhibitors increased bone cystine content, reduced the number of osteoclasts, and alleviated bone loss in an ovariectomized (OVX) mouse model. Together, our findings demonstrate that NFATc1-mediated upregulation of SLC7A11 induces targetable metabolic sensitivity to TXNRD1 inhibitors during osteoclast differentiation. Moreover, we innovatively suggest that TXNRD1 inhibitors, a classic drug for osteoclast-related diseases, selectively kill pre-OCs by inducing intracellular cystine accumulation and subsequent disulfidptosis.

Repurposing 1,2,4-oxadiazoles as SARS-CoV-2 PLpro inhibitors and investigation of their possible viral entry blockade potential

Although vaccines are obviously mitigating the COVID-19 pandemic diffusion, efficient complementary antiviral agents are urgently needed to combat SARS-CoV-2. The viral papain-like protease (PLpro) is a promising therapeutic target being one of only two essential proteases crucial for viral replication. Nevertheless, it dysregulates the host immune sensing response. Here we report repositioning of the privileged 1,2,4-oxadiazole scaffold as promising SARS-CoV-2 PLpro inhibitor with potential viral entry inhibition profile. The design strategy relied on mimicking the general structural features of the lead benzamide PLpro inhibitor GRL0617 with isosteric replacement of its pharmacophoric amide backbone by 1,2,4-oxadiazole core. Inspired by the multitarget antiviral agents, the substitution pattern was rationalized to tune the scaffold's potency against other additional viral targets, especially the spike receptor binding domain (RBD) that is responsible for the viral invasion. The Adopted facial synthetic protocol allowed easy access to various rationally substituted derivatives. Among the evaluated series, the 2-[5-(pyridin-4-yl)-1,2,4-oxadiazol-3-yl]aniline (5) displayed the most balanced dual inhibitory potential against SARS-CoV-2 PLpro (IC50=7.197 μM) and spike protein RBD (IC50 = 8.673 μM), with acceptable ligand efficiency metrics, practical LogP (3.8) and safety profile on Wi-38 (CC50 = 51.78 μM) and LT-A549 (CC50 = 45.77 μM) lung cells. Docking simulations declared the possible structural determinants of activities and enriched the SAR data for further optimization studies.

Nitrovin (difurazone), an antibacterial growth promoter, induces ROS-mediated paraptosis-like cell death by targeting thioredoxin reductase 1 (TrxR1)

Glioblastoma multiforme (GBM) is one of the most lethal malignant tumors in the human brain, with only a few chemotherapeutic drugs available after surgery. Nitrovin (difurazone) is widely used as an antibacterial growth promoter in livestock. Here, we reported that nitrovin might be a potential anticancer lead. Nitrovin showed significant cytotoxicity to a panel of cancer cell lines. Nitrovin induced cytoplasmic vacuolation, reactive oxygen species (ROS) generation, MAPK activation, and Alix inhibition but had no effect on caspase-3 cleavage and activity, suggesting paraptosis activation. Nitrovin-induced cell death of GBM cells was significantly reversed by cycloheximide (CHX), N-acetyl-l-cysteine (NAC), glutathione (GSH), and thioredoxin reductase 1 (TrxR1) overexpression. Vitamins C and E, inhibitors of pan-caspase, MAPKs, and endoplasmic reticulum (ER) stress failed to do so. Nitrovin-triggered cytoplasmic vacuolation was reversed by CHX, NAC, GSH, and TrxR1 overexpression but not by Alix overexpression. Furthermore, nitrovin interacted with TrxR1 and significantly inhibited its activity. In addition, nitrovin showed a significant anticancer effect in a zebrafish xenograft model, which was reversed by NAC. In conclusion, our results showed that nitrovin induced non-apoptotic and paraptosis-like cell death mediated by ROS through targeting TrxR1. Nitrovin might be a promising anticancer lead for further development.

Thioredoxin Signaling Pathways in Cancer

Significance: Thioredoxin (Trx) is a powerful antioxidant that reduces protein disulfides to maintain redox stability in cells and is involved in regulating multiple redox-dependent signaling pathways. Recent Advance: The current accumulation of findings suggests that Trx participates in signaling pathways that interact with various proteins to manipulate their dynamic regulation of structure and function. These network pathways are critical for cancer pathogenesis and therapy. Promising clinical advances have been presented by most anticancer agents targeting such signaling pathways. Critical Issues: We herein link the signaling pathways regulated by the Trx system to potential cancer therapeutic opportunities, focusing on the coordination and strengths of the Trx signaling pathways in apoptosis, ferroptosis, immunomodulation, and drug resistance. We also provide a mechanistic network for the exploitation of therapeutic small molecules targeting the Trx signaling pathways. Future Directions: As research data accumulate, future complex networks of Trx-related signaling pathways will gain in detail. In-depth exploration and establishment of these signaling pathways, including Trx upstream and downstream regulatory proteins, will be critical to advancing novel cancer therapeutics. Antioxid. Redox Signal. 38, 403-424.

