FDA-approved disulfiram as a novel treatment for aggressive leukemia

Acute leukemia continues to be a major cause of death from disease worldwide and current chemotherapeutic agents are associated with significant morbidity in survivors. While better and safer treatments for acute leukemia are urgently needed, standard drug development pipelines are lengthy and drug repurposing therefore provides a promising approach. Our previous evaluation of FDA-approved drugs for their antileukemic activity identified disulfiram, used for the treatment of alcoholism, as a candidate hit compound. This study assessed the biological effects of disulfiram on leukemia cells and evaluated its potential as a treatment strategy. We found that disulfiram inhibits the viability of a diverse panel of acute lymphoblastic and myeloid leukemia cell lines (n = 16) and patient-derived xenograft cells from patients with poor outcome and treatment-resistant disease (n = 15). The drug induced oxidative stress and apoptosis in leukemia cells within hours of treatment and was able to potentiate the effects of daunorubicin, etoposide, topotecan, cytarabine, and mitoxantrone chemotherapy. Upon combining disulfiram with auranofin, a drug approved for the treatment of rheumatoid arthritis that was previously shown to exert antileukemic effects, strong and consistent synergy was observed across a diverse panel of acute leukemia cell lines, the mechanism of which was based on enhanced ROS induction. Acute leukemia cells were more sensitive to the cytotoxic activity of disulfiram than solid cancer cell lines and non-malignant cells. While disulfiram is currently under investigation in clinical trials for solid cancers, this study provides evidence for the potential of disulfiram for acute leukemia treatment. KEY MESSAGES: Disulfiram induces rapid apoptosis in leukemia cells by boosting oxidative stress. Disulfiram inhibits leukemia cell growth more potently than solid cancer cell growth. Disulfiram can enhance the antileukemic efficacy of chemotherapies. Disulfiram strongly synergises with auranofin in killing acute leukemia cells by ROS induction. We propose testing of disulfiram in clinical trial for patients with acute leukemia.

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.

Combination of TrxR1 inhibitor and lenvatinib triggers ROS-dependent cell death in human lung cancer cells

Lung cancer is one of the most lethal diseases in the world. Although there has been significant progress in the treatment of lung cancer, there is still a lack of effective strategies for advanced cases. Lenvatinib, a multi-targeted tyrosine kinase inhibitor, has achieved much attention due to its antitumor properties. Nevertheless, the use of lenvatinib is restricted by the characteristics of poor efficacy and drug resistance. In this study, we assessed the effectiveness of lenvatinib combined with thioredoxin reductase 1 (TrxR1) inhibitors in human lung cancer cells. Our results indicate that the combination therapy involving TrxR1 inhibitors and lenvatinib exhibited significant synergistic antitumor effects in human lung cancer cells. Moreover, siTrxR1 also showed significant synergy with lenvatinib in lung cancer cells. Mechanically, we demonstrated that ROS accumulation significantly contributes to the synergism between lenvatinib and TrxR1 inhibitor auranofin. Furthermore, the combination of lenvatinib and auranofin can activate endoplasmic reticulum stress and JNK signaling pathways to achieve the goal of killing lung cancer cells. Importantly, combination therapy with lenvatinib and auranofin exerted a synergistic antitumor effect in vivo. To sum up, the combination therapy involving lenvatinib and auranofin may be a potential strategy for treating lung cancer.

Auranofin attenuates Schistosoma mansoni egg-induced liver granuloma and fibrosis in mice

Schistosomiasis is a serious tropical disease. Despite extensive research into the etiology of liver fibrosis, effective therapeutic options remain limited. This study aims to assess the effectiveness of auranofin in treating hepatic granuloma and fibrogenesis produced by Schistosoma (S.) mansoni eggs. Auranofin is a gold complex that contains thioglucose tetraacetate and triethylphosphine. Eighty BALB/c male mice were divided into four groups (n=20/group): negative control (GI), positive control (GII), and early (GIII) and late (GIV) treatment groups with oral auranofin according to beginning of treatment 4th week and 6th week post-infection. Mice were infected subcutaneously in a dose of 60±10 cercariae/mouse. Worm counts, egg loads, and oogram patterns were determined. Biochemical, histological, and immunostaining of interleukin-1β (IL-1β), Sirtuin 3 (SIRT3), and smooth muscle actin (SMA) were assessed. GIII showed a significant decrease in the total S. mansoni worm burden and ova/gram in liver tissue (with reduction percent of 63.07% and 78.26%, respectively). Schistosomal oogram patterns, immature and mature ova, also showed a significant decrease. The reduction in granuloma number and size was 40.63% and 48.66%, respectively, in GIII, whereas in GIV, the reduction percent was 76.63% and 67.08%. In addition, the degree of fibrosis was significantly diminished in both treated groups. GIV showed significant reduction in IL-1β and SMA expression and increase in SIRT3 expression. These findings reveal how auranofin suppresses the development of liver fibrosis. Therefore, it is crucial to take another look at auranofin as a prospective medication for the treatment of S. mansoni egg-induced hepatic granuloma and consequent fibrosis.

Direct inhibition of dioxygenases TET1 by the rheumatoid arthritis drug auranofin selectively induces cancer cell death in T-ALL

T-cell acute lymphoblastic leukemia (T-ALL) is a type of hematologic tumor with malignant proliferation of hematopoietic progenitor cells. However, traditional clinical treatment of T-ALL included chemotherapy and stem cell transplantation always lead to recurrence and poor prognosis, thus new therapeutic targets and drugs are urgently needed for T-ALL treatment. In this study, we showed that TET1 (ten-eleven translocation 1), a key participant of DNA epigenetic control, which catalyzes the conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) to modulate gene expression, was highly upregulated in human T-ALL and negatively correlated with the prognosis of patients. Knockdown of TET1 suppressed T-ALL growth and progression, suggesting that TET1 inhibition maybe an effective way to fight T-ALL via DNA epigenetic modulation. Combining structure-guided virtual screening and cell-based high-throughput screening of FDA-approved drug library, we discovered that auranofin, a gold-containing compound, is a potent TET1 inhibitor. Auranofin inhibited the catalytic activity of TET1 through competitive binding to its substrates binding pocket and thus downregulated the genomic level of 5hmC marks and particularly epigenetically reprogramed the expression of oncogene c-Myc in T-ALL in TET1-dependent manner and resulted in suppression of T-ALL in vitro and in vivo. These results revealed that TET1 is a potential therapeutic target in human T-ALL and elucidated the mechanism that TET1 inhibitor auranofin suppressed T-ALL through the TET1/5hmC/c-Myc signaling pathway. Our work thus not only provided mechanism insights for T-ALL treatment, but also discovered potential small molecule therapeutics for T-ALL.

Anti-fibrotic effect of aurocyanide, the active metabolite of auranofin

Drug repositioning has gained significant attention over the past several years. The anti-rheumatoid arthritis drug auranofin has been investigated for the treatment of other diseases, including liver fibrosis. Because auranofin is rapidly metabolized, it is necessary to identify the active metabolites of auranofin that have detectable levels in the blood and reflect its therapeutic effects. In the present study, we investigated whether aurocyanide as an active metabolite of auranofin, can be used to evaluate the anti-fibrotic effects of auranofin. Incubation of auranofin with liver microsomes showed that auranofin was susceptible to hepatic metabolism. Previously, we found that the anti-fibrotic effects of auranofin are mediated via system x_c^--dependent inhibition of the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome. Therefore, we tried to identify active metabolites of auranofin based on their inhibitory effects on system x_c^- and NLRP3 inflammasome in bone marrow-derived macrophages. Among the seven candidate metabolites, 1-thio-β-D-glycopyrano-sato-S-(triethyl-phosphine)-gold(I) and aurocyanide potently inhibited system x_c^- and NLRP3 inflammasome. A pharmacokinetics study on mice detected significant plasma levels of aurocyanide after auranofin administration. Oral administration of aurocyanide significantly prevented thioacetamide-induced liver fibrosis in mice. Moreover, the in vitro anti-fibrotic effects of aurocyanide were assessed in LX-2 cells, where aurocyanide significantly decreased the migratory ability of the cells. In conclusion, aurocyanide is metabolically stable and detectable in plasma, and has inhibitory effects on liver fibrosis, suggesting that it is a potential marker of the therapeutic effects of auranofin.

