Transmissible SARS-CoV-2 variants with resistance to clinical protease inhibitors

Design, synthesis and activity evaluation of 4-(quinoline-2-yl)aniline derivatives as SARS-CoV‑2 main protease inhibitors

Since 2020, numerous compounds have been investigated for their potential use in treating SARS-CoV-2 infections. By identifying the molecular targets during the virus replication process, rationally designed anti-SARS-CoV-2 agents are developed. Among these targets, the main protease (Mpro) is a crucial enzyme required for virus replication, and its highly conserved characteristic make it an important drug target for the development of anti-SARS-CoV-2 drugs. Herein, we utilized warhead-based design strategy to conduct the structural optimization of M-1 developed through virtual screening, leading to a series of novel Mpro inhibitors with 4-(quinolin-2-yl)aniline scaffold. Among them, M-32 exhibited good SARS-CoV-2 Mpro inhibitory activity (IC50 = 5.2 μM) with a nearly 25-fold increase. Isothermal titration calorimetry (ITC) directly proved that M-32 binds directly to SARS-CoV-2 Mpro in an entropy-driven manner. Mass spectrometry (MS) further confirmed the covalent binding ability of M-32 to Mpro. Meanwhile, M-32 effectively inhibited the replication of SARS-CoV-2 in Vero E6 cells (EC50 = 5.29 μM).

A phycobiliprotein-based reporter assay for the evaluation of SARS-CoV-2 main protease activity

SARS-CoV-2 Mpro is crucial for viral replication and transcription and is highly conserved. Therefore, it is an ideal target for developing broad-spectrum antiviral drugs. To address resistance to existing drugs caused by mutations, a simple and sensitive method for detecting the activity of Mpro is needed. Considering the excellent fluorescence properties of phycobiliproteins, this study developed a phycobiliprotein-based reporter assay to evaluate Mpro activity. An engineered lyase was generated by inserting the Mpro recognition sequence between the phycobiliprotein lyases CpcF and CpcE. To ensure that the binding of CpcE and CpcF depended on the linker, a series of truncated forms were constructed. Among them, the activity of CpcE/F-10 was significantly reduced in the presence of Mpro; however, both genetic and chemical inhibition of Mpro activity reversed these results. These data indicated that the fluorescence of phycobiliproteins was negatively correlated with Mpro activity. The reporter assay developed here will contribute to determining the impact of Mpro mutations and screening for new inhibitors.

From N-0385 to N-0920: Unveiling a Host-Directed Protease Inhibitor with Picomolar Antiviral Efficacy against Prevalent SARS-CoV-2 Variants

The worldwide spread of new SARS-CoV-2 variants emphasizes the need to diversify existing therapeutic strategies. TMPRSS2, a host protease crucial for SARS-CoV-2 entry, has garnered significant research attention as a potential target for therapeutic intervention. Here, we optimized N-0385, a previously reported TMPRSS2 ketobenzothiazole-based peptidomimetic inhibitor, by screening 135 derivatives for target affinity and antiviral potency. Among the top candidates, N-0695 exhibited low nanomolar Ki values against three TTSPs associated with respiratory virus entry: TMPRSS2, matriptase, and TMPRSS13. Notably, N-0920 demonstrated exceptional potency in reducing SARS-CoV-2 variants EG.5.1 and JN.1 entry in Calu-3 cells, representing the first in cellulo picomolar inhibitor with EC50 values of 300 and 90 pM, respectively. Additionally, molecular modeling provided insights into the binding interactions between the compounds and their targets. This study underscores the effectiveness of our screening approach in refining an existing peptidomimetic scaffold to enhance selectivity and antiviral activity.

A Reflection on the Use of Molecular Simulation to Respond to SARS-CoV-2 Pandemic Threats

Molecular simulations play important roles in understanding the lifecycle of the SARS-CoV-2 virus and contribute to the design and development of antiviral agents and diagnostic tests for COVID. Here, we discuss the insights that such simulations have provided and the challenges involved, focusing on the SARS-CoV-2 main protease (Mpro) and the spike glycoprotein. Mpro is the leading target for antivirals, while the spike glycoprotein is the target for vaccine design. Finally, we reflect on lessons from this pandemic for the simulation community. Data sharing initiatives and collaborations across the international research community contributed to advancing knowledge and should be built on to help in future pandemics and other global challenges such as antimicrobial resistance.

M49L and other drug resistance mutations emerging in individuals after administration of ensitrelvir in Japanese clinical settings

Recent in-vitro and in-vivo studies and analysis of genomic information registered in GISAID have raised concerns about drug resistance mutations such as M49L after treatment with the 3C-like protease inhibitor ensitrelvir. The aim of this study was to identify resistance gene mutations to 3C-like protease inhibitors, including M49L mutations, in Japanese clinical settings. Genomic analysis of samples from our hospital admissions showed M49L mutations associated with ensitrelvir treatment in three cases and M49L mutation unrelated to ensitrelvir treatment in three cases. In a study of cases with persistent infection or rebound in viral load after 5 days of ensitrelvir treatment, 10 of 16 patients had M49L mutations and 5 had M49I mutations. Resistance gene mutations following treatment with ensitrelvir were shown to emerge even within individual patients who were not immunocompromised. In a study of persistent SARS-CoV-2 infection in severely immunocompromised patients, various drug resistance mutations emerged, with the M49L mutation especially showing a tendency to be a majority mutation. The current status of drug resistance mutations occurring in individuals following administration of ensitrelvir in Japanese clinical settings was clinically investigated for the first time. Considering that the barrier to resistance to ensitrelvir is lower than that to other antiviral drugs and that M49L is a unique mutation that occurs quickly, tends to become a majority mutation, and is maintained thereafter through its ability to replicate, the spread of strains that have acquired ensitrelvir resistance should be closely monitored.

Identification of acrylamide-based covalent inhibitors of SARS-CoV-2 (SCoV-2) Nsp15 using high-throughput screening and machine learning

Non-structural protein 15 (Nsp15) is a SARS-CoV-2 (SCoV-2) endoribonuclease and is a promising target for drug development because of its essential role in evading the host immune system. However, developing inhibitors against Nsp15 has been challenging due to its structural complexity and large RNA binding surface. In this report, we screened a 2640 acrylamide-based compound library against Nsp15 and identified 10 fragments that reacted with cysteine residues on Nsp15 and inhibited its endoribonuclease activity with IC50s less than 5 μM. These compounds had several attractive properties, such as low molecular weight (180-300 g mol-1), log P <3, zero violations to Lipinski's rules, and no apparent pan-assay interference (PAINs) properties. In addition, based on this data as a training set, we developed an artificial intelligence (AI) model that accelerated the hit to lead process and had a 73% accuracy for predicting new acrylamide-based Nsp15 inhibitors. Collectively, these results demonstrate that acrylamide fragments have great potential for developing Nsp15 inhibitors.

Exploring Possible Drug-Resistant Variants of SARS-CoV-2 Main Protease (Mpro) with Noncovalent Preclinical Candidate, Mpro61

SARS-CoV-2 Mpro inhibitors, such as nirmatrelvir, have proven efficacy in clinical use. Nirmatrelvir was developed in a target-based approach against wild-type Mpro, with the anticipation that prolonged usage may cause enrichment of drug-resistant mutations and persistence of COVID infections. Although globally prevalent drug-resistant mutations have not yet been observed, individual cases have recently been reported among patients following treatment with Paxlovid-a formulation of nirmatrelvir. Mutations E166V and E166A have been detected in these drug-resistant clinical isolates, consistent with predictions from in vitro viral passage experiments and therefore necessitate ongoing drug development. In this study, we selected seven Mpro variants (T21I, L50F, E166V, A173V, T190I, E166V/L50F, and A173V/L50F), which have been repeatedly found in viral passage experiments. We investigated their kinetic and structural properties, as well as resistance level to Mpro inhibitors: nirmatrelvir, GC376-a similar peptidomimetic for feline COVID infections, and our in-house-developed nonpeptidomimetic inhibitor Mpro61. Mpro61 maintains potency against the single variants (except for E166V) and the A173/L50F double variant, with K i values similar to those of the wild type. In contrast, while nirmatrelvir and GC376 were still effective against the A173V/L50F double variant, their K i values significantly increased up to 10-fold. None of the inhibitors appeared to be potent against E166V-containing variants. Our structural analysis revealed a significant movement of Ser1 residue in all E166V-containing variants in the presence or absence of an inhibitor. The new orientation of the Ser1 suggested potential strategies for medicinal chemistry modifications of Mpro61 to enhance hydrogen-bonding interactions between these variants and Mpro61 derivatives. These studies provide critical insights into guiding the future design of additional Mpro61 derivatives that would potentially inhibit variants with the pan-drug-resistant E166V mutation.

