Broad-Spectrum Flavivirus Inhibitors: a Medicinal Chemistry Point of View

Dengue Virus Inhibitors as Potential Broad-Spectrum Flavivirus Inhibitors

Background. Flaviviruses spread from endemic to non-endemic areas, causing illness in millions of people worldwide. The lack of effective therapies and the rapid expansion of flaviviral infections worldwide emphasize the importance of finding effective antivirals to treat such diseases. Objectives. To find out the potential broad-spectrum flavivirus inhibitors among previously reported inhibitors of DENV2/DENV4. Methods. The cytotoxicity of compounds was tested using WST-1 assay. The compounds were tested for their ability to inhibit the infection of DENV2, ZIKV, KUNV, and TBEV, and the most active compounds were also analyzed using the replicon-based assay. Interactions of one of the identified inhibitors with possible viral targets were studied using molecular dynamics simulations. Results. Two out of eight previously reported DENV2/DENV4 inhibitors demonstrated the ability to inhibit all studied viruses at low micromolar concentrations. Compound C6 demonstrated the ability to inhibit both DENV2 and TBEV. Compounds C1 (lycorine), C3 (mycophenolic acid), and C7 (vidarabine) were demonstrated as inhibitors of TBEV infection for the first time. Conclusions. Several compounds, previously described as inhibitors of DENV, are also able to inhibit other flaviviruses. This work is the first report on the anti-TBEV activity of lycorine (C1) and mycophenolic acid (C3), as well as vidarabine (C7). In addition, this is the first experimental confirmation of the antiviral activity of compound C5 and the lack of detectable antiviral activity of compound C8, demonstrating the necessity of experimental verification of the computational predictions.

Advances in drug discovery of flavivirus NS2B-NS3pro serine protease inhibitors for the treatment of Dengue, Zika, and West Nile viruses

Flaviviruses are vector-borne RNA viruses that seriously threaten global public health due to their high transmission index in humans, mainly in endemic areas. They spread infectious diseases that affect approximately 400 million people globally, primarily in developing countries struggling with persistent epidemic diseases. Viral infections manifest as hemorrhagic fever, encephalitis, congenital abnormalities, and fatalities. Despite nearly two decades of drug discovery campaigns, researchers have not identified promising lead compounds for clinical trials to treat or prevent flavivirus infections. Although scientists have made substantial progress through drug discovery approaches and vaccine development, resolving this complex issue might need some time. New therapeutic agents that can safely and effectively target key components of flaviviruses need to be identified. NS2B-NS3pro is an extensively studied pharmacological target among viral proteases. It plays a key role in the viral replication cycle by cleaving the polyprotein of flaviviruses and triggering the formation of structural and non-structural proteins. In this review, studies published from 2014 to 2023 were examined, and the specificity profile of compounds targeting NS2B-NS3 pro proteases for treating flavivirus infections was focused on. Additionally, the latest advancements in clinical trials were discussed. This article might provide information on the prospects of this promising pharmacological target.

Inhibitory activity of Euterpe oleracea Mart. fruit extract in West Nile virus infection

West Nile virus (WNV) is a neurovirulent arbovirus whose epidemic capacity is enhanced by the wide occurrence of competent vectors and susceptible avian amplifying hosts. In this study, we investigated the antiviral potential of Euterpe oleracea Mart. fruit extract (EoFE) in WNV infection of monkey kidney (Vero) cell cultures. A chromatographic authentication of the extract revealed a typical two-peak fingerprint attributable to the major anthocyanins of the fruit. As assessed by plaque assays in Vero cells, the extract showed a significant concentration-dependent antiviral effect when present throughout the infection procedure, reaching a maximum inhibition of 66.8 % at 2 mg/mL without significant cytotoxicity or direct action on virus particles. A time-of-addition assay revealed that this anti-WNV effect was mostly exerted after virus entry, as incubation of Vero cells with EoFE before or during virus addition resulted in a nonsignificant decrease of infection efficiency. These results demonstrated a promising potential of EoFE in inhibiting WNV infection that can be further explored as an antiviral strategy.

