Inhibition of hepatitis C virus infection by polyoxometalates

Polyoxometalate exerts broad-spectrum activity against human respiratory viruses hampering viral entry

Human respiratory viruses have an enormous impact on national health systems, societies, and economy due to the rapid airborne transmission and epidemic spread of such pathogens, while effective specific antiviral drugs to counteract infections are still lacking. Here, we identified two Keggin-type polyoxometalates (POMs), [TiW11CoO40]8- (TiW11Co) and [Ti2PW10O40]7- (Ti2PW10), endowed with broad-spectrum activity against enveloped and non-enveloped human respiratory viruses, i.e., coronavirus (HCoV-OC43), rhinovirus (HRV-A1), respiratory syncytial virus (RSV-A2), and adenovirus (AdV-5). Ti2PW10 showed highly favorable selectivity indexes against all tested viruses (SIs >700), and its antiviral potential was further investigated against human coronaviruses and rhinoviruses. This POM was found to inhibit replication of multiple HCoV and HRV strains, in different cell systems. Ti2PW10 did not affect virus binding or intracellular viral replication, but selectively inhibited the viral entry. Serial passaging of virus in presence of the POM revealed a high barrier to development of Ti2PW10-resistant variants of HRV-A1 or HCoV-OC43. Moreover, Ti2PW10 was able to inhibit HRV-A1 production in a 3D model of the human nasal epithelium and, importantly, the antiviral treatment did not determine cytotoxicity or tissue damage. A mucoadhesive thermosensitive in situ hydrogel formulation for nasal delivery was also developed for Ti2PW10. Overall, good biocompatibility on cell lines and human nasal epithelia, broad-spectrum activity, and absence of antiviral resistance development reveal the potential of Ti2PW10 as an antiviral candidate for the development of a treatment of acute respiratory viral diseases, warranting further studies to identify the specific target/s of the polyanion and assess its clinical potential.

Sodium Polyoxotungstate Inhibits the Replication of Influenza Virus by Blocking the Nuclear Import of vRNP

Both pandemic and seasonal influenza are major health concerns, causing significant mortality and morbidity. Current influenza drugs primarily target viral neuraminidase and RNA polymerase, which are prone to drug resistance. Polyoxometalates (POMs) are metal cation clusters bridged by oxide anions. They have exhibited potent anti-tumor, antiviral, and antibacterial effects. They have remarkable activity against various DNA and RNA viruses, including human immunodeficiency virus, herpes simplex virus, hepatitis B and C viruses, dengue virus, and influenza virus. In this study, we have identified sodium polyoxotungstate (POM-1) from an ion channel inhibitor library. In vitro, POM-1 has been demonstrated to have potent antiviral activity against H1N1, H3N2, and oseltamivir-resistant H1N1 strains. POM-1 can cause virion aggregation during adsorption, as well as endocytosis. However, the aggregation is reversible; it does not interfere with virus adsorption and endocytosis. Our results suggest that POM-1 exerts its antiviral activity by inhibiting the nuclear import of viral ribonucleoprotein (vRNP). This distinct mechanism of action, combined with its wide range of efficacy, positions POM-1 as a promising therapeutic candidate for influenza treatment and warrants further investigation.

Discovery of a fused bicyclic derivative of 4-hydroxypyrrolidine and imidazolidinone as a new anti-HCV agent

Hepatitis C virus (HCV) infection causes severe liver diseases and remains a major global public health concern. Current direct-acting antiviral (DAA)-based therapies that target viral proteins involving HCV genome replication are effective, however a minority of patients still fail to cure HCV, rendering a window to develop additional antivirals particularly targeting host functions involving in HCV infection. Here, we utilized the HCV infection cell culture system (HCVcc) to screen in-house compounds bearing host-interacting preferred scaffold for the antiviral activity. Compound HXL-10, a novel fused bicyclic derivative of pyrrolidine and imidazolidinone, was identified as a potent anti-HCV agent with a low cytotoxicity and high specificity. Mechanistic studies showed that HXL-10 neither displayed a virucidal effect nor inhibited HCV genomic RNA replication. Instead, HXL-10 might inhibit HCV assembly by targeting host functions. In summary, we developed a novel anti-HCV agent that may potentially offer additive benefits to the current anti-HCV DDA.