Design, Synthesis, and Unprecedented Interactions of Covalent Dipeptide-Based Inhibitors of SARS-CoV-2 Main Protease and Its Variants Displaying Potent Antiviral Activity

The main protease (Mpro) of SARS-CoV-2 is a key drug target for the development of antiviral therapeutics. Here, we designed and synthesized a series of small-molecule peptidomimetics with various cysteine-reactive electrophiles. Several compounds were identified as potent SARS-CoV-2 Mpro inhibitors, including compounds 8n (IC50 = 0.0752 μM), 8p (IC50 = 0.0887 μM), 8r (IC50 = 0.0199 μM), 10a (IC50 = 0.0376 μM), 10c (IC50 = 0.0177 μM), and 10f (IC50 = 0.0130 μM). Most of them additionally inhibited cathepsin L and were also active against SARS-CoV-1 and MERS-CoV Mpro. In Calu-3 cells, several inhibitors, including 8r, 10a, and 10c, displayed high antiviral activity in the nanomolar range without showing cellular toxicity. The cocrystal structure of SARS-CoV-2 Mpro in complex with 8p revealed covalent binding to the enzyme's catalytic residue Cys145 and showed specific, unprecedented interactions within the substrate binding pocket. Compounds 10c and especially 8n were effective against a panel of naturally occurring nirmatrelvir-resistant mutants, particularly E166V, and showed metabolic stability and additional favorable pharmacokinetic properties, making it a suitable candidate for further preclinical development.

A Heparan Sulfate Mimetic RAFT Copolymer Inhibits SARS-CoV-2 Infection and Ameliorates Viral-Induced Inflammation

The high transmissibility and mutation ability of coronaviruses enable them to easily escape existing immune protection and also pose a challenge to existing antiviral drugs. Moreover, drugs only targeting viruses cannot always attenuate the "cytokine storm". Herein, a synthetic heparan sulfate (HS) mimetic, HMSA-06 is reported, that exhibited antiviral activities against both the SARS-CoV-2 prototype and Omicron strains by targeting viral entry and replication. Of particular note, HMSA-06 demonstrated more potent anti-SARS-CoV-2 effects than PG545 and Roneparstat. SARS-CoV-2 is reported to hijack autophagy to facilitate its replication, therefore boosting autophagy can attenuate SARS-CoV-2 infection. It is revealed that HMSA-06, but not a similar HS mimetic that failed to inhibit SARS-CoV-2, can upregulate cellular autophagy flux. In addition, HMSA-06 was found to robustly block the NLRP3-mediated inflammatory reaction in SARS-CoV-2 infected THP-1 derived macrophages as evidenced by a reduction in inflammasome formation and the subsequent decreased secretion of mature caspase-1 and IL-1β. The HMSA-06's inflammation inhibitory function is further confirmed using a LPS/ATP-stimulated THP-1 macrophage model. Altogether, this study has identified a promising HS mimetic to combat SARS-CoV-2-associated diseases by inhibiting viral infection and attenuating viral-induced inflammatory reaction, providing insights into the development of novel anti-coronavirus drugs in the future.

Structure-guided engineering of a mutation-tolerant inhibitor peptide against variable SARS-CoV-2 spikes

Pathogen mutations present an inevitable and challenging problem for therapeutics and the development of mutation-tolerant anti-infective drugs to strengthen global health and combat evolving pathogens is urgently needed. While spike proteins on viral surfaces are attractive targets for preventing viral entry, they mutate frequently, making it difficult to develop effective therapeutics. Here, we used a structure-guided strategy to engineer an inhibitor peptide against the SARS-CoV-2 spike, called CeSPIACE, with mutation-tolerant and potent binding ability against all variants to enhance affinity for the invariant architecture of the receptor-binding domain (RBD). High-resolution structures of the peptide complexed with mutant RBDs revealed a mechanism of mutation-tolerant inhibition. CeSPIACE bound major mutant RBDs with picomolar affinity and inhibited infection by SARS-CoV-2 variants in VeroE6/TMPRSS2 cells (IC50 4 pM to 13 nM) and demonstrated potent in vivo efficacy by inhalation administration in hamsters. Mutagenesis analyses to address mutation risks confirmed tolerance against existing and/or potential future mutations of the RBD. Our strategy of engineering mutation-tolerant inhibitors may be applicable to other infectious diseases.

Targeting viral suppressor of RNAi confers anti-coronaviral activity

Infections caused by coronaviruses are persistent threats to human health in recent decades, necessitating the development of innovative anti-coronaviral therapies. RNA interference (RNAi) is a conserved cell-intrinsic antiviral mechanism in diverse eukaryotic organisms, including mammals. To counteract, many viruses encode viral suppressors of RNAi (VSRs) to evade antiviral RNAi, implying that targeting VSRs could be a promising strategy to develop antiviral therapies. Here, we designed a series of peptides specifically targeting the SARS-CoV-2-encoded VSR, nucleocapsid (N) protein. Among these peptides, one designated GL directly interacts with N protein and inactivates its VSR activity, which unlocks a potent RNAi response and effectively inhibits severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication. Moreover, GL exhibited RNAi-dependent antiviral effects not only against various SARS-CoV-2 variants, including Delta, Omicron BA.5, XBB, and JN.1, but also against other coronaviruses such as human coronavirus (HCoV)-229E, HCoV-OC43, and mouse hepatitis virus. The in vivo anti-coronaviral activity of GL was also confirmed. Our findings indicate that the VSR-targeting peptide GL has the potential to be further developed as a broad-spectrum anti-coronaviral treatment, highlighting the functional importance and therapeutic potential of antiviral RNAi.

Mining for Potent Inhibitors through Artificial Intelligence and Physics: A Unified Methodology for Ligand Based and Structure Based Drug Design

Determining the viability of a new drug molecule is a time- and resource-intensive task that makes computer-aided assessments a vital approach to rapid drug discovery. Here we develop a machine learning algorithm, iMiner, that generates novel inhibitor molecules for target proteins by combining deep reinforcement learning with real-time 3D molecular docking using AutoDock Vina, thereby simultaneously creating chemical novelty while constraining molecules for shape and molecular compatibility with target active sites. Moreover, through the use of various types of reward functions, we have introduced novelty in generative tasks for new molecules such as chemical similarity to a target ligand, molecules grown from known protein bound fragments, and creation of molecules that enforce interactions with target residues in the protein active site. The iMiner algorithm is embedded in a composite workflow that filters out Pan-assay interference compounds, Lipinski rule violations, uncommon structures in medicinal chemistry, and poor synthetic accessibility with options for cross-validation against other docking scoring functions and automation of a molecular dynamics simulation to measure pose stability. We also allow users to define a set of rules for the structures they would like to exclude during the training process and postfiltering steps. Because our approach relies only on the structure of the target protein, iMiner can be easily adapted for the future development of other inhibitors or small molecule therapeutics of any target protein.

In-cell bioluminescence resonance energy transfer (BRET)-based assay uncovers ceritinib and CA-074 as SARS-CoV-2 papain-like protease inhibitors

Papain-like protease (PLpro) is an attractive anti-coronavirus target. The development of PLpro inhibitors, however, is hampered by the limitations of the existing PLpro assay and the scarcity of validated active compounds. We developed a novel in-cell PLpro assay based on BRET and used it to evaluate and discover SARS-CoV-2 PLpro inhibitors. The developed assay demonstrated remarkable sensitivity for detecting the reduction of intracellular PLpro activity while presenting high reliability and performance for inhibitor evaluation and high-throughput screening. Using this assay, three protease inhibitors were identified as novel PLpro inhibitors that are structurally disparate from those previously known. Subsequent enzymatic assays and ligand-protein interaction analysis based on molecular docking revealed that ceritinib directly inhibited PLpro, showing high geometric complementarity with the substrate-binding pocket in PLpro, whereas CA-074 methyl ester underwent intracellular hydrolysis, exposing a free carboxyhydroxyl group essential for hydrogen bonding with G266 in the BL2 groove, resulting in PLpro inhibition.

