Ebanga™: The most recent FDA-approved drug for treating Ebola

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.

Discovery of novel Ebola entry inhibitors with 1,2,3,4-tetrahydroisoquinoline-3-carboxamide based on (3S,4aS,8aS)-2-(3-amino-2-hydroxypropyl) decahydroisoquinoline-3-carboxamide scaffold

Novel Ebola entry inhibitors were designed and synthesized based on decahydroisoquinolines by streamlining non-essential functional groups that do not compromise activity. All novel derivatives were evaluated for their anti-Ebola activities and cytotoxicitiies in a defective Ebola virus model. A novel tetrahydroisoquinoline Ebola virus entry inhibitor, Hu7, was readily available with antiviral activity comparable to previous findings, while demonstrating a marked reduction in toxicity. Such new compounds with simple and easy-to-synthesize structures could be potential leads for further optimizing the development of anti-Ebola drugs.

Monoclonal Antibodies for Pediatric Viral Disease Prevention and Treatment

Medical advancements over the last century have improved our ability to treat pediatric infectious diseases, significantly reducing associated morbidity and mortality worldwide. Although vaccines have been pivotal in this progress, many viral pathogens still do not currently have effective vaccines. The COVID-19 pandemic highlighted the need for rapid responses to emerging viral pathogens and introduced new tools to combat them. This review addresses human monoclonal antibodies (mAbs) as a strategy for treating and preventing viral infections in pediatric populations. We discuss previously used and currently available mAbs and advancements in mAb discovery. We address the future of mAb therapy by describing novel approaches in drug production and delivery platforms in addition to alternative antibody classes. Finally, we review the challenges and limitations of mAb therapy development for newborns and children.

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.

Drug repositioning as a promising approach for the eradication of emerging and re-emerging viral agents

The global impact of emerging and re-emerging viral agents during epidemics and pandemics leads to serious health and economic burdens. Among the major emerging or re-emerging viruses include SARS-CoV-2, Ebola virus (EBOV), Monkeypox virus (Mpox), Hepatitis viruses, Zika virus, Avian flu, Influenza virus, Chikungunya virus (CHIKV), Dengue fever virus (DENV), West Nile virus, Rhabdovirus, Sandfly fever virus, Crimean-Congo hemorrhagic fever (CCHF) virus, and Rift Valley fever virus (RVFV). A comprehensive literature search was performed to identify existing studies, clinical trials, and reviews that discuss drug repositioning strategies for the treatment of emerging and re-emerging viral infections using databases, such as PubMed, Scholar Google, Scopus, and Web of Science. By utilizing drug repositioning, pharmaceutical companies can take advantage of a cost-effective, accelerated, and effective strategy, which in turn leads to the discovery of innovative treatment options for patients. In light of antiviral drug resistance and the high costs of developing novel antivirals, drug repositioning holds great promise for more rapid substitution of approved drugs. Main repositioned drugs have included chloroquine, ivermectin, dexamethasone, Baricitinib, tocilizumab, Mab114 (Ebanga™), ZMapp (pharming), Artesunate, imiquimod, saquinavir, capmatinib, naldemedine, Trametinib, statins, celecoxib, naproxen, metformin, ruxolitinib, nitazoxanide, gemcitabine, Dorzolamide, Midodrine, Diltiazem, zinc acetate, suramin, 5-fluorouracil, quinine, minocycline, trifluoperazine, paracetamol, berbamine, Nifedipine, and chlorpromazine. This succinct review will delve into the topic of repositioned drugs that have been utilized to combat emerging and re-emerging viral pathogens.

The oral drug obeldesivir protects nonhuman primates against lethal Ebola virus infection

Obeldesivir (ODV; GS-5245) is an orally administered ester prodrug of the parent nucleoside GS-441524 that has broad spectrum antiviral activity inhibiting viral RNA-dependent RNA polymerases. We recently showed that ODV completely protects cynomolgus macaques against lethal infection with Sudan virus when given 24 hours after parenteral exposure. Here, we report that once daily oral ODV treatment of cynomolgus and rhesus macaques for 10 days confers 80 and 100% protection, respectively, against lethal Ebola virus infection when treatment is initiated 24 hours after mucosal (conjunctival) exposure. ODV treatment delayed viral replication to abate excessive inflammation and promote adaptive immunity. For outbreak response, oral antivirals might present substantial advantages over now approved intravenous drugs, such as easy supply, storage, distribution, and administration. Furthermore, these results support the potential of ODV as an oral postexposure prophylaxis with broad spectrum activity across filoviruses.

