Remdesivir (GS-5734) Is Efficacious in Cynomolgus Macaques Infected With Marburg Virus

Marburg Virus Disease: A Narrative Review

Background and Aims

Given the recent deadly outbreaks of the Marburg virus (MARV), in early 2023 in Tanzania and Equatorial Guinea, and the most recent one in Rwanda in 2024, there has been renewed attention across Africa on the threat posed by the re-emergence of MARV as a growing concern for public health. Therefore, it needs to provide a comprehensive overview of the virus and its related infections, encompassing virus classification, historical outbreaks, transmission dynamics, the intricate interface between the virus and its hosts, the methods of diagnosis, core prevention strategies, and current therapeutic options, to better understand the virus and the disease characteristics in responding to future outbreaks.

Methods

For this review, four scientific online databases, including PubMed, Google Scholar, Scopus, and Web of Science were thoroughly searched for peer-reviewed journal papers (original, case reports/series, and review studies) published in English language using the following keywords: Filovirus, Marburg virus, Marburg Haemorrhagic Fever, Marburg virus disease, and Marburg virus outbreak.

Results

MARV shares similarities with its close cousin -the Ebola virus [EBOV]-in terms of viral characteristics and most clinical features. These two viruses are of animal origin and primarily spread to humans through infected bats (both direct and indirect close contact), which serve as the common natural host reservoirs. The potential for interhuman transmission, coupled with the ability to cross borders of endemic regions combined with the absence of a licensed vaccine and effective treatment, have made MARV a significant threat to human health. This virus is clinically characterized by a range of symptoms and organ dysfunctions. The disease is often fatal in a significant proportion of infected individuals. This viral infection is diagnosed by various diagnostic tools, prevented mainly through personal protective measures, and treated usually with clinical management and supportive care.

Conclusion

The outbreaks of MARV are continuously threaten public health; therefore, the world must be alert and well-prepared. For MVD, taking precautions along with investing in research and preparedness at regional, national, and global levels is of crucial importance and should be prioritized.

Remdesivir, mAb114, REGN-EB3, and ZMapp partially rescue nonhuman primates infected with a low passage Kikwit variant of Ebola virus

In 2018, a clinical trial of four investigational therapies for Ebola virus disease (EVD), known as the PALM trial, was conducted in the Democratic Republic of Congo. All patients received either the antiviral remdesivir (RDV) or a monoclonal antibody product: ZMapp, mAb114 (Ebanga), or REGN-EB3 (Inmazeb). The study concluded that both mAb114 and REGN-EB3 were superior to ZMapp and RDV in reducing mortality from EVD. However, the data suggested that some patients in the RDV and ZMapp groups might have been sicker at the time of treatment initiation. Here, we assessed the efficacy of each of these therapies in a uniformly lethal rhesus monkey model of EVD when treatment was initiated 5 days after Ebola exposure. Treatment with RDV, mAb114, REGN-EB3, and ZMapp each resulted in similar survival (approximately 40%). Survival was associated with circulating viral load at treatment initiation. A trend of more escape mutants in the GP1 and GP2 domains was observed for the mAb114 group. Our data show similar suboptimal efficacy of individual therapeutics in the uniformly lethal NHP model of EVD, supporting further clinical investigation of therapeutic combinations to maximize the overall therapeutic effect and improve patient outcomes, particularly for the treatment of advanced stage EVD.

Unlocking the potential of remdesivir: innovative approaches to drug delivery

Given the recurrent waves of COVID-19 and the emergence of new viral infections, optimizing the potential of remdesivir as an antiviral agent is critical. While several reviews have explored the efficacy of remdesivir, few have comprehensively addressed its challenges, such as the necessity for intravenous infusion, suboptimal lung accumulation, and safety concerns related to its formulation. This review critically examines these challenges while proposing innovative solutions and effective combinations with other antiviral agents and repurposed drugs. By highlighting the role of complex generics, we aim to enhance therapeutic efficacy in ways not previously discussed in existing literature. Furthermore, we address the development of novel drug delivery systems which specifically aim to improve remdesivir's pharmacological profile. By analyzing recent findings, we assess both the successes and limitations of current approaches, providing insights into ongoing challenges and strategies for further optimization. This review uniquely focuses on targeted drug delivery systems and innovative formulations, thereby maximizing remdesivir's therapeutic benefits and broadening its application in combating emerging viral threats. In doing so, we fill a critical gap in literature, offering a comprehensive overview that informs future research and clinical strategies.

Semi-automated diagnostic RT-PCR as a screening assay for antiviral compounds in a 96-well format against highly pathogenic RNA viruses

In response to outbreaks of (re)emerging highly pathogenic RNA viruses, simple and scalable antiviral screening methods are urgently needed. Using established and validated diagnostic methods like RT-PCR for antiviral screening offers a rapid readout of viral replication. This becomes particular important when other traditional viral replication readouts, such as TCID50 or plaque assays cannot be used due to the absence of cytopathic effects, lack of reporter gene-containing recombinant viruses or unavailability of appropriate antibodies - the latter two common challenges when so far unknown viruses emerge. This study evaluated semi-automated diagnostic RT-PCR in a 96-well approach for antiviral compound screening using Marburg virus serving as a case study. Remdesivir, a prodrug that exhibits antiviral activities against multiple RNA viruses, was used as positive control inhibiting replication of filoviruses. Applicability of the protocol to other members of the filovirus family was feasible using the same settings, while for other viruses like Middle East respiratory syndrome coronavirus (MERS-CoV) or Crimean-Congo hemorrhagic fever virus (CCHFV) adaptations to optimal infection settings were necessary. Our results demonstrate a high reproducibility and highlight the rapid adaptability of semi-automated RT-PCR assays as an accelerated antiviral screening assay with high scalability against a wide range of newly or (re)emerging RNA viruses. This is critical especially during outbreak situations where timely antiviral assessments are urgently needed.

Oral obeldesivir provides postexposure protection against Marburg virus in nonhuman primates

The recent outbreak of Marburg virus (MARV) in Rwanda underscores the need for effective countermeasures against this highly fatal pathogen, with case fatality rates reaching 90%. Currently, no vaccines or approved treatments exist for MARV infection, distinguishing it from related viruses such as Ebola. Our study demonstrates that the oral drug obeldesivir (ODV), a nucleoside analog prodrug, shows promising antiviral activity against filoviruses in vitro and offers significant protection in animal models. Here with cynomolgus macaques (n = 6), a 10 day regimen of once-daily ODV, initiated 24 h after exposure, provided 80% protection against a thousandfold lethal MARV challenge, delaying viral replication and disease onset. Transcriptome analysis revealed that early adaptive responses correlated with successful outcomes. Compared with intravenous options, oral antivirals such as ODV offer logistical advantages in outbreak settings, enabling easier administration and broader contact coverage. Our findings support the potential of ODV as a broad-spectrum, oral postexposure prophylaxis for filoviruses.

