Novel Herbal Formulation Jing Si Exhibits Multiple Functions to Inhibit Replication Activity and Subsides Viral Load of COVID-19 Variants

Background: SARS-CoV-2 is susceptible to frequent mutations and gets transformed into variants therefore identifying novel multi targeting remedies is necessary in formulating strategies to overcome the pandemic. Methods: Traditional Chinese medicine based formula Jing Si herbal (JSH) was screened and analyzed by HPLC to evaluate its ability to act against infection by SARS-CoV-2 variants. The 3CL protease and RdRp assay kit were utilized to detect the enzyme activity. In order to determine the effect of JSH on the binding efficiency and viral penetration of SARS-CoV-2 variants, Calu-3 lung cells and Caco-2 colon cells were infected with fluorescent SARS-CoV-2 pseudo type lentiviruses. In addition, the effect of JSH (16.22 mg /mice/day and 48.66 mg/mice/day) on the viral load in SKH1J mice exposed to inhalation of luminescent SARS-CoV-2 variants for three days was determined. Results: The JSH was found to be effective in inhibiting the viral entry into Calu-3 and Caco-2 cells and in mice pre-treated with JSH for 3 days also inhibited the viral load exposed to different SARS-CoV-2 variants. Interestingly, JSH also decreased 3cL and RdRp activity thereby revealing the multi targeting nature of JSH and therefore will be a potential preventive SARS-CoV-2 infection.Conclusion: Taken together, our present results revealed that JSH could be a potential candidate for COVID-19 treatment.

Development of a method for evaluating the mRNA transcription activity of influenza virus RNA-dependent RNA polymerase through real-time reverse transcription polymerase chain reaction

Background The development of an influenza RNA-dependent RNA polymerase (RdRp) inhibitor is required; therefore, a method for evaluating the activity of influenza RdRp needs to be developed. The current method uses an ultracentrifuge to separate viral particles and quantifies RdRp activity with radioisotope-labeled nucleosides, such as 32P-GTP. This method requires special equipment and radioisotope management, so it cannot be implemented in all institutions. We have developed a method to evaluate the mRNA transcription activity of RdRp without using ultracentrifugation and radioisotopes. Results RdRp was extracted from viral particles that were purified from the culture supernatant using anionic polymer-coated magnetic beads that can concentrate influenza virus particles from the culture supernatant in approximately 30 min. A strand-specific real-time reverse transcription polymerase chain reaction (RT-PCR) method was developed based on reverse transcription using tagged primers. RT primers were designed to bind to a sequence near the 3' end of mRNA containing a poly A tail for specific recognition of the mRNA, with an 18-nucleotide tag attached to the 5' end of the sequence. The RT reaction was performed with this tagged RT primer, and the amount of mRNA was analyzed using real-time qPCR. Real-time qPCR using the tag sequence as the forward primer and a segment-specific reverse primer ensured the specificity for quantifying the mRNA of segments 1, 4, and 5. The temperature, reaction time, and Mg2+ concentration were determined to select the optimum conditions for in vitro RNA synthesis by RdRp, and the amount of synthesized mRNAs of segments 1, 4, and 5 was determined with a detection sensitivity of 10 copies/reaction. In addition, mRNA synthesis was inhibited by ribavirin triphosphate, an RdRp inhibitor, thus indicating the usefulness of this evaluation method for screening RdRp inhibitors. Conclusion This method makes it possible to analyze the RdRp activity even in a laboratory where ultracentrifugation and radioisotopes cannot be used. This novel method for measuring influenza virus polymerase activity will further promote research to identify compounds that inhibit viral mRNA transcription activity of RdRp.

Molecular Dynamics Simulations Reveal the Interaction Fingerprint of Remdesivir Triphosphate Pivotal in Allosteric Regulation of SARS-CoV-2 RdRp