Development of iminosugar-based glycosidase inhibitors as drug candidates for SARS-CoV-2 virus via molecular modelling and in vitro studies

We developed new iminosugar-based glycosidase inhibitors against SARS-CoV-2. Known drugs (miglustat, migalastat, miglitol, and swainsonine) were chosen as lead compounds to develop three classes of glycosidase inhibitors (α-glucosidase, α-galactosidase, and mannosidase). Molecular modelling of the lead compounds, synthesis of the compounds with the highest docking scores, enzyme inhibition tests, and in vitro antiviral assays afforded rationally designed inhibitors. Two highly active α-glucosidase inhibitors were discovered, where one of them is the most potent iminosugar-based anti-SARS-CoV-2 agent to date (EC90 = 1.94 µM in A549-ACE2 cells against Omicron BA.1 strain). However, galactosidase inhibitors did not exhibit antiviral activity, whereas mannosidase inhibitors were both active and cytotoxic. As our iminosugar-based drug candidates act by a host-directed mechanism, they should be more resilient to drug resistance. Moreover, this strategy could be extended to identify potential drug candidates for other viral infections.

Identification of adenosine analogues as nsp14 N7‑methyltransferase inhibitors for treating coronaviruses infection

Coronaviruses are RNA viruses that have coevolved with humans and animals over time, exhibiting high mutation rates and mortality rates upon epidemic outbreaks. The nonstructural protein (nsp14) is crucial for various coronaviruses processes, including genome replication, protein translation, virus particle assembly, and evasion of host immunity via RNA methylation modification. In this study, a series of adenosine analogs were designed, synthesized, and evaluated for their inhibitory activities. Among them, MTI013 exhibited the strongest nsp14 MTase inhibition and antiviral activity, with an IC50 of 10.33 μM in HCoV-229E-infected Huh7 cells, along with low cytotoxicity. When combined with the RdRp inhibitor ATV014, MTI013 showed a synergistic antiviral effect, indicating its potential both as a standalone therapy and in combination treatments. Furthermore, MTI013 displayed high selectivity against the SARS-CoV-2 nsp10-nsp16 complex and five human methyltransferases. These results offer valuable structural insights for future exploration of nsp14 as a drug target for SARS-CoV-2 and other coronaviruses.

Identification and evaluation of antiviral activity of novel compounds targeting SARS-CoV-2 virus by enzymatic and antiviral assays, and computational analysis

The viral genome of the SARS-CoV-2 coronavirus, the aetiologic agent of COVID-19, encodes structural, non-structural, and accessory proteins. Most of these components undergo rapid genetic variations, though to a lesser extent the essential viral proteases. Consequently, the protease and/or deubiquitinase activities of the cysteine proteases Mpro and PLpro became attractive targets for the design of antiviral agents. Here, we develop and evaluate new bis(benzylidene)cyclohexanones (BBC) and identify potential antiviral compounds. Three compounds were found to be effective in reducing the SARS-CoV-2 load, with EC50 values in the low micromolar concentration range. However, these compounds also exhibited inhibitory activity IC50 against PLpro at approximately 10-fold higher micromolar concentrations. Although originally developed as PLpro inhibitors, the comparison between IC50 and EC50 of BBC indicates that the mechanism of their in vitro antiviral activity is probably not directly related to inhibition of viral cysteine proteases. In conclusion, our study has identified new potential noncytotoxic antiviral compounds suitable for in vivo testing and further improvement.

An orally available Mpro/TMPRSS2 bispecific inhibitor with potent anti-coronavirus efficacy in vivo

Coronaviruses have caused three major endemics in the past two decades. Alarmingly, recent identification of novel zoonotic coronaviruses that caused human infections suggests the risk of future coronavirus outbreak caused by spillover infection from animal reservoirs remains high1,2. Therefore, development of novel therapeutic options with broad-spectrum anti-coronavirus activities are urgently needed. Here, we develop an orally-available bispecific inhibitor, TMP1, which simultaneously targets key coronavirus replication protease Mpro and the essential airway protease TMPRSS23,4. TMP1 shows broad-spectrum protection not only against different SARS-CoV-2 variants but also against multiple human-pathogenic coronaviruses in vitro. By using the K18-hACE2 transgenic mouse, hDPP4 knock-in mouse and golden Syrian hamster models, we demonstrate TMP1 cross-protects against highly-pathogenic coronaviruses (SARS-CoV-1, SARS-CoV-2 and MERS-CoV) in vivo and efficiently abrogates SARS-CoV-2 transmission. Through structural and mutagenesis studies, we confirmed the direct interaction of TMP1 with Mpro and TMPRSS2, and pinpoint the key sites of interactions. Importantly, TMP1 inhibits the infection of nirmatrelvir-resistant SARS-CoV-2 escape mutants. Together, our findings demonstrate the antiviral potential of the novel bispecific Mpro/TMPRSS2 antiviral design against human-pathogenic coronaviruses and other emerging coronaviruses.

The S2 Pocket Governs the Genus-Specific Substrate Selectivity of Coronavirus 3C-Like Protease

Coronavirus 3C-like protease (CoV 3CLpro) is essential for viral replication, providing an attractive target for monitoring the evolution of CoV and developing anti-CoV drugs. Here, the substrate-binding modes of 3CLpros from four CoV genera are analyzed and found that the S2 pocket in 3CLpro is highly conserved within each genus but differs between genera. Functionally, the S2 pocket, in conjunction with S4 and S1' pockets, governs the genus-specific substrate selectivity of 3CLpro. Resurrected ancestral 3CLpros from four CoV genera validate the genus-specific divergence of S2 pocket. Drawing upon the genus-specific S2 pocket as evolutionary marker, eight newly identified 3CLpros uncover the ancestral state of modern 3CLpro and elucidate the possible evolutionary process for CoV. It is also demonstrated that the S2 pocket is highly correlated with the genus-specific inhibitory potency of PF-07321332 (an FDA-approved drug against COVID-19) on different CoV 3CLpros. This study on 3CLpro provides novel insights to inform evolutionary mechanisms for CoV and develop genera-specific or broad-spectrum drugs against CoVs.

Effects of SARS-CoV-2 Main Protease Mutations at Positions L50, E166, and L167 Rendering Resistance to Covalent and Noncovalent Inhibitors

SARS-CoV-2 propagation under nirmatrelvir and ensitrelvir pressure selects for main protease (MPro) drug-resistant mutations E166V (DRM2), L50F/E166V (DRM3), E166A/L167F (DRM4), and L50F/E166A/L167F (DRM5). DRM2-DRM5 undergoes N-terminal autoprocessing to produce mature MPro with dimer dissociation constants (Kdimer) 2-3 times larger than that of the wildtype. Co-selection of L50F restores catalytic activity of DRM2 and DRM4 from ∼10 to 30%, relative to that of the wild-type enzyme, without altering Kdimer. Binding affinities and thermodynamic profiles that parallel the drug selection pressure, exhibiting significant decreases in affinity through entropy/enthalpy compensation, were compared with GC373. Reorganization of the active sites due to mutations observed in the inhibitor-free DRM3 and DRM4 structures as compared to MProWT may account for the reduced binding affinities, although DRM2 and DRM3 complexes with ensitrelvir are almost identical to MProWT-ensitrelvir. Chemical reactivity changes of the mutant active sites due to differences in electrostatic and protein dynamics effects likely contribute to losses in binding affinities.

