Discovery and optimization of potent broad-spectrum arenavirus inhibitors derived from benzimidazole

A chemically diverse library of about 400,000 small molecules was screened for antiviral activity against lentiviral pseudotypes with the Lassa virus envelope glycoprotein (LASV GP) gene incorporated. High-throughput screening resulted in discovery of a hit compound (ST-37) possessing a benzimidazole core which led to a potent compound series. Herein, we report SAR studies which involved structural modifications to the phenyl rings and methylamino linker portion attached to the benzimidazole core. Many analogs in this study possessed single digit nanomolar potency against LASV pseudotypes. Compounds in this benzimidazole series also exhibited nanomolar antiviral activity against pseudotypes generated from other arenavirus envelopes indicating the potential for development of a broad-spectrum inhibitor. Ultimately, lead compound ST-193 was identified and later found to be efficacious in a lethal LASV guinea pig model showing superior protection compared to ribavirin treatment.     

Structures of Arenaviral Nucleoproteins with Triphosphate dsRNA Reveal a Unique Mechanism of Immune Suppression

A hallmark of severe Lassa fever is the generalized immune suppression, the mechanism of which is poorly understood. Lassa virus (LASV) nucleoprotein (NP) is the only known 3′-5′ exoribonuclease that can suppress type I interferon (IFN) production possibly by degrading immune-stimulatory RNAs. How this unique enzymatic activity of LASV NP recognizes and processes RNA substrates is unknown. We provide an atomic view of a catalytically active exoribonuclease domain of LASV NP (LASV NP-C) in the process of degrading a 5′ triphosphate double-stranded (ds) RNA substrate, a typical pathogen-associated molecular pattern molecule, to induce type I IFN production. Additionally, we provide for the first time a high-resolution crystal structure of an active exoribonuclease domain of Tacaribe arenavirus (TCRV) NP. Coupled with the in vitro enzymatic and cell-based interferon suppression assays, these structural analyses strongly support a unified model of an exoribonuclease-dependent IFN suppression mechanism shared by all known arenaviruses. New knowledge learned from these studies should aid the development of therapeutics against pathogenic arenaviruses that can infect hundreds of thousands of individuals and kill thousands annually.     

Lassa virus glycoprotein complex review: insights into its unique fusion machinery

Lassa virus (LASV), an arenavirus endemic to West Africa, causes Lassa fever—a lethal hemorrhagic fever. Entry of LASV into the host cell is mediated by the glycoprotein complex (GPC), which is the only protein located on the viral surface and comprises three subunits: glycoprotein 1 (GP1), glycoprotein 2 (GP2), and a stable signal peptide (SSP). The LASV GPC is a class one viral fusion protein, akin to those found in viruses such as human immunodeficiency virus (HIV), influenza, Ebola virus (EBOV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). These viruses are enveloped and utilize membrane fusion to deliver their genetic material to the host cell. Like other class one fusion proteins, LASV-mediated membrane fusion occurs through an orchestrated sequence of conformational changes in its GPC. The receptor-binding subunit, GP1, first engages with a host cell receptor then undergoes a unique receptor switch upon delivery to the late endosome. The acidic pH and change in receptor result in the dissociation of GP1, exposing the fusion subunit, GP2, such that fusion can occur. These events ultimately lead to the formation of a fusion pore so that the LASV genetic material is released into the host cell. Interestingly, the mature GPC retains its SSP as a third subunit—a feature that is unique to arenaviruses. Additionally, the fusion domain contains two separate fusion peptides, instead of a standard singular fusion peptide. Here, we give a comprehensive review of the LASV GPC components and their unusual features.     

Small mammal diversity and dynamics within Nigeria,with emphasis on reservoirs of the lassa virus

Nigeria has a rich small mammal community, with several species implicated as carriers of zoonotic microbes such as the Lassa virus (LASV). We sought to elucidate the diversity and distribution of these animals (including known LASV reservoirs) geographically, habitat-wise and seasonally. Our DNA-assisted survey detected at least 19 small mammal species amongst 790 specimens. Diversity indices were similar between ecological zones and also between endemic and non-endemic areas for Lassa fever. Mastomys natalensis, the most renowned LASV host, was present in eight out of nine localities sampled. We also described the spatial occurrence of other known LASV hosts such as M. erythroleucus and Hylomyscus pamfi, including carriers of LASV-like arenaviruses such as Mus (Nannomys) spp. The most numerous rodents (Mastomys natalensis, M. erythroleucus, and Praomys daltoni) were captured mainly inside human dwellings. Reproductive activity occurred throughout the year, but led to population peaks for M. natalensis in the dry season and for M. erythroleucus and P. daltoni in the rainy season. Extensive geographic distribution of LASV rodent reservoirs, with population peaks in different seasons, shows that the risk of rodent-to-human transmission of LASV is greater than currently realized.     