Advancements and Challenges in Addressing Zoonotic Viral Infections with Epidemic and Pandemic Threats

Zoonotic viruses have significant pandemic potential, as evidenced by the coronavirus pandemic, which underscores that zoonotic infections have historically caused numerous outbreaks and millions of deaths over centuries. Zoonotic viruses induce numerous types of illnesses in their natural hosts. These viruses are transmitted to humans via biological vectors, direct contact with infected animals or their bites, and aerosols. Zoonotic viruses continuously evolve and adapt to human hosts, resulting in devastating consequences. It is very important to understand pathogenesis pathways associated with zoonotic viral infections across various hosts and develop countermeasure strategies accordingly. In this review, we briefly discuss advancements in diagnostics and therapeutics for zoonotic viral infections. It provides insight into recent outbreaks, viral dynamics, licensed vaccines, as well as vaccine candidates progressing to clinical investigations. Despite advancements, challenges persist in combating zoonotic viruses due to immune evasion, unpredicted outbreaks, and the complexity of the immune responses. Most of these viruses lack effective treatments and vaccines, relying entirely on supportive care and preventive measures. Exposure to animal reservoirs, limited vaccine access, and insufficient coverage further pose challenges to preventive efforts. This review highlights the critical need for ongoing interdisciplinary research and collaboration to strengthen preparedness and response strategies against emerging infectious threats.

Quantification of Neutralizing Antibodies in Serum Using VSV-MARV-GFP

Neutralizing antibodies play an important role in protection against filoviruses. However, the technique to assess neutralization titers with a replicating BSL-4 virus is limited. This chapter explains how to determine the neutralization titer in serum samples against Marburg virus (MARV). This method uses a replicating recombinant vesicular stomatitis virus expressing the MARV glycoprotein and the green fluorescent protein as a surrogate approach.

A pan-orthoebolavirus neutralizing antibody encoded by mRNA effectively prevents virus infection

Orthoebolavirus is a genus of hazardous pathogens that has caused over 30 outbreaks. However, currently approved therapies are limited in scope, as they are only effective against the Ebola virus and lack cross-protection against other orthoebolaviruses. Here, we demonstrate that a previously isolated human-derived antibody, 2G1, can recognize the glycoprotein (GP) of every orthoebolavirus species. The cryo-electron microscopy structure of 2G1 Fab in complex with the GPΔMucin trimer reveals that 2G1 binds a quaternary pocket formed by three subunits from two GP protomers. 2G1 recognizes highly conserved epitopes among filoviruses and achieves neutralization by blocking GP proteolysis. We designed an efficient mRNA module capable of producing test antibodies at expression levels exceeding 1500 ng/mL in vitro. The lipid nanoparticle (LNP)-encapsulated mRNA-2G1 exhibited potent neutralizing activities against the HIV-pseudotyped Ebola and Sudan viruses that were 19.8 and 12.5 times that of IgG format, respectively. In mice, the antibodies encoded by the mRNA-2G1-LNP peaked within 24 h, effectively blocking the invasion of pseudoviruses with no apparent liver toxicity. This study suggests that the 2G1 antibody and its mRNA formulation represent promising candidate interventions for orthoebolavirus disease, and it provides an efficient mRNA framework applicable to antibody-based therapies.

Discovery of Nanosota-EB1 and -EB2 as Novel Nanobody Inhibitors Against Ebola Virus Infection

The Ebola filovirus (EBOV) poses a serious threat to global health and national security. Nanobodies, a type of single-domain antibody, have demonstrated promising therapeutic potential. We identified two anti-EBOV nanobodies, Nanosota-EB1 and Nanosota-EB2, which specifically target the EBOV glycoprotein (GP). Cryo-EM and biochemical data revealed that Nanosota-EB1 binds to the glycan cap of GP1, preventing its protease cleavage, while Nanosota-EB2 binds to critical membrane-fusion elements in GP2, stabilizing it in the pre-fusion state. Nanosota-EB2 is a potent neutralizer of EBOV infection in vitro and offers excellent protection in a mouse model of EBOV challenge, while Nanosota-EB1 provides moderate neutralization and protection. Nanosota-EB1 and Nanosota-EB2 are the first nanobodies shown to inhibit authentic EBOV. Combined with our newly developed structure-guided in vitro evolution approach, they lay the foundation for nanobody-based therapies against EBOV and other viruses within the ebolavirus genus.