Theoretical insights into the binding interaction of Nirmatrelvir with SARS-CoV-2 Mpro mutants (C145A and C145S): MD simulations and binding free-energy calculation to understand drug resistance

Mpro, the main protease and a crucial enzyme in SARS-CoV-2 is the most fascinating molecular target for pharmacological treatment and is also liable for viral protein maturation. For antiviral therapy, no drugs have been approved clinically to date. Targeting the Mpro with a compound having inhibitory properties against it can hinder viral replication. The therapeutic potential of the antiviral compound Nirmatrelvir (NMV) against SARS-CoV-2 Mpro was investigated using a systematic approach of molecular docking, MD simulations, and binding free energy calculation based on the MM-GBSA method. NMV, a covalent inhibitor with a recently revealed chemical structure, is a promising oral antiviral clinical candidate with significant in vitro anti-SARS-CoV-2 action in third-phase clinical trials. To explore the therapeutic ability and possible drug resistance, the Mpro system was studied for WT and two of its primary mutants (C145A & C145S). The protein-ligand (Mpro/NMV) complexes were further examined through long MD simulations to check the possible drug resistance in the mutants. To understand the binding affinity, the MM-GBSA method was applied to the Mpro/NMV complexes. Moreover, PCA analysis confirms the detachment of the linker region from the major domains in C145S and C145A mutants allowing for conformational alterations in the active-site region. Based on the predicted biological activities and binding affinities of NMV to WT and mutant (C145A & C145S) Mpro, it can be stipulated that NMV may have conventional potency to act as an anti-viral agent against WT Mpro, while the catalytic-dyad mutations may show substantial mutation-induced drug resistance.Communicated by Ramaswamy H. Sarma.

SARS-CoV-2 replication and drug discovery

The coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has killed millions of people and continues to wreak havoc across the globe. This sudden and deadly pandemic emphasizes the necessity for anti-viral drug development that can be rapidly administered to reduce morbidity, mortality, and virus propagation. Thus, lacking efficient anti-COVID-19 treatment, and especially given the lengthy drug development process as well as the critical death tool that has been associated with SARS-CoV-2 since its outbreak, drug repurposing (or repositioning) constitutes so far, the ideal and ready-to-go best approach in mitigating viral spread, containing the infection, and reducing the COVID-19-associated death rate. Indeed, based on the molecular similarity approach of SARS-CoV-2 with previous coronaviruses (CoVs), repurposed drugs have been reported to hamper SARS-CoV-2 replication. Therefore, understanding the inhibition mechanisms of viral replication by repurposed anti-viral drugs and chemicals known to block CoV and SARS-CoV-2 multiplication is crucial, and it opens the way for particular treatment options and COVID-19 therapeutics. In this review, we highlighted molecular basics underlying drug-repurposing strategies against SARS-CoV-2. Notably, we discussed inhibition mechanisms of viral replication, involving and including inhibition of SARS-CoV-2 proteases (3C-like protease, 3CLpro or Papain-like protease, PLpro) by protease inhibitors such as Carmofur, Ebselen, and GRL017, polymerases (RNA-dependent RNA-polymerase, RdRp) by drugs like Suramin, Remdesivir, or Favipiravir, and proteins/peptides inhibiting virus-cell fusion and host cell replication pathways, such as Disulfiram, GC376, and Molnupiravir. When applicable, comparisons with SARS-CoV inhibitors approved for clinical use were made to provide further insights to understand molecular basics in inhibiting SARS-CoV-2 replication and draw conclusions for future drug discovery research.

Amidino-rocaglates (ADRs), a class of synthetic rocaglates, are potent inhibitors of SARS-CoV-2 replication through inhibition of viral protein synthesis

Coronaviruses are highly transmissible respiratory viruses that cause symptoms ranging from mild congestion to severe respiratory distress. The recent outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has underscored the need for new antivirals with broad-acting mechanisms to combat increasing emergence of new variants. Currently, there are only a few antivirals approved for treatment of SARS-CoV-2. Previously, the rocaglate natural product silvestrol and synthetic rocaglates such as CR-1-31b were shown to have antiviral effects by inhibiting eukaryotic translation initiation factor 4A1 (eIF4A) function and virus protein synthesis. In this study, we evaluated amidino-rocaglates (ADRs), a class of synthetic rocaglates with the most potent eIF4A-inhibitory activity to-date, for inhibition of SARS-CoV-2 infection. This class of compounds showed low nanomolar potency against multiple SARS-CoV-2 variants and in multiple cell types, including human lung-derived cells, with strong inhibition of virus over host protein synthesis and low cytotoxicity. The most potent ADRs were also shown to be active against two highly pathogenic and distantly related coronaviruses, SARS-CoV and MERS-CoV. Mechanistically, cells with mutations of eIF4A1, which are known to reduce rocaglate interaction displayed reduced ADR-associated loss of cellular function, consistent with targeting of protein synthesis. Overall, ADRs and derivatives may offer new potential treatments for SARS-CoV-2 with the goal of developing a broad-acting anti-coronavirus agent.

Large scale analysis of the SARS-CoV-2 main protease reveals marginal presence of nirmatrelvir-resistant SARS-CoV-2 Omicron mutants in Ontario, Canada, December 2021-September 2023

Background

In response to the COVID-19 pandemic, a new oral antiviral called nirmatrelvir-ritonavir (PaxlovidTM) was authorized for use in Canada in January 2022. In vitro studies have reported mutations in Mpro protein that may be associated with the development of nirmatrelvir resistance.

Objectives

To survey the prevalence, relevance and temporal patterns of Mpro mutations among SARS-CoV-2 Omicron lineages in Ontario, Canada.

Methods

A total of 93,082 Mpro gene sequences from December 2021 to September 2023 were analyzed. Reported in vitro Mpro mutations were screened against our database using in-house data science pipelines to determine the nirmatrelvir resistance. Negative binomial regression was conducted to analyze the temporal trends in Mpro mutation counts over the study time period.

Results

A declining trend was observed in non-synonymous mutations of Mpro sequences, showing a 7.9% reduction (95% CI: 6.5%-‬9.4%; p<0.001) every 30 days. The P132H was the most prevalent mutation (higher than 95%) in all Omicron lineages. In vitro nirmatrelvir-resistant mutations were found in 3.12% (n=29/929) Omicron lineages with very low counts, ranging from one to 19. Only two mutations, A7T (n=19) and M82I (n=9), showed temporal presence among the BA.1.1 in 2022 and the BQ.1.2.3 in 2022, respectively.

Conclusion

The observations suggest that, as of September 2023, no significant or widespread resistance to nirmatrelvir has developed among SARS-CoV-2 Omicron variants in Ontario. This study highlights the importance of creating automated monitoring systems to track the emergence of nirmatrelvir-resistant mutations within the SARS-CoV-2 virus, utilizing genomic data generated in real-time.

Drug susceptibility and the potential for drug-resistant SARS-CoV-2 emergence in immunocompromised animals

The reduced susceptibility of mRNA vaccines and diminished neutralizing activity of therapeutic monoclonal antibodies against Omicron variants, including BQ.1.1, XBB, and their descendants, highlight the importance of antiviral therapies. Here, we assessed the efficacy of two antivirals, molnupiravir, targeting a viral RNA-dependent RNA polymerase, and nirmatrelvir, targeting a main protease, against BQ.1.1 in hamsters. We found that prophylactic or therapeutic treatment with either drug significantly reduced the viral load in the lungs of infected hamsters. We also evaluated the risk of emergence of drug-resistant viruses in immunocompromised hamsters. Although 13 days of drug treatment reduced viral titers, the immunocompromised hosts could not completely clear the virus. Viruses isolated from drug-treated immunocompromised hamsters did not show reduced susceptibility to the drugs. Molnupiravir and nirmatrelvir remain effective in vivo against variants with reduced susceptibility to monoclonal antibodies and mRNA vaccine-induced antibodies, with limited emergence of drug-resistant variants under the conditions tested.

Genetic diversity during selective sweeps in non-recombining populations

Selective sweeps, resulting from the spread of beneficial, neutral, or deleterious mutations through a population, shape patterns of genetic variation at linked neutral sites. While many theoretical, computational, and statistical advances have been made in understanding the genomic signatures of selective sweeps in recombining populations, substantially less is understood in populations with little/no recombination. We present a mathematical framework based on diffusion theory for obtaining the site frequency spectrum (SFS) at linked neutral sites immediately post and during the fixation of moderately or strongly beneficial mutations. We find that when a single hard sweep occurs, the SFS decays as 1/ x for low derived allele frequencies ( x ), similar to the neutral SFS at equilibrium, whereas at higher derived allele frequencies, it follows a 1/ x 2 power law. These power laws are universal in the sense that they are independent of the dominance and inbreeding coefficient, and also characterize the SFS during the sweep. Additionally, we find that the derived allele frequency where the SFS shifts from the 1/ x to 1/ x 2 law, is inversely proportional to the selection strength: thus under strong selection, the SFS follows the 1/ x 2 dependence for most allele frequencies, resembling a rapidly expanding neutral population. When clonal interference is pervasive, the SFS immediately post-fixation becomes U-shaped and is better explained by the equilibrium SFS of selected sites. Our results will be important in developing statistical methods to infer the timing and strength of recent selective sweeps in asexual populations, genomic regions that lack recombination, and clonally propagating tumor populations.