A conserved role for AKT in the replication of emerging flaviviruses in vertebrates and vectors

One third of all emerging infectious diseases are vector-borne, with no licensed antiviral therapies available against any vector-borne viruses. Zika virus and Usutu virus are two emerging flaviviruses transmitted primarily by mosquitoes. These viruses modulate different host pathways, including the PI3K/AKT/mTOR pathway. Here, we report the effect on ZIKV and USUV replication of two AKT inhibitors, Miransertib (ARQ-092, allosteric inhibitor) and Capivasertib (AZD5363, competitive inhibitor) in different mammalian and mosquito cell lines. Miransertib showed a stronger inhibitory effect against ZIKV and USUV than Capivasertib in mammalian cells, while Capivasertib showed a stronger effect in mosquito cells. These findings indicate that AKT plays a conserved role in flavivirus infection, in both the vertebrate host and invertebrate vector. Nevertheless, the specific function of AKT may vary depending on the host species. These findings indicate that AKT may be playing a conserved role in flavivirus infection in both, the vertebrate host and the invertebrate vector. However, the specific function of AKT may vary depending on the host species. A better understanding of virus-host interactions is therefore required to develop new treatments to prevent human disease and new approaches to control transmission by insect vectors.

Small Molecule Drugs Targeting Viral Polymerases

Small molecules that specifically target viral polymerases-crucial enzymes governing viral genome transcription and replication-play a pivotal role in combating viral infections. Presently, approved polymerase inhibitors cover nine human viruses, spanning both DNA and RNA viruses. This review provides a comprehensive analysis of these licensed drugs, encompassing nucleoside/nucleotide inhibitors (NIs), non-nucleoside inhibitors (NNIs), and mutagenic agents. For each compound, we describe the specific targeted virus and related polymerase enzyme, the mechanism of action, and the relevant bioactivity data. This wealth of information serves as a valuable resource for researchers actively engaged in antiviral drug discovery efforts, offering a complete overview of established strategies as well as insights for shaping the development of next-generation antiviral therapeutics.

An equine iPSC-based phenotypic screening platform identifies pro- and anti-viral molecules against West Nile virus

Outbreaks of West Nile virus (WNV) occur periodically, affecting both human and equine populations. There are no vaccines for humans, and those commercialised for horses do not have sufficient coverage. Specific antiviral treatments do not exist. Many drug discovery studies have been conducted, but since rodent or primate cell lines are normally used, results cannot always be transposed to horses. There is thus a need to develop relevant equine cellular models. Here, we used induced pluripotent stem cells to develop a new in vitro model of WNV-infected equine brain cells suitable for microplate assay, and assessed the cytotoxicity and antiviral activity of forty-one chemical compounds. We found that one nucleoside analog, 2'C-methylcytidine, blocked WNV infection in equine brain cells, whereas other compounds were either toxic or ineffective, despite some displaying anti-viral activity in human cell lines. We also revealed an unexpected proviral effect of statins in WNV-infected equine brain cells. Our results thus identify a potential lead for future drug development and underscore the importance of using a tissue- and species-relevant cellular model for assessing the activity of antiviral compounds.

Exploring the Targets of Dengue Virus and Designs of Potential Inhibitors

BACKGROUND

Dengue, a mosquito-borne viral disease spread by the dengue virus (DENV), has become one of the most alarming health issues in the global scenario in recent days. The risk of infection by DENV is mostly high in tropical and subtropical areas of the world. The mortality rate of patients affected with DENV is ever-increasing, mainly due to a lack of anti-dengue viral-specific synthetic drug components.

INTRODUCTION

Repurposing synthetic drugs has been an effective tool in combating several pathogens, including DENV. However, only the Dengvaxia vaccine has been developed so far to fight against the deadly disease despite the grave situation, mainly because of the limitations of understanding the actual pathogenicity of the disease.

METHODS

To address this particular issue and explore the actual disease pathobiology, several potential targets, like three structural proteins and seven non-structural (NS) proteins, along with their inhibitors of synthetic and natural origin, have been screened using docking simulation.

RESULTS

Exploration of these targets, along with their inhibitors, has been extensively studied in culmination with molecular docking-based screening to potentiate the treatment.