Combined Targeting of the Glutathione and Thioredoxin Antioxidant Systems in Pancreatic Cancer

Pancreatic ductal adenocarcinoma is characterized by increased generation of reactive oxygen species that can cause lethal oxidative stress. Here, we evaluated the combined inhibition of the glutathione and thioredoxin antioxidant systems in preclinical models of pancreatic ductal adenocarcinoma, using buthionine sulfoximine (BSO) that targets glutathione synthesis, and auranofin that targets thioredoxin recycling. BSO potentiated the cytotoxicity of auranofin and induced lethal oxidative stress in primary pancreatic cancer cells. As assessed by the cellular thermal shift assay, auranofin engaged with thioredoxin reductase 1 in primary cells at concentrations known to induce cell death. Moreover, we used imaging mass cytometry to map the biodistribution of atomic gold in patient-derived xenografts treated with auranofin, and the drug was readily detectable throughout the epithelial and stromal compartments after treatment with a clinically relevant dose. In conclusion, combinatorial treatment with BSO and auranofin could serve as a potential therapeutic strategy in pancreatic ductal adenocarcinoma.

Analysis of Pleurotin binding to human thioredoxin reductase using docking and molecular dynamics simulation

Thioredoxin reductase (TrxR) has been considered a potential target for cancer chemotherapy. It acts by controlling the redox homeostasis of human cells and, therefore, interfering in its function may trigger apoptosis, which is a crucial tumor suppression mechanism. Despite the great effort in the search for TrxR inhibitors, none was approved for human therapy. In the present study a virtual screening for natural organic compounds is discussed for a set of 72 compounds with known IC-50 for TrxR inhibition. The results suggest the Pleurotin, a naphthoquinone obtained from Hohenbuehelia grisea fungus, as a potential TrxR inhibitor, which acts by binding to the active site of the enzyme, between the N- and C-terminal domains. The presence of the ligand blocks the approximation of the C-terminal arm to the N-terminal, which is an essential step of the enzyme function. Besides, the two equivalent binding sites of TrxR were explored, by docking two ligands simultaneously. The results indicate that both sites have an allosteric correlation and, the presence of the ligand in one site may interfere, or even prevent, the binding of the second ligand at the other site. All these findings are quantitatively discussed based on the analysis of long molecular dynamics trajectories, which provides a full description of the ligand-receptor binding modes, average binding energies and conformational changes.Communicated by Ramaswamy H. Sarma.

Mecheliolide elicits ROS-mediated ERS driven immunogenic cell death in hepatocellular carcinoma

The nonnegligible reason for the poor prognosis of hepatocellular carcinoma (HCC) is resistance to conventional chemotherapy. Immunogenic cell death (ICD) is a rare immunostimulatory form of cell death that can reengage the tumor-specific immune system. ICD can improve the clinical outcomes of chemotherapeutics by promoting a long-term cancer immunity. The discovery of potential ICD inducers is emerging as a promising direction. In the present study, micheliolide (MCL), a natural guaianolide sesquiterpene lactone, was screened out by the virtual screening strategies, identified as an inhibitor of thioredoxin reductase (TrxR) and was evaluated to have high potential to induce ICD. Here, we showed that MCL induced ICD-associated DAMPs (damage-associated molecular patterns, such as CRT exposure, ATP secretion and HMGB1 release). MCL significantly triggered the regression of established tumors in an immunocompetent mouse vaccine model, and induced ICD (DCs maturation, the stimulation of CD4⁺, and CD8⁺ T-cells responses) in vivo. Mechanistically, we found that the magnitude of ICD-associated effects induced upon exposure of HCC cells to MCL was dependent on the generation of reactive oxygen species (ROS)-mediated endoplasmic reticulum stress (ERS). In addition, the suppression of ROS normalized MCL-induced ERS, in contrast, the downregulation of TrxR synergized with the ERS driven by MCL. We also systematically detected the H₂O₂ generation using Hyper7 sensors in HCC cells exposed to MCL. Notably, MCL inhibited the development of HCC organoids. Collectively, our results reveal a potential association between the TrxR inhibitors and ICD, presenting valuable insights into the MCL-activated ICD in HCC cells.

Thiol-Based Antioxidants and the Epithelial/Mesenchymal Transition in Cancer

Significance: The epithelial/mesenchymal transition (EMT) is commonly associated with tumor metastasis. Oxidative and nitrosative stress is maintained in cancer cells and is involved in the EMT. Cancer cells are endowed with high levels of enzymatic and nonenzymatic antioxidants, which counteract the effects of oxidative and nitrosative stress. Thiol-based antioxidant systems such as the thioredoxin/thioredoxin reductase (Trx/TrxR) and glutathione/glutaredoxin (GSH/Grx) are continually active in cancer cells, while the thioredoxin-interacting protein (Txnip), the negative regulator of the Trx/TrxR system, is downregulated. Recent Advances: Trx/TrxR and GSH/Grx systems play a major role in maintaining EMT signaling and cancer cell progression. Critical Issues: Enhanced stress conditions stimulated in cancer cells inhibit EMT signaling. The elevated expression levels of the Trx/TrxR and GSH/Grx systems in these cells provide the antioxidant protection necessary to guarantee the occurrence of the EMT. Future Directions: Elevation of the intracellular reactive oxygen species and nitric oxide concentrations in cancer cells has been viewed as a promising strategy for elimination of these cells. The development of inhibitors of GSH synthesis and of the Trx/TrxR system together with genetic-based strategies to enhance Txnip levels may provide the necessary means to achieve this goal. Antioxid. Redox Signal. 36, 1037-1050.

