Suppression of porcine reproductive and respiratory syndrome virus replication by morpholino antisense oligomers

Inhibition of SARS-CoV-2 growth in the lungs of mice by a peptide-conjugated morpholino oligomer targeting viral RNA

Further development of direct-acting antiviral agents against human SARS-CoV-2 infections remains a public health priority. Here, we report that an antisense peptide-conjugated morpholino oligomer (PPMO) named 5'END-2, targeting a highly conserved sequence in the 5' UTR of SARS-CoV-2 genomic RNA, potently suppressed SARS-CoV-2 growth in vitro and in vivo. In HeLa-ACE 2 cells, 5'END-2 produced IC50 values of between 40 nM and 1.15 μM in challenges using six genetically disparate strains of SARS-CoV-2, including JN.1. In vivo, using K18-hACE2 mice and the WA-1/2020 virus isolate, two doses of 5'END-2 at 10 mg/kg, administered intranasally on the day before and the day after infection, produced approximately 1.4 log10 virus titer reduction in lung tissue at 3 days post-infection. Under a similar dosing schedule, intratracheal administration of 1.0-2.0 mg/kg 5'END-2 produced over 3.5 log10 virus growth suppression in mouse lungs. Electrophoretic mobility shift assays characterized specific binding of 5'END-2 to its complementary target RNA. Furthermore, using reporter constructs containing SARS-CoV-2 5' UTR leader sequence, in an in-cell system, we observed that 5'END-2 could interfere with translation in a sequence-specific manner. The results demonstrate that direct pulmonary delivery of 5'END-2 PPMO is a promising antiviral strategy against SARS-CoV-2 infections and warrants further development.

Zika Virus Induces Degradation of the Numb Protein Required through Embryonic Neurogenesis

Zika virus (ZIKV) is a mosquito-borne flavivirus and causes an infection associated with congenital Zika syndrome and Guillain-Barre syndrome. The mechanism of ZIKV-mediated neuropathogenesis is not well understood. In this study, we discovered that ZIKV induces degradation of the Numb protein, which plays a crucial role in neurogenesis by allowing asymmetric cell division during embryonic development. Our data show that ZIKV reduced the Numb protein level in a time- and dose-dependent manner. However, ZIKV infection appears to have minimal effect on the Numb transcript. Treatment of ZIKV-infected cells with a proteasome inhibitor restores the Numb protein level, which suggests the involvement of the ubiquitin-proteasome pathway. In addition, ZIKV infection shortens the half-life of the Numb protein. Among the ZIKV proteins, the capsid protein significantly reduces the Numb protein level. Immunoprecipitation of the Numb protein co-precipitates the capsid protein, indicating the interaction between these two proteins. These results provide insights into the ZIKV-cell interaction that might contribute to its impact on neurogenesis.

Antiviral Peptide-Based Conjugates: State of the Art and Future Perspectives

Infectious diseases caused by microbial pathogens (bacteria, virus, fungi, parasites) claim millions of deaths per year worldwide and have become a serious challenge to global human health in our century. Viral infections are particularly notable in this regard, not only because humankind is facing some of the deadliest viral pandemics in recent history, but also because the arsenal of drugs to combat the high levels of mutation, and hence the antigenic variability of (mostly RNA) viruses, is disturbingly scarce. Therefore, the search for new antivirals able to successfully fight infection with minimal or no adverse effects on the host is a pressing task. Traditionally, antiviral therapies have relied on relatively small-sized drugs acting as proteases, polymerases, integrase inhibitors, etc. In recent decades, novel approaches involving targeted delivery such as that achieved by peptide-drug conjugates (PDCs) have gained attention as alternative (pro)drugs for tackling viral diseases. Antiviral PDC therapeutics typically involve one or more small drug molecules conjugated to a cell-penetrating peptide (CPP) carrier either directly or through a linker. Such integration of two bioactive elements into a single molecular entity is primarily aimed at achieving improved bioavailability in conditions where conventional drugs are challenged, but may also turn up novel unexpected functionalities and applications. Advances in peptide medicinal chemistry have eased the way to antiviral PDCs, but challenges remain on the way to therapeutic success. In this paper, we review current antiviral CPP-drug conjugates (antiviral PDCs), with emphasis on the types of CPP and antiviral cargo. We integrate the conjugate and the chemical approaches most often applied to combine both entities. Additionally, we comment on various obstacles faced in the design of antiviral PDCs and on the future outlooks for this class of antiviral therapeutics.

A porcine reproductive and respiratory syndrome virus (PRRSV)-specific IgM as a novel adjuvant for an inactivated PRRSV vaccine improves protection efficiency and enhances cell-mediated immunity against heterologous PRRSV challenge

Current strategies for porcine reproductive and respiratory syndrome (PRRS) control are inadequate and mainly restricted to immunization using different PRRS virus (PPRSV) vaccines. Although there are no safety concerns, the poor performance of inactivated PRRSV vaccines has restricted their practical application. In this research, we employed the novel PRRSV-specific IgM monoclonal antibody (Mab)-PR5nf1 as a vaccine adjuvant for the formulation of a cocktail composed of inactivated PRRSV (KIV) and Mab-PR5nf1 along with a normal adjuvant to enhance PRRSV-KIV vaccine-mediated protection and further compared it with a normal KIV vaccine and modified live virus vaccine (MLV). After challenge with highly pathogenic (HP)-PRRSV, our results suggested that the overall survival rate (OSR) and cell-mediated immunity (CMI), as determined by serum IFN-γ quantification and IFN-γ ELISpot assay, were significantly improved by adding PRRSV-specific IgM to the PRRSV-KIV vaccine. It was also notable that both the OSR and CMI in the Mab-PR5nf1-adjuvanted KIV group were even higher than those in the MLV group, whereas the CMI response is normally poorly evoked by KIV vaccines or subunit vaccines. Compared with those in piglets immunized with the normal KIV vaccine, viral shedding and serum neutralizing antibody levels were also improved, and reduced viral shedding appeared to be a result of enhanced CMI caused by the inclusion of IgM as an adjuvant. In conclusion, our data provide not only a new formula for the development of an effective PRRSV-KIV vaccine for practical use but also a novel method for improving antigen-specific CMI induction by inactivated vaccines and subunit vaccines.

Inhibition of SARS-CoV-2 in Vero cell cultures by peptide-conjugated morpholino oligomers

Background

As the causative agent of COVID-19, SARS-CoV-2 is a pathogen of immense importance to global public health. Development of innovative direct-acting antiviral agents is sorely needed to address this virus. Peptide-conjugated morpholino oligomers (PPMO) are antisense compounds composed of a phosphorodiamidate morpholino oligomer covalently conjugated to a cell-penetrating peptide. PPMO require no delivery assistance to enter cells and are able to reduce expression of targeted RNA through sequence-specific steric blocking.

Methods

Five PPMO designed against sequences of genomic RNA in the SARS-CoV-2 5′-untranslated region and a negative control PPMO of random sequence were synthesized. Each PPMO was evaluated for its effect on the viability of uninfected cells and its inhibitory effect on the replication of SARS-CoV-2 in Vero-E6 cell cultures. Cell viability was evaluated with an ATP-based method using a 48 h PPMO treatment time. Viral growth was measured with quantitative RT–PCR and TCID₅₀ infectivity assays from experiments where cells received a 5 h PPMO treatment time.

Results

PPMO designed to base-pair with sequence in the 5′ terminal region or the leader transcription regulatory sequence region of SARS-CoV-2 genomic RNA were highly efficacious, reducing viral titres by up to 4–6 log₁₀ in cell cultures at 48–72 h post-infection, in a non-toxic and dose-responsive manner.

Conclusions

The data indicate that PPMO have the ability to potently and specifically suppress SARS-CoV-2 growth and are promising candidates for further preclinical development.