Emerging Strategies and Progress in the Medical Management of Marburg Virus Disease

During the current outbreak of Marburg virus disease (MVD) in Rwanda, we synthesized evidence from the literature to improve case management. Accordingly, experimental treatment was offered to patients under close follow-up. Remdesivir alone or in combination with monoclonal antibody treatment (MBP091) complemented with supportive care has improved the clinical outcomes of patients. Additionally, we have identified several experimental therapies currently under investigation, including antiviral drugs such as favipiravir, galidesivir, obeldesivir, and remdesivir, along with monoclonal and polyclonal antibodies (e.g., polyclonal IgG, monoclonal antibody MR-78-N; MR82-N; MR191-N; monoclonal antibodies MR186-YTE and MBP091). Furthermore, substantial progress is being made in vaccine development, with promising candidates including adenovirus-vectored vaccines, DNA vaccines, and the recombinant vesicular stomatitis virus (rVSV) vaccine. Moreover, innovative preventive and treatment strategies-such as synthetic hormones like estradiol benzoate, small interfering RNA (siRNA), interferon-β therapy, and phosphorodiamidate morpholino oligomers-are emerging as potential options for MVD management. Further investment is needed to accelerate research and optimize these therapeutics and preventive modalities. Additional epidemiological, preclinical, and clinical studies are warranted to generate the evidence required to inform policymaking, resource mobilization, and the implementation of cost-effective interventions for the prevention, control, and treatment of MVD.

Ebola disease: bridging scientific discoveries and clinical application

The west Africa Ebola disease epidemic (2014-16) marked a historic change of course for patient care during emerging infectious disease outbreaks. The epidemic response was a failure in many ways-a slow, cumbersome, and disjointed effort by a global architecture that was not fit for purpose for a rapidly spreading outbreak. In the most affected countries, health-care workers and other responders felt helpless-dealing with an overwhelming number of patients but with few, if any, tools at their disposal to provide high-quality care. These inadequacies, however, led to attention and innovation. The decade since then has seen remarkable achievements in clinical care for Ebola disease, including the approval of the first vaccines and treatments. In this paper, the first in a two-part Series, we reflect on this progress and provide expert summary of the modern landscape of Ebola disease, highlighting the priorities and ongoing activities aimed at further improving patient survival and wellbeing in the years ahead.

Marburg Virus Medical Countermeasures

Among the Filoviridae, Marburg virus (MARV) is a biological threat for which no licensed vaccines or therapeutics are currently available. In contrast, we have licensed products for Ebola virus (EBOV), another member of the Filoviridae family. The availability of licensed medical countermeasures (MCMs) for EBOV provides an opportunity to test a key objective of many pandemic preparedness plans, which is to apply some of the same technological approaches demonstrated to be successful for one agent, EBOV, to a second agent, MARV. This chapter will discuss (1) lessons learned from EBOV outbreak responses and MCM development that are applicable to MARV MCM development, (2) the likely concept of operations for using vaccines and therapeutics against MARV, and (3) target product profiles based on the concept of operations. Finally, we will discuss the current status of the MCM pipeline for MARV and next steps to advance these countermeasures to licensure.

New reverse sum Revan indices for physicochemical and pharmacokinetic properties of anti-filovirus drugs

Ebola and Marburg viruses, biosafety level 4 pathogens, cause severe hemorrhaging and organ failure with high mortality. Although some FDA-approved vaccines or therapeutics like Ervebo for Zaire Ebola virus exist, still there is a lack of effective therapeutics that cover all filoviruses, including both Ebola and Marburg viruses. Therefore, some anti-filovirus drugs such as Pinocembrin, Favipiravir, Remdesivir and others are used to manage infections. In theoretical chemistry, a chemical molecule is converted into an isomorphic molecular graph, G ( V , E ) by considering atom set V as vertices and bond set E as edges. A topological index is a molecular descriptor derived from the molecular graph of a chemical compound that characterizes its topology. The relationship between a compound's chemical structure and its properties is investigated through the quantitative structure-property relationship (QSPR). This article introduces new reverse sum Revan degree based indices to explore the physicochemical and pharmacokinetic properties of anti-filovirus drugs via multilinear regression. The findings reveal a strong correlation between these proposed indices and the properties of anti-filovirus drugs when compared to reverse and Revan degree-based indices. Thus, reverse sum Revan indices offer valuable insights for analyzing the drugs properties used to treat Ebola and Marburg virus infections. Moreover, the multilinear regression (MLR) results through reverse sum Revan indices are compared with Artificial Neural Network (ANN) modelling technique and it provides the better prediction of the physicochemical and pharmacokinetic properties of anti-filovirus drugs.

A Randomized, Blinded, Vehicle-Controlled Dose-Ranging Study to Evaluate and Characterize Remdesivir Efficacy Against Ebola Virus in Rhesus Macaques

Ebola virus (EBOV) causes severe disease in humans, with mortality as high as 90%. The small-molecule antiviral drug remdesivir (RDV) has demonstrated a survival benefit in EBOV-exposed rhesus macaques. Here, we characterize the efficacy of multiple intravenous RDV dosing regimens on survival of rhesus macaques 42 days after intramuscular EBOV exposure. Thirty rhesus macaques underwent surgical implantation of telemetry devices for the fine-scale monitoring of body temperature and activity, as well as central venous catheters, to enable treatment administration and blood collection. Treatment, consisting of a loading dose of RDV followed by once-daily maintenance doses for 11 days, was initiated 4 days after virus exposure when all animals were exhibiting disease signs consistent with incipient EBOV disease as well as quantifiable levels of EBOV RNA in plasma. In the RDV treatment groups receiving loading/maintenance doses of 5/2.5 mg/kg, 10/5 mg/kg, and 20/10 mg/kg, a total of 6 of 8 (75%), 7 of 8 (87.5%), and 5 of 7 (71.4%) animals survived, respectively. In the vehicle control group, one of seven animals (14.3%) survived. The improved survival rate compared to the control group was statistically significant only for the 10/5 mg/kg RDV treatment group. This treatment regimen also resulted in a significantly lower systemic viral load compared to the vehicle control after a single RDV treatment. All three RDV regimens produced a significantly lower systemic viral load after two treatments. For most animals, RDV treatment, regardless of dose, resulted in the amelioration of many of the clinical-pathological changes associated with EBOV disease in this model.

Evidence-Based Guidance for One Health Preparedness, Prevention, and Response Strategies to Marburg Virus Disease Outbreaks

OBJECTIVES

Marburg virus disease (MVD) is on the WHO list for pandemic-prone pathogens. The current outbreak in Rwanda provides an opportunity to map outbreaks and generate information to inform policymaking, resource mobilization, and guide the implementation of cost-effective response strategies.

METHODS

We synthesized available information about MVD to build holistic, up-to-date evidence to inform policymakers, public health leaders, and healthcare and public health services providers in their development and implementation of cost-effective preparedness, prevention, and control measures.

RESULTS

We have identified 20 outbreaks of MVD that occurred in 14 countries between 1967 and 2024; these outbreaks led to 580 confirmed cases and 423 deaths in total. We summarize the available information about the main clinical signs, diagnostic tools, primary reservoir, transmission dynamics, and case management protocol. We also document the best practices in the prevention and control of MVD outbreaks, including the implementation of a multisectoral One Health strategy for preparedness, prevention, and response to MVD outbreaks that incorporates the strict implementation of WASH and infection prevention measures, contact tracing, and the isolation of infected and suspected humans and animals, and enhances the implementation of the International Health Regulations, particularly efficient cross-country coordination.

