Zika virus, vaccines, and antiviral strategies

Identification of Ascomycin against Zika virus infection through screening of natural product library

Zika virus (ZIKV) infection could lead to Guillain-Barré syndrome in adults and microcephaly in the newborns from infected pregnant women. To date, there is no specific drug for the treatment of ZIKV infection. In this study, we sought to screen inhibitors against ZIKV infection from a natural product library. A ZIKV replicon was used to screen a library containing 1680 natural compounds. We explored the antiviral mechanism of the compound candidate in vitro and in vivo infection models. Ascomycin, a macrolide from Streptomyces hygroscopicus, was identified with inhibitory effect against ZIKV in Vero cells (IC₅₀ = 0.11 μM), hepatoma cell Huh7 (IC₅₀ = 0.38 μM), and glioblastoma cell SNB-19 (IC₅₀ = 0.06 μM), far below the cytotoxic concentrations. Mechanistic study revealed that Ascomycin suppressed ZIKV RNA replication step during the life cycle and the regulation of calcineurin-NFAT pathway maybe involved in this inhibitory effect, independent of innate immunity activation. Moreover, we found that Ascomycin also inhibited the infection of other Flaviviridae members, such as hepatitis C virus and dengue virus. Ascomycin reduced ZIKV load in blood by up to 3500-fold in A129 mice. Meanwhile, the infection in the mice brain was undetectable by immunohistochemistry staining. Together, these findings reveal a critical role of Ascomycin in the inhibition of ZIKV and related viruses, facilitating the development of novel antiviral agents.

G-quadruplex binder pyridostatin as an effective multi-target ZIKV inhibitor

At present, there are still no anti-Zika virus (ZIKV) drugs or vaccines approved by FDA with accurate targets and antiviral mechanisms. Considering the RNA G-quadruplex sequences in ZIKV genome, it is very meaningful to develop G-quadruplex binders as potential anti-ZIKV drugs with novel and accurate targets. In this paper, five classical G-quadruplex binders including Ber, Braco 19, NiL, 360A and PDS have been chosen to discuss their interaction with ZIKV RNA G-quadruplexes. PDS shows higher binding affinity and thermal stability than the other G-quadruplex binders. This property is further evidenced in cells by immunofluorescence microscopy. And PDS shows higher anti-ZIKV activity (EC₅₀ = 4.2 ± 0.4 μM) than the other G-quadruplex binders as well as the positive control ribavirin, with a low cytotoxicity. By time-of-addition assay, PDS exerts antiviral activity at the post-entry process of ZIKV replication cycle, thus inhibiting ZIKV mRNA replication and protein expression. Furthermore, PDS combines with ZIKV NS2B-NS3 protease and reduces its catalytic activity. This study suggests that G-quadruplex binder PDS is an effective multi-target ZIKV inhibitor, which provides more guidance to design some novel anti-ZIKV drugs targeting ZIKV RNA G-quadruplexes.

Identification and Characterization of Zika Virus NS5 Methyltransferase Inhibitors

The recurring outbreak of Zika virus (ZIKV) worldwide makes an emergent demand for novel, safe and efficacious anti-ZIKV agents. ZIKV non-structural protein 5 (NS5) methyltransferase (MTase), which is essential for viral replication, is regarded as a potential drug target. In our study, a luminescence-based methyltransferase assay was used to establish the ZIKV NS5 MTase inhibitor screening model. Through screening a natural product library, we found theaflavin, a polyphenol derived from tea, could inhibit ZIKV NS5 MTase activity with a 50% inhibitory concentration (IC₅₀) of 10.10 μM. Molecular docking and site-directed mutagenesis analyses identified D146 as the key amino acid in the interaction between ZIKV NS5 MTase and theaflavin. The SPR assay indicated that theaflavin had a stronger binding activity with ZIKV NS5 wild-type (WT)-MTase than it with D146A-MTase. Moreover, theaflavin exhibited a dose dependent inhibitory effect on ZIKV replication with a 50% effective concentration (EC₅₀) of 8.19 μM. All these results indicate that theaflavin is likely to be a promising lead compound against ZIKV.

Antiviral activity against Zika virus of a new formulation of curcumin in poly lactic-co-glycolic acid nanoparticles

OBJECTIVES

In the search of an effective antiviral formulation, the natural product curcumin (CUR) was encapsulated into poly(lactic-co-glycolic acid) nanoparticles, a non-toxic bioresorbable and biocompatible copolymer. The resulting CUR containing particles (PLGA-CUR NPs) were characterized and analysed for antiviral activity against Zika virus (ZIKV) infection.