Cytotoxic and Radiosensitising Effects of a Novel Thioredoxin Reductase Inhibitor in Brain Cancers

The thioredoxin (Trx) system, a key antioxidant pathway, represents an attractive target for cancer therapy. This study investigated the chemotherapeutic and radiosensitising effects of a novel Trx reductase (TrxR) inhibitor, IQ10, on brain cancer cells and the underlying mechanisms of action. Five brain cancer cell lines and a normal cell type were used. TrxR activity and expression were assessed by insulin reduction assay and Western blotting, respectively. IQ10 cytotoxicity was evaluated using growth curve, resazurin reduction and clonogenic assays. Radiosensitivity was examined using clonogenic assay. Reactive oxygen species levels were examined by flow cytometry and DNA damage assessed by immunofluorescence. Epithelial-mesenchymal transition (EMT)-related gene expression was examined by RT-PCR array. IQ10 significantly inhibited TrxR activity but did not affect Trx system protein expression in brain cancer cells. The drug exhibited potent anti-proliferative and cytotoxic effects against brain cancer cells under both normoxic and hypoxic conditions in both 2D and 3D systems, with IC₅₀s in the low micromolar range. It was up to ~ 1000-fold more potent than temozolomide. IQ10 substantially sensitised various brain cancer cells to radiation, with such effect being due, in part, to functional inhibition of TrxR, making cells less able to deal with oxidative stress and leading to increased oxidative DNA damage. IQ10 significantly downregulated EMT-associated gene expression suggesting potential anti-invasive and antimetastatic properties. This study suggests that IQ10 is a potent anticancer agent and could be used as either a single agent or combined with radiation, to treat brain cancers.

Minerals and Cancer: Overview of the Possible Diagnostic Value

Cancer is the second leading cause of death worldwide and is expected to increase by one-third over the next two decades, in parallel with the growing proportion of the elderly population. Treatment and control of cancer incidence is a global issue. Since there is no clear way to prevent or cure this deadly malignancy, diagnostic, predictive, and prognostic markers for oncological diseases are of great therapeutic value. Minerals and trace elements are important micronutrients for normal physiological function of the body. They are abundant in natural food sources and are regularly included in dietary supplements whereas highly processed industrial food often contains reduced or altered amounts of them. In modern society, the daily intake, storage pools, and homeostasis of these micronutrients are dependent on certain dietary habits and can be thrown out of balance by malignancies. The current work summarizes the data on minerals and trace elements associated with abnormal accumulation or depletion states in tumor patients and discusses their value as potential tumor-associated biomarkers that could be introduced into cancer therapy.

Synthesis of Mitochondria-targeted menadione cation derivatives: inhibiting mitochondrial thioredoxin reductase (TrxR2) and inducing apoptosis in MGC-803 cells

Menadione (VK3) is used as a powerful inducer of cellular reactive oxygen species (ROS) for many years and displays the high anti-cancer activities in vivo. Recently, the development of mitochondria-targeted drugs has been more and more appreciated. Here, the thirteen derivatives of VK3 were synthesized, which could localize in mitochondria by the triphenylphosphonium (TPP) cation or the nitrogen-based cation. The results of cytotoxicity from six human cancer cell lines showed that the targeted compounds T1-T13 displayed higher activity than VK3 with the average IC₅₀ value around 1 μM. The results of cytotoxicity indicated that the substitutes on C-2, the linear alkyl chains on C-3 and cation moiety all could affect the cytotoxicity. The mechanistic studies showed that five representative compounds (T2, T3, T5, T8 and T13) could localize in cellular mitochondria, elicit ROS burst and collapse mitochondrial membrane potential (ΔΨ_m), leading to cytochrome C release and apoptosis in MGC-803 cells. Particularly, they could obviously inhibit mitochondrial thioredoxin reductase TrxR2 expression, thus leading to aggravate cellular oxidative stress.

Thioredoxin reductase-1 levels are associated with NRF2 pathway activation and tumor recurrence in non-small cell lung cancer