CONCLUSIONS

In the absence of a licensed treatment or vaccine for MVD, the response strategy to MVD should focus on preventive measures, including community engagement to promote the reduction in contact between humans and reservoirs, the supportive care and isolation of patients, and proper waste management. High risk populations such as frontline responders, including healthcare providers and community health workers, should be prioritized so that they can access all currently available protection measures.

An update on nonhuman primate usage for drug and vaccine evaluation against filoviruses

INTRODUCTION

Due to their faithful recapitulation of human disease, nonhuman primates (NHPs) are considered the gold standard for evaluating drugs against Ebolavirus and other filoviruses. The long-term goal is to reduce the reliance on NHPs with more ethical alternatives. In silico simulations and organoid models have the potential to revolutionize drug testing by providing accurate, human-based systems that mimic disease processes and drug responses without the ethical concerns associated with animal testing. However, as these emerging technologies are still in their developmental infancy, NHP models are presently needed for late-stage evaluation of filovirus vaccines and drugs, as they provide critical insights into the efficacy and safety of new medical countermeasures.

AREAS COVERED

In this review, the authors introduce available NHP models and examine the existing literature on drug discovery for all medically significant filoviruses in corresponding models.

EXPERT OPINION

A deliberate shift toward animal-free models is desired to align with the 3Rs of animal research. In the short term, the use of NHP models can be refined and reduced by enhancing replicability and publishing negative data. Replacement involves a gradual transition, beginning with the selection and optimization of better small animal models; advancing organoid systems, and using in silico models to accurately predict immunological outcomes.

Emerging and reemerging infectious diseases: global trends and new strategies for their prevention and control

To adequately prepare for potential hazards caused by emerging and reemerging infectious diseases, the WHO has issued a list of high-priority pathogens that are likely to cause future outbreaks and for which research and development (R&D) efforts are dedicated, known as paramount R&D blueprints. Within R&D efforts, the goal is to obtain effective prophylactic and therapeutic approaches, which depends on a comprehensive knowledge of the etiology, epidemiology, and pathogenesis of these diseases. In this process, the accessibility of animal models is a priority bottleneck because it plays a key role in bridging the gap between in-depth understanding and control efforts for infectious diseases. Here, we reviewed preclinical animal models for high priority disease in terms of their ability to simulate human infections, including both natural susceptibility models, artificially engineered models, and surrogate models. In addition, we have thoroughly reviewed the current landscape of vaccines, antibodies, and small molecule drugs, particularly hopeful candidates in the advanced stages of these infectious diseases. More importantly, focusing on global trends and novel technologies, several aspects of the prevention and control of infectious disease were discussed in detail, including but not limited to gaps in currently available animal models and medical responses, better immune correlates of protection established in animal models and humans, further understanding of disease mechanisms, and the role of artificial intelligence in guiding or supplementing the development of animal models, vaccines, and drugs. Overall, this review described pioneering approaches and sophisticated techniques involved in the study of the epidemiology, pathogenesis, prevention, and clinical theatment of WHO high-priority pathogens and proposed potential directions. Technological advances in these aspects would consolidate the line of defense, thus ensuring a timely response to WHO high priority pathogens.

SARS-CoV-2 resistance to monoclonal antibodies and small-molecule drugs

Over four years have passed since the beginning of the COVID-19 pandemic. The scientific response has been rapid and effective, with many therapeutic monoclonal antibodies and small molecules developed for clinical use. However, given the ability for viruses to become resistant to antivirals, it is perhaps no surprise that the field has identified resistance to nearly all of these compounds. Here, we provide a comprehensive review of the resistance profile for each of these therapeutics. We hope that this resource provides an atlas for mutations to be aware of for each agent, particularly as a springboard for considerations for the next generation of antivirals. Finally, we discuss the outlook and thoughts for moving forward in how we continue to manage this, and the next, pandemic.

Oral administration of obeldesivir protects nonhuman primates against Sudan ebolavirus

Obeldesivir (ODV, GS-5245) is an orally administered prodrug of the parent nucleoside of remdesivir (RDV) and is presently in phase 3 trials for COVID-19 treatment. In this work, we show that ODV and its circulating parent nucleoside metabolite, GS-441524, have similar in vitro antiviral activity against filoviruses, including Marburg virus, Ebola virus, and Sudan virus (SUDV). We also report that once-daily oral ODV treatment of cynomolgus monkeys for 10 days beginning 24 hours after SUDV exposure confers 100% protection against lethal infection. Transcriptomics data show that ODV treatment delayed the onset of inflammation and correlated with antigen presentation and lymphocyte activation. Our results offer promise for the further development of ODV to control outbreaks of filovirus disease more rapidly.

Peripheral immune responses to filoviruses in a reservoir versus spillover hosts reveal transcriptional correlates of disease

Several filoviruses, including Marburg virus (MARV), cause severe disease in humans and nonhuman primates (NHPs). However, the Egyptian rousette bat (ERB, Rousettus aegyptiacus), the only known MARV reservoir, shows no overt illness upon natural or experimental infection, which, like other bat hosts of zoonoses, is due to well-adapted, likely species-specific immune features. Despite advances in understanding reservoir immune responses to filoviruses, ERB peripheral blood responses to MARV and how they compare to those of diseased filovirus-infected spillover hosts remain ill-defined. We thus conducted a longitudinal analysis of ERB blood gene responses during acute MARV infection. These data were then contrasted with a compilation of published primate blood response studies to elucidate gene correlates of filovirus protection versus disease. Our work expands on previous findings in MARV-infected ERBs by supporting both host resistance and disease tolerance mechanisms, offers insight into the peripheral immunocellular repertoire during infection, and provides the most direct known cross-examination between reservoir and spillover hosts of the most prevalently-regulated response genes, pathways and activities associated with differences in filovirus pathogenesis and pathogenicity.

Structural and Dynamical Basis of VP35-RBD Inhibition by Marine Fungi Compounds to Combat Marburg Virus Infection

The Marburg virus (MBV), a deadly pathogen, poses a serious threat to world health due to the lack of effective treatments, calling for an immediate search for targeted and efficient treatments. In this study, we focused on compounds originating from marine fungi in order to identify possible inhibitory compounds against the Marburg virus (MBV) VP35-RNA binding domain (VP35-RBD) using a computational approach. We started with a virtual screening procedure using the Lipinski filter as a guide. Based on their docking scores, 42 potential candidates were found. Four of these compounds-CMNPD17596, CMNPD22144, CMNPD25994, and CMNPD17598-as well as myricetin, the control compound, were chosen for re-docking analysis. Re-docking revealed that these particular compounds had a higher affinity for MBV VP35-RBD in comparison to the control. Analyzing the chemical interactions revealed unique binding properties for every compound, identified by a range of Pi-cation interactions and hydrogen bond types. We were able to learn more about the dynamic behaviors and stability of the protein-ligand complexes through a 200-nanosecond molecular dynamics simulation, as demonstrated by the compounds' consistent RMSD and RMSF values. The multidimensional nature of the data was clarified by the application of principal component analysis, which suggested stable conformations in the complexes with little modification. Further insight into the energy profiles and stability states of these complexes was also obtained by an examination of the free energy landscape. Our findings underscore the effectiveness of computational strategies in identifying and analyzing potential inhibitors for MBV VP35-RBD, offering promising paths for further experimental investigations and possible therapeutic development against the MBV.