Synthesis and anti-HIV-1 activity evaluation of Keggin-type polyoxometalates with amino acid as organic cations

Polyoxometalates (POMs), as a class of multinuclear metal oxygen clusters, have promising biological activities. And their amino acid derivatives will lead to better pharmacological activity by the diversity in structures and properties. With reference to the anti-HIV-1 activities of PM-19 (K7PTi2W10O40) and its pyridinium derivatives, a series of novel Keggin-type POMs with amino acid as organic cations (A7PTi2W10O40) were synthesized by hydrothermal synthetic method. The final products were characterized by 1H NMR, Elemental analyzes and single crystal X-ray diffraction. All the synthesized compounds were obtained in the yields of 44.3-61.7% and evaluated the cytotoxicity and anti-HIV-1 activity in vitro. Compared with the reference compound PM-19, the target compounds had a lower toxicity to TZM-bl cells and a higher inhibitory activity against HIV-1. Among them, compound A3 showed higher anti-HIV-1 activity with IC50 of 0.11 nM than that of PM-19 with 4.68 nM. This study demonstrated that combination of Keggin-type POMs and amino acids can be a new strategy to enhance the anti-HIV-1 biological activity of POMs. All results will be expected to helpful for developing more potent and effective HIV-1 inhibitors.

Synthesis, Characterization, and Antibacterial Activity of Ni-Substituted Krebs-type Sandwich-Tungstobismuthates Functionalized with Amino Acids

Four new Ni-substituted Krebs-type sandwich-tungstobismuthates, K₄Ni₂[{Ni(β-ala)(H₂O)₂}₂{Ni(H₂O)}₂{Ni(H₂O)(η²-β-ala)}₂(B-β-BiW₉O₃₃)₂]·49H₂O {(β-ala)₄(Ni₃)₂(BiW₉)₂}, K_3.5Na_6.5[{Ni(η³-L-asp)}₂(WO₂)₂(B-β-BiW₉O₃₃)₂]·36H₂O·L-asp {(L-asp)₂(NiW)₂(BiW₉)₂}, K₄Na₆[{Ni(gly)(H₂O)₂}₂(WO₂)₂(B-β-BiW₉O₃₃)₂]·86H₂O {(gly)₂(NiW)₂(BiW₉)₂}, and K₂Na₈[{Ni(η²-serinol) (H₂O)}₂{Ni(H₂O)₂}₂(B-β-BiW₉O₃₃)₂]·42H₂O {(serinol)₂Ni₄(BiW₉)₂} have been synthesized by one-pot solution methods. All compounds have been characterized in the solid state by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), elemental and thermogravimetric analyses, and infrared spectroscopy (IR), as well as by UV-vis spectroscopy in solution. The antibacterial activity of all compounds was studied against four bacterial strains by the determination of the minimum inhibitory concentration (MIC). The results showed that only {(β-ala)₄(Ni₃)₂(BiW₉)₂} demonstrates antibacterial activity (MIC is in the range from 8 to 256 μg/mL) compared to three other Ni-Krebs sandwiches.

Promising application of polyoxometalates in the treatment of cancer, infectious diseases and Alzheimer's disease

As shown in studies conducted in recent decades, polyoxometalates (POMs), as inorganic metal oxides, have promising biological activities, including antitumor, anti-infectious and anti-Alzheimer’s activities, due to their special structures and properties. However, some side effects impede their clinical applications to a certain extent. Compared with unmodified POMs, POM-based inorganic–organic hybrids and POM-based nanocomposite structures show significantly enhanced bioactivity and reduced side effects. In this review, we introduce the biological activities of POMs and their derivatives and highlight the side effects of POMs on normal cells and organisms and their possible mechanisms of action. We then propose a development direction for overcoming their side effects. POMs are expected to constitute a new generation of inorganic metal drugs for the treatment of cancer, infectious diseases, and Alzheimer's disease.