Design, synthesis and cytotoxic activities of novel β-amino alcohol derivatives

Three series of novel β-amino alcohols possessing an N-anthranyl group have been obtained using tryptophan as the major starting material. These compounds were screened for cytotoxic activity against five human cancer cell lines in vitro by MTT assay, and some of them exhibited potential ability to be anticancer agents. Structure-activity relationship was carefully investigated. Only the compounds possessing small substituents (H or CH₃) at C-6 position showed the same activity as cisplatin (DDP) did.     

SAR studies of 4-acyl-1,6-dialkylpiperazin-2-one arenavirus cell entry inhibitors

Old World (Africa) and New World (South America) arenaviruses are associated with human hemorrhagic fevers. Efforts to develop small molecule therapeutics have yielded several chemical series including the 4-acyl-1,6-dialkylpiperazin-2-ones. Herein, we describe an extensive exploration of this chemotype. In initial Phase I studies, R¹ and R⁴ scanning libraries were assayed to identify potent substituents against Old World (Lassa) virus. In subsequent Phase II studies, R⁶ substituents and iterative R¹, R⁴ and R⁶ substituent combinations were evaluated to obtain compounds with improved Lassa and New World (Machupo, Junin, and Tacaribe) arenavirus inhibitory activity, in vitro human liver microsome metabolic stability and aqueous solubility.     

Identification of a novel series of potent RON receptor tyrosine kinase inhibitors

A novel series of N-(3-fluoro-4-(2-substituted-thieno[3,2-b]pyridin-7-yloxy)phenyl)-1-phenyl-5-(trifluoromethyl)-1H-pyrazole-4-carboxamides targeting RON receptor tyrosine kinase was designed and synthesized. SAR study of the series allowed us to identify compounds possessing either inhibitory activity of RON kinase enzyme in the low nanomolar range with low residual activity against the closely related c-Met or potent dual inhibitory activity against RON and c-Met, ? with no significant activity against VEGFR2 in both cases.     

Differential pathogenesis of closely related 2018 Nigerian outbreak clade III Lassa virus isolates

Nigeria continues to experience ever increasing annual outbreaks of Lassa fever (LF). The World Health Organization has recently declared Lassa virus (LASV) as a priority pathogen for accelerated research leading to a renewed international effort to develop relevant animal models of disease and effective countermeasures to reduce LF morbidity and mortality in endemic West African countries. A limiting factor in evaluating medical countermeasures against LF is a lack of well characterized animal models outside of those based on infection with LASV strain Josiah originating form Sierra Leone, circa 1976. Here we genetically characterize five recent LASV isolates collected from the 2018 outbreak in Nigeria. Three isolates were further evaluated in vivo and despite being closely related and from the same spatial / geographic region of Nigeria, only one of the three isolates proved lethal in strain 13 guinea pigs and non-human primates (NHP). Additionally, this isolate exhibited atypical pathogenesis characteristics in the NHP model, most notably respiratory failure, not commonly described in hemorrhagic cases of LF. These results suggest that there is considerable phenotypic heterogeneity in LASV infections in Nigeria, which leads to a multitude of pathogenesis characteristics that could account for differences between subclinical and lethal LF infections. Most importantly, the development of disease models using currently circulating LASV strains in West Africa are critical for the evaluation of potential vaccines and medical countermeasures.     

Characterizing the Lassa Virus Envelope Glycoprotein Membrane Proximal External Region for Its Role in Fusogenicity

The membrane-proximal external region(MPER) of Lassa virus(LASV) glycoprotein complex(GPC) is critical in modulating its functionality. Till now, the high-resolution structure of the intact GPC, including MPER is not available. In this study, we used alanine substitution to scan all 16 residues located in LASV MPER. Western blotting and quantification fusion assay showed that the residues located at the C terminus of the HR2(M414 and L415) and N terminus of the MPER(K417 and Y419) are critical for GPC-mediated membrane fusion function. Furthermore, cell surface biotinylation experiments revealed that M414 A, K417 A and Y419 A expressed similar levels as WT, whereas L415 A mutant led to a reduction of mature GPC on the cell surface. Moreover, substitution of these residues with the similar residue such as M414 L, L415 I, K417 R and Y419 F would partly compensate the loss of the fusion activity caused by the alanine mutant in these sites. Results from this study showed that several key residues in the MPER region are indispensable to promote the conformational changes that drive fusion events and shed light on the structure analysis of LASV GPC and anti-LASV therapeutics.     