Activating mutations in the KEAP1/NRF2 pathway characterize a subset of non-small cell lung cancer (NSCLC) associated with chemoresistance and poor prognosis. We herein evaluated the relationship between 64 oxidative stress-related genes and overall survival data from 35 lung cancer datasets. Thioredoxin reductase-1 (TXNRD1) stood out as the most significant predictor of poor outcome. In a cohort of NSCLC patients, high TXNRD1 protein levels correlated with shorter disease-free survival and distal metastasis-free survival post-surgery, including a subset of individuals treated with platinum-based adjuvant chemotherapy. Bioinformatics analysis revealed that NSCLC tumors harboring genetic alterations in the NRF2 pathway (KEAP1, NFE2L2 and CUL3 mutations, and NFE2L2 amplification) overexpress TXNRD1, while no association with EGFR, KRAS, TP53 and PIK3CA mutations was found. In addition, nuclear accumulation of NRF2 overlapped with upregulated TXNRD1 protein in NSCLC tumors. Functional cell assays and gene dependency analysis revealed that NRF2, but not TXNRD1, has a pivotal role in KEAP1 mutant cells' survival. KEAP1 mutants overexpress TXNRD1 and are less susceptible to the cytotoxic effects of the TXNRD1 inhibitor auranofin when compared to wild-type cell lines. Inhibition of NRF2 with siRNA or ML-385, and glutathione depletion with buthionine-sulfoximine, sensitized KEAP1 mutant A549 cells to auranofin. NRF2 knockdown and GSH depletion also augmented cisplatin cytotoxicity in A549 cells, whereas auranofin had no effect. In summary, these findings suggest that TXNRD1 is not a key determinant of malignant phenotypes in KEAP1 mutant cells, although this protein can be a surrogate marker of NRF2 pathway activation, predicting tumor recurrence and possibly other aggressive phenotypes associated with NRF2 hyperactivation in NSCLC.

Azelaic Acid: A Bio-Based Building Block for Biodegradable Polymers

Azelaic acid is a dicarboxylic acid containing nine C atoms, industrially obtained from oleic acid. Besides its important properties and pharmacological applications, as an individual compound, azelaic acid has proved to be a valuable bio-based monomer for the synthesis of biodegradable and sustainable polymers, plasticizers and lubricants. This review discusses the studies and the state of the art in the field of the production of azelaic acid from oleic acid, the chemical and enzymatic synthesis of bio-based oligo and polyester and their properties, including biodegradability and biocompostability.

Thioredoxin reductase is a major regulator of metabolism in leukemia cells

Despite the fact that AML is the most common acute leukemia in adults, patient outcomes are poor necessitating the development of novel therapies. We identified that inhibition of Thioredoxin Reductase (TrxR) is a promising strategy for AML and report a highly potent and specific inhibitor of TrxR, S-250. Both pharmacologic and genetic inhibition of TrxR impairs the growth of human AML in mouse models. We found that TrxR inhibition leads to a rapid and marked impairment of metabolism in leukemic cells subsequently leading to cell death. TrxR was found to be a major and direct regulator of metabolism in AML cells through impacts on both glycolysis and the TCA cycle. Studies revealed that TrxR directly regulates GAPDH leading to a disruption of glycolysis and an increase in flux through the pentose phosphate pathway (PPP). The combined inhibition of TrxR and the PPP led to enhanced leukemia growth inhibition. Overall, TrxR abrogation, particularly with S-250, was identified as a promising strategy to disrupt AML metabolism.

Lichens as a repository of bioactive compounds: an open window for green therapy against diverse cancers

Lichens, algae and fungi-based symbiotic associations, are sources of many important secondary metabolites, such as antibiotics, anti-inflammatory, antioxidants, and anticancer agents. Wide range of experiments based on in vivo and in vitro studies revealed that lichens are a rich treasure of anti-cancer compounds. Lichen extracts and isolated lichen compounds can interact with all biological entities currently identified to be responsible for tumor development. The critical ways to control the cancer development include induction of cell cycle arrests, blocking communication of growth factors, activation of anti-tumor immunity, inhibition of tumor-friendly inflammation, inhibition of tumor metastasis, and suppressing chromosome dysfunction. Also, lichen-based compounds induce the killing of cells by the process of apoptosis, autophagy, and necrosis, that inturn positively modulates metabolic networks of cells against uncontrolled cell division. Many lichen-based compounds have proven to possess potential anti-cancer activity against a wide range of cancer cells, either alone or in conjunction with other anti-cancer compounds. This review primarily emphasizes on an updated account of the repository of secondary metabolites reported in lichens. Besides, we discuss the anti-cancer potential and possible mechanism of the most frequently reported secondary metabolites derived from lichens.

Gold(I) Complexes with a Quinazoline Carboxamide Alkynyl Ligand: Synthesis, Cytotoxicity, and Mechanistic Studies

A series of gold(I) complexes with the general formula [Au(L2)(L')] (L2=4-phenyl-N-(prop-2-yn-1-yl)quinazoline-2-carboxamide, L'=PPh3 (triphenylphosphine), 1; TPA (1,3,5-triaza-7-phosphaadamantane), 2, and Me2-imy (1,3-dimethylimidazol-2-ylidene), 3) were synthesized and fully characterized by spectroscopic methods. The alkynyl ligand L2 belongs to the quinazoline carboxamide class of ligands that are known to bind to the translocator protein (TSPO) at the outer mitochondrial membrane. 1 and 2 exert cytotoxic effects in bladder cancer cells with IC50 values in the low micromolar range. Further mechanistic analysis indicated that the two complexes both act by inducing reactive oxygen species and caspase-mediated apoptosis. The complexes inhibit thioredoxin reductase, an established target of anticancer gold(I) complexes. Docking studies confirmed that after ligand exchange the free ligand L2 can interact with the TSPO binding site.