Auranofin inhibits virulence pathways in Pseudomonas aeruginosa

Pseudomonas aeruginosa is widely attributed as the leading cause of hospital-acquired infections. Due to intrinsic antibiotic resistance mechanisms and the ability to form biofilms, P. aeruginosa infections are challenging to treat. P. aeruginosa employs multiple virulence mechanisms to establish infections, many of which are controlled by the global virulence regulator Vfr. An attractive strategy to combat P. aeruginosa infections is thus the use of anti-virulence compounds. Here, we report the discovery that FDA-approved drug auranofin attenuates virulence pathways in P. aeruginosa, including quorum sensing (QS) and Type IV pili (TFP). We show that auranofin acts via multiple targets, one of which being Vfr. Consistent with inhibition of QS and TFP expression, we show that auranofin attenuates biofilm maturation, and when used in combination with colistin, displays strong synergy in eradicating P. aeruginosa biofilms. Auranofin may have immediate applications as an anti-virulence drug against P. aeruginosa infections.

Disruption of RBMS3 suppresses PD-L1 and enhances antitumor immune activities and therapeutic effects of auranofin against triple-negative breast cancer

Programmed cell death protein-1 (PD-1)/programmed cell death ligand-1 (PD-L1) interaction exerts a vital role in tumor-associated immune evasion. While strategies disrupting PD-1/PD-L1 axis have shown clinical benefits in various cancers, the limited response rate prompts us to investigate the complex mechanisms underlying the molecular regulation of PD-L1. Here, we identify the RNA binding protein RBMS3 as a crucial PD-L1 regulator in triple-negative breast cancer (TNBC). Correlation analysis shows that Rbms3 significantly correlates with immunosuppressive CD274, Rbms1, NT5E and ENTPD1. RBMS3 protein binds to CD274 mRNA specifically in TNBC cells to increase PD-L1 levels. Mechanistically, RBMS3 stabilizes CD274 mRNA by interacting with its 3'UTR, which represents as an intrinsic cancer cell mechanism for driving PL-D1 upregulation in TNBC. RBMS3 depletion not only destabilizes the mRNA stability and protein expression of PD-L1, but also suppresses the migratory abilities of TNBC MDA-MB-231 cells. Importantly, combination of RBMS3 ablation with auranofin (AUF), an FDA-approved thioredoxin reductase inhibitor, facilitates anti-tumor T-cell immunity in vivo and improves AUF-mediated anti-cancer effect. Taken together, our findings reveal RBMS3 as a key post-transcriptional regulator of PD-L1 and how they contribute to immune escape in TNBC, which could lead to novel combinatorial therapeutic strategies to enhance the efficacy of cancer immunotherapy.

Omics-based identification of an NRF2-related auranofin resistance signature in cancer: Insights into drug repurposing

Auranofin is a thioredoxin reductase-1 inhibitor originally approved for the treatment of rheumatoid arthritis. Recently, auranofin has been repurposed as an anticancer drug, with pharmacological activity reported in multiple cancer types. In this study, we characterized transcriptional and genetic alterations associated with auranofin response in cancer. By integrating data from an auranofin cytotoxicity screen with transcriptome profiling of lung cancer cell lines, we identified an auranofin resistance signature comprising 29 genes, most of which are classical targets of the transcription factor NRF2, such as genes involved in glutathione metabolism (GCLC, GSR, SLC7A11) and thioredoxin system (TXN, TXNRD1). Pan-cancer analysis revealed that mutations in NRF2 pathway genes, namely KEAP1 and NFE2L2, are strongly associated with overexpression of the auranofin resistance gene set. By clustering cancer types based on auranofin resistance signature expression, hepatocellular carcinoma, and a subset of non-small cell lung cancer, head-neck squamous cell carcinoma, and esophageal cancer carrying NFE2L2/KEAP1 mutations were predicted resistant, whereas leukemia, lymphoma, and multiple myeloma were predicted sensitive to auranofin. Cell viability assays in a panel of 20 cancer cell lines confirmed the augmented sensitivity of hematological cancers to auranofin; an effect associated with dependence upon glutathione and decreased expression of NRF2 target genes involved in GSH synthesis and recycling (GCLC, GCLM and GSR) in these cancer types. In summary, the omics-based identification of sensitive/resistant cancers and genetic alterations associated with these phenotypes may guide an appropriate repurposing of auranofin in cancer therapy.

Targeted inhibition of TXNRD1 prevents cartilage extracellular matrix degeneration by activating Nrf2 pathway in osteoarthritis

Osteoarthritis, a prevalent orthopedic disease, can affect the elderly and causes impairment. The degradation and aberrant homeostasis of cartilage extracellular matrix figure pivotally in the progression of osteoarthritis. Thioredoxin systems plays a role in a wide range of biological processes, including cell proliferation, apoptosis, and oxidative stress. The present study aimed to investigate the unique function and underlying pathophysiological mechanism of TXNRD1 in chondrocytes. An upregulated expression of TXNRD1 was observed in the articular cartilage of osteoarthritis patients compared with normal articular cartilage. Furthermore, in vitro experiments showed that the expression of TXNRD1 was also abnormally increased in IL-1β-induced primary mouse chondrocytes. Silencing TXNRD1 using siRNA in chondrocytes could effectively inhibit the expression of ADAMTS5 and MMP13, and enhance the expression of COL2A1 and SOX9. The same was true for auranofin, an inhibitor of TXNRD1. This phenomenon indicated that inhibition of TXNRD1 attenuated il-1β-induced metabolic imbalance of extracellular matrix (ECM) and the progression of chondrocyte osteoarthritis. Further mechanism analysis revealed that the activation of Nrf2 signaling pathway and the expression of heme oxygenase-1 (HO-1) were increased upon TXNRD1 inhibition. Furthermore, auranofin was found to attenuate DMM-induced osteoarthritis progression in vivo. Therefore, the pharmacological downregulation of TXNRD1 may provide an effective novel therapy for OA.

Gold-Based Metal Drugs as Inhibitors of Coronavirus Proteins: The Inhibition of SARS-CoV-2 Main Protease by Auranofin and Its Analogs

Gold compounds have a long tradition in medicine and offer many opportunities for new therapeutic applications. Herein, we evaluated the lead compound Auranofin and five related gold(I) complexes as possible inhibitors of SARS-CoV-2 Main Protease (SARS-CoV-2 Mpro), a validated drug target for the COVID-19 disease. The investigational panel of gold compounds included Auranofin; three halido analogues, i.e., Au(PEt3)Cl, Au(PEt3)Br, and Au(PEt3)I; and two gold carbene complexes, i.e., Au(NHC)Cl and [Au(NHC)2]PF6. Notably, all these gold compounds, with the only exception of [Au(NHC)2]PF6, turned out to be potent inhibitors of the catalytic activity of SARS-CoV-2 Mpro: the measured Ki values were in the range 2.1-0.4 μM. The reactions of the various gold compounds with SARS-CoV-2 Mpro were subsequently investigated through electrospray ionization (ESI) mass spectrometry (MS) upon a careful optimization of the experimental conditions; the ESI MS spectra provided clear evidence for the formation of tight metallodrug-protein adducts and for the coordination of well defined gold-containing fragments to the SARS-CoV-2 Mpro, again with the only exception of [Au(NHC)2]PF6, The metal-protein stoichiometry was unambiguously determined for the resulting species. The crystal structures of the metallodrug- Mpro adducts were solved in the case of Au(PEt3)Br and Au(NHC)Cl. These crystal structures show that gold coordination occurs at the level of catalytic Cys 145 in the case of Au(NHC)Cl and at the level of both Cys 145 and Cys 156 for Au(PEt3)Br. Tight coordination of gold atoms to functionally relevant cysteine residues is believed to represent the true molecular basis of strong enzyme inhibition.