Fc-FcγR interactions during infections: From neutralizing antibodies to antibody-dependent enhancement

Advances in antibody technologies have resulted in the development of potent antibody-based therapeutics with proven clinical efficacy against infectious diseases. Several monoclonal antibodies (mAbs), mainly against viruses such as SARS-CoV-2, HIV-1, Ebola virus, influenza virus, and hepatitis B virus, are currently undergoing clinical testing or are already in use. Although these mAbs exhibit potent neutralizing activity that effectively blocks host cell infection, their antiviral activity results not only from Fab-mediated virus neutralization, but also from the protective effector functions mediated through the interaction of their Fc domains with Fcγ receptors (FcγRs) on effector leukocytes. Fc-FcγR interactions confer pleiotropic protective activities, including the clearance of opsonized virions and infected cells, as well as the induction of antiviral T-cell responses. However, excessive or inappropriate activation of specific FcγR pathways can lead to disease enhancement and exacerbated pathology, as seen in the context of dengue virus infections. A comprehensive understanding of the diversity of Fc effector functions during infection has guided the development of engineered antiviral antibodies optimized for maximal effector activity, as well as the design of targeted therapeutic approaches to prevent antibody-dependent enhancement of disease.

Discovery of Thiophene Derivatives as Potent, Orally Bioavailable, and Blood-Brain Barrier-Permeable Ebola Virus Entry Inhibitors

The endemic nature of the Ebola virus disease in Africa underscores the need for prophylactic and therapeutic drugs that are affordable and easy to administer. Through a phenotypic screening employing viral pseudotypes and our in-house chemical library, we identified a promising hit featuring a thiophene scaffold, exhibiting antiviral activity in the micromolar range. Following up on this thiophene hit, a new series of compounds that retain the five-membered heterocyclic scaffold while modifying several substituents was synthesized. Initial screening using a pseudotype viral system and validation assays employing authentic Ebola virus demonstrated the potential of this new chemical class as viral entry inhibitors. Subsequent investigations elucidated the mechanism of action through site-directed mutagenesis. Furthermore, we conducted studies to assess the pharmacokinetic profile of selected compounds to confirm its pharmacological and therapeutic potential.

Ebola virus-induced eye sequelae: a murine model for evaluating glycoprotein-targeting therapeutics

BACKGROUND

Ebola virus disease (EVD) survivors experience ocular sequelae including retinal lesions, cataracts, and vision loss. While monoclonal antibodies targeting the Ebola virus glycoprotein (EBOV-GP) have shown promise in improving prognosis, their effectiveness in mitigating ocular sequelae remains uncertain.

METHODS

We developed and characterized a BSL-2-compatible immunocompetent mouse model to evaluate therapeutics targeting EBOV-GP by inoculating neonatal mice with vesicular stomatitis virus expressing EBOV-GP (VSV-EBOV). To examine the impact of anti-EBOV-GP antibody treatment on acute retinitis and ocular sequelae, VSV-EBOV-infected mice were treated with polyclonal antibodies or monoclonal antibody preparations with antibody-dependent cellular cytotoxicity (ADCC-mAb) or neutralizing activity (NEUT-mAb).

FINDINGS

Treatment with all anti-EBOV-GP antibodies tested dramatically reduced viremia and improved survival. Further, all treatments reduced the incidence of cataracts. However, NEUT-mAb alone or in combination with ADCC-mAb reduced viral load in the eyes, downregulated the ocular immune and inflammatory responses, and minimized retinal damage more effectively.

INTERPRETATION

Anti-EBOV-GP antibodies can improve survival among EVD patients, but improved therapeutics are needed to reduce life altering sequelae. This animal model offers a new platform to examine the acute and long-term effect of the virus in the eye and the relative impact of therapeutic candidates targeting EBOV-GP. Results indicate that even antibodies that improve systemic viral clearance and survival can differ in their capacity to reduce acute ocular inflammation, and long-term retinal pathology and corneal degeneration.

FUNDING

This study was partly supported by Postgraduate Research Fellowship Awards from ORISE through an interagency agreement between the US DOE and the US FDA.

