Construction of a macrophage-tropic subtype C HIV-1 mGreenLantern reporter virus for studies on HIV-1 replication and the impact of methamphetamine.

HIV-1 subtype C viruses are responsible for 50% of global HIV burden. However, nearly all currently available reporter viruses widely used in HIV research are based on subtype B. We constructed and characterized a replication competent HIV-1 subtype C reporter virus expressing mGreenLantern. mGreenLantern sequences were inserted in-frame with nef ATG in HIV-1 IndieC1 . As controls, we employed HIV-1 IndieC1 , HIV-1 ADA, and HIV-1 NLAD8-GFP-Nef viruses. HIV-1 IndieC1-mGreenLantern (HIV-1 IndieC1-mGL ) exhibited characteristics of the parental HIV-1 IndieC1 virus, including its infectivity in TZMbl reporter cells and replication competence in macrophages. To further characterize HIV-1 IndieC1-mGL virus, we tested its responsiveness to CCL2 levels, a characteristic feature of subtype B HIV-1 that is missing in subtype C. CCL2 immunodepletion inhibited the production of HIV-1 ADA and HIV-1 NLAD8-GFP-Nef as expected, but not that of HIV-1 IndieC1-mGL as previously reported. We also tested the effect of Methamphetamine, as its effect is mediated by NF-κB and since subtype C viruses carry an additional copy of NFκB. We found that methamphetamine increased the replication of all viruses tested in macrophages, however, its effect was much more robust for HIV-1 IndieC1 and HIV-1 IndieC1-mGL . Our studies established that HIV-1 IndieC1-mGL retains all the characteristics of the parental HIV-1 IndieC1 and can be a useful tool for HIV-1 subtype C investigations.

An In Vitro Model of Blood-Brain Barrier for Studies on HIV Neuroinflammation and CNS Antibody Penetration.

The blood-brain barrier (BBB) is one of several barriers between the brain and the peripheral blood system to maintain homeostasis. Understanding the interactions between infectious agents such as human immunodeficiency virus type 1 (HIV-1), which are capable of traversing the BBB and causing neuroinflammation requires modeling an authentic BBB in vitro. Such an in vitro BBB model also helps develop means of targeting viruses that reside in the brain via natural immune effectors such as antibodies. The BBB consists of human brain microvascular endothelial cells (HBMECs), astrocytes, and pericytes. Here we report in vitro methods to establish a dual-cell BBB model consisting of primary HBMECs and primary astrocytes to measure the integrity of the BBB and antibody penetration of the BBB, as well as a method to establish a single cell BBB model to study the impact of HIV-1 infected medium on the integrity of such a BBB.

In vitro and in vivo characterization of erythrosin B and derivatives against Zika virus.

Zika virus (ZIKV) causes significant human diseases without specific therapy. Previously we found erythrosin B, an FDA-approved food additive, inhibited viral NS2B-NS3 interactions, leading to inhibition of ZIKV infection in cell culture. In this study, we performed pharmacokinetic and in vivo studies to demonstrate the efficacy of erythrosin B against ZIKV in 3D mini-brain organoid and mouse models. Our results showed that erythrosin B is very effective in abolishing ZIKV replication in the 3D organoid model. Although pharmacokinetics studies indicated that erythrosin B had a low absorption profile, mice challenged by a lethal dose of ZIKV showed a significantly improved survival rate upon oral administration of erythrosin B, compared to vehicle control. Limited structure-activity relationship studies indicated that most analogs of erythrosin B with modifications on the xanthene ring led to loss or reduction of inhibitory activities towards viral NS2B-NS3 interactions, protease activity and antiviral efficacy. In contrast, introducing chlorine substitutions on the isobenzofuran ring led to slightly increased activities, suggesting that the isobenzofuran ring is well tolerated for modifications. Cytotoxicity studies indicated that all derivatives are nontoxic to human cells. Overall, our studies demonstrated erythrosin B is an effective antiviral against ZIKV both in vitro and in vivo.

Bat influenza vectored NS1-truncated live vaccine protects pigs against heterologous virus challenge.