CONCLUSION

These screened inhibitors could possibly be helpful for the designing of new congeneric potential compounds to combat dengue fever and its complications.

Utility of an In-Vitro Micro-Neutralizing Test in Comparison to a Plaque Reduction Neutralization Test for Dengue Virus, Japanese Encephalitis Virus, and Zika Virus Serology and Drug Screening

Flavivirus infections, including dengue virus (DENV), Japanese encephalitis virus (JEV), and Zika virus (ZIKV), present significant global public health challenges. For successful vaccine design, the assessment of neutralizing antibody activity requires reliable and robust methodologies for determining antibody titers. Although the plaque reduction neutralization test (PRNT) is commonly acknowledged as the gold standard, it has limitations in terms of time and cost, and its usage may be limited in resource-limited settings. To address these challenges, we introduced the micro-neutralization test (MNT) as a simplified alternative to the PRNT. The MNT employs a 96-well plate format, conducts microscale neutralization assays, and assesses cell viability by dissolving cells to create a uniform color solution, which is measured with a spectrometer. In this study, we evaluated the utility of the MNT by contrasting the end-point titers of the MNT and PRNT using 4 monoclonal antibodies, 15 non-human primate serum samples, and 2 therapeutic drug candidates across flaviviruses. The results demonstrated a strong correlation between the MNT and PRNT titers, affirming the robustness and reproducibility of the MNT for evaluating control measures against flaviviruses. This research contributes valuable insights toward the development of a cost-effective antibody titer testing approach that is particularly suitable for resource-limited settings.

Discovery of ZFD-10 of a pyridazino[4,5-b]indol-4(5H)-one derivative as an anti-ZIKV agent and a ZIKV NS5 RdRp inhibitor

Zika virus (ZIKV) infection is associated with the birth defect microcephaly and Guillain-Barré syndrome in adults. There is no approved vaccine or specific antiviral agent against ZIKV. ZFD-10, a novel structural skeleton of 1H-pyridazino[4,5-b]indol-4(5H)-one, was firstly synthesized and discovered to be a potent anti-ZIKV inhibitor with very low cytotoxicity. ZFD-10's anti-ZIKV potency is independent of cell lines and ZFD-10 mainly targets the post-entry stages of ZIKV life cycle. Time-of-addition and time-of-withdrawal assays showed that 10 μM ZFD-10 displayed the ability to decrease mainly at the RNA level and weakly the viral progeny particle load. Furthermore, ZFD-10 could protect ZIKV NS5 from thermal unfolding and aggregation and increase the Tagg value of ZIKV NS5 protein from 44.6 to 49.3 °C, while ZFD-10 dose-dependently inhibits ZIKV NS5 RdRp activity using in vitro RNA polymerase assays. Molecular docking study suggests that ZFD-10 affects RdRp enzymatic function through interfering with the fingers and thumb subdomains. These results supported that ZFD-10's cell-based anti-ZIKV activity is related to its anti-RdRp activity of ZIKV NS5. The in vivo anti-ZIKV study shows that the middle-dose (4.77 mg/kg/d) of ZFD-10 protected mice from ZIKV infection and the viral loads of the blood, liver, kidney and brain in the middle-dose and high-dose (9.54 mg/kg/d) were significantly reduced compared to those of the ZIKV control. These results confirm that ZFD-10 has a certain antiviral effect against ZIKV infection in vivo.

Functionalized sulfonyl anthranilic acid derivatives inhibit replication of all the four dengue serotypes

Dengue virus (DENV), a mosquito-borne flavivirus, continues to be a major public health threat in many countries and no approved antiviral therapeutics are available yet. In this work, we designed and synthesized a series of sulfonyl anthranilic acid (SAA) derivatives using a ligand-based scaffold morphing approach of the 2,1-benzothiazine 2,2-dioxide core, previously used by us to develop DENV polymerase inhibitors resulting devoid of any cell-based antiviral activity. Several derivatives based on the new SAA chemotype exhibited potent inhibition against DENV infection in the cell-based assay but did not inhibit DENV NS5 polymerase activity in the in vitro de novo initiation and elongation assays. Notably, best compounds 26 and 39 showed EC50 values in the range of 0.54-1.36 μM against cells infected with the four dengue serotypes (DENV-1-4). Time-of-drug-addition assay revealed that analogue 26 is a post-entry replication inhibitor that appears to be specific for cells of primate origin, implicating a host target with a high barrier to resistance. In conclusion, SAA derivatives offer a valuable starting point for developing effective Dengue antiviral therapeutics.