Auranofin attenuates hepatic steatosis and fibrosis in nonalcoholic fatty liver disease via NRF2 and NF- κB signaling pathways

BACKGROUND/AIMS

We aim to evaluate the effects of auranofin, a known antioxidant, on hepatic steatosis, inflammation, and fibrosis, contributing to non-alcoholic steatohepatitis (NASH) development in vivo and in vitro.

METHODS

Transcriptome analysis of LX-2 cells was that expression patterns of genes changed by auranofin, and their related pathways were estimated. We used the gene set enrichment analysis (GSEA) program to determine the pathway involved in overall genetic change. In vitro, LX-2 and HepG2 cells were treated with transforming growth factor (TGF)-β1 and palmitic acid (PA), respectively, and the antifibrotic and antiadipogenic effect function of auranofin was evaluated.

RESULTS

Transcriptome analysis revealed that auranofin decreased the expression of 15 genes, including thrombospondin 1, endothelin 1 (ET-1), fibronectin 1, and LOX. The molecular functions of these genes are involved in collagen binding. GSEA of the overall gene expression pattern revealed that many genes increased in the reactive oxygen species pathway and decreased in the inflammatory response. Auranofin decreased nuclear factor kappa B (NF-κB) and IκBα in TGF-β1-induced LX-2 cells, thereby reducing ET-1 and fibrosis. Furthermore, increased pNRF2 in PA-induced HepG2 cells led to increased antioxidant marker expression and decreased lipid accumulation. In the bile duct ligation model mice, auranofin reduced the fibrosis area and increased the survival rate. Auranofin reduced liver fibrosis and lipid accumulation in NASH model mice fed on a Western diet.

CONCLUSION

Auranofin inhibits lipogenesis and fibrosis formation and is a proposed candidate for NASH treatment.

Auranofin promotes antibacterial effect of doripenem against carbapenem-resistant Acinetobacter baumannii

AIMS

This study was performed to identify the potential for repurposing auranofin as an antibiotic adjuvant against carbapenemase-producing A. baumannii.

METHODS AND RESULTS

The clinically isolated A. baumannii strains used in this study were all resistant to carbapenems and harbored the bla_OXA-23 gene. The synergistic effect of auranofin and doripenem against carbapenemase-producing A. baumannii was confirmed through checkerboard and growth kinetic analyses. This study also demonstrated the inhibitory effects of auranofin against A. baumannii biofilms. The anti-biofilm effects of auranofin were visualized by confocal laser scanning microscopy (CLSM). Furthermore, auranofin inhibited motility, one of the virulence factors. Additionally, the changes in the expression of carbapenemase-, biofilm- and efflux pump-related genes induced by auranofin were confirmed via quantitative polymerase chain reaction (qPCR).

CONCLUSIONS

Our results demonstrated that auranofin has an antibacterial effect with doripenem and an inhibitory effect on several factors related to carbapenem resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study suggests that auranofin is a promising antibiotic adjuvant that can be used to prevent antibiotic resistance in carbapenem-resistant A. baumannii.

Transcriptional changes of proteins of the thioredoxin and glutathione systems in Acanthamoeba spp. under oxidative stress - an RNA approach

The thioredoxin (Trx) and the glutathione (GSH) systems represent important antioxidant systems in cells and in particular thioredoxin reductase (TrxR) has been shown to constitute a promising drug target in parasites. For the facultative protozoal pathogen Acanthamoeba, it was demonstrated that a bacterial TrxR as well as a TrxR, characteristic of higher eukaryotes, mammals and humans is expressed on the protein level. However, only bacterial TrxR is strongly induced by oxidative stress in Acanthamoeba castellanii. In this study, the impact of oxidative stress on key enzymes involved in the thioredoxin and the glutathione system of A. castellanii under different culture conditions and of clinical Acanthamoeba isolates was evaluated on the RNA level employing RT-qPCR. Additionally, the effect of auranofin, a thioredoxin reductase inhibitor, already established as a potential drug in other parasites, on target enzymes in A. castellanii was investigated. Oxidative stress induced by hydrogen peroxide led to significant stimulation of bacterial TrxR and thioredoxin, while diamide had a strong impact on all investigated enzymes. Different strains displayed distinct transcriptional responses, rather correlating to sensitivity against the respective stressor than to respective pathogenic potential. Culture conditions appear to have a major effect on transcriptional changes in A. castellanii. Treatment with auranofin led to transcriptional activation of the GSH system, indicating its role as a potential backup for the Trx system. Altogether, our data provide more profound insights into the complex redox system of Acanthamoeba, preparing the ground for further investigations on this topic.

Auranofin and its analogs as prospective agents for the treatment of colorectal cancer

Today colorectal cancer (CRC) is one of the leading causes of cancer death worldwide. This disease is poorly chemo-sensitive toward the existing medical treatments so that new and more effective therapeutic agents are urgently needed and intensely sought. Platinum drugs, oxaliplatin in particular, were reported to produce some significant benefit in CRC treatment, triggering the general interest of medicinal chemists and oncologists for metal-based compounds as candidate anti-CRC drugs. Within this frame, gold compounds and, specifically, the established antiarthritic drug auranofin with its analogs, form a novel group of promising anticancer agents. Owing to its innovative mechanism of action and its favorable pharmacological profile, auranofin together with its derivatives are proposed here as novel experimental agents for CRC treatment, capable of overcoming resistance to platinum drugs. Some encouraging results in this direction have already been obtained. A few recent studies demonstrate that the action of auranofin may be further potentiated through the preparation of suitable pharmaceutical formulations capable of protecting the gold pharmacophore from unselective reactivity or through the design of highly synergic drug combinations. The perspectives of the research in this field are outlined.

Revisiting the anticancer properties of phosphane(9-ribosylpurine-6-thiolato)gold(I) complexes and their 9H-purine precursors

New mono- and di-nuclear thio-purine and thio-purine nucleoside gold(I) complexes were synthesized, characterized, and evaluated in vitro for biological activities in comparison to related known purine complexes. By combining known anti-tumoral thio-purines with R₃PAu moieties as present in auranofin, complexes with enhanced effects and selectivities were obtained, which not only act as cytostatics, but also disrupt tumor-specific processes. Their IC₅₀ values in cytotoxicity test with tumor cell lines ranged from three-digit nanomolar to single-digit micromolar, revealing a tentative structure-activity relationship (SAR). Both the residues R² of the phosphane ligand and R¹ at C2 of the pyrimidine ring had a significant impact on the cytotoxicity. In most cases, the introduction of a ribo-furanosyl group at N9 of the purine led to a distinctly more cytotoxic complex. Most complexes were more active against multi-drug-resistant tumor cells or such lacking functional p53 when compared to the respective untreated wild type cell lines. Some nucleoside complexes displayed an interesting dose-dependent dual mode of action regarding cell cycle arrest and DNA repair mechanism. Some phosphane(purine-6-thiolato)gold (I) complexes had a stronger inhibitory effect on the thioredoxin reductase (TrxR) and on the reactive oxygen species (ROS) generation in cancer cells than is typical of other gold complexes. They also led to DNA fragmentation and showed anti-angiogenic effects. Their stability under test conditions was demonstrated by ⁷⁷Se NMR monitoring of an exemplary selenopurine complex.

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

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

The mechanisms and therapeutic targets of ferroptosis in cancer

INTRODUCTION

Ferroptosis, a form of programmed cell death, is mediated primarily by lipid peroxidation via a unique iron-dependent process. The mechanisms of ferroptosis involve the metabolisms of amino acids, irons, and lipids, and the regulation of antioxidant systems. Evidence supports the roles of ferroptosis in cancer, while metabolic reprogramming (a hallmark of cancer) renders tumor cells highly vulnerable to ferroptosis and thus provides a rationale for ferroptosis-targeted therapy for cancer.

