Primary resistance mechanism of the canine distemper virus fusion protein against a small-molecule membrane fusion inhibitor

Highly Potent Host-Specific Small-Molecule Inhibitor of Paramyxovirus and Pneumovirus Replication with High Resistance Barrier

Multiple enveloped RNA viruses of the family Paramyxoviridae and Pneumoviridae, like measles virus (MeV), Nipah virus (NiV), canine distemper virus (CDV), or respiratory syncytial virus (RSV), are of high clinical relevance. Each year a huge number of lives are lost as a result of these viral infections. Worldwide, MeV infection alone is responsible for over a hundred thousand deaths each year despite available vaccine. Therefore, there is an urgent need for treatment options to counteract these viral infections. The development of antiviral drugs in general stands as a huge challenge due to the rapid emergence of viral escape mutants. Here, we disclose the discovery of a small-molecule antiviral, compound 1 (ZHAWOC9045), active against several pneumo-/paramyxoviruses, including MeV, NiV, CDV, RSV, and parainfluenza virus type 5 (PIV-5). A series of mechanistic characterizations revealed that compound 1 targets a host factor which is indispensable for viral genome replication. Drug resistance profiling against a paramyxovirus model (CDV) demonstrated no detectable adaptation despite prolonged time of investigation, thereby mitigating the rapid emergence of escape variants. Furthermore, a thorough structure-activity relationship analysis of compound 1 led to the invention of 100-times-more potent-derivatives, e.g., compound 2 (ZHAWOC21026). Collectively, we present in this study an attractive host-directed pneumoviral/paramyxoviral replication inhibitor with potential therapeutic application.

Antiviral Screen against Canine Distemper Virus-Induced Membrane Fusion Activity

Canine distemper virus (CDV), a close relative of the human pathogen measles virus (MeV), is an enveloped, negative sense RNA virus that belongs to the genus Morbillivirus and causes severe diseases in dogs and other carnivores. Although the vaccination is available as a preventive measure against the disease, the occasional vaccination failure highlights the importance of therapeutic alternatives such as antivirals against CDV. The morbilliviral cell entry system relies on two interacting envelope glycoproteins: the attachment (H) and fusion (F) proteins. Here, to potentially discover novel entry inhibitors targeting CDV H, F and/or the cognate receptor: signaling lymphocyte activation molecule (SLAM) proteins, we designed a quantitative cell-based fusion assay that matched high-throughput screening (HTS) settings. By screening two libraries of small molecule compounds, we successfully identified two membrane fusion inhibitors (F2736-3056 and F2261-0043). Although both inhibitors exhibited similarities in structure and potency with the small molecule compound 3G (an AS-48 class morbilliviral F-protein inhibitor), F2736-3056 displayed improved efficacy in blocking fusion activity when a 3G-escape variant was employed. Altogether, we present a cell-based fusion assay that can be utilized not only to discover antiviral agents against CDV but also to dissect the mechanism of morbilliviral-mediated cell-binding and cell-to-cell fusion activity.

Development of a double monoclonal antibody-based sandwich enzyme-linked immunosorbent assay for detecting canine distemper virus

Abstract

Canine distemper virus (CDV) infection causes mass mortality in diverse carnivore species. For effective virus surveillance, rapid and sensitive assays are needed to detect CDV in field samples. In this study, after BABL/c mice were immunized with recombinant CDV-fusion (F) protein, monoclonal antibodies (mAbs) against recombinant CDV-F protein (designated 1A5, 1A6, and 7D5) were produced using traditional hybridoma cell technology. Next, capture antibody (1A6, 800 ng/well) and horseradish peroxidase (HRP)–conjugated detection antibody (HRP-7D5, 1:100, 500 ng/well) were used in a double monoclonal antibody–based sandwich enzyme-linked immunosorbent assay (ELISA) for CDV detection after optimization of both mAb amounts per well using a checkerboard titration test. Based on sandwich ELISA test results for 120 known CDV-negative samples, the cutoff value for a positive result was set to an OD_450 nm value ≥ 0.196. As compared with test results obtained from commercial immune colloidal gold test strips, the low limits of detection for the two assays were revealed to be 100 TCID₅₀ per 100 μL. In addition, the sandwich ELISA agreed 100% and 96.4% with commercial immune colloidal gold test strips when testing serum and stool samples. The sandwich ELISA assay provided statistically similar CDV detection. Thus, the sandwich ELISA developed here to detect CDV in fecal and serum samples provided good sensitivity, high specificity, and good reproducibility and should serve as an ideal method for large-scale surveillance of CDV infections in carnivores.

Key points

• Three CDV mAbs that recognized different epitopes and bound to virion were generated.

• The sandwich ELISA based mAbs to detect CDV in fecal and serum samples was developed.

• The sandwich ELISA is an ideal method for detecting CDV infections in the field.

Isolation and molecular characterizations of canine distemper virus from a naturally infected Korean dog using Vero cells expressing dog signaling lymphocyte activation molecule

Background

Canine distemper virus (CDV) infection results in high morbidity and mortality in dogs. There has been no report about isolation of Korean CDV since 1980 in Korea.

Objectives

To investigate the biological properties and the genetic characterization of Korean CDV.