Emergence of transmissible SARS-CoV-2 variants with decreased sensitivity to antivirals in immunocompromised patients with persistent infections

We investigated the impact of antiviral treatment on the emergence of SARS-CoV-2 resistance during persistent infections in immunocompromised patients (n = 15). All patients received remdesivir and some also received nirmatrelvir-ritonavir (n = 3) or therapeutic monoclonal antibodies (n = 4). Sequence analysis showed that nine patients carried viruses with mutations in the nsp12 (RNA dependent RNA polymerase), while four had viruses with nsp5 (3C protease) mutations. Infectious SARS-CoV-2 with a double mutation in nsp5 (T169I) and nsp12 (V792I) was recovered from respiratory secretions 77 days after initial COVID-19 diagnosis from a patient sequentially treated with nirmatrelvir-ritonavir and remdesivir. In vitro characterization confirmed its decreased sensitivity to remdesivir and nirmatrelvir, which was overcome by combined antiviral treatment. Studies in golden Syrian hamsters demonstrated efficient transmission to contact animals. This study documents the isolation of SARS-CoV-2 carrying resistance mutations to both nirmatrelvir and remdesivir from a patient and demonstrates its transmissibility in vivo.

Nonpeptidic Irreversible Inhibitors of SARS-CoV-2 Main Protease with Potent Antiviral Activity

SARS-CoV-2 infections pose a high risk for vulnerable patients. In this study, we designed benzoic acid halopyridyl esters bearing a variety of substituents as irreversible inhibitors of the main viral protease (Mpro). Altogether, 55 benzoyl chloro/bromo-pyridyl esters were synthesized, with broad variation of the substitution pattern on the benzoyl moiety. A workflow was employed for multiparametric optimization, including Mpro inhibition assays of SARS-CoV-2 and related pathogenic coronaviruses, the duration of enzyme inhibition, the compounds' stability versus glutathione, cytotoxicity, and antiviral activity. Several compounds showed IC50 values in the low nanomolar range, kinact/Ki values of >100,000 M-1 s-1 and high antiviral activity. High-resolution X-ray cocrystal structures indicated an important role of ortho-fluorobenzoyl substitution, forming a water network that stabilizes the inhibitor-bound enzyme. The most potent antiviral compound was the p-ethoxy-o-fluorobenzoyl chloropyridyl ester (PSB-21110, 29b, MW 296 g/mol; EC50 2.68 nM), which may serve as a lead structure for broad-spectrum anticoronaviral therapeutics.

A comprehensive study of SARS-CoV-2 main protease (Mpro) inhibitor-resistant mutants selected in a VSV-based system

Nirmatrelvir was the first protease inhibitor specifically developed against the SARS-CoV-2 main protease (3CLpro/Mpro) and licensed for clinical use. As SARS-CoV-2 continues to spread, variants resistant to nirmatrelvir and other currently available treatments are likely to arise. This study aimed to identify and characterize mutations that confer resistance to nirmatrelvir. To safely generate Mpro resistance mutations, we passaged a previously developed, chimeric vesicular stomatitis virus (VSV-Mpro) with increasing, yet suboptimal concentrations of nirmatrelvir. Using Wuhan-1 and Omicron Mpro variants, we selected a large set of mutants. Some mutations are frequently present in GISAID, suggesting their relevance in SARS-CoV-2. The resistance phenotype of a subset of mutations was characterized against clinically available protease inhibitors (nirmatrelvir and ensitrelvir) with cell-based, biochemical and SARS-CoV-2 replicon assays. Moreover, we showed the putative molecular mechanism of resistance based on in silico molecular modelling. These findings have implications on the development of future generation Mpro inhibitors, will help to understand SARS-CoV-2 protease inhibitor resistance mechanisms and show the relevance of specific mutations, thereby informing treatment decisions.

SARS-CoV-2 Resistance to Small Molecule Inhibitors

Purpose of the Review

SARS-CoV-2 undergoes genetic mutations like many other viruses. Some mutations lead to the emergence of new Variants of Concern (VOCs), affecting transmissibility, illness severity, and the effectiveness of antiviral drugs. Continuous monitoring and research are crucial to comprehend variant behavior and develop effective response strategies, including identifying mutations that may affect current drug therapies.

Recent Findings

Antiviral therapies such as Nirmatrelvir and Ensitrelvir focus on inhibiting 3CLpro, whereas Remdesivir, Favipiravir, and Molnupiravir target nsp12, thereby reducing the viral load. However, the emergence of resistant mutations in 3CLpro and nsp12 could impact the efficiency of these small molecule drug therapeutics.

Summary

This manuscript summarizes mutations in 3CLpro and nsp12, which could potentially reduce the efficacy of drugs. Additionally, it encapsulates recent advancements in small molecule antivirals targeting SARS-CoV-2 viral proteins, including their potential for developing resistance against emerging variants.

SARS-CoV-2 Mpro inhibitor identification using a cellular gain-of-signal assay for high-throughput screening

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2, SARS2) is responsible for the COVID-19 pandemic and infections that continue to affect the lives of millions of people worldwide, especially those who are older and/or immunocompromised. The SARS2 main protease enzyme, Mpro (also called 3C-like protease, 3CLpro), is a bona fide drug target as evidenced by potent inhibition with nirmatrelvir and ensitrelvir, the active components of the drugs Paxlovid and Xocova, respectively. However, the existence of nirmatrelvir and ensitrelvir-resistant isolates underscores the need to develop next-generation drugs with different resistance profiles and/or distinct mechanisms of action. Here, we report the results of a high-throughput screen of 649,568 compounds using a cellular gain-of-signal assay. In this assay, Mpro inhibits expression of a luciferase reporter, and 8,777 small molecules were considered hits by causing a gain in luciferase activity 3x SD above the sample field activity (6.8% gain-of-signal relative to 100 µM GC376). Single concentration and dose-response gain-of-signal experiments confirmed 3,522/8,762 compounds as candidate inhibitors. In parallel, all initial high-throughput screening hits were tested in a peptide cleavage assay with purified Mpro and only 39/8,762 showed inhibition. Importantly, 19/39 compounds (49%) re-tested positive in both SARS2 assays, including two previously reported Mpro inhibitors, demonstrating the efficacy of the overall screening strategy. This approach led to the rediscovery of known Mpro inhibitors such as calpain inhibitor II, as well as to the discovery of novel compounds that provide chemical information for future drug development efforts.

Non-Covalent Inhibitors of SARS-CoV-2 Papain-Like Protease (PLpro): In Vitro and In Vivo Antiviral Activity

The SARS-CoV-2 papain-like protease (PLpro), essential for viral processing and immune response disruption, is a promising target for treating acute infection of SARS-CoV-2. To date, there have been no reports of PLpro inhibitors with both submicromolar potency and animal model efficacy. To address the challenge of PLpro's featureless active site, a noncovalent inhibitor library with over 50 new analogs was developed, targeting the PLpro active site by modulating the BL2-loop and engaging the BL2-groove. Notably, compounds 42 and 10 exhibited strong antiviral effects and were further analyzed pharmacokinetically. 10, in particular, showed a significant lung accumulation, up to 12.9-fold greater than plasma exposure, and was effective in a mouse model of SARS-CoV-2 infection, as well as against several SARS-CoV-2 variants. These findings highlight the potential of 10 as an in vivo chemical probe for studying PLpro inhibition in SARS-CoV-2 infection.

