Antiviral Activity In Cell Culture Research Articles

Discovery of potent SARS-CoV-2 nsp3 macrodomain inhibitors uncovers lack of translation to cellular antiviral response.

A strategy for pandemic preparedness is the development of antivirals against a wide set of viral targets with complementary mechanisms of action. SARS-CoV-2 nsp3-mac1 is a viral macrodomain with ADP-ribosylhydrolase activity, which counteracts host immune response. Targeting the virus' immunomodulatory functionality offers a differentiated strategy to inhibit SARS-CoV-2 compared to approved therapeutics, which target viral replication directly. Here we report a fragment-based lead generation campaign guided by computational approaches. We discover tool compounds which inhibit nsp3-mac1 activity at low nanomolar concentrations, and with responsive structure-activity relationships, high selectivity, and drug-like properties. Using our inhibitors, we show that inhibition of nsp3-mac1 increases ADP-ribosylation, but surprisingly does not translate to demonstrable antiviral activity in cell culture and iPSC-derived pneumocyte models. Further, no synergistic activity is observed in combination with interferon gamma, a main protease inhibitor, nor a papain-like protease inhibitor. Our results question the extent to which targeting modulation of innate immunity-driven ADP-ribosylation can influence SARS-CoV-2 replication. Moreover, these findings suggest that nsp3-mac1 might not be a suitable target for antiviral therapeutics development.

An Elastin-like Polypeptide-fusion peptide targeting capsid-tegument interface as an antiviral against cytomegalovirus infection

The tegument protein pp150 of Human Cytomegalovirus (HCMV) is known to be essential for the final stages of virus maturation and mediates its functions by interacting with capsid proteins. Our laboratory has previously identified the critical regions in pp150 important for pp150-capsid interactions and designed peptides similar in sequence to these regions, with a goal to competitively inhibit capsid maturation. Treatment with a specific peptide (PepCR2 or P10) targeted to pp150 conserved region 2 led to a significant reduction in murine CMV (MCMV) growth in cell culture, paving the way for in vivo testing in a mouse model of CMV infection. However, the general pharmacokinetic parameters of peptides, including rapid degradation and limited tissue and cell membrane permeability, pose a challenge to their successful use in vivo. Therefore, we designed a biopolymer-stabilized elastin-like polypeptide (ELP) fusion construct (ELP-P10) to enhance the bioavailability of P10. Antiviral efficacy and cytotoxic effects of ELP-P10 were studied in cell culture, and pharmacokinetics, biodistribution, and antiviral efficacy were studied in a mouse model of CMV infection. ELP-P10 maintained significant antiviral activity in cell culture, and this conjugation significantly enhanced P10 bioavailability in mouse tissues. The fluorescently labeled ELP-P10 accumulated to higher levels in mouse liver and kidneys as compared to the unconjugated P10. Moreover, viral titers from vital organs of MCMV-infected mice indicated a significant reduction of virus load upon ELP-P10 treatment. Therefore, ELP-P10 has the potential to be developed into an effective antiviral against CMV infection.

Certification of a pharmacopoeial reference standard for potency testing of recombinant interferon α-2b

SCIENTIFIC RELEVANCE. Potency testing of recombinant interferons requires a reference standard. The availability of International Standards (ISs) that are commonly used to assess the quality of recombinant interferons is currently limited. Therefore, the quality of interferons should be assessed using pharmacopoeial reference standards (RSs) certified using ISs (if available).AIM. This study aimed to certify a pharmacopoeial RS for potency testing of recombinant interferon α-2b.MATERIALS AND METHODS. The potency determination involved comparing the inhibition of the virus-induced cytopathic effect observed in cell culture with the candidate RS and the WHO International Standard for Human rDNA-derived interferon α-2b. The study used A-549 and MDBK cell lines with encephalomyocarditis (EMC) and vesicular stomatitis (VSV) viruses. The authors followed the requirements of the State Pharmacopoeia of the Russian Federation (Cell-Culture Bioassays for Interferon Products, OFS.1.7.2.0002.15). The results were recorded using instrumental and visual methods. The calculations used mathematical statistics. To factor in the influence of intermediate precision, the authors applied Student’s t-test.RESULTS. The authors developed a certification programme and procedure and certified the pharmacopoeial RS for recombinant human interferon α-2b (rhIFN α-2b) to identify the corresponding medicinal products (by virus neutralisation) and test their potency (by antiviral activity in cell culture). Upon receipt, the candidate RS was verified for compliance with regulatory specifications. According to the test results, the potency of the candidate pharmacopoeial RS was 4.47×108 IU/mL, and the expanded uncertainty was 8.12×107 IU/mL, with a coverage factor of k=2 and a confidence level of 95%. The pharmacopoeial RS for rhIFN α-2b was considered to have the same shelf-life period as the corresponding medicinal products if stored at a temperature not higher than –40 ºC. When thawed, the pharmacopoeial RS for rhIFN α-2b can be stored at a temperature of 2–8 ºC for up to 1 month.CONCLUSIONS. Upon certification for potency testing, the pharmacopoeial RS for rhIFN α-2b has been included in the Register of Reference Standards of the Russian Pharmacopoeia as Recombinant Human Interferon α-2b (Potency) FSO.3.2.00455. The introduction of this pharmacopoeial RS will help to conduct the identification and potency testing of all Russian interferon α-2b products at an appropriate scientific and methodological level. As a result, Russian pharmaceutical manufacturers and quality control agencies will no longer depend on imported ISs.

