Cytosolic Thioredoxin Reductase Research Articles

The C-terminal selenenylsulfide of extracellular/non-reduced thioredoxin reductase endows this protein with selectivity to small-molecule electrophilic reagents under oxidative conditions.

Mammalian cytosolic thioredoxin reductase (TrxR1) serves as an antioxidant protein by transferring electrons from NADPH to various substrates. The action of TrxR1 is achieved via reversible changes between NADPH-reduced and non-reduced forms, which involves C-terminal selenolthiol/selenenylsulfide exchanges. TrxR1 may be released into extracellular environment, where TrxR1 is present mainly in the non-reduced form with active-site disulfide and selenenylsulfide bonds. The relationships between extracellular TrxR1 and tumor metastasis or cellular signaling have been discovered, but there are few reports on small-molecule compounds in targeted the non-reduced form of TrxR1. Using eight types of small-molecule thiol-reactive reagents as electrophilic models, we report that the selenenylsulfide bond in the non-reduced form of TrxR1 functions as a selector for the thiol-reactive reagents at pH 7.5. The non-reduced form of TrxR1 is resistant to hydrogen peroxide/oxidized glutathione, but is sensitive to certain electrophilic reagents in different ways. With 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) and S-nitrosoglutathione (GSNO), the polarized selenenylsulfide bond breaks, and selenolate anion donates electron to the dynamic covalent bond in DTNB or GSNO, forming TNB-S-Se-TrxR1 complex or ON-Se-TrxR1 complex. The both complexes lose the ability to transfer electrons from NADPH to substrate. For diamide, the non-reduced TrxR1 actually prevents irreversible damage by this oxidant. This is consistent with the regained activity of TrxR1 through removal of diamide via dialysis. Diamide shows effective in the presence of human cytosolic thioredoxin (hTrx1), Cys residue(s) of which is/are preferentially affected by diamide to yield disulfide, hTrx1 dimer and the mixed disulfide between TrxR1-Cys497/Sec498 and hTrx1-Cys73. In human serum samples, the non-reduced form of TrxR1 exists as dithiothreitol-reducible polymer/complexes, which might protect the non-reduced TrxR1 from inactivation by certain electrophilic reagents under oxidative conditions, because cleavage of these disulfides can lead to regain the activity of TrxR1. The details of the selective response of the selenenylsulfide bond to electrophilic reagents may provide new information for designing novel small-molecule inhibitors (drugs) in targeted extracellular/non-reduced TrxR1.

Benzophenanthridine Alkaloid Chelerythrine Elicits Necroptosis of Gastric Cancer Cells via Selective Conjugation at the Redox Hyperreactive C-Terminal Sec498 Residue of Cytosolic Selenoprotein Thioredoxin Reductase.

Targeting thioredoxin reductase (TXNRD) with low-weight molecules is emerging as a high-efficacy anti-cancer strategy in chemotherapy. Sanguinarine has been reported to inhibit the activity of TXNRD1, indicating that benzophenanthridine alkaloid is a fascinating chemical entity in the field of TXNRD1 inhibitors. In this study, the inhibition of three benzophenanthridine alkaloids, including chelerythrine, sanguinarine, and nitidine, on recombinant TXNRD1 was investigated, and their anti-cancer mechanisms were revealed using three gastric cancer cell lines. Chelerythrine and sanguinarine are more potent inhibitors of TXNRD1 than nitidine, and the inhibitory effects take place in a dose- and time-dependent manner. Site-directed mutagenesis of TXNRD1 and in vitro inhibition analysis proved that chelerythrine or sanguinarine is primarily bound to the Sec498 residue of the enzyme, but the neighboring Cys497 and remaining N-terminal redox-active cysteines could also be modified after the conjugation of Sec498. With high similarity to sanguinarine, chelerythrine exhibited cytotoxic effects on multiple gastric cancer cell lines and suppressed the proliferation of tumor spheroids derived from NCI-N87 cells. Chelerythrine elevated cellular levels of reactive oxygen species (ROS) and induced endoplasmic reticulum (ER) stress. Moreover, the ROS induced by chelerythrine could be completely suppressed by the addition of N-acetyl-L-cysteine (NAC), and the same is true for sanguinarine. Notably, Nec-1, an RIPK1 inhibitor, rescued the chelerythrine-induced rapid cell death, indicating that chelerythrine triggers necroptosis in gastric cancer cells. Taken together, this study demonstrates that chelerythrine is a novel inhibitor of TXNRD1 by targeting Sec498 and possessing high anti-tumor properties on multiple gastric cancer cell lines by eliciting necroptosis.