Swine influenza is an important disease for the swine industry. Currently used whole inactivated virus (WIV) vaccines can induce vaccine-associated enhanced respiratory disease (VAERD) in pigs when the vaccine strains mismatch with the infected viruses. Live attenuated influenza virus vaccine (LAIV) is effective to protect pigs against homologous and heterologous swine influenza virus infections without inducing VAERD but has safety concerns due to potential reassortment with circulating viruses. Herein, we used a chimeric bat influenza Bat09:mH3mN2 virus, which contains both surface HA and NA gene open reading frames of the A/swine/Texas/4199-2/1998 (H3N2) and six internal genes from the novel bat H17N10 virus, to develop modified live-attenuated viruses (MLVs) as vaccine candidates which cannot reassort with canonical influenza A viruses by co-infection. Two attenuated MLV vaccine candidates including the virus that expresses a truncated NS1 (Bat09:mH3mN2-NS1-128, MLV1) or expresses both a truncated NS1 and the swine IL-18 (Bat09:mH3mN2-NS1-128-IL-18, MLV2) were generated and evaluated in pigs against a heterologous H3N2 virus using the WIV vaccine as a control. Compared to the WIV vaccine, both MLV vaccines were able to reduce lesions and virus replication in lungs and limit nasal virus shedding without VAERD, also induced significantly higher levels of mucosal IgA response in lungs and significantly increased numbers of antigen-specific IFN-γ secreting cells against the challenge virus. However, no significant difference was observed in efficacy between the MLV1 and MLV2. These results indicate that bat influenza vectored MLV vaccines can be used as a safe live vaccine to prevent swine influenza.

Small-molecule inhibitors for the Prp8 intein as antifungal agents.

Self-splicing proteins, called inteins, are present in many human pathogens, including the emerging fungal threats Cryptococcus neoformans (Cne) and Cryptococcus gattii (Cga), the causative agents of cryptococcosis. Inhibition of protein splicing in Cryptococcus sp. interferes with activity of the only intein-containing protein, Prp8, an essential intron splicing factor. Here, we screened a small-molecule library to find addititonal, potent inhibitors of the Cne Prp8 intein using a split-GFP splicing assay. This revealed the compound 6G-318S, with IC50 values in the low micromolar range in the split-GFP assay and in a complementary split-luciferase system. A fluoride derivative of the compound 6G-318S displayed improved cytotoxicity in human lung carcinoma cells, although there was a slight reduction in the inhibition of splicing. 6G-318S and its derivative inhibited splicing of the Cne Prp8 intein in vivo in Escherichia coli and in C. neoformans Moreover, the compounds repressed growth of WT C. neoformans and C. gattii In contrast, the inhibitors were less potent at inhibiting growth of the inteinless Candida albicans Drug resistance was observed when the Prp8 intein was overexpressed in C. neoformans, indicating specificity of this molecule toward the target. No off-target activity was observed, such as inhibition of serine/cysteine proteases. The inhibitors bound covalently to the Prp8 intein and binding was reduced when the active-site residue Cys1 was mutated. 6G-318S showed a synergistic effect with amphotericin B and additive to indifferent effects with a few other clinically used antimycotics. Overall, the identification of these small-molecule intein-splicing inhibitors opens up prospects for a new class of antifungals.

The nucleocapsid protein of zoonotic betacoronaviruses is an attractive target for antiviral drug discovery.

Betacoronaviruses are in one genera of coronaviruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome-related coronavirus (MERS-CoV), etc. These viruses threaten public health and cause dramatic economic losses. The nucleocapsid (N) protein is a structural protein of betacoronaviruses with multiple functions such as forming viral capsids with viral RNA, interacting with viral membrane protein to form the virus core with RNA, binding to several cellular kinases for signal transductions, etc. In this review, we highlighted the potential of the N protein as a suitable antiviral target from different perspectives, including structure, functions, and antiviral strategies for combatting betacoronaviruses.

Methylene blue is a potent and broad-spectrum inhibitor against Zika virus in vitro and in vivo.

