Scorpion-Derived Antiviral Peptides with a Special Focus on Medically Important Viruses: An Update

The global burden of viral infection, especially the current pandemics of SARS-CoV-2, HIV/AIDS, and hepatitis, is a very risky one. Additionally, HCV expresses the necessity for antiviral therapeutic elements. Venoms are known to contain an array of bioactive peptides that are commonly used in the treatment of various medical issues. Several peptides isolated from scorpion venom have recently been proven to possess an antiviral activity against several viral families. The aim of this review is to provide an up-to-date overview of scorpion antiviral peptides and to discuss their modes of action and potential biomedical application against different viruses.

Therapeutic targeting of measles virus polymerase with ERDRP-0519 suppresses all RNA synthesis activity

Morbilliviruses, such as measles virus (MeV) and canine distemper virus (CDV), are highly infectious members of the paramyxovirus family. MeV is responsible for major morbidity and mortality in non-vaccinated populations. ERDRP-0519, a pan-morbillivirus small molecule inhibitor for the treatment of measles, targets the morbillivirus RNA-dependent RNA-polymerase (RdRP) complex and displayed unparalleled oral efficacy against lethal infection of ferrets with CDV, an established surrogate model for human measles. Resistance profiling identified the L subunit of the RdRP, which harbors all enzymatic activity of the polymerase complex, as the molecular target of inhibition. Here, we examined binding characteristics, physical docking site, and the molecular mechanism of action of ERDRP-0519 through label-free biolayer interferometry, photoaffinity cross-linking, and in vitro RdRP assays using purified MeV RdRP complexes and synthetic templates. Results demonstrate that unlike all other mononegavirus small molecule inhibitors identified to date, ERDRP-0519 inhibits all phosphodiester bond formation in both de novo initiation of RNA synthesis at the promoter and RNA elongation by a committed polymerase complex. Photocrosslinking and resistance profiling-informed ligand docking revealed that this unprecedented mechanism of action of ERDRP-0519 is due to simultaneous engagement of the L protein polyribonucleotidyl transferase (PRNTase)-like domain and the flexible intrusion loop by the compound, pharmacologically locking the polymerase in pre-initiation conformation. This study informs selection of ERDRP-0519 as clinical candidate for measles therapy and identifies a previously unrecognized druggable site in mononegavirus L polymerase proteins that can silence all synthesis of viral RNA.

The mononegavirus order contains major established and recently emerged human pathogens. Despite the threat to human health, antiviral therapeutics directed against this order remain understudied. The mononegavirus polymerase complex represents a promising drug target due to its central importance for both virus replication and viral mitigation of the innate host antiviral response. In this study, we have mechanistically characterized a clinical candidate small-molecule MeV polymerase inhibitor. The compound blocked all phosphodiester bond formation activity, a unique mechanism of action unlike all other known mononegavirus polymerase inhibitors. Photocrosslinking-based target site mapping demonstrated that this class-defining prototype inhibitor stabilizes a pre-initiation conformation of the viral polymerase complex that sterically cannot accommodate template RNA. Function-equivalent druggable sites exist in all mononegavirus polymerases. In addition to its direct anti-MeV impact, the insight gained in this study can therefore serve as a blueprint for indication spectrum expansion through structure-informed scaffold engineering or targeted drug discovery.

The effect of time since measles vaccination and age at first dose on measles vaccine effectiveness - A systematic review

BACKGROUND

In settings where measles has been eliminated, vaccine-derived immunity may in theory wane more rapidly due to a lack of immune boosting by circulating measles virus. We aimed to assess whether measles vaccine effectiveness (VE) waned over time, and if so, whether differentially in measles-eliminated and measles-endemic settings.

METHODS

We performed a systematic literature review of studies that reported VE and time since vaccination with measles-containing vaccine (MCV). We extracted information on case definition (clinical symptoms and/or laboratory diagnosis), method of vaccination status ascertainment (medical record or vaccine registry), as well as any biases which may have arisen from cold chain issues and a lack of an age at first dose of MCV. We then used linear regression to evaluate VE as a function of age at first dose of MCV and time since MCV.

RESULTS

After screening 14,782 citations, we identified three full-text articles from measles-eliminated settings and 33 articles from measles-endemic settings. In elimination settings, two-dose VE estimates increased as age at first dose of MCV increased and decreased as time since MCV increased; however, the small number of studies available limited interpretation. In measles-endemic settings, one-dose VE increased by 1.5% (95% CI 0.5, 2.5) for every month increase in age at first dose of MCV. We found no evidence of waning VE in endemic settings.

CONCLUSIONS

The paucity of data from measles-eliminated settings indicates that additional studies and approaches (such as studies using proxies including laboratory correlates of protection) are needed to answer the question of whether VE in measles-eliminated settings wanes. Age at first dose of MCV was the most important factor in determining VE. More VE studies need to be conducted in elimination settings, and standards should be developed for information collected and reported in such studies.

Structure-Stability-Function Mechanistic Links in the Anti-Measles Virus Action of Tocopherol-Derivatized Peptide Nanoparticles

Measles remains one of the leading causes of child mortality worldwide and is re-emerging in some countries due to poor vaccine coverage, concomitant with importation of measles virus (MV) from endemic areas. The lack of specific chemotherapy contributes to negative outcomes, especially in infants or immunodeficient individuals. Fusion inhibitor peptides derived from the MV Fusion protein C-terminal Heptad Repeat (HRC) targeting MV envelope fusion glycoproteins block infection at the stage of entry into host cells, thus preventing viral multiplication. To improve efficacy of such entry inhibitors, we have modified a HRC peptide inhibitor by introducing properties of self-assembly into nanoparticles (NP) and higher affinity for both viral and cell membranes. Modification of the peptide consisted of covalent grafting with tocopherol to increase amphipathicity and lipophilicity (HRC5). One additional peptide inhibitor consisting of a peptide dimer grafted to tocopherol was also used (HRC6). Spectroscopic, imaging, and simulation techniques were used to characterize the NP and explore the molecular basis for their antiviral efficacy. HRC5 forms micellar stable NP while HRC6 aggregates into amorphous, loose, unstable NP. Interpeptide cluster bridging governs NP assembly into dynamic metastable states. The results are consistent with the conclusion that the improved efficacy of HRC6 relative to HRC5 can be attributed to NP instability, which leads to more extensive partition to target membranes and binding to viral target proteins.

Virucidal and Synergistic Activity of Polyphenol-Rich Extracts of Seaweeds against Measles Virus

Although preventable by vaccination, Measles still causes thousands of deaths among young children worldwide. The discovery of new antivirals is a good approach to control new outbreaks that cause such death. In this study, we tested the antiviral activity against Measles virus (MeV) of Polyphenol-rich extracts (PPs) coming from five seaweeds collected and cultivated in Mexico. An MTT assay was performed to determine cytotoxicity effect, and antiviral activity was measured by syncytia reduction assay and confirmed by qPCR. PPs from Ecklonia arborea (formerly Eisenia arborea, Phaeophyceae) and Solieria filiformis (Rhodophyta) showed the highest Selectivity Index (SI), >3750 and >576.9 respectively. Both PPs extracts were selected to the subsequent experiments owing to their high efficacy and low cytotoxicity compared with ribavirin (SI of 11.57). The combinational effect of PPs with sulphated polysaccharides (SPs) and ribavirin were calculated by using Compusyn software. Synergistic activity was observed by combining both PPs with low concentrations of Solieria filiformis SPs (0.01 µg/mL). The antiviral activity of the best combinations was confirmed by qPCR. Virucidal assay, time of addition, and viral penetration evaluations suggested that PPs act mainly by inactivating the viral particle. To our knowledge, this is the first report of the virucidal effect of Polyphenol-rich extracts of seaweeds.

