An orally available, small-molecule interferon inhibits viral replication

Mechanism of interferon alpha therapy for chronic hepatitis B and potential approaches to improve its therapeutic efficacy

Hepatitis B virus (HBV) chronically infects 296 million people worldwide and causes more than 820,000 deaths annually due to cirrhosis and hepatocellular carcinoma. Current standard-of-care medications for chronic hepatitis B (CHB) include nucleos(t)ide analogue (NA) viral DNA polymerase inhibitors and pegylated interferon alpha (PEG-IFN-α). NAs can efficiently suppress viral replication and improve liver pathology, but not eliminate or inactivate HBV covalently closed circular DNA (cccDNA). CCC DNA is the most stable HBV replication intermediate that exists as a minichromosome in the nucleus of infected hepatocyte to transcribe viral RNA and support viral protein translation and genome replication. Consequentially, a finite duration of NA therapy rarely achieves a sustained off-treatment suppression of viral replication and life-long NA treatment is most likely required. On the contrary, PEG-IFN-α has the benefit of finite treatment duration and achieves HBsAg seroclearance, the indication of durable immune control of HBV replication and functional cure of CHB, in approximately 5% of treated patients. However, the low antiviral efficacy and poor tolerability limit its use. Understanding how IFN-α suppresses HBV replication and regulates antiviral immune responses will help rational optimization of IFN therapy and development of novel immune modulators to improve the rate of functional cure. This review article highlights mechanistic insight on IFN control of HBV infection and recent progress in development of novel IFN regimens, small molecule IFN mimetics and combination therapy of PEG-IFN-α with new direct-acting antivirals and therapeutic vaccines to facilitate the functional cure of CHB.

A small molecule iCDM-34 identified by in silico screening suppresses HBV DNA through activation of aryl hydrocarbon receptor

IFN-alpha have been reported to suppress hepatitis B virus (HBV) cccDNA via APOBEC3 cytidine deaminase activity through interferon signaling. To develop a novel anti-HBV drug for a functional cure, we performed in silico screening of the binding compounds fitting the steric structure of the IFN-alpha-binding pocket in IFNAR2. We identified 37 compounds and named them in silico cccDNA modulator (iCDM)-1-37. We found that iCDM-34, a new small molecule with a pyrazole moiety, showed anti-HCV and anti-HBV activities. We measured the anti-HBV activity of iCDM-34 dependent on or independent of entecavir (ETV). iCDM-34 suppressed HBV DNA, pgRNA, HBsAg, and HBeAg, and also clearly exhibited additive inhibitory effects on the suppression of HBV DNA with ETV. We confirmed metabolic stability of iCDM-34 was stable in human liver microsomal fraction. Furthermore, anti-HBV activity in human hepatocyte-chimeric mice revealed that iCDM-34 was not effective as a single reagent, but when combined with ETV, it suppressed HBV DNA compared to ETV alone. Phosphoproteome and Western blotting analysis showed that iCDM-34 did not activate IFN-signaling. The transcriptome analysis of interferon-stimulated genes revealed no increase in expression, whereas downstream factors of aryl hydrocarbon receptor (AhR) showed increased levels of the expression. CDK1/2 and phospho-SAMHD1 levels decreased under iCDM-34 treatment. In addition, AhR knockdown inhibited anti-HCV activity of iCDM-34 in HCV replicon cells. These results suggest that iCDM-34 decreases the phosphorylation of SAMHD1 through CDK1/2, and suppresses HCV replicon RNA, HBV DNA, and pgRNA formation.

MTHFD2 promotes PD-L1 expression via activation of the JAK/STAT signalling pathway in bladder cancer

Although combination chemotherapy is widely used for bladder cancer (BC) treatment, the recurrence and progression rates remain high. Therefore, novel therapeutic targets are required. Methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) contributes to tumourigenesis and immune evasion in several cancers; however, its biological function in BC remains unknown. This study aimed to investigate the expression, prognostic value and protumoural function of MTHFD2 in BC and elucidate the mechanism of programmed death-ligand 1 (PD-L1) upregulation by MTHFD2. An analysis using publicly available databases revealed that a high MTHFD2 expression was correlated with clinical features and a poor prognosis in BC. Furthermore, MTHFD2 promoted the growth, migration, invasion and tumourigenicity and decreased the apoptosis of BC cells in vivo and in vitro. The results obtained from databases showed that MTHFD2 expression was correlated with immune infiltration levels, PD-L1 expression, and the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. The expression of MTHFD2, PD-L1 and JAK/STAT signalling pathway-related proteins increased after interferon gamma treatment and decreased after MTHFD2 knockdown. Moreover, addition of a JAK/STAT pathway activator partially reduced the effect of MTHFD2 knockdown on BC cells. Collectively, our findings suggest that MTHFD2 promotes the expression of PD-L1 through the JAK/STAT signalling pathway in BC.

hESC-Derived Epicardial Cells Promote Repair of Infarcted Hearts in Mouse and Swine

Myocardial infarction (MI) causes excessive damage to the myocardium, including the epicardium. However, whether pluripotent stem cell-derived epicardial cells (EPs) can be a therapeutic approach for infarcted hearts remains unclear. Here, the authors report that intramyocardial injection of human embryonic stem cell-derived EPs (hEPs) at the acute phase of MI ameliorates functional worsening and scar formation in mouse hearts, concomitantly with enhanced cardiomyocyte survival, angiogenesis, and lymphangiogenesis. Mechanistically, hEPs suppress MI-induced infiltration and cytokine-release of inflammatory cells and promote reparative macrophage polarization. These effects are blocked by a type I interferon (IFN-I) receptor agonist RO8191. Moreover, intelectin 1 (ITLN1), abundantly secreted by hEPs, interacts with IFN-β and mimics the effects of hEP-conditioned medium in suppression of IFN-β-stimulated responses in macrophages and promotion of reparative macrophage polarization, whereas ITLN1 downregulation in hEPs cancels beneficial effects of hEPs in anti-inflammation, IFN-I response inhibition, and cardiac repair. Further, similar beneficial effects of hEPs are observed in a clinically relevant porcine model of reperfused MI, with no increases in the risk of hepatic, renal, and cardiac toxicity. Collectively, this study reveals hEPs as an inflammatory modulator in promoting infarct healing via a paracrine mechanism and provides a new therapeutic approach for infarcted hearts.