Zika virus NS2A protein induces the degradation of KPNA2 (karyopherin subunit alpha 2) via chaperone-mediated autophagy

KPNA2/importin-alpha1 (karyopherin subunit alpha 2) is the primary nucleocytoplasmic transporter for some transcription factors to activate cellular proliferation and differentiation. Aberrant increase of KPNA2 level is identified as a prognostic marker in a variety of cancers. Yet, the turnover mechanism of KPNA2 remains unknown. Here, we demonstrate that KPNA2 is degraded via the chaperone-mediated autophagy (CMA) and that Zika virus (ZIKV) enhances the KPNA2 degradation. KPNA2 contains a CMA motif, which possesses an indispensable residue Gln109 for the CMA-mediated degradation. RNAi-mediated knockdown of LAMP2A, a vital component of the CMA pathway, led to a higher level of KPNA2. Moreover, ZIKV reduced KPNA2 via the viral NS2A protein, which contains an essential residue Thr100 for inducing the CMA-mediated KPNA2 degradation. Notably, mutant ZIKV with T100A alteration in NS2A replicates much weaker than the wild-type virus. Also, knockdown of KPNA2 led to a higher ZIKV viral yield, which indicates that KPNA2 mediates certain antiviral effects. These data provide insights into the KPNA2 turnover and the ZIKV-cell interactions.

Porcine Reproductive and Respiratory Syndrome Virus Promotes SLA-DR-Mediated Antigen Presentation of Nonstructural Proteins To Evoke a Nonneutralizing Antibody Response In Vivo

The humoral immune response against porcine reproductive and respiratory syndrome virus (PRRSV) infection is characterized by a rapid induction of nonneutralizing antibodies (non-NAbs) against nonstructural proteins (NSPs). Here, we systematically investigated the potential mechanism for the induction of PRRSV NSP-specific non-NAbs. Our data suggested that PRRSV NSP-specific antibodies appeared within 10 days after PRRSV infection in vivo In the in vitro model, functional upregulation of swine leukocyte antigen (SLA)-DR was observed in bone marrow-derived dendritic cells (BMDCs) and porcine alveolar macrophages (PAMs), whereas remarkable inhibition at the mRNA level was observed after infection by both PRRSV-1 and PRRSV-2 isolates. Notably, the inconsistency in SLA-DR expression between the mRNA and protein levels resulted from deubiquitination of SLA-DR via the ovarian tumor (OTU) domain of PRRSV NSP2, which inhibited ubiquitin-mediated degradation. Moreover, mass spectrometry-based immunopeptidome analysis identified immunopeptides originating from multiple PRRSV NSPs within SLA-DR of PRRSV-infected BMDCs. Meanwhile, these PRRSV NSP-derived immunopeptides could be specifically recognized by serum from PRRSV-infected piglets. Notably, certain NSP-derived immunopeptides characterized in vitro could be identified from PAMs or hilar lymph nodes from PRRSV-infected piglets. More importantly, an in vitro neutralizing assay indicated that serum antibodies against NSP immunopeptides were unable to neutralize PRRSV in vitro Conversely, certain structural protein (SP)-derived immunopeptides were identified and could be recognize by pig hyperimmune serum against PRRSV, which further indicates that the NSP-derived antibody response is nonprotective in vivo In conclusion, our data suggested that PRRSV infection interferes with major histocompatibility complex class II (MHC-II) molecule-mediated antigen presentation in antigen-presenting cells (APCs) via promoting SLA-DR expression to present immunopeptides from PRRSV NSPs, which contributes to the induction of non-NAbs in vivo IMPORTANCE PRRSV has haunted the swine industry for over 30 years since its emergence. Besides the limited efficacy of PRRSV modified live vaccines (MLVs) against heterogeneous PRRSV isolates, rapid induction of nonneutralizing antibodies (non-NAbs) against PRRSV NSPs after MLV immunization or wild-strain infection is one of the reasons why development of an effective vaccine has been hampered. By using in vitro-generated BMDCs as models to understand the antigen presentation process of PRRSV, we obtained data indicating that PRRSV infection of BMDCs promotes functional SLA-DR upregulation to present PRRSV NSP-derived immunopeptides for evoking a non-NAb response in vivo Our work not only uncovered a novel mechanism for interference in host antigen presentation by PRRSV but also revealed a novel insight for understanding the rapid production of nonneutralizing antibodies against PRRSV NSPs, which may have benefit for developing an effective vaccine against PRRSV in the future.

Inhibition of SARS-CoV-2 in Vero cell cultures by peptide-conjugated morpholino-oligomers

Background

SARS-CoV-2 is the causative agent of COVID-19 and a pathogen of immense global public health importance. Development of innovative direct-acting antiviral agents is sorely needed to address this virus. Peptide-conjugated morpholino oligomers (PPMO) are antisense agents composed of a phosphordiamidate morpholino oligomer covalently conjugated to a cell-penetrating peptide. PPMO require no delivery assistance to enter cells and are able to reduce expression of targeted RNA through sequence-specific steric blocking.

Objectives and Methods

Five PPMO designed against sequences of genomic RNA in the SARS-CoV-2 5'-untranslated region and a negative control PPMO of random sequence were synthesized. Each PPMO was evaluated for its effect on the viability of uninfected cells and its inhibitory effect on the replication of SARS-CoV-2 in Vero-E6 cell cultures. Cell viability was evaluated with an ATP-based method and viral growth was measured with quantitative RT-PCR and TCID ₅₀ infectivity assays.

Results

PPMO designed to base-pair with sequence in the 5'-terminal region or the leader transcription regulatory sequence-region of SARS-CoV-2 genomic RNA were highly efficacious, reducing viral titers by up to 4-6 log10 in cell cultures at 48-72 hours post-infection, in a non-toxic and dose-responsive manner.

Conclusion

The data indicate that PPMO have the ability to potently and specifically suppress SARS-CoV-2 growth and are promising candidates for further pre-clinical development.

PRRSV Vaccine Strain-Induced Secretion of Extracellular ISG15 Stimulates Porcine Alveolar Macrophage Antiviral Response against PRRSV

Porcine reproductive and respiratory syndrome virus (PRRSV) has disrupted the global swine industry since the 1980s. PRRSV-host interactions are largely still unknown but may involve host ISG15 protein. In this study, we developed a monoclonal antibody (Mab-3D5E6) specific for swine ISG15 (sISG15) by immunizing mice with recombinant sISG15. A sandwich enzyme-linked immunosorbent assay (ELISA) incorporating this sISG15-specific Mab was developed to detect sISG15 and provided a lower limit of sISG15 detection of 200 pg/mL. ELISA results demonstrated that infection of porcine alveolar macrophages (PAMs) with low-virulence or attenuated PRRSV vaccine strains induced intracellular ISG15 expression that was independent of type I IFN production, while PAMs infection with a PRRSV vaccine strain promoted extracellular ISG15 secretion from infected PAMs. Conversely, the addition of recombinant sISG15 to PAMs mimicked natural extracellular ISG15 effects whereby sISG15 functioned as a cytokine by activating PAMs. Once activated, PAMs could inhibit PRRSV replication and resist infection with PRRSV vaccine strain TJM. In summary, a sandwich ELISA incorporating homemade anti-ISG15 Mab detected ISG15 secretion induced by PAMs infection with a PRRSV vaccine strain. Recombinant ISG15 added to cells exhibited cytokine-like activity that stimulated PAMs to assume an anti-viral state that enabled them to inhibit PRRSV replication and resist viral infection.

Broad neutralization activity against both PRRSV-1 and PRRSV-2 and enhancement of cell mediated immunity against PRRSV by a novel IgM monoclonal antibody

Porcine reproductive and respiratory syndrome (PRRS) is the most economically important infectious disease affecting the global swine industry, especially since vaccination has had limited impact on PRRSV prevention and control. In this study, the monoclonal antibody PR5nf1 (Mab-PR5nf1, IgM isotype) was shown to react with heterogeneous PRRSV isolates belonging to both PRRSV-1 and PRRSV-2 species. Pepsin digestion of Mab-PR5nf1 did not affect Mab binding to virions, as F(ab)₂ fragments demonstrated the same reactivity as undigested Mab. Upon further investigation, Mab-PR5nf1 could neutralize all tested PRRSV isolates of both PRRSV-1 and PRRSV-2, suggesting it was a broadly neutralizing Mab against PRRSV. Interestingly, Mab-PR5nf1 appeared to recognize a specific virus epitope that required post-translational modification within the host cellular Golgi apparatus. Deglycosylation of PRRSV virions with PNGase F abolished Mab binding, suggesting that a novel Mab-binding epitope may exist that confers cross-protection against isolates of both PRRSV species. Additionally, immunization of mice with a cocktail of inactivated PRRSV virus and Mab-PR5nf1 enhanced cell-mediated immunity, as determined by IFN-γ ELIspot. In conclusion, this is the first report describing a novel Mab that recognizes a conserved epitope common to both PRRSV-1 and PRRSV-2 and provides valuable insights to guide future PRRSV vaccine development.