Methods

Vero cells expressing dog signaling lymphocyte activation molecule (dSLAM) gene named as Vero/dSLAM were used to isolate CDV using 17 samples. Diagnostic methods such as cytopathic effects, immunofluorescence assay, peroxidase linked assay, electron microscopy, rapid immunodiagnostic assay, and reverse transcription polymerase chain reaction were used to confirm the Korean CDV isolate as a CDV. The genetic analysis was performed through cloning and sequencing of hemagglutinin gene of CDV isolate.

Results

A virus propagated in Vero/dSLAM cell was confirmed as CDV (CD1901 strain) based on the above methods. The CD1901 strain showed the highest viral titer (10^5.5 50% tissue culture infectious dose [TCID₅₀]/mL) in the Vero/dSLAM cells at 4 days post inoculation, but did not form a fork on chorioallantoic membrane of 7-day-old egg. Ribavirin, a nucleotide analogue anti-viral agent, inhibits moderately the Korean CDV propagation in the Vero/dSLAM cells. The nucleotide and amino acid sequences of the H gene of CD1901 strain were compared with those of other CDV strains. The CD1901 strain belonged to Asia 1 group and had the highest similarity (99.9%) with the BA134 strain, which was isolated in China in 2008.

Conclusions

We constructed successfully Vero/dSLAM and isolated one Korean CDV isolate (CD1901 strain) from a naturally infected dog. The CD1901 strain belonged to Asia 1 genotype.

Cryo-EM structure of the prefusion state of canine distemper virus fusion protein ectodomain

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Expression and purification of prefusion CDV solF in presence of a fusion inhibitor.

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Elucidation of the CDV fusion protein ectodomain by cryo-EM.

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High structural similarity between MeV and CDV solF suggests common fusion mechanisms.

Measles virus (MeV) and canine distemper virus (CDV), two members of the Morbillivirus genus, are still causing important global diseases of humans and animals, respectively. To enter target cells, morbilliviruses rely on an envelope-anchored machinery, which is composed of two interacting glycoproteins: a tetrameric receptor binding (H) protein and a trimeric fusion (F) protein. To execute membrane fusion, the F protein initially adopts a metastable, prefusion state that refolds into a highly stable postfusion conformation as the result of a finely coordinated activation process mediated by the H protein. Here, we employed cryo-electron microscopy (cryo-EM) and single particle reconstruction to elucidate the structure of the prefusion state of the CDV F protein ectodomain (solF) at 4.3 Å resolution. Stabilization of the prefusion solF trimer was achieved by fusing the GCNt trimerization sequence at the C-terminal protein region, and expressing and purifying the recombinant protein in the presence of a morbilliviral fusion inhibitor class compound. The three-dimensional cryo-EM map of prefusion CDV solF in complex with the inhibitor clearly shows density for the ligand at the protein binding site suggesting common mechanisms of membrane fusion activation and inhibition employed by different morbillivirus members.

Measles Resurgence and Drug Development

Measles caused an estimated minimum of one million fatalities annually before vaccination. Outstanding progress towards controlling the virus has been made since the measles vaccine was introduced, but reduction of measles case-fatalities has stalled at around 100,000 annually for the last decade and a 2019 resurgence in several geographical regions threatens some of these past accomplishments. Whereas measles eradication through vaccination is feasible, a potentially open-ended endgame of elimination may loom. Other than doubling-down on existing approaches, is it worthwhile to augment vaccination efforts with antiviral therapeutics to solve the conundrum? This question is hypothetical at present, since no drugs have yet been approved specifically for the treatment of measles, or infection by any other pathogen of the paramyxovirus family. This article will consider obstacles that have hampered anti-measles and anti-paramyxovirus drug development, discuss MeV-specific challenges of clinical testing, and define drug properties suitable to address some of these problems.

Antivirals in medical biodefense

The viruses historically implicated or currently considered as candidates for misuse in bioterrorist events are poxviruses, filoviruses, bunyaviruses, orthomyxoviruses, paramyxoviruses and a number of arboviruses causing encephalitis, including alpha- and flaviviruses. All these viruses are of concern for public health services when they occur in natural outbreaks or emerge in unvaccinated populations. Recent events and intelligence reports point to a growing risk of dangerous biological agents being used for nefarious purposes. Public health responses effective in natural outbreaks of infectious disease may not be sufficient to deal with the severe consequences of a deliberate release of such agents. One important aspect of countermeasures against viral biothreat agents are the antiviral treatment options available for use in post-exposure prophylaxis. These issues were adressed by the organizers of the 16th Medical Biodefense Conference, held in Munich in 2018, in a special session on the development of drugs to treat infections with viruses currently perceived as a threat to societies or associated with a potential for misuse as biothreat agents. This review will outline the state-of-the-art methods in antivirals research discussed and provide an overview of antiviral compounds in the pipeline that are already approved for use or still under development.

Phylogenomic Analysis of Two Co-Circulating Canine Distemper Virus Lineages in Colombia

Canine distemper virus (CDV) is considered a reemerging disease-causing agent in domestic dogs because it presents high divergence among circulating strains worldwide. In Colombia, the South America-3 and South America/North America-4 lineages co-circulate in domestic dogs, both in the Medellin metropolitan area. In this paper, two full CDV genomes from each viral lineage circulating in Medellin were sequenced; we explored the phylogenetic relationship with the available genome sequences; we described the presence of CDV mutations in the South America-3 and South America/North America-4 lineages associated with adaptation to human cells and a crossing of the species barrier and pathogenicity; and we established the evolutionary rates and time of the closest common ancestor for each gene and characterized the presentation of multiple genomic sites by positive selection.