Imidazonaphthyridine effects on Chikungunya virus replication: Antiviral activity by dependent and independent of interferon type 1 pathways

The Chikungunya virus (CHIKV) causes Chikungunya fever, a disease characterized by symptoms such as arthralgia/polyarthralgia. Currently, there are no antivirals approved against CHIKV, emphasizing the need to develop novel therapies. The imidazonaphthyridine compound (RO8191), an interferon-α (IFN-α) agonist, was reported as a potent inhibitor of HCV. Here RO8191 was investigated for its potential to inhibit CHIKV replication in vitro. RO8191 inhibited CHIKV infection in BHK-21 and Vero-E6 cells with a selectivity index (SI) of 12.3 and 37.3, respectively. Additionally, RO8191 was capable to protect cells against CHIKV infection, inhibit entry by virucidal activity, and strongly impair post-entry steps of viral replication. An effect of RO8191 on CHIKV replication was demonstrated in BHK-21 through type-1 IFN production mechanism and in Vero-E6 cells which has a defective type-1 IFN production, also suggesting a type-1 IFN independent mode of action. Molecular docking calculations demonstrated interactions of RO8191 with the CHIKV E proteins, corroborated by the ATR-FTIR assay, and with non-structural proteins, supported by the CHIKV-subgenomic replicon cells assay.

Crosstalk between TBK1/IKKε and the type I interferon pathway contributes to tubulointerstitial inflammation and kidney tubular injury

The type I interferon (TI-IFN) pathway regulates innate immunity, inflammation, and apoptosis during infection. However, the contribution of the TI-IFN pathway or upstream signaling pathways to tubular injury in kidney disease is poorly understood. Upon observing evidence of activation of upstream regulators of the TI-IFN pathway in a transcriptomics analysis of murine kidney tubulointerstitial injury, we have now addressed the impact of the TI-IFN and upstream signaling pathways on kidney tubulointerstitial injury. In cultured tubular cells and kidney tissue, IFNα/β binding to IFNAR activated the TI-IFN pathway and recruited antiviral interferon-stimulated genes (ISG) and NF-κB-associated proinflammatory responses. TWEAK and lipopolysaccharide (LPS) signaled through TBK1/IKKε and IRF3 to activate both ISGs and NF-κB. In addition, TWEAK recruited TLR4 to stimulate TBK1/IKKε-dependent ISG and inflammatory responses. Dual pharmacological inhibition of TBK1/IKKε with amlexanox decreased TWEAK- or LPS-induced ISG and cytokine responses, as well as cell death induced by a complex inflammatory milieu that included TWEAK. TBK1 or IRF3 siRNA prevented the TWEAK-induced ISG and inflammatory gene expression while IKKε siRNA did not. In vivo, kidney IFNAR and IFNβ were increased in murine LPS and folic acid nephrotoxicity while IFNAR was increased in human kidney biopsies with tubulointerstitial damage. Inhibition of TBK1/IKKε with amlexanox or IFNAR neutralization decreased TI-IFN pathway activation and protected from kidney injury induced by folic acid or LPS. In conclusion, TI-IFNs, TWEAK, and LPS engage interrelated proinflammatory and antiviral responses in tubular cells. Moreover, inhibition of TBK1/IKKε with amlexanox, and IFNAR targeting, may protect from tubulointerstitial kidney injury.

Interferon‑α and its effects on cancer cell apoptosis (Review)

Interferon (IFN)-α is a cytokine that exhibits a wide range of biological activities and is used in various cancer treatments. It regulates numerous genes that serve roles in antiviral, antiproliferative and proapoptotic activities. For decades, one of the main aspects of clinical oncology has been the development of anticancer therapeutics that promote the effective elimination of cancer cells via apoptosis. However, the updated available information concerning IFN-α-induced cancer cell apoptosis needs to be assembled, so as to provide an improved theoretical reference for the basic scientific research and clinical treatment of malignant tumors. Therefore, the present review focuses on the potential effects of IFN-α in inducing cancer cell apoptosis. The biological characteristics of IFN-α, the apoptotic signaling pathways and molecular mechanisms of apoptosis caused by IFN-α are discussed in different types of cancer cells. The present review provided a comprehensive understanding of the effects of IFN-α on cancer cell apoptosis, which will aid in developing more efficient strategies to effectively control the progression of certain cancers.

Interferon-α exerts proinflammatory properties in experimental radiation-induced esophagitis: Possible involvement of plasmacytoid dendritic cells

AIMS

Radiation-induced esophagitis, experienced during radiation therapy for lung cancer and head and neck cancer, is a major dose-limiting side effect of the treatment. This study aimed to elucidate the role of interferon-α (IFN-α) in radiation-induced esophagitis.

MAIN METHODS

C57BL/6 mice were exposed to 10 and 25Gy of single thoracic irradiation. Esophageal mucosal damage and inflammatory reactions were assessed for 5 days after irradiation.

KEY FINDINGS

Irradiation induced esophagitis, characterized by reduction in the thickness of epithelial layer, upregulation of proinflammatory cytokines and chemokines, infiltration of inflammatory cells into the esophageal mucosa, and apoptosis of epithelial cells. Irradiation upregulated the level of gene expression for IFN-α in the esophageal tissue, and the neutralizing antibody against IFN-α ameliorated radiation-induced esophageal mucosal damage, while administration of IFN-α receptor agonist (RO8191) had an inverse effect. Depletion of plasmacytoid dendritic cells (pDCs) by anti-CD317 antibody or pharmacological inactivation with bortezomib suppressed radiation-induced mucosal inflammation and damage, accompanied by decrease in IFN-α expression level.

SIGNIFICANCE

These findings suggest that IFN-α and pDCs exert proinflammatory properties in the pathophysiology of radiation-induced esophagitis.