Antiviral effects of the fused tricyclic derivatives of indoline and imidazolidinone on ZIKV infection and RdRp activities of ZIKV and DENV

The prevalence and ravages of Zika virus (ZIKV) seriously endanger human health, especially causing significant neurological defects in both neonates as pediatric microcephaly and adults as Guillain-Barré syndrome. In this work, we studied anti-ZIKV effects of the fused tricyclic derivatives of indoline and imidazolidinone and discovered that some of them are valuable leads for drug discovery of anti-ZIKV agents. The current results show that certain compounds are broad-spectrum inhibitors of ZIKV- and dengue virus (DENV)-infection while distinctive compounds are selective ZIKV inhibitors or selective DENV inhibitors. Compounds of 12, 17 and 28 are more active against Asian ZIKV SZ-VIV01 strain than African ZIKV MR766 strain. It is valued that silylation makes six TBS compounds of 4-nitrophenyl hydrazine series and phenyl hydrazine series more active against ZIKV infection than their phenols. Time-of-addition and withdrawal studies indicate that compound 12 majorly acts on post-infection of RNA synthesis stage of ZIKV life cycle. Moreover, compounds of 12, 17 and 18 are anti-ZIKV agents with the inhibitory activities to ZIKV NS5 RdRp while 12 doesn't inhibit DENV infection even though it is a DENV RdRp inhibitor, 17 is an active agent against DENV infection but is only a weak DENV NS5 RdRp inhibitor, and 28 is inactive against DENV infection and not a DENV NS5 RdRp inhibitor. As a result, a compound's antiviral difference between ZIKV and DENV is not always related to anti-RdRp difference between ZIKV RdRp and DENV RdRp, and structural features of a compound play important roles in executing antiviral and anti-RdRp functions. Further discovery of highly potent broad-spectrum or selective agents against infection by ZIKV and DENV will be facilitated.

Synthesis and evaluation of anti-yellow fever virus activity of new 6-aryl-3-R-amino-1,2,4-triazin-5(4H)-ones

Yellow fever disease is one of public health concerns in the tropics. Despite its significant medicinal and economic impact among large groups of the population, there is a lack of effective treatment against yellow fever. In this regard, here we describe the synthesis of a series of new 6-aryl-3-R-amino-1,2,4-triazin-5(4H)-ones and evaluation of their in vitro inhibitory activity against yellow fever virus. Among all tested compounds 4 derivatives possessing strong inhibitory activity at μM concentrations were identified. All the active compounds revealed a good toxicity profile. These facts make the compounds interesting candidates for further evaluation of their efficacy in the treatment of yellow fever virus infection in vivo.

Safety and immunogenicity following co-administration of Yellow fever vaccine with Tick-borne encephalitis or Japanese encephalitis vaccines: Results from an open label, non-randomized clinical trial

BACKGROUND

Flavivirus infections pose a significant global health burden underscoring the need for the development of safe and effective vaccination strategies. Available flavivirus vaccines are from time to time concomitantly delivered to individuals. Co-administration of different vaccines saves time and visits to health care units and vaccine clinics. It serves to provide protection against multiple pathogens in a shorter time-span; e.g., for individuals travelling to different endemic areas. However, safety and immunogenicity-related responses have not been appropriately evaluated upon concomitant delivery of these vaccines. Therefore, we performed an open label, non-randomized clinical trial studying the safety and immunogenicity following concomitant delivery of the yellow fever virus (YFV) vaccine with tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JE) virus vaccines.