Graphical abstract

New composition of tungsten has a broad range of antiviral activity

The water-based combination of two inorganic chemical compounds such as sodium tungstate dihydrate-Na₂WO₄ × 2H₂O and Aluminum sulfate octadecahydrate-Al₂ (SO₄) 3 × 18H₂O that we have conditionally named ‘Vomifal’ has a broad antiviral activity in various DNA and RNA viruses, including Human Herpes Virus (HHV), African Swine Fever Virus (ASFV), Vaccinia Virus (VV), Hepatitis C Virus (HCV), Foot and Mouth Disease Virus (FMDV), Influenza A virus (A/Aichi/2/68 (H3N2)). In vitro and In vivo assays in several tissue cultures as well as in laboratory animals, conformed ‘Vomifal’ has a very low toxicity and the antiviral properties partially are due to its ability to induce gamma-IFN. Based on the results obtained, we can assume the presence of at least two mechanisms of the antiviral action of the studied drug. First or early stage - an unknown mechanism, possibly related to the effect on cellular receptors. Second or late stage – main antiviral properties probably associated with an interferonogenic effect.

Photo-catalyzed TiO2 inactivates pathogenic viruses by attacking viral genome

Previous observations have been reported that viruses were inactivated using strong irradiation. Here, new evidence was disclosed by studying the effects of nanosized TiO₂ on viral pathogens under a low irradiation condition (0.4 mW/cm² at UVA band) that mimics the field setting. We showed that photo-activated TiO₂ efficiently inhibits hepatitis C virus infection, and weak indoor light with intensity of 0.6 mW/cm² at broad-spectrum wavelength and around 0.15 mW/cm² of UVA band also lead to partial inhibition. Mechanistic studies demonstrated that hydroxyl radicals produced by photo-activated TiO₂ do not destroy virion structure and contents, but attack viral RNA genome, thus inactivating the virus. Furthermore, we showed that photo-activated TiO₂ inactivates a broad range of human viral pathogens, including SARS-CoV-2, a novel coronavirus responsible for the ongoing COVID-19 pandemic. In conclusion, we showed that photo-catalyzed nanosized TiO₂ inactivates pathogenic viruses, paving a way to its field application in control of viral infectious diseases.

Synthesis, Anti-Tumor Activity and Apoptosis-Inducing Effect of Novel Dimeric Keggin-Type Phosphotungstate

A dimeric Keggin-type phosphotungstate (ODA)₁₀[(PW₁₁FeO₃₉)₂O]·9H₂O (abbreviated as ODA₁₀[(PW₁₁Fe)₂], ODA = octadecyltrimethylammonium bromide) was synthesized and investigated comprehensively its antitumor activity on MCF-7 and A549 cells. The dimeric structure and amorphous morphology were characterized by FT-IR, UV-vis-DRS, SEM and XRD. The in vitro MTT assay of ODA₁₀[(PW₁₁Fe)₂] showed anticancer activity on MCF-7 and A549 cells in a dose- and time-dependent manner, and the IC₅₀ values for MCF-7 and A549 cells at 48 h were 5.83 μg/ml and 3.23 μg/ml, respectively. The images of the ODA₁₀[(PW₁₁Fe)₂]-treated cells observed by inverted biological microscope exhibited the characteristic morphology of apoptosis. Flow cytometric analysis showed cell apoptosis and cycle arrested at S phase induced by ODA₁₀[(PW₁₁Fe)₂]. The above results illuminated the main mechanism of the antitumor action of ODA₁₀[(PW₁₁Fe)₂] on MCF-7 and A549 cells, indicating that this dimeric phosphotungstate is a promising anticancer drug.