Establishment of a Rapid Detection System for ISG20-Dependent SARS-CoV-2 Subreplicon RNA Degradation Induced by Interferon-α

Inhaled nebulized interferon (IFN)-α and IFN-β have been shown to be effective in the management of coronavirus disease 2019 (COVID-19). We aimed to construct a virus-free rapid detection system for high-throughput screening of IFN-like compounds that induce viral RNA degradation and suppress the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We prepared a SARS-CoV-2 subreplicon RNA expression vector which contained the SARS-CoV-2 5′-UTR, the partial sequence of ORF1a, luciferase, nucleocapsid, ORF10, and 3′-UTR under the control of the cytomegalovirus promoter. The expression vector was transfected into Calu-3 cells and treated with IFN-α and the IFNAR2 agonist CDM-3008 (RO8191) for 3 days. SARS-CoV-2 subreplicon RNA degradation was subsequently evaluated based on luciferase levels. IFN-α and CDM-3008 suppressed SARS-CoV-2 subreplicon RNA in a dose-dependent manner, with IC50 values of 193 IU/mL and 2.54 μM, respectively. HeLa cells stably expressing SARS-CoV-2 subreplicon RNA were prepared and treated with the IFN-α and pan-JAK inhibitor Pyridone 6 or siRNA-targeting ISG20. IFN-α activity was canceled with Pyridone 6. The knockdown of ISG20 partially canceled IFN-α activity. Collectively, we constructed a virus-free rapid detection system to measure SARS-CoV-2 RNA suppression. Our data suggest that the SARS-CoV-2 subreplicon RNA was degraded by IFN-α-induced ISG20 exonuclease activity.

Catalyst-Free Visible-Light-Promoted Cyclization of Aldehydes: Access to 2,5-Disubstituted 1,3,4-Oxadiazole Derivatives

An efficient synthesis of a variety of 2,5-disubstituted 1,3,4-oxadiazole derivatives via a cyclization reaction by photoredox catalysis between aldehydes and hypervalent iodine(III) reagents is described. The reaction proceeds under mild conditions and affords various target compounds in excellent yields. The commercially available aldehydes without preactivation and a simple visible-light-promoted procedure without any catalysts make this strategy an alternative to the conventional methods.

1,8-naphthyridine derivatives: an updated review on recent advancements of their myriad biological activities

Among all nitrogen-containing heterocycles, the 1,8-naphthyridine scaffold has recently gained an immense amount of curiosity from numerous researchers across fields of medicinal chemistry and drug discovery. This new attention can be ascribed to its versatility of synthesis, its reactiveness and the variety of biological activities it has exhibited. Over the past half-decade, numerous diverse biological evaluations have been conducted on 1,8-naphthyridine and its derivatives in a quest to unravel novel pharmacological facets to this scaffold. Its potency to treat neurodegenerative and immunomodulatory disorders, along with its anti-HIV, antidepressant and antioxidant properties, has enticed researchers to look beyond its broad-spectrum activities, providing further scope for exploration. This review is a consolidated update of previous works on 1,8-naphthyridines and their analogs, focusing on the past 5 years.

Epigenetic reprogramming promotes the antiviral action of IFNα in HBV-infected cells

Chronic hepatitis B virus (HBV) infections remain a health burden affecting ~250 million people worldwide. Thus far, available interferon-alpha (IFNα)-based therapies have shown unsatisfactory cure rates, and alternative therapeutic molecules are still required. However, their development has been hampered because accessible cell models supporting relevant HBV replication and appropriate antiviral activity are lacking. Strategies that reverse epigenetic alterations offer a unique opportunity for cell reprogramming, which is valuable for restoring altered cellular functions in human cell lines. This work aimed to investigate the feasibility of converting HepG2 cells that stably overexpress the HBV entry receptor (sodium/taurocholate cotransporting polypeptide, NTCP) toward IFNα-responsive cells using epigenetic reprogramming. Herein, we showed that an epigenetic regimen with non-cytotoxic doses of the demethylating compound 5-azacytidine restored the anti-HBV action of IFNα in epigenetically reprogrammed HepG2-NTCP-C4 cells, named REP-HepG2-NTCP cells. Thus, a significant inhibition in HBV DNA levels was measured in REP-HepG2-NTCP cells after IFNα treatment. This inhibitory effect was associated with the enhancement of IFNα-mediated induction of critical interferon-stimulated genes (ISGs), which was limited in non-reprogrammed cells. In particular, our data indicated that re-expression of 2’-5’-oligoadenylate synthetase 1 (OAS1) and interferon regulatory factor 9 (IRF9) was the result of an epigenetically driven unmasking of these genes in reprogrammed cells. At last, we evaluated the therapeutic potential of the IFN analog CDM-3008 in REP-HepG2-NTCP cells and demonstrated the efficiency of this chemical compound in triggering ISG induction and HBV inhibition. In summary, this study shows that epigenetic reprogramming promotes the IFNα response in HBV-infected cells and is potentially attractive for cell-based experimental screening of IFN-like compounds.

Discovery of an imidazonaphthyridine and a riminophenazine as potent anti-Zika virus agents through a replicon-based high-throughput screening

The 2015/16 Zika virus (ZIKV) epidemic led to almost 1 million confirmed cases in 84 countries and was associated to the development of congenital microcephaly and Guillain-Barré syndrome. More recently, a ZIKV African lineage was identified in Brazil raising concerns about a future outbreak. The long-term consequences of viral infection emphasizes the need for the development of effective anti-ZIKV drugs. In this study, we developed and characterized a ZIKV replicon cell line for the screening of viral replication inhibitors. The replicon system was developed by engineering the IRES-Neo cassette into the 3' UTR terminus of the ZIKV Rluc DNA construct. After in vitro transcription, replicon RNA was used to transfect BHK-21 cells, that were selected with G418, thus generating the BHK-21-RepZIKV_IRES-Neo cell line. Through this replicon-based cell system, we identified two molecules with potent anti-ZIKV activities, an imidazonaphthyridine and a riminophenazine, both from the MMV/DNDi Pandemic Response Box library of 400 drug-like compounds. The imidazonaphthyridine, known as RO8191, showed remarkable selectivity against ZIKV, while the riminophenazine, the antibiotic Clofazimine, could act as a non-nucleoside analog inhibitor of viral RNA-dependent RNA polymerase (RdRp), as evidenced both in vitro and in silico. The data showed herein supports the use of replicon-based assays in high-throughput screening format as a biosafe and reliable tool for antiviral drug discovery.

