Antivirals acting on viral envelopes via biophysical mechanisms of action

Molecular pharmacology and therapeutic advances of monoterpene perillyl alcohol

BACKGROUND

Perillyl alcohol (POH) is a aroma monoterpene commonly obtained from various plants' essential oil. Recently, increasing researches have demonstrated that POH may be useful, not only as flavor compound, but also as bioactive molecule because of a variety of biological activities.

PURPOSE

The aim of this review is to summarize the production, pharmacological activities and molecular mechanism, active derivatives, toxicity and parmacokinetics, and industrial application of POH.

METHODS

A systematic search of published articles up to January 2024 in Web of Science, China Knowledge Network, and PubMed databases is conducted using the following keywords: POH, POH derivatives, biological or pharmacological, production or synthesis, pharmacokinetics, toxicity and application.

RESULTS

Biotechnological production is considered to be a potential alternative approach to generate POH. POH provides diverse pharmacological benefits, including anticancer, antimicrobial, insecticidal, antioxidant, anti-inflammatory, hypotensive, vasorelaxant, antinociceptive, antiasthmatic, hepatoprotective effects, etc. The underlying mechanisms of action include modulation of NF-κB, JNK/c-Jun, Notch, Akt/mTOR, PI3K/Akt/eNOS, STAT3, Nrf2 and ERS response pathways, mitigation of mitochondrial dysfunction and membrane integrity damage, and inhibition of ROS accumulation, pro-inflammatory cytokines release and NLRP3 activation. What's more, the proteins or genes influenced by POH against diseases refer to Bax, Bcl-2, cyclin D1, CDK, p21, p53, HIF-1α, AP-1, caspase-3, M6P/IGF2R, PARP, VEGF, etc. Some clinical studies report that intranasal delivery of POH is a safe and effective treatment for cancer, but further clinical investigations are needed to confirm other health benefits of POH in human healthy. Depending on these health-promoting properties together with desirable flavor and safety, POH can be employed as dietary supplement, preservative and flavor additive in food and cosmetic fields, as building block in synthesis fields, as anticancer drug in medicinal fields, and as pesticides and herbicides in agricultural fields.

CONCLUSION

This review systematically summarizes the recent advances in POH and highlights its therapeutic effects and potential mechanisms as well as the clinical settings, which is helpful to develop POH into functional food and new candidate drug for prevention and management of diseases. Future studies are needed to conduct more biological activity studies of POH and its derivatives, and check their clinical efficacy and potential side effects.

Designing nanodiscs as versatile platforms for on-demand therapy

Nowadays, there has been an increasing utilization of nanomedicines for disease treatment. Nanodiscs (NDs) have emerged as a novel platform technology that garners significant attention in biomedical research and drug discovery. NDs are nanoscale phospholipid bilayer discs capable of incorporating membrane proteins and lipids within a native-like environment. They are assembled using amphiphilic biomacromolecular materials, such as apolipoprotein A1 or membrane scaffold proteins (MSPs), peptides, and styrene-maleic acid polymers (SMAs). NDs possess well-defined sizes and shapes, offering a stable, homogeneous, and biologically relevant environment for studying membrane proteins and lipids. Their unique properties have made them highly desirable for diverse applications, including cancer immunotherapy, vaccine development, antibacterial and antiviral therapy, and treating Alzheimer's disease (AD) and diabetes-related conditions. This review discusses the classifications, advantages, and applications of NDs in disease therapy.

Lipid-Centric Approaches in Combating Infectious Diseases: Antibacterials, Antifungals and Antivirals with Lipid-Associated Mechanisms of Action

One of the global challenges of the 21st century is the increase in mortality from infectious diseases against the backdrop of the spread of antibiotic-resistant pathogenic microorganisms. In this regard, it is worth targeting antibacterials towards the membranes of pathogens that are quite conservative and not amenable to elimination. This review is an attempt to critically analyze the possibilities of targeting antimicrobial agents towards enzymes involved in pathogen lipid biosynthesis or towards bacterial, fungal, and viral lipid membranes, to increase the permeability via pore formation and to modulate the membranes' properties in a manner that makes them incompatible with the pathogen's life cycle. This review discusses the advantages and disadvantages of each approach in the search for highly effective but nontoxic antimicrobial agents. Examples of compounds with a proven molecular mechanism of action are presented, and the types of the most promising pharmacophores for further research and the improvement of the characteristics of antibiotics are discussed. The strategies that pathogens use for survival in terms of modulating the lipid composition and physical properties of the membrane, achieving a balance between resistance to antibiotics and the ability to facilitate all necessary transport and signaling processes, are also considered.