Characterization of the Cynomolgus Macaque Model of Marburg Virus Disease and Assessment of Timing for Therapeutic Treatment Testing

Marburg virus (MARV) causes severe disease and high mortality in humans. The objective of this study was to characterize disease manifestations and pathogenesis in cynomolgus macaques exposed to MARV. The results of this natural history study may be used to identify features of MARV disease useful in defining the ideal treatment initiation time for subsequent evaluations of investigational therapeutics using this model. Twelve cynomolgus macaques were exposed to a target dose of 1000 plaque-forming units MARV by the intramuscular route, and six control animals were mock-exposed. The primary endpoint of this study was survival to Day 28 post-inoculation (PI). Anesthesia events were minimized with the use of central venous catheters for periodic blood collection, and temperature and activity were continuously monitored by telemetry. All mock-exposed animals remained healthy for the duration of the study. All 12 MARV-exposed animals (100%) became infected, developed illness, and succumbed on Days 8-10 PI. On Day 4 PI, 11 of the 12 MARV-exposed animals had statistically significant temperature elevations over baseline. Clinically observable signs of MARV disease first appeared on Day 5 PI, when 6 of the 12 animals exhibited reduced responsiveness. Ultimately, systemic inflammation, coagulopathy, and direct cytopathic effects of MARV all contributed to multiorgan dysfunction, organ failure, and death or euthanasia of all MARV-exposed animals. Manifestations of MARV disease, including fever, systemic viremia, lymphocytolysis, coagulopathy, and hepatocellular damage, could be used as triggers for initiation of treatment in future therapeutic efficacy studies.

Emergence of Marburg virus: a global perspective on fatal outbreaks and clinical challenges

The Marburg virus (MV), identified in 1967, has caused deadly outbreaks worldwide, the mortality rate of Marburg virus disease (MVD) varies depending on the outbreak and virus strain, but the average case fatality rate is around 50%. However, case fatality rates have varied from 24 to 88% in past outbreaks depending on virus strain and case management. Designated a priority pathogen by the National Institute of Allergy and Infectious Diseases (NIAID), MV induces hemorrhagic fever, organ failure, and coagulation issues in both humans and non-human primates. This review presents an extensive exploration of MVD outbreak evolution, virus structure, and genome, as well as the sources and transmission routes of MV, including human-to-human spread and involvement of natural hosts such as the Egyptian fruit bat (Rousettus aegyptiacus) and other Chiroptera species. The disease progression involves early viral replication impacting immune cells like monocytes, macrophages, and dendritic cells, followed by damage to the spleen, liver, and secondary lymphoid organs. Subsequent spread occurs to hepatocytes, endothelial cells, fibroblasts, and epithelial cells. MV can evade host immune response by inhibiting interferon type I (IFN-1) synthesis. This comprehensive investigation aims to enhance understanding of pathophysiology, cellular tropism, and injury sites in the host, aiding insights into MVD causes. Clinical data and treatments are discussed, albeit current methods to halt MVD outbreaks remain elusive. By elucidating MV infection's history and mechanisms, this review seeks to advance MV disease treatment, drug development, and vaccine creation. The World Health Organization (WHO) considers MV a high-concern filovirus causing severe and fatal hemorrhagic fever, with a death rate ranging from 24 to 88%. The virus often spreads through contact with infected individuals, originating from animals. Visitors to bat habitats like caves or mines face higher risk. We tailored this search strategy for four databases: Scopus, Web of Science, Google Scholar, and PubMed. we primarily utilized search terms such as "Marburg virus," "Epidemiology," "Vaccine," "Outbreak," and "Transmission." To enhance comprehension of the virus and associated disease, this summary offers a comprehensive overview of MV outbreaks, pathophysiology, and management strategies. Continued research and learning hold promise for preventing and controlling future MVD outbreaks. GRAPHICAL ABSTRACT.

Rescue and characterization of the first West African Marburg virus 2021 from Guinea

Marburg virus (MARV) is a causative agent of a severe hemorrhagic fever with high fatality rates endemic in central Africa. Current outbreaks of MARV in Equatorial Guinea and Tanzania underline the relevance of MARV as a public health emergency pathogen. In 2021, the first known human MARV case was confirmed in Guinea, West Africa. Since no infectious virus could be isolated from that fatal case in 2021, we generated recombinant (rec) MARV Guinea by reverse genetics in order to study and characterize this new MARV, which occurred in West Africa for the first time, in terms of its growth properties, detection by antibodies, and therapeutic potential compared to known MARV strains. Our results showed a solid viral replication of recMARV Guinea in human, bat, and monkey cell lines in comparison to other known MARV strains. We further demonstrated that replication of recMARV Guinea in cells can be inhibited by the nucleoside analogue remdesivir. Taken together, we could successfully reconstitute de novo the first West African MARV from Guinea showing similar replication kinetics in cells compared to other central African MARV strains. Our reverse genetics approach has proven successful in characterizing emerging viruses, especially when virus isolates are missing and viral genome sequences are incomplete.

Reemergence of Marburgvirus disease: Update on current control and prevention measures and review of the literature

In 1967, the very first case of the Marburgvirus disease (MVD) was detected in Germany and Serbia sequentially. Since then, MVD has been considered one of the most serious and deadly infectious diseases in the world with a case-fatality rate between 23% and 90% and a substantial number of recorded deaths. Marburgvirus belongs to the family of Filoviridae (filoviruses), which causes severe viral hemorrhagic fever (VHF). Some major risk factors for human infections are close contact with African fruit bats, MVD-infected non-human primates, and MVD-infected individuals. Currently, there is no vaccine or specific treatment for MVD, which emphasizes the seriousness of this disease. In July 2022, the World Health Organization reported outbreaks of MVD in Ghana after two suspected VHF cases were detected. This was followed in February and March 2023 with the emergence of the virus in two countries new to the virus: Equatorial Guinea and Tanzania, respectively. In this review, we aim to highlight the characteristics, etiology, epidemiology, and clinical symptoms of MVD, along with the current prevention measures and the possible treatments to control this virus.

Computed Tomography Imaging for Monitoring of Marburg Virus Disease: a Nonhuman Primate Proof-Of-Concept Study

Marburg virus (MARV) is a highly virulent zoonotic filovirid that causes Marburg virus disease (MVD) in humans. The pathogenesis of MVD remains poorly understood, partially due to the low number of cases that can be studied, the absence of state-of-the-art medical equipment in areas where cases are reported, and limitations on the number of animals that can be safely used in experimental studies under maximum containment animal biosafety level 4 conditions. Medical imaging modalities, such as whole-body computed tomography (CT), may help to describe disease progression in vivo, potentially replacing ethically contentious and logistically challenging serial euthanasia studies. Towards this vision, we performed a pilot study, during which we acquired whole-body CT images of 6 rhesus monkeys before and 7 to 9 days after intramuscular MARV exposure. We identified imaging abnormalities in the liver, spleen, and axillary lymph nodes that corresponded to clinical, virological, and gross pathological hallmarks of MVD in this animal model. Quantitative image analysis indicated hepatomegaly with a significant reduction in organ density (indicating fatty infiltration of the liver), splenomegaly, and edema that corresponded with gross pathological and histopathological findings. Our results indicated that CT imaging could be used to verify and quantify typical MVD pathogenesis versus altered, diminished, or absent disease severity or progression in the presence of candidate medical countermeasures, thus possibly reducing the number of animals needed and eliminating serial euthanasia. IMPORTANCE Marburg virus (MARV) is a highly virulent zoonotic filovirid that causes Marburg virus disease (MVD) in humans. Much is unknown about disease progression and, thus, prevention and treatment options are limited. Medical imaging modalities, such as whole-body computed tomography (CT), have the potential to improve understanding of MVD pathogenesis. Our study used CT to identify abnormalities in the liver, spleen, and axillary lymph nodes that corresponded to known clinical signs of MVD in this animal model. Our results indicated that CT imaging and analyses could be used to elucidate pathogenesis and possibly assess the efficacy of candidate treatments.