Natural Molecules Targeting Thioredoxin System and Their Therapeutic Potential

Significance: Thioredoxin (Trx) and thioredoxin reductase are two core members of the Trx system. The system bridges the gap between the universal reducing equivalent NADPH and various biological molecules and plays an essential role in maintaining cellular redox homeostasis and regulating multiple cellular redox signaling pathways. Recent Advance: In recent years, the Trx system has been well documented as an important regulator of many diseases, especially tumorigenesis. Thus, the development of potential therapeutic molecules targeting the system is of great significance for disease treatment. Critical Issues: We herein first discuss the physiological functions of the Trx system and the role that the Trx system plays in various diseases. Then, we focus on the introduction of natural small molecules with potential therapeutic applications, especially the anticancer activity, and review their mechanisms of pharmacological actions via interfering with the Trx system. Finally, we further discuss several natural molecules that harbor therapeutic potential and have entered different clinical trials. Future Directions: Further studies on the functions of the Trx system in multiple diseases will not only improve our understanding of the pathogenesis of many human disorders but also help develop novel therapeutic strategies against these diseases. Antioxid. Redox Signal. 34, 1083-1107.

Beyond direct Nrf2 activation; reinvestigating 1,2,4-oxadiazole scaffold as a master key unlocking the antioxidant cellular machinery for cancer therapy

Harnessing the antioxidant cellular machinery has sparked considerable interest as an efficient anticancer strategy. Activating Nrf2, the master switch of the cellular redox system, suppresses ROS, alleviates oxidative stress, and halts cancer progression. 1,2,4-oxadiazoles are iconic direct Nrf2 activators that disrupt Nrf2 interaction with its endogenous repressor Keap1. This study introduces rationally designed 1,2,4-oxadiazole derivatives that inhibit other Nrf2 suppressors (TrxR1, IKKα, and NF-kB) thus enhancing Nrf2 activation for preventing oxidative stress and carcinogenesis. Preliminary screening showed that the phenolic oxadiazoles 11, 15, and 19 were comparable to ascorbic acid (ROS scavenging) and EDTA (iron chelation), and superior to doxorubicin against HepG-2, MDA-MB231, and Caco-2 cells. They suppressed ROS by 3 folds and activated Nrf2 by 2 folds in HepG-2 cells. Mechanistically, they inhibited TrxR1 (IC₅₀; 13.19, 17.89, and 9.21 nM) and IKKα (IC₅₀; 11.0, 15.94, and 19.58 nM), and downregulated NF-κB (7.6, 1.4 and 1.9 folds in HepG-2), respectively. They inhibited NADPH oxidase (IC₅₀; 16.4, 21.94, and 10.71 nM, respectively) that potentiates their antioxidant activities. Docking studies predicted their important structural features. Finally, they recorded drug-like in silico physicochemical properties, ADMET, and ligand efficiency metrics.

A focus on the biological targets for coinage metal-NHCs as potential anticancer complexes

Metal complexes of N-heterocyclic carbene (NHC) ligands are the object of increasing attention for therapeutic purposes. Among the different metal centres, interest on Au-based compounds started with the application as anti-arthritis drugs. On the other hand, Ag(I) antimicrobial properties have been known for a long time. For Au(I)/Au(III)-NHC and Ag(I)-NHC anti-tumour and anti-proliferative properties have been quite recently demonstrated. In addition to these and as for Group 11, copper is a much less investigated metal centre, but a few papers underline its pharmacological potential. This review wants to focus on the different biological targets for these metal-based compounds. It is divided into chapters which are respectively devoted on: i) mitochondria and thiol oxidoreductase systems; ii) other relevant enzymes; iii) nucleic acids. Examples of representative coinage NHCs for each of the targets are provided together with significant references on recent advances on the topic. Moreover, a final comment summarises the aspects enlightened by each chapter and provides some hints to better understand the metal-NHCs mechanistic behaviour based on structure-activity relationships.

The effects of chrysin and naringin on cyclophosphamide-induced erythrocyte damage in rats: biochemical evaluation of some enzyme activities in vivo and in vitro

In recent years, there have been efforts to develop therapeutic agents that target metabolic enzyme systems in addition to existing treatment in possible cancer treatments. Cyclophosphamide (CYP) is an anticancer drug commonly used in various cancer treatments. Chrysin (CH) and naringin (NR) are natural flavonoids that possess many medicinal and pharmacological properties. In the present study, we aimed to investigate the effect of CH and NR against CYP-induced toxicity on some metabolic enzyme activities. For this purpose, 56 male rats were randomly divided into 8 groups in our in vivo study. The rats were pretreated with CH (25 and 50 mg/kg bw) and NR (50 and 100 mg/kg bw) for 7 days before administering a single dose of CYP (200 mg/kg bw) on the seventh day. According to the in vivo results of our study, it was observed that CH and NR regulated abnormal changes in CYP-induced enzyme activities. In addition, our in vitro study, G6PD enzyme was purified from rat erythrocyte using affinity chromatography. The effects of CH, NR, and CYP were investigated on the purified enzyme. It was determined that CH increased the enzyme activity, CYP ineffective on the enzyme activity, whereas NR inhibited the enzyme activity noncompetitively. Graphical abstract.