Single domain antibodies from camelids in the treatment of microbial infections

Infectious diseases continue to pose significant global health challenges. In addition to the enduring burdens of ailments like malaria and HIV, the emergence of nosocomial outbreaks driven by antibiotic-resistant pathogens underscores the ongoing threats. Furthermore, recent infectious disease crises, exemplified by the Ebola and SARS-CoV-2 outbreaks, have intensified the pursuit of more effective and efficient diagnostic and therapeutic solutions. Among the promising options, antibodies have garnered significant attention due to their favorable structural characteristics and versatile applications. Notably, nanobodies (Nbs), the smallest functional single-domain antibodies of heavy-chain only antibodies produced by camelids, exhibit remarkable capabilities in stable antigen binding. They offer unique advantages such as ease of expression and modification and enhanced stability, as well as improved hydrophilicity compared to conventional antibody fragments (antigen-binding fragments (Fab) or single-chain variable fragments (scFv)) that can aggregate due to their low solubility. Nanobodies directly target antigen epitopes or can be engineered into multivalent Nbs and Nb-fusion proteins, expanding their therapeutic potential. This review is dedicated to charting the progress in Nb research, particularly those derived from camelids, and highlighting their diverse applications in treating infectious diseases, spanning both human and animal contexts.

Computational and experimental identification of keystone interactions in Ebola virus matrix protein VP40 dimer formation

The Ebola virus (EBOV) is a lipid-enveloped virus with a negative sense RNA genome that can cause severe and often fatal viral hemorrhagic fever. The assembly and budding of EBOV is regulated by the matrix protein, VP40, which is a peripheral protein that associates with anionic lipids at the inner leaflet of the plasma membrane. VP40 is sufficient to form virus-like particles (VLPs) from cells, which are nearly indistinguishable from authentic virions. Due to the restrictions of studying EBOV in BSL-4 facilities, VP40 has served as a surrogate in cellular studies to examine the EBOV assembly and budding process from the host cell plasma membrane. VP40 is a dimer where inhibition of dimer formation halts budding and formation of new VLPs as well as VP40 localization to the plasma membrane inner leaflet. To better understand VP40 dimer stability and critical amino acids to VP40 dimer formation, we integrated computational approaches with experimental validation. Site saturation/alanine scanning calculation, combined with molecular mechanics-based generalized Born with Poisson-Boltzmann surface area (MM-GB/PBSA) method and molecular dynamics simulations were used to predict the energetic contribution of amino acids to VP40 dimer stability and the hydrogen bonding network across the dimer interface. These studies revealed several previously unknown interactions and critical residues predicted to impact VP40 dimer formation. In vitro and cellular studies were then pursued for a subset of VP40 mutations demonstrating reduction in dimer formation (in vitro) or plasma membrane localization (in cells). Together, the computational and experimental approaches revealed critical residues for VP40 dimer stability in an alpha-helical interface (between residues 106-117) as well as in a loop region (between residues 52-61) below this alpha-helical region. This study sheds light on the structural origins of VP40 dimer formation and may inform the design of a small molecule that can disrupt VP40 dimer stability.

Design and characterization of protective pan-ebolavirus and pan-filovirus bispecific antibodies

Monoclonal antibodies (mAbs) are an important class of antiviral therapeutics. MAbs are highly selective, well tolerated, and have long in vivo half-life as well as the capacity to induce immune-mediated virus clearance. Their activities can be further enhanced by integration of their variable fragments (Fvs) into bispecific antibodies (bsAbs), affording simultaneous targeting of multiple epitopes to improve potency and breadth and/or to mitigate against viral escape by a single mutation. Here, we explore a bsAb strategy for generation of pan-ebolavirus and pan-filovirus immunotherapeutics. Filoviruses, including Ebola virus (EBOV), Sudan virus (SUDV), and Marburg virus (MARV), cause severe hemorrhagic fever. Although there are two FDA-approved mAb therapies for EBOV infection, these do not extend to other filoviruses. Here, we combine Fvs from broad ebolavirus mAbs to generate novel pan-ebolavirus bsAbs that are potently neutralizing, confer protection in mice, and are resistant to viral escape. Moreover, we combine Fvs from pan-ebolavirus mAbs with those of protective MARV mAbs to generate pan-filovirus protective bsAbs. These results provide guidelines for broad antiviral bsAb design and generate new immunotherapeutic candidates.