Piperlongumine Inhibits Thioredoxin Reductase 1 by Targeting Selenocysteine Residues and Sensitizes Cancer Cells to Erastin.

Piperlongumine, a natural alkaloid substance extracted from the fruit of the long pepper (Piper longum Linn.), is known to inhibit the cytosolic thioredoxin reductase (TXNRD1 or TrxR1) and selectively kill cancer cells. However, the details and mechanism of the inhibition by piperlongumine against TXNRD1 remain unclear. In this study, based on the classical DTNB reducing assay, irreversible inhibition of recombinant TXNRD1 by piperlongumine was found and showed an apparent kinact value of 0.206 × 10−3 µM−1 min−1. Meanwhile, compared with the wild-type TXNRD1 (-GCUG), the UGA-truncated form (-GC) of TXNRD1 was resistant to piperlongumine, suggesting the preferential target of piperlongumine is the selenol (-SeH) at the C-terminal redox motif of the enzyme. Interestingly, the high concentration of piperlongumine-inhibited TXNRD1 showed that its Sec-dependent activity is decayed but its intrinsic NADPH oxidase activity is retained. Furthermore, piperlongumine did not induce ferroptosis in HCT116 cells at 10 µM, whereas significantly promoted erastin-induced lipid oxidation, which could be alleviated by supplying glutathione (GSH) or N-acetyl L-cysteine (NAC). However, restricting GSH synthesis by inhibiting glutaminase (GLS) using the small molecule inhibitor CB-839 only slightly enhanced erastin-induced cell death. Taken together, this study elucidates the molecular mechanism of the antitumor capacity of piperlongumine by targeting TXNRD1 and reveals the potential possibility of inhibiting TXNRD1 to strengthen cancer cells’ ferroptosis.

Spatial and temporal control of mitochondrial H2O2 release in intact human cells

Hydrogen peroxide (H2O2) has key signaling roles at physiological levels, while causing molecular damage at elevated concentrations. H2O2 production by mitochondria is implicated in regulating processes inside and outside these organelles. However, it remains unclear whether and how mitochondria in intact cells release H2O2. Here, we employed a genetically encoded high‐affinity H2O2 sensor, HyPer7, in mammalian tissue culture cells to investigate different modes of mitochondrial H2O2 release. We found substantial heterogeneity of HyPer7 dynamics between individual cells. We further observed mitochondria‐released H2O2 directly at the surface of the organelle and in the bulk cytosol, but not in the nucleus or at the plasma membrane, pointing to steep gradients emanating from mitochondria. Gradient formation is controlled by cytosolic peroxiredoxins, which act redundantly and with a substantial reserve capacity. Dynamic adaptation of cytosolic thioredoxin reductase levels during metabolic changes results in improved H2O2 handling and explains previously observed differences between cell types. Our data suggest that H2O2‐mediated signaling is initiated only in close proximity to mitochondria and under specific metabolic conditions.

Thioredoxin Reductase Inhibition for Cancer Therapy.

The cytosolic selenoprotein thioredoxin reductase 1 (TrxR1, TXNRD1), and to some extent mitochondrial TrxR2 (TXNRD2), can be inhibited by a wide range of electrophilic compounds. Many such compounds also yield cytotoxicity toward cancer cells in culture or in mouse models, and most compounds are likely to irreversibly modify the easily accessible selenocysteine residue in TrxR1, thereby inhibiting its normal activity to reduce cytosolic thioredoxin (Trx1, TXN) and other substrates of the enzyme. This leads to an oxidative challenge. In some cases, the inhibited forms of TrxR1 are not catalytically inert and are instead converted to prooxidant NADPH oxidases, named SecTRAPs, thus further aggravating the oxidative stress, particularly in cells expressing higher levels of the enzyme. In this review, the possible molecular and cellular consequences of these effects are discussed in relation to cancer therapy, with a focus on outstanding questions that should be addressed if targeted TrxR1 inhibition is to be further developed for therapeutic use.

Inhibition of Thioredoxin Reductase by Triosmium Carbonyl Clusters.