METHODS

The PLGA-CUR NPs were characterized by Fourier transform infrared, differential scanning calorimetry, dynamic light scattering, scanning electron microscopy and thermogravimetric analysis and release profile. Cytotoxicity of PLGA-CUR and the antiviral activity against ZIKV were determined in Vero cells. The effect of PLGA-CUR NPs on viral RNA synthesis and protein expression was analysed by RT-qPCR and immunofluorescence staining, respectively.

KEY FINDINGS

The PLGA-CUR NPs showed an appropriate in vitro drug release profile. Our studies of the antiviral activity of PLGA-CUR NPs and CUR against ZIKV by virus yield reduction as well as viral RNA synthesis and protein expression have shown that PLGA-CUR formulation is more effective than free CUR to inhibit ZIKV infection of Vero cells.

CONCLUSIONS

Our results demonstrate for the first time the antiviral activity against ZIKV of PLGA nanoparticles charged with CUR, suggesting that PLGA-CUR NPs are promising candidates for a drug formulation against human pathogenic flaviviruses.

Zika Virus

Zika virus (ZIKV), a neurotropic single-stranded RNA flavivirus, remains an important cause of congenital infection, fetal microcephaly, and Guillain-Barré syndrome in populations where ZIKV has adapted to a nexus involving the Aedes mosquitoes and humans. To date, outbreaks of ZIKV have occurred in Africa, Southeast Asia, the Pacific islands, the Americas, and the Caribbean. Emerging evidence, however, suggests that the virus also has the potential to cause infections in Europe, where autochtonous transmission of the virus has been identified. This review focuses on evolving ZIKV epidemiology, modes of transmission and host-virus interactions. The clinical manifestations, diagnostic issues relating to cross-reactivity to the dengue flavivirus and concerns surrounding ZIKV infection in pregnancy are discussed. In the last section, current challenges in treatment and prevention are outlined.

Novel Nucleoside Analogues as Effective Antiviral Agents for Zika Virus Infections

Previously considered a neglected flavivirus, Zika virus has recently emerged as a public health concern due to its ability to spread rapidly and cause severe neurological disorders, such as microcephaly in newborn babies from infected mothers, and Guillain-Barré syndrome in adults. Despite extensive efforts towards the identification of effective therapies, specific antivirals are still not available. As part of ongoing medicinal chemistry studies to identify new antiviral agents, we screened against Zika virus replication in vitro in a targeted internal library of small-molecule agents, comprising both nucleoside and non-nucleoside agents. Among the compounds evaluated, novel aryloxyphosphoramidate prodrugs of the nucleosides 2′-C-methyl-adenosine, 2-CMA, and 7-deaza-2′C-methyl-adenosine, 7-DMA, were found to significantly inhibit the virus-induced cytopathic effect in multiple relevant cell lines. In addition, one of these prodrugs exhibits a synergistic antiviral effect against Zika virus when applied in combination with an indirect antiviral agent, a l-dideoxy bicyclic pyrimidine nucleoside analogue, which potently inhibits vaccinia and measles viruses in vitro by targeting a host pathway. Our findings provide a solid basis for further development of an antiviral therapy for Zika virus infections, possibly exploiting a dual approach combining two different agents, one targeting the viral polymerase (direct-acting antiviral), the second targeting a host-directed autophagy mechanism.

In vitro Studies on The Inhibition of Replication of Zika and Chikungunya Viruses by Dolastane Isolated from Seaweed Canistrocarpus cervicornis

The lack of vaccines and antiviral treatment, along with the increasing number of cases of Zika virus (ZIKV) and Chikungunya virus (CHIKV) infections, emphasize the need for searching for new therapeutic strategies. In this context, the marine brown seaweed Canistrocarpus cervicornis has been proved to hold great antiviral potential. Hence, the aim of this work was to evaluate the anti-ZIKV and anti-CHIKV activity of a marine dolastane isolated from brown seaweed C. cervicornis and its crude extract. Vero cells were used in antiviral assays, submitted to ZIKV and CHIKV, and treated with different concentrations of C. cervicornis extract or dolastane. The crude extract of C. cervicornis showed inhibitory activities for both ZIKV and CHIKV, with EC50 values of 3.3 μg/mL and 3.1 μg/mL, respectively. However, the isolated dolastane showed a more significant and promising inhibitory effect (EC50 = 0.95 µM for ZIKV and 1.3 µM for CHIKV) when compared to both the crude extract and ribavirin, which was used as control. Also, the dolastane showed a very potent virucidal activity against CHIKV and was able to inhibit around 90% of the virus infectivity at 10 μM. For the ZIKV, the effects were somewhat lower, although interesting, at approximately 64% in this same concentration. Further, we observed that both the extract and the dolastane were able to inhibit the replication of ZIKV and CHIKV at different times of addition post-infection, remaining efficient even if added after 8 hours post-infection, but declining soon after. A synergistic effect using sub-doses of the extract and isolates was associated with ribavirin, inhibiting above 80% replication even at the lowest concentrations. Therefore, this work has unveiled the anti-ZIKV and CHIKV potential of C. cervicornis crude extract and an isolated dolastane, which, in turn, can be used as a preventive or therapeutic strategy in the future.