AREA COVERED

This article examines the current understanding of the mechanisms and related signaling pathways involving ferroptosis; it focuses on novel targets in cancer and its treatment and drug resistance. The development of ferroptosis-targeted therapy, especially in combination with conventional or non-conventional therapies, are considered with dilemmas and key questions in this research area.

EXPERT OPINION

An increasing number of potential targets and ferroptosis inducers (FINs) have been identified to treat cancer. However, no specific FIN has entered clinical trials thus far, likely due to poor efficacy and high toxicity in vivo. Thus, new FINs with high selectivity and bioavailability are required to target tumor cells more specifically and potently. Particularly, the combination of FINs with chemotherapy, radiotherapy, targeted therapy, and immunotherapy warrants clinical investigation in the future.

Auranofin: Past to Present, and repurposing

Auranofin (AF), a gold compound, has been used to treat rheumatoid arthritis (RA) for more than 40 years; however, its mechanism of action remains unknown. We revealed that AF inhibited the induction of proinflammatory proteins and their mRNAs by the inflammatory stimulants, cyclooxygenase-2 and inducible nitric oxide synthase, and their upstream regulator, NF-κB. AF also activated the proteins peroxyredoxin-1, Kelch-like ECH-associated protein 1, and NF-E2-related factor 2, and inhibited thioredoxin reductase, all of which are involved in oxidative or electrophilic stress under physiological conditions. Although the cell membrane was previously considered to be permeable to AF because of its hydrophobicity, the mechanisms responsible for transporting AF into and out of cells as well as its effects on the uptake and excretion of other drugs have not yet been elucidated. Antibodies for cytokines have recently been employed in the treatment of RA, which has had an impact on the use of AF. Trials to repurpose AF as a risk-controlled agent to treat cancers or infectious diseases, including severe acute respiratory syndrome coronavirus 2/coronavirus disease 2019, are ongoing. Novel gold compounds are also under development as anti-cancer and anti-infection agents.

The gold complex auranofin: new perspectives for cancer therapy

Advanced stages of cancer are highly associated with short overall survival in patients due to the lack of long-term treatment options following the standard form of care. New options for cancer therapy are needed to improve the survival of cancer patients without disease recurrence. Auranofin is a clinically approved agent against rheumatoid arthritis that is currently enrolled in clinical trials for potential repurposing against cancer. Auranofin mainly targets the anti-oxidative system catalyzed by thioredoxin reductase (TrxR), which protects the cell from oxidative stress and death in the cytoplasm and the mitochondria. TrxR is over-expressed in many cancers as an adaptive mechanism for cancer cell proliferation, rendering it an attractive target for cancer therapy, and auranofin as a potential therapeutic agent for cancer. Inhibiting TrxR dysregulates the intracellular redox state causing increased intracellular reactive oxygen species levels, and stimulates cellular demise. An alternate mechanism of action of auranofin is to mimic proteasomal inhibition by blocking the ubiquitin-proteasome system (UPS), which is critically important in cancer cells to prevent cell death when compared to non-cancer cells, because of its role on cell cycle regulation, protein degradation, gene expression, and DNA repair. This article provides new perspectives on the potential mechanisms used by auranofin alone, in combination with diverse other compounds, or in combination with platinating agents and/or immune checkpoint inhibitors to combat cancer cells, while assessing the feasibility for its repurposing in the clinical setting.

Methionine restriction exposes a targetable redox vulnerability of triple-negative breast cancer cells by inducing thioredoxin reductase

PURPOSE

Tumor cells are dependent on the glutathione and thioredoxin antioxidant pathways to survive oxidative stress. Since the essential amino acid methionine is converted to glutathione, we hypothesized that methionine restriction (MR) would deplete glutathione and render tumors dependent on the thioredoxin pathway and its rate-limiting enzyme thioredoxin reductase (TXNRD).

METHODS

Triple (ER/PR/HER2)-negative breast cancer (TNBC) cells were treated with control or MR media and the effects on reactive oxygen species (ROS) and antioxidant signaling were examined. To determine the role of TXNRD in MR-induced cell death, TXNRD1 was inhibited by RNAi or the pan-TXNRD inhibitor auranofin, an antirheumatic agent. Metastatic and PDX TNBC mouse models were utilized to evaluate in vivo antitumor activity.

RESULTS

MR rapidly and transiently increased ROS, depleted glutathione, and decreased the ratio of reduced glutathione/oxidized glutathione in TNBC cells. TXNRD1 mRNA and protein levels were induced by MR via a ROS-dependent mechanism mediated by the transcriptional regulators NRF2 and ATF4. MR dramatically sensitized TNBC cells to TXNRD1 silencing and the TXNRD inhibitor auranofin, as determined by crystal violet staining and caspase activity; these effects were suppressed by the antioxidant N-acetylcysteine. H-Ras-transformed MCF-10A cells, but not untransformed MCF-10A cells, were highly sensitive to the combination of auranofin and MR. Furthermore, dietary MR induced TXNRD1 expression in mammary tumors and enhanced the antitumor effects of auranofin in metastatic and PDX TNBC murine models.

CONCLUSION

MR exposes a vulnerability of TNBC cells to the TXNRD inhibitor auranofin by increasing expression of its molecular target and creating a dependency on the thioredoxin pathway.

Repurposing auranofin for treatment of Experimental Cerebral Toxoplasmosis

PURPOSES

Evaluate the effect of auranofin on the early and late stages of chronic infection with Toxoplasma gondii avirulent ME49 strain.

METHODS

Swiss albino mice were orally inoculated with 10 cysts of Toxoplasma gondii, and orally treated with auranofin or septazole in daily doses of 20 mg/kg or 100 mg /kg, respectively, for 30 days. Treatment began either on the same day of infection and mice were sacrificed at the 60th day postinfection or the treatment started after 60 days of infection and mice were sacrificed at the 90th day postinfection.

RESULTS

Auranofin significantly reduced the brain cyst burden and inflammatory reaction at both stages of infection compared to the infected non-treated control. More remarkably, auranofin significant reduced the brain cyst burden in the late stage, while septazole failed. Hydrogen peroxide level was significantly increased in the brain homogenate of mice treated with auranofin only at the early stage of infection. Ultrastructral studies revealed that the anti-Toxoplasma effect of auranofin is achieved by changing the membrane permeability and inducing apoptosis.

CONCLUSIONS

Thus, auranofin could be an alternative for the standard treatment regimen of toxoplasmosis and these results are considered another achievement for the drug against parasitic infection. Being a FDA-approved drug, it can be rapidly evaluated in clinical trials.

Identification of COVID-19 prognostic markers and therapeutic targets through meta-analysis and validation of Omics data from nasopharyngeal samples

Background

While our battle with the COVID-19 pandemic continues, a multitude of Omics data have been generated from patient samples in various studies. Translation of these data into clinical interventions against COVID-19 remains to be accomplished. Exploring host response to COVID-19 in the upper respiratory tract can unveil prognostic markers and therapeutic targets.

Methods

We conducted a meta-analysis of published transcriptome and proteome profiles of respiratory samples of COVID-19 patients to shortlist high confidence upregulated host factors. Subsequently, mRNA overexpression of selected genes was validated in nasal swabs from a cohort of COVID-19 positive/negative, symptomatic/asymptomatic individuals. Guided by this analysis, we sought to check for potential drug targets. An FDA-approved drug, Auranofin, was tested against SARS-CoV-2 replication in cell culture and Syrian hamster challenge model.

Findings

The meta-analysis and validation in the COVID-19 cohort revealed S100 family genes (S100A6, S100A8, S100A9, and S100P) as prognostic markers of severe COVID-19. Furthermore, Thioredoxin (TXN) was found to be consistently upregulated. Auranofin, which targets Thioredoxin reductase, was found to mitigate SARS-CoV-2 replication in vitro. Furthermore, oral administration of Auranofin in Syrian hamsters in therapeutic as well as prophylactic regimen reduced viral replication, IL-6 production, and inflammation in the lungs.