Tumor cells are characterized by increased reactive oxygen species production in parallel with an enhanced antioxidant system to avoid oxidative damage. The inhibition of antioxidant systems is an effective way to kill cancer cells, and the thioredoxin system or, more specifically, the cytosolic selenocysteine-containing enzyme thioredoxin reductase (TrxR) has become an interesting target for cancer therapy. We show here that the known cytotoxic and apoptosis-inducing osmium carbonyl cluster Os3(CO)10(NCCH3)2 (1) is a nonsubstrate inhibitor of mammalian TrxR, with an IC50 of 5.3 ± 0.9 μM. It inhibits TrxR selectively over the closely related glutathione reductase (GR) and in the presence of excess reduced glutathione (GSH). This inhibition has also been demonstrated in cell lysates, suggesting that TrxR inhibition is a potential apoptotic pathway for 1.

Selenium supplementation can relieve the clinical complications of COVID-19 and other similar viral infections

Selenium supplementation can relieve the clinical complications of COVID-19 and other similar viral infections

The mammalian cytosolic thioredoxin reductase pathway acts via a membrane protein to reduce ER-localised proteins.

ABSTRACTFolding of proteins entering the mammalian secretory pathway requires the insertion of the correct disulfides. Disulfide formation involves both an oxidative pathway for their insertion and a reductive pathway to remove incorrectly formed disulfides. Reduction of these disulfides is crucial for correct folding and degradation of misfolded proteins. Previously, we showed that the reductive pathway is driven by NADPH generated in the cytosol. Here, by reconstituting the pathway using purified proteins and ER microsomal membranes, we demonstrate that the thioredoxin reductase system provides the minimal cytosolic components required for reducing proteins within the ER lumen. In particular, saturation of the pathway and its protease sensitivity demonstrates the requirement for a membrane protein to shuttle electrons from the cytosol to the ER. These results provide compelling evidence for the crucial role of the cytosol in regulating ER redox homeostasis, ensuring correct protein folding and facilitating the degradation of misfolded ER proteins.

Antiproliferative Activity of Gold(I) N‐Heterocyclic Carbene and Triphenylphosphine Complexes with Ibuprofen Derivatives as Effective Enzyme Inhibitors

A series of gold(I) complexes of ligand ibuprofen‐alkynyl (but‐3‐yn‐1‐yl 2‐(4‐isobutylphenyl)propanoate, LE) with N‐heterocyclic carbene (LC: 1,3‐dimethylimidazol‐2‐ylidene) and triphenylphosphine (PPh3) ligands with formula (LE)Au (LC) (complex 1) and (LE)Au (PPh3) (complex 2) were synthesized and fully characterized by spectroscopic methods. In order to reveal the cytotoxicity mechanism, the interaction of complex 1 or 2 with cysteine (HCys) has been studied by experimental and density functional theory (DFT) methods. The compounds were investigated for their anticancer activity against MCF‐7, MDAMB 231 breast cancer cells, HT‐29 colon cancer cells and MCF‐10A non‐tumor breast cell line. The results were compared with cisplatin and auranofin as reference drugs. The complex 2 showed more cytotoxic activity than complex 1. The complex 2 was 4.2, 3.7, and 1.7 fold more active than cisplatin against HT‐29, MDA‐MB‐231, MCF‐7 cancer cell lines, respectively. The inhibition of thioredoxin reductase of complexes 1 and 2 including cytosolic (TrxR1) and mitochondrial (TrxR2) thioredoxin reductase and also the inhibition of glutathione reductase (GR) were studied in detail. Moreover, the cellular uptake and reactive oxygen species (ROS) generation of compounds were investigated. Based on the DFT calculations a relationship between the σ‐donor ability of the isolated ligands and cytotoxicity is suggested.

Inhibition of thioredoxin reductase 1 correlates with platinum-based chemotherapeutic induced tissue injury

Platinum-containing drugs (PtDs; e.g. cisplatin, carboplatin, and oxaliplatin) have been widely used as anticancer reagents against various cancers. However, treatment with these drugs results in undesirable adverse effects with unknown mechanisms. Herein, we found a strong correlation between the inhibitory effects of PtDs on cytosolic thioredoxin reductase (TXNRD1) and tissue injury. Of the PtDs tested, cisplatin was found to be the most effective inhibitory PtD against TXRND1, causing the severest kidney injury. The initial inhibition of TXNRD1 in the kidney resulted from cisplatin-induced transcriptional activation of Nrf2-regulated genes including Txnrd1. However, the antioxidant responses in the kidney did not reverse the cisplatin-induced oxidation process. Nephrotoxicity was accompanied with an increase of protein glutathionylation and a cellular thiol redox environment oxidation. These results suggest that the changes of the cellular thiol-dependent redox environment regulated by TXNRD1 is a major event in the adverse effects of cisplatin in kidney.