Alteration of Anticancer and Protein-Binding Properties of Gold(I) Alkynyl by Phenolic Schiff Bases Moieties

A set of five gold complexes with the general formula Au(PR₃)(C≡C-C₆H₄-4-R′) (R = PPh₃, R′ = –CHO (1), R = PCy₃, R′ = –CHO (2), R = PPh₃, R′ = –N=CH-C₆H₄-2-OH (3), R = PPh₃, R′ = –N=CH-C₆H₄-4-OH (4), R = PCy₃, R′ = –N=CH-C₆H₄-2-OH (5)) were synthesized and characterized by elemental analysis, ¹H-NMR spectroscopy, ³¹P-NMR spectroscopy, and mass spectrometry. The structures of complexes 2 and 5 were determined by X-ray crystallography. The effects of the structural modifications on the protein binding affinities and anticancer activities of the five gold complexes were assessed. Fluorescence quenching experiments to assess binding to human serum albumin (HSA) revealed that the Schiff base complexes (3, 4, and 5) had binding constants that were superior to their parent aldehyde complexes and highlighted the position of the hydroxy group because complex 4 (4-hydroxy) had a binding constant 6400 times higher than complex 3 (2-hydroxy). The anticancer activities of the complexes against the OVCAR-3 (ovarian carcinoma) and HOP-62 (non-small-cell lung) cancer cell lines showed that the Schiff bases (3–5) were more cytotoxic than the aldehyde-containing complexes (1 and 2). Notably, compound 4 had cytotoxic activity comparable to that of cisplatin against OVCAR-3, demonstrating the significance of the para position for the hydroxy group. Molecular docking studies against the enzyme thioredoxin reductase (TrxR) and human serum albumin were conducted, with docking scores in good agreement with the experimental data. The current study highlights how small structural modifications can alter physiochemical and anticancer properties. Moreover, this simple design strategy using the aldehyde group can generate extensive opportunities to explore new gold(I)-based anticancer drugs via condensation, cyclization, or nucleophilic addition reactions of the aldehyde.

Screening for gene expression fluctuations reveals latency-promoting agents of HIV

Upon treatment removal, spontaneous reactivation of latently infected T cells remains a major barrier toward curing HIV. Therapies that reactivate and clear the latent reservoir are only partially effective, while latency-promoting agents (LPAs) used to suppress reactivation and stabilize latency are understudied and lack diversity in their mechanisms of action. Here, we identify additional LPAs using a screen for gene-expression fluctuations (or "noise") that drive cell-fate specification and control HIV reactivation from latency. Single-cell protein dynamics of a minimal HIV gene circuit were monitored with time-lapse fluorescence microscopy. We screened 1,806 drugs, out of which 279 modulate noise magnitude or half autocorrelation time. Next, we tested the strongest noise modulators in a Jurkat T cell latency model and discovered three LPAs that would be overlooked by quantifying their mean expression levels alone. The LPAs reduced reactivation of latency in both Jurkat and primary cell models when challenged by synergistic and potent combinations of HIV activators. The two strongest LPAs, NSC 401005 and NSC 400938, are structurally and functionally related to inhibitors of thioredoxin reductase, a protein involved in maintaining redox balance in host cells. Experiments with multiple functional analogs revealed two additional LPAs, PX12 and tiopronin, and suggest a potential LPA family, within which some are commercially available and Food and Drug Administration-approved. The LPAs presented here may provide new strategies to complement antiretroviral treatments. Screening for gene expression noise holds the potential for drug discovery in other diseases.

Guided Antitumoural Drugs: (Imidazol-2-ylidene)(L)gold(I) Complexes Seeking Cellular Targets Controlled by the Nature of Ligand L

Three [1,3-diethyl-4-(p-methoxyphenyl)-5-(3,4,5-trimethoxyphenyl)imidazol-2-ylidene](L)gold(I) complexes, 4 a (L=Cl), 5 a (L=PPh3 ), and 6 a (L=same N-heterocyclic carbene (NHC)), and their fluorescent [4-(anthracen-9-yl)-1,3-diethyl-5-phenylimidazol-2-ylidene](L)gold(I) analogues, 4 b, 5 b, and 6 b, respectively, were studied for their localisation and effects in cancer cells. Despite their identical NHC ligands, the last three accumulated in different compartments of melanoma cells, namely, the nucleus (4 b), mitochondria (5 b), or lysosomes (6 b). Ligand L was also more decisive for the site of accumulation than the NHC ligand because the couples 4 a/4 b, 5 a/5 b, and 6 a/6 b, carrying different NHC ligands, afforded similar results in cytotoxicity tests, and tests on targets typically found at their sites of accumulation, such as DNA in nuclei, reactive oxygen species and thioredoxin reductase in mitochondria, and lysosomal membranes. Regardless of the site of accumulation, cancer cell apoptosis was eventually induced. The concept of guiding a bioactive complex fragment to a particular subcellular target by secondary ligand L could reduce unwanted side effects.