A Recombinant Vesicular Stomatitis Virus-Based Lassa Fever Vaccine Protects Guinea Pigs and Macaques against Challenge with Geographically and Genetically Distinct Lassa Viruses

Background

Lassa virus (LASV) is endemic in several West African countries and is the etiological agent of Lassa fever. Despite the high annual incidence and significant morbidity and mortality rates, currently there are no approved vaccines to prevent infection or disease in humans. Genetically, LASV demonstrates a high degree of diversity that correlates with geographic distribution. The genetic heterogeneity observed between geographically distinct viruses raises concerns over the potential efficacy of a “universal” LASV vaccine. To date, several experimental LASV vaccines have been developed; however, few have been evaluated against challenge with various genetically unique Lassa virus isolates in relevant animal models.

Methodologies/principle findings

Here we demonstrate that a single, prophylactic immunization with a recombinant vesicular stomatitis virus (VSV) expressing the glycoproteins of LASV strain Josiah from Sierra Leone protects strain 13 guinea pigs from infection / disease following challenge with LASV isolates originating from Liberia, Mali and Nigeria. Similarly, the VSV-based LASV vaccine yields complete protection against a lethal challenge with the Liberian LASV isolate in the gold-standard macaque model of Lassa fever.

Conclusions/significance

Our results demonstrate the VSV-based LASV vaccine is capable of preventing morbidity and mortality associated with non-homologous LASV challenge in two animal models of Lassa fever. Additionally, this work highlights the need for the further development of disease models for geographical distinct LASV strains, particularly those from Nigeria, in order to comprehensively evaluate potential vaccines and therapies against this prominent agent of viral hemorrhagic fever.     

拉沙热研究进展

拉沙热(Lassa fever,LF)由拉沙病毒(Lassa virus,LASV)引起,是一种通过鼠类传播给人的急性出血性动物源性传染病,病死率高。主要在西非地区流行,但在全球多个国家发现输入性病例。本文主要针对拉沙病毒的病原学特点、疾病流行现状、临床特征、实验室检测、治疗及预防进展进行综述。同时,建议在全球经济一体化的大形势下,加强对拉沙热国际防控的关注度,建立国际联防联控防治策略和措施,并将其纳入全球防控体系。     

Synthesis of novel di- and tricationic carbapenems with potent anti-MRSA activity

A new series of 1β-methyl carbapenems possessing a 6,7-disubstituted imidazo[5,1-b]thiazol-2-yl group directly attached to the C-2 position of the carbapenem nucleus was prepared, and their activities against methicillin-resistant Staphylococcus aureus (MRSA) were evaluated. First, a benzyl moiety was introduced at the C-6 position of imidazo[5,1-b]thiazole attached to the carbapenem. These benzylated molecules showed potent anti-MRSA activity, but poor water solubility. In order to overcome this drawback, we designed and synthesized di- and tricationic carbapenems and finally discovered a novel carbapenem (15i), which exhibited excellent anti-MRSA activity and good water solubility.     

Design, synthesis, and antiproliferative activity of some novel aminosubstituted xanthenones, able to overcome multidrug resistance toward MES-SA/Dx5 cells

A series of novel xanthenone aminoderivatives and their pyrazole-fused counterparts possessing structural analogy to the potent anticancer agent 9-methoxypyrazoloacridine (PZA) reported. These compounds exhibited an interesting cytotoxic activity against a panel of cell lines. Most noticeably, they retain activity against the multidrug resistant MES-SA/Dx5 subline, showing resistant factors close to 1.     

Carbonic anhydrase inhibitors. Synthesis of 2,4,6-trimethylpyridinium derivatives of 2-(hydrazinocarbonyl)-3-aryl-1H-indole-5-sulfonamides acting as potent inhibitors of the tumor-associated isoform IX and XII

A series of 2-(hydrazinocarbonyl)-3-aryl-1H-indole-5-sulfonamides possessing various 2-, 3- or 4- substituted phenyl groups with methyl-, halogeno- and methoxy-functionalities, or a perfluorophenyl moiety, has been derivatized by reaction with 2,4,6-trimethylpyrylium perchlorate. The new sulfonamides were evaluated as inhibitors of four mammalian carbonic anhydrase (CA, EC 4.2.1.1) isoforms, that is, CA I, II (cytosolic), CA IX and XII (transmembrane, tumor-associated forms). Excellent inhibitory activity was observed against hCA IX with most of these sulfonamides, and against hCA XII with some of the new compounds. These compounds were generally less effective inhibitors of hCA II. Being membrane impermeant, these positively-charged sulfonamides are interesting candidates for targeting the tumor-associated CA IX and XII, as possible diagnostic tools or therapeutic agents.     

