Discovery of a novel, monocationic, small-molecule inhibitor of scrapie prion accumulation in cultured sheep microglia and Rov cells

Benzimidazole-Triazole Hybrids as Antimicrobial and Antiviral Agents: A Systematic Review

Bacterial infections have attracted the attention of researchers in recent decades, especially due to the special problems they have faced, such as their increasing diversity and resistance to antibiotic treatment. The emergence and development of the SARS-CoV-2 infection stimulated even more research to find new structures with antimicrobial and antiviral properties. Among the heterocyclic compounds with remarkable therapeutic properties, benzimidazoles, and triazoles stand out, possessing antimicrobial, antiviral, antitumor, anti-Alzheimer, anti-inflammatory, analgesic, antidiabetic, or anti-ulcer activities. In addition, the literature of the last decade reports benzimidazole-triazole hybrids with improved biological properties compared to the properties of simple mono-heterocyclic compounds. This review aims to provide an update on the synthesis methods of these hybrids, along with their antimicrobial and antiviral activities, as well as the structure-activity relationship reported in the literature. It was found that the presence of certain groups grafted onto the benzimidazole and/or triazole nuclei (-F, -Cl, -Br, -CF₃, -NO₂, -CN, -CHO, -OH, OCH₃, COOCH₃), as well as the presence of some heterocycles (pyridine, pyrimidine, thiazole, indole, isoxazole, thiadiazole, coumarin) increases the antimicrobial activity of benzimidazole-triazole hybrids. Also, the presence of the oxygen or sulfur atom in the bridge connecting the benzimidazole and triazole rings generally increases the antimicrobial activity of the hybrids. The literature mentions only benzimidazole-1,2,3-triazole hybrids with antiviral properties. Both for antimicrobial and antiviral hybrids, the presence of an additional triazole ring increases their biological activity, which is in agreement with the three-dimensional binding mode of compounds. This review summarizes the advances of benzimidazole triazole derivatives as potential antimicrobial and antiviral agents covering articles published from 2000 to 2023.

Small Molecules with Anti-Prion Activity

Prion pathologies are fatal neurodegenerative diseases caused by the misfolding of the physiological Prion Protein (PrP^C) into a β-structure-rich isoform called PrP^Sc. To date, there is no available cure for prion diseases and just a few clinical trials have been carried out. The initial approach in the search of anti-prion agents had PrP^Sc as a target, but the existence of different prion strains arising from alternative conformations of PrP^Sc, limited the efficacy of the ligands to a straindependent ability. That has shifted research to PrP^C ligands, which either act as chaperones, by stabilizing the native conformation, or inhibit its interaction with PrP^Sc. The role of transition-metal mediated oxidation processes in prion misfolding has also been investigated. Another promising approach is the indirect action via other cellular targets, like membrane domains or the Protein- Folding Activity of Ribosomes (PFAR). Also, new prion-specific high throughput screening techniques have been developed. However, so far no substance has been found to be able to extend satisfactorily survival time in animal models of prion diseases. This review describes the main features of the Structure-Activity Relationship (SAR) of the various chemical classes of anti-prion agents.

Therapies for prion diseases

Recent advances in understanding of the molecular biology of prion diseases and improved clinical diagnostic techniques might allow researchers to think about therapeutic trials in Creutzfeldt-Jakob disease (CJD) patients. Some attempts have been made in the past and various compounds have been tested in single case reports and patient series. Controlled trials are rare. However, in the past few years, it has been demonstrated that clinical trials are feasible. The clinicians might face several specific problems when evaluating the efficacy of the drug in CJD, such as rareness of the disease, lack of appropriate preclinical tests and heterogeneous clinical presentation in humans. These problems have to be carefully addressed in future.

Immortalized sheep microglial cells are permissive to a diverse range of ruminant viruses

BACKGROUND

Ruminants, including sheep and goats (small ruminants), are key agricultural animals in many parts of the world. Infectious diseases, including many viral diseases, are significant problems to efficient production of ruminants. Unfortunately, reagents tailored to viruses of ruminants, and especially small ruminants, are lacking compared to other animals more typically used for biomedical research.

OBJECTIVE

The purpose of this study was to determine the permissibility of a stably immortalized, sheep microglial cell line to viruses that are reported to infect ruminants: bovine viral diarrhea virus (BVDV), bovine herpesvirus 1 (BoHV-1), small ruminant lentiviruses (SRLV), and bovine respiratory syncytial virus (BRSV).

METHODS

Sublines A and H of previously isolated, immortalized, and characterized (CD14-positive) ovine microglial cells were used. Bovine turbinate cells and goat synovial membrane cells were used for comparison. Cytopathic changes were used to confirm infection of individual wells, which were then counted and used to calculate the 50% tissue culture infectious dose. Uninoculated cells served as negative controls and confirmed that the cells were not previously infected with these viruses using polymerase chain reaction (PCR).

RESULTS

Inoculation of the two microglial cell sublines with laboratory and field isolates of BVDV, BoHV-1, and BRSV resulted in viral infection in a manner similar to bovine turbinate cells. Immortalized microglia cells are also permissive to SRLV, similar to goat synovial membrane cells.

