Progress towards the treatment of Ebola haemorrhagic fever

Induction of Apoptosis and Subsequent Phagocytosis of Virus-Infected Cells As an Antiviral Mechanism

Viruses are infectious entities that hijack host replication machineries to produce their progeny, resulting, in most cases, in disease and, sometimes, in death in infected host organisms. Hosts are equipped with an array of defense mechanisms that span from innate to adaptive as well as from humoral to cellular immune responses. We previously demonstrated that mouse cells underwent apoptosis in response to influenza virus infection. These apoptotic, virus-infected cells were then targeted for engulfment by macrophages and neutrophils. We more recently reported similar findings in the fruit fly Drosophila melanogaster, which lacks adaptive immunity, after an infection with Drosophila C virus. In these experiments, the inhibition of phagocytosis led to severe influenza pathologies in mice and early death in Drosophila. Therefore, the induction of apoptosis and subsequent phagocytosis of virus-infected cells appear to be an antiviral innate immune mechanism that is conserved among multicellular organisms. We herein discuss the underlying mechanisms and significance of the apoptosis-dependent phagocytosis of virus-infected cells. Investigations on the molecular and cellular features responsible for this underrepresented virus–host interaction may provide a promising avenue for the discovery of novel substances that are targeted in medical treatments against virus-induced intractable diseases.

Repurposed Therapeutic Agents Targeting the Ebola Virus: A Systematic Review

BACKGROUND

The Ebola virus has been responsible for numerous outbreaks since the 1970s, with the most recent outbreak taking place between 2014 and 2016 and causing an international public health emergency. Ebola virus disease (EVD) has a high mortality rate and no approved targeted treatment exists to date. A number of established drugs are being considered as potential therapeutic agents for the treatment of EVD.

OBJECTIVE

We aimed to identify potential drug repositioning candidates and to assess the scientific evidence available on their efficacy.

METHODS

We conducted a systematic literature search in MEDLINE, Embase, and other relevant trial registry platforms for studies published between January 1976 and January 2017. We included drug screening, preclinical studies, and clinical studies on repurposed drugs for the treatment of EVD. The risk of bias for animal studies and nonrandomized clinical studies was assessed. The quality of reporting for case series and case reports was evaluated. Finally, we selected drugs approved by established regulatory authorities, which have positive in vitro study outcomes and at least one additional animal or clinical trial.

RESULTS

We identified 3301 publications, of which 37 studies fulfilled our inclusion criteria. Studies were highly heterogeneous in terms of study type, methodology, and intervention. The risk of bias was high for 13 out of 14 animal studies. We selected 11 drugs with potential anti-EVD therapeutic effects and summarized their evidence.

CONCLUSIONS

Several established drugs may have therapeutic effects on EVD, but the quality and quantity of current scientific evidence is lacking. This review highlights the need for well-designed and conducted preclinical and clinical research to establish the efficacy of potential repurposed drugs against EVD.

Repurposed therapeutic agents targeting the Ebola virus: a protocol for a systematic review

BACKGROUND

The recent Ebola epidemic in western Africa developed into an acute public health emergency of unprecedented level in modern times. The treatment provided in most cases has been limited to supportive care, as no approved therapies are available to date. Several established, licenced drugs have been suggested as potential repurposed therapeutic agents for Ebola. However, scientific data on their efficacy in treating Ebola is limited. The purpose of this review is to systematically assess scientific evidence on potential drugs targeting Ebola. In specific, we aim to (1) identify drug library screens involving therapeutic agents targeting the Ebola virus, (2) list potential approved drugs identified from drug screens and review their mechanism of action against the Ebola virus and (3) summarise the outcome of preclinical and clinical trials investigating approved drugs targeting the Ebola virus.

METHODS/DESIGN

We will develop comprehensive systematic search strategies and will perform a systematic literature search in MEDLINE, Embase and Cochrane Central Register of Controlled Trials (CENTRAL). Two authors will independently screen the titles, abstracts and the references of all selected articles on the basis of inclusion criteria. These include any available drug screening, preclinical studies and clinical studies examining the efficacy of approved therapeutic agents targeting the Ebola virus. There will be no restrictions on the type of participants, the type of comparator, time or setting. Data extraction and quality assessment will be undertaken by two review authors working independently.

DISCUSSION

This systematic review will provide systematic knowledge on potential repurposed therapeutic agents targeting Ebola. It aims to help guide future investigations on repurposed drugs and avoid repetitive studies.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42015024349.