Effect of remdesivir post-exposure prophylaxis and treatment on pathogenesis of measles in rhesus macaques

Measles is a systemic disease initiated in the respiratory tract with widespread measles virus (MeV) infection of lymphoid tissue. Mortality can be substantial, but no licensed antiviral therapy is available. We evaluated both post-exposure prophylaxis and treatment with remdesivir, a broad-spectrum antiviral, using a well-characterized rhesus macaque model of measles. Animals were treated with intravenous remdesivir for 12 days beginning either 3 days after intratracheal infection (post-exposure prophylaxis, PEP) or 11 days after infection at the onset of disease (late treatment, LT). As PEP, remdesivir lowered levels of viral RNA in peripheral blood mononuclear cells, but RNA rebounded at the end of the treatment period and infectious virus was continuously recoverable. MeV RNA was cleared more rapidly from lymphoid tissue, was variably detected in the respiratory tract, and not detected in urine. PEP did not improve clinical disease nor lymphopenia and reduced the antibody response to infection. In contrast, LT had little effect on levels of viral RNA or the antibody response but also did not decrease clinical disease. Therefore, remdesivir transiently suppressed expression of viral RNA and limited dissemination when provided as PEP, but virus was not cleared and resumed replication without improvement in the clinical disease parameters evaluated.

Dexamethasone mitigates remdesivir-induced liver toxicity in human primary hepatocytes and COVID-19 patients

BACKGROUND

Coronavirus disease 2019 (COVID-19) is a global pandemic that has caused more than 600 million cases and over six million deaths worldwide. Despite the availability of vaccination, COVID-19 cases continue to grow making pharmacological interventions essential. Remdesivir (RDV) is an FDA-approved antiviral drug for treatment of both hospitalized and non-hospitalized COVID-19 patients, albeit with potential for hepatotoxicity. This study characterizes the hepatotoxicity of RDV and its interaction with dexamethasone (DEX), a corticosteroid often co-administered with RDV for inpatient treatment of COVID-19.

METHODS

Human primary hepatocytes and HepG2 cells were used as in vitro models for toxicity and drug-drug interaction studies. Real-world data from hospitalized COVID-19 patients were analyzed for drug-induced elevation of serum ALT and AST.

RESULTS

In cultured hepatocytes, RDV markedly reduced the hepatocyte viability and albumin synthesis, while it increased the cleavage of caspase-8 and caspase-3, phosphorylation of histone H2AX, and release of ALT and AST in a concentration-dependent manner. Importantly, co-treatment with DEX partially reversed RDV-induced cytotoxic responses in human hepatocytes. Moreover, data from COVID-19 patients treated with RDV with and without DEX co-treatment suggested that among 1037 patients matched by propensity score, receiving the drug combination was less likely to result in elevation of serum AST and ALT levels (≥ 3 × ULN) compared to the RDV alone treated patients (OR = 0.44, 95% CI = 0.22-0.92, p = 0.03).

CONCLUSION

Our findings obtained from in vitro cell-based experiments and patient data analysis provide evidence suggesting combination of DEX and RDV holds the potential to reduce the likelihood of RDV-induced liver injury in hospitalized COVID-19 patients.

Expanded profiling of Remdesivir as a broad-spectrum antiviral and low potential for interaction with other medications in vitro

Remdesivir (GS-5734; VEKLURY) is a single diastereomer monophosphoramidate prodrug of an adenosine analog (GS-441524). Remdesivir is taken up by target cells and metabolized in multiple steps to form the active nucleoside triphosphate (GS-443902), which acts as a potent inhibitor of viral RNA-dependent RNA polymerases. Remdesivir and GS-441524 have antiviral activity against multiple RNA viruses. Here, we expand the evaluation of remdesivir's antiviral activity to members of the families Flaviviridae, Picornaviridae, Filoviridae, Orthomyxoviridae, and Hepadnaviridae. Using cell-based assays, we show that remdesivir can inhibit infection of flaviviruses (such as dengue 1-4, West Nile, yellow fever, Zika viruses), picornaviruses (such as enterovirus and rhinovirus), and filoviruses (such as various Ebola, Marburg, and Sudan virus isolates, including novel geographic isolates), but is ineffective or is significantly less effective against orthomyxoviruses (influenza A and B viruses), or hepadnaviruses B, D, and E. In addition, remdesivir shows no antagonistic effect when combined with favipiravir, another broadly acting antiviral nucleoside analog, and has minimal interaction with a panel of concomitant medications. Our data further support remdesivir as a broad-spectrum antiviral agent that has the potential to address multiple unmet medical needs, including those related to antiviral pandemic preparedness.

A bibliometric study on Marburg virus research with prevention and control strategies

Marburg virus (MARV) is a pathogenic zoonotic RNA virus etiologic for Marburg virus disease (MVD), a severe hemorrhagic fever. This is a rare disease, with a high fatality rate, that spreads via infected blood or body fluids or indirectly via fomites (contaminated objects and substances such as clothed, beds, personal protective equipment, or medical equipments). A few vaccines to protect against MARV are undergoing clinical trials, but there is not yet an approved vaccine against this disease. Eventually, prevention and control guidelines should be adhered to rigorously to alleviate this infection. This bibliometric analysis aimed to harness narrative evaluation, emphasizing the significance of quantitative approaches and delineating the most thought-provoking concerns for researchers using VOSviewer software (Centre for Science and Technology Studies, Leiden University, the Netherlands). “Marburg Virus” OR “MARV” AND “Diseases” search criteria were used for the analysis of articles published between 1962 and 2022. Co-occurrence analysis was carried out, which characterized different thematic clusters. From this analysis, we found that 1688 published articles, and the number of publications increased across that period annually, with a growth rate of 8.78%. It is also conspicuous that the number of publications in the United States reached its acme during this period (i.e., 714 publications, accounting for 42.29% of the total), and the United States Army Medical Research Institute of Infectious Diseases published the most literature (i.e., 146 papers). Our study found that the three pre-eminent authors of Marburg virus papers were “FELDMANN, HEINZ“ of the National Institute of Allergy and Infectious Diseases, United States, “BECKER, STEPHAN” of the Philipps University of Marburg, Germany, and “GEISBERT, THOMAS W” of the University of Texas Medical Branch, United States. In this study we found that “JOURNAL OF VIROLOGY” has published the most pertinent literature, totaling 88 articles, followed by “The journal of Infectious Diseases”, which published 76 relevant papers, and “VIRUSES”, which published 52 corresponding papers. The most cited paper on the Marburg virus was published in Nature Medicine, with 522 total citations and 29 citations/year. Studies of the changing epidemiology and evolving nature of the virus and its ecological niche are required; breakthrough and implementation of the efficacious vaccine candidate(s), prophylaxis and therapeutic alternatives and supervision strategies, unveiling awareness-raising programs, and developing apposite and timely preparedness, prevention, and proactive control strategies are of utmost importance.