METHODS AND FINDINGS

Following screening, healthy study participants were enrolled into different cohorts receiving either TBEV and YFV vaccines, JEV and YFV vaccines, or in control groups receiving only the TBEV, JEV, or YFV vaccine. Concomitant delivery was given in the same or different upper arms for comparison in the co-vaccination cohorts. Adverse effects were recorded throughout the study period and blood samples were taken before and at multiple time-points following vaccination to evaluate immunological responses to the vaccines. Adverse events were predominantly mild in the study groups. Four serious adverse events (SAE) were reported, none of them deemed related to vaccination. The development of neutralizing antibodies (nAbs) against TBEV, JEV, or YFV was not affected by the concomitant vaccination strategy. Concomitant vaccination in the same or different upper arms did not significantly affect safety or immunogenicity-related outcomes. Exploratory studies on immunological effects were additionally performed and included studies of lymphocyte activation, correlates associated with germinal center activation, and plasmablast expansion.

CONCLUSIONS

Inactivated TBEV or JEV vaccines can be co-administered with the live attenuated YFV vaccine without an increased risk of adverse events and without reduced development of nAbs to the respective viruses. The vaccines can be delivered in the same upper arm without negative outcome. In a broader perspective, the results add valuable information for simultaneous administration of live and inactivated flavivirus vaccines in general.

TRIAL REGISTRATION

Eudra CT 2017-002137-32.

New Anti-Flavivirus Fusion Loop Human Antibodies with Zika Virus-Neutralizing Potential

Zika virus infections exhibit recurrent outbreaks and can be responsible for disease complications such as congenital Zika virus syndrome. Effective therapeutic interventions are still a challenge. Antibodies can provide significant protection, although the antibody response may fail due to antibody-dependent enhancement reactions. The choice of the target antigen is a crucial part of the process to generate effective neutralizing antibodies. Human anti-Zika virus antibodies were selected by phage display technology. The antibodies were selected against a mimetic peptide based on the fusion loop region in the protein E of Zika virus, which is highly conserved among different flaviviruses. Four rounds of selection were performed using the synthetic peptide in two strategies: the first was using the acidic elution of bound phages, and the second was by applying a competing procedure. After panning, the selected VH and VL domains were determined by combining NGS and bioinformatic approaches. Three different human monoclonal antibodies were expressed as scFvs and further characterized. All showed a binding capacity to Zika (ZIKV) and showed cross-recognition with yellow fever (YFV) and dengue (DENV) viruses. Two of these antibodies, AZ1p and AZ6m, could neutralize the ZIKV infection in vitro. Due to the conservation of the fusion loop region, these new antibodies can potentially be used in therapeutic intervention against Zika virus and other flavivirus illnesses.

An overview on small molecules acting as broad spectrum-agents for yellow fever infection

INTRODUCTION

Yellow Fever virus (YFV) is a mosquito-borne flavivirus, endemic in 47 countries in Africa and South America, which causes febrile symptoms that can evolve in 15% of the patients to serious haemorrhagic conditions, liver injury, and multiorgan failure. Although a highly effective vaccine (YF-17D vaccine) is available, to date, no antiviral drugs have been approved for the prevention and treatment of YFV infections.

AREAS COVERED

This review article focuses on the description of viral targets that have been considered within YFV and flavivirus drug discovery studies and on the most relevant candidates reported so far that elicit broad-spectrum inhibition against relevant strains and mutants of YFV.

EXPERT OPINION

Considering the growing interest on (re)emerging vector-borne viral infections, it is expected that flavivirus drug discovery will quickly deliver potential candidates for clinical evaluation. Due to similarity among flaviviral targets, several candidates identified against different flaviviruses have shown broad-spectrum activity, thus exhibiting anti-YFV activity, as well. In this regard, it would be desirable to routinely include the assessment of antiviral activity against different YFV strains. On the other hand, the development of host targeting agents are still at an initial stage and deserve further focused efforts.