Many flaviviruses including the Dengue virus (DENV), Zika virus (ZIKV), West Nile virus, Yellow Fever virus, and Japanese encephalitis virus are significant human pathogens, unfortunately without any specific therapy. Here, we demonstrate that methylene blue, an FDA-approved drug, is a broad-spectrum and potent antiviral against Zika virus and Dengue virus both in vitro and in vivo. We found that methylene blue can considerably inhibit the interactions between viral protease NS3 and its NS2B co-factor, inhibit viral protease activity, inhibit viral growth, protect 3D mini-brain organoids from ZIKV infection, and reduce viremia in a mouse model. Mechanistic studies confirmed that methylene blue works in both entry and post entry steps, reduces virus production in replicon cells and inhibited production of processed NS3 protein. Overall, we have shown that methylene blue is a potent antiviral for management of flavivirus infections, particularly for Zika virus. As an FDA-approved drug, methylene blue is well-tolerated for human use. Therefore, methylene blue represents a promising and easily developed therapy for management of infections by ZIKV and other flaviviruses.

JMX0207, a Niclosamide Derivative with Improved Pharmacokinetics, Suppresses Zika Virus Infection Both In Vitro and In Vivo.

Flaviviruses causes significant human disease. Recent outbreaks of the Zika virus highlight the need to develop effective therapies for this class of viruses. Previously we identified niclosamide as a broad-spectrum inhibitor for flaviviruses by targeting the interface between viral protease NS3 and its cofactor NS2B. Here, we screened a small library of niclosamide derivatives and identified a new analogue with improved pharmacokinetic properties. Compound JMX0207 showed improved efficacy in inhibition of the molecular interaction between NS3 and NS2B, better inhibition of viral protease function, and enhanced antiviral efficacy in the cell-based antiviral assay. The derivative also significantly reduced Zika virus infection on 3D mini-brain organoids derived from pluripotent neural stem cells. Intriguingly, the compound significantly reduced viremia in a Zika virus (ZIKV) animal model. In summary, a niclosamide derivative, JMX0207, was identified, which shows improved pharmacokinetics and efficacy against Zika virus both in vitro and in vivo.

Analysis of Protein-Protein Interactions by Split Luciferase Complementation Assay.

Protein-protein interactions are important in human disease. Developing and refining tools to understand physical contacts between signaling proteins is crucial. This article describes a split luciferase complementation (SLC) method designed to discover inhibitors of protein-protein interaction. Different fusion proteins with split luciferase are constructed, expressed, and purified, and then assessed to determine the best pair that generates the strongest luminescence. SLC specificity and affinity are further confirmed. Step-by-step instructions are provided for performing these assays using the NS2B-NS3 interaction as an example. NS2B is an essential cofactor for flaviviral NS3 protease function. Advantages and disadvantages of these assays are further discussed. © 2019 by John Wiley & Sons, Inc. Basic Protocol 1: Expression and purification of fusion proteins Basic Protocol 2: Analysis of prey/bait pairs by SLC-based NS2B-NS3 interaction assay Support Protocol 1: Interaction specificity assay Support Protocol 2: Competition binding assay: Dose-response inhibition using cold prey or bait Support Protocol 3: Competition binding assay: Inhibition by MBP-NS3 versus irrelevant MBP tag Support Protocol 4: SLC-based NS2B-NS3 interaction assay using NS2B mutations known to disrupt NS2B-NS3 interactions.

Comparison of Pathogenicity and Transmissibility of Influenza B and D Viruses in Pigs.

Influenza viruses are important pathogens causing respiratory disease in humans and animals. In contrast to influenza A virus (IAV) that can infect a wide range of animal species, other influenza viruses, including influenza B virus (IBV), influenza C virus (ICV), and influenza D virus (IDV) have a limited host range. Swine can be infected with all four different genera of influenza viruses. IAV infection of pigs causes the well-known swine influenza that poses significant threats to human and animal health. However, influenza virus infection of pigs with IBV, ICV, and IDV are not well-characterized. Herein, we compared pathogenicity of IBV and IDV using intratracheal and intranasal infection of pigs, which are IAV seropositive, and commingled naïve pigs with the infected animals to determine their transmissibility. Both viruses caused fever and some lung lesions, replicated in the lungs of infected pigs, but only IDV transmitted to the contact animals. Although IBV and IDV displayed differing levels of replication in the respiratory tract of infected pigs, no significant differences in pathogenicity of both viruses were observed. These results indicate that both IBV and IDV can replicate, and are pathogenic in pigs.