The COVID-19 pandemic has now strengthened its hold on human health and coronavirus’ lethal existence does not seem to be going away soon. In this regard, the optimization of reported information for understanding the mechanistic insights that facilitate the discovery towards new therapeutics is an unmet need. Remdesivir (RDV) is established to inhibit RNA-dependent RNA polymerase (RdRp) in distinct viral families including Ebola and SARS-CoV-2. Therefore, its derivatives have the potential to become a broad-spectrum antiviral agent effective against many other RNA viruses. In this study, we performed comparative analysis of RDV, RMP (RDV monophosphate), and RTP (RDV triphosphate) to undermine the inhibition mechanism caused by RTP as it is a metabolically active form of RDV. The MD results indicated that RTP rearranges itself from its initial RMP-pose at the catalytic site towards NTP entry site, however, RMP stays at the catalytic site. The thermodynamic profiling and free-energy analysis revealed that a stable pose of RTP at NTP entrance site seems critical to modulate the inhibition as its binding strength improved more than its initial RMP-pose obtained from docking at the catalytic site. We found that RTP not only occupies the residues K545, R553, and R555, essential to escorting NTP towards the catalytic site, but also interacts with other residues D618, P620, K621, R624, K798, and R836 that contribute significantly to its stability. From the interaction fingerprinting it is revealed that the RTP interact with basic and conserved residues that are detrimental for the RdRp activity, therefore it possibly perturbed the catalytic site and blocked the NTP entrance site considerably. Overall, we are highlighting the RTP binding pose and key residues that render the SARS-CoV-2 RdRp inactive, paving crucial insights towards the discovery of potent inhibitors.

SARS-CoV-2 RdRp Inhibitors Selected from a Cell-Based SARS-CoV-2 RdRp Activity Assay System

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), urgently needs effective prophylactic and therapeutic drugs. RNA-dependent RNA polymerase (RdRp), essential for replicating and transcribing a viral RNA genome, is highly conserved in coronaviruses; thus, it is a potential target for inhibiting coronavirus infection. In this study, we generated the cell-based SARS-CoV-2 RdRp activity assay system by modifying a previously reported cell-based MERS-CoV RdRp activity assay system to screen for SARS-CoV-2 RdRp inhibitors. The assay system consisted of an expression plasmid encoding SARS-CoV-2 RdRp and an RdRp activity reporter plasmid. RdRp activity in the cells could be conveniently detected by luminescence after transfection. We confirmed that SARS-CoV-2 RdRp replicated double-stranded RNA using immunofluorescence staining and the inhibition of RdRp activity by remdesivir and lycorine using this system. Moreover, the Z-factor of this system was calculated to be 0.798, suggesting the reproducibility and reliability of the high-throughput screening system. Finally, we screened nucleoside and nucleotide analogs and identified adefovir dipivoxil, emtricitabine, telbivudine, entecavir hydrate, moroxydine and rifampin as novel SARS-CoV-2 RdRp inhibitors and therapeutic candidates for COVID-19. This system provides an effective high-throughput screening system platform for developing potential prophylactic and therapeutic drugs for COVID-19 and emerging coronavirus infections.

Proline to Threonine Mutation at Position 162 of NS5B of Classical Swine Fever Virus Vaccine C Strain Promoted Genome Replication and Infectious Virus Production by Facilitating Initiation of RNA Synthesis

The 3′untranslated region (3′UTR) and NS5B of classical swine fever virus (CSFV) play vital roles in viral genome replication. In this study, two chimeric viruses, vC/SM3′UTR and vC/b3′UTR, with 3′UTR substitution of CSFV Shimen strain or bovine viral diarrhea virus (BVDV) NADL strain, were constructed based on the infectious cDNA clone of CSFV vaccine C strain, respectively. After virus rescue, each recombinant chimeric virus was subjected to continuous passages in PK-15 cells. The representative passaged viruses were characterized and sequenced. Serial passages resulted in generation of mutations and the passaged viruses exhibited significantly increased genomic replication efficiency and infectious virus production compared to parent viruses. A proline to threonine mutation at position 162 of NS5B was identified in both passaged vC/SM3′UTR and vC/b3′UTR. We generated P162T mutants of two chimeras using the reverse genetics system, separately. The single P162T mutation in NS5B of vC/SM3′UTR or vC/b3′UTR played a key role in increased viral genome replication and infectious virus production. The P162T mutation increased vC/SM3′UTRP162T replication in rabbits. From RNA-dependent RNA polymerase (RdRp) assays in vitro, the NS5B containing P162T mutation (NS5BP162T) exhibited enhanced RdRp activity for different RNA templates. We further identified that the enhanced RdRp activity originated from increased initiation efficiency of RNA synthesis. These findings revealed a novel function for the NS5B residue 162 in modulating pestivirus replication.