Marburg virus and the disease it causes

Over the 50 years since its discovery, many properties of the Marburg virus have been studied, but no reliable medical remedies of preventing and treating the infection it causes have been developed, although it can potentially cause large-scale epidemics. Marburg fever is relevant due to the risk of importation to other countries. The source of infection in nature is bats (reservoir) and monkeys (intermediate host), and the routes of transmission are aerosol, contact and alimentary. The mortality rate in recent outbreaks has reached 90%. In convalescents the causative agent was identified in tears, semen, and liver biopsies weeks and months after recovery. The lack of therapeutic and prophylactic antiviral drugs, high rates of mortality, infectivity, the ability of aerosol contamination, and a high epidemic potential all together define Marburg fever as a serious global threat to international health. The development of medical protection against this infection should be an urgent task of ensuring the biological safety of the population of the Russian Federation. The most promising ways to develop vaccines against Marburg fever are the construction of recombinants based on adenovirus, vesicular stomatitis virus or alphavirus replicon, DNA vaccines. A reliable protective effect of the chemotherapy drug remdesivir in combination with human antibodies, as well as an etiotropic drug with an antisense mechanism of action and an interferon inducer has been shown. In model experiments with pseudovirus, fundamentally new ways of developing pathogen inhibitors were found preventing its exit from cells, as well as the construction of anti-gene-binding Fab fragments that inhibit the synthesis of viral RNA.

Pathogenicity and virulence of Marburg virus

Marburg virus (MARV) has been a major concern since 1967, with two major outbreaks occurring in 1998 and 2004. Infection from MARV results in severe hemorrhagic fever, causing organ dysfunction and death. Exposure to fruit bats in caves and mines, and human-to-human transmission had major roles in the amplification of MARV outbreaks in African countries. The high fatality rate of up to 90% demands the broad study of MARV diseases (MVD) that correspond with MARV infection. Since large outbreaks are rare for MARV, clinical investigations are often inadequate for providing the substantial data necessary to determine the treatment of MARV disease. Therefore, an overall review may contribute to minimizing the limitations associated with future medical research and improve the clinical management of MVD. In this review, we sought to analyze and amalgamate significant information regarding MARV disease epidemics, pathophysiology, and management approaches to provide a better understanding of this deadly virus and the associated infection.

Inhibition of Viral RNA-Dependent RNA Polymerases by Nucleoside Inhibitors: An Illustration of the Unity and Diversity of Mechanisms

RNA-dependent RNA polymerase (RdRP) is essential for the replication and expression of RNA viral genomes. This class of viruses comprise a large number of highly pathogenic agents that infect essentially all species of plants and animals including humans. Infections often lead to epidemics and pandemics that have remained largely out of control due to the lack of specific and reliable preventive and therapeutic regimens. This unmet medical need has led to the exploration of new antiviral targets, of which RdRP is a major one, due to the fact of its obligatory need in virus growth. Recent studies have demonstrated the ability of several synthetic nucleoside analogs to serve as mimics of the corresponding natural nucleosides. These mimics cause stalling/termination of RdRP, or misincorporation, preventing virus replication or promoting large-scale lethal mutations. Several such analogs have received clinical approval and are being routinely used in therapy. In parallel, the molecular structural basis of their inhibitory interactions with RdRP is being elucidated, revealing both traditional and novel mechanisms including a delayed chain termination effect. This review offers a molecular commentary on these mechanisms along with their clinical implications based on analyses of recent results, which should facilitate the rational design of structure-based antiviral drugs.

An introduction to the Marburg virus vaccine consortium, MARVAC

The emergence of Marburg virus (MARV) in Guinea and Ghana triggered the assembly of the MARV vaccine "MARVAC" consortium representing leaders in the field of vaccine research and development aiming to facilitate a rapid response to this infectious disease threat. Here, we discuss current progress, challenges, and future directions for MARV vaccines.

Mapping Scientific Productivity Trends and Hotspots in Remdesivir Research Publications: A Bibliometric Study from 2016 to 2021

In response to global efforts to control and exterminate infectious diseases, this study aims to provide insight into the productivity of remdesivir research and highlight future directions. To achieve this, there is a need to summarize and curate evidence from the literature. As a result, this study carried out comprehensive scientific research to detect trends in published articles related to remdesivir using a bibliometric analysis. Keywords associated with remdesivir were used to access pertinent published articles using the Scopus database. A total of 5321 research documents were retrieved, primarily as novel research articles (n = 2440; 46%). The number of publications increased exponentially from 2020 up to the present. The papers published by the top 12 institutions focusing on remdesivir accounted for 25.69% of the overall number of articles. The USA ranked as the most productive country, with 906 documents (37.1%), equivalent to one-third of the global publications in this field. The most productive institution was Icahn School of Medicine, Mount Sinai, in the USA (103 publications). The New England Journal of Medicine was the most cited, with an h-index of 13. The publication of research on remdesivir has gained momentum in the past year. The importance of remdesivir suggests that it needs continued research to help global health organizations detect areas requiring instant action to implement suitable measures. Furthermore, this study offers evolving hotspots and valuable insights into the scientific advances in this field and provides scaling-up analysis and evidence diffusion on remdesivir.

Combination therapy with remdesivir and monoclonal antibodies protects nonhuman primates against advanced Sudan virus disease

A major challenge in managing acute viral infections is ameliorating disease when treatment is delayed. Previously, we reported the success of a 2-pronged mAb and antiviral remdesivir therapeutic approach to treat advanced illness in rhesus monkeys infected with Marburg virus (MARV). Here, we explored the benefit of a similar combination therapy for Sudan ebolavirus (Sudan virus; SUDV) infection. Importantly, no licensed anti-SUDV therapeutics currently exist, and infection of rhesus macaques with SUDV results in a rapid disease course similar to MARV with a mean time to death of 8.3 days. When initiation of therapy with either remdesivir or a pan-ebolavirus mAb cocktail (MBP431) was delayed until 6 days after inoculation, only 20% of macaques survived. In contrast, when remdesivir and MBP431 treatment were combined beginning 6 days after inoculation, significant protection (80%) was achieved. Our results suggest that combination therapy may be a viable treatment for patients with advanced filovirus disease that warrants further clinical testing in future outbreaks.

Pharmacological treatment of COVID-19: an opinion paper

The precocity and efficacy of the vaccines developed so far against COVID-19 has been the most significant and saving advance against the pandemic. The development of vaccines has not prevented, during the whole period of the pandemic, the constant search for therapeutic medicines, both among existing drugs with different indications and in the development of new drugs. The Scientific Committee of the COVID-19 of the Illustrious College of Physicians of Madrid wanted to offer an early, simplified and critical approach to these new drugs, to new developments in immunotherapy and to what has been learned from the immune response modulators already known and which have proven effective against the virus, in order to help understand the current situation.