Pharmacological inhibition of thioredoxin reductase increases insulin secretion and diminishes beta cell viability

Apparently, both a decrease in beta cell function and in beta cell mass contribute to the progressive worsening of type 2 diabetes. So, it is of particular interest to define factors which are relevant for the regulation of insulin secretion and at the same time for the maintenance of beta cell mass. The NADPH-thioredoxin system has a candidate role for such a dual function. Here, we have characterized the effects of a highly specific inhibitor of thioredoxin reductase, AM12, on the viability and function of insulin-secreting MIN6 cells and isolated NMRI mouse islets. Viability was checked by MTT testing and the fluorescent live-dead assay. Apoptosis was assessed by annexin V assay. Insulin secretion of perifused islets was measured by ELISA. The cytosolic Ca²⁺ concentration was measured by the Fura technique. Acute exposure of perifused pancreatic islets to 5 μM AM12 was without significant effect on insulin secretion. Islets cultured for 24 h in 0.5 or 5 μM AM12 showed unchanged basal secretion during perifusion, but the response to 30 mM glucose was significantly enhanced by 5 μM. Twenty-four-hour exposure to 5 μM AM12 proved to be without effect on the viability of MIN6 cells, whereas longer exposure was clearly toxic. Islets were more susceptible, showing initial signs of apoptosis after 24-h exposure to 5 μM AM12. The activity of the NADPH-thioredoxin system is indispensable for beta cell viability but may have a limiting effect on glucose-induced insulin secretion.

Redox interactome in malaria parasite Plasmodium falciparum

The malaria-causing parasite Plasmodium falciparum is a severe threat to human health across the globe. This parasite alone causes the highest morbidity and mortality than any other species of Plasmodium. The parasites dynamically multiply in the erythrocytes of the vertebrate hosts, a large number of reactive oxygen species that damage biological macromolecules are produced in the cell during parasite growth. To relieve this intense oxidative stress, the parasite employs an NADPH-dependent thioredoxin and glutathione system that acts as an antioxidant and maintains redox status in the parasite. The mutual interaction of both redox proteins is involved in various biological functions and the survival of the erythrocytic stage of the parasite. Since the Plasmodium species is deficient in catalase and classical glutathione peroxidase, so their redox balance relies on a complex set of five peroxiredoxins, differentially positioned in the cytosol, mitochondria, apicoplast, and nucleus with partly overlapping substrate preferences. Moreover, Plasmodium falciparum possesses a set of members belonging to the thioredoxin superfamily, such as three thioredoxins, two thioredoxin-like proteins, one dithiol, three monocysteine glutaredoxins, and one redox-active plasmoredoxin with largely redundant functions. This review paper aims to discuss and encapsulate the biological function and current knowledge of the functional redox network of Plasmodium falciparum.

Multi-Targeted Anticancer Activity of Imidazolate Phosphane Gold(I) Compounds by Inhibition of DHFR and TrxR in Breast Cancer Cells

A class of phosphane gold(I) compounds, made of azoles and phosphane ligands, was evaluated for a screening on the regards of Breast Cancer cell panels (BC). The compounds possess N-Au-P or Cl-Au-P bonds around the central metal, and they differ for the presence of aprotic or protic polar groups in the azoles and/or the phosphane moieties to tune their hydrophilicity. Among the six candidates, only the compounds having the P-Au-N environment and not displaying neither the hydroxyl nor carboxyl groups in the ligands were found active. The compounds were screened by MTT tests in SKBR3, A17, and MDA-MB231 cancer cells, and two compounds (namely the 4,5-dicyano-imidazolate-1yl-gold(I)-(triphenylphosphane, 5, and 4,5-dichloro-imidazolate-1yl-gold(I)-triphenylphosphane, 6) were found very cytotoxic, with the most active with an IC₅₀ value of 3.46 μM in MDA-MB231 cells. By performing enzymatic assays in the treated cells lysates, the residual enzymatic activity of dihydrofolate reductase (DHFR) has been measured after cell treatment for 4 or 12 h in comparison with control cells. Upon 12 h of treatment, the activity of DHFR was significantly reduced in both SKBR3 and A17 cells by compounds 5 and 6, but not in human MDA-MB231 cells; interestingly, it was found remarkably high after 4 h of treatment, revealing a time dependence for the DHFR enzymatic assays. The DHFR inhibition data have been compared to those for the thioredoxin reductase (TrxR), the most recognized molecular target for gold compounds. For this latter, similar residual activities (i.e., 37 and 49% for the match of SKBR3 cells and compound 5 or 6, respectively) were found. Binding studies on the regards of ct-DNA (calf-thymus-DNA) and of plasma transporters proteins, such as BSA (bovine serum albumin) and ATF (apo transferrin), were performed. As expected for gold compounds, the data support strong binding to proteins (K_sv values range: 1.51 ÷ 2.46 × 10⁴ M⁻¹) and a weaker interaction with ct-DNA's minor groove (K_sv values range: 1.55 ÷ 6.12 × 10³ M⁻¹).