Non-coding RNAs derived from the foot-and-mouth disease virus genome trigger broad antiviral activity against coronaviruses.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of a potentially severe respiratory disease, the coronavirus disease 2019 (COVID-19), an ongoing pandemic with limited therapeutic options. Here, we assessed the anti-coronavirus activity of synthetic RNAs mimicking specific domains in the non-coding regions of the foot-and-mouth disease virus (FMDV) genome (ncRNAs). These molecules are known to exert broad-spectrum antiviral activity in cell culture, mice and pigs effectively triggering the host innate immune response. The ncRNAs showed potent antiviral activity against SARS-CoV-2 after transfection in human intestinal Caco-2 and lung epithelium Calu-3 2B4 cells. When the in vivo efficacy of the FMDV ncRNAs was assessed in K18-hACE2 mice, administration of naked ncRNA before intranasal SARS-CoV-2 infection significantly decreased the viral load and the levels of pro-inflammatory cytokines in the lungs compared with untreated infected mice. The ncRNAs were also highly efficacious when assayed against common human HCoV-229E and porcine transmissible gastroenteritis virus (TGEV) in hepatocyte-derived Huh-7 and swine testis ST cells, respectively. These results are a proof of concept of the pan-coronavirus antiviral activity of the FMDV ncRNAs including human and animal divergent coronaviruses and potentially enhance our ability to fight future emerging variants.

Effect of different carbon sources on callus formation, pigment accumulation, and antiviral activity in cell cultures of Euphorbia milii

Effect of different carbon sources on callus formation, pigment accumulation, and antiviral activity in cell cultures of Euphorbia milii

Design, synthesis, and biological evaluation of novel double-winged galloyl derivatives as HIV-1 RNase H inhibitors

Human immunodeficiency virus (HIV) reverse transcriptase (RT)-associated ribonuclease H (RNase H) remains as the only enzyme encoded within the viral genome not clinically validated as an antiviral target. We have previously reported that the galloyl derivative II-25 had RNase H inhibitory activity in enzymatic assays but showed weak antiviral activity in phenotypic assays due its large polarity and poor membrane permeability. In this report, we report on a series of II-25 derivatives, obtained by addition of different hydrophobic moieties (“the wings”) at the C-2 and C-3 positions of the piperazine ring that showed improved RNase H inhibitory activity. Six compounds showed strong inhibitory activity and were found to be more potent than β-thujaplicinol in enzymatic assays. The most potent compound was IA-6 and exhibited the best inhibitory activity (IC50 = 0.067 ± 0.02 μM). IA-6 was around 11 and 30 times more potent than II-25 and β-thujaplicinol, respectively. Molecular modeling studies predict a strong hydrophobic interaction between the furylmethylaminyl group of IA-6 and the side chain of His539, explaining the potent HIV-1 RNase H inhibition. Unfortunately, none of the derivatives showed significant antiviral activity in cell culture. It is worth emphasizing that most of the obtained compounds show low cytotoxicity (CC50 > 20 μM), which confirms the significance of identifying galloyl derivatives as valuable leads for further optimization.

The Basicity Makes the Difference: Improved Canavanine-Derived Inhibitors of the Proprotein Convertase Furin.

Furin activates numerous viral glycoproteins, and its inhibition prevents virus replication and spread. Through the replacement of arginine by the less basic canavanine, new inhibitors targeting furin in the trans-Golgi network were developed. These inhibitors exert potent antiviral activity in cell culture with much lower toxicity than arginine-derived analogues, most likely due to their reduced protonation in the blood circulation. Thus, despite its important physiological functions, furin might be a suitable antiviral drug target.