Nonstructural Protein 11 of Porcine Reproductive and Respiratory Syndrome Virus Induces STAT2 Degradation To Inhibit Interferon Signaling

Interferons (IFNs) play a crucial role in host antiviral response by activating the JAK/STAT (Janus kinase/signal transducer and activator of transcription) signaling pathway to induce the expression of myriad genes. STAT2 is a key player in the IFN-activated JAK/STAT signaling. Porcine reproductive and respiratory syndrome virus (PRRSV) is an important viral pathogen, causing huge losses to the swine industry. PRRSV infection elicits a meager protective immune response in pigs. The objective of this study was to investigate the effect of PRRSV on STAT2 signaling. Here, we demonstrated that PRRSV downregulated STAT2 to inhibit IFN-activated signaling. PRRSV strains of both PRRSV-1 and PRRSV-2 species reduced the STAT2 protein level, whereas the STAT2 transcript level had minimal change. PRRSV reduced the STAT2 level in a dose-dependent manner and shortened STAT2 half-life significantly from approximately 30 to 5 h. PRRSV-induced STAT2 degradation could be restored by treatment with the proteasome inhibitor MG132 and lactacystin. In addition, PRRSV nonstructural protein 11 (nsp11) was identified to interact with and reduce STAT2. The N-terminal domain (NTD) of nsp11 was responsible for STAT2 degradation and interacted with STAT2 NTD and the coiled-coil domain. Mutagenesis analysis showed that the amino acid residue K59 of nsp11 was indispensable for inducing STAT2 reduction. Mutant PRRSV with the K59A mutation generated by reverse genetics almost lost the ability to reduce STAT2. Together, these results demonstrate that PRRSV nsp11 antagonizes IFN signaling via mediating STAT2 degradation and provide further insights into the PRRSV interference of the innate immunity.IMPORTANCE PRRSV infection elicits a meager protective immune response in pigs. One of the possible reasons is that PRRSV antagonizes interferon induction and its downstream signaling. Interferons are key components in the innate immunity and play crucial roles against viral infection and in the activation of adaptive immune response via JAK/STAT signaling. STAT2 is indispensable in the JAK/STAT signaling since it is also involved in activation of antiviral activity in the absence of STAT1. Here, we discovered that PRRSV nsp11 downregulates STAT2. Interestingly, the N-terminal domain of nsp11 is responsible for inducing STAT2 degradation and directly interacts with STAT2 N-terminal domain. We also identified a crucial amino acid residue K59 in nsp11 since a mutation of it led to loss of the ability to downregulate STAT2. A mutant PRRSV with mutation of K59 had minimal effect on STAT2 reduction. Our data provide further insights into PRRSV interference with interferon signaling.

The 40 kDa Linear Polyethylenimine Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection by Blocking Its Attachment to Permissive Cells

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically devastating infectious diseases in pigs worldwide. The causative agent is the PRRS virus (PRRSV). In this study, we explored polyethylenimine (PEI), a cationic polymer with different forms (linear or branched), to inhibit the replication of PRRSV. Our results demonstrate that the linear but not the 40 kDa branched PEI, or the 25 kDa linear PEI, were well tolerated in cultured cells and exhibited a broad-spectrum inhibition of heterogeneous PRRSV-2 isolates in both MARC-145 cells and primary porcine pulmonary alveolar macrophages (PAMs). Further analysis suggests that PEI could prevent the attachment of PRRSV virions to the susceptible cells. Notably, PEI had a minimal effect on PRRSV internalization in MARC-145 cells, whereas PEI promoted the internalization of PRRSV virions in PAMs, which suggests that these two types of cells might have different internalization processes of PRRSV virions. In conclusion, our data demonstrate that PEI could be used as a novel inhibitor against PRRSV.

Isolation and genetic analysis of a nidovirus from crucian carp (Carassius auratus)

A nidovirus was isolated from crucian carp (Carassius auratus). The complete genome of the crucian carp nidovirus (CCNV) is 25,971 nt long and has five open reading frames, encoding the polyprotein 1ab (pp1ab), spike glycoprotein (S), membrane protein (M), and nucleocapsid protein (N). CCNV has the highest similarity to Chinook salmon nidovirus (CSNV). However, the CCNV HB93 pp1ab protein sequence has three long fragment deletions compared with the CSNV. Phylogenetic analysis based on the complete genome sequence showed that CCNV HB93 clusters with CSNV, indicating that CCNV represents a second species in the new genus Oncotshavirus within the new family Tobaniviridae in the order Nidovirales.

The Threat from Viruses

Infectious disease represent the most significant threat to human health. Significant geologic cataclysmic events have caused the extinction of countless species, but these “Wrath of God” events predate the emergence of Homo sapiens. Pandemic infections have accompanied the rise of human civilization frequently re-occurring leaving a lasting imprint on human history punctuated by profound loss of life. Emerging infections become endemic and are here to stay marking their presence with an annual death toll. Each decade brings a new onslaught of emerging infectious agents. We are surprised again and again but are never prepared. The long-term consequences often remain unrecognized and are always inconvenient including cancer, cardiovascular disease and immune associated diseases that threaten our health. Reliance on clusters of clinical symptoms in the face of diverse and non-descriptive viral infection symptoms is a foolhardy form of crisis management. Viral success is based on rapid replication resulting in large numbers. Single-stranded RNA viruses with their high replication error rate represent a paradigm for resilience.

Recombinant MYH9 protein C-terminal domain blocks porcine reproductive and respiratory syndrome virus internalization by direct interaction with viral glycoprotein 5

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important infectious diseases impacting the swine industry worldwide. Prevention and control of PRRS have been problematic, as vaccination has achieved little success. MYH9 (encoded by the gene MYH9) is an essential cellular factor for PRRS virus (PRRSV) infection. The MYH9 C-terminal domain (designated PRA) interacts with viral glycoprotein 5 (GP5), a major PRRSV envelope protein. In this study, we investigated whether soluble PRA could serve as a novel blocking agent of PRRSV infection. Our data showed that preincubation of PRRSV with PRA inhibited virus infection of susceptible cells in a dose-dependent manner. Notably, PRA also exhibited broad-spectrum ability to inhibit infection with diverse strains of both PRRSV genotype 1 and 2. Analysis of the interaction between PRA and PRRSV GP5 revealed that PRA is able to capture PRRSV virions. In conclusion, our data suggest that PRA could serve as a novel broad-spectrum inhibitor of infection by heterogeneous PRRSV strains in vivo.

Karyopherin Alpha 6 Is Required for Replication of Porcine Reproductive and Respiratory Syndrome Virus and Zika Virus

Movement of macromolecules between the cytoplasm and the nucleus occurs through the nuclear pore complex (NPC). Karyopherins comprise a family of soluble transport factors facilitating the nucleocytoplasmic translocation of proteins through the NPC. In this study, we found that karyopherin α6 (KPNA6; also known as importin α7) was required for the optimal replication of porcine reproductive and respiratory syndrome virus (PRRSV) and Zika virus (ZIKV), which are positive-sense, single-stranded RNA viruses replicating in the cytoplasm. The KPNA6 protein level in virus-infected cells was much higher than that in mock-infected controls, whereas the KPNA6 transcript remains stable. Viral infection blocked the ubiquitin-proteasomal degradation of KPNA6, which led to an extension of the KPNA6 half-life and the elevation of the KPNA6 level in comparison to mock-infected cells. PRRSV nsp12 protein induced KPNA6 stabilization. KPNA6 silencing was detrimental to the replication of PRRSV, and KPNA6 knockout impaired ZIKV replication. Moreover, KPNA6 knockout blocked the nuclear translocation of PRRSV nsp1β but had a minimal effect on two other PRRSV proteins with nuclear localization. Exogenous restitution of KPNA6 expression in the KPNA6-knockout cells results in restoration of the nuclear translocation of PRRSV nsp1β and the replication of ZIKV. These results indicate that KPNA6 is an important cellular factor for the replication of PRRSV and ZIKV.IMPORTANCE Positive-sense, single-stranded RNA (+ssRNA) viruses replicate in the cytoplasm of infected cells. The roles of transport factors in the nucleocytoplasmic trafficking system for the replication of +ssRNA viruses are not known. In this study, we discovered that PRRSV and ZIKV viruses needed karyopherin α6 (KPNA6), one of the transport factors, to enhance the virus replication. Our data showed that viral infection induced an elevation of the KPNA6 protein level due to an extension of the KPNA6 half-life via viral interference of the ubiquitin-proteasomal degradation of KPNA6. Notably, KPNA6 silencing or knockout dramatically reduced the replication of PRRSV and ZIKV. PRRSV nsp1β depended on KPNA6 to translocate into the nucleus. In addition, exogenous restitution of KPNA6 expression in KPNA6-knockout cells led to the restoration of nsp1β nuclear translocation and ZIKV replication. These results reveal a new aspect in the virus-cell interaction and may facilitate the development of novel antiviral therapeutics.