Neutralizing antibodies to block viral entry and for identification of entry inhibitors

Neutralizing antibodies (NAbs) are naturally produced by our immune system to combat viral infections. Clinically, neutralizing antibodies with potent efficacy and high specificity have been extensively used to prevent and treat a wide variety of viral infections, including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), Human Immunodeficiency Virus (HIV), Dengue Virus (DENV) and Hepatitis B Virus (HBV). An overwhelmingly large subset of clinically effective NAbs operates by targeting viral envelope proteins to inhibit viral entry into the host cell. Binding of viral envelope protein to the host receptor is a critical rate limiting step triggering a cascade of downstream events, including endocytosis, membrane fusion and pore formation to allow viral entry. In recent years, improved structural knowledge on these processes have allowed researchers to also leverage NAbs as an indispensable tool in guiding discovery of novel antiviral entry inhibitors, providing drug candidates with high efficacy and pan-genus specificity. This review will summarize the latest progresses on the applications of NAbs as effective entry inhibitors and as important tools to develop antiviral therapeutics by high-throughput drug screenings, rational design of peptidic entry inhibitor mimicking NAbs and in silico computational modeling approaches.

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.

PI(4,5)P2 binding sites in the Ebola virus matrix protein VP40 modulate assembly and budding

Ebola virus (EBOV) causes severe hemorrhagic fever in humans and is lethal in a large percentage of those infected. The EBOV matrix protein viral protein 40 kDa (VP40) is a peripheral binding protein that forms a shell beneath the lipid bilayer in virions and virus-like particles (VLPs). VP40 is required for virus assembly and budding from the host cell plasma membrane. VP40 is a dimer that can rearrange into oligomers at the plasma membrane interface, but it is unclear how these structures form and how they are stabilized. We therefore investigated the ability of VP40 to form stable oligomers using in vitro and cellular assays. We characterized two lysine-rich regions in the VP40 C-terminal domain (CTD) that bind phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) and play distinct roles in lipid binding and the assembly of the EBOV matrix layer. The extensive analysis of VP40 with and without lipids by hydrogen deuterium exchange mass spectrometry revealed that VP40 oligomers become extremely stable when VP40 binds PI(4,5)P2. The PI(4,5)P2-induced stability of VP40 dimers and oligomers is a critical factor in VP40 oligomerization and release of VLPs from the plasma membrane. The two lysine-rich regions of the VP40 CTD have different roles with respect to interactions with plasma membrane phosphatidylserine (PS) and PI(4,5)P2. CTD region 1 (Lys221, Lys224, and Lys225) interacts with PI(4,5)P2 more favorably than PS and is important for VP40 extent of oligomerization. In contrast, region 2 (Lys270, Lys274, Lys275, and Lys279) mediates VP40 oligomer stability via lipid interactions and has a more prominent role in release of VLPs.

Navigating the Complex Landscape of Ebola Infection Treatment: A Review of Emerging Pharmacological Approaches

In 1976 Ebola revealed itself to the world, marking the beginning of a series of localized outbreaks. However, it was the Ebola outbreak that began in 2013 that incited fear and anxiety around the globe. Since then, our comprehension of the virus has been steadily expanding. Ebola virus (EBOV), belonging to the Orthoebolavirus genus of the Filoviridae family, possesses a non-segmented, negative single-stranded RNA genome comprising seven genes that encode multiple proteins. These proteins collectively orchestrate the intricate process of infecting host cells. It is not possible to view each protein as monofunctional. Instead, they synergistically contribute to the pathogenicity of the virus. Understanding this multifaceted replication cycle is crucial for the development of effective antiviral strategies. Currently, two antibody-based therapeutics have received approval for treating Ebola virus disease (EVD). In 2022, the first evidence-based clinical practice guideline dedicated to specific therapies for EVD was published. Although notable progress has been made in recent years, deaths still occur. Consequently, there is an urgent need to enhance the therapeutic options available to improve the outcomes of the disease. Emerging therapeutics can target viral proteins as direct-acting antivirals or host factors as host-directed antivirals. They both have advantages and disadvantages. One way to bypass some disadvantages is to repurpose already approved drugs for non-EVD indications to treat EVD. This review offers detailed insight into the role of each viral protein in the replication cycle of the virus, as understanding how the virus interacts with host cells is critical to understanding how emerging therapeutics exert their activity. Using this knowledge, this review delves into the intricate mechanisms of action of current and emerging therapeutics.