Zika Virus NS3 Protease Pharmacophore Anchor Model and Drug Discovery

A high-throughput cell-based screening method for Zika virus protease inhibitor discovery

Zika virus (ZIKV) continues to pose a significant global public health threat, with recurring regional outbreaks and potential for pandemic spread. Despite often being asymptomatic, ZIKV infections can have severe consequences, including neurological disorders and congenital abnormalities. Unfortunately, there are currently no approved vaccines or antiviral drugs for the prevention or treatment of ZIKV. One promising target for drug development is the ZIKV NS2B-NS3 protease due to its crucial role in the virus life cycle. In this study, we established a cell-based ZIKV protease inhibition assay designed for high-throughput screening (HTS). Our assay relies on the ZIKV protease's ability to cleave a cyclised firefly luciferase fused to a natural cleavage sequence between NS2B and NS3 protease within living cells. We evaluated the performance of our assay in HTS setting using the pharmacologic controls (JNJ-40418677 and MK-591) and by screening a Library of Pharmacologically Active Compounds (LOPAC). The results confirmed the feasibility of our assay for compound library screening to identify potential ZIKV protease inhibitors.

ZIKV Inhibitors Based on Pyrazolo[3,4-d]pyridazine-7-one Core: Rational Design, In Vitro Evaluation, and Theoretical Studies

The Zika virus (ZIKV) is believed to cause birth defects, and no anti-ZIKV drugs have been approved by medical organizations to date. Starting from antimicrobial lead compounds with a pyrazolo[3,4-d]pyridazine-7-one scaffold, we synthesized 16 derivatives and screened their ability to interfere with ZIKV infection utilizing a cell-based phenotypic assay. Of these, five compounds showed significant inhibition of ZIKV with a selective index value greater than 4.6. In particular, compound 9b showed the best anti-ZIKV activity with a selectivity index of 22.4 (half-maximal effective concentration = 25.6 μM and 50% cytotoxic concentration = 572.4 μM). Through the brine shrimp lethality bioassay, 9b, 10b, 12, 17a, and 19a showed median lethal dose values in a range of 87.2-100.3 μg/mL. Compound 9b was also targeted to the NS2B-NS3 protease of ZIKV using molecular docking protocols, in which it acted as a noncompetitive inhibitor and strongly bound to five key amino acids (His51, Asp75, Ser135, Ala132, Tyr161). Utilizing the pharmacophore model of 9b, the top 20 hits were identified as prospective inhibitors of NS2B-NS3 protease, and six of them were confirmed for their stability with the protease via redocking and molecular dynamics simulations.

Identification of synthetically tractable MERS-CoV main protease inhibitors using structure-based virtual screening and molecular dynamics potential of mean force (PMF) calculations

The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) is a potentially lethal infection that presents a substantial threat to health, especially in Middle East nations. Given that no FDA-approved specific therapy for MERS infection exists, designing and discovering a potent antiviral therapy for MERS-CoV is crucial. One pivotal strategy for inhibiting MERS replication is to focus on the viral main protease (Mpro). In this study, we identify potential novel Mpro inhibitors employing structure-based virtual screening of our recently reported Ugi reaction-derived library (URDL) consisting of cherry-picked molecules from the literature. The key features of the URDL library include synthetic tractability (1-2 pot synthesis) of the molecules scaffold and unexplored chemical space. The hits were ranked based on the docking score, MM-GBSA free energy of binding, and the interaction pattern with the active site residues. A molecular dynamics (MD) simulation study was performed for the first two top-ranked compounds to analyze the stability and free binding energy based on the molecular mechanics Poisson-Boltzmann surface area. The potential mean force calculated from the steered molecular dynamics (SMD) simulations of the hits indicates improved H-bond potential, enhanced conformational stability, and binding affinity toward the target, compared to the cocrystallized ligand. The discovered hits represent novel synthetically tractable scaffolds as potential MERS-CoV Mpro inhibitors.Communicated by Ramaswamy H. Sarma.

Repurposing of antiparasitic drugs against the NS2B-NS3 protease of the Zika virus

To date, no approved drugs are available to treat the Zika virus (ZIKV) infection. Therefore, it is necessary to urgently identify potential drugs against the ZIKV infection. Here, the repurposing of 30 antiparasitic drugs against the NS2B-NS3 protease of the ZIKV has been carried out by using combined docking and molecular dynamics- (MD) simulations. Based on the docking results, 5 drugs, such as Amodiaquine, Primaquine, Paromomycin, Dichlorophene, and Ivermectin were screened for further analysis by MD simulations and free energy calculations. Among these drugs, Amodiaquine and Dichlorophen are found to produce the most stable complexes and possess relative binding free energies of about -44.3 ± 3.7 kcal/mol and -41.1 ± 5.3 kcal/mol respectively. Therefore, they would act as potent small-molecule inhibitors of the ZIKV protease.However, evaluations of biological and safety activities of these drugs against the ZIKV protease are required before their clinical use.Communicated by Ramaswamy H. Sarma.