Interpretation

Elevated mRNA level of S100s in the nasal swabs indicate severe COVID-19 disease, and FDA-approved drug Auranofin mitigated SARS-CoV-2 replication in preclinical hamster model.

Funding

This study was supported by the DBT-IISc partnership program (DBT (IED/4/2020-MED/DBT)), the Infosys Young Investigator award (YI/2019/1106), DBT-BIRAC grant (BT/CS0007/CS/02/20) and the DBT-Wellcome Trust India Alliance Intermediate Fellowship (IA/I/18/1/503613) to ST lab.

Encephalitozoon intestinalis: A new target for auranofin in a mice model

Despite the fact that many approaches have been developed over years to find efficient and well-tolerated therapeutic regimens for microsporidiosis, the effectiveness of current drugs remains doubtful, and effective drugs against specific targets are still scarce. The present study is the first that was designed to evaluate the potency of auranofin, an anti-rheumatoid FDA approved drug, against intestinal Encephalitozoon intestinalis. Evaluation of the drug was achieved through counting of fecal and intestinal spores, studying the intestinal histopathological changes, measuring of intestinal hydrogen peroxide level, and post therapy follow-up of mice for 2 weeks for detection of relapse. Results showed that auranofin has promising anti-microsporidia potential. It showed a promising efficacy in mice experimentally infected with E. intestinalis. It has revealed an obvious reduction in fecal spore shedding and intestinal tissue spore load, amelioration of intestinal tissue pathological changes, and improvement of the local inflammatory infiltration without significant changes in hydrogen peroxide level. Interestingly, auranofin prevented the relapse of infection. Thus, considering the results of the present work, auranofin could be considered a therapeutic alternative for the gold standard drug 'albendazole' against the intestinal E. intestinalis infection especially in relapsing cases.

Review: Using isolated mitochondria to investigate mitochondrial hydrogen peroxide metabolism

Mitochondria are recognized as centrally important to cellular reactive oxygen species (ROS), both as a potential source and due to their substantial antioxidant capacity. While much of the initial ROS formed by mitochondria is superoxide, this is rapidly converted to hydrogen peroxide (H₂O₂) which more readily crosses membranes making H₂O₂ important in both redox signalling mechanisms and conditions of oxidative stress. Here I outline our studies on mitochondrial H₂O₂ metabolism with a focus on some of the challenges and strategies involved with developing an integrated model of mitochondria being intrinsic regulators of H₂O₂. This view of mitochondria as regulators of H₂O₂ goes beyond the simpler contention of them being net producers or consumers. Moreover, the integration of both consumption and production can then be tied to a putative mechanism linking energy sensing at the level of the mitochondrial protonmotive force. This mechanism would provide a means of mitochondria communicating their energetic status the extramitochondrial compartment via local H₂O₂ concentrations. I conclude by explaining how these concepts developed using rodent muscle as a model have high relevance and applicability to comparative studies.

Anticancer effects against colorectal cancer models of chloro(triethylphosphine)gold(I) encapsulated in PLGA-PEG nanoparticles

Chloro(triethylphosphine)gold(I), (Et₃PAuCl hereafter), is an Auranofin (AF)-related compound showing very similar biological and pharmacological properties. Like AF, Et₃PAuCl exhibits potent antiproliferative properties in vitro toward a variety of cancer cell lines and is a promising anticancer drug candidate. We wondered whether Et₃PAuCl encapsulation might lead to an improved pharmacological profile also considering the likely reduction of unwanted side-reactions that are responsible for adverse effects and for drug inactivation. Et₃PAuCl was encapsulated in biocompatible PLGA–PEG nanoparticles (NPs) and the new formulation evaluated in colorectal HCT-116 cancer cells in comparison to the free gold complex. Notably, encapsulated Et₃PAuCl (nano-Et₃PAuCl hereafter) mostly retains the cellular properties of the free gold complex and elicits even greater cytotoxic effects in colorectal cancer (CRC) cells, mediated by apoptosis and autophagy. Moreover, a remarkable inhibition of two crucial signaling pathways, i.e. ERK and AKT, by nano-Et₃PAuCl, was clearly documented. The implications of these findings are discussed.

NMR spectroscopy to study the fate of metallodrugs in cells

Metal-based drugs can modulate various biological processes and exhibit a rich variety of properties that foster their use in biomedicine and chemical biology. On the way to intracellular targets, ligand exchange and redox reactions can take place, thus making metallodrug speciation in vivo a challenging task. Advances in NMR spectroscopy have made it possible to move from solution to live-cell studies and elucidate the transport of metallodrugs and interactions with macromolecular targets in a physiological setting. In turn, the electronic properties and supramolecular chemistry of metal complexes can be exploited to characterize drug delivery nanosystems by NMR. The recent evolution of in-cell NMR methodology is presented with special emphasis on metal-related processes. Applications to paradigmatic cases of platinum and gold drugs are highlighted.

Auranofin reveals therapeutic anticancer potential by triggering distinct molecular cell death mechanisms and innate immunity in mutant p53 non-small cell lung cancer

Auranofin (AF) is an FDA-approved antirheumatic drug with anticancer properties that acts as a thioredoxin reductase 1 (TrxR) inhibitor. The exact mechanisms through which AF targets cancer cells remain elusive. To shed light on the mode of action, this study provides an in-depth analysis on the molecular mechanisms and immunogenicity of AF-mediated cytotoxicity in the non-small cell lung cancer (NSCLC) cell line NCI–H1299 (p53 Null) and its two isogenic derivates with mutant p53 R175H or R273H accumulation.

TrxR is highly expressed in a panel of 72 NSCLC patients, making it a valid druggable target in NSCLC for AF. The presence of mutant p53 overexpression was identified as an important sensitizer for AF in (isogenic) NSCLC cells as it was correlated with reduced thioredoxin (Trx) levels in vitro. Transcriptome analysis revealed dysregulation of genes involved in oxidative stress response, DNA damage, granzyme A (GZMA) signaling and ferroptosis. Although functionally AF appeared a potent inhibitor of GPX4 in all NCI–H1299 cell lines, the induction of lipid peroxidation and consequently ferroptosis was limited to the p53 R273H expressing cells. In the p53 R175H cells, AF mainly induced large-scale DNA damage and replication stress, leading to the induction of apoptotic cell death rather than ferroptosis. Importantly, all cell death types were immunogenic since the release of danger signals (ecto-calreticulin, ATP and HMGB1) and dendritic cell maturation occurred irrespective of (mutant) p53 expression. Finally, we show that AF sensitized cancer cells to caspase-independent natural killer cell-mediated killing by downregulation of several key targets of GZMA.

Our data provides novel insights on AF as a potent, clinically available, off-patent cancer drug by targeting mutant p53 cancer cells through distinct cell death mechanisms (apoptosis and ferroptosis). In addition, AF improves the innate immune response at both cytostatic (natural killer cell-mediated killing) and cytotoxic concentrations (dendritic cell maturation).

Gold Metallodrugs to Target Coronavirus Proteins: Inhibitory Effects on the Spike-ACE2 Interaction and on PLpro Protease Activity by Auranofin and Gold Organometallics*

Gold complexes have a long tradition in medicine and for many examples antirheumatic, anticancer or anti-infective effects have been confirmed. Herein, we evaluated the lead compound Auranofin and five selected gold organometallics as inhibitors of two relevant drug targets of severe acute respiratory syndrome coronaviruses (SARS-CoV). The gold metallodrugs were effective inhibitors of the interaction of the SARS-CoV-2 spike protein with the angiotensin converting enzyme 2 (ACE2) host receptor and might thus interfere with the viral entry process. The gold metallodrugs were also efficient inhibitors of the papain-like protease (PLpro) of SARS-CoV-1 and SARS-CoV-2, which is a key enzyme in the viral replication. Regarding PLpro from SARS-CoV-2, the here reported inhibitors are among the very first experimentally confirmed examples with activity against this target enzyme. Importantly, the activity of the complexes against both PLpro enzymes correlated with the ability of the inhibitors to remove zinc ions from the labile zinc center of the enzyme. Taken together, the results of this pilot study suggest further evaluation of gold complexes as SARS-CoV antiviral drugs.