In vitro inhibition of porcine reproductive and respiratory syndrome virus replication by short antisense oligonucleotides with locked nucleic acid modification

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) causes porcine reproductive and respiratory syndrome (PRRS), which is currently insufficiently controlled. From a previous small-scale screen we identified an effective DNA-based short antisense oligonucleotide (AS-ON) targeting viral NSP9, which could inhibit PRRSV replication in both Marc-145 cells and pulmonary alveolar macrophages (PAMs). The objective of this study was to explore the strategy of incorporating locked nucleic acids (LNAs) to achieve better inhibition of PRRSV replication in vitro.

Methods

The effective DNA-based AS-ON (YN8) was modified with LNAs at both ends as gap-mer (LNA-YN8-A) or as mix-mer (LNA-YN8-B). Marc-145 cells or PAMs were infected with PRRSV and subsequently transfected.

Results

Compared with the DNA-based YN8 control, the two AS-ONs modified with LNAs were found to be significantly more effective in decreasing the cytopathic effect (CPE) induced by PRRSV and thus in maintaining cell viability. LNA modifications conferred longer lifetimes to the AS-ON in the cell culture model. Viral ORF7 levels were more significantly reduced at both RNA and protein levels as shown by quantitative PCR, western blot and indirect immunofluorescence staining. Moreover, transfection with LNA modified AS-ON reduced the PRRSV titer by 10-fold compared with the YN8 control.

Conclusion

Taken together, incorporation of LNA into AS-ON technology holds higher therapeutic promise for PRRS control.

Porcine reproductive and respiratory syndrome virus induces HMGB1 secretion via activating PKC-delta to trigger inflammatory response

Porcine reproductive and respiratory syndrome virus (PRRSV) causes inflammatory injuries in infected pigs. PRRSV induces secretion of high mobility group box 1 (HMGB1) that enhances inflammatory response. However, the mechanism of PRRSV-induced HMGB1 secretion is unknown. Here, we discovered PRRSV induced HMGB1 secretion via activating protein kinase C-delta (PKCδ). HMGB1 secretion was positively correlated with PKCδ activation in PRRSV-infected cells in a dose and time-dependent manner. Suppression of PKCδ with inhibitor and siRNA significantly blocked PRRSV-induced HMGB1 translocation and secretion, which indicates PKCδ activation is essential for the PRRSV-mediated HMGB1 secretion. In addition, PKCδ knockdown in PRRSV-infected cells led to downregulation of inflammatory cytokines, including IL-1beta and IL-6. Moreover, PRRSV E and pORF5a proteins were found to activate PKCδ and consequent HMGB1 secretion. These results demonstrate PRRSV activates PKCδ to induce HMGB1 secretion via E and pORF5a. This finding provides insights on the inflammatory response and pathogenesis of PRRSV infection.

The middle half genome of interferon-inducing porcine reproductive and respiratory syndrome virus strain A2MC2 is essential for interferon induction

Porcine reproductive and respiratory syndrome virus (PRRSV) is known to antagonize the innate immune response. An atypical PRRSV strain A2MC2 is capable of inducing synthesis of type I interferons (IFNs) in cultured cells. Here, we show that the middle half of the A2MC2 genome is needed for triggering the IFN synthesis. First, a cDNA infectious clone of this atypical strain was constructed as a DNA-launched version. Virus recovery was achieved from the infectious clone and the recovered virus, rA2MC2, was characterized. The rA2MC2 retained the feature of IFN induction in cultured cells. Infection of pigs with the rA2MC2 virus caused viremia similar to that of the wild-type virus. Chimeric infectious clones were constructed by swapping genomic fragments with a cDNA clone of a moderately virulent strain VR-2385 that antagonizes IFN induction. Analysis of the rescued chimeric viruses demonstrated that the middle two fragments, ranging from nt4545 to nt12709 of the A2MC2 genome, were needed for the IFN induction, whereas the chimeric viruses containing any one of the two A2MC2 fragments failed to do so. The results and the cDNA infectious clone of the IFN-inducing A2MC2 will facilitate further study of its biology, ultimately leading towards the development of an improved vaccine against PRRS.

Porcine Reproductive and Respiratory Syndrome Virus Antagonizes JAK/STAT3 Signaling via nsp5, Which Induces STAT3 Degradation

Signal transducer and activator of transcription 3 (STAT3) is a pleiotropic signaling mediator of many cytokines, including interleukin-6 (IL-6) and IL-10. STAT3 is known to play critical roles in cell growth, proliferation, differentiation, immunity and inflammatory responses. The objective of this study was to determine the effect of porcine reproductive and respiratory syndrome virus (PRRSV) infection on the STAT3 signaling since PRRSV induces a weak protective immune response in host animals. We report here that PRRSV infection of MARC-145 cells and primary porcine pulmonary alveolar macrophages led to significant reduction of STAT3 protein level. Several strains of both PRRSV type 1 and type 2 led to a similar reduction of STAT3 protein level but had a minimal effect on its transcripts. The PRRSV-mediated STAT3 reduction was in a dose-dependent manner as the STAT3 level decreased, along with incremental amounts of PRRSV inocula. Further study showed that nonstructural protein 5 (nsp5) of PRRSV induced the STAT3 degradation by increasing its polyubiquitination level and shortening its half-life from 24 h to ∼3.5 h. The C-terminal domain of nsp5 was shown to be required for the STAT3 degradation. Moreover, the STAT3 signaling in the cells transfected with nsp5 plasmid was significantly inhibited. These results indicate that PRRSV antagonizes the STAT3 signaling by accelerating STAT3 degradation via the ubiquitin-proteasomal pathway. This study provides insight into the PRRSV interference with the JAK/STAT3 signaling, leading to perturbation of the host innate and adaptive immune responses.

IMPORTANCE

The typical features of immune responses in PRRSV-infected pigs are delayed onset and low levels of virus neutralizing antibodies, as well as weak cell-mediated immunity. Lymphocyte development and differentiation rely on cytokines, many of which signal through the JAK/STAT signaling pathway to exert their biological effects. Here, we discovered that PRRSV antagonizes the JAK/STAT3 signaling by inducing degradation of STAT3, a master transcription activator involved in multiple cellular processes and the host immune responses. The nsp5 protein of PRRSV is responsible for the accelerated STAT3 degradation. The PRRSV-mediated antagonizing STAT3 could lead to suppression of a broad spectrum of cytokines and growth factors to allow virus replication and spread in host animals. This may be one of the reasons for the PRRSV interference with the innate immunity and its poor elicitation of protective immunity. This finding provides insight into PRRSV pathogenesis and its interference with the host immune responses.