Alkyl Derivatives of Perylene Photosensitizing Antivirals: Towards Understanding the Influence of Lipophilicity

Amphipathic perylene derivatives are broad-spectrum antivirals against enveloped viruses that act as fusion inhibitors in a light-dependent manner. The compounds target the lipid bilayer of the viral envelope using the lipophilic perylene moiety and photogenerating singlet oxygen, thereby causing damage to unsaturated lipids. Previous studies show that variation of the polar part of the molecule is important for antiviral activity. Here, we report modification of the lipophilic part of the molecule, perylene, by the introduction of 4-, 8-, and 12-carbon alkyls into position 9(10) of the perylene residue. Using Friedel-Crafts acylation and Wolff-Kishner reduction, three 3-acetyl-9(10)-alkylperylenes were synthesized from perylene and used to prepare 9 nucleoside and 12 non-nucleoside amphipathic derivatives. These compounds were characterized as fluorophores and singlet oxygen generators, as well as tested as antivirals against herpes virus-1 (HSV-1) and vesicular stomatitis virus (VSV), both known for causing superficial skin/mucosa lesions and thus serving as suitable candidates for photodynamic therapy. The results suggest that derivatives with a short alkyl chain (butyl) have strong antiviral activity, whereas the introduction of longer alkyl substituents (n = 8 and 12) to the perylenyethynyl scaffold results in a dramatic reduction of antiviral activity. This phenomenon is likely attributable to the increased lipophilicity of the compounds and their ability to form insoluble aggregates. Moreover, molecular dynamic studies revealed that alkylated perylene derivatives are predominately located closer to the middle of the bilayer compared to non-alkylated derivatives. The predicted probability of superficial positioning correlated with antiviral activity, suggesting that singlet oxygen generation is achieved in the subsurface layer of the membrane, where the perylene group is more accessible to dissolved oxygen.

Antiviral activity of singlet oxygen-photogenerating perylene compounds against SARS-CoV-2: Interaction with the viral envelope and photodynamic virion inactivation

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has prompted great interest in novel broad-spectrum antivirals, including perylene-related compounds. In the present study, we performed a structure-activity relationship analysis of a series of perylene derivatives, which comprised a large planar perylene residue, and structurally divergent polar groups connected to the perylene core by a rigid ethynyl or thiophene linker. Most of the tested compounds did not exhibit significant cytotoxicity towards multiple cell types susceptible to SARS-CoV-2 infection, and did not change the expressions of cellular stress-related genes under normal light conditions. These compounds showed nanomolar or sub-micromolar dose-dependent anti-SARS-CoV-2 activity, and also suppressed the in vitro replication of feline coronavirus (FCoV), also termed feline infectious peritonitis virus (FIPV). Perylene compounds exhibited high affinity for liposomal and cellular membranes, and efficiently intercalated into the envelopes of SARS-CoV-2 virions, thereby blocking the viral-cell fusion machinery. Furthermore, the studied compounds were demonstrated to be potent photosensitizers, generating reactive oxygen species (ROS), and their anti-SARS-CoV-2 activities were considerably enhanced after irradiation with blue light. Our results indicated that photosensitization is the major mechanism underlying the anti-SARS-CoV-2 activity of perylene derivatives, with these compounds completely losing their antiviral potency under red light. Overall, perylene-based compounds are broad-spectrum antivirals against multiple enveloped viruses, with antiviral action based on light-induced photochemical damage (ROS-mediated, likely singlet oxygen-mediated), causing impairment of viral membrane rheology.

Membrane-Targeting Perylenylethynylphenols Inactivate Medically Important Coronaviruses via the Singlet Oxygen Photogeneration Mechanism

Perylenylethynyl derivatives have been recognized as broad-spectrum antivirals that target the lipid envelope of enveloped viruses. In this study, we present novel perylenylethynylphenols that exhibit nanomolar or submicromolar antiviral activity against Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) and feline infectious peritonitis virus (FIPV) in vitro. Perylenylethynylphenols incorporate into viral and cellular membranes and block the entry of the virus into the host cell. Furthermore, these compounds demonstrate an ability to generate singlet oxygen when exposed to visible light. The rate of singlet oxygen production is positively correlated with antiviral activity, confirming that the inhibition of fusion is primarily due to singlet-oxygen-induced damage to the viral envelope. The unique combination of a shape that affords affinity to the lipid bilayer and the capacity to generate singlet oxygen makes perylenylethynylphenols highly effective scaffolds against enveloped viruses. The anticoronaviral activity of perylenylethynylphenols is strictly light-dependent and disappears in the absence of daylight (under red light). Moreover, these compounds exhibit negligible cytotoxicity, highlighting their significant potential for further exploration of the precise antiviral mechanism and the broader scope and limitations of this compound class.