Mutations in the Fusion Protein of Measles Virus That Confer Resistance to the Membrane Fusion Inhibitors Carbobenzoxy-d-Phe-l-Phe-Gly and 4-Nitro-2-Phenylacetyl Amino-Benzamide

The inhibitors carbobenzoxy (Z)-d-Phe-l-Phe-Gly (fusion inhibitor peptide [FIP]) and 4-nitro-2-phenylacetyl amino-benzamide (AS-48) have similar efficacies in blocking membrane fusion and syncytium formation mediated by measles virus (MeV). Other homologues, such as Z-d-Phe, are less effective but may act through the same mechanism. In an attempt to map the site of action of these inhibitors, we generated mutant viruses that were resistant to the inhibitory effects of Z-d-Phe-l-Phe-Gly. These 10 mutations were localized to the heptad repeat B (HRB) region of the fusion protein, and no changes were observed in the viral hemagglutinin, which is the receptor attachment protein. Mutations were validated in a luciferase-based membrane fusion assay, using transfected fusion and hemagglutinin expression plasmids or with syncytium-based assays in Vero, Vero-SLAM, and Vero-Nectin 4 cell lines. The changes I452T, D458N, D458G/V459A, N462K, N462H, G464E, and I483R conferred resistance to both FIP and AS-48 without compromising membrane fusion. The inhibitors did not block hemagglutinin protein-mediated binding to the target cell. Edmonston vaccine/laboratory and IC323 wild-type strains were equally affected by the inhibitors. Escape mutations were mapped upon a three-dimensional (3D) structure modeled from the published crystal structure of parainfluenzavirus 5 fusion protein. The most effective mutations were situated in a region located near the base of the globular head and its junction with the alpha-helical stalk of the prefusion protein. We hypothesize that the fusion inhibitors could interfere with the structural changes that occur between the prefusion and postfusion conformations of the fusion protein.IMPORTANCE Due to lapses in vaccination worldwide that have caused localized outbreaks, measles virus (MeV) has regained importance as a pathogen. Antiviral agents against measles virus are not commercially available but could be useful in conjunction with MeV eradication vaccine programs and as a safeguard in oncolytic viral therapy. Three decades ago, the small hydrophobic peptide Z-d-Phe-l-Phe-Gly (FIP) was shown to block MeV infections and syncytium formation in monkey kidney cell lines. The exact mechanism of its action has yet to be determined, but it does appear to have properties similar to those of another chemical inhibitor, AS-48, which appears to interfere with the conformational change in the viral F protein that is required to elicit membrane fusion. Escape mutations were used to map the site of action for FIP. Knowledge gained from these studies could help in the design of new inhibitors against morbilliviruses and provide additional knowledge concerning the mechanism of virus-mediated membrane fusion.

Measles Virus Enters Breast and Colon Cancer Cell Lines through a PVRL4-Mediated Macropinocytosis Pathway

Measles virus (MeV) is a member of the family Paramixoviridae that causes a highly contagious respiratory disease but has emerged as a promising oncolytic platform. Previous studies of MeV entry focused on the identification of cellular receptors. However, the endocytic and trafficking pathways utilized during MeV entry remain poorly described. The contribution of each endocytic pathway has been examined in cells that express the MeV receptors SLAM (signaling lymphocyte-activating molecule) and PVRL4 (poliovirus receptor-like 4) (nectin-4). Recombinant MeVs expressing either firefly luciferase or green fluorescent protein together with a variety of inhibitors were used. The results showed that MeV uptake was dynamin independent in the Vero.hPVRL4, Vero.hSLAM, and PVRL4-positive MCF7 breast cancer cell lines. However, MeV infection was blocked by 5-(N-ethyl-N-propyl)amiloride (EIPA), the hallmark inhibitor of macropinocytosis, as well as inhibitors of actin polymerization. By using phalloidin staining, MeV entry was shown to induce actin rearrangements and the formation of membrane ruffles accompanied by transient elevated fluid uptake. Small interfering RNA (siRNA) knockdown of p21-activated kinase 1 (PAK1) demonstrated that MeV enters both Vero.hPVRL4 and Vero.hSLAM cells in a PAK1-independent manner using a macropinocytosis-like pathway. In contrast, MeV entry into MCF7 human breast cancer cells relied upon Rac1 and its effector PAK1 through a PVRL4-mediated macropinocytosis pathway. MeV entry into DLD-1 colon and HTB-20 breast cancer cells also appeared to use the same pathway. Overall, these findings provide new insight into the life cycle of MeV, which could lead to therapies that block virus entry or methods that improve the uptake of MeV by cancer cells during oncolytic therapy.IMPORTANCE In the past decades, measles virus (MeV) has emerged as a promising oncolytic platform. Previous studies concerning MeV entry focused mainly on the identification of putative receptors for MeV. Nectin-4 (PVRL4) was recently identified as the epithelial cell receptor for MeV. However, the specific endocytic and trafficking pathways utilized during MeV infections are poorly documented. In this study, we demonstrated that MeV enters host cells via a dynamin-independent and actin-dependent endocytic pathway. Moreover, we show that MeV gains entry into MCF7, DLD-1, and HTB-20 cancer cells through a PVRL4-mediated macropinocytosis pathway and identified the typical cellular GTPase and kinase involved. Our findings provide new insight into the life cycle of MeV, which may lead to the development of therapies that block the entry of the virus into the host cell or alternatively promote the uptake of oncolytic MeV into cancer cells.

A Novel Peptide Derived from the Fusion Protein Heptad Repeat Inhibits Replication of Subacute Sclerosing Panencephalitis Virus In Vitro and In Vivo

Subacute sclerosing panencephalitis (SSPE) is a persistent, progressive, and fatal degenerative disease resulting from persistent measles virus (MV) infection of the central nervous system. Most drugs used to treat SSPE have been reported to have limited effects. Therefore, novel therapeutic strategies are urgently required. The SSPE virus, a variant MV strain, differs virologically from wild-type MV strain. One characteristic of the SSPE virus is its defective production of cell-free virus, which leaves cell-to-cell infection as the major mechanism of viral dissemination. The fusion protein plays an essential role in this cell-to-cell spread. It contains two critical heptad repeat regions that form a six-helix bundle in the trimer similar to most viral fusion proteins. In the case of human immunodeficiency virus type-1 (HIV-1), a synthetic peptide derived from the heptad repeat region of the fusion protein enfuvirtide inhibits viral replication and is clinically approved as an anti-HIV-1 agent. The heptad repeat regions of HIV-1 are structurally and functionally similar to those of the MV fusion protein. We therefore designed novel peptides derived from the fusion protein heptad repeat region of the MV and examined their effects on the measles and SSPE virus replication in vitro and in vivo. Some of these synthetic novel peptides demonstrated high antiviral activity against both the measles (Edmonston strain) and SSPE (Yamagata-1 strain) viruses at nanomolar concentrations with no cytotoxicity in vitro. In particular, intracranial administration of one of the synthetic peptides increased the survival rate from 0% to 67% in an SSPE virus-infected nude mouse model.