Metallo therapeutics for COVID-19. Exploiting metal-based compounds for the discovery of new antiviral drugs

INTRODUCTION

The COVID-19 pandemic poses an unprecedented challenge for the rapid discovery of drugs against this life-threatening disease. Owing to the peculiar features of the metal centers that are currently used in medicinal chemistry, metallodrugs might offer an excellent opportunity to achieve this goal.

AREAS COVERED

Two main strategies for developing metal-based drugs against the SARS-CoV-2 are herein illustrated. Firstly, a few clinically approved metallodrugs could be evaluated in patients according to a 'drug repurposing' approach. To this respect, the gold drug auranofin seems a promising candidate, but some other clinically established metal compounds are worthy of a careful evaluation as well. On the other hand, libraries of inorganic compounds, featuring a large chemical diversity, should be screened to identify the most effective molecules. This second strategy might be assisted by a pathway-driven discovery approach arising from a preliminary knowledge of the mode of action, exploitable to inhibit the functional activities of the key viral proteins. Also, attention must be paid to selectivity and toxicity issues.

EXPERT OPINION

The medicinal inorganic chemistry community may offer a valuable contribution against COVID-19. The screening of metallodrugs' libraries can expand the explored 'chemical space' and increase the chance of finding effective anti-COVID agents.

Synergistic Induction of Apoptosis by the Combination of an Axl Inhibitor and Auranofin in Human Breast Cancer Cells

Axl receptor tyrosine kinase has been implicated in cancer progression, invasion, and metastasis in various cancer types. Axl overexpression has been observed in many cancers, and selective inhibitors of Axl, including R428, may be promising therapeutic agents for several human cancers, such as breast, lung, and pancreatic cancers. Here, we examined the cell growth inhibition mediated by R428 and auranofin individually as well as in combination in the human breast cancer cell lines MCF-7 and MDA-MB-231 to identify new advanced combination treatments for human breast cancer. Our data showed that combination therapy with R428 and auranofin markedly inhibited cancer cell proliferation. Isobologram analyses of these cells indicated a clear synergism between R428 and auranofin with a combination index value of 0.73. The combination treatment promoted apoptosis as indicated by caspase 3 activation and poly (ADP-ribose) polymerase cleavage. Cancer cell migration was also significantly inhibited by this combination treatment. Moreover, we found that combination therapy significantly increased the expression level of Bax, a mitochondrial proapoptotic factor, but decreased that of the X-linked inhibitor of apoptosis protein. Furthermore, the suppression of cell viability and induction of Bax expression by the combination treatment were recovered by treatment with N-acetylcysteine. In conclusion, our data demonstrated that combined treatment with R428 and auranofin synergistically induced apoptosis in human breast cancer cells and may thus serve as a novel and valuable approach for cancer therapy.

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.

Selenium-independent antioxidant and anti-inflammatory effects of thioredoxin reductase inhibition in alveolar macrophages

AIMS

Interleukin-1β (IL-1β) contributes to the development of bronchopulmonary dysplasia (BPD). Thioredoxin reductase-1 (Txnrd1) inhibition activates nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent responses. Txnrd1 activity is selenium (Se) dependent and Se deficiency is common in prematurity. Auranofin (AFN), a Txnrd1 inhibitor, decreases IL-1β levels and increases Nrf2 activation in lipopolysaccharide (LPS) treated alveolar macrophages. In lung epithelia, AFN-induced Nrf2 activation is Se dependent. We tested the hypothesis that the effects of Txnrd1 inhibition in alveolar macrophages are Se dependent.

MAIN METHODS

To establish Se sufficient (Se+) and deficient (Se-) conditions, alveolar (MH-S) macrophages were cultured in 2.5% fetal bovine serum (FBS) ± 25 nM Na₂SeO₃. Se- (2.5% FBS) and Se+ (2.5% FBS + 25 nM Na₂SeO₃) cells were cultured in the presence or absence of 0.05 μg/mL LPS and/or 0.5 μM AFN. Nrf2 activation was determined by measuring NADPH quinone oxidoreductase-1 (Nqo1) and glutathione levels. IL-1β mRNA (Il1b) and protein levels were measured using qRT-PCR and ELISA. Data were analyzed by ANOVA followed by Tukey's post-hoc.

KEY FINDINGS

We detected an independent effect of AFN, but not LPS, on Nqo1 expression and GSH levels in Se+ and Se- cells. LPS significantly increased Il1b and IL-1β levels in both groups. AFN-mediated attenuation of this effect was not impacted by Se status.

SIGNIFICANCE

The beneficial effects of Txnrd1 inhibition in alveolar macrophages are Se-independent and therefore unlikely to be diminished by clinical Se deficiency.

Mitochondrial TXNRD3 confers drug resistance via redox-mediated mechanism and is a potential therapeutic target in vivo

Alterations in ROS metabolism and redox signaling are often observed in cancer cells and play a significant role in tumor development and drug resistance. However, the mechanisms by which redox alterations impact cellular sensitivity to anticancer drugs remain elusive. Here we have identified the mitochondrial isoform of thioredoxin reductase 3 (mtTXNRD3), through RT-PCR microarray screen, as a key molecule that confers drug resistance to sorafenib and other clinical anticancer agents. High expression of mtTXNRD3 is detected in drug-resistant leukemia and hepatocellular carcinoma cells associated with significant metabolic alterations manifested by low mitochondrial respiration and high glycolysis. Mechanistically, high mtTXNRD3 activity keeps the mitochondrial thioredoxin2 (Trx2) in a reduced stage that in turn stabilizes several key survival molecules including HK2, Bcl-XL, Bcl-2, and MCL-1, leading to increased cell survival and drug resistance. Pharmacological inhibition of thioredoxin reductase by auranofin effectively overcomes such drug resistance in vitro and in vivo, suggesting that targeting this redox mechanism may be a feasible strategy to treat drug-resistant cancer.

Subchronic administration of auranofin reduced amyloid-β plaque pathology in a transgenic APPNL-G-F/NL-G-F mouse model

Alzheimer's disease (AD) is the most common cause of dementia. Neuropathological processes, including the accumulation of amyloid-β (Aβ) plaques and neurofibrillary tangles, and neuroinflammation, lead to cognitive impairment at middle and eventually later stages of AD progression. Over the last decade, focused efforts have explored repurposed drug approaches for AD pathophysiological mechanisms. Recently, auranofin, an anti-inflammatory drug, was shown to have therapeutic potential in a number of diseases in addition to rheumatoid arthritis. Surprisingly, no data regarding the effects of auranofin on cognitive deficits in AD mice or the influence of auranofin on Aβ pathology and neuroinflammatory processes are available. In the present study, we used 14-month-old transgenic male APP^{NL-G-F/NL-G-F} mice to assess the effects of subchronic administration of auranofin at low doses (1 and 5 mg/kg, intraperitoneal) on spatial memory, Aβ pathology and the expression of cortical and hippocampal proteins (glial fibrillary acidic protein (GFAP), ionized calcium binding adaptor molecule-1 (Iba-1)) and proteins related to synaptic plasticity (glutamic acid decarboxylase 67 (GAD67), homer proteins homologue-1 (Homer-1)). The data demonstrated that auranofin significantly decreased Aβ deposition in the hippocampus and the number of Aβ plaques in the cingulate cortex, but it did not have memory-enhancing effects or induce changes in the expression of the studied proteins. Our current results highlight the importance of considering further pre-clinical research to investigate the possible beneficial effects of auranofin on the other pathological aspects of AD.

Repurposing of auranofin against bacterial infections: An In silico and In vitro study

AIM

The aim of the study was to find out the role of auranofin as a promising broad spectrum antibacterial agent.