Clinical manifestations and case management of Ebola haemorrhagic fever caused by a newly identified virus strain, Bundibugyo, Uganda, 2007-2008

A confirmed Ebola haemorrhagic fever (EHF) outbreak in Bundibugyo, Uganda, November 2007–February 2008, was caused by a putative new species (Bundibugyo ebolavirus). It included 93 putative cases, 56 laboratory-confirmed cases, and 37 deaths (CFR = 25%). Study objectives are to describe clinical manifestations and case management for 26 hospitalised laboratory-confirmed EHF patients. Clinical findings are congruous with previously reported EHF infections. The most frequently experienced symptoms were non-bloody diarrhoea (81%), severe headache (81%), and asthenia (77%). Seven patients reported or were observed with haemorrhagic symptoms, six of whom died. Ebola care remains difficult due to the resource-poor setting of outbreaks and the infection-control procedures required. However, quality data collection is essential to evaluate case definitions and therapeutic interventions, and needs improvement in future epidemics. Organizations usually involved in EHF case management have a particular responsibility in this respect.

Nonhuman primates as models for the discovery and development of ebolavirus therapeutics

INTRODUCTION

Ebolaviruses are human pathogenic Category A priority pathogens for which no vaccines or therapeutics are currently licensed; however, several therapeutic agents have shown promising efficacy in nonhuman primate models of infection and are potential candidates for use in humans. Demonstration of efficacy in nonhuman primate models of ebolavirus infection will probably be central to the development and eventual licensure of ebolavirus medical countermeasures given the ethical and feasibility constraints of human efficacy assessments.

AREAS COVERED

The authors describe ebolavirus hemorrhagic fever (EHF), with an emphasis on comparing human and nonhuman primate pathophysiology. Published data examining human and animal clinical disease parameters, histopathological findings, and immune responses in fatal and nonfatal cases are synthesized and evaluated. Importantly, the authors also introduce and describe the FDA Animal Efficacy Rule as well as recent advances in antiviral drug development strategies for the treatment of EHF.

EXPERT OPINION

Well-characterized models of ebolavirus infection are currently under development and scrutiny as to their accuracy and utility for modeling fatal infection in humans. The advanced development and eventual licensure of therapeutic agents will require demonstration that mechanisms conferring protection in nonhuman primate models of infection are predictive of protective responses in humans.

Potential vaccines and post-exposure treatments for filovirus infections

Viruses of the family Filoviridae represent significant health risks as emerging infectious diseases as well as potentially engineered biothreats. While many research efforts have been published offering possibilities toward the mitigation of filoviral infection, there remain no sanctioned therapeutic or vaccine strategies. Current progress in the development of filovirus therapeutics and vaccines is outlined herein with respect to their current level of testing, evaluation, and proximity toward human implementation, specifically with regard to human clinical trials, nonhuman primate studies, small animal studies, and in vitro development. Contemporary methods of supportive care and previous treatment approaches for human patients are also discussed.

Therapeutics of Ebola hemorrhagic fever: whole-genome transcriptional analysis of successful disease mitigation

The mechanisms of Ebola (EBOV) pathogenesis are only partially understood, but the dysregulation of normal host immune responses (including destruction of lymphocytes, increases in circulating cytokine levels, and development of coagulation abnormalities) is thought to play a major role. Accumulating evidence suggests that much of the observed pathology is not the direct result of virus-induced structural damage but rather is due to the release of soluble immune mediators from EBOV-infected cells. It is therefore essential to understand how the candidate therapeutic may be interrupting the disease process and/or targeting the infectious agent. To identify genetic signatures that are correlates of protection, we used a DNA microarray-based approach to compare the host genome-wide responses of EBOV-infected nonhuman primates (NHPs) responding to candidate therapeutics. We observed that, although the overall circulating immune response was similar in the presence and absence of coagulation inhibitors, surviving NHPs clustered together. Noticeable differences in coagulation-associated genes appeared to correlate with survival, which revealed a subset of distinctly differentially expressed genes, including chemokine ligand 8 (CCL8/MCP-2), that may provide possible targets for early-stage diagnostics or future therapeutics. These analyses will assist us in understanding the pathogenic mechanisms of EBOV infection and in identifying improved therapeutic strategies.

The use of a mobile laboratory unit in support of patient management and epidemiological surveillance during the 2005 Marburg Outbreak in Angola

Background

Marburg virus (MARV), a zoonotic pathogen causing severe hemorrhagic fever in man, has emerged in Angola resulting in the largest outbreak of Marburg hemorrhagic fever (MHF) with the highest case fatality rate to date.