Cisplatin protects mice from challenge of Cryptococcus neoformans by targeting the Prp8 intein.

The Prp8 intein is one of the most widespread eukaryotic inteins, present in important pathogenic fungi, including Cryptococcus and Aspergillus species. Because the processed Prp8 carries out essential and non-redundant cellular functions, a Prp8 intein inhibitor is a mechanistically novel antifungal agent. In this report, we demonstrated that cisplatin, an FDA-approved cancer drug, significantly arrested growth of Prp8 intein-containing fungi C. neoformans and C. gattii, but only poorly inhibited growth of intein-free Candida species. These results suggest that cisplatin arrests fungal growth through specific inhibition of the Prp8 intein. Cisplatin was also found to significantly inhibit growth of C. neoformans in a mouse model. Our results further showed that cisplatin inhibited Prp8 intein splicing in vitro in a dose-dependent manner by direct binding to the Prp8 intein. Crystal structures of the apo- and cisplatin-bound Prp8 inteins revealed that two degenerate cisplatin molecules bind at the intein active site. Mutation of the splicing-site residues led to loss of cisplatin binding, as well as impairment of intein splicing. Finally, we found that overexpression of the Prp8 intein in cryptococcal species conferred cisplatin resistance. Overall, these results indicate that the Prp8 intein is a novel antifungal target worth further investigation.

Development of a multiplex real-time RT-PCR assay for simultaneous detection and differentiation of influenza A, B, C, and D viruses.

Influenza is a common and contagious respiratory disease caused by influenza A, B, C, and D viruses (IAV, IBV, ICV, and IDV). A multiplex real-time RT-PCR assay was developed for simultaneous detection of IAV, IBV, ICV, and IDV. The assay was designed to target unique sequences in the matrix gene of IBV and ICV, the RNA polymerase subunit PB1 of IDV, and combined with USDA and CDC IAV assays, both target the matrix gene. The host 18S rRNA gene was included as an internal control. In silico analyses indicated high strain coverages: 97.9% for IBV, 99.5% for ICV, and 100% for IDV. Transcribed RNA, viral isolates and clinical samples were used for validation. The assay specifically detected target viruses without cross-reactivity, nor detection of other common pathogens. The limit of detection was approximately 30 copies for each viral RNA template, which was equivalent to a threshold cycle value of ~37.

Virus survival and fitness when multiple genotypes and subtypes of influenza A viruses exist and circulate in swine.

We performed swine influenza virus (SIV) surveillance in Midwest USA and isolated 100 SIVs including endemic and reassortant H1 and H3 viruses with 2009 pandemic H1N1 genes. To determine virus evolution when different genotypes and subtypes of influenza A viruses circulating in the same swine herd, a virus survival experiment was conducted in pigs mimicking field situations. Five different SIVs were used to infect five pigs individually, then two groups of sentinel pigs were introduced to investigate virus transmission. Results showed that each virus replicated efficiently in lungs of each infected pig, but only reassortant H3N2 and H1N2v viruses transmitted to the primary contact pigs. Interestingly, the parental H1N2v was the majority of virus detected in the second group of sentinel pigs. These data indicate that the H1N2v seems to be more viable in swine herds than other SIV genotypes, and reassortment can enhance viral fitness and transmission.

Identification and evaluation of antivirals for Rift Valley fever virus.

Rift Valley fever virus (RVFV) is the causative agent of Rift Valley fever (RVF) that affects both livestock and humans. There are neither fully licensed RVF vaccines available for human or animal use, nor effective antiviral drugs approved for human use in the U.S. To identify antiviral compounds effective for RVF, we developed and employed a cell-based high-throughput assay using a recombinant RVFV MP-12 strain, which expresses Renilla luciferase in place of the NSs protein, to screen 727 small compounds purchased from the National Institutes of Health. Twenty-three compounds were initially identified using the screening assay. Two compounds, 6-azauridine and mitoxantrone, also inhibited the replication of the parental MP-12 strain encoding the NSs gene, with limited cytotoxic effects. The respective 50% inhibitory concentrations were 29.07 µM and 79.85 µM when tested with the parental MP-12 strain at a multiplicity of infection of 2. The compounds were further evaluated using the STAT-1 KO mouse model. At one hour post intranasal inoculation of MP-12 strain, mice were intranasally treated with each indicated compound twice daily. Mice treated with either placebo or 6-azauridine displayed severe weight loss and reached the threshold for euthanasia with obvious neurologic symptoms. Onset of disease was, however, delayed in mice treated with either ribavirin or mitoxantrone. The results indicated that mitoxantrone can reduce the severity of diseases in RVFV-infected mice. Our studies build the foundation for the initial screening and efficacy studies of RVF antivirals in a BSL-2 environment, avoiding the higher risks of BSL-3 exposure with wild-type virus.