Identification of Interferon Receptor IFNAR2 As a Novel HCV Entry Factor by Using Chemical Probes

Upon sensing pathogen-associated patterns and secreting interferons (IFNs) into the environment, host cells perceive extracellular type I IFNs by the IFNα/β receptors IFNAR1 and IFNAR2 to stimulate downstream innate immune signaling cascades. Through the use of chemical probes, we demonstrated that IFNAR2 facilitates hepatitis C virus (HCV) entry. Silencing of IFNAR2 significantly attenuated HCV proliferation. IFNAR2 binds infectious HCV virions through a direct interaction of its D2 domain with the C-terminal end of apolipoprotein E (apoE) on the viral envelope and facilitates virus entry into host cells. The antibody against the IFNAR2 D2 domain attenuates IFNAR2-apoE interaction and impairs HCV infection. The recombinant IFNAR2 protein and the chemical probe potently inhibit major HCV genotypes in various human liver cells in vitro. Moreover, the impact of a chemical probe on HCV genotype 2a is also documented in immune-compromised humanized transgenic mice. Our results not only expand the understanding of the biology of HCV entry and the virus-host relationship but also reveal a new target for the development of anti-HCV entry inhibitors.

Repurposing approved drugs on the pathway to novel therapies

The time and cost of developing new drugs have led many groups to limit their search for therapeutics to compounds that have previously been approved for human use. Many "repurposed" drugs, such as derivatives of thalidomide, antibiotics, and antivirals have had clinical success in treatment areas well beyond their original approved use. These include applications in treating antibiotic-resistant organisms, viruses, cancers and to prevent burn scarring. The major theoretical justification for reusing approved drugs is that they have known modes of action and controllable side effects. Coadministering antibiotics with inhibitors of bacterial toxins or enzymes that mediate multidrug resistance can greatly enhance their activity. Drugs that control host cell pathways, including inflammation, tumor necrosis factor, interferons, and autophagy, can reduce the "cytokine storm" response to injury, control infection, and aid in cancer therapy. An active compound, even if previously approved for human use, will be a poor clinical candidate if it lacks specificity for the new target, has poor solubility or can cause serious side effects. Synergistic combinations can reduce the dosages of the individual components to lower reactivity. Preclinical analysis should take into account that severely ill patients with comorbidities will be more sensitive to side effects than healthy trial subjects. Once an active, approved drug has been identified, collaboration with medicinal chemists can aid in finding derivatives with better physicochemical properties, specificity, and efficacy, to provide novel therapies for cancers, emerging and rare diseases.

Type I interferon protects neurons from prions in in vivo models

Infectious prions comprising abnormal prion protein, which is produced by structural conversion of normal prion protein, are responsible for transmissible spongiform encephalopathies including Creutzfeldt-Jakob disease in humans. Prions are infectious agents that do not possess a genome and the pathogenic protein was not thought to evoke any immune response. Although we previously reported that interferon regulatory factor 3 (IRF3) was likely to be involved in the pathogenesis of prion diseases, suggesting the protective role of host innate immune responses mediated by IRF3 signalling, this remained to be clarified. Here, we investigated the reciprocal interactions of type I interferon evoked by IRF3 activation and prion infection and found that infecting prions cause the suppression of endogenous interferon expression. Conversely, treatment with recombinant interferons in an ex vivo model was able to inhibit prion infection. In addition, cells and mice deficient in type I interferon receptor (subunit interferon alpha/beta receptor 1), exhibited higher susceptibility to 22L-prion infection. Moreover, in in vivo and ex vivo prion-infected models, treatment with RO8191, a selective type I interferon receptor agonist, inhibited prion invasion and prolonged the survival period of infected mice. Taken together, these data indicated that the interferon signalling interferes with prion propagation and some interferon-stimulated genes might play protective roles in the brain. These findings may allow for the development of new strategies to combat fatal diseases.

Inhibition of Chikungunya Virus Replication in Primary Human Fibroblasts by Liver X Receptor Agonist

The mosquito-borne chikungunya virus (CHIKV) causes acute pain and joint inflammation, and in recent years the virus has caused large epidemics in previously CHIKV-free geographic areas. To advance the understanding of host factors that antagonize CHIKV, we show that synthetic agonist of liver X receptor (LXR-623) inhibits CHIKV replication by upregulating the cholesterol exporter ABCA1 and that endogenous and pharmacological activation of interferon signaling pathway partners with LXR-623 to generate a superior antiviral state.

An interferon-like small chemical compound CDM-3008 suppresses hepatitis B virus through induction of interferon-stimulated genes

Oral administration of nucleotide analogues and injection of interferon-α (IFNα) are used to achieve immediate suppression in replication of hepatitis B virus (HBV). Nucleotide analogs and IFNα inhibit viral polymerase activity and cause long-term eradication of the virus at least in part through removing covalently closed circular DNA (cccDNA) via induction of the APOBEC3 deaminases family of molecules, respectively. This study aimed to explore whether the orally administrable low molecular weight agent CDM-3008 (RO8191), which mimics IFNα through the binding to IFNα/β receptor 2 (IFNAR2) and the activation of the JAK/STAT pathway, can suppress HBV replication and reduce cccDNA levels. In primary cultured human hepatocytes, HBV DNA levels were decreased after CDM-3008-treatment in a dose-dependent manner with a half-maximal inhibitory concentration (IC₅₀) value of 0.1 μM, and this was accompanied by significant reductions in cellular cccDNA levels, both HBeAg and HBsAg levels in the cell culture medium. Using a microarray we comprehensively analyzed and compared changes in gene (mRNA) expression in CDM-3008- and IFNα-treated primary cultured human hepatocytes. As reported previously, CDM-3008 mimicked the induction of genes that participate in the interferon signaling pathway. OAS1 and ISG20 mRNA expression was similarly enhanced by both CDM-3008 and IFNα. Thus, CDM-3008 could suppress pgRNA expression to show anti-HBV activity. APOBEC3F and 3G mRNA expression was also induced by CDM-3008 and IFNα treatments, suggesting that cccDNA could be degraded through induced APOBEC3 family proteins. We identified the genes whose expression was specifically enhanced in CDM-3008-treated cells compared to IFNα-treated cells. The expression of SOCS1, SOCS2, SOCS3, and CISH, which inhibit STAT activation, was enhanced in CDM-3008-treated cells suggesting that a feedback inhibition of the JAK/STAT pathway was enhanced in CDM-3008-treated cells compared to IFNα-treated cells. In addition, CDM-3008 showed an additive effect with a clinically-used nucleoside entecavir on inhibition of HBV replication. In summary, CDM-3008 showed anti-HBV activity through activation of the JAK/STAT pathway, inducing the expression of interferon-stimulated genes (ISGs), with greater feedback inhibition than IFNα.