Methodology/Principal Findings

A mobile laboratory unit (MLU) was deployed as part of the World Health Organization outbreak response. Utilizing quantitative real-time PCR assays, this laboratory provided specific MARV diagnostics in Uige, the epicentre of the outbreak. The MLU operated over a period of 88 days and tested 620 specimens from 388 individuals. Specimens included mainly oral swabs and EDTA blood. Following establishing on site, the MLU operation allowed a diagnostic response in <4 hours from sample receiving. Most cases were found among females in the child-bearing age and in children less than five years of age. The outbreak had a high number of paediatric cases and breastfeeding may have been a factor in MARV transmission as indicated by the epidemiology and MARV positive breast milk specimens. Oral swabs were a useful alternative specimen source to whole blood/serum allowing testing of patients in circumstances of resistance to invasive procedures but limited diagnostic testing to molecular approaches. There was a high concordance in test results between the MLU and the reference laboratory in Luanda operated by the US Centers for Disease Control and Prevention.

Conclusions/Significance

The MLU was an important outbreak response asset providing support in patient management and epidemiological surveillance. Field laboratory capacity should be expanded and made an essential part of any future outbreak investigation.

A mobile laboratory unit (MLU) was deployed to Uige, Angola as part of the World Health Organization response to an outbreak of viral hemorrhagic fever caused by Marburg virus (MARV). Utilizing mainly quantitative real-time PCR assays, this laboratory provided specific MARV diagnostics in the field. The MLU operated for 88 consecutive days allowing MARV-specific diagnostic response in <4 hours from sample receiving. Most cases were found among females in the child-bearing age and in children less than five years of age including a high number of paediatric cases implicating breastfeeding as potential transmission route. Oral swabs were identified as a useful alternative specimen source to the standard whole blood/serum specimens for patients refusing blood draw. There was a high concordance in test results between the MLU and the reference laboratory in Luanda operated by the US Centers for Disease Control and Prevention. The MLU was an important outbreak response asset providing valuable support in patient management and epidemiological surveillance. Field laboratory capacity should be expanded and made an essential part of any future outbreak investigation.

Discovery, synthesis, and biological evaluation of a novel group of selective inhibitors of filoviral entry

Herein, we report the development of an antifiloviral screening system, based on a pseudotyping strategy, and its application in the discovery of a novel group of small molecules that selectively inhibit the Ebola and Marburg glycoprotein (GP)-mediated infection of human cells. Using Ebola Zaire GP-pseudotyped HIV particles bearing a luciferase reporter gene and 293T cells, a library of 237 small molecules was screened for inhibition of GP-mediated viral entry. From this assay, lead compound 8a was identified as a selective inhibitor of filoviral entry with an IC(50) of 30 μM. To analyze functional group requirements for efficacy, a structure-activity relationship analysis of this 3,5-disubstituted isoxazole was then conducted with 56 isoxazole and triazole derivatives prepared using "click" chemistry. This study revealed that while the isoxazole ring can be replaced by a triazole system, the 5-(diethylamino)acetamido substituent found in 8a is required for inhibition of viral-cell entry. Variation of the 3-aryl substituent provided a number of more potent antiviral agents with IC(50) values ranging to 2.5 μM. Lead compound 8a and three of its derivatives were also found to block the Marburg glycoprotein (GP)-mediated infection of human cells.

Filovirus emergence and vaccine development: a perspective for health care practitioners in travel medicine

Recent case reports of viral hemorrhagic fever in Europe and the United States have raised concerns about the possibility for increased importation of filoviruses to non-endemic areas. This emerging threat is concerning because of the increase in global air travel and the rise of tourism in central and eastern Africa and the greater dispersion of military troops to areas of infectious disease outbreaks. Marburg viruses (MARV) and Ebola viruses (EBOV) have been associated with outbreaks of severe hemorrhagic fever involving high mortality (25-90% case fatality rates). First recognized in 1967 and 1976 respectively, subtypes of MARV and EBOV are the only known viruses of the Filoviridae family, and are among the world's most virulent pathogens. This article focuses on information relevant for health care practitioners in travel medicine to include, the epidemiology and clinical features of filovirus infection and efforts toward development of a filovirus vaccine.