Sustaining Interferon Induction by a High-Passage Atypical Porcine Reproductive and Respiratory Syndrome Virus Strain

Porcine reproductive and respiratory syndrome virus (PRRSV) strain A2MC2 induces type I interferons in cultured cells. The objective of this study was to attenuate this strain by serial passaging in MARC-145 cells and assess its virulence and immunogenicity in pigs. The A2MC2 serially passaged 90 times (A2MC2-P90) retains the feature of interferon induction. The A2MC2-P90 replicates faster with a higher virus yield than wild type A2MC2 virus. Infection of primary pulmonary alveolar macrophages (PAMs) also induces interferons. Sequence analysis showed that the A2MC2-P90 has genomic nucleic acid identity of 99.8% to the wild type but has a deletion of 543 nucleotides in nsp2. The deletion occurred in passage 60. The A2MC2-P90 genome has a total of 35 nucleotide variations from the wild type, leading to 26 amino acid differences. Inoculation of three-week-old piglets showed that A2MC2-P90 is avirulent and elicits immune response. Compared with Ingelvac PRRS^® MLV strain, A2MC2-P90 elicits higher virus neutralizing antibodies. The attenuated IFN-inducing A2MC2-P90 should be useful for development of an improved PRRSV vaccine.

Downregulation of protein kinase PKR activation by porcine reproductive and respiratory syndrome virus at its early stage infection

The interferon-induced double-strand RNA activated protein kinase (PKR) plays an important role in antiviral response. The objective of this study was to assess the effect of porcine reproductive and respiratory syndrome virus (PRRSV) on PKR activation. Here we report that PRRSV inhibited PKR activation during its early stage infection of primary pulmonary alveolar macrophages (PAMs). PRRSV infection led to lower level of phosphorylated PKR in comparison with mock-infected cells. The PKR inhibition was sustained until 10h post infection in the presence of polyI:C, a synthetic analog of double-stranded RNA activating PKR. PKR-mediated phosphorylation of the eukaryotic translation initiation factor eIF2α was also lower in the PRRSV-infected PAMs during the early stage infection. Interestingly, inactivated PRRSV was capable to inhibit the PKR activation until 6h post infection. This suggests that structural components of PRRSV virions were responsible for the inhibition, although PRRSV replication was needed for longer inhibition. These results indicate that the downregulation of PKR activation during early infection stage should be essential for PRRSV to avoid the antiviral response to initiate replication. This finding contributes to our understanding on PRRSV interaction with host innate immune response and reveal a target for control of PRRSV infection.

Probe-free real-time reverse transcription polymerase chain reaction assays for the detection and typing of porcine reproductive and respiratory syndrome virus in Canada

Porcine reproductive and respiratory syndrome (PRRS) has tremendous impact on the pork industry in North America. The molecular diagnosis of infection with PRRS virus (PRRSV) is hampered by its considerable strain diversity. In this study, 43 previously published or newly developed primers for probe-free real-time reverse transcription polymerase chain reaction (RT-PCR) were evaluated on their sensitivity, specificity, reproducibility, and repeatability, using a diverse panel of 36 PRRSV strains as well as other arteriviruses and unrelated porcine viruses. Three primer pairs had excellent diagnostic and analytical sensitivity on par with a probe-based reference assay, absolute specificity to virus genotype and species, as well as over 95% reproducibility and repeatability across a wide dynamic range.

Inhibition of hepatitis E virus replication by peptide-conjugated morpholino oligomers

Hepatitis E virus (HEV) infection is a cause of hepatitis in humans worldwide and has been associated with a case-fatality rate of up to 30% in pregnant women. Recently, persistent and chronic HEV infections have been recognized as a serious clinical problem, especially in immunocompromised individuals. To date, there are no FDA-approved HEV-specific antiviral drugs. In this study, we evaluated antisense peptide-conjugated morpholino oligomers (PPMO) designed against HEV genomic sequences as potential HEV-specific antiviral compounds. Two genetically-distinct strains of human HEV, genotype 1 Sar55 and genotype 3 Kernow-C1, isolated from patients with acute and chronic hepatitis, respectively, were used to evaluate inhibition of viral replication by PPMO in liver cells. The anti-HEV PPMO produced a significant reduction in the levels of HEV RNA and capsid protein, indicating effective inhibition of HEV replication. PPMO HP1, which targets a highly conserved sequence in the start site region of ORF1, was also effective against the genotype 3 Kernow-C1 strain in stably-infected HepG2/C3A liver cells. The antiviral activity observed was specific, dose-responsive and potent, suggesting that further exploration of PPMO HP1 as a potential HEV-specific antiviral agent is warranted.

Suppression of porcine reproductive and respiratory syndrome virus proliferation by glycyrrhizin

Glycyrrhizin is a natural component extracted from the roots of Glycyrrhiza glabra. In this study, we investigated the antiviral activity of glycyrrhizin against porcine reproductive and respiratory syndrome virus (PRRSV), an Arterivirus that has been devastating the swine industry worldwide since the late 1980s. Our results showed that treatment with glycyrrhizin significantly reduced PRRSV proliferation and PRRSV-encoded protein expression in a dose-dependent manner. Mechanistically, glycyrrhizin mainly inhibits the penetration stage, and has little effect on the steps of adsorption or release of PRRSV in its life cycle. Furthermore, we were able to exclude a direct inhibitory action of glycyrrhizin on PRRSV particles. Given these results, glycyrrhizin may be a candidate component for a novel porcine reproductive and respiratory syndrome (PRRS) control strategy.

KSHV targeted therapy: an update on inhibitors of viral lytic replication

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi’s sarcoma, primary effusion lymphoma and multicentric Castleman’s disease. Since the discovery of KSHV 20 years ago, there is still no standard treatment and the management of virus-associated malignancies remains toxic and incompletely efficacious. As the majority of tumor cells are latently infected with KSHV, currently marketed antivirals that target the virus lytic cycle have shown inconsistent results in clinic. Nevertheless, lytic replication plays a major role in disease progression and virus dissemination. Case reports and retrospective studies have pointed out the benefit of antiviral therapy in the treatment and prevention of KSHV-associated diseases. As a consequence, potent and selective antivirals are needed. This review focuses on the anti-KSHV activity, mode of action and current status of antiviral drugs targeting KSHV lytic cycle. Among these drugs, different subclasses of viral DNA polymerase inhibitors and compounds that do not target the viral DNA polymerase are being discussed. We also cover molecules that target cellular kinases, as well as the potential of new drug targets and animal models for antiviral testing.

Inhibition of HSP90 attenuates porcine reproductive and respiratory syndrome virus production in vitro

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) infection leads to substantial economic losses to the swine industry worldwide. However, no effective countermeasures exist to combat this virus infection so far. The most common antiviral strategy relies on directly inhibiting viral proteins. However, this strategy invariably leads to the emergence of drug resistance due to the error-prone nature of viral ploymerase. Targeting cellular proteins required for viral infection for developing new generation of antivirals is gaining concern. Recently, heat shock protein 90 (HSP90) was found to be an important host factor for the replication of multiple viruses and the inhibition of HSP90 showed significant antiviral effects. It is thought that the inhibition of HSP90 could be a promising broad-range antiviral approach. However, the effects of HSP90 inhibition on PRRSV infection have not been evaluated. In the current research, we tried to inhibit HSP90 and test whether the inhibition affect PRRSV infection.

Methods

We inhibit the function of HSP90 with two inhibitors, geldanamycin (GA) and 17- allylamono-demethoxygeldanamycin (17-AAG), and down-regulated the expression of endogenous HSP90 with specific small-interfering RNAs (siRNAs). Cell viability was measured with alamarBlue. The protein level of viral N was determined by western blotting and indirect immunofluorescence (IFA). Besides, IFA was employed to examine the level of viral double-stranded RNA (dsRNA). The viral RNA copy number and the level of IFN-β mRNA were determined by quantitative real-time PCR (qRT-PCR).

Results

Our results indicated that both HSP90 inhibitors showed strong anti-PRRSV activity. They could reduce viral production by preventing the viral RNA synthesis. These inhibitory effects were not due to the activation of innate interferon response. In addition, we observed that individual knockdown targeting HSP90α or HSP90β did not show dramatic inhibitory effect. Combined knockdown of these two isoforms was required to reduce viral infection.

Conclusions

Our results shed light on the possibility of developing potential therapeutics targeting HSP90 against PRRSV infection.