Recent Advances in Molecular Mechanisms of Nucleoside Antivirals

The search for new drugs has been greatly accelerated by the emergence of new viruses and drug-resistant strains of known pathogens. Nucleoside analogues (NAs) are a prospective class of antivirals due to known safety profiles, which are important for rapid repurposing in the fight against emerging pathogens. Recent improvements in research methods have revealed new unexpected details in the mechanisms of action of NAs that can pave the way for new approaches for the further development of effective drugs. This review accounts advanced techniques in viral polymerase targeting, new viral and host enzyme targeting approaches, and prodrug-based strategies for the development of antiviral NAs.

Lipid Membrane Interface Viewpoint: From Viral Entry to Antiviral and Vaccine Development

Membrane-enveloped viruses are responsible for most viral pandemics in history, and more effort is needed to advance broadly applicable countermeasures to mitigate the impact of future outbreaks. In this Perspective, we discuss how biosensing techniques associated with lipid model membrane platforms are contributing to improving our mechanistic knowledge of membrane fusion and destabilization that is closely linked to viral entry as well as vaccine and antiviral drug development. A key benefit of these platforms is the simplicity of interpreting the results which can be complemented by other techniques to decipher more complicated biological observations and evaluate the biophysical functionalities that can be correlated to biological activities. Then, we introduce exciting application examples of membrane-targeting antivirals that have been refined over time and will continue to improve based on biophysical insights. Two ways to abrogate the function of viral membranes are introduced here: (1) selective disruption of the viral membrane structure and (2) alteration of the membrane component. While both methods are suitable for broadly useful antivirals, the latter also has the potential to produce an inactivated vaccine. Collectively, we emphasize how biosensing tools based on membrane interfacial science can provide valuable information that could be translated into biomedicines and improve their selectivity and performance.

5-(Perylen-3-ylethynyl)uracil as an antiviral scaffold: Potent suppression of enveloped virus reproduction by 3-methyl derivatives in vitro

Amphipathic nucleoside and non-nucleoside derivatives of pentacyclic aromatic hydrocarbon perylene are known as potent non-cytotoxic broad-spectrum antivirals. Here we report 3-methyl-5-(perylen-3-ylethynyl)-uracil-1-acetic acid and its amides, a new series of compounds based on a 5-(perylen-3-ylethynyl)-uracil scaffold. The compounds demonstrate pronounced in vitro activity against arthropod-borne viruses, namely tick-borne encephalitis virus (TBEV) and yellow fever virus (YFV), in plaque reduction assays with EC₅₀ values below 1.9 and 1.3 nM, respectively, and Chikungunya virus (CHIKV) in cytopathic effect inhibition test with EC₅₀ values below 3.2 μM. The compounds are active against respiratory viruses as well: severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) in cytopathic effect inhibition test and influenza A virus (IAV) in virus titer reduction experiments are inhibited - EC₅₀ values below 51 nM and 2.2 μM, respectively. The activity stems from the presence of a hydrophobic perylene core, and all of the synthesized compounds exhibit comparable ¹O₂ generation rates. Nonetheless, activity can vary by orders of magnitude depending on the hydrophilic part of the molecule, suggesting a complex mode of action. A time-of-addition experiment and fluorescent imaging indicate that the compounds inhibit viral fusion in a dose-dependent manner. The localization of the compound in the lipid bilayers and visible damage to the viral envelope suggest the membrane as the primary target. Dramatic reduction of antiviral activity with limited irradiation or under treatment with antioxidants further cements the idea of photoinduced ROS-mediated viral envelope damage being the mode of antiviral action.

Emerging roles of ferroptosis in infectious diseases

In living organisms, lipid peroxidation is a continuously occurring cellular process and therefore involved in various physiological and pathological contexts. Among the broad variety of lipids, polyunsaturated fatty acids (PUFA) constitute a major target of oxygenation either when released as mediators by phospholipases or when present in membranous phospholipids. The last decade has seen the characterization of an iron- and lipid peroxidation-dependent cell necrosis, namely, ferroptosis, that involves the accumulation of peroxidized PUFA-containing phospholipids. Further studies could link ferroptosis in a very large body of (physio)-pathological processes, including cancer, neurodegenerative, and metabolic diseases. In this review, we mostly focus on the emerging involvement of lipid peroxidation-driven ferroptosis in infectious diseases, and the immune consequences. We also discuss the putative ability of microbial virulence factors to exploit or to dampen ferroptosis regulatory pathways to their own benefit.