Predictive Assessment of the Antiviral Properties of Imperata cylindrica against SARS-CoV-2

The omicron variant and its sublineages are highly contagious, and they still constitute a global source of concern despite vaccinations. Hospitalizations and mortality rates resulting from infections by these variants of concern are still common. The existing therapeutic alternatives have presented various setbacks such as low potency, poor pharmacokinetic profiles, and drug resistance. The need for alternative therapeutic options cannot be overemphasized. Plants and their phytochemicals present interesting characteristics that make them suitable candidates for the development of antiviral therapeutic agents. This study aimed to investigate the antiviral potential of Imperata cylindrica (I. cylindrica). Specifically, the objective of this study was to identify I. cylindrica phytochemicals that display inhibitory effects against SARS-CoV-2 main protease (Mpro), a highly conserved protein among coronaviruses. Molecular docking and in silico pharmacokinetic assays were used to assess 72 phytocompounds that are found in I. cylindrica as ligands and Mpro (6LU7) as the target. Only eight phytochemicals (bifendate, cylindrene, tabanone, siderin, 5-hydroxy-2-[2-(2-hydroxyphenyl)ethyl]-4H-1-benzopyran-4-one, maritimin, 5-methoxyflavone, and flavone) displayed high binding affinities with Mpro with docking scores ranging from -5.6 kcal/mol to -9.1 kcal/mol. The in silico pharmacokinetic and toxicological assays revealed that tabanone was the best and safest phytochemical for the development of an inhibitory agent against coronavirus main protease. Thus, the study served as a baseline for further in vitro and in vivo assessment of this phytochemical against Mpro of SARS-CoV-2 variants of concern to validate these in silico findings.

In vitro selection and analysis of SARS-CoV-2 nirmatrelvir resistance mutations contributing to clinical virus resistance surveillance

To facilitate the detection and management of potential clinical antiviral resistance, in vitro selection of drug-resistant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) against the virus Mpro inhibitor nirmatrelvir (Paxlovid active component) was conducted. Six Mpro mutation patterns containing T304I alone or in combination with T21I, L50F, T135I, S144A, or A173V emerged, with A173V+T304I and T21I+S144A+T304I mutations showing >20-fold resistance each. Biochemical analyses indicated inhibition constant shifts aligned to antiviral results, with S144A and A173V each markedly reducing nirmatrelvir inhibition and Mpro activity. SARS-CoV-2 surveillance revealed that in vitro resistance-associated mutations from our studies and those reported in the literature were rarely detected in the Global Initiative on Sharing All Influenza Data database. In the Paxlovid Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients trial, E166V was the only emergent resistance mutation, observed in three Paxlovid-treated patients, none of whom experienced COVID-19-related hospitalization or death.

New Strategies for Responding to SARS-CoV-2: The Present and Future of Dual-Target Drugs

The 2019 coronavirus disease (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in millions of deaths, posing a serious threat to public health and safety. Rapid mutations of SARS-CoV-2 and complex interactions among multiple targets during infection pose a risk of expiry for small molecule inhibitors. This suggests that the traditional concept of "one bug, one drug" could be ineffective in dealing with the coronavirus. The dual-target drug strategy is expected to be the key to ending coronavirus infections. However, the lack of design method and improper combination of dual-targets poses obstacle to the discovery of new dual-target drugs. In this Perspective, we summarized the profiles concerning drug design methods, structure-activity relationships, and pharmacological parameters of dual-target drugs for the treatment of COVID-19. Importantly, we underscored how target combination and rational drug design illuminate the development of dual-target drugs for SARS-CoV-2.

Computational Insights into SARS-CoV-2 Main Protease Mutations and Nirmatrelvir Efficacy: The Effects of P132H and P132H-A173V

Nirmatrelvir, a pivotal component of the oral antiviral Paxlovid for COVID-19, targets the SARS-CoV-2 main protease (Mpro) as a covalent inhibitor. Here, we employed combined computational methods to explore how the prevalent Omicron variant mutation P132H, alone and in combination with A173V (P132H-A173V), affects nirmatrelvir's efficacy. Our findings suggest that P132H enhances the noncovalent binding affinity of Mpro for nirmatrelvir, whereas P132H-A173V diminishes it. Although both mutants catalyze the rate-limiting step more efficiently than the wild-type (WT) Mpro, P132H slows the overall rate of covalent bond formation, whereas P132H-A173V accelerates it. Comprehensive analysis of noncovalent and covalent contributions to the overall binding free energy of the covalent complex suggests that P132H likely enhances Mpro sensitivity to nirmatrelvir, while P132H-A173V may confer resistance. Per-residue decompositions of the binding and activation free energies pinpoint key residues that significantly affect the binding affinity and reaction rates, revealing how the mutations modulate these effects. The mutation-induced conformational perturbations alter drug-protein local contact intensities and the electrostatic preorganization of the protein, affecting noncovalent binding affinity and the stability of key reaction states, respectively. Our findings inform the mechanisms of nirmatrelvir resistance and sensitivity, facilitating improved drug design and the detection of resistant strains.

A Phase 3, Randomized, Controlled Trial Evaluating the Efficacy and Safety of Ropeginterferon Alfa-2b in Patients with Moderate COVID-19

INTRODUCTION

Ropeginterferon alfa-2b is a novel mono-pegylated proline-interferon. This clinical study aimed to evaluate its antiviral efficacy of ropeginterferon alfa-2b against SARS-CoV-2 infection.

METHODS

This is a multicenter, randomized, open-label study. Adult patients with confirmed SARS-CoV-2 infection with initial cycle threshold (Ct) value < 30 and symptom onset within 4 days were enrolled. Eligible patients were randomized in a 2:1 ratio to receive a single 250-µg dose of ropeginterferon alfa-2b subcutaneously plus standard of care (SOC) or to receive SOC alone. The primary endpoint was the proportion of patients with a negative RT-PCR result for SARS-CoV-2 or discharged from the hospital before Day 8. Change in clinical status based on the World Health Organization (WHO) clinical progression scale and pulmonary infiltrations through chest radiograph were also evaluated.

RESULTS

A total of 132 patients were enrolled and treated with study medication. Higher percentages of patients who achieved Ct ≥ 30 or were discharged from the hospital were observed on Day 8 and every other time point of assessment, i.e., Days 5, 11, 15, and 22, in the ropeginterferon alfa-2b group compared to the SOC alone group. However, the difference was statistically significant on Day 11 but not on Day 8. The primary endpoint was not met. The ropeginterferon alfa-2b group showed a higher improvement rate in lung infiltration on Day 5 (27.6% vs. 0.0%, p = 0.0087) and a higher improvement rate in WHO clinical progression scores on Day 8 (69.4% vs. 35.3%, p = 0.03) than those in the SOC group. No ropeginterferon alfa-2b-related serious adverse event was observed.

CONCLUSION

Our data show that ropeginterferon alfa-2b with SOC shortened the duration of SARS-CoV-2 shedding compared with SOC alone. In addition, ropeginterferon alfa-2b as an additional therapy could be beneficial by improving lung infiltration.

Low Prevalence of Nirmatrelvir-Ritonavir Resistance-Associated Mutations in SARS-CoV-2 Lineages From Botswana

Background

We evaluated naturally occurring nirmatrelvir-ritonavir (NTV/r) resistance-associated mutations (RAMs) among severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) strains from Botswana, a country with no NTV/r use to date, in order to recommend the usage of the agent for high-risk patients with coronavirus disease 2019 (COVID-19).

Methods

We conducted a retrospective analysis using 5254 complete SARS-CoV-2 sequences from Botswana (September 2020-September 2023). We evaluated the mutational landscape of SARS-CoV-2 3-Chymotrypsin-like protease (3CLpro) relative to the highlighted list of RAMs granted Food and Drug Administration Emergency Use Authorization in 2023.

Results

The sequenced 5254 samples included Beta variants of concerns (VOCs; n = 323), Delta VOCs (n = 1314), and Omicron VOCs (n = 3354). Overall, 77.8% of the sequences exhibited at least 1 polymorphism within 76/306 amino acid positions in the nsp5 gene. NTV/rRAMs were identified in 34/5254 (0.65%; 95% CI, 0.43%-0.87%) and occurred at 5 distinct positions. Among the NTV/r RAMS detected, A191V was the most prevalent (24/34; 70.6%). Notably, T21I mutation had a prevalence of 20.6% (7/34) and coexisted with either K90R (n = 3) polymorphism in Beta sequences with RAMs or P132H (n = 3) polymorphism for Omicron sequences with RAMs. Other NTV/r RAMs detected included P108S, with a prevalence of 5.88% (2/34), and L50F, with a prevalence of 2.94% (1/34). NTV/r RAMs were significantly higher (P < .001) in Delta (24/35) compared with Beta (4/34) and Omicron (6/34) sequences.