Enhancing neutralizing antibody production by an interferon-inducing porcine reproductive and respiratory syndrome virus strain

Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) continues to cause substantial economic losses to the global swine industry. PRRSV appears to inhibit synthesis of type I interferons (IFNs), such as IFN-α and -β, which are critical for the innate immunity and play an important role in the modulation of adaptive immunity. An atypical PRRSV strain, A2MC2, is able to induce type I IFNs in vitro. In this study, A2MC2 induction of neutralizing antibodies in vivo was compared with the Ingelvac PRRS modified live virus (MLV) vaccine strain and VR-2385 (a moderate virulent strain). Three-week-old pigs were exposed to these PRRSV strains via intranasal or intramuscular routes to also account for a possible effect of inoculation routes. The interferon-inducing A2MC2 resulted in earlier onset and significantly higher levels of PRRSV neutralizing antibodies than the MLV. In addition, the A2MC2-induced neutralizing antibodies were capable of neutralizing VR-2385, a heterologous strain. The pigs exposed via intranasal route had higher titers of neutralizing antibodies than those injected via intramuscular route. Macroscopic and microscopic lung lesions 14 days post-exposure indicated that A2MC2 had similar virulence in vivo as VR-2385. Pulmonary alveolar macrophages (PAMs) collected during the necropsy 14 days post-exposure in the A2MC2 group had higher level expression of IFN-γ than the MLV group. These results indicate that A2MC2 can be further explored for development of an improved vaccine against PRRS.

Porcine reproductive and respiratory syndrome virus Nsp1β inhibits interferon-activated JAK/STAT signal transduction by inducing karyopherin-α1 degradation

Porcine reproductive and respiratory syndrome virus (PRRSV) inhibits the interferon-mediated antiviral response. Type I interferons (IFNs) induce the expression of IFN-stimulated genes by activating phosphorylation of both signal transducer and activator of transcription 1 (STAT1) and STAT2, which form heterotrimers (interferon-stimulated gene factor 3 [ISGF3]) with interferon regulatory factor 9 (IRF9) and translocate to the nucleus. PRRSV Nsp1β blocks the nuclear translocation of the ISGF3 complex by an unknown mechanism. In this study, we discovered that Nsp1β induced the degradation of karyopherin-α1 (KPNA1, also called importin-α5), which is known to mediate the nuclear import of ISGF3. Overexpression of Nsp1β resulted in a reduction of KPNA1 levels in a dose-dependent manner, and treatment of the cells with the proteasome inhibitor MG132 restored KPNA1 levels. Furthermore, the presence of Nsp1β induced an elevation of KPNA1 ubiquitination and a shortening of its half-life. Our analysis of Nsp1β deletion constructs showed that the N-terminal domain of Nsp1β was involved in the ubiquitin-proteasomal degradation of KPNA1. A nucleotide substitution resulting in an amino acid change from valine to isoleucine at residue 19 of Nsp1β diminished its ability to induce KPNA1 degradation and to inhibit IFN-mediated signaling. Interestingly, infection of MARC-145 cells by PRRSV strains VR-2332 and VR-2385 also resulted in KPNA1 reduction, whereas infection by an avirulent strain, Ingelvac PRRS modified live virus (MLV), did not. MLV Nsp1β had no effect on KPNA1; however, a mutant with an amino acid change at residue 19 from isoleucine to valine induced KPNA1 degradation. These results indicate that Nsp1β blocks ISGF3 nuclear translocation by inducing KPNA1 degradation and that valine-19 in Nsp1β correlates with the inhibition.

Therapeutic delivery opportunities, obstacles and applications for cell-penetrating peptides

Advancements in the development of large bioactive molecules as therapeutic agents have made drug delivery an active and important field of research. Cell-penetrating peptides (CPPs) have the ability to deliver an array of molecules and even nano-size particles into cells in an efficient and non-toxic manner, both in vitro and in vivo. This review aims to give a perspective on the obstacles that CPP-mediated drug delivery is currently facing as well as the great opportunities for improvements that lie ahead. Strategies for delivery of novel gene-modulating agents and enhancing efficacy of classical drugs will be discussed, as well as methods for increasing bioavailability and tissue specificity of CPPs. The usefulness and potential of CPPs as therapeutic drug-delivery vectors will be exemplified by their use in the treatment of cancer, viral infection and muscular dystrophy.

Induction of type I interferons by a novel porcine reproductive and respiratory syndrome virus isolate

Porcine reproductive and respiratory syndrome virus (PRRSV) is known to interfere with the signaling of type I interferons (IFNs). Here we found PRRSV A2MC2 induced type I IFNs in cultured cells. A2MC2 replication in MARC-145 cells resulted in the synthesis of IFN-α2 protein, transcript elevation of the IFN-stimulated genes ISG15 and ISG56, and the proteins of the signal transducer and activator of transcription 2 (STAT2) and ISG56. A2MC2 infection of primary porcine pulmonary alveolar macrophages (PAMs) also led to the elevation of the two proteins, but had little cytopathic effect. Furthermore, A2MC2 infection of MARC-145 or PAM cells had no detectable inhibitory effect on the ability of IFN-α to induce an antiviral response. Sequencing analysis indicated that A2MC2 was closely related to VR-2332 and Ingelvac PRRS MLV with an identity of 99.8% at the nucleotide level. The identification of this IFN-inducing PRRSV isolate may be beneficial for vaccine development against PRRS.

Bioactive hydroanthraquinones and anthraquinone dimers from a soft coral-derived Alternaria sp. fungus

Five new hydroanthraquinone derivatives, tetrahydroaltersolanols C-F (1-4) and dihydroaltersolanol A (5), and five new alterporriol-type anthranoid dimers, alterporriols N-R (12-16), along with seven known analogues (6-11 and 17), were isolated from the culture broth and the mycelia of Alternaria sp. ZJ-2008003, a fungus obtained from a Sarcophyton sp. soft coral collected from the South China Sea. Their structures and the relative configurations were elucidated using comprehensive spectroscopic methods including 1D and 2D NOE spectra as well as single-crystal X-ray crystallography. Compound 13 represents the first isolated alterporriol dimer with a C-4-C-4' linkage, and the absolute configuration of 4 was determined using the modified Mosher's method. Compounds 1 and 15 exhibited antiviral activity against the porcine reproductive and respiratory syndrome virus (PRRSV), with IC₅₀ values of 65 and 39 μM, respectively. Compound 14 showed cytotoxic activity against PC-3 and HCT-116 cell lines, with IC₅₀ values of 6.4 and 8.6 μM, respectively.

Advanced morpholino oligomers: a novel approach to antiviral therapy

Phosphorodiamidate morpholino oligomers (PMOs) are synthetic antisense oligonucleotide analogs that are designed to interfere with translational processes by forming base-pair duplexes with specific RNA sequences. Positively charged PMOs (PMOplus™) are effective for the postexposure protection of two fulminant viral diseases, Ebola and Marburg hemorrhagic fever in nonhuman primates, and this class of antisense agent may also have possibilities for treatment of other viral diseases. PMOs are highly stable, are effective by a variety of routes of administration, can be readily formulated in common isotonic delivery vehicles, and can be rapidly designed and synthesized. These are properties which may make PMOs good candidates for use during responses to emerging or reemerging viruses that may be insensitive to available therapies or for use during outbreaks, especially in regions that lack a modern medical infrastructure. While the efficacy of sequence-specific therapies can be limited by target-site sequence variations that occur between variants or by the emergence of resistant mutants during infections, various PMO design strategies can minimize these impacts. These strategies include the use of promiscuous bases such as inosine to compensate for predicted base-pair mismatches, the use of sequences that target conserved sites between viral strains, and the use of sequences that target host products that viruses utilize for infection.

Inhibitory effects of indigowoad root polysaccharides on porcine reproductive and respiratory syndrome virus replication in vitro

BACKGROUND

Indigowoad root polysaccharide (IRPS) is a natural polysaccharide isolated from the traditional Chinese medicinal herb Radix Isatidis, and has many kinds of biological activities. However, the IRPS antiviral activity, especially the anti-porcine reproductive and respiratory syndrome virus (PRRSV) effect, has not been evaluated.

METHODS

PRRSV was propagated in the MARC-145 cell line, and viral titre was determined by cytopathic effect and expressed as the 50% tissue culture infection dose (TCID(50)) in the current study. The cell cytotoxic effect of IRPS toward MARC-145 was evaluated by MTT assay firstly, then the inhibitory effects of IRPS on PRRSV replication in vitro were investigated by determining the effect of IRPS upon a single replicative cycle of PRRSV in MARC-145 cells. The effects of IRPS on viral RNA and protein synthesis in PRRSV-infected cells were investigated using real-time PCR and double-antibody (sandwich) ELISA.