CONCLUSION AND CLINICAL RELEVANCE

These immortalized sheep microglial cells provide a new tool for the study of ruminant viruses in ruminant microglial cell line.

Correlation of cellular factors and differential scrapie prion permissiveness in ovine microglia

Prion diseases are fatal neurodegenerative disorders by which the native cellular prion protein (PrP^C) is misfolded into an accumulating, disease-associated isoform (PrP^D). To improve the understanding of prion pathogenesis and develop effective treatments, it is essential to elucidate factors contributing to cellular permissiveness. We previously isolated five clones from an immortalized subline of ovine microglia, two of which had demonstrated differential permissiveness to a natural isolate of sheep scrapie and distinct transcriptomic profiles. To more robustly identify factors contributing to this activity, relative permissiveness, cell proliferation, selected gene transcript level, and matrix metalloproteinase 2 (MMP2) activity were compared amongst all five clones. Differences in cell proliferation were not detected between clones; however, significant correlations were identified between relative permissiveness and genes associated with cell growth (i.e., RARRES1 and PTN), protein degradation (i.e., CTSB and SQSTM1), and heparin binding (i.e., SEPP1). MMP2 activity varied amongst clones, but did not correlate with permissiveness. These associations support the contribution of cell division and protein degradation on the permissiveness of cultured ovine microglia to PrP^D.

Anti-Prion Screening for Acridine, Dextran, and Tannic Acid using Real Time-Quaking Induced Conversion: A Comparison with PrPSc-Infected Cell Screening

Prion propagation is mediated by the structural alteration of normal prion protein (PrPC) to generate pathogenic prion protein (PrPSc). To date, compounds for the inhibition of prion propagation have mainly been screened using PrPSc-infected cells. Real time-quaking-induced conversion (RT-QuIC) is one alternative screening method. In this study, we assessed the propagation inhibition effects of known anti-prion compounds using RT-QuIC and compared the results with those from a PrPSc-infected cell assay. Compounds were applied to RT-QuIC reactions at 0 h or 22 h after prion propagation to determine whether they inhibited propagation or reduced amplified aggregates. RT-QuIC reactions in presence of acridine, dextran sulfate sodium (DSS), and tannic acid inhibited seeded aggregation with sporadic Creutzfeldt-Jakob disease at 0 h. After treatment at 22 h, amplified fluorescence was decreased in wells treated with either acridine or tannic acid. Compound activities were verified by western blot of RT-QuIC products and in a dye-independent conversion assay, the Multimer Detection System. Protease K-resistant PrPSc fragments (PrPres) were reduced by DSS and tannic acid in the PrPSc-infected cell assay. Importantly, these inhibitory effects were similar despite different treatment times (0 h versus 3 days). Consequentially, RT-QuIC enabled the more specific classification of compounds according to action (i.e., inhibition of prion propagation versus reduction of amplified aggregates). RT-QuIC addresses the limitations of cell-based screening methods and can be used to further aid our understanding of the mechanisms of action of anti-prion compounds.

Antiprion Activity of DB772 and Related Monothiophene- and Furan-Based Analogs in a Persistently Infected Ovine Microglia Culture System

The transmissible spongiform encephalopathies are fatal neurodegenerative disorders characterized by the misfolding of the native cellular prion protein (PrP^C) into the accumulating, disease-associated isoform (PrP^Sc). Despite extensive research into the inhibition of prion accumulation, no effective treatment exists. Previously, we demonstrated the inhibitory activity of DB772, a monocationic phenyl-furan-benzimidazole, against PrP^Sc accumulation in sheep microglial cells. In an effort to determine the effect of structural substitutions on the antiprion activity of DB772, we employed an in vitro strategy to survey a library of structurally related, monothiophene- and furan-based compounds for improved inhibitory activity. Eighty-nine compounds were screened at 1 μM for effects on cell viability and prion accumulation in a persistently infected ovine microglia culture system. Eleven compounds with activity equivalent to or higher than that of DB772 were identified as preliminary hit compounds. For the preliminary hits, cytotoxicities and antiprion activities were compared to calculate the tissue culture selectivity index. A structure-activity relationship (SAR) analysis was performed to determine molecular components contributing to antiprion activity. To investigate potential mechanisms of inhibition, effects on PrP^C and PrP^Sc were examined. While inhibition of total PrP^C was not observed, the results suggest that a potential target for inhibition at biologically relevant concentrations is through PrP^C misfolding to PrP^Sc. Further, SAR analysis suggests that two structural elements were associated with micromolar antiprion activity. Taken together, the described data provide a foundation for deeper investigation into untested DB compounds and in the design of effective therapeutics.

