Auranofin

Correction: Auranofin Inhibits Retinal Pigment Epithelium Cell Survival through Reactive Oxygen Species-Dependent Epidermal Growth Factor Receptor/ Mitogen-Activated Protein Kinase Signaling Pathway.[Pubmed:28222166]

PLoS One. 2017 Feb 21;12(2):e0172599.

[This corrects the article DOI: 10.1371/journal.pone.0166386.].

Repurposing Approach Identifies Auranofin with Broad Spectrum Antifungal Activity That Targets Mia40-Erv1 Pathway.[Pubmed:28149831]

Front Cell Infect Microbiol. 2017 Jan 18;7:4.

Current antifungal therapies have limited effectiveness in treating invasive fungal infections. Furthermore, the development of new antifungal is currently unable to keep pace with the urgent demand for safe and effective new drugs. Auranofin, an FDA-approved drug for the treatment of rheumatoid arthritis, inhibits growth of a diverse array of clinical isolates of fungi and represents a new antifungal agent with a previously unexploited mechanism of action. In addition to Auranofin's potent antifungal activity against planktonic fungi, this drug significantly reduces the metabolic activity of Candida cells encased in a biofilm. Unbiased chemogenomic profiling, using heterozygous S. cerevisiae deletion strains, combined with growth assays revealed three probable targets for Auranofin's antifungal activity-mia40, acn9, and coa4. Mia40 is of particular interest given its essential role in oxidation of cysteine rich proteins imported into the mitochondria. Biochemical analysis confirmed Auranofin targets the Mia40-Erv1 pathway as the drug inhibited Mia40 from interacting with its substrate, Cmc1, in a dose-dependent manner similar to the control, MB-7. Furthermore, yeast mitochondria overexpressing Erv1 were shown to exhibit resistance to Auranofin as an increase in Cmc1 import was observed compared to wild-type yeast. Further in vivo antifungal activity of Auranofin was examined in a Caenorhabditis elegans animal model of Cryptococcus neoformans infection. Auranofin significantly reduced the fungal load in infected C. elegans. Collectively, the present study provides valuable evidence that Auranofin has significant promise to be repurposed as a novel antifungal agent and may offer a safe, effective, and quick supplement to current approaches for treating fungal infections.

Cystatin SN inhibits auranofin-induced cell death by autophagic induction and ROS regulation via glutathione reductase activity in colorectal cancer.[Pubmed:28300829]

Cell Death Dis. 2017 Mar 16;8(3):e2682.

Cystatin SN (CST1) is a specific inhibitor belonging to the cystatin superfamily that controls the proteolytic activities of cysteine proteases such as cathepsins. Our previous study showed that high CST1 expression enhances tumor metastasis and invasiveness in colorectal cancer. Recently, Auranofin (AF), a gold(I)-containing thioredoxin reductase 1 (TrxR1) inhibitor, has been used clinically to treat rheumatoid arthritis. AF is a proteasome-associated deubiquitinase inhibitor and can act as an anti-tumor agent. In this study, we investigated whether CST1 expression induces autophagy and tumor cell survival. We also investigated the therapeutic effects of AF as an anti-tumor agent in colorectal cancer (CRC) cells. We found that CRC cells expressing high levels of CST1 undergo increased autophagy and exhibit chemotherapeutic resistance to AF-induced cell death, while those expressing low levels of CST1 are sensitive to AF. We also observed that knockdown of CST1 in high-CST1 CRC cells using CST1-specific small interfering RNAs attenuated autophagic activation and restored AF-induced cell mortality. Conversely, the overexpression of CST1 increased autophagy and viability in cells expressing low levels of CST1. Interestingly, high expression of CST1 attenuates AF-induced cell death by inhibiting intracellular reactive oxygen species (ROS) generation, as demonstrated by the fact that the blockage of ROS production reversed AF-induced cell death in CRC cells. In addition, upregulation of CST1 expression increased cellular glutathione reductase (GR) activity, reducing the cellular redox state and inducing autophagy in AF-treated CRC cells. These results suggest that high CST1 expression may be involved in autophagic induction and protects from AF-induced cell death by inhibition of ROS generation through the regulation of GR activity.

Auranofin, an inhibitor of thioredoxin reductase, induces apoptosis in hepatocellular carcinoma Hep3B cells by generation of reactive oxygen species.[Pubmed:28218611]

Gen Physiol Biophys. 2017 Apr;36(2):117-128.

Mammalian thioredoxin reductase (TrxR) plays a vital role in restoring cellular redox balance disrupted by reactive oxygen species (ROS) generation and oxidative damage. Here, we evaluated whether Auranofin, a selective inhibitor of TrxR, could serve as a potential anti-cancer agent through its selective targeting of TrxR activity in Hep3B hepatocellular carcinoma cells. Auranofin treatment reduced the TrxR activity of these cells and induced apoptosis, which were accompanied by up-regulation of death receptors (DRs) and activation of caspases, as well as promotion of proteolytic degradation of poly(ADP-ribose)-polymerase. Treatment with a pan-caspase inhibitor reversed the Auranofin-induced apoptosis and growth suppression, indicating that Auranofin may induce apoptosis through a caspase-dependent mechanism involving both the intrinsic and extrinsic apoptotic pathways. Auranofin also significantly altered mitochondrial function, promoting mitochondrial membrane permeabilization and cytochrome c release by regulating Bcl-2 family proteins; these events were accompanied by an accumulation of ROS. Inhibition of ROS generation with the ROS quencher significantly attenuated the inactivation of TrxR in Auranofin-treated cells and almost completely suppressed the Auranofin-induced up-regulation of DRs and activation of caspases, thereby preventing Auranofin-induced apoptosis and loss of cell viability. Taken together, these findings indicate that Auranofin inhibition of TrxR activity in Hep3B cells activates ROS- and caspase-dependent apoptotic signaling pathways and triggers cancer cell death.