Yeast thioredoxin reductase Trr1p controls TORC1-regulated processes

The thioredoxin system plays a predominant role in the control of cellular redox status. Thioredoxin reductase fuels the system with reducing power in the form of NADPH. The TORC1 complex promotes growth and protein synthesis when nutrients, particularly amino acids, are abundant. It also represses catabolic processes, like autophagy, which are activated during starvation. We analyzed the impact of yeast cytosolic thioredoxin reductase TRR1 deletion under different environmental conditions. It shortens chronological life span and reduces growth in grape juice fermentation. TRR1 deletion has a global impact on metabolism during fermentation. As expected, it reduces oxidative stress tolerance, but a compensatory response is triggered, with catalase and glutathione increasing. Unexpectedly, TRR1 deletion causes sensitivity to the inhibitors of the TORC1 pathway, such as rapamycin. This correlates with low Tor2p kinase levels and indicates a direct role of Trr1p in its stability. Markers of TORC1 activity, however, suggest increased TORC1 activity. The autophagy caused by nitrogen starvation is reduced in the trr1Δ mutant. Ribosomal protein Rsp6p is dephosphorylated in the presence of rapamycin. This dephosphorylation diminishes in the TRR1 deletion strain. These results show a complex network of interactions between thioredoxin reductase Trr1p and the processes controlled by TOR.

Thioredoxin-related protein of 14kDa as a modulator of redox signalling pathways.

Thioredoxin-related protein of 14kDa (TRP14; also named TXNDC17 for thioredoxin domain-containing protein 17) is a highly conserved and ubiquitously expressed oxidoreductase. It is expressed in parallel with thioredoxin 1 (Trx1, TXN; TXN1), an efficient substrate for the mammalian cytosolic selenoprotein thioredoxin reductase 1 (TrxR1; TXNRD1). However, TRP14, in sharp contrast to Trx1, cannot support the activities of ribonucleotide reductase, peroxiredoxins or methionine sulfoxide reductases, thus is unable to directly support cell proliferation or antioxidant defence through these pathways. However, TRP14 has been shown to efficiently reduce l-cystine, which thereby indirectly supports glutathione synthesis. TRP14 can also suppress NF-κB signalling, is functionally linked to STAT3 signalling, and can directly reactivate oxidized protein-tyrosine phosphatase PTP1B. Furthermore, TRP14 can efficiently reduce persulfidated or nitrosylated cysteine residues in many proteins, thereby having the capacity to modulate signalling through hydrogen sulfide or NO. Additional bioinformatics analyses and observations suggest further roles for TRP14; therefore, further studies of its functions are warranted. Collectively, the results available suggest that TRP14 is a member of the thioredoxin system dedicated to the control of cellular redox signalling pathways. LINKED ARTICLES: This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc.

Specific irreversible targeting of the selenoprotein thioredoxin reductase 1 in cancer therapy

The cytosolic selenoprotein thioredoxin reductase 1 (TrxR1, TXNRD1) is a key enzyme for redox control of cell function and antioxidant capacity. Many cancer cells have high levels of TrxR1 as a means of surviving their increased endogenous oxidative stress. This in turn has led to the hypothesis that TrxR1 may be an anticancer drug target, especially as the enzyme is dispensable for normal adult cells. Interestingly TrxR1 is also inhibited by several anticancer drugs in clinical use, including cisplatin, chlorambucil, nitrosoureas and melphalan. It is also a well-known target of gold compounds such as auranofin, currently in clinical trials for anticancer treatment. It has not been known, however, whether inhibition of TrxR1 is a mechanism leading to some of the anticancer effects seen upon use of some of these compounds, or whether this enzyme inhibition is merely a correlative event due to a high inherent reactivity of TrxR1. Novel findings with more specific inhibitors however suggest that TrxR1 can indeed be an authentic anticancer drug target, the inhibition of which yields anticancer efficacy in mouse models without overt toxicity to normal cells and tissues.