On the Sensitivity of the Virion Envelope to Lipid Peroxidation

Emerging viruses are a public health threat best managed with broad spectrum antivirals. Common viral structures, like capsids or virion envelopes, have been proposed as targets for broadly active antiviral drugs. For example, a number of lipoperoxidators have been proposed to preferentially affect viral infectivity by targeting metabolically inactive enveloped virions while sparing metabolically active cells. However, this presumed preferential virion sensitivity to lipoperoxidation remains untested. To test whether virions are indeed more sensitive to lipoperoxidation than are cells, we analyzed the effects of two classic generic lipoperoxidators: lipophilic 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) and hydrophilic 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH) on Vero and human foreskin fibroblasts (HFF) cell viability, HSV-1 plaquing efficiency, and virion and cell lipoperoxidation. Cells or virions were incubated with the lipoperoxidators at 37°C for 2 h or incubated in atmospheric O₂, and dose responses (half maximal cytotoxic and effective concentration [CC₅₀ and EC₅₀]) were evaluated by three or four parameter regression. The HSV-1 virions were slightly more sensitive to lipoperoxidators than were the cells (selectivity index [SI], 3.3 to 7.4). The effects of the lipophilic AMVN on both cell and virion viability directly correlated with the extent of membrane lipoperoxidation as evaluated by two different probes, C11-Bodipy and liperfluo. Moreover, the hydrophilic AAPH-induced virion inactivation at lower concentrations than did lipoperoxidation. Known lipoperoxidators inhibit infectivity via lipoperoxidation-independent mechanisms. Antioxidants protected against a loss of viral infectivity by less than 5-fold. Carrier bovine serum albumin (BSA) protected against both peroxidators to a similar extent when present together with the lipoperoxidating agents, suggesting that BSA quenches them as expected. Virions incubated in atmospheric oxidative conditions suffered losses of infectivity that were similar to those of chemically peroxidated virions, and they were protected by water soluble vitamin C and BSA with no evident lipoperoxidation, indicating predominant peroxidative damage to nonlipid virion components. Thus, lipoperoxidation is not a mechanism by which to specifically inhibit the infectivity of enveloped viruses, and the effects of known lipoperoxidators on virion infectivity are not solely mediated by lipoperoxidation. IMPORTANCE Small molecules that induce lipoperoxidation have been proposed repeatedly as potential antiviral drugs based on a presumed unique sensitivity of virions to this type of damage. Several small molecules that inactivate virions without affecting cells have been proposed to act primarily by inducing lipoperoxidation. However, the preferential sensitivity of virions to lipoperoxidators had not been experimentally evaluated. Using two of the best characterized small molecule lipoperoxidators, which are widely considered to be the prototypical water soluble and liposoluble lipoperoxidators, we show that lipoperoxidators have no preference for virions over cells. Moreover, they also inactivate virions by mechanisms other than the induction of lipoperoxidation. Therefore, the general induction of lipoperoxidation is not a path by which to develop antivirals. Moreover, molecules with specific antiviral activity which are not cytotoxic and have no preference to localize to virions over cells are unlikely to act primarily by inducing lipoperoxidation.

Synthesis and biological evaluation of novel rhodanine-based structures with antiviral activity towards HHV-6 virus

An increased awareness of diseases associated with Human herpesvirus 6 (HHV-6) infection or reactivation has resulted in a growing interest in the evaluation of the best treatment options available for the clinical management of HHV-6 disease. However, no compound has yet been approved exclusively for HHV-6 infection treatment. For this reason, the identification of anti-HHV6 compounds provides a valuable opportunity for developing efficient antiviral therapies. A possible target for antiviral drugs is the virus-cell fusion step. In this study, we synthetized potential fusion intermediates inhibitors based on the rhodanine structure. The obtained derivatives were tested for cytotoxicity and for antiviral activity in human cells infected with HHV6. Level of infection was monitored by viral DNA quantification at different time points up to 7 days post infection. Among the synthetized derivatives, 9e showed a significative inhibitory effect on viral replication that lasted over 7 days, probably attributable to the particular combination of hydrophilic and hydrophobic substituents to the rhodanine moiety. Our results support the use of these amphipathic fusion inhibitors for the treatment of HHV-6 infections.

Photosensitizing Antivirals

Antiviral action of various photosensitizers is already summarized in several comprehensive reviews, and various mechanisms have been proposed for it. However, a critical consideration of the matter of the area is complicated, since the exact mechanisms are very difficult to explore and clarify, and most publications are of an empirical and "phenomenological" nature, reporting a dependence of the antiviral action on illumination, or a correlation of activity with the photophysical properties of the substances. Of particular interest is substance-assisted photogeneration of highly reactive singlet oxygen (1O2). The damaging action of 1O2 on the lipids of the viral envelope can probably lead to a loss of the ability of the lipid bilayer of enveloped viruses to fuse with the lipid membrane of the host cell. Thus, lipid bilayer-affine 1O2 photosensitizers have prospects as broad-spectrum antivirals against enveloped viruses. In this short review, we want to point out the main types of antiviral photosensitizers with potential affinity to the lipid bilayer and summarize the data on new compounds over the past three years. Further understanding of the data in the field will spur a targeted search for substances with antiviral activity against enveloped viruses among photosensitizers able to bind to the lipid membranes.