Biological evaluation of Keggin-type polyoxometalates on tyrosinase: Kinetics and molecular modeling

Abnormal overexpression of tyrosinase activity can lead to the production of hyperpigmentation in human skin and enzymatic browning in fruits and vegetables. Herein, the inhibition and mechanism of the H₃ PMo₁₂ O₄₀ and two transition metal-substituted Keggin-type polyoxometalates (Na₇ PMo₁₁ CoO₄₀ and Na₇ PMo₁₁ ZnO₄₀ ) on tyrosinase were studied by kinetics and molecular modeling. Kinetic studies indicated that all compounds had more potent inhibitory activities than standard arbutin, and H₃ PMo₁₂ O₄₀ (IC₅₀  = 0.443 ± 0.006 mm) is ~15-fold stronger inhibition than arbutin. Additionally, all compounds inhibited tyrosinase in a reversible competitive manner. Intriguingly, molecular modeling elucidated that three compounds competitively bind to tyrosinase mainly through more interactions with Cu²⁺ ions and the amino acid residue capable of forming cation-π and hydrogen bonding, forming a reversible non-covalent complex. Molecular simulation study correlated well with the biological activity of three compounds in vitro. This work provided new insights into design and synthesis of polyoxometalates as tyrosinase inhibitors in the field of medicine, cosmetic, and food.

Anti-flavivirus activity of polyoxometalate

Viruses in the Flaviviridae family such as Zika virus (ZIKV), dengue virus (DENV), and Japanese encephalitis virus (JEV) are major public health concerns. The development of antiviral agents against these viruses is urgently needed. We have previously discovered that the Keggin structured polyoxometalate POM-12 has potent inhibitory activity against hepatitis C virus, another member of the Flaviviridae family. In this study, we tested its antiviral activity of DENV, JEV and ZIKV, and found that POM-12 dramatically inhibited their infection with IC50 value of 1.16 μM, 1.9 μM and 0.64 μM, respectively. Mechanistic studies indicated that POM-12 directly disrupted the integrity of these virions. Moreover, POM-12 also targeted the post-entry steps of viral replication of JEV, but having no similar activities on ZIKV and DENV. The differential actions of POM-12 on these viruses suggest that surface topology and charge of virion may have influence on its drug effect, and thus POM-12 may be modified to more efficiently inhibit these and other similar viruses.

Polyoxometalates in Biomedicine: Update and Overview

BACKGROUND

Polyoxometalates (POMs) are negatively charged metal-oxo clusters of early transition metal ions in high oxidation states (e.g., WVI, MoVI, VV). POMs are of interest in the fields of catalysis, electronics, magnetic materials and nanotechnology. Moreover, POMs were shown to exhibit biological activities in vitro and in vivo, such as antitumor, antimicrobial, and antidiabetic.

METHODS

The literature search for this peer-reviewed article was performed using PubMed and Scopus databases with the help of appropriate keywords.

RESULTS

This review gives a comprehensive overview of recent studies regarding biological activities of polyoxometalates, and their biomedical applications as promising anti-viral, anti-bacterial, anti-tumor, and anti-diabetic agents. Additionally, their putative mechanisms of action and molecular targets are particularly considered.

CONCLUSION

Although a wide range of biological activities of Polyoxometalates (POMs) has been reported, they are to the best of our knowledge not close to a clinical trial or a final application in the treatment of diabetes or infectious and malignant diseases. Accordingly, further studies should be directed towards determining the mechanism of POM biological actions, which would enable fine-tuning at the molecular level, and consequently efficient action towards biological targets and as low toxicity as possible. Furthermore, biomedical studies should be performed on solutionstable POMs employing physiological conditions and concentrations.

In vivo toxicity evaluation of two polyoxotungstates with potential antidiabetic activity using Wistar rats as a model system

Study of the in vivo hypoglycemic effect, hepatotoxicity and nephrotoxicity of a donut-shaped polyanion salt (NH₄)₁₄[Na@P₅W₃₀O₁₁₀]·31H₂O {NaP5W30} and its Ag-containing derivative K₁₄[Ag@P₅W₃₀O₁₁₀]·22H₂O·6KCl {AgP5W30}.