Inhibitors of Measles Virus

Measles virus (MV) infections have been almost eradicated in some industrialized nations. However, MV continues to cause severe disease and mortality in the world and is responsible for clusters of exogenous-borne disease in essentially disease-free countries. Because of the ebb and flow of immunization campaigns, especially in the poverty-stricken and war-torn Third World, and the ominous potential for severe disease and mortality, it is vital that research for discovery of therapeutic countermeasures should continue. To that end, a number of compounds have been evaluated for efficacy in vitro and in animal models, and several therapeutic modalities have been tested in the clinic. The only current therapies used in the clinic include ribavirin administered orally or intravenously, alone or in combination with immune serum globulin; these therapies have demonstrated variable efficacy. Therefore, drug discovery efforts have been launched to supplement the existing treatments for MV infections. Antisense molecules, adenosine and guanosine nucleosides, including ring-expanded ‘fat’ nucleoside analogues, brassinosteroids, coumarins, peptide inhibitors, modulators of cholesterol synthesis and a variety of natural products have been screened for efficacy and toxicity both in vitro and in animals. However, none of these agents has gone into human clinical trials and most will not merit further development due to toxicity concerns and/or low potency. Thus, further research is needed to develop more potent and less toxic drugs that could be used for treating MV infections to supplement the existing MV vaccine campaigns.

Antiviral activities of diarylheptanoids isolated from Alpinia officinarum against respiratory syncytial virus, poliovirus, measles virus, and herpes simplex virus type 1 in vitro

Alpinia officinarum has been used as a folk medicine and contains diarylheptanoids that have various biological activities. However, their antiviral activities are less elucidated. We examined the antiviral activities of nine diarylheptanoids isolated from A. officinarum against respiratory syncytial virus (RSV), poliovirus, measles virus, and herpes simplex virus type 1 (HSV-1) using a plaque reduction assay. The 50% inhibitory concentrations of seven of the nine diarylheptanoids for RSV were moderately but significantly lower than their 50% cytotoxic concentrations, as determined by a trypan blue exclusion assay. Four diarylheptanoids with anti-RSV activity also showed anti-poliovirus and anti-measles virus activities and three of the four exhibited anti-HSV-1 activity. Thus, seven of the nine diarylheptanoids examined exhibited potential antiviral activity against RSV, and most of the diarylheptanoids with anti-RSV activity, including two diarylheptanoids without anti-RSV activity, were effective against poliovirus, measles virus, and/or HSV-1 in vitro. Diarylheptanoids were suggested to have a broad spectrum of antiviral activity.

RIG-I is required for the inhibition of measles virus by retinoids

Vitamin A can significantly decrease measles-associated morbidity and mortality. Vitamin A can inhibit the replication of measles virus (MeV) in vitro through an RARα- and type I interferon (IFN)-dependent mechanism. Retinoid-induced gene I (RIG-I) expression is induced by retinoids, activated by MeV RNA and is important for IFN signaling. We hypothesized that RIG-I is central to retinoid-mediated inhibition of MeV in vitro. We demonstrate that RIG-I expression is increased in cells treated with retinoids and infected with MeV. The central role of RIG-I in the retinoid-anti-MeV effect was demonstrated in the Huh-7/7.5 model; the latter cells having non-functional RIG-I. RAR-dependent retinoid signaling was required for the induction of RIG-I by retinoids and MeV. Retinoid signaling was also found to act in combination with IFN to induce high levels of RIG-I expression. RIG-I promoter activation required both retinoids and MeV, as indicated by markers of active chromatin. IRF-1 is known to be regulated by retinoids and MeV, but we found recruitment of IRF-1 to the RIG-I promoter by retinoids alone. Using luciferase expression constructs, we further demonstrated that the IRF-1 response element of RIG-I was required for RIG-I activation by retinoids or IFN. These results reveal that retinoid treatment and MeV infection induces significant RIG-I. RIG-I is required for the retinoid-MeV antiviral response. The induction is dependent on IFN, retinoids and IRF-1.

[Influence of polyelectrolytes on measles virus infectivity]

AIM

Mechanism of virus inhibiting action against measles virus of polyelectrolytes (PE) polystyrolsulfonate (PSS) of various polymerization degree and 60 kDa molecular weight polyallylamine (PAA) was studied.

MATERIALS AND METHODS

Measles virus Leningrad-16 strain was used for the study. Virus infectious titer reduction kinetics after interaction with PSS with the degree of polymerization of 8 (PSS 8), 31, 77, 170, 360, 430 and PAA were determined by titration method with cytopathogenic effect detection in Vero continuous cell line. Circular dichroism and fluorescence spectra of viral proteins were obtained by using Zenith 200st spectrophotometer (Russian Federation) and Jasco J-810 dichrograph (Japan).

RESULTS

A significant decrease of measles virus infectious titers after interaction with PSS with the degree of polymerization of 8 and PAA in concentration of 30 mM was detected. Analysis of circular dichroism spectra and protein fluorescence allowed to determine the mechanism of interaction of the indicated PE with measles virus surface proteins. The secondary structure of viral proteins is damaged by hydrophobic polar frame of these PE, polyanion PSS 8 also interacts with positive charges of protein groups that leads to the formation of loops and tails that disrupt alpha-spirals.

CONCLUSION

The studied PE could be considered as potential antiviral preparations, and methods of circular dichroism and protein fluorescence could be used to detect damage of viral protein secondary structure by agents of different kinds.

Evaluation of the LTK63 adjuvant effect on cellular immune responses to measles virus nucleoprotein

BACKGROUND

A lot of pathogens enter the body via the nasal route. The construction of non-toxic mutants of heat labile Escherichia coli enterotoxin (LT), which is a potent mucosal adjuvant, represents a major breakthrough for the development of mucosal vaccines.

OBJECTIVE

This study was undertaken to critically evaluate the adjuvanticity of the mutant of LT (LTK63) on the cellular immune responses to intranasally co-administered recombinant measles virus nucleoprotein (rMVNP).

METHODS

Groups of CBA mice were immunized intranasally with rMVNP with or without LT or LTK63 as adjuvants. Another group was immunized subcutaneously with rMVNP in Freund's adjuvant. rMVNP and measles virus (MV) were used in a proliferation assay to test the LTK63 potentiating ability to induce T cell responses. Subsequently MVNP synthetic peptides spanning the length of the N protein were used with a proliferation assay to identify the T cell epitopes.

RESULTS

Splenocytes from mice immunized intranasally with rMVNP plus LT or LTK63, showed strong dose dependent proliferative responses to both the MVNP and MV. However, proliferative responses from the latter group were significantly lower than the former group (P < 0.05). Splenocytes tested recognized peptides 20, 21, 28, 31, 39, 40 and 50, suggesting these to be among important epitopes. Subcutaneous route was not effective in priming for T cell responses to rMVNP.

CONCLUSION

These data further demonstrate the great potential of LTK63 as a safe mucosal vaccine adjuvant.

In vivo evaluation of the antiviral activity of Cajanus cajan on measles virus

Cajanus cajan, a tropical shrub, serves as source of food and traditional medicines. The evaluation of aqueous and ethanol extracts for activity against measles virus and toxicity to embryonated chicken eggs was carried out in this study. In vivo and in vitro assay techniques using embryonated chicken eggs and tissue culture (Hep-2 cell lines) as media for both virus cultivation and anti-virus assay showed that a hot-water extract yielded higher activity against measles virus. The hot-water extract of the stem yielded a Log(2) titre of 0.1 for the in vivo assay and an inhibition of cytopathic effect (CPE) in Hep-2 cells by 100% for the in vitro assay. At all concentrations of the extracts, there was a lowering of virus concentration (p = 0.05), indicated by hemagglutination (HA) titration, which is the advantage of HA titration over the tissue culture technique using CPE. This study validates embryonated chicken eggs as suitable media for anti-virus assay and the use of C. cajan in the treatment of some diseases of viral origin.