A SARS-CoV-2 cytopathicity dataset generated by high-content screening of a large drug repurposing collection

SARS-CoV-2 is a novel coronavirus responsible for the COVID-19 pandemic, in which acute respiratory infections are associated with high socio-economic burden. We applied high-content screening to a well-defined collection of 5632 compounds including 3488 that have undergone previous clinical investigations across 600 indications. The compounds were screened by microscopy for their ability to inhibit SARS-CoV-2 cytopathicity in the human epithelial colorectal adenocarcinoma cell line, Caco-2. The primary screen identified 258 hits that inhibited cytopathicity by more than 75%, most of which were not previously known to be active against SARS-CoV-2 in vitro. These compounds were tested in an eight-point dose response screen using the same image-based cytopathicity readout. For the 67 most active molecules, cytotoxicity data were generated to confirm activity against SARS-CoV-2. We verified the ability of known inhibitors camostat, nafamostat, lopinavir, mefloquine, papaverine and cetylpyridinium to reduce the cytopathic effects of SARS-CoV-2, providing confidence in the validity of the assay. The high-content screening data are suitable for reanalysis across numerous drug classes and indications and may yield additional insights into SARS-CoV-2 mechanisms and potential therapeutic strategies.

Stopping Membrane-Enveloped Viruses with Nanotechnology Strategies: Toward Antiviral Drug Development and Pandemic Preparedness

Membrane-enveloped viruses are a leading cause of viral epidemics, and there is an outstanding need to develop broad-spectrum antiviral strategies to treat and prevent enveloped virus infections. In this review, we critically discuss why the lipid membrane surrounding enveloped virus particles is a promising antiviral target and cover the latest progress in nanotechnology research to design and evaluate membrane-targeting virus inhibition strategies. These efforts span diverse topics such as nanomaterials, self-assembly, biosensors, nanomedicine, drug delivery, and medical devices and have excellent potential to support the development of next-generation antiviral drug candidates and technologies. Application examples in the areas of human medicine and agricultural biosecurity are also presented. Looking forward, research in this direction is poised to strengthen capabilities for virus pandemic preparedness and demonstrates how nanotechnology strategies can help to solve global health challenges related to infectious diseases.

Broad-spectrum antivirals of protoporphyrins inhibit the entry of highly pathogenic emerging viruses

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PPIX possesses broad antiviral activities in vitro against a panel of enveloped viruses.

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PPIX interacts with the lipids of enveloped virions, thereby inhibiting the entry of enveloped viruses into host cells.

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PPIX shows the antiviral effect in vivo by testing mice infected with the influenza A/Puerto Rico/8/34 (H1N1) virus.

Severe emerging and re-emerging viral infections such as Lassa fever, Avian influenza (AI), and COVID-19 caused by SARS-CoV-2 urgently call for new strategies for the development of broad-spectrum antivirals targeting conserved components in the virus life cycle. Viral lipids are essential components, and viral-cell membrane fusion is the required entry step for most unrelated enveloped viruses. In this paper, we identified a porphyrin derivative of protoporphyrin IX (PPIX) that showed broad antiviral activities in vitro against a panel of enveloped pathogenic viruses including Lassa virus (LASV), Machupo virus (MACV), and SARS-CoV-2 as well as various subtypes of influenza A viral strains with IC₅₀ values ranging from 0.91 ± 0.25 μM to 1.88 ± 0.34 μM. A mechanistic study using influenza A/Puerto Rico/8/34 (H1N1) as a testing strain showed that PPIX inhibits the infection in the early stage of virus entry through biophysically interacting with the hydrophobic lipids of enveloped virions, thereby inhibiting the entry of enveloped viruses into host cells. In addition, the preliminary antiviral activities of PPIX were further assessed by testing mice infected with the influenza A/Puerto Rico/8/34 (H1N1) virus. The results showed that compared with the control group without drug treatment, the survival rate and mean survival time of the mice treated with PPIX were apparently prolonged. These data encourage us to conduct further investigations using PPIX as a lead compound for the rational design of lipid-targeting antivirals for the treatment of infection with enveloped viruses.