Antiviral effects of a niobium-substituted heteropolytungstate on hepatitis B virus-transgenic mice

To study the efficacy of a polyoxometalate, Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O, as an antiviral treatment in HBV transgenic mice. HBV transgenic mice were treated with Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O by intragastric administration. Adefovir and distilled water were administered as controls. Serum HBV DNA, liver HBV RNA levels were measured by quantitative RT-PCR. Serum HBsAg levels were measured by ELISA. The hepatitis B virus surface antigen (HBsAg) in liver cells was detected by immunohistochemistry (IHC). Pathological changes in the liver tissues were also observed by light and electron microscopy. Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O significantly decreased serum HBsAg and HBV DNA levels. Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O resulted in a 98% decrease in serum HBV DNA at 28 days, from 4.3 log₁₀ copies/ml at baseline to 2.5 log₁₀ copies/ml after treatment, and the inhibition rate of HBV DNA was higher than ADV at the same dose. The HBV replication levels in each group slightly increased at 7 days after withdrawal, but rebounded slightly more in the Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O treatment group compared to the H₂ O control group (p < .05). There were no differences in HBV RNA levels. No significant differences were observed in the pathology, but there were decreased HBsAg levels in the Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O-treated group compared to the control group. The results demonstrated that Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O displayed potent anti-HBV activity in HBV transgenic mice and supported for future clinic study.

Experimental and theoretical insights of functionalized hexavanadates on Na+/K+-ATPase activity; molecular interaction field, ab initio calculations and in vitro assays

The influence of three functionalized hexavanadates (V₆): Na₂ [V₆O₁₃{(OCH₂)₃CCH₃}₂], [H₂]₂ [V₆O₁₃{(OCH₂)₃CCH₂OCOCH₂CH₃}₂] and [(C₄H₉)₄N]₂ [V₆O₁₃{(OCH₂)₃CCH₂OOC(CH₃)₂-COOH}₂ on Na⁺/K⁺-ATPase activity, was investigated in vitro. Including compounds already tested by Xu et al. (Journal of Inorganic Biochemistry 161 (2016) 27-36), all functionalized hexavanadates inhibit the activity of Na⁺/K⁺-ATPase in a dose-dependent manner but with different inhibitory potencies. Na₂ [V₆O₁₃{(OCH₂)₃CCH₃}₂] was found to have the best inhibition properties - showing 50% inhibition IC₅₀ = 5.50 × 10^-5 M, while [(C₄H₉)₄N]₂ [V₆O₁₃{(OCH₂)₃CCH₂OOC(CH₃)₂-COOH}₂] showed the lowest inhibitory power, IC₅₀ = 1.31 × 10^-4 M. In order to understand the bioactivity of functionalized hexavanadates series, we have also used a combined theoretical approach: determination of electrostatic potential from ab initio theoretical calculations and computation of the molecular interaction field (MIF) surface.

Polyoxomolybdates as α-glucosidase inhibitors: Kinetic and molecular modeling studies

Noninsulin dependent diabetes mellitus is a serious global disease that is treated by inhibiting α-glucosidase to reduce the glucose content in the blood. Several incompletely satisfactory therapeutic drugs are already on the market. In this report, we showed that polyoxomolybdates based on Keggin-type architecture are promising candidates. Kinetic studies indicate that H₃PMo₁₂O₄₀, Na₄PMo₁₁VO₄₀, Na₆PMo₁₁FeO₄₀ and Na₇PMo₁₁CoO₄₀ strongly inhibit α-glucosidase with IC₅₀ values of 6.14 ± 0.38 μM, 52.33 ± 1.41 μM, 161.90 ± 7.68 μM and 103.10 ± 2.88 μM, respectively. Moreover, H₃PMo₁₂O₄₀, Na₄PMo₁₁VO₄₀, and Na₇PMo₁₁CoO₄₀ are reversible, competitive inhibitors with K_I values of 0.018 mM, 0.146 mM and 0.121 mM, respectively. Na₆PMo₁₁FeO₄₀ inhibited α-glucosidase in a reversible noncompetitive manner with K_I and K_IS of 0.312 mM and 0.412 mM, respectively. Molecular docking simulation suggested that H₃PMo₁₂O₄₀ binds into the substrate binding site in accordance with competitive inhibition behavior and offered, in addition, an initial insight into the polypeptide-inhibitor interactions. This work presents a promising new perspective for designing effective α-glucosidase inhibitors and further demonstrates the enormous potential of polyoxomolybdates as enzyme inhibitors.