Manumycin A Is a Potent Inhibitor of Mammalian Thioredoxin Reductase-1 (TrxR-1)

The anticancer effect of manumycin A (Man A) has been attributed to the inhibition of farnesyl transferase (FTase), an enzyme that is responsible for post-translational modification of Ras proteins. However, we have discovered that Man A inhibits mammalian cytosolic thioredoxin reductase 1 (TrxR-1) in a time-dependent manner, with an IC50 of 272 nM with preincubation and 1586 nM without preincubation. The inhibition of TrxR-1 by Man A is irreversible and is the result of a covalent interaction between Man A and TrxR-1. Evidence presented herein demonstrates that Man A forms a Michael adduct with the selenocysteine residue, which is located in the C-terminal redox center of TrxR-1. Inhibitors of TrxR-1, which act through this mechanism, convert TrxR-1 into a SecTRAP, which utilizes NADPH to reduce oxygen to superoxide radical anion (O2-•).

Irreversible inhibition of cytosolic thioredoxin reductase 1 as a mechanistic basis for anticancer therapy.

Cancer cells adapt to their inherently increased oxidative stress through activation of the glutathione (GSH) and thioredoxin (TXN) systems. Inhibition of both of these systems effectively kills cancer cells, but such broad inhibition of antioxidant activity also kills normal cells, which is highly unwanted in a clinical setting. We therefore evaluated targeting of the TXN pathway alone and, more specifically, selective inhibition of the cytosolic selenocysteine-containing enzyme TXN reductase 1 (TXNRD1). TXNRD1 inhibitors were discovered in a large screening effort and displayed increased specificity compared to pan-TXNRD inhibitors, such as auranofin, that also inhibit the mitochondrial enzyme TXNRD2 and additional targets. For our lead compounds, TXNRD1 inhibition correlated with cancer cell cytotoxicity, and inhibitor-triggered conversion of TXNRD1 from an antioxidant to a pro-oxidant enzyme correlated with corresponding increases in cellular production of H2O2 In mice, the most specific TXNRD1 inhibitor, here described as TXNRD1 inhibitor 1 (TRi-1), impaired growth and viability of human tumor xenografts and syngeneic mouse tumors while having little mitochondrial toxicity and being better tolerated than auranofin. These results display the therapeutic anticancer potential of irreversibly targeting cytosolic TXNRD1 using small molecules and present potent and selective TXNRD1 inhibitors. Given the pronounced up-regulation of TXNRD1 in several metastatic malignancies, it seems worthwhile to further explore the potential benefit of specific irreversible TXNRD1 inhibitors for anticancer therapy.

Early response of glutathione- and thioredoxin-dependent antioxidant defense systems to Tl(I)- and Tl(III)-mediated oxidative stress in adherent pheochromocytoma (PC12adh) cells.

Thallium (Tl) is a toxic heavy metal that causes oxidative stress both in vitro and in vivo. In this work, we evaluated the production of oxygen (ROS)- and nitrogen (RNS)-reactive species in adherent PC12 (PC12adh) cells exposed for 0.5-6h to Tl(I) or Tl(III) (10-100µM). In this system, Tl(I) induced mostly H2O2 generation while Tl(III) induced H2O2 and ONOO·- generation. Both cations enhanced iNOS expression and activity, and decreased CuZnSOD expression but without affecting its activity. Tl(I) increased MnSOD expression and activity but Tl(III) decreased them. NADPH oxidase (NOX) activity remained unaffected throughout the period assessed. Oxidant levels returned to baseline values after 6h of incubation, suggesting a response of the antioxidant defense system to the oxidative insult imposed by the cations. Tl also affected the glutathione-dependent system: while Tl(III) increased glutathione peroxidase (GPx) expression and activity, Tl(I) and Tl(III) decreased glutathione reductase (GR) expression. However, GR activity was mildly enhanced by Tl(III). Finally, thioredoxin-dependent system was evaluated. Only Tl(I) increased 2-Cys peroxiredoxins (2-Cys Prx) expression, although both cations increased their activity. Tl(I) increased cytosolic thioredoxin reductase (TrxR1) and decreased mitochondrial (TrxR2) expression. Tl(III) had a biphasic effect on TrxR1 expression and slightly increased TrxR2 expression. Despite of this, both cations increased total TrxR activity. Obtained results suggest that in Tl(I)-exposed PC12adh cells, there is an early response to oxidative stress mainly by GSH-dependent system while in Tl(III)-treated cells both GSH- and Trx-dependent systems are involved.

GSR is not essential for the maintenance of antioxidant defenses in mouse cochlea: Possible role of the thioredoxin system as a functional backup for GSR.