Various Facets of Pathogenic Lipids in Infectious Diseases: Exploring Virulent Lipid-Host Interactome and Their Druggability

Lipids form an integral, structural, and functional part of all life forms. They play a significant role in various cellular processes such as membrane fusion, fission, endocytosis, protein trafficking, and protein functions. Interestingly, recent studies have revealed their more impactful and critical involvement in infectious diseases, starting with the manipulation of the host membrane to facilitate pathogenic entry. Thereafter, pathogens recruit specific host lipids for the maintenance of favorable intracellular niche to augment their survival and proliferation. In this review, we showcase the lipid-mediated host pathogen interplay in context of life-threatening viral and bacterial diseases including the recent SARS-CoV-2 infection. We evaluate the emergent lipid-centric approaches adopted by these pathogens, while delineating the alterations in the composition and organization of the cell membrane within the host, as well as the pathogen. Lastly, crucial nexus points in their interaction landscape for therapeutic interventions are identified. Lipids act as critical determinants of bacterial and viral pathogenesis by altering the host cell membrane structure and functions.

5-(Perylen-3-ylethynyl)uracil Derivatives Inhibit Reproduction of Respiratory Viruses

In this work, we describe the synthesis of 5-(perylen-3-ylethynyl)uridine and its ability to effectively inhibit the replication of respiratory disease pathogens in cell culture, namely: influenza A virus (IVA); type 3 parainfluenza virus (PIV-3); and human respiratory syncytial virus (RSV). Related known compounds were also analyzed: 5-(perylen-3-ylethynyl)-2'-deoxy-uridine; 5-(perylen-3-ylethynyl)-arabino-uridine; and 1-carboxymethyl-3-pivaloyloxymethyl-5-(perylen-3-ylethynyl)uracil.

The seafood Musculus senhousei shows anti-influenza A virus activity by targeting virion envelope lipids

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Pyropheophorbide a (PPa) was isolated from the seafood of M. senhousei.

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PPa shows a potent activity against a broad panel of influenza A viral strains.

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The mechanism of PPa is to block the entry of virus in the early stage of infection.

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The target of PPa may be that of lipid bilayer of the enveloped viruses.

Marine environments are known to be a new source of structurally diverse bioactive molecules. In this paper, we identified a porphyrin derivative of Pyropheophorbide a (PPa) from the mussel Musculus senhousei (M. senhousei) that showed broad anti-influenza A virus activity in vitro against a panel of influenza A viral strains. The analysis of the mechanism of action indicated that PPa functions in the early stage of virus infection by interacting with the lipid bilayer of the virion, resulting in an alteration of membrane-associated functions, thereby blocking the entry of enveloped viruses into host cells. In addition, the anti-influenza A virus activity of PPa was further assessed in mice infected with the influenza A virus. The survival rate and mean survival time of mice were apparently prolonged compared with the control group which was not treated with the drug. Therefore, PPa and its derivatives may represent lead compounds for controlling influenza A virus infection.

Simplistic perylene-related compounds as inhibitors of tick-borne encephalitis virus reproduction

Rigid amphipathic fusion inhibitors are potent broad-spectrum antivirals based on the perylene scaffold, usually decorated with a hydrophilic group linked via ethynyl or triazole. We have sequentially simplified these structures by removing sugar moiety, then converting uridine to aniline, then moving to perylenylthiophenecarboxylic acids and to perylenylcarboxylic acid. All these polyaromatic compounds, as well as antibiotic heliomycin, still showed pronounced activity against tick-borne encephalitis virus (TBEV) with limited toxicity in porcine embryo kidney (PEK) cell line. 5-(Perylen-3-yl)-2-thiophenecarboxylic acid (5a) showed the highest antiviral activity with 50% effective concentration of approx. 1.6 nM.

Perillyl alcohol and perillic acid exert efficient action upon HSV-1 maturation and release of infective virus

BACKGROUND

Infection by herpes simplex type-1 virus (HSV-1) causes several pathological processes, including cutaneous, oral and genital infections, fatal encephalitis and cognitive dysfunction due to grey matter loss. Acyclovir is the reference compound used as HSV-1 antiviral therapy. However, with the emergence of HSV-resistant strains to current antiviral drugs, development of new antiviral agents with distinct modes of action is urgently needed.

METHODS

In this study, we examined the mechanism of action of monoterpenes perillyl alcohol (POH) and perillic acid (PA) upon in vitro replication of HSV-1 KOS wild-type and the syn-mutant 17+ strain on Vero cells by plaque assay.

RESULTS

The cytotoxicity of POH and PA was measured by MTT assay and indicated that both compounds had high anti-HSV-1 activities in a concentration range that was not toxic for Vero cells. In addition, PCR analysis showed that POH and PA did not inhibit viral genome replication, but rather the release of infective virion particles from Vero cells.

