Better late than never: antivirals for dengue

Efficacy of geraniin on dengue virus type-2 infected BALB/c mice

BACKGROUND

Dengue continues to be a major international public health concern. Despite that, there is no clinically approved antiviral for treatment of dengue virus (DENV) infections. In this study, geraniin extracted from the rind of Nephelium lappaceum was shown to inhibit the replication of DENV-2 in both in vitro and in vivo experiments.

METHODS

The effect of geraniin on DENV-2 RNA synthesis in infected Vero cells was tested using quantitative RT-PCR. The in vivo efficacy of geraniin in inhibiting DENV-2 infection was then tested using BALB/c mice with geraniin administered at three different times. The differences in spleen to body weight ratio, DENV-2 RNA load and liver damage between the three treatment groups as compared to DENV-2 infected mice without geraniin administration were determined on day eight post-infection.

RESULTS

Quantitative RT-PCR confirmed the decrease in viral RNA synthesis of infected Vero cells when treated with geraniin. Geraniin seemed to provide a protective effect on infected BALB/c mice liver when given at 24 h pre- and 24 h post-infection as liver damage was observed to be very mild even though a significant reduction of DENV-2 RNA load in serum was not observed in these two treatment groups. However, when administered at 72 h post-infection, severe liver damage in the form of necrosis and haemorrhage had prevailed despite a substantial reduction of DENV-2 RNA load in serum.

CONCLUSIONS

Geraniin was found to be effective in reducing DENV-2 RNA load when administered at 72 h post-infection while earlier administration could prevent severe liver damage caused by DENV-2 infection. These results provide evidence that geraniin is a potential candidate for the development of anti-dengue drug.

Geraniin extracted from the rind of Nephelium lappaceum binds to dengue virus type-2 envelope protein and inhibits early stage of virus replication

Background

The rapid rise and spread in dengue cases, together with the unavailability of safe vaccines and effective antiviral drugs, warrant the need to discover and develop novel anti-dengue treatments. In this study the antiviral activity of geraniin, extracted from the rind of Nephelium lappaceum, against dengue virus type-2 (DENV-2) was investigated.

Methods

Geraniin was prepared from Nephelium lappaceum rind by reverse phase C-18 column chromatography. Cytotoxicity of geraniin towards Vero cells was evaluated using MTT assay while IC₅₀ value was determined by plaque reduction assay. The mode-of-action of geraniin was characterized using the virucidal, attachment, penetration and the time-of-addition assays’. Docking experiments with geraniin molecule and the DENV envelope (E) protein was also performed. Finally, recombinant E Domain III (rE-DIII) protein was produced to physiologically test the binding of geraniin to DENV-2 E-DIII protein, through ELISA competitive binding assay.

Results

Cytotoxicity assay confirmed that geraniin was not toxic to Vero cells, even at the highest concentration tested. The compound exhibited DENV-2 plaque formation inhibition, with an IC₅₀ of 1.75 μM. We further revealed that geraniin reduced viral infectivity and inhibited DENV-2 from attaching to the cells but had little effect on its penetration. Geraniin was observed to be most effective when added at the early stage of DENV-2 infection. Docking experiments showed that geraniin binds to DENV E protein, specifically at the DIII region, while the ELISA competitive binding assay confirmed geraniin’s interaction with rE-DIII with high affinity.

Conclusions

Geraniin from the rind of Nephelium lappaceum has antiviral activity against DENV-2. It is postulated that the compound inhibits viral attachment by binding to the E-DIII protein and interferes with the initial cell-virus interaction. Our results demonstrate that geraniin has the potential to be developed into an effective antiviral treatment, particularly for early phase dengue viral infection.

The in vitro and in vivo antiviral properties of combined monoterpene alcohols against West Nile virus infection

West Nile Virus (WNV) is a mosquito-borne flavivirus that can cause neuroinvasive disease in humans and animals for which no therapies are currently available. We studied an established combination of monoterpene alcohols (CMA) derived from Melaleuca alternifolia, against WNV infection. The in vitro results show that CMA exhibits virucidal activity, as well as reduces the viral titres and percentage of infected cells. The antiviral mechanism of action of CMA was studied. We found that CMA did not alter the intracellular pH, neither induced apoptosis, but did induce cell cycle arrest in the G0/G1-phase although that was not the antiviral mechanism. Furthermore, we tested CMA in vivo using IRF 3(-)(/)(-)/7(-/-)mice and it was found that CMA treatment significantly delayed morbidity due to WNV infection, reduced the loss of body weight and reduced the viral titres in brain. These findings suggest that CMA could be a therapeutic agent against WNV infection.

Drug-drug interactions between antiretrovirals and drugs used in the management of neglected tropical diseases: important considerations in the WHO 2020 Roadmap and London Declaration on Neglected Tropical Diseases

The group of infections known as the neglected tropical diseases (NTDs) collectively affect one billion people worldwide, equivalent to one-sixth of the world's population. The NTDs cause severe physical and emotional morbidity, and have a profound effect on cycles of poverty; it is estimated that NTDs account for 534 000 deaths per year. NTDs such as soil-transmitted helminth infections and the vector-borne protozoal infections leishmaniasis and trypanosomiasis occur predominantly in the most economically disadvantaged and marginalized communities. It is estimated that all low-income countries harbour at least five of the NTDs simultaneously. NTDs are neglected because they do not individually rank highly in terms of mortality data, and because they affect populations with little political voice. There is considerable geographic overlap between areas with high prevalence of NTDs and HIV, raising the possibility of complex polypharmacy and drug-drug interactions. Antiretrovirals pose a particularly high risk for potential drug-drug interactions, which may be pharmacokinetic or pharmacodynamic in nature and can result in raising or lowering plasma or tissue concentrations of co-prescribed drugs. Elevated drug concentrations may be associated with drug toxicity and lower drug concentrations may be associated with therapeutic failure. The aim of this paper is to review the currently available data on interactions between antiretrovirals and drugs used in the management of NTDs. It is intended to serve as a resource for policy makers and clinicians caring for these patients, and to support the recent WHO 2020 Roadmap and the 2012 London Declaration on NTDs.

Novel approaches to flavivirus drug discovery

INTRODUCTION

The members of the family Flaviviridae, including West Nile virus, yellow fever virus and dengue virus, are important human pathogens that are expanding their impact around the globe. The four serotypes of dengue infect 50-100 million people each year, yet the only clinical treatment is supportive care to reduce symptoms. Drugs that employ novel inhibition mechanisms and targets are urgently needed to combat the growing incidence of dengue worldwide.

AREAS COVERED

The authors discuss recently discovered flavivirus inhibitors with a focus on antivirals targeting non-enzymatic proteins of the dengue virus lifecycle. Specifically, the authors discuss the flaviviruses, the need for novel inhibitors and the criteria for successful antiviral drug development. Current literature describing new advances in antiviral therapy at each stage of the flavivirus lifecycle (entry, endosomal escape, viral RNA processing and replication, assembly and immune evasion) are evaluated and summarized.

EXPERT OPINION

Overall, the prognosis of flavivirus antiviral drug development is positive: new effective compounds have been discovered and studied. However, repurposing existing compounds and a greater translation to the clinical setting are recommended in order to combat the growing threat of flaviviruses.