Disease modeling for Ebola and Marburg viruses

The filoviruses Ebola and Marburg are zoonotic agents that are classified as both biosafety level 4 and category A list pathogens. These viruses are pathogenic in humans and cause isolated infections or epidemics of viral hemorrhagic fever, mainly in Central Africa. Their natural reservoir has not been definitely identified, but certain species of African bat have been associated with Ebola and Marburg infections. Currently, there are no licensed options available for either treatment or prophylaxis. Different animal models have been developed for filoviruses including mouse, guinea pig and nonhuman primates. The 'gold standard' animal models for pathogenesis, treatment and vaccine studies are rhesus and cynomolgus macaques. This article provides a brief overview of the clinical picture and the pathology/pathogenesis of human filovirus infections. The current animal model options are discussed and compared with regard to their value in different applications. In general, the small animal models, in particular the mouse, are the most feasible for high biocontainment facilities and they offer the most options for research owing to the greater availability of immunologic and genetic tools. However, their mimicry of the human diseases as well as their predictive value for therapeutic efficacy in primates is limited, thereby making them, at best, valuable initial screening tools for pathophysiology, treatment and vaccine studies.

The temporal program of peripheral blood gene expression in the response of nonhuman primates to Ebola hemorrhagic fever

Primate blood cells were analysed for changes in global gene expression patterns at several time points following infection with Ebola virus, providing insights into potential mechanisms of viral pathogenesis and host defense.

Background

Infection with Ebola virus (EBOV) causes a fulminant and often fatal hemorrhagic fever. In order to improve our understanding of EBOV pathogenesis and EBOV-host interactions, we examined the molecular features of EBOV infection in vivo.

Results

Using high-density cDNA microarrays, we analyzed genome-wide host expression patterns in sequential blood samples from nonhuman primates infected with EBOV. The temporal program of gene expression was strikingly similar between animals. Of particular interest were features of the data that reflect the interferon response, cytokine signaling, and apoptosis. Transcript levels for tumor necrosis factor-α converting enzyme (TACE)/α-disintegrin and metalloproteinase (ADAM)-17 increased during days 4 to 6 after infection. In addition, the serum concentration of cleaved Ebola glycoprotein (GP_{2 delta}) was elevated in late-stage EBOV infected animals. Of note, we were able to detect changes in gene expression of more than 300 genes before symptoms appeared.

Conclusion

These results provide the first genome-wide ex vivo analysis of the host response to systemic filovirus infection and disease. These data may elucidate mechanisms of viral pathogenesis and host defense, and may suggest targets for diagnostic and therapeutic development.

Development of an immunofiltration-based antigen-detection assay for rapid diagnosis of Ebola virus infection

Ebola virus (EBOV) has caused outbreaks of severe viral hemorrhagic fever in regions of Central Africa where medical facilities are ill equipped and diagnostic capabilities are limited. To obtain a reliable test that can be implemented easily under these conditions, monoclonal antibodies to the EBOV matrix protein (VP40), which previously had been found to work in a conventional enzyme-linked immunosorbent assay, were used to develop an immunofiltration assay for the detection of EBOV antigen in chemically inactivated clinical specimens. The assay was evaluated by use of defined virus stocks and specimens from experimentally infected animals. Its field application was tested during an outbreak of Ebola hemorrhagic fever in 2003. Although the original goal was to develop an assay that would detect all EBOV species, only the Zaire and Sudan species were detected in practice. The assay represents a first-generation rapid field test for the detection of EBOV antigen that can be performed in 30 min without electrical power or expensive or sensitive equipment.

Ebolavirus and Marburgvirus: insight the Filoviridae family

Ebolavirus and Marburgvirus (belonging to the Filoviridae family) emerged four decades ago and cause epidemics of haemorrhagic fever with high case-fatality rates. The genome of filoviruses encodes seven proteins. No significant homology is observed between filovirus proteins and any known macromolecule. Moreover, Marburgvirus and Ebolavirus show significant differences in protein homology. The natural maintenance cycle of filoviruses is unknown, the natural reservoir, the mode of transmission, the epidemic disease generation, and temporal dynamics are unclear. Lastly, Ebolavirus and Marburgvirus are considered as potential biological weapons. Vaccine appears the unique therapeutic frontier. Here, molecular and clinical aspects of filoviral haemorrhagic fevers are summarized.

The ecology of Ebola virus

Since Ebola virus was first identified more than 30 years ago, tremendous progress has been made in understanding the molecular biology and pathogenesis of this virus. However, the means by which Ebola virus is maintained and transmitted in nature remains unclear despite dedicated efforts to answer these questions. Recent work has provided new evidence that fruit bats might have a role as a reservoir species, but it is not clear whether other species are also involved or how transmission to humans or apes takes place. Two opposing hypotheses for Ebola emergence have surfaced; one of long-term local persistence in a cryptic and infrequently contacted reservoir, versus another of a more recent introduction of the virus and directional spread through susceptible populations. Nevertheless, with the increasing frequency of human filovirus outbreaks and the tremendous impact of infection on the already threatened great ape populations, there is an urgent need to better understand the ecology of Ebola virus in nature.