Anti-zika virus activity of polyoxometalates

Zika virus (ZIKV) is an emerging infectious viral pathogen associated with severe fetal cerebral anomalies and the paralytic Guillain-Barrè syndrome in adults. It was the cause of a recent global health crisis following its entrance into a naïve population in the Americas. Nowadays, no vaccine or specific antiviral against ZIKV is available. In this study, we identified three polyoxometalates (POMs), the Anderson-Evans type [TeW₆O₂₄]^6- (TeW₆), and the Keggin-type [TiW₁₁CoO₄₀]^8-_ (TiW₁₁Co), and [Ti₂PW₁₀O₄₀]^7- (Ti₂PW₁₀), that inhibit ZIKV infection with EC₅₀s in the low micromolar range. Ti₂PW₁₀, the POM with the greatest selectivity index (SI), was selected and the step of ZIKV replicative cycle putatively inhibited was investigated by specific antiviral assays. We demonstrated that Ti₂PW₁₀ targets the entry process of ZIKV infection and it is able to significantly reduce ZIKV progeny production. These results suggest that the polyanion Ti₂PW₁₀ could be a good starting point to develop an effective therapeutic to treat ZIKV infection.

Synthesis and Antibacterial Activity of Polyoxometalates with Different Structures

A new inorganic-organic hybrid compound, [{Cu(phen)2}2(H4W12O40)], was synthesized, and its crystal structure was determined. The Keggin anion H4W12O40 4- was grafted with two coordination units {Cu(phen)2}, forming an electrically neutral molecule. The antibacterial activity of several polyoxometalate compounds with different anionic structures including the new compound was studied. The results show that the compound 1 can inhibit the growth of Enterococcus faecalis FA2 strains and that antibacterial activity of the polyoxometalate compounds is dependent with component elements of POM but is less relative with the anion structures.

Inhibition of Human Immunodeficiency Virus Type 1 Entry by a Keggin Polyoxometalate

Here, we report the anti-human immunodeficiency virus (HIV) potency and underlying mechanisms of a Keggin polyoxometalate (PT-1, K₆HPTi₂W₁₀O₄₀). Our findings showed that PT-1 exhibited highly potent effects against a diverse group of HIV type 1 (HIV-1) strains and displayed low cytotoxicity and genotoxicity. The time-addition assay revealed that PT-1 acted at an early stage of infection, and these findings were supported by the observation that PT-1 had more potency against Env-pseudotyped virus than vesicular stomatitis virus glycoprotein (VSVG) pseudotyped virus. Surface plasmon resonance binding assays and flow cytometry analysis showed that PT-1 blocked the gp120 binding site in the CD4 receptor. Moreover, PT-1 bound directly to gp41 NHR (N36 peptide), thereby interrupting the core bundle formation of gp41. In conclusion, our data suggested that PT-1 may be developed as a new anti-HIV-1 agent through its effects on entry inhibition.

POM-1 inhibits P2 receptors and exhibits anti-inflammatory effects in macrophages