Structure-activity relationship of flavonoid bifunctional inhibitors against Zika virus infection

Zika virus (ZIKV) infection is a global public health problem due to its rapid spread and the possibility of causing microcephaly. Currently, no specific antivirals against ZIKV are available for treatment. In the present study, several flavonoids (galangin, kaempferide, quercetin, myricetin and EGCG) were found to reduce ZIKV induced plaques and viral RNA copies with negligible cytotoxic effects on host cells. In addition, inhibition of ZIKV propagation by flavonoids showed structure-activity relationship. Our results demonstrate flavonoids as inhibitors of ZIKV entry and NS2B-NS3 protease. Hence, these flavonoids could be used as potential bifunctional drugs for treating ZIKV infections.

Identification and characterization of Zika virus NS5 RNA-dependent RNA polymerase inhibitors

The current outbreak of Zika virus (ZIKV) is the impetus for novel, safe and efficacious anti-ZIKV agents. ZIKV non-structural protein 5 RNA-dependent RNA polymerase (RdRp) is essential for viral replication and is logically regarded as an attractive drug target. This study used a fluorescence-based polymerase assay to find an anti-infective drug 10-undecenoic acid zinc salt (UA) which could inhibit RdRp activity with a half maximal inhibitory concentration (IC₅₀) of 1.13-1.25 µM. Molecular docking and site-directed mutagenesis analyses identified D535 as the key amino acid in the interaction between RdRp and UA. Importantly, the surface plasmon resonance assay showed that UA had strong direct binding with ZIKV wild-type RdRp and a relatively weak interaction with D535A-RdRp. As a control, the nucleoside inhibitor sofosbuvir triphosphate (PSI-7409) conferred insensitivity to the fluorescence-based RdRp assay and cannot bind directly with RdRp. Moreover, UA showed anti-ZIKV activity comparable to sofosbuvir. All these results indicate that UA is likely to be a promising lead compound against ZIKV, exhibiting a different mechanism than sofosbuvir.

Pre-Clinical Pregnancy Models for Evaluating Zika Vaccines

Zika virus (ZIKV) infection during pregnancy can result in a variety of developmental abnormalities in the fetus, referred to as Congenital Zika Syndrome (CZS). The effects of CZS can range from the loss of the viable fetus to a variety of neurological defects in full-term infants, including microcephaly. The clinical importance of ZIKV-induced CZS has driven an intense effort to develop effective vaccines. Consequently, there are approximately 45 different ZIKV vaccine candidates at various stages of development with several undergoing phase I and II clinical trials. These vaccine candidates have been shown to effectively prevent infection in adult animal models, however, there has been less extensive testing for their ability to block vertical transmission to the fetus during pregnancy or prevent the development of CZS. In addition, it is becoming increasingly difficult to test vaccines in the field as the intensity of the ZIKV epidemic has declined precipitously, making clinical endpoint studies difficult. These ethical and practical challenges in determining efficacy of ZIKV vaccine candidates in preventing CZS have led to increased emphasis on pre-clinical testing in animal pregnancy models. Here we review the current status of pre-clinical pregnancy models for testing the ability of ZIKV vaccines to prevent CZS.

The Multifaceted Roles of Autophagy in Flavivirus-Host Interactions

Autophagy is an evolutionarily conserved cellular process in which intracellular components are eliminated via lysosomal degradation to supply nutrients for organelle biogenesis and metabolic homeostasis. Flavivirus infections underlie multiple human diseases and thus exert an immense burden on public health worldwide. Mounting evidence indicates that host autophagy is subverted to modulate the life cycles of flaviviruses, such as hepatitis C virus, dengue virus, Japanese encephalitis virus, West Nile virus and Zika virus. The diverse interplay between autophagy and flavivirus infection not only regulates viral growth in host cells but also counteracts host stress responses induced by viral infection. In this review, we summarize the current knowledge on the role of autophagy in the flavivirus life cycle. We also discuss the impacts of virus-induced autophagy on the pathogeneses of flavivirus-associated diseases and the potential use of autophagy as a therapeutic target for curing flavivirus infections and related human diseases.