Broad-Spectrum Antiviral Activity of 3'-Deoxy-3'-Fluoroadenosine against Emerging Flaviviruses.

Emerging flaviviruses are causative agents of severe and life-threatening diseases, against which no approved therapies are available. Among the nucleoside analogues, which represent a promising group of potentially therapeutic compounds, fluorine-substituted nucleosides are characterized by unique structural and functional properties. Despite having first been synthesized almost 5 decades ago, they still offer new therapeutic opportunities as inhibitors of essential viral or cellular enzymes active in nucleic acid replication/transcription or nucleoside/nucleotide metabolism. Here, we report evaluation of the antiflaviviral activity of 28 nucleoside analogues, each modified with a fluoro substituent at different positions of the ribose ring and/or heterocyclic nucleobase. Our antiviral screening revealed that 3'-deoxy-3'-fluoroadenosine exerted a low-micromolar antiviral effect against tick-borne encephalitis virus (TBEV), Zika virus, and West Nile virus (WNV) (EC50 values from 1.1 ± 0.1 μM to 4.7 ± 1.5 μM), which was manifested in host cell lines of neural and extraneural origin. The compound did not display any measurable cytotoxicity up to concentrations of 25 μM but had an observable cytostatic effect, resulting in suppression of cell proliferation at concentrations of >12.5 μM. Novel approaches based on quantitative phase imaging using holographic microscopy were developed for advanced characterization of antiviral and cytotoxic profiles of 3'-deoxy-3'-fluoroadenosine in vitro In addition to its antiviral activity in cell cultures, 3'-deoxy-3'-fluoroadenosine was active in vivo in mouse models of TBEV and WNV infection. Our results demonstrate that fluoro-modified nucleosides represent a group of bioactive molecules with excellent potential to serve as prospective broad-spectrum antivirals in antiviral research and drug development.

Promising antiviral protease inhibitors

Coronavirus With no vaccine or proven effective drug against the virus that causes coronavirus disease 2019 (COVID-19), scientists are racing to find clinical antiviral treatments. A promising drug target is the viral main protease Mpro, which plays a key role in viral replication and transcription. Dai et al. designed two inhibitors, 11a and 11b, based on analyzing the structure of the Mpro active site. Both strongly inhibited the activity of Mpro and showed good antiviral activity in cell culture. Compound 11a had better pharmacokinetic properties and low toxicity when tested in mice and dogs, suggesting that this compound is a promising drug candidate. Science , this issue p. [1331][1] [1]: /lookup/doi/10.1126/science.abb4489

Aspects of a Methodological Approach to Determination of Interferon Alpha Specific Activity

Specific antiviral activity is one of the key indicators characterising pharmaceutical quality and pharmacological efficacy of interferon alpha products (IFN-α). Specific activity is determined using a bioassay measuring antiviral activity in cell culture. The aim of the study was to select the most appropriate conditions for in vitro determination of IFN-α product specific activity. Materials and methods: Vero, MDBK, Hep-2, and A-549 homologous and heterologous cell cultures, as well as vesicular stomatitis Indiana virus (VSV) and murine encephalomyocarditis (EMC) virus at a dose of 100 TCD50 /0.1 mL were used for determination of specific antiviral activity. The international reference standard of recombinant interferon alpha-2b activity (Interferon alpha 2b, human, rDNA, E. coli-derived, 2nd WHO International Standard, 1999, NIBSC Code No. 95/566) and human recombinant interferon alpha 2b in the form of solution (batch No. 040214, Pharmapark LLC, Russia) were used as IFN-α samples. Results: the analysis of the obtained data helped to determine: the combinations of cell lines and the indicator virus most sensitive to IFN-α; the optimal concentration of fetal serum in the medium, and the optimal time parameters; the preferred method of reporting test results. Conclusions: the following test conditions were found to be optimal: the MDBK/VSV and Hep-2/EMC combinations proved to be the most sensitive to IFN-α; the optimal period of interferon and cell culture incubation—24 hours; the optimal concentration of fetal bovine serum in the culture medium used for diluting interferon products—2–5%. The instrumental procedure is preferred for reporting the results of interferon antiviral activity determination, because it is up-to-date, reliable, accurate and time-efficient.