Transcriptomic Determinants of Scrapie Prion Propagation in Cultured Ovine Microglia

Susceptibility to infection by prions is highly dependent on the amino acid sequence and host expression of the cellular prion protein (PrP^C); however, cellular expression of a genetically susceptible PrP^C is insufficient. As an example, it has been shown in cultured cells that permissive and resistant sublines derived from the same parental population often have similar expression levels of PrP^C. Thus, additional cellular factors must influence susceptibility to prion infection. The aim of this study was to elucidate the factors associated with relative permissiveness and resistance to scrapie prions in cultured cells derived from a naturally affected species. Two closely related ovine microglia clones with different prion susceptibility, but no detectable differences in PrP^C expression levels, were inoculated with either scrapie-positive or scrapie-negative sheep brainstem homogenates. Five passages post-inoculation, the transcriptional profiles of mock and infected clones were sequenced using Illumina technology. Comparative transcriptional analyses identified twenty-two differentially transcribed genes, most of which were upregulated in poorly permissive microglia. This included genes encoding for selenoprotein P, endolysosomal proteases, and proteins involved in extracellular matrix remodeling. Furthermore, in highly permissive microglia, transforming growth factor β–induced, retinoic acid receptor response 1, and phosphoserine aminotranspherase 1 gene transcripts were upregulated. Gene Set Enrichment Analysis identified proteolysis, translation, and mitosis as the most affected pathways and supported the upregulation trend of several genes encoding for intracellular proteases and ribosomal proteins in poorly permissive microglia. This study identifies new genes potentially involved in scrapie prion propagation, corroborates results from other studies, and extends those results into another cell culture model.

hTERT-immortalized ovine microglia propagate natural scrapie isolates

Ex vivo propagation of natural prion isolates (i.e., propagated solely in the natural host) is crucial for the characterization and study of transmissible spongiform encephalopathies (TSEs). Several well-established, prion-permissive cell culture systems are available; however, only a few cell lines are permissive to natural prion isolates and these cells are not pathophysiologically relevant (e.g., renal epithelium and fibroblast-like cells). Therefore, a pathophysiologically relevant cell line derived from a natural TSE host could be used for propagation of natural prion isolates. In this study, ovine brain macrophages (microglia) were immortalized by transfection with the human telomerase reverse transcriptase (hTERT) gene to identify cell lines (hTERT-microglia) permissive to natural scrapie prion isolates. Following transfection, hTERT-microglia were passaged up to 100 times and their lifespan was significantly longer compared to parental cells (Fisher's exact test, P<0.001). Multiple sublines were permissive to cell culture-adapted prions; two sublines were also permissive to natural scrapie isolates (i.e., derived from brain homogenates of sheep infected with scrapie). Prion infectivity and partial protease resistance of the prion protein were maintained in hTERT-microglia. Comparisons between scrapie-permissive and non-permissive hTERT-microglia sublines revealed that overall quantity of the normal cellular prion protein was not associated with prion permissiveness. The use of hTERT-microglia in future TSE studies may be more germane to the characterization of the cellular and subcellular pathophysiology of natural scrapie prion isolates and to investigate host-specific factors involved in prion replication.

G-quadruplexes within prion mRNA: the missing link in prion disease?

Cellular ribonucleic acid (RNA) plays a crucial role in the initial conversion of cellular prion protein PrP(C) to infectious PrP(Sc) or scrapie. The nature of this RNA remains elusive. Previously, RNA aptamers against PrP(C) have been isolated and found to form G-quadruplexes (G4s). PrP(C) binding to G4 RNAs destabilizes its structure and is thought to trigger its conversion to PrP(Sc). Here it is shown that PrP messenger RNA (mRNA) itself contains several G4 motifs, located in the octarepeat region. Investigation of the RNA structure in one of these repeats by circular dichroism, nuclear magnetic resonance and ultraviolet melting studies shows evidence of G4 formation. In vitro translation of full-length PrP mRNA, naturally harboring five consecutive G4 motifs, was specifically affected by G4-binding ligands, lending support to G4 formation in PrP mRNA. A possible role of PrP binding to its own mRNA and the role of anti-prion drugs, many of which are G4-binding ligands, in prion disease are discussed.

Piperazine derivatives inhibit PrP/PrP(res) propagation in vitro and in vivo

Prion diseases are fatal neurodegenerative disorders, which are not curable and no effective treatment exists so far. The major neuropathological change in diseased brains is the conversion of the normal cellular form of the prion protein PrPc(C) into a disease-associated isoform PrP(Sc). PrP(Sc) accumulates into multimeres and fibrillar aggregates, which leads to the formation of amyloid plaques. Increasing evidence indicates a fundamental role of PrP(Sc) species and its aggregation in the pathogenesis of prion diseases, which initiates the pathological cascade and leads to neurodegeneration accompanied by spongiform changes. In search of compounds that have the potential to interfere with PrP(Sc) formation and propagation, we used a cell based assay for the screening of potential aggregation inhibitors. The assay deals with a permanently prion infected cell line that was adapted for a high-throughput screening of a compound library composed of 10,000 compounds (DIVERset 2, ChemBridge). We could detect six different classes of highly potent inhibitors of PrP(Sc) propagation in vitro and identified piperazine derivatives as a new inhibitory lead structure, which increased incubation time of scrapie infected mice.