The development of broad-spectrum antiviral medical countermeasures to treat viral hemorrhagic fevers caused by natural or weaponized virus infections

The Joint Program Executive Office for Chemical, Biological, Radiological, and Nuclear Defense (JPEO-CBRND) began development of a broad-spectrum antiviral countermeasure against deliberate use of high-consequence viral hemorrhagic fevers (VHFs) in 2016. The effort featured comprehensive preclinical research, including laboratory testing and rapid advancement of lead molecules into nonhuman primate (NHP) models of Ebola virus disease (EVD). Remdesivir (GS-5734, Veklury, Gilead Sciences) was the first small molecule therapeutic to successfully emerge from this effort. Remdesivir is an inhibitor of RNA-dependent RNA polymerase, a viral enzyme that is essential for viral replication. Its robust potency and broad-spectrum antiviral activity against certain RNA viruses including Ebola virus and Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) led to its clinical evaluation in randomized, controlled trials (RCTs) in human patients during the 2018 EVD outbreak in the Democratic Republic of the Congo (DRC) and the ongoing Coronavirus Disease 2019 (COVID-19) pandemic today. Remdesivir was recently approved by the US Food and Drug Administration (FDA) for the treatment of COVID-19 requiring hospitalization. Substantial gaps remain in improving the outcomes of acute viral infections for patients afflicted with both EVD and COVID-19, including how to increase therapeutic breadth and strategies for the prevention and treatment of severe disease. Combination therapy that joins therapeutics with complimentary mechanisms of action appear promising, both preclinically and in RCTs. Importantly, significant programmatic challenges endure pertaining to a clear drug and biological product development pathway for therapeutics targeting biodefense and emerging pathogens when human efficacy studies are not ethical or feasible. For example, remdesivir's clinical development was facilitated by outbreaks of Ebola and SARS-CoV-2; as such, the development pathway employed for remdesivir is likely to be the exception rather than the rule. The current regulatory licensure pathway for therapeutics targeting rare, weaponizable VHF agents is likely to require use of FDA's established Animal Rule (21 CFR 314.600-650 for drugs; 21 CFR 601.90-95 for biologics). The FDA may grant marketing approval based on adequate and well-controlled animal efficacy studies when the results of those studies establish that the drug is safe and likely to produce clinical benefit in humans. In practical terms, this is anticipated to include a series of rigorous, well-documented, animal challenge studies, to include aerosol challenge, combined with human safety data. While small clinical studies against naturally occurring, high-consequence pathogens are typically performed where possible, approval for the therapeutics currently under development against biodefense pathogens will likely require the Animal Rule pathway utilizing studies in NHPs. We review the development of remdesivir as illustrative of the effort that will be needed to field future therapeutics against highly lethal, infectious agents.

Journey of remdesivir from the inhibition of hepatitis C virus to the treatment of COVID-19

If a planned path reaches a dead-end, one can simply stop. Or one can turn around, walk back to the last intersection and take another path, or one can consider taking few paths in parallel. The last scenario is reflective of the journey of remdesivir, the first antiviral for the treatment of COVID-19, that was approved by FDA less than 10 months after the isolation of SARS-CoV-2, the virus responsible for the COVID-19 pandemic. As of January 2022, 10 million COVID-19 patients have been treated with remdesivir worldwide, but the journey of this molecule started more than a decade earlier with the search for a cure of hepatitis C virus. The development path of remdesivir before the emergence of COVID-19 represents a valuable example of a preemptive pandemic preparedness, but the pursuit of this path would not have been possible without sustaining support of John C. Martin, whom we will sorely miss for his piercing vision, uncompromising leadership, and genuine compassion for patients suffering around the world.

The discovery and development of novel treatment strategies for filoviruses

INTRODUCTION

Filoviruses are negative-stranded, enveloped RNA viruses that can cause hemorrhagic fever in humans and include Ebola and Marburg viruses. Lethality rates can reach 90% in isolated outbreaks. The 2013-2016 Ebola virus epidemic demonstrated the global threat of filoviruses and hastened development of vaccines and therapeutics. There are six known filoviruses that cause disease in humans, but still few therapeutics are available for treatment.

AREAS COVERED

This review summarizes identification, testing, and development of therapeutics based on the peer-reviewed scientific literature beginning with the discovery of filoviruses in 1967. Small molecules, antibodies, cytokines, antisense, post-exposure vaccination, and host-targeted therapeutic approaches are discussed. An emphasis is placed on therapeutics that have shown promise in in vivo studies.

EXPERT OPINION

Two monoclonal antibody regimens are approved for use in humans for one filovirus (Ebola virus), and preclinical nonhuman primate studies suggest that other monoclonal-based therapies are likely to be effective against other filoviruses. Significant progress has been made in small-molecule antivirals and host-targeted approaches. An important consideration is the necessity of pan-filovirus therapeutics via broadly effective small molecules, antibody cocktails, and cross-reactive antibodies. The use of filovirus therapeutics as prophylactic treatment or in chronically infected individuals should be considered.

The nucleoside antiviral prodrug remdesivir in treating COVID-19 and beyond with interspecies significance

Infectious pandemics result in hundreds and millions of deaths, notable examples of the Spanish Flu, the Black Death and smallpox. The current pandemic, caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), is unprecedented even in the historical term of pandemics. The unprecedentedness is featured by multiple surges, rapid identification of therapeutic options and accelerated development of vaccines. Remdesivir, originally developed for Ebola viral disease, is the first treatment of COVID-19 (Coronavirus disease 2019) approved by the United States Food and Drug Administration. As demonstrated by in vitro and preclinical studies, this therapeutic agent is highly potent with a broad spectrum activity against viruses from as many as seven families even cross species. However, randomized controlled trials have failed to confirm the efficacy and safety. Remdesivir improves some clinical signs but not critical parameters such as mortality. This antiviral agent is an ester/phosphorylation prodrug and excessive hydrolysis which increases cellular toxicity. Remdesivir is given intravenously, leading to concentration spikes and likely increasing the potential of hydrolysis-based toxicity. This review has proposed a conceptual framework for improving its efficacy and minimizing toxicity not only for the COVID-19 pandemic but also for future ones caused by remdesivir-sensitive viruses.

Remdesivir: Quo vadis?

Remdesivir (GS-5734, Veklury®) has remained the only antiviral drug formally approved by the US FDA for the treatment of Covid-19 (SARS-CoV-2 infection). Its key structural features are the fact that it is a C-nucleoside (adenosine) analogue, contains a 1'-cyano function, and could be considered as a ProTide based on the presence of a phosphoramidate group. Its antiviral spectrum and activity in animal models have been well established and so has been its molecular mode of action as a delayed chain terminator of the viral RdRp (RNA-dependent RNA polymerase). Its clinical efficacy has been evaluated, but needs to be optimized with regard to timing, dosage and duration of treatment, and route of administration. Safety, toxicity and pharmacokinetics need to be further addressed, and so are its potential combinations with other drugs such as corticosteroids (i.e. dexamethasone) and ribavirin.