Piperazine-derived small molecules as potential Flaviviridae NS3 protease inhibitors. In vitro antiviral activity evaluation against Zika and Dengue viruses

Since 2011 Direct Acting antivirals (DAAs) drugs targeting different non-structural (NS) viral proteins (NS3, NS5A or NS5B inhibitors) have been approved for clinical use in HCV therapies. However, currently there are not licensed therapeutics to treat Flavivirus infections and the only licensed DENV vaccine, Dengvaxia, is restricted to patients with preexisting DENV immunity. Similarly to NS5 polymerase, the NS3 catalytic region is evolutionarily conserved among the Flaviviridae family sharing strong structural similarity with other proteases belonging to this family and therefore is an attractive target for the development of pan-flavivirus therapeutics. In this work we present a library of 34 piperazine-derived small molecules as potential Flaviviridae NS3 protease inhibitors. The library was developed through a privileged structures-based design and then biologically screened using a live virus phenotypic assay to determine the half-maximal inhibitor concentration (IC₅₀) of each compound against ZIKV and DENV. Two lead compounds, 42 and 44, with promising broad-spectrum activity against ZIKV (IC₅₀ 6.6 µM and 1.9 µM respectively) and DENV (IC₅₀ 6.7 µM and 1.4 µM respectively) and a good security profile were identified. Besides, molecular docking calculations were performed to provide insights about key interactions with residues in NS3 proteases' active sites.

Identification of Potent Zika Virus NS5 RNA-Dependent RNA Polymerase Inhibitors Combining Virtual Screening and Biological Assays

The Zika virus (ZIKV) epidemic poses a significant threat to human health globally. Thus, there is an urgent need for developing effective anti-ZIKV agents. ZIKV non-structural protein 5 RNA-dependent RNA polymerase (RdRp), a viral enzyme for viral replication, has been considered an attractive drug target. In this work, we screened an anti-infection compound library and a natural product library by virtual screening to identify potential candidates targeting RdRp. Then, five selected candidates were further applied for RdRp enzymatic analysis, cytotoxicity, and binding examination by SPR. Finally, posaconazole (POS) was confirmed to effectively inhibit both RdRp activity with an IC₅₀ of 4.29 μM and the ZIKV replication with an EC₅₀ of 0.59 μM. Moreover, POS was shown to reduce RdRp activity by binding with the key amino acid D666 through molecular docking and site-directed mutation analysis. For the first time, our work found that POS could inhibit ZIKV replication with a stronger inhibitory activity than chloroquine. This work also demonstrated fast anti-ZIKV screening for inhibitors of RdRp and provided POS as a potential anti-ZIKV agent.

Advances in Computational Methods to Discover New NS2B-NS3 Inhibitors Useful Against Dengue and Zika Viruses

The Flaviviridae virus family consists of the genera Hepacivirus, Pestivirus, and Flavivirus, with approximately 70 viral types that use arthropods as vectors. Among these diseases, dengue (DENV) and zika virus (ZIKV) serotypes stand out, responsible for thousands of deaths worldwide. Due to the significant increase in cases, the World Health Organization (WHO) declared DENV a potential threat for 2019 due to being transmitted by infected travelers. Furthermore, ZIKV also has a high rate of transmissibility, highlighted in the outbreak in 2015, generating consequences such as Guillain-Barré syndrome and microcephaly. According to clinical outcomes, those infected with DENV can be asymptomatic, and in other cases, it can be lethal. On the other hand, ZIKV has severe neurological symptoms in newborn babies and adults. More serious symptoms include microcephaly, brain calcifications, intrauterine growth restriction, and fetal death. Despite these worrying data, no drug or vaccine is approved to treat these diseases. In the drug discovery process, one of the targets explored against these diseases is the NS2B-NS3 complex, which presents the catalytic triad His51, Asp75, and Ser135, with the function of cleaving polyproteins, with specificity for basic amino acid residues, Lys- Arg, Arg-Arg, Arg-Lys or Gln-Arg. Since NS3 is highly conserved in all DENV serotypes and plays a vital role in viral replication, this complex is an excellent drug target. In recent years, computer-aided drug discovery (CADD) is increasingly essential in drug discovery campaigns, making the process faster and more cost-effective, mainly explained by discovering new drugs against DENV and ZIKV. Finally, the main advances in computational methods applied to discover new compounds against these diseases will be presented here. In fact, molecular dynamics simulations and virtual screening is the most explored approach, providing several hit and lead compounds that can be used in further optimizations. In addition, fragment-based drug design and quantum chemistry/molecular mechanics (QM/MM) provides new insights for developing anti-DENV/ZIKV drugs. We hope that this review offers further helpful information for researchers worldwide and stimulates the use of computational methods to find a promising drug for treating DENV and ZIKV.