Virucidal Activity of the Pyridobenzothiazolone Derivative HeE1-17Y against Enveloped RNA Viruses

Pyridobenzothiazolone derivatives are a promising class of broad-spectrum antivirals. However, the mode of action of these compounds remains poorly understood. The HeE1-17Y derivative has already been shown to be a potent compound against a variety of flaviviruses of global relevance. In this work, the mode of action of HeE1-17Y has been studied for West Nile virus taking advantage of reporter replication particles (RRPs). Viral infectivity was drastically reduced by incubating the compound with the virus before infection, thus suggesting a direct interaction with the viral particles. Indeed, RRPs incubated with the inhibitor appeared to be severely compromised in electron microscopy analysis. HeE1-17Y is active against other enveloped viruses, including SARS-CoV-2, but not against two non-enveloped viruses, suggesting a virucidal mechanism that involves the alteration of the viral membrane.

Discovery of 2-Phenylquinolines with Broad-Spectrum Anti-coronavirus Activity

A selection of compounds from a proprietary library, based on chemical diversity and various biological activities, was evaluated as potential inhibitors of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in a phenotypic-based screening assay. A compound based on a 2-phenylquinoline scaffold emerged as the most promising hit, with EC₅₀ and CC₅₀ values of 6 and 18 μM, respectively. The subsequent selection of additional analogues, along with the synthesis of ad hoc derivatives, led to compounds that maintained low μM activity as inhibitors of SARS-CoV-2 replication and lacked cytotoxicity at 100 μM. In addition, the most promising congeners also show pronounced antiviral activity against the human coronaviruses HCoV-229E and HCoV-OC43, with EC₅₀ values ranging from 0.2 to 9.4 μM. The presence of a 6,7-dimethoxytetrahydroisoquinoline group at the C-4 position of the 2-phenylquinoline core gave compound 6g that showed potent activity against SARS-CoV-2 helicase (nsp13), a highly conserved enzyme, highlighting a potentiality against emerging HCoVs outbreaks.

Field trials reveal the complexities of deploying and evaluating the impacts of yeast-baited ovitraps on Aedes mosquito densities in Trinidad, West Indies

The use of lure-and-kill, large-volume ovitraps to control Aedes aegypti and Aedes albopictus populations has shown promise across multiple designs that target gravid females (adulticidal) or larvae post-oviposition (larvicidal). Here we report on a pilot trial to deploy 10 L yeast-baited ovitraps at select sites in Curepe, Trinidad, West Indies during July to December, 2019. Oviposition rates among ovitraps placed in three Treatment sites were compared to a limited number of traps placed in three Control areas (no Aedes management performed), and three Vector areas (subjected to standard Ministry of Health, Insect Vector Control efforts). Our goal was to gain baseline information on efforts to saturate the Treatment sites with ovitraps within 20–25 m of each other and compare oviposition rates at these sites with background oviposition rates in Control and Vector Areas. Although yeast-baited ovitraps were highly attractive to gravid Aedes females, a primary limitation encountered within the Treatment sites was the inability to gain access to residential compounds for trap placement, primarily due to residents being absent during the day. This severely limited our intent to saturate these areas with ovitraps, indicating that future studies must include plans to account for these inaccessible zones during trap placement.

Antiviral Agents against Flavivirus Protease: Prospect and Future Direction

Flaviviruses cause a significant amount of mortality and morbidity, especially in regions where they are endemic. A recent example is the outbreak of Zika virus throughout the world. Development of antiviral drugs against different viral targets is as important as the development of vaccines. During viral replication, a single polyprotein precursor (PP) is produced and further cleaved into individual proteins by a viral NS2B-NS3 protease complex together with host proteases. Flavivirus protease is one of the most attractive targets for development of therapeutic antivirals because it is essential for viral PP processing, leading to active viral proteins. In this review, we have summarized recent development in drug discovery targeting the NS2B-NS3 protease of flaviviruses, especially Zika, dengue, and West Nile viruses.

Antivirals against (Re)emerging Flaviviruses: Should We Target the Virus or the Host?

The COVID pandemic has evidenced how vulnerable we are to emerging infectious diseases and how short our current armamentarium is. Flavivirus, single stranded RNA viruses transmitted by arthropods, are considered a global health challenge. No drugs to treat these infections have been approved. In this Viewpoint, we analyze the advantages and disadvantages of two different, but probably also complementary, therapeutic approaches: virus-targeting antivirals and host-targeting drugs.