Auranofin blocks interleukin-6 signalling by inhibiting phosphorylation of JAK1 and STAT3.[Pubmed:17645497]

Immunology. 2007 Dec;122(4):607-14.

Auranofin (AF) is a sulphur-containing gold compound. Because of its anti-inflammatory and immunosuppressive activities, AF has been widely used for the therapeutic treatment of rheumatoid arthritis. However, little is known about its mechanism of action. To elucidate the molecular mechanism underlying the anti-inflammatory effect of AF, we studied the effects of AF on cellular responses to interleukin-6 (IL-6). In HepG2 human hepatoma cells, AF markedly inhibited IL-6-induced phosphorylation of janus kinase 1 (JAK1) and signal transducer and activator of transcription 3 (STAT3) and STAT3 translocation into the nucleus. Consistent with this, AF diminished IL-6-induced production of the acute-phase proteins, haptoglobin, fibrinogen, C3 complement and alpha(1)-acid glycoprotein, and gene expression of vascular endothelial growth factor, all of whose transcriptional activities are regulated by STAT3. The inhibitory activity of AF on STAT3 phosphorylation was also demonstrated in primary cells, i.e. fibroblast-like synoviocytes from rheumatoid arthritis patients, human umbilical vein endothelial cells and rat astrocytes. Auranofin-mediated inhibition of STAT3 phosphorylation was recovered by pretreatment with antioxidants containing thiol groups. These findings suggest that the anti-inflammatory action of AF is associated with a blockade of JAK1/STAT3 signalling. Thiol-group-reactive proteins may be involved in AF-induced suppression of JAK1/STAT3 phosphorylation.

Induction of mitochondrial permeability transition by auranofin, a gold(I)-phosphine derivative.[Pubmed:12163349]

Br J Pharmacol. 2002 Aug;136(8):1162-8.

1 Gold(I)-thiolate drugs are compounds that specifically interact with thiol and/or selenol groups and are essentially utilized in the treatment of rheumatoid arthritis. 2 Considering the importance of thiol groups in regulating mitochondrial membrane permeability, the effects of Auranofin (S-triethylphosphinegold(I)-2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranoside) , a second-generation gold drug, were studied on mitochondria isolated from rat liver. 3 Auranofin, at submicromolar concentrations, was able to induce the mitochondrial membrane permeability transition observed as swelling and loss of membrane potential. Both events are completely inhibited by cyclosporin A, the specific inhibitor of mitochondrial permeability transition. Calcium ions and energization by succinate are required for the occurrence of permeability transition. 4 By interacting with the active site selenol group, Auranofin results as an extremely potent inhibitor of mitochondrial thioredoxin reductase, both isolated and in its mitochondrial environment. 5 It is concluded that Auranofin, in the presence of calcium ions, is a highly efficient inducer of mitochondrial membrane permeability transition, potentially referable to its inhibition of mitochondrial thioredoxin reductase.

Human placenta thioredoxin reductase. Isolation of the selenoenzyme, steady state kinetics, and inhibition by therapeutic gold compounds.[Pubmed:9685351]

J Biol Chem. 1998 Aug 7;273(32):20096-101.

Human thioredoxin reductase is a pyridine nucleotide-disulfide oxidoreductase closely related to glutathione reductase but differing from the latter in having a Cys-SeCys (selenocysteine) sequence as an additional redox center. Because selenoproteins cannot be expressed yet in heterologous systems, we optimized the purification of the protein from placenta with respect to final yield (1-2 mg from one placenta), specific activity (42 units/mg), and selenium content (0.94 +/- 0.03 mol/mol subunit). The steady state kinetics showed that the enzyme operates by a ping-pong mechanism; the value of kcat was 3330 +/- 882 min-1, and the Km values were 18 microM for NADPH and 25 microM for Escherichia coli thioredoxin. The activation energy of the reaction was found to be 53.2 kJ/mol, which allows comparisons of the steady state data with previous pre-steady state measurements. In its physiological, NADPH-reduced form, the enzyme is strongly inhibited by organic gold compounds that are widely used in the treatment of rheumatoid arthritis; for Auranofin, the Ki was 4 nM when measured in the presence of 50 microM thioredoxin. At 1000-fold higher concentrations, that is at micromolar levels, the drugs also inhibited human glutathione reductase and the selenoenzyme glutathione peroxidase.

Auranofin stimulates LTA hydrolase and inhibits 5-lipoxygenase/LTA synthase activity of isolated human neutrophils.[Pubmed:2157444]

Biochem Pharmacol. 1990 Apr 1;39(7):1233-7.

The effect of Auranofin on the 5-lipoxygenase pathway was studied in human neutrophils stimulated with either fMLP or A23187 (with or without arachidonic acid). The synthesis of leukotriene B4 (LTB4), 5-HETE and the all-trans isomers of LTB4 was measured by HPLC. At low concentrations (0.5-2.0 microM), Auranofin stimulated LTB4 synthesis, but inhibited it at higher concentrations (100% inhibition at less than 10 microM). In contrast Auranofin caused dose-dependent inhibition of the synthesis of 5-HETE and the all-trans isomers of LTB4. Similar observations were made with each agonist. The stimulation of LTB4 synthesis and inhibition of the trans isomer production suggests that Auranofin at low concentrations stimulates LTA hydrolase--the enzyme that converts LTA4 to LTB4, whereas the inhibition of synthesis of all lipoxygenase products at higher Auranofin concentrations, suggests inhibition of 5-lipoxygenase/LTA synthase.