RESULTS

IRPS was able to effectively suppress the infectivity of the PRRSV in a dose-dependent manner, especially by adding IRPS during the PRRSV infection. IRPS could affect the attachment of PRRSV to MARC-145 cells, and also inhibit the viral RNA and protein synthesis.

CONCLUSIONS

IRPS has an antiviral effect on PRRSV replication in MARC-145 cells and might be useful in medical development for antiviral research. However, the precise mechanism of the host and viral targets of IRPS are unknown, so further studies should be conducted to investigate the precise mechanism of IRPS inhibitory effect on PRRSV infection.

Inhibition of porcine reproductive and respiratory syndrome virus infection in piglets by a peptide-conjugated morpholino oligomer

Porcine reproductive and respiratory syndrome (PRRS) causes substantial economic losses to the swine industry in many countries, and current control strategies are inadequate. Previously, we explored the strategy of using peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) to inhibit PRRS virus (PRRSV) replication. PPMOs are nuclease-resistant and single-stranded DNA analogs containing a modified backbone conjugated to a cell-penetrating peptide and can act as antisense agents through steric blockade of complementary messenger RNA. A PPMO (designated 5UP2) targeting highly conserved sequence in the 5'-terminal region of the PRRSV genome was found to produce multi-log10 inhibition of PRRSV replication in cultured cells. To evaluate 5UP2 in vivo, we here administrated the PPMO to 3-week-old piglets via intranasal instillation at 24h before, and 2 and 24h after infection with PRRSV (strain VR2385). Blood samples were collected at 6, 10 and 14 days post-infection (dpi) for detection of PRRSV RNA and antibodies. Necropsy was performed at 14 dpi. Monitoring weight gain in all piglet groups throughout the experiment indicated that PPMO was well tolerated at the doses used. PPMO 5UP2 treatment significantly reduced PRRSV viremia at 6 dpi. On day 14, piglets receiving 5UP2 had significantly less interstitial pneumonia and lower level of anti-PRRSV antibodies than untreated piglets. In alveolar macrophages isolated at the time of necropsy, the expression of antiviral genes in PPMO-treated piglets was elevated in comparison with untreated. This study provides further data indicating that the 5UP2 PPMO can be considered a candidate component for a novel PRRS control strategy.

Porcine reproductive and respiratory syndrome virus inhibits type I interferon signaling by blocking STAT1/STAT2 nuclear translocation

Type I interferons (IFNs) IFN-α/β play an important role in innate immunity against viral infections by inducing antiviral responses. Porcine reproductive and respiratory syndrome virus (PRRSV) inhibits the synthesis of type I IFNs. However, whether PRRSV can inhibit IFN signaling is less well understood. In the present study, we found that PRRSV interferes with the IFN signaling pathway. The transcript levels of IFN-stimulated genes ISG15 and ISG56 and protein level of signal transducer and activator of transcription 2 (STAT2) in PRRSV VR2385-infected MARC-145 cells were significantly lower than those in mock-infected cells after IFN-α treatment. IFN-induced phosphorylation of both STAT1 and STAT2 and their heterodimer formation in the PRRSV-infected cells were not affected. However, the majority of the STAT1/STAT2/IRF9 (IFN regulatory factor 9) heterotrimers remained in the cytoplasm of PRRSV-infected cells, which indicates that the nuclear translocation of the heterotrimers was blocked. Overexpression of NSP1β of PRRSV VR2385 inhibited expression of ISG15 and ISG56 and blocked nuclear translocation of STAT1, which suggests that NSP1β might be the viral protein responsible for the inhibition of IFN signaling. PRRSV infection in primary porcine pulmonary alveolar macrophages (PAMs) also inhibited IFN-α-stimulated expression of the ISGs and the STAT2 protein. In contrast, a licensed low-virulence vaccine strain, Ingelvac PRRS modified live virus (MLV), activated expression of IFN-inducible genes, including those of chemokines and antiviral proteins, in PAMs without the addition of external IFN and had no detectable effect on IFN signaling. These findings suggest that PRRSV interferes with the activation and signaling pathway of type I IFNs by blocking ISG factor 3 (ISGF3) nuclear translocation.

Curing of HeLa cells persistently infected with equine arteritis virus by a peptide-conjugated morpholino oligomer

A significant consequence of equine arteritis virus (EAV) infection of horses is persistence of the virus in a variable percentage of infected stallions. We recently established an in vitro model of EAV persistence in cell culture for the purpose of furthering our understanding of EAV biology in general and viral persistence in the stallion in particular. In this study we investigated whether persistently infected HeLa cells could be cured of EAV infection by treatment with an antisense peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) designed to target the 5'-terminal region of the EAV genome. We found that persistently infected HeLa cells passaged three times in the presence of 5-10 microM EAV-specific PPMO produced no detectable virus. The PPMO-cured HeLa cells were free of infectious virus, viral antigen and EAV RNA as measured by plaque assay, indirect immunofluorescence assay and RT-PCR, respectively. Furthermore, when re-challenged with EAV at several passages after discontinuation of PPMO treatments, PPMO-cured HeLa cells were found to be refractory to re-infection and to the re-establishment of viral persistence. While these findings demonstrate that PPMO can be used to eliminate persistent EAV infection in cell culture, the efficacy of PPMO against EAV in vivo remains to be addressed.

Cell-Penetrating Peptides for Antiviral Drug Development

Viral diseases affect hundreds of millions of people worldwide, and the few available drugs to treat these diseases often come with limitations. The key obstacle to the development of new antiviral agents is their delivery into infected cells in vivo. Cell-penetrating peptides (CPPs) are short peptides that can cross the cellular lipid bilayer with the remarkable capability to shuttle conjugated cargoes into cells. CPPs have been successfully utilized to enhance the cellular uptake and intracellular trafficking of antiviral molecules, and thereby increase the inhibitory activity of potential antiviral proteins and oligonucleotide analogues, both in cultured cells and in animal models. This review will address the notable findings of these studies, highlighting some promising results and discussing the challenges CPP technology has to overcome for further clinical applications.

Morpholino oligomer-mediated protection of porcine pulmonary alveolar macrophages from arterivirus-induced cell death

BACKGROUND

Porcine reproductive and respiratory syndrome (PRRS) causes extensive economic losses in the swine industry. Current strategies and vaccines to control the disease are inadequate. We previously demonstrated that peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs) could potently inhibit PRRS virus (PRRSV) replication in cell cultures. PPMOs are single-stranded DNA analogues containing a modified backbone and cell-penetrating peptide. PPMOs are nuclease-resistant, water-soluble, can enter cells readily and exhibit highly specific binding to complementary RNA. In this study, we examined PPMO-mediated inhibition of PRRSV replication in a primary culture of porcine pulmonary alveolar macrophages (PAMs).

METHODS

PAMs were collected from piglets, pre-incubated in culture and infected with PRRSV. Viability, cytopathic effects, virus yield and apoptosis of PAMs in the presence or absence of a PPMO (5UP2) were examined. The 5UP2 PPMO is complementary to a conserved sequence in the 5'-terminal region of the PRRSV genome. The level of several interferon-associated gene products and activity of caspases were monitored.

RESULTS

PRRSV infection induced the activity of caspases-3/7, -8 and -9 significantly. Treatment of PAMs with 5UP2 resulted in protection of the cells from PRRSV-induced cell death for at least 7 days and avoided the activation of the caspases evaluated. 5UP2 treatment of PRRSV-infected PAMs also prevented the vigorous induction of interferon-beta and chemokines observed in infected and mock-treated PAMs.

CONCLUSIONS

PPMO-mediated suppression of PRRSV replication in PAMs was associated with a reduction of apoptotic and inflammatory responses. These results provide further rationale for the development of PPMO 5UP2 as an antiviral to control PRRSV infection.