Erratum: Author Correction: Newcastle disease virus-based H5 influenza vaccine protects chickens from lethal challenge with a highly pathogenic H5N2 avian influenza virus.

[This corrects the article DOI: 10.1038/s41541-017-0034-4.].

Newcastle disease virus-based H5 influenza vaccine protects chickens from lethal challenge with a highly pathogenic H5N2 avian influenza virus.

Since December 2014, Eurasian-origin, highly pathogenic avian influenza H5 viruses including H5N1, H5N2, and H5N8 subtypes (called H5Nx viruses), which belong to the H5 clade 2.3.4.4, have been detected in U.S. wild birds. Subsequently, highly pathogenic H5N2 and H5N8 viruses have caused outbreaks in U.S. domestic poultry. Vaccination is one of the most effective ways to control influenza outbreaks and protect animal and public health. Newcastle disease virus (NDV)-based influenza vaccines have been demonstrated to be efficacious and safe in poultry. Herein, we developed an NDV-based H5 vaccine (NDV-H5) that expresses a codon-optimized ectodomain of the hemagglutinin from the A/chicken/Iowa/04-20/2015 (H5N2) virus and evaluated its efficacy in chickens. Results showed that both live and inactivated NDV-H5 vaccines induced hemagglutinin inhibition antibody titers against the H5N2 virus in immunized chickens after prime and booster, and both NDV-H5 vaccines completely protected chickens from lethal challenge with the highly pathogenic H5N2 A/turkey/Minnesota/9845-4/2015 virus. No clinical signs and only minimal virus shedding was observed in both vaccinated groups. In contrast, all mock-vaccinated, H5N2-infected chickens shed virus and died within 5 days post challenge. Furthermore, one dose of the live NDV-H5 vaccine also provided protection of 90% chickens immunized by coarse spraying; after exposure to H5N2 challenge, sera from vaccinated surviving chickens neutralized both highly pathogenic H5N1 and H5N8 viruses. Taken together, our results suggest that the NDV-based H5 vaccine is able to protect chickens against intercontinental highly pathogenic H5Nx viruses and can be used by mass application to protect the poultry industry.

Impacts of different expressions of PA-X protein on 2009 pandemic H1N1 virus replication, pathogenicity and host immune responses.

Although several studies have investigated the functions of influenza PA-X, the impact of different expressions of PA-X protein including full-length, truncated or PA-X deficient forms on virus replication, pathogenicity and host response remains unclear. Herein, we generated two mutated viruses expressing a full-length or deficient PA-X protein based on the A/California/04/2009 (H1N1) virus that expresses a truncated PA-X to understand three different expressions of PA-X protein on virus replication, pathogenicity and host immune responses. The results showed that expression of either full-length or truncated PA-X protein enhanced viral replication and pathogenicity as well as reduced host innate immune response in mice by host shutoff activity when compared to the virus expressing the deficient PA-X form. Furthermore, the full-length PA-X expression exhibited a greater effect on virus pathogenicity than the truncated PA-X form. Our results provide novel insights of PA-X on viral replication, pathogenicity and host immune responses.

Pathogenicity of modified bat influenza virus with different M genes and its reassortment potential with swine influenza A virus.