Glutathione reductase (GSR), a key member of the glutathione antioxidant defense system, converts oxidized glutathione (GSSG) to reduced glutathione (GSH) and maintains the intracellular glutathione redox state to protect the cells from oxidative damage. Previous reports have shown that Gsr deficiency results in defects in host defense against bacterial infection, while diquat induces renal injury in Gsr hypomorphic mice. In flies, overexpression of GSR extended lifespan under hyperoxia. In the current study, we investigated the roles of GSR in cochlear antioxidant defense using Gsr homozygous knockout mice that were backcrossed onto the CBA/CaJ mouse strain, a normal-hearing strain that does not carry a specific Cdh23 mutation that causes progressive hair cell degeneration and early onset of hearing loss. Gsr-/- mice displayed a significant decrease in GSR activity and GSH/GSSG ratios in the cytosol of the inner ears. However, Gsr deficiency did not affect ABR (auditory brainstem response) hearing thresholds, wave I amplitudes or wave I latencies in young mice. No histological abnormalities were observed in the cochlea of Gsr-/- mice. Furthermore, there were no differences in the activities of cytosolic glutathione-related enzymes, including glutathione peroxidase and glutamate-cysteine ligase, or the levels of oxidative damage markers in the inner ears between WT and Gsr-/- mice. In contrast, Gsr deficiency resulted in increased activities of cytosolic thioredoxin and thioredoxin reductase in the inner ears. Therefore, under normal physiological conditions, GSR is not essential for the maintenance of antioxidant defenses in mouse cochlea. Given that the thioredoxin system is known to reduce GSSG to GSH in multiple species, our findings suggest that the thioredoxin system can support GSSG reduction in the mouse peripheral auditory system.

Cytosolic thioredoxin reductase 1 is required for correct disulfide formation in the ER

Folding of proteins entering the secretory pathway in mammalian cells frequently requires the insertion of disulfide bonds. Disulfide insertion can result in covalent linkages found in the native structure as well as those that are not, so‐called non‐native disulfides. The pathways for disulfide formation are well characterized, but our understanding of how non‐native disulfides are reduced so that the correct or native disulfides can form is poor. Here, we use a novel assay to demonstrate that the reduction in non‐native disulfides requires NADPH as the ultimate electron donor, and a robust cytosolic thioredoxin system, driven by thioredoxin reductase 1 (TrxR1 or TXNRD1). Inhibition of this reductive pathway prevents the correct folding and secretion of proteins that are known to form non‐native disulfides during their folding. Hence, we have shown for the first time that mammalian cells have a pathway for transferring reducing equivalents from the cytosol to the ER, which is required to ensure correct disulfide formation in proteins entering the secretory pathway.

Targeting the Selenoprotein Thioredoxin Reductase 1 for Anticancer Therapy.

The cytosolic selenoprotein thioredoxin reductase 1 (TrxR1, encoded in human by TXNRD1) is implied to have several different roles in relation to cancer. Its physiologic functions may protect normal cells from carcinogenesis, but may also promote cancer progression if carcinogenesis nonetheless occurs. With distinct links to Nrf2 signaling, ribonucleotide reductase-dependent production of deoxyribonucleotides and its support of several antioxidant systems counteracting oxidative stress, the metabolic pathways regulated, and affected by TrxR1, are altogether of crucial importance in cancer. These pathways and causal relationships are at the same time highly intricate. In spite of the complexity in the cellular redox networks, several observations discussed in this chapter suggest that specific targeting of TrxR1 may be promising as a mechanistic principle for anticancer therapy.

Bioassay-guided isolation of dehydrocostus lactone from Saussurea lappa: A new targeted cytosolic thioredoxin reductase anticancer agent

In a screen for mammalian thioredoxin reductases inhibitors, an MeOH extract from the roots of Saussurea lappa C.B. Clarke (Compositae) inhibited the activity of cytosolic thioredoxin reductase (TrxR1). Bioassay-guided separation of the extract led to the isolation of a new TrxR1 inhibitor, dehydrocostus lactone (DHC), a guaiane-type sesquiterpene. The content of DHC in the extract was determined to be 0.4%. DHC inhibited human cervical carcinoma HeLa cells with an IC50 of ∼12.00 μM but displayed less cytotoxicity to human immortalized normal liver cells L02. We observed that DHC killed HeLa cells through induction of apoptosis. DHC inhibited the activity of TrxR1 in HeLa cells, which elicited an accumulation of reactive oxygen species (ROS) in cells and a collapse of the intracellular redox equilibrium and eventually induced apoptosis of HeLa cells.