Advancement in the Development of Therapeutics Against Zika Virus Infection

Zika virus (ZIKV), a re-emerging arbovirus, causes teratogenic effects on the fetus and normal nerve functions, resulting in harmful autoimmune responses, which call for the development of therapeutics against ZIKV infection. In this review, we introduce the pathogenesis of ZIKV infection and summarize the advancement in the development of therapeutics against ZIKV infection. It provides guidance for the development of effective therapeutics against ZIKV infection.

C-Terminal Extended Hexapeptides as Potent Inhibitors of the NS2B-NS3 Protease of the ZIKA Virus

The Zika virus (ZIKV) protease is an attractive drug target for the design of novel inhibitors to control the ZIKV infection. As the protease substrate-binding site contains acidic residues, inhibitors with basic residues can be beneficial for the inhibition of protease activities. Molecular dynamics (MD) simulation and molecular mechanics with generalized Born and surface area solvation (MM/GBSA) techniques are employed herein to design potent peptide inhibitors and to understand the nature of the basic residues that can potentially stabilize the acidic residues of the protease substrate-binding site. It is found that the inclusion of K, R, and K at P1, P2, and P3 positions, respectively, and Y at the P4 position (YKRK) would generate a highly stable tetrapeptide-protease complex with a ΔG_bind of ~ −80 kcal/mol. We have also shown that the C-terminal extension of this and the second most stable tetrapeptide (YRRR) with small polar residues, such as S and T would generate even more stable hexapeptide-protease complexes. The modes of interactions of these inhibitors are discussed in detail, which are in agreement with earlier experimental studies. Thus, this study is expected to aid in the design of novel antiviral drugs against the ZIKV.

Structures and dynamics of peptide and peptidomimetic inhibitors bound to the NS2B-NS3 protease of the ZIKA virus

Infections caused by the Zika virus (ZIKV) have detrimental effects on human health, in particular on infants. As no potent drug or vaccine is available to date to contain this viral disease, it is necessary to design inhibitors that can target the NS2B-NS3 protease of the ZIKV, which is mainly responsible for the proliferation of the virus inside the host cells . Here, molecular dynamics (MD) simulation and molecular mechanics energies combined with the generalized Born and surface area continuum solvation model (MM/GBSA) are used to understand the binding modes and stabilities of R, KR, KKR, WKR, WKKR, YKKR, and FKKR peptide inhibitors bound to the NS3-NS2B protease. The results are compared with the corresponding results obtained for covalent (compound 1) and non-covalent (compound 4*) peptidomimetic inhibitors . It is revealed that peptide inhibitors can bind strongly with the ZIKV protease with the ΔG_bind ranging from -12 kcal/mol to -73 kcal/mol. Among these peptides, YKKR is found to make the most stable complex with the protease and fully occupy the electrostatically active substrate binding site. Hence, it would inhibit the protease activities of ZIKV strongly. The residue-wise decomposition of ΔG_bind indicates that Asp75, Asp129, Tyr130, Ser135, Gly151, Asn152, Glys153, and Tyr161 of NS3 and Ser81, Asp83, and Phe84 of NS2B play a prominent role in the inhibitor binding. Therefore, any future design of inhibitors should be aimed to target these residues.

NS2B-NS3 protease inhibitors as promising compounds in the development of antivirals against Zika virus: A systematic review

Zika virus (ZIKV) infections are associated with severe neurological complications and are a global public health concern. There are no approved vaccines or antiviral drugs to inhibit ZIKV replication. NS2B-NS3 protease (NS2B-NS3 pro), which is essential for viral replication, is a promising molecular target for anti-ZIKV drugs. We conducted a systematic review to identify compounds with promising effects against ZIKV; we discussed their pharmacodynamic and pharmacophoric characteristics. The online search, performed using the PubMed/MEDLINE and SCOPUS databases, yielded 56 articles; seven relevant studies that reported nine promising compounds with inhibitory activity against ZIKV NS2B-NS3 pro were selected. Of these, five (niclosamide, nitazoxanide, bromocriptine, temoporfin, and novobiocin) are currently available on the market and have been tested for off-label use against ZIKV. The 50% inhibitory concentration values of these compounds for the inhibition of NS2B-NS3 pro ranged at 0.38-21.6 µM; most compounds exhibited noncompetitive inhibition (66%). All compounds that could inhibit the NS2B-NS3 pro complex showed potent in vitro anti-ZIKV activity with a 50% effective concentration ranging 0.024-50 µM. The 50% cytotoxic concentration of the compounds assayed using A549, Vero, and WRL-69 cell lines ranged at 0.6-1388.02 µM and the selectivity index was 3.07-1698. This review summarizes the most promising antiviral agents against ZIKV that have inhibitory activity against viral proteases.