The synthetic bacterial lipopeptide Pam3CSK4 modulates respiratory syncytial virus infection independent of TLR activation

Respiratory syncytial virus (RSV) is an important cause of acute respiratory disease in infants, immunocompromised subjects and the elderly. However, it is unclear why most primary RSV infections are associated with relatively mild symptoms, whereas some result in severe lower respiratory tract infections and bronchiolitis. Since RSV hospitalization has been associated with respiratory bacterial co-infections, we have tested if bacterial Toll-like receptor (TLR) agonists influence RSV-A2-GFP infection in human primary cells or cell lines. The synthetic bacterial lipopeptide Pam3-Cys-Ser-Lys4 (Pam3CSK4), the prototype ligand for the heterodimeric TLR1/TLR2 complex, enhanced RSV infection in primary epithelial, myeloid and lymphoid cells. Surprisingly, enhancement was optimal when lipopeptides and virus were added simultaneously, whereas addition of Pam3CSK4 immediately after infection had no effect. We have identified two structurally related lipopeptides without TLR-signaling capacity that also modulate RSV infection, whereas Pam3CSK4-reminiscent TLR1/2 agonists did not, and conclude that modulation of infection is independent of TLR activation. A similar TLR-independent enhancement of infection could also be demonstrated for wild-type RSV strains, and for HIV-1, measles virus and human metapneumovirus. We show that the effect of Pam3CSK4 is primarily mediated by enhanced binding of RSV to its target cells. The N-palmitoylated cysteine and the cationic lysines were identified as pivotal for enhanced virus binding. Surprisingly, we observed inhibition of RSV infection in immortalized epithelial cell lines, which was shown to be related to interactions between Pam3CSK4 and negatively charged glycosaminoglycans on these cells, which are known targets for binding of laboratory-adapted but not wild-type RSV. These data suggest a potential role for bacterial lipopeptides in enhanced binding of RSV and other viruses to their target cells, thus affecting viral entry or spread independent of TLR signaling. Moreover, our results also suggest a potential application for these synthetic lipopeptides as adjuvants for live-attenuated viral vaccines.

Respiratory syncytial virus (RSV) infections are an important cause of hospitalization of infants during the winter season. However, RSV is often not the only detectable pathogen, but co-infections with respiratory bacteria are common. It has been hypothesized that this results from epithelial damage caused by the virus, facilitating colonization by pathogenic bacteria such as Streptococcus pneumoniae. However, an inverse order of events is not impossible: bacterial infections may activate respiratory epithelial cells through TLR signaling, resulting in increased susceptibility to virus infections. We tested this hypothesis by screening bacterial TLR agonists for their capacity to modulate RSV infection in different cell types, and identified the lipopeptide and prototype TLR1/2 agonist Pam3CSK4 as an enhancer of RSV infections. However, to our surprise this proved independent of TLR activation, but was mediated by enhancement of binding between virus and target cell. Two structurally related lipopeptides unable to stimulate TLR responses were identified that enhanced infections with RSV, but also with other enveloped viruses including HIV-1, human metapneumovirus, and measles virus. We speculate that bacterial infections may influence the pathogenesis of virus infections by facilitating binding to target cells.

Target analysis of the experimental measles therapeutic AS-136A

No effective therapeutic is currently in place for improved case management of severe measles or the rapid control of outbreaks. Through high-throughput screening, we recently identified a novel small-molecule class that potently blocks activity of the measles virus (MeV) RNA-dependent RNA polymerase (RdRp) complex in transient replicon assays. However, the nature of the block in RdRp activity and the physical target of the compound remained elusive. Through real-time reverse transcription-PCR analysis, we demonstrate that the lead compound AS-136A blocks viral RNA synthesis in the context of an infection. Adaptation of different MeV strains to growth in the presence of the compound identified three candidate hot spots for resistance that are located in conserved domains of the viral polymerase (L protein) subunit of the RdRp complex. Rebuilding of individual mutations in RdRp-driven reporter assays and recombinant MeV traced the molecular basis for resistance to specific mutations in L. Mutations responsible for resistance cluster in the immediate vicinity of the proposed catalytic center for phosphodiester bond formation and neighboring conserved domains of L, providing support for effective inhibition of a paramyxovirus RdRp complex through interaction of a nonnucleoside small-molecule inhibitor with the L protein. Resistance mutations are located in regions of L that are fully conserved among viral isolates, and recombinant MeV harboring individual resistance mutations show some delay in the onset of viral growth in vitro. Taken together, these data support the hypothesis that acquiring mutations in these L domains may reduce virus fitness.

Measles control--can measles virus inhibitors make a difference?

Infection by measles virus (MV) is a major cause of human morbidity and mortality worldwide. In 2001, the WHO, UNICEF and their partners launched the Measles Initiative, the goals of which are to interrupt the transmission of MV in large geographic areas by increasing vaccination coverage and to assess the feasibility of eradicating MV worldwide. An estimated 74% reduction in mortality resulting from measles was achieved between 2000 and 2007, equivalent to a reduction of approximately 200,000 deaths annually. Despite this progress in the control of measles, the highest number of measles cases in more than a decade was observed in 2008 in several European countries and the US, and the virus was again declared endemic in the UK. In the light of this resurgence in the UK and the limitations associated with the current live-attenuated vaccine, this review discusses the means by which safe and effective measles antivirals could augment vaccination and strengthen global efforts to control measles. Important aspects of treatment are the potential to prevent infection effectively after exposure to MV, the improvement of case management, the amelioration of complications that frequently follow MV infection and the influence of antivirals on a potential strategy for global measles eradication.

[Antiviral activity of panavir in experimental Measles virus infection in cell cultures]

Antiviral activity of Panavir was studied in a model of experimental infection due to Morbillivirus in subcultures of cells Vero and B-16. It was shown that at multiplicity of the infection (0.001-0.0001 TCD50/cell) Panavir inhibited reproduction of the virus in concentrations of 12-100 mcg/0.2 ml.

Potent non-nucleoside inhibitors of the measles virus RNA-dependent RNA polymerase complex

Measles virus (MV) is one of the most infectious pathogens known. In spite of the existence of a vaccine, approximately 350000 deaths/year result from MV or associated complications. Antimeasles compounds could conceivably diminish these statistics and provide a therapy that complements vaccine treatment. We recently described a high-throughput screening hit compound 1 (16677) against MV-infected cells with the capacity to eliminate viral reproduction at 250 nM by inhibiting the action of the virus's RNA-dependent RNA polymerase complex (RdRp). The compound, 1-methyl-3-(trifluoromethyl)- N-[4-sulfonylphenyl]-1 H-pyrazole-5-carboxamide, 1 carries a critical CF 3 moiety on the 1,2-pyrazole ring. Elaborating on the preliminary structure-activity (SAR) study, the present work presents the synthesis and SAR of a much broader range of low nanomolar nonpeptidic MV inhibitors and speculates on the role of the CF 3 functionality.