Conclusions

The frequency of NTV/r RAMs in Botswana was low. Higher rates were observed in Delta VOCs compared to Omicron and Beta VOCs. As NTV/r use expands globally, continuous surveillance for drug-resistant variants is essential, given the RAMs identified in our study.

Analysis of SARS-CoV-2 Mutations after Nirmatrelvir Treatment in a Lung Cancer Xenograft Mouse Model

Paxlovid is the first approved oral treatment for coronavirus disease 2019 and includes nirmatrelvir, a protease inhibitor targeting the main protease (Mpro) of SARS-CoV-2, as one of the key components. While some specific mutations emerged in Mpro were revealed to significantly reduce viral susceptibility to nirmatrelvir in vitro, there is no report regarding resistance to nirmatrelvir in patients and animal models for SARS-CoV-2 infection yet. We recently developed xenograft tumors derived from Calu-3 cells in immunodeficient mice and demonstrated extended replication of SARS-CoV-2 in the tumors. In this study, we investigated the effect of nirmatrelvir administration on SARS-CoV-2 replication. Treatment with nirmatrelvir after virus infection significantly reduced the replication of the parental SARS-CoV-2 and SARS-CoV-2 Omicron at 5 days post-infection (dpi). However, the virus titers were completely recovered at the time points of 15 and 30 dpi. The virus genomes in the tumors at 30 dpi were analyzed to investigate whether nirmatrelvir-resistant mutant viruses had emerged during the extended replication of SARS-CoV-2. Various mutations in several genes including ORF1ab, ORF3a, ORF7a, ORF7b, ORF8, and N occurred in the SARS-CoV-2 genome; however, no mutations were induced in the Mpro sequence by a single round of nirmatrelvir treatment, and none were observed even after two rounds of treatment. The parental SARS-CoV-2 and its sublineage isolates showed similar IC50 values of nirmatrelvir in Vero E6 cells. Therefore, it is probable that inducing viral resistance to nirmatrelvir in vivo is challenging differently from in vitro passage.

Glycyrrhizic acid conjugates with amino acid methyl esters target the main protease, exhibiting antiviral activity against wild-type and nirmatrelvir-resistant SARS-CoV-2 variants

COVID-19 pandemic is predominantly caused by SARS-CoV-2, with its main protease, Mpro, playing a pivotal role in viral replication and serving as a potential target for inhibiting different variants. In this study, potent Mpro inhibitors were identified from glycyrrhizic acid (GL) derivatives with amino acid methyl/ethyl esters. Out of the 17 derivatives semisynthesized, Compounds 2, 6, 9, and 15, with methionine methyl esters, D-tyrosine methyl esters, glutamic acid methyl esters, and methionines in the carbohydrate moiety, respectively, significantly inhibited wild-type SARS-CoV-2 Mpro-mediated proteolysis, with IC50 values ranging from 0.06 μM to 0.84 μM. They also demonstrated efficacy in inhibiting trans-cleavage by mutant Mpro variants (Mpro_P132H, Mpro_E166V, Mpro_P168A, Mpro_Q189I), with IC50 values ranging from 0.05 to 0.92 μM, surpassing nirmatrelvir (IC50: 1.17-152.9 μM). Molecular modeling revealed stronger interactions with Valine166 in the structural complex of Mpro_E166V with the compounds compared to nirmatrelvir. Moreover, these compounds efficiently inhibited the post-entry viral processes of wild-type SARS-CoV-2 single-round infectious particles (SRIPs), mitigating viral cytopathic effects and reducing replicon-driven GFP reporter signals, as well as in vitro infectivity of wild-type, Mpro_E166V, and Mpro_Q189I SRIPs, with EC50 values ranging from 0.02 to 0.53 μM. However, nirmatrelvir showed a significant decrease in inhibiting the replication of mutant SARS-CoV-2 SRIPs carrying Mpro_E166V (EC50: >20 μM) and Mpro_Q189I (EC50: 13.2 μM) compared to wild-type SRIPs (EC50: 0.06 μM). Overall, this study identifies four GL derivatives as promising lead compounds for developing treatments against various SARS-CoV-2 strains, including Omicron, and nirmatrelvir-resistant variants.

Progress in SARS-CoV-2, diagnostic and clinical treatment of COVID-19

Background

Corona Virus Disease 2019(COVID-19)is a global pandemic novel coronavirus infection disease caused by Severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2). Although rapid, large-scale testing plays an important role in patient management and slowing the spread of the disease. However, there has been no good and widely used drug treatment for infection and transmission of SARS-CoV-2.

Key findings

Therefore, this review updates the body of knowledge on viral structure, infection routes, detection methods, and clinical treatment, with the aim of responding to the large-section caused by SARS-CoV-2. This paper focuses on the structure of SARS-CoV-2 viral protease, RNA polymerase, serine protease and main proteinase-like protease as well as targeted antiviral drugs.

Conclusion

In vitro or clinical trials have been carried out to provide deeper thinking for the pathogenesis, clinical diagnosis, vaccine development and treatment of SARS-CoV-2.

Study of key residues in MERS-CoV and SARS-CoV-2 main proteases for resistance against clinically applied inhibitors nirmatrelvir and ensitrelvir

The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) is an epidemic, zoonotically emerging pathogen initially reported in Saudi Arabia in 2012. MERS-CoV has the potential to mutate or recombine with other coronaviruses, thus acquiring the ability to efficiently spread among humans and become pandemic. Its high mortality rate of up to 35% and the absence of effective targeted therapies call for the development of antiviral drugs for this pathogen. Since the beginning of the SARS-CoV-2 pandemic, extensive research has focused on identifying protease inhibitors for the treatment of SARS-CoV-2. Our intention was therefore to assess whether these protease inhibitors are viable options for combating MERS-CoV. To that end, we used previously established protease assays to quantify inhibition of SARS-CoV-2, MERS-CoV and other main proteases. Nirmatrelvir inhibited several of these proteases, whereas ensitrelvir was less broadly active. To simulate nirmatrelvir's clinical use against MERS-CoV and subsequent resistance development, we applied a safe, surrogate virus-based system. Using the surrogate virus, we previously selected hallmark mutations of SARS-CoV-2-Mpro, such as T21I, M49L, S144A, E166A/K/V and L167F. In the current study, we selected a pool of MERS-CoV-Mpro mutants, characterized the resistance and modelled the steric effect of catalytic site mutants S142G, S142R, S147Y and A171S.

Emergence of transmissible SARS-CoV-2 variants with decreased sensitivity to antivirals in immunocompromised patients with persistent infections

We investigated the impact of antiviral treatment on the emergence of SARS-CoV-2 resistance during persistent infections in immunocompromised patients (n=15). All patients received remdesivir and some also received nirmatrelvir-ritonavir or monoclonal antibodies. Sequence analysis showed that nine patients carried viruses with mutations in the nsp12 (RNA dependent RNA polymerase), while four had viruses with nsp5 (3C protease) mutations. Infectious SARS-CoV-2 with a double mutation in nsp5 (T169I) and nsp12 (V792I) was recovered from respiratory secretions 77 days after initial COVID-19 diagnosis from a patient treated with remdesivir and nirmatrelvir-ritonavir. In vitro characterization confirmed its decreased sensitivity to remdesivir and nirmatrelvir, which was overcome by combined antiviral treatment. Studies in golden Syrian hamsters demonstrated efficient transmission to contact animals. This study documents the isolation of SARS-CoV-2 carrying resistance mutations to both nirmatrelvir and remdesivir from a patient and demonstrates its transmissibility in vivo.