Global virus outbreaks: Interferons as 1st responders

Outbreaks of severe virus infections with the potential to cause global pandemics are increasing. In many instances these outbreaks have been newly emerging (SARS coronavirus), re-emerging (Ebola virus, Zika virus) or zoonotic (avian influenza H5N1) virus infections. In the absence of a targeted vaccine or a pathogen-specific antiviral, broad-spectrum antivirals would function to limit virus spread. Given the direct antiviral effects of type I interferons (IFNs) in inhibiting the replication of both DNA and RNA viruses at different stages of their replicative cycles, and the effects of type I IFNs on activating immune cell populations to clear virus infections, IFNs-α/β present as ideal candidate broad-spectrum antivirals.

Development of an anti-hepatitis B virus (HBV) agent through the structure-activity relationship of the interferon-like small compound CDM-3008

Hepatitis B, a viral infectious disease caused by hepatitis B virus (HBV), is a life-threatening disease that leads liver cirrhosis and liver cancer. Because the current treatments for HBV, such as an interferon (IFN) formulation or nucleoside/nucleotide analogues, are not sufficient, the development of a more effective agent for HBV is urgent required. CDM-3008 (1, 2-(2,4-bis(trifluoromethyl)imidazo[1,2-a][1,8]naphthyridin-8-yl)-1,3,4-oxadiazole) (RO8191)) is a small molecule with an imidazo[1,2-a][1,8]naphthyridine scaffold that shows anti-HCV activity with an IFN-like effect. Here, we report that 1 was also effective for HBV, although the solubility and metabolic stability were insufficient for clinical use. Through the structure-activity relationship (SAR), we discovered that CDM-3032 (11, N-(piperidine-4-yl)-2,4-bis(trifluoromethyl)imidazo[1,2-a][1,8]naphthyridine-8-carboxamide hydrochloride) was more soluble than 1 (>30 mg/mL for 11 versus 0.92 mg/mL for 1). In addition, the half-life period of 11 was dramatically improved in both mouse and human hepatic microsomes (T1/2, >120 min versus 58.2 min in mouse, and >120 min versus 34.1 min in human, for 11 and 1, respectively).

A potent prolyl tRNA synthetase inhibitor antagonizes Chikungunya and Dengue viruses

Arboviruses represent a group of pathogens that can spread efficiently throughout human populations by hematophagous arthropod vectors. The mosquito-borne (re)emerging Chikungunya and Dengue viruses belong to the alphavirus and flavivirus genus, respectively, with no approved therapeutics or safe vaccines for humans. Transmitted by the same vector Aedes spp., these viruses cause significant morbidity and mortality in endemic areas. Due to the increasing likelihood of co-circulation and co-infection with viruses, we aimed to identify a pharmacologically targetable host factor that can inhibit multiple viruses and show that a potent antagonist of prolyl tRNA synthetase (halofuginone) suppresses both Chikungunya and Dengue viruses. Host tRNA synthetase inhibition may signify an additional approach to combat present and future epidemic pathogens.

A novel compound which sensitizes BRAF wild-type melanoma cells to vemurafenib in a TRIM16-dependent manner

There is an urgent need for better therapeutic options for advanced melanoma patients, particularly those without the BRAFV600E/K mutation. In melanoma cells, loss of TRIM16 expression is a marker of cell migration and metastasis, while the BRAF inhibitor, vemurafenib, induces melanoma cell growth arrest in a TRIM16-dependent manner. Here we identify a novel small molecule compound which sensitized BRAF wild-type melanoma cells to vemurafenib. High throughput, cell-based, chemical library screening identified a compound (C012) which significantly reduced melanoma cell viability, with limited toxicity for normal human fibroblasts. When combined with the BRAFV600E/K inhibitor, vemurafenib, C012 synergistically increased vemurafenib potency in 5 BRAFWT and 4 out of 5 BRAFV600E human melanoma cell lines (Combination Index: CI < 1), and, dramatically reduced colony forming ability. In addition, this drug combination was significantly anti-tumorigenic in vivo in a melanoma xenograft mouse model. The combination of vemurafenib and C012 markedly increased expression of TRIM16 protein, and knockdown of TRIM16 significantly reduced the growth inhibitory effects of the vemurafenib and C012 combination. These findings suggest that the combination of C012 and vemurafenib may have therapeutic potential for the treatment of melanoma, and, that reactivation of TRIM16 may be an effective strategy for patients with this disease.

Dietary quercetin potentiates the antiproliferative effect of interferon-α in hepatocellular carcinoma cells through activation of JAK/STAT pathway signaling by inhibition of SHP2 phosphatase

Type I interferons (IFN-α/β) have broad and potent immunoregulatory and antiproliferative activities, which are negatively regulated by Src homology domain 2 containing tyrosine phosphatase-2 (SHP-2). Inhibition of SHP2 by small molecules may be a new strategy to enhance the effcacy of type I IFNs. Using an in vitro screening assay for new inhibitors of SHP2 phosphatase, we found that quercetin was a potent inhibitor of SHP2. Computational modeling showed that quercetin exhibited an orientation favorable to nucleophilic attack in the phosphatase domain of SHP2. Quercetin enhanced the phosphorylation of signal transducer and activator of transcription proteins 1 (STAT1) and promoted endogenous IFN-α-regulated gene expression. Furthermore, quercetin also sensitized the antiproliferative effect of IFN-α on hepatocellular carcinoma HepG2 and Huh7 cells. The overexpression of SHP2 attenuated the effect of quercetin on IFN-α-stimulated STAT1 phosphorylation and antiproliferative effect, whereas the inhibition of SHP2 promoted the effect of quercetin on IFN-α-induced STAT1 phosphorylation and antiproliferative effect. The results suggested that quercetin potentiated the inhibitory effect of IFN-α on cancer cell proliferation through activation of JAK/STAT pathway signaling by inhibiting SHP2. Quercetin warrants further investigation as a novel therapeutic method to enhance the efficacy of IFN-α/β.