An Immunocompetent Murine Model for Oncolysis with an Armed and Targeted Measles Virus

An immunocompetent model is required to test therapeutic regimens for clinical trials with the oncolytic measles virus (MV). Toward developing this model, a retargeted MV that enters murine colon adenocarcinoma cells forming tumors in syngeneic C57BL/6 mice was generated. Since MV infection tends to be less efficient in murine than in human cells, the targeted virus was also armed with the prodrug convertase, purine nucleoside phosphorylase (PNP), and named MV-PNP-antiCEA. We have shown before that in cultured cells, infection with this virus activated the prodrug, 6-methylpurine-2'-deoxyriboside (MeP-dR), causing extensive cytotoxicity. When injected intratumorally (IT), MV-PNP-antiCEA inhibited subcutaneous tumor growth marginally, but subsequent administration of the prodrug enhanced the oncolytic effect. Systemic delivery of MV-PNP-antiCEA alone had no substantial oncolytic effects, but in combination with the prodrug it was therapeutic, revealing synergistic effects between virus and prodrug. Immunosuppression with cyclophosphamide (CPA) retarded the appearance of MV neutralizing antibodies and enhanced oncolytic efficacy: survival was 100%, with 9 out of 10 animals going into complete remission. This immunocompetent murine model facilitates the testing of therapeutic regimens for clinical trials.

Traditional dietary additives of the Maasai are antiviral against the measles virus

Although ethnopharmacological investigations emphasize the importance of medicinal plants in developing countries, species used regularly with diet are under-investigated and potentially make greater contributions to health. Thirteen traditional plants most commonly added to milk/soups by the Maasai for perceived health benefits were tested for activity against measles virus (MV) using non-medicinal plants as controls. Antiviral effects of plant extracts were sought using a modified neutralization assay. Methanolic extracts of medicinal species exhibited significantly greater activity neutralizing MV in vitro in comparison to non-medicinal extracts (p<0.02). Four of 13 (31%) medicinal species versus 0/13 controls had measurable effects against MV in vitro. Olinia rochetiana (Olkirenyi) and Warburgia ugandensis (Osokonoi) extracts were most potent with the number of plaque forming units reduced 37- and 34-fold, respectively. Given the importance of monocytes in the dissemination of MV, we assessed the capacity of a subset of plant extracts to inhibit MV growth in monocytoid cell line, U937. MV output from U937 cells was significantly reduced by four of seven medicinal plant extracts (mean reduction 48 h: 39.0+/-26.0%, range 3.5-87%; 72 h: 56.4+/-29.5%, range 14.1-103.1%) (p<0.05). This study provides evidence that medicinal plants added to the Maasai diet may contribute to the modulation of viral infections.

Buthionine sulfoximine inhibits cytopathic effects and apoptosis induced by infection with AIK-HDC strain of measles virus

BACKGROUND

Measles virus (MV) is a highly contagious agent which causes a major health problem in developing countries. We studied the effect of buthionine sulfoximine (BSO) on the replication of an AIK-HDC strain of MV and its induced apoptosis in Vero cell lines.

METHODS

In this study, toxicity of BSO on Vero cells was investigated first, resulted in determination of sub-lethal or non-toxic concentration zone of BSO for cells. Next, anti-viral effect of BSO at various time limits was evaluated and virus titer was determined at each stage either as 50% tissue culture infective dose (TCID) 50 or by plaque assay method. Using specific anti-measles IgG, anti-viral effect of BSO on MV replication cycle was evaluated through indirect immunofluorescence assay, meanwhile presence of viral RNA was investigated by RT-PCR and gel electrophoresis.

RESULTS

According to the experiments, BSO, at concentration of 50 microM, markedly inhibited the cytopathic effect (CPE) induced by MV. BSO also significantly inhibited apoptosis induced by MV. BSO either influences replication of MV genome, or may inhibit virion formation.

CONCLUSION

These results suggest that the inhibition of CPE and apoptosis by BSO induced by MV may be associated with the effect of BSO on viral RNA genome. Therefore, it is suggested that MV infections can induce apoptosis through the activation of a common pathway that can be inhibited by BSO.

Suppression of virus replication via down-modulation of mitochondrial short chain enoyl-CoA hydratase in human glioblastoma cells

Several viruses have been demonstrated to be the etiologic agent in chronic progressive diseases, associated with persistence; however, major questions concerning the pathogenic mechanisms of viral persistence are still unanswered. With the aim of identifying host cellular proteins that may play a role in viral replication, we established long-term persistently infected human glioblastoma cell lines with mutant measles virus (MV) and analyzed the host proteins by two-dimensional gel electrophoresis (2-DE) with mass spectrometry. We observed significant down-modulation in the expression of mitochondrial short chain enoyl-CoA hydratase (ECHS), which catalyzes the beta-oxidation pathway of fatty acid. Knockdown of this gene by a short interference RNA (siRNA) apparently impaired wild-type MV replication and the cytopathic effects (CPEs) of MV were significantly reduced in siRNA-transfected cells. These findings will shed light upon a new important notion for the interaction between virus replication and lipid metabolism in host cells and might provide a new strategy for virus control.

Reversible inhibition of the fusion activity of measles virus F protein by an engineered intersubunit disulfide bridge

In search of target sites for the development of paramyxovirus inhibitors, we have engineered disulfide bridges to introduce covalent links into the prefusion F protein trimer of measles virus. F-Edm-452C/460C, predicted to bridge head and stalk domains of different F monomers, shows a high degree of proteolytic maturation and surface expression, predominantly as stable, dithiothreitol-sensitive trimers, but no fusion activity. Reduction of disulfide bridges partially restores activity. These findings underscore the importance of reversible intersubunit interactions between the stalk and head domains for F activity. Noncovalent small molecules mimicking this behavior may constitute a potent strategy for preventing paramyxovirus entry.

Nonnucleoside inhibitor of measles virus RNA-dependent RNA polymerase complex activity

Paramyxoviruses comprise several major human pathogens. Although a live-attenuated vaccine protects against measles virus (MV), a member of the paramyxovirus family, the virus remains a principal cause of worldwide mortality and accounts for approximately 21 million cases and 300,000 to 400,000 deaths annually. The development of novel antivirals that allow improved case management of severe measles and silence viral outbreaks is thus highly desirable. We have previously described the development of novel MV fusion inhibitors. The potential for preexisting or emerging resistance in the field constitutes the rationale for the identification of additional MV inhibitors with a diverse target spectrum. Here, we report the development and implementation of a cell-based assay for high-throughput screening of MV antivirals, which has yielded several hit candidates. Following confirmation by secondary assays and chemical synthesis, the most potent hit was found to act as a target-specific inhibitor of MV replication with desirable drug-like properties. The compound proved highly active against multiple primary isolates of diverse MV genotypes currently circulating worldwide, showing active concentrations of 35 to 145 nM. Significantly, it does not interfere with viral entry and lacks cross-resistance with the MV fusion inhibitor class. Mechanistic characterization on a subinfection level revealed that the compound represents a first-in-class nonnucleoside inhibitor of MV RNA-dependent RNA polymerase complex activity. Singly or in combination with the fusion inhibitors, this novel compound class has high developmental potential as a potent therapeutic against MV and will likely further the mechanistic characterization of the viral polymerase complex.

Nonpeptide Inhibitors of Measles Virus Entry

Measles virus (MV) is one of the most infectious pathogens known. Despite the existence of a vaccine, over 500,000 deaths/year result from MV or associated complications. Anti-measles compounds could conceivably reverse these statistics. Previously, we described a homology model of the MV fusion protein trimer and a putative binding site near the head-neck region. The resulting model permitted the identification of two nonpeptidic entry inhibitors. Here, we present the design, synthesis, and bioevaluation of several series of fusion inhibitors and describe their structure-activity relationships (SAR). Five simply substituted anilides show low-microM blockade of the MV, one of which (AS-48) exhibits IC50 = 0.6-3.0 microM across a panel of wild-type MV strains found in the field. Molecular field topology analysis (MFTA), a 2D QSAR approach based on local molecular properties (atomic charges, hydrogen-bonding capacity and local lipophilicity), applied to the anilide series suggests structural modifications to improve potency.