In our previous studies, the reassortant virus containing only the PR8 H1N1 matrix (M) gene in the background of the modified bat influenza Bat09 : mH1mN1 virus could be generated. However, whether M genes from other origins can be rescued in the background of the Bat09 : mH1mN1 virus and whether the resulting novel reassortant virus is virulent remain unknown. Herein, two reassortant viruses were generated in the background of the Bat09 : mH1mN1 virus containing either a North American or a Eurasian swine influenza virus M gene. These two reassortant viruses and the reassortant virus with PR8 M as well as the control Bat09 : mH1mN1 virus replicated efficiently in cultured cells, while the reassortant virus with PR8 M grew to a higher titre than the other three viruses in tested cells. Mouse studies showed that reassortant viruses with either North American or Eurasian swine influenza virus M gene did not enhance virulence, whereas the reassortant virus with PR8 M gene displayed higher pathogenicity when compared to the Bat09 : mH1mN1 virus. This is most likely due to the fact that the PR8 H1N1 virus is a mouse-adapted virus. Furthermore, reassortment potential between the Bat09 : mH1mN1 virus and an H3N2 swine influenza virus (A/swine/Texas/4199-2/1998) was investigated using co-infection of Madin-Darby canine kidney cells, but no reassortant viruses were detected. Taken together, our results indicate that the modified bat influenza virus is most likely incapable of reassortment with influenza A viruses with in vitro co-infection experiments, although reassortant viruses with different M genes can be generated by reverse genetics.

Effects of PB1-F2 on the pathogenicity of H1N1 swine influenza virus in mice and pigs.

Although several studies have exploited the effects of PB1-F2 in swine influenza viruses, its contribution to the pathogenicity of swine influenza viruses remains unclear. Herein, we investigated the effects of PB1-F2 on the pathogenicity of influenza virus using a virulent H1N1 A/swine/Kansas/77778/2007 (KS07) virus, which expresses a full-length PB1-F2, in mice and pigs. Using reverse genetics, we generated the wild-type KS07 (KS07_WT), a PB1-F2 knockout mutant (KS07_K/O) and its N66S variant (KS07_N66S). KS07_K/O showed similar pathogenicity in mice to the KS07_WT, whereas KS07_N66S displayed enhanced virulence when compared to the other two viruses. KS07_WT exhibited more efficient replication in lungs and nasal shedding in infected pigs than the other two viruses. Pigs infected with the KS07_WT had higher pulmonary levels of granulocyte-macrophage colony-stimulating factor, IFN-γ, IL-6 and IL-8 at 3 and 5 days post-infection, as well as lower levels of IL-2, IL-4 and IL-12 at 1 day post-infection compared to those infected with the KS07_K/O. These results indicate that PB1-F2 modulates KS07 H1N1 virus replication, pathogenicity and innate immune responses in pigs and the single substitution at position 66 (N/S) in the PB1-F2 plays a critical role in virulence in mice. Taken together, our results provide new insights into the effects of PB1-F2 on the virulence of influenza virus in swine and support PB1-F2 as a virulence factor of influenza A virus in a strain- and host-dependent manner.

Mouse model for the Rift Valley fever virus MP12 strain infection.

Rift Valley fever virus (RVFV), a Category A pathogen and select agent, is the causative agent of Rift Valley fever. To date, no fully licensed vaccine is available in the U.S. for human or animal use and effective antiviral drugs have not been identified. The RVFV MP12 strain is conditionally licensed for use for veterinary purposes in the U.S. which was excluded from the select agent rule of Health and Human Services and the U.S. Department of Agriculture. The MP12 vaccine strain is commonly used in BSL-2 laboratories that is generally not virulent in mice. To establish a small animal model that can be used in a BSL-2 facility for antiviral drug development, we investigated susceptibility of six mouse strains (129S6/SvEv, STAT-1 KO, 129S1/SvlmJ, C57BL/6J, NZW/LacJ, BALB/c) to the MP12 virus infection via an intranasal inoculation route. Severe weight loss, obvious clinical and neurologic signs, and 50% mortality was observed in the STAT-1 KO mice, whereas the other 5 mouse strains did not display obvious and/or severe disease. Virus replication and histopathological lesions were detected in brain and liver of MP12-infected STAT-1 KO mice that developed the acute-onset hepatitis and delayed-onset encephalitis. In conclusion, the STAT-1 KO mouse strain is susceptible to MP12 virus infection, indicating that it can be used to investigate RVFV antivirals in a BSL-2 environment.