Identification of a small molecule that primes the type I interferon response to cytosolic DNA

The type I interferon response plays a pivotal role in host defense against infectious agents and tumors, and promising therapeutic approaches rely on small molecules designed to boost this system. To identify such compounds, we developed a high-throughput screening assay based on HEK-293 cells expressing luciferase under the control of Interferon-Stimulated Response Elements (ISRE). An original library of 10,000 synthetic compounds was screened, and we identified a series of 1H-benzimidazole-4-carboxamide compounds inducing the ISRE promoter sequence, specific cellular Interferon-Stimulated Genes (ISGs), and the phosphorylation of Interferon Regulatory Factor (IRF) 3. ISRE induction by ChX710, a prototypical member of this chemical series, was dependent on the adaptor MAVS and IRF1, but was IRF3 independent. Although it was unable to trigger type I IFN secretion per se, ChX710 efficiently primed cellular response to transfected plasmid DNA as assessed by potent synergistic effects on IFN-β secretion and ISG expression levels. This cellular response was dependent on STING, a key adaptor involved in the sensing of cytosolic DNA and immune activation by various pathogens, stress signals and tumorigenesis. Our results demonstrate that cellular response to cytosolic DNA can be boosted with a small molecule, and potential applications in antimicrobial and cancer therapies are discussed.

Generation and characterization of monoclonal antibodies against human LGR6

Leucine-rich repeat-containing G protein-coupled receptor 6 (LGR6) is a seven-pass transmembrane protein known to be a marker of stem cells in several organs. To deepen our understanding of the cell biology of LGR6-positive cells, including stem cells, we generated monoclonal antibodies (mAbs) against human LGR6. DNA immunization followed by whole-cell immunization with LGR6-expressing transfectants was performed to obtain mAbs that recognized the native form of LGR6. Hybridomas were screened by flow cytometry using LGR6-transfected cells. Because the molecules of LGR4, LGR5, and LGR6 are 50% homologous at the amino acid level, specificity of the mAbs was confirmed by transfectants expressing LGR4, LGR5, or LGR6. Three LGR6-specific mAbs were generated. Two of the three mAbs (designated 43A6 and 43D10) recognized the large N-terminal extracellular domain of LGR6, and competitively blocked the binding of R-spondin 1, which is known to be the ligand for LGR6. The other mAb, 43A25, recognized the seven-pass transmembrane domain of LGR6, and was able to be used for immunoblot analysis. In addition, mAbs 43A6 and 43D10 detected endogenous expression of LGR6 in cancer cell lines. We expect that our mAbs will contribute to widening our understanding of LGR6-positive cells in humans.

Emodin potentiates the antiproliferative effect of interferon α/β by activation of JAK/STAT pathway signaling through inhibition of the 26S proteasome

The 26S proteasome is a negative regulator of type I interferon (IFN-α/β) signaling. Inhibition of the 26S proteasome by small molecules may be a new strategy to enhance the efficacy of type I IFNs and reduce their side effects. Using cell-based screening assay for new 26S proteasome inhibitors, we found that emodin, a natural anthraquinone, was a potent inhibitor of the human 26S proteasome. Emodin preferably inhibited the caspase-like and chymotrypsin-like activities of the human 26S proteasome and increased the ubiquitination of endogenous proteins in cells. Computational modeling showed that emodin exhibited an orientation/conformation favorable to nucleophilic attack in the active pocket of the β1, β2, and β5 subunits of the 26S proteasome. Emodin increased phosphorylation of STAT1, decreased phosphorylation of STAT3 and increased endogenous gene expression stimulated by IFN-α. Emodin inhibited IFN-α-stimulated ubiquitination and degradation of type I interferon receptor 1 (IFNAR1). Emodin also sensitized the antiproliferative effect of IFN-α in HeLa cervical carcinoma cells and reduced tumor growth in Huh7 hepatocellular carcinoma-bearing mice. These results suggest that emodin potentiates the antiproliferative effect of IFN-α by activation of JAK/STAT pathway signaling through inhibition of 26S proteasome-stimulated IFNAR1 degradation. Therefore, emodin warrants further investigation as a new means to enhance the efficacy of IFN-α/β.

Dietary apigenin potentiates the inhibitory effect of interferon-α on cancer cell viability through inhibition of 26S proteasome-mediated interferon receptor degradation

Background

Type I interferons (IFN-α/β) have broad and potent immunoregulatory and antiproliferative activities. However, it is still known whether the dietary flavonoids exhibit their antiviral and anticancer properties by modulating the function of type I IFNs.

Objective

This study aimed at determining the role of apigenin, a dietary plant flavonoid abundant in common fruits and vegetables, on the type I IFN-mediated inhibition of cancer cell viability.

Design

Inhibitory effect of apigenin on human 26S proteasome, a known negative regulator of type I IFN signaling, was evaluated in vitro. Molecular docking was conducted to know the interaction between apigenin and subunits of 26S proteasome. Effects of apigenin on JAK/STAT pathway, 26S proteasome-mediated interferon receptor stability, and cancer cells viability were also investigated.

Results

Apigenin was identified to be a potent inhibitor of human 26S proteasome in a cell-based assay. Apigenin inhibited the chymotrypsin-like, caspase-like, and trypsin-like activities of the human 26S proteasome and increased the ubiquitination of endogenous proteins in cells. Results from computational modeling of the potential interactions of apigenin with the chymotrypsin site (β5 subunit), caspase site (β1 subunit), and trypsin site (β2 subunit) of the proteasome were consistent with the observed proteasome inhibitory activity. Apigenin enhanced the phosphorylation of signal transducer and activator of transcription proteins (STAT1 and STAT2) and promoted the endogenous IFN-α-regulated gene expression. Apigenin inhibited the IFN-α-stimulated ubiquitination and degradation of type I interferon receptor 1 (IFNAR1). Apigenin also sensitized the inhibitory effect of IFN-α on viability of cervical carcinoma HeLa cells.