The effects of topical ketorolac and indomethacin on measles conjunctivitis: randomized controlled trial

PURPOSE

To compare the effect of topical ketorolac and indomethacin on measles conjunctivitis.

DESIGN

Prospective double-masked placebo-controlled randomized trial.

METHODS

Sixty-two patients with severe measles conjunctivitis were included in this study. All patients were hospitalized and randomly assigned to receive ketorolac 0.5% or indomethacin 0.1% in the right eye and artificial tears in the left eye. Conjunctival hyperemia, burning sensations, foreign-body sensations, and photophobia scores were conducted at baseline and at days seven and 14. A satisfaction score was evaluated at the end of the study.

RESULTS

The conjunctival injection score of the control eyes was significantly higher than those of the ketorolac- and indomethacin-treated eyes at day seven (P < .05). The conjunctival injection score of the ketorolac-treated eyes was lower than that of the indomethacin-treated eyes at days seven and 14, but this did not reach statistical significance. There was no significant difference in the burning and foreign-body sensations and in the photophobia scores among the study eyes at baseline, day seven, and day 14 (P > .05). There was no significant difference in the satisfaction score among the study eyes at the end of the study (P > .05).

CONCLUSIONS

In patients with measles during the first two weeks of infection, ketorolac and indomethacin were more effective than artificial tears in decreasing conjunctival hyperemia, but burning sensations, foreign-body sensations, and photophobia were unaffected.

Two domains that control prefusion stability and transport competence of the measles virus fusion protein

Most viral glycoproteins mediating membrane fusion adopt a metastable native conformation and undergo major conformational changes during fusion. We previously described a panel of compounds that specifically prevent fusion induced by measles virus (MV), most likely by interfering with conformational rearrangements of the MV fusion (F) protein. To further elucidate the basis of inhibition and better understand the mechanism of MV glycoprotein-mediated fusion, we generated and characterized resistant MV variants. Spontaneous mutations conferring drug resistance were confirmed in transient assays and in the context of recombinant virions and were in all cases located in the fusion protein. Several mutations emerged independently at F position 462, which is located in the C-terminal heptad repeat (HR-B) domain. In peptide competition assays, all HR-B mutants at residue 462 revealed reduced affinity for binding to the HR-A core complex compared to unmodified HR-B. Combining mutations at residue 462 with mutations in the distal F head region, which we had previously identified as mediating drug resistance, causes intracellular retention of the mutant proteins. The transport competence and activity of the mutants can be restored, however, by incubation at reduced temperature or in the presence of the inhibitory compounds, indicating that the F escape mutants have a reduced conformational stability and that the inhibitors stabilize a transport-competent conformation of the F trimer. The data support the conclusion that residues located in the head domain of the F trimer and the HR-B region contribute jointly to controlling F conformational stability.

Inhibition of measles virus and subacute sclerosing panencephalitis virus by RNA interference

Subacute sclerosing panencephalitis (SSPE) is a rare, but fatal outcome of measles virus (MeV) infection. SSPE develops after prolonged persistence of mutated MeV called SSPE virus. Although a combination therapy using interferon and inosiplex or ribavirin appears to prolong survival time to some extent, there is currently no effective treatment to completely cure SSPE and a new treatment strategy is greatly needed. In this study, we adopted RNA interference (RNAi) strategy and examined whether small interfering RNAs (siRNAs) can be used to inhibit replication of MeV and SSPE virus. We report here that siRNAs targeted against L mRNA of MeV, either synthetic siRNAs or those generated by pcPUR + U6i-based expression plasmids, effectively and specifically inhibited replication of both MeV and SSPE virus without exhibiting any cytotoxic effect. The L protein of MeV is a major component of RNA-dependent RNA polymerase that is essential for viral RNA replication, and yet it is least abundant among all the MeV proteins expressed. Therefore, mRNA encoding the L protein would be a good target for RNAi strategy. The present results imply the possibility that our siRNAs against MeV L mRNA are among the potential candidates to be used to treat patients with SSPE.

Prospects and strategies for the discovery and development of small-molecule inhibitors of six-helix bundle formation in class 1 viral fusion proteins

Class I viral fusion proteins have an important role in the fusion of viral membranes with host cell membranes, a critical step in the viral life-cycle. These proteins all have similar structural features and form six-helix bundles in their fusogenic form, a general mechanism of action for virus-cell fusion. The successful discovery of peptide-based inhibitors of fusion proteins, in addition to the US Food and Drug Administration approval of one of these inhibitors as an anti-HIV-1 drug, confirmed that the inhibition of six-helix bundle formation is a viable strategy for identifying antiviral drugs. Because peptide-based drugs have several limitations, research has been undertaken to identify potent small-molecule inhibitors of six-helix bundle formation in a variety of viruses, including HIV-1, human respiratory syncytial virus and measles virus. Small-molecule inhibitors that disrupt six-helix bundle formation and prevent viral infection have been identified. This review will focus on the discovery of these small-molecule inhibitors.

Design of a small-molecule entry inhibitor with activity against primary measles virus strains

The incidence of measles virus (MV) infection has been significantly reduced in many nations through extensive vaccination; however, the virus still causes significant morbidity and mortality in developing countries. Measles outbreaks also occur in some developed countries that have failed to maintain high vaccine coverage rates. While vaccination is essential in preventing the spread of measles, case management would greatly benefit from the use of therapeutic agents to lower morbidity. Thus, the development of new therapeutic strategies is desirable. We previously reported the generation of a panel of small-molecule MV entry inhibitors. Here we show that our initial lead compound, although providing proof of concept for our approach, has a short half-life (<16 h) under physiological conditions. In order to combine potent antiviral activity with increased compound stability, a targeted library of candidate molecules designed on the structural basis of the first lead has been synthesized and tested against MV. We have identified an improved lead with low toxicity and high stability (half-life >> 16 h) that prevents viral entry and hence infection. This compound shows high MV specificity and strong activity (50% inhibitory concentration = 0.6 to 3.0 microM, depending on the MV genotype) against a panel of wild-type MV strains representative of viruses that are currently endemic in the field.

[Preliminary study on nasal spray of interferon alpha-2b used for prevention of rubella and measles virus infections]

OBJECTIVE

To evaluate the efficacy of the interferon alpha-2b nasal spray in prevention of rubella and measles virus infections.

METHODS

The properly selected volunteer groups have been divided into interferon alpha-2b experimental and control group. The experimental group received interferon alpha-2b treatment by nasal spray for 2 days before the immunization, then both groups were challenged with rubella and measles attenuated live vaccine respectively through nasal spray. The sera from pre-immunization and 21 and 28 days after immunization were collected to test the IgG antibody titers. The influence on the viral antibody titer reflects the viral preventive effect by interferon alpha-2b.

RESULTS

The antibody titer difference of measles virus between experimental and control group was 1.26 (21 day) and 2.96 (28 day), there were statistically difference between them; the difference of rubella virus was 0.95 (21 day) and 0.37 (28 day), but there were no statistically differences found.

CONCLUSION

The preliminary results showed that the interferon alpha-2b can be used as prevention method for measles and rubella viral infections.