Extracellular nucleotides can modulate the immunological response by activating purinergic receptors (P2Rs) on the cell surface of macrophages, dendritic, and other immune cells. In particular, the activation of P2X7R can induce release of cytokines and cell death as well as the uptake of large molecules through the cell membrane by a mechanism still poorly understood. Polyoxotungstate-1 (POM-1) has been proposed as a potent inhibitor of ecto-nucleotidases, enzymes that hydrolyze extracellular nucleotides, regulating the activity of P2Rs. However, the potential impact of POM-1 on P2Rs has not been evaluated. Here, we used fluorescent dye uptake, cytoplasmic free Ca2+ concentration measurement, patch-clamp recordings, scanning electron microscopy, and quantification of inflammatory mediators to investigate the effects of POM-1 on P2Rs of murine macrophages. We observed that POM-1 blocks the P2YR-dependent cytoplasmic Ca2+ increase and has partial effects on the cytoplasmic Ca2+, increasing dependence on P2XRs. POM-1 can inhibit the events related with ATP-dependent inflammasome activation, anionic dye uptake, and also the opening of large conductance channels, which are associated with P2X7R-dependent pannexin-1 activation. On the other hand, this compound has no effects on cationic fluorescent dye uptake, apoptosis, and bleb formation, also dependent on P2X7R. Moreover, POM-1 can be considered an anti-inflammatory compound, because it prevents TNF-α and nitric oxide release from LPS-treated macrophages.

The [Mo₆Cl14]2- Cluster is Biologically Secure and Has Anti-Rotavirus Activity In Vitro

The molybdenum cluster [Mo₆Cl14]2- is a fluorescent component with potential for use in cell labelling and pharmacology. Biological safety and antiviral properties of the cluster are as yet unknown. Here, we show the effect of acute exposition of human cells and red blood cells to the molybdenum cluster and its interaction with proteins and antiviral activity in vitro. We measured cell viability of HepG2 and EA.hy926 cell lines exposed to increasing concentrations of the cluster (0.1 to 250 µM), by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. Hemolysis and morphological alterations of red blood cells, obtained from healthy donors, exposed to the cluster (10 to 200 µM) at 37 °C were analyzed. Furthermore, quenching of tryptophan residues of albumin was performed. Finally, plaque formation by rotavirus SA11 in MA104 cells treated with the cluster (100 to 300 µM) were analyzed. We found that all doses of the cluster showed similar cell viability, hemolysis, and morphology values, compared to control. Quenching of tryptophan residues of albumin suggests a protein-cluster complex formation. Finally, the cluster showed antiviral activity at 300 µM. These results indicate that the cluster [Mo₆Cl14]2- could be intravenously administered in animals at therapeutic doses for further in vivo studies and might be studied as an antiviral agent.

Genotoxicity and acute and subchronic toxicity studies of a bioactive polyoxometalate in Wistar rats

Background

Cs₂K₄Na [SiW₉Nb₃O₄₀] (POM93) is a novel broad-spectrum antiviral agent with high activity, high stability, and low toxicity in vitro. Most toxicity studies for POM93 have been performed in cultured cell lines rather than in animals. Like other POMs, there is a lack of evidence for in vivo toxicity limits, oral bioavailability, and therapeutic applications.

Methods

The toxic properties of POM93 were evaluated comprehensively in vivo, including the acute and subchronic oral toxicity studies and genotoxicity tests.

Results

The acute toxicity study showed no abnormal changes or mortality in rats treated with POM93 even at the single high dose of 5000 mg/kg body weight. In the subchronic toxicity study, regardless of the body weight, the organ weight, and the hematological parameters, similar results were observed between the control group and the experimental groups. POM93 produced mild changes in rare hematological parameters in the liver and kidneys, but did not induce the clinical symptoms of liver or kidneys injury in rats as confirmed by histopathological analysis. Moreover, neither mutagenicity nor clastogenicity was caused by POM93 treatment in vitro and in vivo.

Conclusions

The present study demonstrates that the oral administration of POM93 is presumed safe and poses a low risk of potential health risks.

Electronic supplementary material

The online version of this article (doi:10.1186/s40360-017-0133-x) contains supplementary material, which is available to authorized users.

Inhibitory effects of different substituted transition metal-based krebs-type sandwich structures on human hepatocellular carcinoma cells

POMs induced apoptosis in HepG2 cells, which indicated sub-G1 hypodiploid cell population before the G1 phase via flow cytometry. POM3 showed the highest apoptotic rate of these POMs. This reveals the structure–function relationship of bioactive transition metal ions.