Structure and Dynamics of Zika Virus Protease and Its Insights into Inhibitor Design

Zika virus (ZIKV)—a member of the Flaviviridae family—is an important human pathogen. Its genome encodes a polyprotein that can be further processed into structural and non-structural proteins. ZIKV protease is an important target for antiviral development due to its role in cleaving the polyprotein to release functional viral proteins. The viral protease is a two-component protein complex formed by NS2B and NS3. Structural studies using different approaches demonstrate that conformational changes exist in the protease. The structures and dynamics of this protease in the absence and presence of inhibitors were explored to provide insights into the inhibitor design. The dynamic nature of residues binding to the enzyme cleavage site might be important for the function of the protease. Due to the charges at the protease cleavage site, it is challenging to develop small-molecule compounds acting as substrate competitors. Developing small-molecule compounds to inhibit protease activity through an allosteric mechanism is a feasible strategy because conformational changes are observed in the protease. Herein, structures and dynamics of ZIKV protease are summarized. The conformational changes of ZIKV protease and other proteases in the same family are discussed. The progress in developing allosteric inhibitors is also described. Understanding the structures and dynamics of the proteases are important for designing potent inhibitors.

Structure-Based Virtual Screening: Identification of a Novel NS2B-NS3 Protease Inhibitor with Potent Antiviral Activity against Zika and Dengue Viruses

Zika virus (ZIKV), which is associated with severe diseases in humans, has spread rapidly and globally since its emergence. ZIKV and dengue virus (DENV) are closely related, and antibody-dependent enhancement (ADE) of infection between cocirculating ZIKV and DENV may exacerbate disease. Despite these serious threats, there are currently no approved antiviral drugs against ZIKV and DENV. The NS2B-NS3 viral protease is an attractive antiviral target because it plays a pivotal role in polyprotein cleavage, which is required for viral replication. Thus, we sought to identify novel inhibitors of the NS2B-NS3 protease. To that aim, we performed structure-based virtual screening using 467,000 structurally diverse chemical compounds. Then, a fluorescence-based protease inhibition assay was used to test whether the selected candidates inhibited ZIKV protease activity. Among the 123 candidate inhibitors selected from virtual screening, compound 1 significantly inhibited ZIKV NS2B-NS3 protease activity in vitro. In addition, compound 1 effectively inhibited ZIKV and DENV infection of human cells. Molecular docking analysis suggested that compound 1 binds to the NS2B-NS3 protease of ZIKV and DENV. Thus, compound 1 could be used as a new therapeutic option for the development of more potent antiviral drugs against both ZIKV and DENV, reducing the risks of ADE.

Uncovering Flexible Active Site Conformations of SARS-CoV-2 3CL Proteases through Protease Pharmacophore Clusters and COVID-19 Drug Repurposing

The infectious SARS-CoV-2 causes COVID-19, which is now a global pandemic. Aiming for effective treatments, we focused on the key drug target, the viral 3C-like (3CL) protease. We modeled a big dataset with 42 SARS-CoV-2 3CL protease-ligand complex structures from ∼98.7% similar SARS-CoV 3CL protease with abundant complex structures. The diverse flexible active site conformations identified in the dataset were clustered into six protease pharmacophore clusters (PPCs). For the PPCs with distinct flexible protease active sites and diverse interaction environments, we identified pharmacophore anchor hotspots. A total of 11 "PPC consensus anchors" (a distinct set observed in each PPC) were observed, of which three "PPC core anchors" EHV2, HV1, and V3 are strongly conserved across PPCs. The six PPC cavities were then applied in virtual screening of 2122 FDA drugs for repurposing, using core anchor-derived "PPC scoring S" to yield seven drug candidates. Experimental testing by SARS-CoV-2 3CL protease inhibition assay and antiviral cytopathic effect assays discovered active hits, Boceprevir and Telaprevir (HCV drugs) and Nelfinavir (HIV drug). Specifically, Boceprevir showed strong protease inhibition with micromolar IC₅₀ of 1.42 μM and an antiviral activity with EC₅₀ of 49.89 μM, whereas Telaprevir showed moderate protease inhibition only with an IC₅₀ of 11.47 μM. Nelfinavir solely showed antiviral activity with a micromolar EC₅₀ value of 3.28 μM. Analysis of binding mechanisms of protease inhibitors revealed the role of PPC core anchors. Our PPCs revealed the flexible protease active site conformations, which successfully enabled drug repurposing.