Redox regulation of immunometabolism

Metabolic pathways and redox reactions are at the core of life. In the past decade(s), numerous discoveries have shed light on how metabolic pathways determine the cellular fate and function of lymphoid and myeloid cells, giving rise to an area of research referred to as immunometabolism. Upon activation, however, immune cells not only engage specific metabolic pathways but also rearrange their oxidation-reduction (redox) system, which in turn supports metabolic reprogramming. In fact, studies addressing the redox metabolism of immune cells are an emerging field in immunology. Here, we summarize recent insights revealing the role of reactive oxygen species (ROS) and the differential requirement of the main cellular antioxidant pathways, including the components of the thioredoxin (TRX) and glutathione (GSH) pathways, as well as their transcriptional regulator NF-E2-related factor 2 (NRF2), for proliferation, survival and function of T cells, B cells and macrophages.

Auranofin Enhances Sulforaphane-Mediated Apoptosis in Hepatocellular Carcinoma Hep3B Cells through Inactivation of the PI3K/Akt Signaling Pathway

The thioredoxin (Trx) system plays critical roles in regulating intracellular redox levels and defending organisms against oxidative stress. Recent studies indicated that Trx reductase (TrxR) was overexpressed in various types of human cancer cells indicating that the Trx-TrxR system may be a potential target for anti-cancer drug development. This study investigated the synergistic effect of auranofin, a TrxR-specific inhibitor, on sulforaphane-mediated apoptotic cell death using Hep3B cells. The results showed that sulforaphane significantly enhanced auranofin-induced apoptosis by inhibiting TrxR activity and cell proliferation compared to either single treatment. The synergistic effect of sulforaphane and auranofin on apoptosis was evidenced by an increased annexin-V-positive cells and Sub-G1 cells. The induction of apoptosis by the combined treatment caused the loss of mitochondrial membrane potential (ΔΨm) and upregulation of Bax. In addition, the proteolytic activities of caspases (-3, -8, and -9) and the degradation of poly (ADP-ribose) polymerase, a substrate protein of activated caspase-3, were also higher in the combined treatment. Moreover, combined treatment induced excessive generation of reactive oxygen species (ROS). However, treatment with N-acetyl-L-cysteine, a ROS scavenger, reduced combined treatment-induced ROS production and apoptosis. Thereby, these results deduce that ROS played a pivotal role in apoptosis induced by auranofin and sulforaphane. Furthermore, apoptosis induced by auranofin and sulforaphane was significantly increased through inhibition of the phosphoinositide 3-kinase (PI3K)/Akt pathway. Taken together, the present study demonstrated that down-regulation of TrxR activity contributed to the synergistic effect of auranofin and sulforaphane on apoptosis through ROS production and inhibition of PI3K/Akt signaling pathway.

Thioredoxin, Glutathione and Related Molecules in Tumors of the Nervous System

BACKGROUND

Central Nervous System (CNS) tumors have a poor survival prognosis due to their invasive and heterogeneous nature, in addition to the resistance to multiple treatments.

OBJECTIVE

In this paper, the main aspects of brain tumor biology and pathogenesis are reviewed both for primary tumors of the brain, (i.e., gliomas) and for metastasis from other malignant tumors, namely lung cancer, breast cancer and malignant melanoma which account for a high percentage of overall malignant brain tumors. We review the role of antioxidant systems, namely the thioredoxin and glutathione systems, in the genesis and/or progression of brain tumors.

METHODS

Although overexpression of Thioredoxin Reductase (TrxR) and Thioredoxin (Trx) is often linked to increased malignancy rate of brain tumors, and higher expression of Glutathione (GSH) and Glutathione S-Transferases (GST) are associated to resistance to therapy, several knowledge gaps still exist regarding for example, the role of Peroxiredoxins (Prx), and Glutaredoxins (Grx).

CONCLUSION

Due to their central role in redox homeostasis and ROS scavenging, redox systems are potential targets for new antitumorals and examples of innovative therapeutics aiming at improving success rates in brain tumor treatment are discussed.

Targeting the Redox Landscape in Cancer Therapy

Reactive oxygen species (ROS) are produced predominantly by the mitochondrial electron transport chain and by NADPH oxidases in peroxisomes and in the endoplasmic reticulum. The antioxidative defense counters overproduction of ROS with detoxifying enzymes and molecular scavengers, for instance, superoxide dismutase and glutathione, in order to restore redox homeostasis. Mutations in the redox landscape can induce carcinogenesis, whereas increased ROS production can perpetuate cancer development. Moreover, cancer cells can increase production of antioxidants, leading to resistance against chemo- or radiotherapy. Research has been developing pharmaceuticals to target the redox landscape in cancer. For instance, inhibition of key players in the redox landscape aims to modulate ROS production in order to prevent tumor development or to sensitize cancer cells in radiotherapy. Besides the redox landscape of a single cell, alternative strategies take aim at the multi-cellular level. Extracellular vesicles, such as exosomes, are crucial for the development of the hypoxic tumor microenvironment, and hence are explored as target and as drug delivery systems in cancer therapy. This review summarizes the current pharmaceutical and experimental interventions of the cancer redox landscape.