CONCLUSIONS

Such findings suggest that POH and PA exert action upon late stages of HSV-1 maturation, therefore, indicating a promising perspective to its application in clinical investigation as effective anti-HSV-1 therapy preventing intermittent reactivation and progressive grey matter loss.

Synthetic surfactin analogues have improved anti-PEDV properties

Surfactin has antiviral activity against various enveloped viruses by inhibiting viral membrane fusion. However, the potential utility of surfactin as an antiviral drug is limited by its cytotoxicity. In this study, 10 surfactin analogues were obtained by chemical synthesis and evaluated to determine their anti-PEDV activities, hemolytic activities, and critical micelle concentrations. The main goal of our study was to develop a safer drug; a surfactin analogue with high anti-PEDV activity and low hemolytic activity. Compared with surfactin, one of the analogues we developed, SLP5, has lower hemolytic activity, with the same antiviral activity. The selectivity index of SLP5 is 52, while the SI for surfactin is 4, in other words, the safe and effective concentration range of SLP5 is 12 times greater than that of surfactin. Like surfactin, SLP5 has a direct antiviral effect on PEDV. Structurally, SLP5 is a linear lipopeptide with three carboxyl groups. Surfactin derivatives similar to SLP5 could be obtained by lactone bond hydrolyzation of surfactin, as well as total synthesis.

Compounds based on 5-(perylen-3-ylethynyl)uracil scaffold: High activity against tick-borne encephalitis virus and non-specific activity against enterovirus A

Rigid amphipathic fusion inhibitors (RAFIs) are potent antivirals based on a perylene core linked with a nucleoside moiety. Sugar-free analogues of RAFIs, 5-(perylen-3-ylethynyl)uracil-1-acetic acid 1 and its amides 2, were synthesized using combined protection group strategy. Compounds 1 and 2 appeared to have low toxicity on porcine embryo kidney (PEK) or rhabdomiosarcoma (RD) cells together with remarkable activity against enveloped tick-borne encephalitis virus (TBEV): EC₅₀ values vary from 0.077 μM to subnanomolar range. Surprisingly, 3-pivaloyloxymethyl (Pom) protected precursors 7 and 8 showed even more pronounced activity. All the compounds showed no activity against several non-enveloped enteroviruses, except 4-hydroxybutylamides 2d,g, which inhibited the reproduction of enterovirus A71 with EC₅₀ 50-100 μM, with a non-specific mode of action. The results suggest that the carbohydrate moiety of RAFI nucleosides does not play a crucial role in their antiviral action, and biological activity of the 5-(perylen-3-ylethynyl)uracil scaffold can be effectively modulated by substituents in positions 1 and 3. The high antiviral activity of these new compounds, coupled with low toxicity advocate their potential role in antiviral therapy.

Tick-borne encephalitis in Europe and Russia: Review of pathogenesis, clinical features, therapy, and vaccines

Tick-borne encephalitis (TBE) is an illness caused by tick-borne encephalitis virus (TBEV) infection which is often limited to a febrile illness, but may lead to very aggressive downstream neurological manifestations. The disease is prevalent in forested areas of Europe and northeastern Asia, and is typically caused by infection involving one of three TBEV subtypes, namely the European (TBEV-Eu), the Siberian (TBEV-Sib), or the Far Eastern (TBEV-FE) subtypes. In addition to the three main TBEV subtypes, two other subtypes; i.e., the Baikalian (TBEV-Bkl) and the Himalayan subtype (TBEV-Him), have been described recently. In Europe, TBEV-Eu infection usually results in only mild TBE associated with a mortality rate of <2%. TBEV-Sib infection also results in a generally mild TBE associated with a non-paralytic febrile form of encephalitis, although there is a tendency towards persistent TBE caused by chronic viral infection. TBE-FE infection is considered to induce the most severe forms of TBE. Importantly though, viral subtype is not the sole determinant of TBE severity; both mild and severe cases of TBE are in fact associated with infection by any of the subtypes. In keeping with this observation, the overall TBE mortality rate in Russia is ∼2%, in spite of the fact that TBEV-Sib and TBEV-FE subtypes appear to be inducers of more severe TBE than TBEV-Eu. On the other hand, TBEV-Sib and TBEV-FE subtype infections in Russia are associated with essentially unique forms of TBE rarely seen elsewhere if at all, such as the hemorrhagic and chronic (progressive) forms of the disease. For post-exposure prophylaxis and TBE treatment in Russia and Kazakhstan, a specific anti-TBEV immunoglobulin is currently used with well-documented efficacy, but the use of specific TBEV immunoglobulins has been discontinued in Europe due to concerns regarding antibody-enhanced disease in naïve individuals. Therefore, new treatments are essential. This review summarizes available data on the pathogenesis and clinical features of TBE, plus different vaccine preparations available in Europe and Russia. In addition, new treatment possibilities, including small molecule drugs and experimental immunotherapies are reviewed. The authors caution that their descriptions of approved or experimental therapies should not be considered to be recommendations for patient care.