Conclusion

These results suggest that apigenin potentiates the inhibitory effect of IFN-α on cancer cell viability by activating JAK/STAT signaling pathway through inhibition of 26S proteasome-mediated IFNAR1 degradation. This may provide a novel mechanism for increasing the efficacy of IFN-α/β.

Small Molecule Agonists for the Type I Interferon Receptor: An In Silico Approach

Type I interferons (IFNs) exhibit broad-spectrum antiviral activity, with potential utility against emerging acute virus infections that pose a threat to global health. Recombinant IFN-αs that have been approved for clinical use require cold storage and are administered through intramuscular or subcutaneous injection, features that are problematic for global distribution, storage, and administration. Cognizant that the biological potency of an IFN-α subtype is determined by its binding affinity to the type I IFN receptor, IFNAR, we identified a panel of small molecule nonpeptide compounds using an in silico screening strategy that incorporated specific structural features of amino acids in the receptor-binding domains of the most potent IFN-α, IFN alfacon-1. Hit compounds were selected based on ease of synthesis and formulation properties. In preliminary biological assays, we provide evidence that these compounds exhibit antiviral activity. This proof-of-concept study validates the strategy of in silico design and development for IFN mimetics.

[Stimulating Type I interferon response with small molecules: revival of an old idea]

Type I interferons play a central role in the establishment of an innate immune response against viral infections and tumor cells. Shortly after their discovery in 1957, several groups have looked for small molecules capable of inducing the expression of these cytokines with therapeutic applications in mind. A set of active compounds in mice were identified, but because of their relative inefficiency in humans for reasons not understood at the time, these studies fell into oblivion. In recent years, the characterization of pathogen recognition receptors and the signaling pathways they activate, together with the discovery of plasmacytoid dendritic cells, have revolutionized our understanding of innate immunity. These discoveries and the popularization of high-throughput screening technologies have renewed the interest for small molecules that can induce type I interferons. Proofs about their therapeutic potency in humans are expected very soon.

Discovery of Imidazo[1,2-α][1,8]naphthyridine Derivatives as Potential HCV Entry Inhibitor

RO8191 represents a newly discovered small-molecule IFN-like agent that displays potent anti-HCV activity. With it as lead, a series of compounds bearing an imidazo[1,2-α][1,8]naphthyridine core and an amide bond-linked side chain were designed and synthesized. These compounds were evaluated on HCV cell culture system (HCVcc-hRluc-JFH1), and some of them exhibited remarkable anti-HCV activity (EC50 = 0.017-0.159 μM) and low toxicity (CC50 > 25 μM). Moreover, it was revealed that these newly identified anti-HCV agents exert their antiviral effect through a distinct mechanism of action from that of RO8191 by targeting the viral entry process. Thus, our study provides a starting point for the development of potential HCV entry inhibitor.

p-Type mesoscopic NiO as an active interfacial layer for carbon counter electrode based perovskite solar cells

Replacement of the ZrO₂insulator layer in the state-of-the-art TiO₂/ZrO₂/carbon structure by mesoscopic p-type NiO particles led to 39% increase of energy conversion efficiency of perovskite solar cells.

Design and synthesis of imidazo[1,2-α][1,8]naphthyridine derivatives as anti-HCV agents via direct C-H arylation

RO8191 represents a newly identified small-molecule IFN-α-substitute, which displays potent anti-HCV activity. In this communication, we reported the design and synthesis of two series of imidazo[1,2-α][1,8]naphthyridine derivatives, as RO8191 analogues, via a direct C-H arylation approach. Notably, by adjusting the reaction conditions, we could achieve the two series of analogues via regioselective single- and double-arylations, respectively. The anti-HCV activities of the synthesized compounds were evaluated within the HCV cell culture system, and the preliminary results showed that some of them displayed promising anti-HCV activities.

Hepatic interferon-gamma-induced protein-10 expression is more strongly associated with liver fibrosis than interleukin-28B single nucleotide polymorphisms in hepatocellular carcinoma resected patients with chronic hepatitis C

AIM

Single nucleotide polymorphisms (SNP) around IL-28B and interferon (IFN)-stimulated gene (ISG) expression are predictors of response to standard therapy involving IFN for chronic hepatitis C virus (HCV) infection. We analyzed the association between these predictors to improve the prediction of the response to IFN therapy after liver resection for hepatocellular carcinoma (HCC).

METHODS

Data were collected from 74 patients with HCV-induced HCC. The IL-28B genotype and hepatic ISG mRNA levels were analyzed to clarify their association, focusing on the progression of liver fibrosis.

RESULTS

Fifty patients were identified as having major alleles (rs8099917 TT) and the remaining 24 patients had minor alleles (rs8099917 TG or GG). Hepatic ISG15 expression was lower in the IL-28B major group than that in the IL-28B minor group (P < 0.005). IP-10 expression was similar between the IL-28B major and minor groups (P = 0.44). IP-10 expression was elevated with advancing stages of liver fibrosis in HCV infected patients (P = 0.005). In patients with mild or no fibrosis, the IL-28B major group had lower IP-10 expression than the IL-28B minor group (P = 0.02). However, in patients with advanced fibrosis, IP-10 expression was not different between the IL-28B major and minor groups (P = 0.66).

CONCLUSION

Hepatic ISG15 expression is associated with IL-28B polymorphisms, while IP-10 is strongly affected by liver fibrosis.