Identifying SARS-CoV-2 antiviral compounds by screening for small molecule inhibitors of nsp12/7/8 RNA-dependent RNA polymerase

The coronavirus disease 2019 (COVID-19) global pandemic has turned into the largest public health and economic crisis in recent history impacting virtually all sectors of society. There is a need for effective therapeutics to battle the ongoing pandemic. Repurposing existing drugs with known pharmacological safety profiles is a fast and cost-effective approach to identify novel treatments. The COVID-19 etiologic agent is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a single-stranded positive-sense RNA virus. Coronaviruses rely on the enzymatic activity of the replication–transcription complex (RTC) to multiply inside host cells. The RTC core catalytic component is the RNA-dependent RNA polymerase (RdRp) holoenzyme. The RdRp is one of the key druggable targets for CoVs due to its essential role in viral replication, high degree of sequence and structural conservation and the lack of homologues in human cells. Here, we have expressed, purified and biochemically characterised active SARS-CoV-2 RdRp complexes. We developed a novel fluorescence resonance energy transfer-based strand displacement assay for monitoring SARS-CoV-2 RdRp activity suitable for a high-throughput format. As part of a larger research project to identify inhibitors for all the enzymatic activities encoded by SARS-CoV-2, we used this assay to screen a custom chemical library of over 5000 approved and investigational compounds for novel SARS-CoV-2 RdRp inhibitors. We identified three novel compounds (GSK-650394, C646 and BH3I-1) and confirmed suramin and suramin-like compounds as in vitro SARS-CoV-2 RdRp activity inhibitors. We also characterised the antiviral efficacy of these drugs in cell-based assays that we developed to monitor SARS-CoV-2 growth.

Comparative Analysis of Small Moleclues and Natural Plants Compounds as Therapeutic Inhibitors Targeting RdRp and Nucleocapsid Proteins of SARS CoV 2: An in Silico Approach

Nucleocapsid protein and RNA-dependent RNA polymerase (RdRp) activity in viral structural membrane, transcription and replication has been recognized as an attractive target to design novel antiviral strategies. The essential feature of the N protein of SARS COV 2 is to bind to the viral genome to promote the exact folding of the hammerhead ribozyme averting unproductive RNA confirmations and lead them to right into a helical capsid shape or RNP complex, whose packaging is crucial to viability. RdRp is an essential enzyme that helps in RNA synthesis by catalyzing the RNA template-dependent development of phosphodiester bonds. RdRp makes a complex with two cofactors nsp7 and nsp8 to play a key role in RNA synthesis, transcription and replication of the SARS-CoV-2. In our study we used small molecules and natural plants compounds as therapeutic inhibitors targeting RdRp and N proteins of SARS COV 2. Their structures were geometrically optimized and energetically minimized using Hyperchem software. Molecular docking was performed using Molegro virtual docker and top ligands were selected based on MolDock score,Rerank score and H-bonding energy. Our results showed that 9 compounds against N protein and 7 compounds against RdRp protein forming better inhibitory effect with most lowest MolDock score − 285.68kcal/mol and − 201.5kcal/mol respectively. we hope that these small molecules and natural plants compounds can inhibit the viral enzymes and helps the patients in reducing specific symptoms of SARS-CoV-2 infection. However in vivo experimental studies and clinical trials need to get that more favorable result.

Human Sorting Nexin 2 Protein Interacts With Influenza A Virus PA Protein and Has a Negative Regulatory Effect on the Virus Replication

Replication of the influenza A viruses occurs in the cells through the viral RdRP consisting of PB1, PB2, and PA. Several cellular proteins are involved in these processes. To identify potential host interacting proteins to the viral PA, we have carried out a yeast two-hybrid screen using a HEK293 cell cDNA library. We focused our study on human SNX2 protein, which interacts with the PA protein in yeast cells. By using the co-immunoprecipitation assays, we have demonstrated that the amino-terminal part of the PA was important for binding to the SNX2 protein. Subcellular localization of the PA and human SNX2 proteins in HeLa cells supported this interaction. Knockdown of SNX2 with siRNA transfection in the cells resulted in a significant increase in both viral transcripts and proteins, suggesting that SNX2 could be a negative factor. However, the increase of SNX2 proteins in transfected cells didn’t cause a significant change in the viral RdRP activity in mini-replicon assay. This may suggest that the negative effect of SNX2 on the influenza A virus replication could be saturated with its authentic intra-cellular amount. Therefore, the regulatory mechanism for the amount of SNX2 is important to be studied in terms of influenza A virus replication.