6-Arylthio-3-hydroxypyrimidine-2,4-diones potently inhibited HIV reverse transcriptase-associated RNase H with antiviral activity

Human immunodeficiency virus (HIV) reverse transcriptase (RT) associated ribonuclease H (RNase H) remains the only virally encoded enzymatic function not targeted by current drugs. Although a few chemotypes have been reported to inhibit HIV RNase H in biochemical assays, their general lack of significant antiviral activity in cell culture necessitates continued efforts in identifying highly potent RNase H inhibitors to confer antiviral activity. We report herein the design, synthesis, biochemical and antiviral evaluations of a new 6-arylthio subtype of the 3-hydroxypyrimidine-2,4-dione (HPD) chemotype. In biochemical assays these new analogues inhibited RT RNase H in single-digit nanomolar range without inhibiting RT polymerase (pol) at concentrations up to 10 μM, amounting to exceptional biochemical inhibitory selectivity. Many analogues also inhibited integrase strand transfer (INST) activity in low to sub micromolar range. More importantly, most analogues inhibited HIV in low micromolar range without cytotoxicity. In the end, compound 13j (RNase H IC50 = 0.005 μM; RT pol IC50 = 10 μM; INST IC50 = 4.0 μM; antiviral EC50 = 7.7 μM; CC50 > 100 μM) represents the best analogues within this series. These results characterize the new 6-arylthio-HPD subtype as a promising scaffold for HIV RNase H inhibitor discovery.

Defensins in Viral Infection and Pathogenesis.

α, β, and θ defensins are effectors of the innate immune system with potent antibacterial, antiviral, and antifungal activity. Defensins have direct antiviral activity in cell culture, with varied mechanisms for individual viruses, although some common themes have emerged. In addition, defensins have potent immunomodulatory activity that can alter innate and adaptive immune responses to viral infection. In some cases, there is evidence for paradoxical escape from defensin neutralization or enhancement of viral infection. The direct and indirect activities of defensins have led to their development as therapeutics and vaccine components. The major area of investigation that continues to lag is the connection between the effects of defensins in cell culture models and viral pathogenesis in vivo. Model systems to study defensin biology, including more physiologic models designed to bridge this gap, are also discussed.

First-in-human application of the novel hepatitis B and hepatitis D virus entry inhibitor myrcludex B

Myrcludex B is a first-in-class compound, which blocks entry of hepatitis B and D virus into hepatocytes in vitro and in animal models. Based on the required preclinical data we aimed to translate this compound into the first application in humans. Single ascending doses of myrcludex B, a 47 amino acid peptide, were administered up to 20mg intravenously and 10mg subcutaneously in a prospective open first-in-human, phase I clinical trial to 36 healthy volunteers. Safety, tolerability and plasma concentrations of myrcludex B were assessed and a pharmacokinetic model was derived. Myrcludex B was well tolerated and no serious or relevant AEs representing off-target effects, and no immunogenic effects were observed up to the highest applied dose of 20mg (intravenously). Myrcludex B showed dose-dependent pharmacokinetics, best described by a 2-compartment target-mediated drug disposition model. Bioavailability of the subcutaneous application was large (85%). Interindividual variability was moderate. The pharmacokinetic model suggested that subcutaneous doses of 10mg and above reach a target saturation of over 80% for at least 15h. Myrcludex B showed excellent tolerability up to high doses. Pharmacologic properties followed a 2-compartment target-mediated drug disposition model. These findings are vital for planning of further multiple dose efficacy trials in patients. After showing antiviral activity in cell culture and animal models, myrcludex B, a new drug intended for the treatment of hepatitis B and D, has been administered the first time in humans. Healthy volunteers received the drug intravenously and subcutaneously up to high doses (20mg). The drug was well tolerated and the characteristics of the drug determining its way in the human body could be described. These results will allow testing myrcludex B in hepatitis B and D patients.

Tannic Acid Inhibits Hepatitis C Virus Entry into Huh7.5 Cells.