Remdesivir is efficacious in rhesus monkeys exposed to aerosolized Ebola virus

Efficacious therapeutics for Ebola virus disease are in great demand. Ebola virus infections mediated by mucosal exposure, and aerosolization in particular, present a novel challenge due to nontypical massive early infection of respiratory lymphoid tissues. We performed a randomized and blinded study to compare outcomes from vehicle-treated and remdesivir-treated rhesus monkeys in a lethal model of infection resulting from aerosolized Ebola virus exposure. Remdesivir treatment initiated 4 days after exposure was associated with a significant survival benefit, significant reduction in serum viral titer, and improvements in clinical pathology biomarker levels and lung histology compared to vehicle treatment. These observations indicate that remdesivir may have value in countering aerosol-induced Ebola virus disease.

Remdesivir inhibits the polymerases of the novel filoviruses Lloviu and Bombali virus

In recent years, a number of novel filoviruses (e.g. Lloviu virus (LLOV) and Bombali virus (BOMV)) have been discovered. While antibody-based therapeutics have recently been approved for treatment of infections with the filovirus Ebola virus (EBOV), no treatment options for novel filoviruses currently exist. Further, the development of antivirals against them is complicated by the fact that only sequence information, but no actual virus isolates, are available. To address this issue, we developed a reverse genetics-based minigenome system for BOMV, which allows us to assess the activity of the BOMV polymerase. Together with similar systems that we have developed for other filoviruses in the past (i.e. LLOV and Reston virus (RESTV)), we then assessed the efficiency of remdesivir, a known inhibitor of the EBOV polymerase that has recently been tested in a clinical trial for efficacy against Ebola disease. We show that remdesivir is indeed also active against the polymerases of BOMV, LLOV, and RESTV, with comparable IC₅₀ values to its activity against EBOV. This suggests that treatment with remdesivir might represent a viable option in case of infections with novel filoviruses.

SARS-CoV-2 RNA-dependent RNA polymerase as a therapeutic target for COVID-19

Introduction: The current SARS-CoV-2 pandemic urgently demands for both prevention and treatment strategies. RNA-dependent RNA-polymerase (RdRp), which has no counterpart in human cells, is an excellent target for drug development. Given the time-consuming process of drug development, repurposing drugs approved for other indications or at least successfully tested in terms of safety and tolerability, is an attractive strategy to rapidly provide an effective medication for severe COVID-19 cases.Areas covered: The currently available data and upcominSg studies on RdRp which can be repurposed to halt SARS-CoV-2 replication, are reviewed.Expert opinion: Drug repurposing and design of novel compounds are proceeding in parallel to provide a quick response and new specific drugs, respectively. Notably, the proofreading SARS-CoV-2 exonuclease activity could limit the potential for drugs designed as immediate chain terminators and favor the development of compounds acting through delayed termination. While vaccination is awaited to curb the SARS-CoV-2 epidemic, even partially effective drugs from repurposing strategies can be of help to treat severe cases of disease. Considering the high conservation of RdRp among coronaviruses, an improved knowledge of its activity in vitro can provide useful information for drug development or drug repurposing to combat SARS-CoV-2 as well as future pandemics.

Combination therapy protects macaques against advanced Marburg virus disease

Monoclonal antibodies (mAbs) and remdesivir, a small-molecule antiviral, are promising monotherapies for many viruses, including members of the genera Marburgvirus and Ebolavirus (family Filoviridae), and more recently, SARS-CoV-2. One of the major challenges of acute viral infections is the treatment of advanced disease. Thus, extending the window of therapeutic intervention is critical. Here, we explore the benefit of combination therapy with a mAb and remdesivir in a non-human primate model of Marburg virus (MARV) disease. While rhesus monkeys are protected against lethal infection when treatment with either a human mAb (MR186-YTE; 100%), or remdesivir (80%), is initiated 5 days post-inoculation (dpi) with MARV, no animals survive when either treatment is initiated alone beginning 6 dpi. However, by combining MR186-YTE with remdesivir beginning 6 dpi, significant protection (80%) is achieved, thereby extending the therapeutic window. These results suggest value in exploring combination therapy in patients presenting with advanced filovirus disease.

Off-Target In Vitro Profiling Demonstrates that Remdesivir Is a Highly Selective Antiviral Agent

Remdesivir (RDV, GS-5734), the first FDA-approved antiviral for the treatment of COVID-19, is a single diastereomer monophosphoramidate prodrug of an adenosine analogue. It is intracellularly metabolized into the active triphosphate form, which in turn acts as a potent and selective inhibitor of multiple viral RNA polymerases.

Remdesivir (RDV, GS-5734), the first FDA-approved antiviral for the treatment of COVID-19, is a single diastereomer monophosphoramidate prodrug of an adenosine analogue. It is intracellularly metabolized into the active triphosphate form, which in turn acts as a potent and selective inhibitor of multiple viral RNA polymerases. RDV has broad-spectrum activity against members of the coronavirus family, such as SARS-CoV-2, SARS-CoV, and MERS-CoV, as well as filoviruses and paramyxoviruses. To assess the potential for off-target toxicity, RDV was evaluated in a set of cellular and biochemical assays. Cytotoxicity was evaluated in a set of relevant human cell lines and primary cells. In addition, RDV was evaluated for mitochondrial toxicity under aerobic and anaerobic metabolic conditions, and for the effects on mitochondrial DNA content, mitochondrial protein synthesis, cellular respiration, and induction of reactive oxygen species. Last, the active 5′-triphosphate metabolite of RDV, GS-443902, was evaluated for potential interaction with human DNA and RNA polymerases. Among all of the human cells tested under 5 to 14 days of continuous exposure, the 50% cytotoxic concentration (CC₅₀) values of RDV ranged from 1.7 to >20 μM, resulting in selectivity indices (SI, CC₅₀/EC₅₀) from >170 to 20,000, with respect to RDV anti-SARS-CoV-2 activity (50% effective concentration [EC₅₀] of 9.9 nM in human airway epithelial cells). Overall, the cellular and biochemical assays demonstrated a low potential for RDV to elicit off-target toxicity, including mitochondria-specific toxicity, consistent with the reported clinical safety profile.

Marburg virus disease: A summary for clinicians

OBJECTIVES

This article summarizes the countermeasures for Marburg virus disease, focusing on pathogenesis, clinical features and diagnostics. There is an emphasis on therapies and vaccines that have demonstrated, through their evaluation in nonhuman primates (NHPs) and/or in humans, potential for use in an emergency situation.

METHODS

A standardized literature review was conducted on vaccines and treatments for Marburg virus disease, with a focus on human and nonhuman primate data published in the last five years. More detail on the methods that were used is summarized in a companion methods paper.

RESULTS

The study identified six treatments and four vaccine platforms that have demonstrated, through their efficacy in NHPs, potential benefit for treating or preventing infection in humans.

CONCLUSION

Succinct summaries of Marburg countermeasures are provided to give the busy clinician a head start in reviewing the literature if faced with a patient with Marburg virus disease. Links to other authoritative sources of information are also provided.

GS-5734: a potentially approved drug by FDA against SARS-Cov-2

We highlighted the discovery process, preparation techniques, broad-spectrum activities, antiviral mechanism, and future perspectives of GS-5734.