Indoleamine 2,3-dioxygenase mediates cell type-specific anti-measles virus activity of gamma interferon

Gamma interferon (IFN-gamma) has been shown to be increased in sera from patients with acute measles and after vaccination, to exhibit protective functions in brains of patients with subacute sclerosing panencephalitis, and to mediate a noncytolytic clearance of measles virus (MV) from rodent brains. In order to reveal a possible intracellular antiviral activity in the absence of antigen presentation and cytotoxic T cells, we investigated IFN-gamma-induced effects on MV replication in various tissue culture cells. While attenuated MV strains are more sensitive to IFN-alpha/beta than are wild-type strains, IFN-gamma inhibits the replication of all MV strains in epithelial, endothelial, and astroglial cells, but not in lymphoid and neuronal cell lines. The antiviral activity induced by IFN-gamma correlates with the induction of indoleamine 2,3-dioxygenase (IDO), an enzyme of the tryptophan degradation pathway known to mediate antiviral as well as antibacterial and antiparasitic effects. The IFN-gamma-induced antiviral activity can be overcome by the addition of excess amounts of l-tryptophan, which indicates a specific role of IDO in the anti-MV activity. Our data suggest that the IFN-gamma-induced enzyme IDO plays an important antiviral role in MV infections of epithelial, endothelial, and astroglial cells.

Effect of certain polypeptides on the biological activities of Measles virus

The effect of a selected tripeptide, Z-d-Phe-Phe-Arg(NO(2)) (SV-4814) on the kinetics of lysis of green monkey erythrocytes by measles virus hemolysin suggested conditions of competitive inhibition. SV-4814 prevented not only hemoglobin release, but also the preceding leakage of K(+) through the cell membrane. The capacity of 12 different dipeptides, 6 tripeptides, including SV-4814, and 4 tetrapeptides to inhibit measles virus-specific hemolysis and infectivity was analyzed. Tri- and tetrapeptides were more active than dipeptides. The presence of aromatic amino acids and a free carboxyl terminal appeared to be a prerequisite for inhibitory activity. Two compounds, one tripeptide (Z-Phe-d-Phe-d-Tyr) and one tetrapeptide [Z-d-Phe-Arg(NO(2))-d-Met], carried an inhibitory activity, which was about two times higher than that of SV-4814.

[In vitro study of antiviral activity of Myramistin against measles and mumps viruses]

The study was aimed at in vitro investigation of the Myramistin antiviral activity against the measles and mumps viruses in the Vero cell culture. The experiments with addition of myramistin simultaneously or at various periods after inoculation of the monolayer by the measles virus (Edmonson strain) or mumps virus (PetroNov/03 strain) revealed pronounced dose-dependent antiviral effect of the drug. It was shown that for prevention of replication of the measles and mumps viruses the optimal concentrations were 0.05 to 0.005%. The prospects of myramistin use as a prophylactic agent for infections caused by the measles and mumps viruses are discussed.

Synthesis and anti-measles virus activity of new isoquinolin-4-one derivatives

Despite intense efforts to increase vaccine coverage, measles virus (MV) still causes significant morbidity and mortality in the world sometimes as a results of severe, chronic and lethal diseases. In an effort to develop therapies to supplement immunization strategies a number of 1-oxo-2-[[(1E)-phenylmethylene]amino]-1,2-dihydroisoquinoline-4-carboxylic acid derivatives were synthesized and evaluated for anti-measles activity. The substituents on the aromatic ring were chosen in order to evaluate the influence of electron-withdrawing or electron-donating effects on the electronic density of the aromatic moiety. We also evaluated the introduction of a vinyl chain between the exocyclic nitrogen and phenyl moiety. The biological results allow to outline some preliminary considerations on structure-activity relationship.

Improved antiviral activity in vitro of ribavirin against measles virus after complexation with cyclodextrins

Despite vaccination, measles remains a burden in both developed and developing countries and complications may necessitate an efficient therapy. Measles virus (MEV) is susceptible to ribavirin (RBV), but the use of this drug is limited by its toxicity. Cyclodextrins (CDs) can form complexes with numerous molecules, improving their bioavailability and their biological properties. We have evaluated in vitro the antiviral effects of complexes of RBV with alpha-, beta- or gamma-CD against two clade A laboratory strains of MEV (Edmonston and CAM/RB) grown on Vero cells. Complexation of RBV with alpha-CD or beta-CD lead to a five-fold or a two-fold decrease in the 50% inhibitory concentration, respectively, against both MEV strains. In contrast, gamma-CD complexation showed no modification.

A target site for template-based design of measles virus entry inhibitors

Measles virus (MV) constitutes a principal cause of worldwide mortality, accounting for almost 1 million deaths annually. Although a live-attenuated vaccine protects against MV, vaccination efficiency of young infants is low because of interference by maternal antibodies. Parental concerns about vaccination safety further contribute to waning herd immunity in developed countries, resulting in recent MV outbreaks. The development of novel antivirals that close the vaccination gap in infants and silence viral outbreaks is thus highly desirable. We previously identified a microdomain in the MV fusion protein (F protein) that is structurally conserved in the paramyxovirus family and constitutes a promising target site for rationally designed antivirals. Here we report the template-based development of a small-molecule MV inhibitor, providing proof-of-concept for our approach. This lead compound specifically inhibits fusion and spread of live MV and MV glycoprotein-induced membrane fusion. The inhibitor induces negligible cytotoxicity and does not interfere with receptor binding or F protein biosynthesis or transport but prevents F protein-induced lipid mixing. Mutations in the postulated target site alter viral sensitivity to inhibition. In silico docking of the compound in this microdomain suggests a binding model that is experimentally corroborated by a structure-activity analysis of the compound and the inhibition profile of mutated F proteins. A second-generation compound designed on the basis of the interaction model shows a 200-fold increase in antiviral activity, creating the basis for novel MV therapeutics. This template-based design approach for MV may be applicable to other clinically relevant members of the paramyxovirus family.

Inhibitory potential of Crotalus durissus terrificus venom on measles virus growth

This paper presents the antiviral activity found in a snake with Crotalus durissus terrificus venom (Cdt), studied by use of microplate inhibition assay, using measles virus (MV). Cdt at concentrations below 100 microg/ml showed no cytotoxicity for Vero cells. This study shows the optimal conditions for cell treatment and infection. Two factors that affect virus binding and infection efficiency were studied: the use of an adsorption step, where infection volume was varied; and the concentration of fetal bovine serum (FBS). The adsorption step, with or without FBS, increased the bound virus percentage, whereas it increased bound virus at equilibrium only in FBS-free until 2.5% FBS. In contrast, the addition of 10% FBS decreased the bound virus percentage. The inhibition of MV replication in Vero cells was observed when Cdt was added either before or during cell infection with virus. Its inhibitory concentration against MV replication was 0.1 until 100 microg/ml, respectively. The anti-MV effect of the Cdt was gradually decreased when it was added before or during infection, and little inhibition was observed when Cdt was added 1 h after infection, suggesting that the MV infection was inhibited at the time of the initial events such as at the moment of adsorption and penetration of the viral cycle. In conclusion, Cdt contains anti-MV effects that may be of potential clinical interest.