Antimycobacterial activity of 9-sulfonylated/sulfenylated-6-mercaptopurine derivatives.

A series of 9-sulfonylated/sulfenylated-6-mercaptopurines has been prepared by reaction of 6-mercaptopurine with sulfonyl/sulfenyl halides. These compounds constitute a new class of potent antimycobacterial agents, possessing MIC values against Mycobacterium tuberculosis H37Rv in the range of 0.39-3.39 microg/mL, as well as appreciable activity against Mycobacterium avium. Furthermore, a compound of this small series exhibited good activity (MIC under 1 microg/mL) against several drug resistant strains of M. tuberculosis.     

Geographic Distribution and Genetic Characterization of Lassa Virus in Sub-Saharan Mali

Background

Lassa fever is an acute viral illness characterized by multi-organ failure and hemorrhagic manifestations. Lassa fever is most frequently diagnosed in Nigeria, Sierra Leone, Liberia, and Guinea, although sporadic cases have been recorded in other West African countries, including Mali. The etiological agent of Lassa fever is Lassa virus (LASV), an Arenavirus which is maintained in nature and frequently transmitted to humans by Mastomys natalensis. The purpose of this study was to better define the geographic distribution of LASV-infected rodents in sub-Saharan Mali.

Methodologies/Principal Findings

Small mammals were live-trapped at various locations across Mali for the purpose of identifying potential zoonotic pathogens. Serological and molecular assays were employed and determined LASV infected rodents were exclusively found in the southern Mali near the border of Côte d''Ivoire. Overall, 19.4% of Mastomys natalensis sampled in this region had evidence of LASV infection, with prevalence rates for individual villages ranging from 0 to 52%. Full-length genomic sequences were determined using high throughput sequencing methodologies for LASV isolates generated from tissue samples of rodents collected in four villages and confirmed the phylogenetic clustering of Malian LASV with strain AV.

Conclusions/Significance

The risk of human infections with LASV is greatest in villages in southern Mali. Lassa fever should be considered in the differential diagnosis for febrile individuals and appropriate diagnostic techniques need to be established to determine the incidence of infection and disease in these regions.     

Lassa viral dynamics in non-human primates treated with favipiravir or ribavirin

Lassa fever is an haemorrhagic fever caused by Lassa virus (LASV). There is no vaccine approved against LASV and the only recommended antiviral treatment relies on ribavirin, despite limited evidence of efficacy. Recently, the nucleotide analogue favipiravir showed a high antiviral efficacy, with 100% survival obtained in an otherwise fully lethal non-human primate (NHP) model of Lassa fever. However the mechanism of action of the drug is not known and the absence of pharmacokinetic data limits the translation of these results to the human setting. Here we aimed to better understand the antiviral effect of favipiravir by developping the first mathematical model recapitulating Lassa viral dynamics and treatment. We analyzed the viral dynamics in 24 NHPs left untreated or treated with ribavirin or favipiravir, and we put the results in perspective with those obtained with the same drugs in the context of Ebola infection. Our model estimates favipiravir EC₅₀ in vivo to 2.89 μg.mL^-1, which is much lower than what was found against Ebola virus. The main mechanism of action of favipiravir was to decrease virus infectivity, with an efficacy of 91% at the highest dose. Based on our knowledge acquired on the drug pharmacokinetics in humans, our model predicts that favipiravir doses larger than 1200 mg twice a day should have the capability to strongly reduce the production infectious virus and provide a milestone towards a future use in humans.     

Maturation cleavage within the ectodomain of Lassa virus glycoprotein relies on stabilization by the cytoplasmic tail

The Lassa virus glycoprotein consists of an ectodomain, a transmembrane anchor, and a cytoplasmic domain. It is synthesized as an inactive precursor and cleaved within the ectodomain to yield the mature form. Here, we show that this maturation cleavage can be abolished by mutation of single conserved amino acids within the cytoplasmic domain at the carboxy-terminus of the glycoprotein. Moreover, substitutions and deletions of multiple amino acids result in destabilization of the glycoprotein oligomers. These results indicate that conformation changes in the cytoplasmic domain travel across the membrane and subsequently abolish the maturation cleavage. Therefore, we postulate that the cytoplasmic domain is an important maturation factor stabilizing the overall conformation of the glycoprotein.

Structured summary

MINT-7997004: LASV GP (uniprotkb:P08669) and LASV GP (uniprotkb:P08669) physically interact (MI:0915) by cosedimentation through density gradient (MI:0029)