METHODS

In-vitro assays (Percentage growth retardation, Bacterial growth kinetics, Biofilm formation assay) and In-silico study (Molegro virtual docker (MVD) version 6.0 and Molecular operating environment (MOE) version 2008.10 software).

RESULTS

The in vitro assays have shown that auranofin has good antibacterial activity against Gram positive and Gram negative bacterial strains. Further, auranofin has shown synergistic activity in combination with ampicillin against S. aureus and B. subtilis whereas in combination with neomycin has just shown additive effect against E. coli, P. aeruginosa and B. pumilus. In vivo results have revealed that auranofin alone and in combination with standard drugs significantly decreased the bioburden in zebrafish infection model as compared to control. The molecular docking study have shown good interaction of auranofin with penicillin binding protein (2Y2M), topoisomerase (3TTZ), UDP-3-O-[3- hydroxymyristoyl] N-acetylglucosaminedeacetylase (3UHM), cell adhesion protein (4QRK), β-lactamase (5CTN) and arylsulphatase (1HDH) enzyme as that of reference ligand which indicate multimodal mechanism of action of auranofin. Finally, MTT assay has shown non-cytotoxic effect of auranofin.

CONCLUSION

In conclusion, auranofin in combination with existing antibiotics could be developed as a broad spectrum antibacterial agent; however, further studies are required to confirm its safety and efficacy. This study provides possibility of use of auranofin apart from its established therapeutic indication in combination with existing antibiotics to tackle the problem of resistance.

The FDA-approved gold drug auranofin inhibits novel coronavirus (SARS-COV-2) replication and attenuates inflammation in human cells

SARS-COV-2 has recently emerged as a new public health threat. Herein, we report that the FDA-approved drug, auranofin, inhibits SARS-COV-2 replication in human cells at low micro molar concentration. Treatment of cells with auranofin resulted in a 95% reduction in the viral RNA at 48 h after infection. Auranofin treatment dramatically reduced the expression of SARS-COV-2-induced cytokines in human cells. These data indicate that auranofin could be a useful drug to limit SARS-CoV-2 infection and associated lung injury due to its antiviral, anti-inflammatory and anti-reactive oxygen species (ROS) properties. Further animal studies are warranted to evaluate the safety and efficacy of auranofin for the management of SARS-COV-2 associated disease.

•

Auranofin inhibits replication of SARS-COV-2 in human cells at low micro molar concentration.

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Auranofin treatment resulted in significant reduction in SARS-COV-2-induced cytokines in human cells.

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Auranofin could mitigate SARS-COV-2 infection and lung damage due to its anti-viral and anti-inflammatory properties.

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Auranofin is a gold-containing FDA-approved drug.

Antibiofilm and antibacterial activities of repurposing auranofin against Bacteroides fragilis

The aim of this study is to evaluate the antibiofilm and antibacterial effects of auranofin against WT-ETBF, rETBF, WT-NTBF and clinically isolated Bacteroides fragilis strains. The minimum inhibitory concentration and biofilm inhibitory concentration of 0.25 μg/ml for auranofin against B. fragilis were determined, and the biofilm eradication concentration was 1 μg/ml. At an auranofin concentration of 0.5 μg/ml, little cellular metabolic activity was found. Confocal laser scanning microcopy results confirmed the inhibition of biofilm by auranofin. The effects of auranofin on the outer membrane protein (ompA) gene and the RND-type efflux pump (bmeB3) gene were investigated using quantitative real-time polymerase chain reaction (qRT-PCR). The qRT-PCR results showed that treatment with auranofin significantly reduced the gene expression compared to controls without auranofin. These data indicate the applicability of auranofin as a repurposed drug due to its inhibitory effect against biofilm formation of B. fragilis. Therefore, our study demonstrates that auranofin, already approved for human use, is a promising drug that has strong antibiofilm and antibacterial activity against B. fragilis.

Ligand Exchange/Scrambling Study of Gold(I)-Phosphine Complexes in the Solid Phase by DESI-MS Analysis

Only a few analytical techniques are available for the characterization of mechanochemical synthetic reaction products. We demonstrate here that DESI-MS is a powerful technique for this purpose, combining the selectivity of MS-based assays with the simplicity and in situ analysis capability of ambient ionization methods. In this work, we report that auranofin, a gold-based drug, and its precursor triethylphosphine gold(I) chloride undergo a complex array of ligand exchange/scrambling reactions with thiol-containing amino acids in the solid state. The products were readily characterized by DESI-MS analysis from the solid-phase reaction, clearly exhibiting ligand exchange and scrambling, with independent confirmation by solid state ¹³C-NMR. The thioglucose and triethylphosphine moieties exchanged with cysteine and its derivatives, whereas the glutathione replaced 2,3,4,6-tetra-o-acetyl-β-1-D-glucopyranose only. It was concluded that ligand exchange and scrambling reactions can be carried out in the solid state, and some of the unique products reported in this study can be conveniently prepared through mechanochemical synthesis in good yields (> 98%), as demonstrated by synthesis of (L-cysteinato-S)-triethylphosphine gold(I) from triethylphosphine gold(I) chloride and L-cysteine.

Antivirulence activity of auranofin against vancomycin-resistant enterococci: in vitro and in vivo studies

INTRODUCTION

Vancomycin-resistant enterococci (VRE) are a leading cause of nosocomial infections because of the limited number of effective therapeutic options. In an effort to repurpose FDA-approved drugs against antibiotic-resistant bacteria, auranofin has been identified as a potent drug against VRE.

METHODS AND RESULTS

The present study determined that auranofin's antibacterial activity was not affected when evaluated against a higher inoculum size of VRE (~10⁷ CFU/mL), and auranofin successfully reduced the burden of stationary phase VRE cells via a time-kill assay. In addition, auranofin reduced VRE production of key virulence factors, including proteases, lipase and haemagglutinin. The promising features of auranofin prompted evaluation of its in vivo efficacy in a lethal mouse model of VRE septicaemia. All mice receiving auranofin at 0.125 mg/kg orally, 0.125 mg/kg subcutaneously (SC) or 0.0625 mg/kg (SC) survived the lethal VRE challenge. Additionally, auranofin was superior to linezolid, the current drug of choice, in reducing VRE burden in the liver, kidneys and spleen of mice. Remarkably, auranofin successfully reduced VRE below the limit of detection in murine internal organs after 4 days of oral or subcutaneous treatment.

CONCLUSION

These results indicate that auranofin warrants further investigation as a new treatment for systemic VRE infections.

Targeting PKCι-PAK1 in EGFR-mutation positive non-small cell lung cancer

Background

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) induce significant responses in EGFR-mutation positive non-small cell lung cancer (NSCLC). However, universal progression is observed.

Methods

The effect of the anti-rheumatoid agent, auranofin, a selective inhibitor of oncogenic protein kinase C iota (PKCι) signaling and IPA-3, a non-ATP competitive p21-activated kinase 1 (PAK1) inhibitor in treatment-naïve and EGFR TKI-resistant EGFR-mutation positive NSCLC cell lines was investigated. PC9 and HCC827 cells were used. The four EGFR-TKI resistant cell lines were established from PC9. Cell viability assays, drug combination studies, and western blotting were performed. The combination index, and RTK or non-RTK expression were performed.

Results

The combination of IPA-3 and auranofin was highly synergistic in all 6 cell lines (combination indexes ranged from 0.37-0.62). The activities on EGFR, CDCP1, AXL, MET, and downstream effector pathways, including PAK1, PKCι, ERK, AKT, STAT3, Src, and YAP1 were abrogated.

Conclusions

The combination of auranofin with IPA-3 could be a potential therapy for EGFR-mutation positive NSCLC resistant to EGFR TKIs. Auranofin with IPA-3 could become a therapeutic solution for EGFR-mutation positive NSCLC patients resistant to EGFR TKIs.