Associations between measles antibody levels and the protein structure of class II human leukocyte antigens

In this study, we describe associations between variation in human leukocyte antigen (HLA) DP and DQ amino acid sequences and low measles antibody levels after measles immunization. We tested serum samples from 242 children for measles immunoglobulin G antibodies. We performed class II HLA typing and examined associations between DQ and DP exon 2 amino acid sequences and antibody levels. No DP amino acid variants were associated with seronegativity. However, 11 DQA and 6 DQB amino acid variants were associated with seronegativity (p<0.005). These amino acid variants were highly correlated, and the significant DQA amino acids were only found in alleles *0201, *0301, *0401, *0501, and *0601. Two of the amino acids associated with measles seronegativity were located in predicted binding pockets of the DQ molecule; one was present in the leader sequence. Among the DQB alleles, all of the amino acid variants associated with seronegativity were present only in the DQB*0201 allele. Two of the amino acids associated with seronegativity were located in predicted binding pockets of the DQ molecule; two were located in the leader sequence. Our data suggest that specific DQA and DQB amino acid variations are associated with measles seronegativity after vaccination.

in vitro inhibition of the measles virus by novel ring-expanded ('fat') nucleoside analogues containing the imidazo[4,5-e]diazepine ring system

The synthesis and in vitro anti-measles virus (anti-MV) activity of a class of ring-expanded ('fat') nucleoside analogues (1-4) containing the title heterocyclic ring system are reported. The target compounds were synthesized by base-catalyzed condensations of 4,5-dicarboxylic acid esters of the appropriately substituted imidazole-1-ribosides with suitably substituted guanidine derivatives. Compounds were screened for anti-MV activity in African green monkey kidney cells (CV-1), employing ribavirin as the control standard. While the parent compound 1 itself failed to show any significant antiviral activity against MV, its analogues containing hydrophobic substituents at the 2-position (2) or the 6-position (4) showed promising antiviral activity at submicromolar or micromolar concentration levels with no apparent toxicity to the host cell line. Both compounds showed higher anti-MV activity than the control drug ribavirin.

Novel strategy for inhibiting viral entry by use of a cellular receptor-plant virus chimera

The plant virus cowpea mosaic virus (CPMV) has recently been developed as a biomolecular platform to display heterologous peptide sequences. Such CPMV-peptide chimeras can be easily and inexpensively produced in large quantities from experimentally infected plants. This study utilized the CPMV chimera platform to create an antiviral against measles virus (MV) by displaying a peptide known to inhibit MV infection. This peptide sequence corresponds to a portion of the MV binding site on the human MV receptor CD46. The CPMV-CD46 chimera efficiently inhibited MV infection of HeLa cells in vitro, while wild-type CPMV did not. Furthermore, CPMV-CD46 protected mice from mortality induced by an intracranial challenge with MV. Our results indicate that the inhibitory CD46 peptide expressed on the surface of CPMV retains virus-binding activity and is capable of inhibiting viral entry both in vitro and in vivo. The CD46 peptide presented in the context of CPMV is also up to 100-fold more effective than the soluble CD46 peptide at inhibiting MV infection in vitro. To our knowledge, this study represents the first utilization of a plant virus chimera as an antiviral agent.

Antiviral activity of brassinosteroids derivatives against measles virus in cell cultures

Twenty-seven brassinosteroid derivatives were tested for antiviral activity against measles virus (MV) via a virus-yield reduction assay. Compounds 6b [(22S,235)-3beta-bromo-5alpha,22,23-trihydroxystigmastan-6-one], 1d [(22R,23R)-2alpha,3alpha,22,23-tetrahydroxy-beta-Homo-7-oxa-stigmastan-6-one], 8a [(22R,23R)-3beta-fluoro-22,23-dihydroxystigmastan-6-one], 9b [(22S,23S)-3beta-fluoro-5alpha,22,23-trihydroxystigmastan-6-one] and 10b [(22S,23S)-5alpha-fluor-3beta,22,23-trihydroxystigmastan-6-one], with selectivity indexes (SI) of 40, 57, 31, 37 and 53, are the derivatives with good antiviral activity against MV. These SI values are higher than those obtained with ribavirin (used as reference drug). A comparative analysis of 50% cytotoxic concentration (CC50) values, using confluent non-growing cells, gives and indication of structure-activity relationship. According to their degree of cytotoxicity the compounds were divided in three groups: low, intermediate and high cytotoxicity. By observing the chemical structures of compounds belonging to the first group we can see that less cytotoxic activities are related to the presence of a 3beta-hydroxy group on C-3 (ring A) and a double bond between C-22 and C-23 (side chain). The replacement of a 5alpha-hydroxy group by a 5alpha-fluoro group enhances cytotoxicity. Halogenated brassinosteroid derivatives in C-3 position are more cytotoxic than those with an acetoxy group in the same position. For compounds 1d, 6b, 10b and ribavirin, cytotoxicity measurements were also done with replicating cells; CC50 values were low, but they still competed favourably with ribavirin against MV.

Coumarins and pyranocoumarins, potential novel pharmacophores for inhibition of measles virus replication

A series of coumarin and pyranocoumarin analogues were evaluated in vitro for antiviral efficacy against measles virus (MV), strain Chicago. Of the 22 compounds tested for inhibition, six were found to have selectivity indices greater than 10. These were compounds 5-hydroxy-7-propionyloxy-4-propylcoumarin (2a), 5,7-bis(tosyloxy)-4-propylcoumarin (7); 5-hydroxy-4-propyl-7-tosyloxy-coumarin (8); 6,6-dimethyl-9-propionyloxy-4-propyl-2H,6H-benzo[1,2-b:3,4-b']dipyran-2-one (9); 6,6-dimethyl-9-pivaloyloxy-4-propyl-2H,6H-benzo[1,2-b:3,4-b']dipyran-2-one (10); and 7,8-cis-10,11,12-trans-4-propyl-6,6,10,11-tetramethyl-7,8,9-trihydroxy-2H,6H,12H-benzo[1 ,2-b:3,4-b':5,6-b'']tripyran-2-one (18). Three of the active drugs were propyl coumarin analogues (2a, 7 and 8), two were dipyranone or chromeno-coumarins (9 and 10), and one was a benzotripyranone with a coumarin nucleus (18). Some appeared to be rather specific and potent inhibitors of MV with EC50 values ranging from 0.2 to 50 microg/ml and the majority of the EC50 values being less than 5 pg/ml. The compounds inhibited an additional nine strains of MV, and in virucidal tests the drugs did not physically disrupt the virion to inhibit virus replication. The inhibitory activity for one of the compounds tested (7) was somewhat dependent on virus concentration and it was still active when added to cells up to 24 h after virus exposure. When used in combination with ribavirin, compound 7 appeared not to profoundly affect the antiviral efficacy of ribavirin or its cell-associated toxicity. However, a slightly antagonistic MV-inhibitory effect was observed at the highest concentration of ribavirin used in combination with most concentrations of compound 7 tested. This and related compounds may be valuable leads in the development of a potent and selective class of MV inhibitors that could be used in future in the clinic.

Effects of cyclosporin A on cell fusion in a monkey kidney cell line persistently infected with measles virus

The authors studied the effects of immunosuppressive peptide cyclosporin A (CsA) on cell fusion efficiency in cells persistently infected with measles virus (448-PI-Vero cells). Treatment of 448-PI-Vero cells with 5 microM CsA enhanced the infusion. In addition, the expression of measles virus antigen on cell surface was increased by treatment with CsA. The addition of phenothiazine, an anti-calmodulin drug, enhanced the fusion of 448-PI-Vero cells in the presence of CsA, although treatment with phenothiazine alone did not affect polykaryocyte formation. The enhancement of fusion efficiency in 448-PI-Vero cells by CsA was suppressed by oligopeptide Z-D-Phe-Phe-Gly, a synthetic oligopeptide that inhibits fusion induced by measles virus. Since the cell content of major virus-specific polypeptides, such as hemagglutinin, nucleoprotein or matrix protein is the same as in untreated controls, this fusion enhancement may be related to transport and accumulation of measles virus glycoproteins.