Construction of two novel borotungstates modified by different ligands connected with single/double bridges

Unusual copper complex units modified by two types of ligands are introduced into the {BW₁₂} systems, leading to the assembly of intricate borotungstate networks, which exhibit good photo-/electro-catalytic activities.

A novel small-molecule inhibitor of hepatitis C virus replication acts by suppressing signal transducer and activator of transcription 3

OBJECTIVES

Hepatitis C virus (HCV) infects hepatocytes and causes liver damage. The aim of this study was to identify new classes of host-targeting anti-HCV compounds that may provide novel approaches for antiviral treatment regimens.

METHODS

Cell culture-derived HCV (HCVcc), replicons and pseudoparticles were used in combination with high-throughput screening, reporter gene assays and cytotoxicity and signalling pathway analyses.

RESULTS

A small-molecule inhibitor of HCV, N-(cyclopropyl(phenyl)methyl)thieno[2,3-d]pyrimidin-4-amine, designated IB-32, was identified by screening a compound library with a Jc1-luc HCVcc assay. By using various virus models, HCV replication was identified as the predominant step of IB-32's action. IB-32 inhibited HCVcc (genotype 2a) and HCV replicons (genotype 1b) at low nanomolar ranges (with IC50s of 40 ± 8 and 100 ± 15 nM, respectively). IB-32 was found to be non-toxic when tested against a panel of human cell lines in vitro at the effective antiviral dose. Mechanistically, IB-32 strongly inhibited STAT3 (Tyr705) phosphorylation, a necessary cellular factor for HCV replication and a pivotal therapeutic target for multiple cancers. Furthermore, the inhibition of HCV replication by IB-32 was augmented in cells with STAT3 knockdown. In contrast, the inhibitory effect of IB-32 was attenuated in cells overexpressing a constitutively active form of STAT3.

CONCLUSION

The results presented here identify a promising STAT3-targeting anti-HCV therapeutic candidate. This novel small molecule could be further optimized and developed for use as both an antiviral and an anti-cancer drug.

Polyoxometalates--potent and selective ecto-nucleotidase inhibitors

Polyoxometalates (POMs) are inorganic cluster metal complexes that possess versatile biological activities, including antibacterial, anticancer, antidiabetic, and antiviral effects. Their mechanisms of action at the molecular level are largely unknown. However, it has been suggested that the inhibition of several enzyme families (e.g., phosphatases, protein kinases or ecto-nucleotidases) by POMs may contribute to their pharmacological properties. Ecto-nucleotidases are cell membrane-bound or secreted glycoproteins involved in the hydrolysis of extracellular nucleotides thereby regulating purinergic (and pyrimidinergic) signaling. They comprise four distinct families: ecto-nucleoside triphosphate diphosphohydrolases (NTPDases), ecto-nucleotide pyrophosphatases/phosphodiesterases (NPPs), alkaline phosphatases (APs) and ecto-5'-nucleotidase (eN). In the present study, we evaluated the inhibitory potency of a series of polyoxometalates as well as chalcogenide hexarhenium cluster complexes at a broad range of ecto-nucleotidases. [Co4(H2O)2(PW9O34)2](10-) (5, PSB-POM142) was discovered to be the most potent inhibitor of human NTPDase1 described so far (Ki: 3.88 nM). Other investigated POMs selectively inhibited human NPP1, [TiW11CoO40](8-) (4, PSB-POM141, Ki: 1.46 nM) and [NaSb9W21O86](18-) (6, PSB-POM143, Ki: 4.98 nM) representing the most potent and selective human NPP1 inhibitors described to date. [NaP5W30O110](14-) (8, PSB-POM144) strongly inhibited NTPDase1-3 and NPP1 and may therefore be used as a pan-inhibitor to block ATP hydrolysis. The polyoxoanionic compounds displayed a non-competitive mechanism of inhibition of NPPs and eN, but appeared to be competitive inhibitors of TNAP. Future in vivo studies with selected inhibitors identified in the current study are warranted.