Discovery of a Novel Respiratory Syncytial Virus Replication Inhibitor

A high-throughput screen of a Roche internal chemical library based on inhibition of the respiratory syncytial virus (RSV)-induced cytopathic effect (CPE) on HEp-2 cells was performed to identify RSV inhibitors. Over 2000 hits were identified and confirmed to be efficacious against RSV infection in vitro. Herein, we report the discovery of a Triazole-oxadiazole derivative, designated Triazole-1, as an RSV replication inhibitor and the characterization of its mechanism of action. Triazole-1 inhibited the replication of both RSV A and B subtypes with IC50 values of approximately 1 μM but was not effective against other viruses, including influenza virus A, human enterovirus 71, and vaccinia virus. Triazole-1 was shown to inhibit RSV replication when added at up to 8 hrs after viral entry, suggesting it inhibits RSV after the viral entry. In a minigenome reporter assay in which RSV transcription regulatory sequences flanking a luciferase gene was co-transfected with RSV N/P/L/M2-1 genes into HEp-2 cells, Triazole-1 demonstrated specific and dose-dependent RSV transcription inhibitory effects. Consistent with these findings, deep sequencing of the genomes of Triazole-1-resistant mutants revealed a single point mutation (A to G) at nucleotide 13546 of the RSV genome, leading to a T to A change at amino acid position 1684 of the L protein, which is the RSV RNA polymerase for both viral transcription and replication. The effect of Triazole-1 on minigenome transcription, which was mediated by the L protein containing the T1684A mutation, was significantly reduced, suggesting that the T1684A mutation alone conferred viral resistance to Triazole-1.

Virtual screening of potential therapeutic inhibitors against spike, helicase and polymerase of SARS-CoV-2 (COVID-19)

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected around 13 million people and has caused more than 5.7 lakh deaths worldwide since December 2019. In the absence of FDA approved drug for its treatment, only symptomatic management is done. Methods: We attempted to uncover potential therapeutic targets of spike, helicase and RNA dependent RNA polymerase (RdRp) proteins of the SARS-CoV-2 employing computational approach. The PDB structure of spike and RdRp and predicted structure of helicase proteins were docked with 100 approved antiviral drugs, natural compounds and some other chemical compounds. Results: The anti-SARS ligands EK1 and CID_23631927, and NCGC00029283 are potential entry inhibitor as it showed affinity with immunogenic receptor binding domain (RBD) of spike protein. This RBD interacts with angiotensin converting enzyme (ACE2) receptor facilitating the entry of virion in the host cells. The FDA approved drugs including Nelfinavir, Saquinavir, Tipranavir, Setrobuvir, Indinavir and Atazanavir showed potential inhibitory activity against targeted domains and thus may act as entry or replication inhibitor or both. Furthermore, several anti-HCoV natural compounds including Amentoflavone, Rutin and Tannin are also potential entry and replication inhibitor as they showed affinity with RBD, Ploop containing nucleoside triphosphate hydrolase and catalytic domain of the respective protein. Dithymoquinone showed significant inhibitory potential against the fusion peptide of S2 domain. Importantly, Tannin, Dithymoquinone and Rutin can be extracted from Nigella sativa seeds and thus may prove to be one of the most potential anti-SARS-CoV-2 inhibitor. Conclusion: Several potential ligands were identified with already known anti-HCoVs activities. Furthermore, as our study showed that some of the ligands acted as both entry or replication inhibitor against SARS-CoV-2, it is envisaged that a combination of either inhibitors with a dual mode of action would prove to be a much desired therapeutic option against this viral infection.

Discovery, SAR study and ADME properties of methyl 4-amino-3-cyano-1-(2-benzyloxyphenyl)-1H-pyrazole-5-carboxylate as an HIV-1 replication inhibitor

Identified as an HIV-1 inhibitor in cellulo, this pyrazole does not belong to the three main classes of anti HIV-drugs, a feature of prime interest in the context of viral resistance.