Enhanced inhibition of porcine reproductive and respiratory syndrome virus replication by combination of morpholino oligomers

Porcine reproductive and respiratory syndrome (PRRS) has caused heavy economic losses in the swine industry worldwide and current strategies to control PRRS are inadequate. Previous studies have shown that peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) can be an effective antiviral against the PRRS virus (PRRSV). PPMO is structurally similar to DNA with modified backbone and is resistant to nuclease. This study was designed to examine increasing inhibitory effect of PPMO combination. Two pairs of PPMOs were identified to have enhanced suppression of PRRSV replication in cell culture, while individual constituents did not work under the same testing conditions. PPMO 5UP1 that is complementary to 5′ terminus of PRRSV genome was paired with 4P1 or 7P1 that are complementary to sequence in the translation initiation regions of ORFs 4 and 7, respectively. The PPMO combination also inhibited replication of heterologous strains in the North American PRRSV genotype. Treatment of the cells with the combinations reduced PRRSV RNA and protein levels. In cell-free or cell-based luciferase reporter assays, the PPMO combination suppressed target mRNA translation more effectively than individual constituents, indicating that the suppression was due to their antisense effect. These results suggest potential application of these PPMO combinations for PRRS control.

Inhibition of measles virus infections in cell cultures by peptide-conjugated morpholino oligomers

Measles virus (MeV) is a highly contagious human pathogen. Despite the success of measles vaccination programs, measles is still responsible for an estimated 245,000 deaths each year. There are currently no antiviral compounds available for the treatment of measles. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO) are antisense compounds that enter cells readily and can interfere with mRNA function by steric blocking. A panel of PPMO was designed to target various sequences of MeV RNA that are known to be important for viral replication. Five PPMO, targeting MeV genomic RNA or mRNA, inhibited the replication of MeV, in a dose-responsive and sequence-specific manner in cultured cells. One of the highly active PPMO (PPMO 454), targeting a conserved sequence in the translation start site of the mRNA coding for the nucleocapsid protein, inhibited multiple genotypes of MeV. This report provides evidence that PPMO treatment represents a promising approach for developing antiviral agents against measles and other paramyxoviruses.

Blockade of viral interleukin-6 expression of Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8, is associated with several malignant disorders, including Kaposi's sarcoma, primary effusion lymphoma (PEL), and multicentric Castleman's disease. An early lytic gene of KSHV encodes viral interleukin-6 (vIL-6), a viral homologue of the proinflammatory cytokine and an autocrine/paracrine growth factor human IL-6. In this study, we examined the effects of suppressing vIL-6 expression in PEL cells with antisense peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO). PPMO are ssDNA-analogues that have a modified backbone and enter cells readily. Treatment of PEL cells with a PPMO designed against vIL-6 mRNA led to a marked reduction in the proportion of vIL-6-positive cells detected by immunofluorescence assay. Analysis by Western blot confirmed a specific reduction in the vIL-6 protein level and showed that the reduction was dependent on the dose of vIL-6 PPMO. PEL cells treated with the vIL-6 PPMO exhibited reduced levels of cellular growth, IL-6 expression and KSHV DNA, and an elevated level of p21 protein. Treatment of PEL cells with a combination of two vIL-6 PPMO compounds targeting different sequences in the vIL-6 mRNA led to an inhibitory effect that was greater than that achieved with either PPMO alone. These results show that PPMO targeting vIL-6 mRNA can potently reduce vIL-6 protein translation and indicate that further exploration of these compounds in an animal model for potential clinical application is warranted.

Inhibition of alphavirus infection in cell culture and in mice with antisense morpholino oligomers

The genus Alphavirus contains members that threaten human health, both as natural pathogens and as potential biological weapons. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO) enter cells readily and can inhibit viral replication through sequence-specific steric blockade of viral RNA. Sindbis virus (SINV) has low pathogenicity in humans and is regularly utilized as a model alphavirus. PPMO targeting the 5′-terminal and AUG translation start site regions of the SINV genome blocked the production of infectious SINV in tissue culture. PPMO designed against corresponding regions in Venezuelan equine encephalitis virus (VEEV) were likewise found to be effective in vitro against several strains of VEEV. Mice treated with PPMO before and after VEEV infection were completely protected from lethal outcome while mice receiving only post-infection PPMO treatment were partially protected. Levels of virus in tissue samples correlated with animal survival. Uninfected mice suffered no apparent ill-effects from PPMO treatment. Thus, PPMO appear promising as candidates for therapeutic development against alphaviruses.

Inhibition of influenza A H3N8 virus infections in mice by morpholino oligomers

New methods to combat influenza A virus (FLUAV) in humans and animals are needed. The H3N8 subtype virus was the cause of the pandemic of 1890 and has recently undergone cross-species transmission from horses to dogs in the USA. In 2007 H3N8 spread to Australia, a continent previously devoid of equine influenza. Here, we show that antisense-peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs), delivered by intranasal administration, are able to inhibit the replication of FLUAV A/Eq/Miami/1/63 (H3N8) in mice by over 95% compared to controls. Monitoring of body weight and immune cell infiltrates in the lungs of noninfected mice indicated that PPMO treatment was not toxic at a concentration shown to be effectively antiviral in vivo. In addition, we detected a naturally occurring mutation within the PPMO target site of a viral gene that may be the cause of resistance to one of the two antisense PPMO sequences tested. These data indicate that PPMOs targeting highly conserved regions of FLUAV are promising novel therapeutic candidates.

Peptide-conjugated morpholino oligomers inhibit porcine reproductive and respiratory syndrome virus replication

Porcine reproductive and respiratory syndrome (PRRS) has been devastating the global swine industry for more than a decade, and current strategies to control PRRS are inadequate. In this study we characterized the inhibition of PRRS virus (PRRSV) replication by antisense phosphorodiamidate morpholino oligomers (PMO). Of 12 peptide-conjugated PMO (PPMO), four were found to be highly effective at inhibiting PRRSV replication in cell culture in a dose-dependant and sequence-specific manner. PPMO 5UP2 and 5HP are complementary to sequence in the 5′ end of the PRRSV genome, and 6P1 and 7P1 to sequence in the translation initiation regions of ORF6 and ORF7, respectively. Treatment of cells with 5UP2 or 5HP caused a 4.5 log₁₀ reduction in PRRSV yield, compared to a control PPMO. Combination of 6P1 and 7P1 led to higher level reduction than 6P1 or 7P1 alone. 5UP2, 5HP, and a combination of 6P1 and 7P1 inhibited PRRSV replication in porcine alveolar macrophages and protected the cells from PRRSV-induced cytopathic effect. Northern blot and real-time RT-PCR results demonstrated that the effective PPMO led to a reduction of PRRSV RNA level. 5UP2 and 5HP inhibited virus replication of 10 other strains of PRRSV. Results from this study suggest potential applications of PPMO for PRRS control.

Antiviral effects of antisense morpholino oligomers in murine coronavirus infection models

The recent emergence of novel pathogenic human and animal coronaviruses has highlighted the need for antiviral therapies that are effective against a spectrum of these viruses. We have used several strains of murine hepatitis virus (MHV) in cell culture and in vivo in mouse models to investigate the antiviral characteristics of peptide-conjugated antisense phosphorodiamidate morpholino oligomers (P-PMOs). Ten P-PMOs directed against various target sites in the viral genome were tested in cell culture, and one of these (5TERM), which was complementary to the 5' terminus of the genomic RNA, was effective against six strains of MHV. Further studies were carried out with various arginine-rich peptides conjugated to the 5TERM PMO sequence in order to evaluate efficacy and toxicity and thereby select candidates for in vivo testing. In uninfected mice, prolonged P-PMO treatment did not result in weight loss or detectable histopathologic changes. 5TERM P-PMO treatment reduced viral titers in target organs and protected mice against virus-induced tissue damage. Prophylactic 5TERM P-PMO treatment decreased the amount of weight loss associated with infection under most experimental conditions. Treatment also prolonged survival in two lethal challenge models. In some cases of high-dose viral inoculation followed by delayed treatment, 5TERM P-PMO treatment was not protective and increased morbidity in the treated group, suggesting that P-PMO may cause toxic effects in diseased mice that were not apparent in the uninfected animals. However, the strong antiviral effect observed suggests that with further development, P-PMO may provide an effective therapeutic approach against a broad range of coronavirus infections.