Organogold drug Auranofin exhibits anti-melanogenic activity in B16F10 and MNT-1 melanoma cells

Auranofin (AF) is an organogold FDA-approved drug for treating rheumatism and has been repurposed for several pharmacological applications based on its anti-bacterial, anti-fungal and anti-inflammatory activities. To the best of our knowledge, there has been no study on effects of AF on melanogenesis yet. Hence, in this work, we studied the effect of AF on melanogenesis using B16F10 mouse melanoma cells and validated results in MNT-1 human melanoma cells. Melanogenesis assay was conducted with concentrations of AF determined to be nontoxic in B16F10 cells as well as HaCaT human epidermal cell line for a duration of 48 h, followed by various assays to delineate mechanisms of melanogenesis inhibition. Ultrastructural analysis was conducted to study further if AF affected melanosome maturation and protein levels of a key melanogenic protein, tyrosinase, and the maturation signaling molecule, cyclic adenosine monophosphate (cAMP), was estimated. Our results demonstrate that AF at nontoxic concentrations of 0.25-1 µM significantly inhibited melanin synthesis in a dose-dependent manner with significant inhibition of 32.85% at 1 µM. The study of mechanisms of melanogenesis inhibition revealed that AF inhibited tyrosinase activity in lysates of B16F10 cells but did not show a direct effect on purified mushroom tyrosinase activity or on copper chelation in a cell-free system, nor did it affect levels of B16F10 tyrosinase protein levels. However, AF significantly down-regulated cAMP levels, inhibited cellular ROS and increased number of melanosomes in immature stages, and also exhibited anti-melanogenic activity in B16F10-HaCaT cocultures. Furthermore, AF showed anti-melanogenic efficacy in MNT-1 cell monocultures and cocultures with an inhibition of intracellular tyrosinase activity. In summary, our results demonstrate a proof-of-principle for AF as a depigmenting agent for hyperpigmentation disorders and adjuvant for melanoma therapeutics.

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

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

Combination treatment with auranofin and nutlin-3a induces synergistic cytotoxicity in breast cancer cells

Auranofin is a gold complex categorized as an anti-rheumatic agent. Recently, several investigators suggested that auranofin may act as a potent anti-cancer drug for breast tumors. Nutlin-3a is a cis-imidazoline analog which prevents interaction between mouse double minute 2 homolog (MDM2) and the tumor suppressor p53. The aim of this study was to examine cell growth inhibition mediated by auranofin or nutlin-3a individually as well as in combination with MCF-7 and MDA-MB-231 cells. To assess any potential synergistic effects between auranofin and nutlin-3a, low concentrations of auranofin and nutlin-3a were simultaneously incubated with MCF-7 and MDA-MB-231 cells. Cell viability assay, caspase-3/7 assay, and poly (ADP-ribose) polymerase cleavage revealed that auranofin and nutlin-3a exerted a synergistic effect on cancer cell apoptosis. Isobologram analysis of MCF-7 and MDA-MB-231 cells noted evident synergism between auranofin and nutlin-3a. The combined treatment increased the expression of mitochondrial pro-apoptotic factors such as Bcl-2 associated X protein and Bcl-2 homologous antagonist/killer. Further, combination treatment significantly enhanced reactive oxygen species (ROS) generation in MCF-7 and MDA-MB-231 cells. In conclusion, data demonstrated that combined treatment with auranofin and nutlin-3a exhibited a synergistic action on breast cancer cells and this combination may be considered for use as a novel therapeutic strategy for breast cancer.

Repurposing of auranofin: Thioredoxin reductase remains a primary target of the drug

Auranofin is a gold (I)-containing compound used for the treatment of rheumatic arthritis. Auranofin has anticancer activity in animal models and is approved for clinical trials for lung and ovarian carcinomas. Both the cytosolic and mitochondrial forms of the selenoprotein thioredoxin reductase (TrxR) are well documented targets of auranofin. Auranofin was recently reported to also inhibit proteasome activity at the level of the proteasome-associated deubiquitinases (DUBs) UCHL5 and USP14. We here set out to re-examine the molecular mechanism underlying auranofin cytotoxicity towards cultured cancer cells. The effects of auranofin on the proteasome were examined in cells and in vitro, effects on DUB activity were assessed using different substrates. The cellular response to auranofin was compared to that of the 20S proteasome inhibitor bortezomib and the 19S DUB inhibitor b-AP15 using proteomics. Auranofin was found to inhibit mitochondrial activity and to an induce oxidative stress response at IC₅₀ doses. At 2-3-fold higher doses, auranofin inhibits proteasome processing in cells. At such supra-pharmacological concentrations USP14 activity was inhibited. Analysis of protein expression profiles in drug-exposed tumor cells showed that auranofin induces a response distinct from that of the 20S proteasome inhibitor bortezomib and the DUB inhibitor b-AP15, both of which induced similar responses. Our results support the notion that the primary mechanism of action of auranofin is TrxR inhibition and suggest that proteasome DUB inhibition is an off-target effect. Whether proteasome inhibition will contribute to the antineoplastic effect of auranofin in treated patients is unclear but remains a possibility.

A high-throughput drug screen identifies auranofin as a potential sensitizer of cisplatin in small cell lung cancer

Small cell lung cancer (SCLC) is a highly lethal malignancy with the 5-year survival rate of less than 7%. Chemotherapy-resistance is a major challenge for SCLC treatment in clinic. In the study, we developed a high-throughput drug screen strategy to identify new drugs that can enhance the sensitivity of chemo-drug cisplatin in SCLC. This screen identified auranofin, a US Food and Drug Administration (FDA)-approved drug used therapeutically for rheumatoid arthritis, as a sensitizer of cisplatin. Further study validated that auranofin synergistically enhanced the anti-tumor activity of cisplatin in chemo-resistant SCLC cells, which was accompanied by the enhanced induction of cell cycle arrest and apoptosis. The synergistic action of auranofin and cisplatin was through ROS overproduction, thereby leading to mitochondrial dysfunction and DNA damage. Furthermore, in vivo study demonstrated that the combination treatment of auranofin and cisplatin dramatically inhibited tumor growth in SCLC. Therefore, our study provides a rational basis for further clinical study to test whether auranofin could enhance the sensitivity of cisplatin-based therapy in SCLC patients.

Knockdown on aPKC-ι inhibits epithelial-mesenchymal transition, migration and invasion of colorectal cancer cells through Rac1-JNK pathway

BACKGROUND

Atypical protein kinase C-ι (aPKC-ι) is an oncogenic factor, and required for the epithelial-mesenchymal transition (EMT) of different types of cancer. Our study aimed to investigate the role of aPKC-ι in the EMT, migration and invasion of colorectal cancer (CRC) cells.

METHODS

Expression of aPKC-ι was evaluated in CRC cell lines treated with TGF-β1 using qPCR and western blot. After aPKC-ι was knocked down using shRNA, migration and invasion abilities of CRC cell lines were evaluated by wound healing assay and transwell assay, respectively. Activation status of downstream signaling factors of aPKC-ι, including Rac1, JNK, STAT3 and β-catenin, was measured using western blot. Furthermore, auranofin, an aPKC-ι inhibitor, was used to treat CRC cell lines to investigate its possible inhibition on the EMT of CRC cell lines, as well as on the expression of aPKC-ι and its downstream signaling factors.

RESULTS

TGF-β1 induced the expression of aPKC-ι in CRC cells, and knockdown on aPKC-ι inhibited the TGF-β1-induced EMT, migration and invasion of CRC cells. Interestingly, Rac1 GTPase level was decreased when aPKC-ι was knocked down, and overexpression of Rac1G12V rescued the cell EMT, migration and invasion in CRC cells as inhibited by sh-aPKC-ι. Moreover, knockdown on aPKC-ι suppressed the phosphorylation of JNK and STAT3, and nuclear translocation of β-catenin. The aPKC- ι inhibitor, Auranofin, showed similar inhibitory effects as aPKC-ι knockdown.

CONCLUSION

Knockdown on aPKC-ι inhibited the EMT, migration and invasion of CRC cells through suppressing of Rac1-JNK pathway. Those findings indicate that aPKC-ι may serve as a novel therapeutic target for CRC.