Macrocyclic Azapeptide Nitriles: Structure-Based Discovery of Potent SARS-CoV-2 Main Protease Inhibitors as Antiviral Drugs

Given the crucial role of the main protease (Mpro) in the replication cycle of SARS-CoV-2, this viral cysteine protease constitutes a high-profile drug target. We investigated peptidomimetic azapeptide nitriles as auspicious, irreversibly acting inhibitors of Mpro. Our systematic approach combined an Mpro active-site scanning by combinatorially assembled azanitriles with structure-based design. Encouraged by the bioactive conformation of open-chain inhibitors, we conceptualized the novel chemotype of macrocyclic azanitriles whose binding mode was elucidated by cocrystallization. This strategy provided a favorable entropic contribution to target binding and resulted in the development of the extraordinarily potent Mpro inhibitor 84 with an IC50 value of 3.23 nM and a second-order rate constant of inactivation, kinac/Ki, of 448,000 M-1s-1. The open-chain Mpro inhibitor 58, along with the macrocyclic compounds 83 and 84, a broad-spectrum anticoronaviral agent, demonstrated the highest antiviral activity with EC50 values in the single-digit micromolar range. Our findings are expected to promote the future development of peptidomimetic Mpro inhibitors as anti-SARS-CoV-2 agents.

Inhibition of endocytic uptake of severe acute respiratory syndrome coronavirus 2 and endo-lysosomal acidification by diphenoxylate

Cell culture-based screening of a chemical library identified diphenoxylate as an antiviral agent against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The observed 50% effective concentrations ranged between 1.4 and 4.9 µM against the original wild-type strain and its variants. Time-of-addition experiments indicated that diphenoxylate is an entry blocker targeting a host factor involved in viral infection. Fluorescence microscopic analysis visualized that diphenoxylate prevented SARS-CoV-2 particles from penetrating the cell membrane and also impaired endo-lysosomal acidification. Diphenoxylate exhibited a synergistic inhibitory effect on SARS-CoV-2 infection in human lung epithelial Calu-3 cells when combined with a transmembrane serine protease 2 (TMPRSS2) inhibitor, nafamostat. This synergy suggested that efficient antiviral activity is achieved by blocking both TMPRSS2-mediated early and endosome-mediated late SARS-CoV-2 entry pathways. The antiviral efficacy of diphenoxylate against SARS-CoV-2 was reproducible in a human tonsil organoids system. In a transgenic mouse model expressing the obligate SARS-CoV-2 receptor, human angiotensin-converting enzyme 2, intranasal administration of diphenoxylate (10 mg/kg/day) significantly reduced the viral RNA copy number in the lungs by 70% on day 3. This study underscores that diphenoxylate represents a promising core scaffold, warranting further exploration for chemical modifications aimed at developing a new class of clinically effective antiviral drugs against SARS-CoV-2.

Sporadic Occurrence of Ensitrelvir-Resistant SARS-CoV-2, Japan

Using the GISAID EpiCoV database, we identified 256 COVID-19 patients in Japan during March 31-December 31, 2023, who had mutations in the SARS-CoV-2 nonstructural protein 5 conferring ensitrelvir resistance. Ongoing genomic surveillance is required to monitor emergence of SARS-CoV-2 mutations that are resistant to anticoronaviral drugs.

The host-targeted antiviral drug Zapnometinib exhibits a high barrier to the development of SARS-CoV-2 resistance

Host targeting antiviral drugs (HTA) are directed against cellular mechanisms which can be exploited by viruses. These mechanisms are essential for viral replication, because missing functions cannot be compensated by the virus. However, this assumption needs experimental proof. Here we compared the HTA Zapnometinib (ZMN), with direct acting antivirals (DAA) (Remdesivir (RDV), Molnupiravir (MPV), Nirmatrelvir (NTV), Ritonavir (RTV), Paxlovid PAX)), in terms of their potency to induce reduced drug susceptibilities in SARS-CoV-2. During serial passage of δ-B1.617.2 adaptation to all DAAs occurred, while the inhibitory capacity of ZMN was not altered. Known single nucleotide polymorphisms (SNPs) responsible for partial resistances were found for RDV, NTV and PAX. Additionally, the high mutagenic potential of MPV was confirmed and decreased drug efficacies were found for the first time. Reduced DAA efficacy did not alter the inhibitory potential of ZMN. These results show that ZMN confers a high barrier towards the development of viral resistance and has the potential to act against partially DAA-insensitive viruses.

SARS-CoV-2 Mpro oligomerization as a potential target for therapy

The main protease (Mpro) of SARS-CoV-2 is critical in the virus's replication cycle, facilitating the maturation of polyproteins into functional units. Due to its conservation across taxa, Mpro is a promising target for broad-spectrum antiviral drugs. Targeting Mpro with small molecule inhibitors, such as nirmatrelvir combined with ritonavir (Paxlovid™), which the FDA has approved for post-exposure treatment and prophylaxis, can effectively interrupt the replication process of the virus. A key aspect of Mpro's function is its ability to form a functional dimer. However, the mechanics of dimerization and its influence on proteolytic activity remain less understood. In this study, we utilized biochemical, structural, and molecular modelling approaches to explore Mpro dimerization. We evaluated critical residues, specifically Arg4 and Arg298, that are essential for dimerization. Our results show that changes in the oligomerization state of Mpro directly affect its enzymatic activity and dimerization propensity. We discovered a synergistic relationship influencing dimer formation, involving both intra- and intermolecular interactions. These findings highlight the potential for developing allosteric inhibitors targeting Mpro, offering promising new directions for therapeutic strategies.

SARS-CoV-2 resistance to monoclonal antibodies and small-molecule drugs

Over four years have passed since the beginning of the COVID-19 pandemic. The scientific response has been rapid and effective, with many therapeutic monoclonal antibodies and small molecules developed for clinical use. However, given the ability for viruses to become resistant to antivirals, it is perhaps no surprise that the field has identified resistance to nearly all of these compounds. Here, we provide a comprehensive review of the resistance profile for each of these therapeutics. We hope that this resource provides an atlas for mutations to be aware of for each agent, particularly as a springboard for considerations for the next generation of antivirals. Finally, we discuss the outlook and thoughts for moving forward in how we continue to manage this, and the next, pandemic.

Review: The Landscape of Antiviral Therapy for COVID-19 in the Era of Widespread Population Immunity and Omicron-Lineage Viruses

The goals of coronavirus disease 2019 (COVID-19) antiviral therapy early in the pandemic were to prevent severe disease, hospitalization, and death. As these outcomes have become infrequent in the age of widespread population immunity, the objectives have shifted. For the general population, COVID-19-directed antiviral therapy should decrease symptom severity and duration and minimize infectiousness, and for immunocompromised individuals, antiviral therapy should reduce severe outcomes and persistent infection. The increased recognition of virologic rebound following ritonavir-boosted nirmatrelvir (NMV/r) and the lack of randomized controlled trial data showing benefit of antiviral therapy for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection for standard-risk, vaccinated individuals remain major knowledge gaps. Here, we review data for selected antiviral agents and immunomodulators currently available or in late-stage clinical trials for use in outpatients. We do not review antibody products, convalescent plasma, systemic corticosteroids, IL-6 inhibitors, Janus kinase inhibitors, or agents that lack Food and Drug Administration approval or emergency use authorization or are not appropriate for outpatients.

Resistance mechanisms of SARS-CoV-2 3CLpro to the non-covalent inhibitor WU-04

Drug resistance poses a significant challenge in the development of effective therapies against SARS-CoV-2. Here, we identified two double mutations, M49K/M165V and M49K/S301P, in the 3C-like protease (3CLpro) that confer resistance to a novel non-covalent inhibitor, WU-04, which is currently in phase III clinical trials (NCT06197217). Crystallographic analysis indicates that the M49K mutation destabilizes the WU-04-binding pocket, impacting the binding of WU-04 more significantly than the binding of 3CLpro substrates. The M165V mutation directly interferes with WU-04 binding. The S301P mutation, which is far from the WU-04-binding pocket, indirectly affects WU-04 binding by restricting the rotation of 3CLpro's C-terminal tail and impeding 3CLpro dimerization. We further explored 3CLpro mutations that confer resistance to two clinically used inhibitors: ensitrelvir and nirmatrelvir, and revealed a trade-off between the catalytic activity, thermostability, and drug resistance of 3CLpro. We found that mutations at the same residue (M49) can have distinct effects on the 3CLpro inhibitors, highlighting the importance of developing multiple antiviral agents with different skeletons for fighting SARS-CoV-2. These findings enhance our understanding of SARS-CoV-2 resistance mechanisms and inform the development of effective therapeutics.