Chronic infection with the hepatitis C virus (HCV) is a cause of cirrhosis and hepatocellular carcinoma worldwide. Although antiviral therapy has dramatically improved recently, a number of patients remain untreated and some do not clear infection with treatment. Viral entry is an essential step in initiating and maintaining chronic HCV infections. One dramatic example of this is the nearly 100% infection of newly transplanted livers in patients with chronic hepatitis C. HCV entry inhibitors could play a critical role in preventing HCV infection of newly transplanted livers. Tannic acid, a polymer of gallic acid and glucose molecules, is a plant-derived polyphenol that defends some plants from insects and microbial infections. It has been shown to have a variety of biological effects, including antiviral activity, and is used as a flavoring agent in foods and beverages. In this study, we demonstrate that tannic acid is a potent inhibitor of HCV entry into Huh7.5 cells at low concentrations (IC50 5.8 μM). It also blocks cell-to-cell spread in infectious HCV cell cultures, but does not inhibit HCV replication following infection. Moreover, experimental results indicate that tannic acid inhibits an early step of viral entry, such as the docking of HCV at the cell surface. Gallic acid, tannic acid’s structural component, did not show any anti-HCV activity including inhibition of HCV entry or replication at concentrations up to 25 μM. It is possible the tannin structure is related on the effect on HCV inhibition. Tannic acid, which is widely distributed in plants and foods, has HCV antiviral activity in cell culture at low micromolar concentrations, may provide a relative inexpensive adjuvant to direct-acting HCV antivirals and warrants future investigation.

An integrated biological approach to guide the development of metal-chelating inhibitors of influenza virus PA endonuclease.

The influenza virus PA endonuclease, which cleaves capped cellular pre-mRNAs to prime viral mRNA synthesis, is a promising target for novel anti-influenza virus therapeutics. The catalytic center of this enzyme resides in the N-terminal part of PA (PA-Nter) and contains two (or possibly one or three) Mg(2+) or Mn(2+) ions, which are critical for its catalytic function. There is great interest in PA inhibitors that are optimally designed to occupy the active site and chelate the metal ions. We focused here on a series of β-diketo acid (DKA) and DKA-bioisosteric compounds containing different scaffolds, and determined their structure-activity relationship in an enzymatic assay with PA-Nter, in order to build a three-dimensional pharmacophore model. In addition, we developed a molecular beacon (MB)-based PA-Nter assay that enabled us to compare the inhibition of Mn(2+) versus Mg(2+), the latter probably being the biologically relevant cofactor. This real-time MB assay allowed us to measure the enzyme kinetics of PA-Nter or perform high-throughput screening. Several DKA derivatives were found to cause strong inhibition of PA-Nter, with IC50 values comparable to that of the prototype L-742,001 (i.e., below 2 μM). Among the different compounds tested, L-742,001 appeared unique in having equal activity against either Mg(2+) or Mn(2+). Three compounds ( 10: , with a pyrrole scaffold, and 40: and 41: , with an indole scaffold) exhibited moderate antiviral activity in cell culture (EC99 values 64-95 μM) and were proven to affect viral RNA synthesis. Our approach of integrating complementary enzymatic, cellular, and mechanistic assays should guide ongoing development of improved influenza virus PA inhibitors.

Strain-specific antiviral activity of iminosugars against human influenza A viruses.

ObjectivesDrugs that target host cell processes can be employed to complement drugs that specifically target viruses, and iminosugar compounds that inhibit host α-glucosidases have been reported to show antiviral activity against multiple viruses. Here the effect and mechanism of two iminosugar α-glucosidase inhibitors, N-butyl-deoxynojirimycin (NB-DNJ) and N-nonyl-deoxynojirimycin (NN-DNJ), on human influenza A viruses was examined.MethodsThe viruses examined were a recently circulating seasonal influenza A(H3N2) virus strain A/Brisbane/10/2007, an older H3N2 strain A/Udorn/307/72, and A/Lviv/N6/2009, a strain representative of the currently circulating pandemic influenza A(H1N1)pdm09 virus.ResultsThe inhibitors had the strongest effect on Brisbane/10 and NN-DNJ was more potent than NB-DNJ. Both compounds showed antiviral activity in cell culture against three human influenza A viruses in a strain-specific manner. Consistent with its action as an α-glucosidase inhibitor, NN-DNJ treatment resulted in an altered glycan processing of influenza haemagglutinin (HA) and neuraminidase (NA), confirmed by MS. NN-DNJ treatment was found to reduce the cell surface expression of the H3 subtype HA. The level of sialidase activity of NA was reduced in infected cells, but the addition of exogenous sialidase to the cells did not complement the NN-DNJ-mediated inhibition of virus replication. Using reassortant viruses, the drug susceptibility profile was determined to correlate with the origin of the HA.ConclusionsNN-DNJ inhibits influenza A virus replication in a strain-specific manner that is dependent on the HA.

Selective inhibition of hepatitis C virus infection by hydroxyzine and benztropine.

