In vitro study of Hesperetin and Hesperidin as inhibitors of zika and chikungunya virus proteases.

The potential outcome of flavivirus and alphavirus co-infections is worrisome due to the development of severe diseases. Hundreds of millions of people worldwide live under the risk of infections caused by viruses like chikungunya virus (CHIKV, genus Alphavirus), dengue virus (DENV, genus Flavivirus), and zika virus (ZIKV, genus Flavivirus). So far, neither any drug exists against the infection by a single virus, nor against co-infection. The results described in our study demonstrate the inhibitory potential of two flavonoids derived from citrus plants: Hesperetin (HST) against NS2B/NS3pro of ZIKV and nsP2pro of CHIKV and, Hesperidin (HSD) against nsP2pro of CHIKV. The flavonoids are noncompetitive inhibitors and the determined IC50 values are in low µM range for HST against ZIKV NS2B/NS3pro (12.6 ± 1.3 µM) and against CHIKV nsP2pro (2.5 ± 0.4 µM). The IC50 for HSD against CHIKV nsP2pro was 7.1 ± 1.1 µM. The calculated ligand efficiencies for HST were > 0.3, which reflect its potential to be used as a lead compound. Docking and molecular dynamics simulations display the effect of HST and HSD on the protease 3D models of CHIKV and ZIKV. Conformational changes after ligand binding and their effect on the substrate-binding pocket of the proteases were investigated. Additionally, MTT assays demonstrated a very low cytotoxicity of both the molecules. Based on our results, we assume that HST comprise a chemical structure that serves as a starting point molecule to develop a potent inhibitor to combat CHIKV and ZIKV co-infections by inhibiting the virus proteases.

Development of an ELISA assay for screening inhibitors against divalent metal ion dependent alphavirus capping enzyme.

Alphavirus non-structural protein, nsP1 has a distinct molecular mechanism of capping the viral RNAs than the conventional capping mechanism of host. Thus, alphavirus capping enzyme nsP1 is a potential drug target. nsP1 catalyzes the methylation of guanosine triphosphate (GTP) by transferring the methyl group from S-adenosylmethionine (SAM) to a GTP molecule at its N7 position with the help of nsP1 methyltransferase (MTase) followed by guanylylation (GT) reaction which involves the formation of m7GMP-nsP1 covalent complex by nsP1 guanylyltransferase (GTase). In subsequent reactions, m7GMP moiety is added to the 5' end of the viral ppRNA by nsP1 GTase resulting in the formation of cap0 structure. In the present study, chikungunya virus (CHIKV) nsP1 MTase and GT reactions were confirmed by an indirect non-radioactive colorimetric assay and western blot assay using an antibody specific for the m7G cap, respectively. The purified recombinant CHIKV nsP1 has been used for the development of a rapid and sensitive non-radioactive enzyme linked immunosorbent assay (ELISA) to identify the inhibitors of CHIKV nsP1. The MTase reaction is followed by GT reaction and resulted in m7GMP-nsP1 covalent complex formation. The developed ELISA nsP1 assay measures this m7GMP-nsP1 complex by utilizing anti-m7G cap monoclonal antibody. The mutation of a conserved residue Asp63 to Ala revealed its role in nsP1 enzyme reaction. Inductively coupled plasma mass spectroscopy (ICP-MS) was used to determine the presence of magnesium ions (Mg2+) in the purified nsP1 protein. The divalent metal ion selectivity and investigation show preference for Mg2+ ion by CHIKV nsP1. Additionally, using the developed ELISA nsP1 assay, the inhibitory effects of sinefungin, aurintricarboxylic acid (ATA) and ribavirin were determined and the IC50 values were estimated to be 2.69 µM, 5.72 µM and 1.18 mM, respectively.

Potential Antivirals: Natural Products Targeting Replication Enzymes of Dengue and Chikungunya Viruses.

Dengue virus (DENV) and chikungunya virus (CHIKV) are reemergent arboviruses that are transmitted by mosquitoes of the Aedes genus. During the last several decades, these viruses have been responsible for millions of cases of infection and thousands of deaths worldwide. Therefore, several investigations were conducted over the past few years to find antiviral compounds for the treatment of DENV and CHIKV infections. One attractive strategy is the screening of compounds that target enzymes involved in the replication of both DENV and CHIKV. In this review, we describe advances in the evaluation of natural products targeting the enzymes involved in the replication of these viruses.

Structural basis for complementary and alternative medicine: Phytochemical interaction with non-structural protein 2 protease-a reverse engineering strategy.

OBJECTIVE: To understand the druggability of the bioactive compounds from traditional herbal formulations "Nilavembu Kudineer" and "Swasthya Raksha Amruta Peya" to heal chikungunya virus (CHIKV) infection. METHODS: The efficiency of twenty novel chemical entities from "Nilavembu Kudineer" and "Swasthya Raksha Amruta Peya" to inhibit CHIKV infection in silico were evaluated. Ligands were prepared using Ligprep module of Schrödinger. Active site was identified using SiteMap program. Grid box was generated using receptor grid generation wizard. Molecular docking was carried out using Grid Based Ligand Docking with Energetics (GLIDE) program. RESULTS: Molecular docking studies showed that among twenty compounds, andrographoside, deoxyandrographoside, neoandrographolide, 14-deoxy-11-oxoandrographolide, butoxone and oleanolic acid showed GLIDE extra precision (XP) score of -9.10, -8.72, -8.25, -7.38, -7.28 and -7.01, respectively which were greater than or comparable with chloroquine (reference compound) XP score (-7.08) and were found to interact with the key residues GLU 1043, LYS 1045, GLY 1176, LEU 1203, HIS 1222 and LYS 1239 which were characteristic functional unit crucial for replication of CHIKV. CONCLUSION: The binding affinity and the binding mode of chemical entities taken from herbal formulations with non-structural protein 2 protease were understood and our study provided a novel strategy in the development and design of drugs for CHIKV infection.