Oral administration of pentachlorophenol induces interferon signaling mRNAs in C57BL/6 male mouse liver

Pentachlorophenol (PCP) was monitored for transcriptome responses in adult mouse liver at 2, 4, 8 and 24 hr after a single oral administration at four dose levels, 0, 10, 30 and 100 mg/kg. The expression data obtained using Affymetrix GeneChip MOE430 2.0 were absolutized by the Percellome method and expressed as three dimensional (3D) surface graphs with axes of time, dose and copy numbers of mRNA per cell. We developed the programs RSort, for comprehensive screening of the 3D surface data and PercellomeExploror for cross-referencing and confirmed the significant responses by visual inspection. In the first 8 hr, approximately 100 probe sets (PSs) related to PXR/SXR and Cyp2a4 and other metabolic enzymes were induced whereas Fos and JunB were suppressed. At 24 hr, about 1,200 PSs were strongly induced. We cross-referenced the Percellome database consisting of 111 chemicals on the liver transcriptome and found that about half of the PSs belonged to the metabolic pathways including Nrf2-mediated oxidative stress response networks shared with some of the 111 chemicals. The other half of the induced genes were interferon signaling network genes (ISG) and their induction was unique to PCP. Toll like receptors and other pattern recognition receptors, interferon regulatory factors and interferon alpha itself were included but inflammatory cytokines were not induced. In summary, these data indicated that functional symptoms of PCP treatment, such as hyperthermia and profuse sweating might be mediated by the ISG rather than the previously documented mitochondrial uncoupling mechanism. PCP might become a hint for developing low molecular weight orally available interferon mimetic drugs following imiquimod and RO4948191 as agonists of toll-like receptor and interferon receptor.

Inhibition of pyrimidine biosynthesis pathway suppresses viral growth through innate immunity

Searching for stimulators of the innate antiviral response is an appealing approach to develop novel therapeutics against viral infections. Here, we established a cell-based reporter assay to identify compounds stimulating expression of interferon-inducible antiviral genes. DD264 was selected out of 41,353 compounds for both its immuno-stimulatory and antiviral properties. While searching for its mode of action, we identified DD264 as an inhibitor of pyrimidine biosynthesis pathway. This metabolic pathway was recently identified as a prime target of broad-spectrum antiviral molecules, but our data unraveled a yet unsuspected link with innate immunity. Indeed, we showed that DD264 or brequinar, a well-known inhibitor of pyrimidine biosynthesis pathway, both enhanced the expression of antiviral genes in human cells. Furthermore, antiviral activity of DD264 or brequinar was found strictly dependent on cellular gene transcription, nuclear export machinery, and required IRF1 transcription factor. In conclusion, the antiviral property of pyrimidine biosynthesis inhibitors is not a direct consequence of pyrimidine deprivation on the virus machinery, but rather involves the induction of cellular immune response.

Our therapeutic arsenal to treat viral diseases is extremely limited, and there is a critical need for molecules that could be used against multiple viruses. Among possible strategies, there is a growing interest for molecules stimulating cellular defense mechanisms. We recently developed a functional assay to identify stimulators of antiviral genes, and selected compound DD264 from a chemical library using this approach. While searching for its mode of action, we identified this molecule as an inhibitor of pyrimidine biosynthesis, a metabolic pathway that fuels the cell with pyrimidine nucleobases for both DNA and RNA synthesis. Interestingly, it was recently shown that inhibitors of this metabolic pathway prevent the replication of RNA viruses. Here, we established a functional link between pyrimidine biosynthesis pathway and the induction of antiviral genes, and demonstrated that pyrimidine biosynthesis inhibitors like DD264 or brequinar critically rely on cellular immune response to inhibit virus growth. Thus, pyrimidine deprivation is not directly responsible for the antiviral activity of pyrimidine biosynthesis inhibitors, which rather involves the induction of a metabolic stress and subsequent triggering of cellular defense mechanisms.

IFNβ autocrine feedback is required to sustain TLR induced production of MCP-1 in macrophages

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MCP-1 mRNA levels and protein secretion in macrophages are induced by TLR activation.

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In response to LPS, the initial induction of MCP-1 mRNA is IFNβ independent.

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The sustained production of MCP-1 by LPS requires an IFNβ mediated feedback loop.

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The sustained production of MCP-1 by poly IC also requires IFNβ.

Chemokines, including MCP-1, are crucial to mounting an effective immune response due to their ability to recruit other immune cells. We show that sustained LPS or poly(I:C)-stimulated MCP-1 production requires an IFNβ-mediated feedback loop. Consistent with this, exogenous IFNβ was able to induce MCP-1 transcription in the absence of other stimuli. Blocking IFNβ signaling with Ruxolitinib, a JAK inhibitor, inhibited MCP-1 transcription. The MCP-1 promoter contains potential STAT binding sites and we demonstrate that STAT1 is recruited upon IFNβ stimulation. Furthermore we find that IL-10 knockout increases MCP-1 production in response to LPS, which may reflect an ability of IL-10 to repress IFNβ production. Overall, these results show the importance of the balance between IFNβ and IL-10 in the regulation of MCP-1.

Antiviral activity of the interferon α family: biological and pharmacological aspects of the treatment of chronic hepatitis C

INTRODUCTION

Type I interferons (IFNs) comprise a group of at least 13 structurally related subtypes of IFN-α with similar, but not identical, biological activities. Each subtype displays a unique activity profile; only IFN-α2a and IFN-α2b subtypes together with natural IFN-α preparations are currently used in the clinical practice, so that the remaining IFN-α subtypes are a still unexploited reservoir of opportunity also in the new era of direct-acting antiviral agents for the treatment of hepatitis C virus (HCV).

AREAS COVERED

This paper reviews recent progress in the study of the biology of IFN family, the antiviral action mechanism and the strategies employed by HCV to evade IFN action. Currently available IFN preparations for the treatment of chronic hepatitis C infection are described and what is currently known on the pharmacokinetics, pharmacodynamics and immunogenicity of IFN-α preparations used in clinical practice are summarized.

EXPERT OPINION

The characterization of multifunctional nature of IFN system together with recent advances in the identification of HCV IFN evasion strategies and the variety of host factors influencing IFN treatment response should be considered to improve HCV and other infectious diseases treatment in the future.

The application and mechanism of action of ribavirin in therapy of hepatitis C

Ribavirin has been used as an antiviral agent for several decades. Although it has activity against numerous viruses, its major use clinically has been in the treatment of respiratory syncytial virus in paediatric patients and chronic HCV infection in both children and adults. This review highlights the clinical application and mechanism of action of ribavirin and discusses the future role of ribavirin in treatment of HCV where there are intense research efforts to improve therapy.