Virucidal nano-perforator of viral membrane trapping viral RNAs in the endosome

Membrane-disrupting agents that selectively target virus versus host membranes could potentially inhibit a broad-spectrum of enveloped viruses, but currently such antivirals are lacking. Here, we develop a nanodisc incorporated with a decoy virus receptor that inhibits virus infection. Mechanistically, nanodiscs carrying the viral receptor sialic acid bind to influenza virions and are co-endocytosed into host cells. At low pH in the endosome, the nanodiscs rupture the viral envelope, trapping viral RNAs inside the endolysosome for enzymatic decomposition. In contrast, liposomes containing a decoy receptor show weak antiviral activity due to the lack of membrane disruption. The nanodiscs inhibit influenza virus infection and reduce morbidity and mortality in a mouse model. Our results suggest a new class of antivirals applicable to other enveloped viruses that cause irreversible physical damage specifically to virus envelope by viruses' own fusion machine. In conclusion, the lipid nanostructure provides another dimension for antiviral activity of decoy molecules.

Targeting the Achilles Heel of Mosquito-Borne Viruses for Antiviral Therapy

Mosquito-borne viruses encompass a wide range of pathogens, such as dengue and Zika viruses, that often cocirculate geographically. These viruses affect hundreds of millions of people worldwide, yet no clinically approved therapy is currently available for treating these viral infections. Thus, innovative therapies, especially inhibitors with broad antiviral activities against all these viruses, are urgently needed. While traditional therapeutic strategies mainly focus on inhibiting viral replication in a "one lock, one key" manner (e.g., viral protease and polymerase inhibitors), inhibitors targeting virions have recently emerged as a promising approach to achieve broad antiviral activities. Within this approach, Lipid Envelope Antiviral Disruption (LEAD) molecules were shown to broadly inhibit mosquito-borne viruses and other lipid membrane-enveloped viruses. Several LEAD molecules have been demonstrated to act against viral membranes in vitro, some of which have even shown in vivo efficacy to treat mosquito-borne viral infections. This therapeutic potential is further enhanced by molecular engineering to improve the inhibitors' pharmacological properties, laying the foundation for the LEAD antiviral strategy to be explored for possible treatment of mosquito-borne viral infections.

Ramified derivatives of 5-(perylen-3-ylethynyl)uracil-1-acetic acid and their antiviral properties

The propargylamide of N3-Pom-protected 5-(perylen-3-ylethynyl)uracil acetic acid, a universal precursor, was used in a CuAAC click reaction for the synthesis of several derivatives, including three ramified molecules with high activities against tick-borne encephalitis virus (TBEV). Pentaerythritol-based polyazides were used for the assembly of molecules containing 2⋯4 antiviral 5-(perylen-3-ylethynyl)uracil scaffolds, the first examples of polyvalent perylene antivirals. Cluster compounds showed enhanced absorbance, however, their fluorescence was reduced due to self-quenching. Due to the solubility issues, Pom group removal succeeded only for compounds with one peryleneethynyluracil unit. Four compounds, including one ramified cluster 9f, showed remarkable 1⋯3 nM EC₅₀ values against TBEV in cell culture.

Ramified clusters of antiviral perylenylethynyl scaffold were prepared using CuAAC reaction of 5-(perylen-3-ylethynyl)-3-pivaloyloxymethyl-1-(propargylamidomethyl)uracil with azides. Compounds inhibited TBEV reproduction at nanomolar concentrations.

Novel broad spectrum virucidal molecules against enveloped viruses

Viral infections are an important cause of death worldwide. Unfortunately, there is still a lack of antiviral drugs or vaccines for a large number of viruses, and this represents a remarkable challenge particularly for emerging and re-emerging viruses. For this reason, the identification of broad spectrum antiviral compounds provides a valuable opportunity for developing efficient antiviral therapies. Here we report on a class of rhodanine and thiobarbituric derivatives displaying a broad spectrum antiviral activity against seven different enveloped viruses including an HSV-2 acyclovir resistant strain with favorable selectivity indexes. Due to their selective action on enveloped viruses and to their lipid oxidation ability, we hypothesize a mechanism on the viral envelope that affects the fluidity of the lipid bilayer, thus compromising the efficiency of virus-cell fusion and preventing viral entry.