Antiviral therapeutics directed against RNA dependent RNA polymerases from positive-sense viruses

Viruses with positive-sense single stranded RNA (+ssRNA) genomes are responsible for different diseases and represent a global health problem. In addition to developing new vaccines that protect against severe illness on infection, it is imperative to identify new antiviral molecules to treat infected patients. The genome of these RNA viruses generally codes for an enzyme with RNA dependent RNA polymerase (RdRP) activity. This molecule is centrally involved in the duplication of the RNA genome. Inhibition of this enzyme by small molecules will prevent duplication of the RNA genome and thus reduce the viral titer. An overview of the different therapeutic strategies used to inhibit RdRPs from +ssRNA viruses is provided, along with an analysis of these enzymes to highlight new binding sites for inhibitors.

4,7-Disubstituted 7H-Pyrrolo[2,3-d]pyrimidines and Their Analogs as Antiviral Agents against Zika Virus

Discovery of compound 1 as a Zika virus (ZIKV) inhibitor has prompted us to investigate its 7H-pyrrolo[2,3-d]pyrimidine scaffold, revealing structural features that elicit antiviral activity. Furthermore, we have demonstrated that 9H-purine or 1H-pyrazolo[3,4-d]pyrimidine can serve as an alternative core structure. Overall, we have identified 4,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidines and their analogs including compounds 1, 8 and 11 as promising antiviral agents against flaviviruses ZIKV and dengue virus (DENV). While the molecular target of these compounds is yet to be elucidated, 4,7-disubstituted 7H-pyrrolo[2,3-d]pyrimidines and their analogs are new chemotypes in the design of small molecules against flaviviruses, an important group of human pathogens.

Triazolopyrimidine Nuclei: Privileged Scaffolds for Developing Antiviral Agents with a Proper Pharmacokinetic Profile

Viruses are a continuing threat to global health. The lack or limited therapeutic armamentarium against some viral infections and increasing drug resistance issues make the search for new antiviral agents urgent. In recent years, a growing literature highlighted the use of triazolopyrimidine (TZP) heterocycles in the development of antiviral agents, with numerous compounds that showed potent antiviral activities against different RNA and DNA viruses. TZP core represents a privileged scaffold for achieving biologically active molecules, thanks to: i) the synthetic feasibility that allows to variously functionalize TZPs in the different positions of the nucleus, ii) the ability of TZP core to establish multiple interactions with the molecular target, and iii) its favorable pharmacokinetic properties. In the present review, after mentioning selected examples of TZP-based compounds with varied biological activities, we will focus on those antivirals that appeared in the literature in the last 10 years. Approaches used for their identification, the hit-to-lead studies, and the emerged structure-activity relationship will be described. A mention of the synthetic methodologies to prepare TZP nuclei will also be given. In addition, their mechanism of action, the binding mode within the biological target, and pharmacokinetic properties will be analyzed, highlighting the strengths and weaknesses of compounds based on the TZP scaffold, which is increasingly used in medicinal chemistry.

Potential for Protein Kinase Pharmacological Regulation in Flaviviridae Infections

Protein kinases (PKs) are enzymes that catalyze the transfer of the terminal phosphate group from ATP to a protein acceptor, mainly to serine, threonine, and tyrosine residues. PK catalyzed phosphorylation is critical to the regulation of cellular signaling pathways that affect crucial cell processes, such as growth, differentiation, and metabolism. PKs represent attractive targets for drugs against a wide spectrum of diseases, including viral infections. Two different approaches are being applied in the search for antivirals: compounds directed against viral targets (direct-acting antivirals, DAAs), or against cellular components essential for the viral life cycle (host-directed antivirals, HDAs). One of the main drawbacks of DAAs is the rapid emergence of drug-resistant viruses. In contrast, HDAs present a higher barrier to resistance development. This work reviews the use of chemicals that target cellular PKs as HDAs against virus of the Flaviviridae family (Flavivirus and Hepacivirus), thus being potentially valuable therapeutic targets in the control of these pathogens.