Hepatitis C virus (HCV) infection is a major biomedical problem worldwide as it causes severe liver disease in millions of humans around the world. Despite the recent approval of specific drugs targeting HCV replication to be used in combination with alpha interferon (IFN-α) and ribavirin, there is still an urgent need for pangenotypic, interferon-free therapies to fight this genetically diverse group of viruses. In this study, we used an unbiased screening cell culture assay to interrogate a chemical library of compounds approved for clinical use in humans. This system enables identifying nontoxic antiviral compounds targeting every aspect of the viral life cycle, be the target viral or cellular. The aim of this study was to identify drugs approved for other therapeutic applications in humans that could be effective components of combination therapies against HCV. As a result of this analysis, we identified 12 compounds with antiviral activity in cell culture, some of which had previously been identified as HCV inhibitors with antiviral activity in cell culture and had been shown to be effective in patients. We selected two novel HCV antivirals, hydroxyzine and benztropine, to characterize them by determining their specificity and genotype spectrum as well as by defining the step of the replication cycle targeted by these compounds. We found that both compounds effectively inhibited viral entry at a postbinding step of genotypes 1, 2, 3, and 4 without affecting entry of other viruses.

Dead-end complexes contribute to the synergistic inhibition of HIV-1 RT by the combination of rilpivirine, emtricitabine, and tenofovir

The single tablet regimen of the nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) tenofovir disoproxil fumarate (TDF), emtricitabine (FTC), and the non-nucleoside reverse transcriptase inhibitor (NNRTI) rilpivirine (RPV) is approved for the treatment of HIV-1 infection in treatment-naïve adults. Previous studies have shown that two-drug combinations of these drugs show additive to synergistic HIV-1 antiviral activity in cell culture. In this study, two-drug combinations of tenofovir (TFV)+FTC, RPV+TFV, and RPV+FTC inhibited HIV-1 replication in cell culture with strong synergy and no evidence of antagonism. The triple drug combination of RPV+FTC+TFV displayed moderate synergy comparable to efavirenz (EFV)+FTC+TFV. The formation of dead-end complexes (DEC) of HIV-1 reverse transcriptase (RT), NRTI chain-terminated primer/template, and the next complementary nucleotide or NNRTIs was studied using gel mobility shift assays. DEC formation was seen with TFV-terminated DNA primer/template, HIV-1 RT, and FTC-triphosphate (TP) in addition to the natural nucleotide dCTP, thus stabilizing chain-termination. The NNRTI RPV also formed DEC-like complexes with TFV- and FTC-monophosphate (MP)-terminated DNA primer/templates and HIV-1 RT, and stabilized chain-termination by both NRTIs. Overall, the combinations of RPV, FTC, and TFV inhibit HIV-1 replication with moderate to strong synergy. This may be partially explained by enhanced DEC formation of NRTI chain-terminated DNA primer/template and HIV-1 RT in the presence of the other drugs in the combination, leading to more stable chain-termination and replication inhibition by NRTIs.

Thiazolidinone–Peptide Hybrids as Dengue Virus Protease Inhibitors with Antiviral Activity in Cell Culture

The protease of dengue virus is a promising target for antiviral drug discovery. We here report a new generation of peptide-hybrid inhibitors of dengue protease that incorporate N-substituted 5-arylidenethiazolidinone heterocycles (rhodanines and thiazolidinediones) as N-terminal capping groups of the peptide moiety. The compounds were extensively characterized with respect to inhibition of various proteases, inhibition mechanisms, membrane permeability, antiviral activity, and cytotoxicity in cell culture. A sulfur/oxygen exchange in position 2 of the capping heterocycle (thiazolidinedione-capped vs rhodanine-capped peptide hybrids) has a significant effect on these properties and activities. The most promising in vitro affinities were observed for thiazolidinedione-based peptide hybrids containing hydrophobic groups with Ki values between 1.5 and 1.8 μM and competitive inhibition mechanisms. Rhodanine-capped peptide hybrids with hydrophobic substituents have, in correlation with their membrane permeability, a more pronounced antiviral activity in cell culture than the thiazolidinediones.

Regioselective synthesis of 6-substituted-2-amino-5-bromo-4(3H)-pyrimidinones and evaluation of their antiviral activity

A series of 2-amino-5-bromo-4(3H)-pyrimidinone derivatives bearing different substituents at the C-6 position were synthesized using a highly regioselective lithiation–substitution protocol, and the effect of structural variation at the C-6 position on their antiviral activity in cell culture was evaluated. Although some of the derivatives were found to be active against various virus strains, they were effective only close to their toxicity threshold.