Multicountry Spread of Influenza A(H1N1)pdm09 Viruses with Reduced Oseltamivir Inhibition, May 2023-February 2024.

Since May 2023, a novel combination of neuraminidase mutations, I223V + S247N, has been detected in influenza A(H1N1)pdm09 viruses collected in countries spanning 5 continents, mostly in Europe (67/101). The viruses belong to 2 phylogenetically distinct groups and display ≈13-fold reduced inhibition by oseltamivir while retaining normal susceptibility to other antiviral drugs.

Modular Biomimetic Strategy Enables Discovery and SAR Exploration of Oxime Macrocycles as Influenza A Virus (H1N1) Inhibitors.

Although vaccination remains the prevalent prophylactic means for controlling Influenza A virus (IAV) infections, novel structural antivirus small-molecule drugs with new mechanisms of action for treating IAV are highly desirable. Herein, we describe a modular biomimetic strategy to expeditiously achieve a new class of macrocycles featuring oxime, which might target the hemagglutinin (HA)-mediated IAV entry into the host cells. SAR analysis revealed that the size and linker of the macrocycles play an important role in improving potency. Particularly, as a 14-membered macrocyclic oxime, 37 exhibited potent inhibitory activity against IAV H1N1 with an EC50 value of 23 nM and low cytotoxicity, which alleviated cytopathic effects and protected cell survival obviously after H1N1 infection. Furthermore, 37 showed significant synergistic activity with neuraminidase inhibitor oseltamivir in vitro.

Natural Product-Derived Phytochemicals for Influenza A Virus (H1N1) Prevention and Treatment.

Influenza A (H1N1) viruses are prone to antigenic mutations and are more variable than other influenza viruses. Therefore, they have caused continuous harm to human public health since the pandemic in 2009 and in recent times. Influenza A (H1N1) can be prevented and treated in various ways, such as direct inhibition of the virus and regulation of human immunity. Among antiviral drugs, the use of natural products in treating influenza has a long history, and natural medicine has been widely considered the focus of development programs for new, safe anti-influenza drugs. In this paper, we focus on influenza A (H1N1) and summarize the natural product-derived phytochemicals for influenza A virus (H1N1) prevention and treatment, including marine natural products, flavonoids, alkaloids, terpenoids and their derivatives, phenols and their derivatives, polysaccharides, and derivatives of natural products for prevention and treatment of influenza A (H1N1) virus. We further discuss the toxicity and antiviral mechanism against influenza A (H1N1) as well as the druggability of natural products. We hope that this review will facilitate the study of the role of natural products against influenza A (H1N1) activity and provide a promising alternative for further anti-influenza A drug development.

Effects and mechanism of Qingke Pingchuan granules against influenza virus infection.

Qingke Pingchuan granules (QPGs), which contain Houttuynia cordata Thunb, Fritillaria cirrhosa, fired licorice, and fired bitter almonds, among other components, can clear heat and ventilate the lungs, relieving cough and asthma. Clinically, QPGs are mainly used to treat cough, asthma, fever and other discomforts caused by acute or chronic bronchitis. In this study, the antiviral activity of QPGs against respiratory syncytial virus (RSV), influenza A virus A/FM/1/47 (H1N1), oseltamivir-resistant H1N1, A/Beijing/32/92 (H3N2), Sendai virus, and human adenovirus type 3 in Hep-2 or MDCK cells was evaluated using the CCK-8 method, and the cytotoxicity of QPGs to these two cell lines was tested. The effect of QPGs on mice infected with influenza A virus A/FM/1/47 (H1N1) was evaluated by measuring body weight, survival time, and survival rate, as well as virus titers and lesions in the lungs and levels of inflammatory factors in serum. In addition, the expression of TLR-7-My88-NF-κB signaling pathway-related proteins in lung tissues was analyzed by Western blotting and qRT-PCR. The results showed that QPGs had a potent inhibitory effect on the six viruses tested in vitro. Interestingly, QPGs also displayed particularly pronounced antiviral activity against H1N1-OC, similar to that of oseltamivir, a well-known antiviral drug. QPGs effectively protected mice from infection by H1N1, as indicated by significantly increased body weights, survival times, and survival rates and reduced lung virus titers of inflammatory factors and lung tissue injury. The levels of TLR-7-MyD88-NF-κB-pathway-related proteins in the lung tissue of infected mice were found to be decreased after QPG treatment, thereby alleviating lung injury caused by excessive release of inflammatory factors. Taken together, these findings indicate that QPGs have satisfactory activity against influenza virus infection.

Novel Acyl Thiourea-Based Hydrophobic Tagging Degraders Exert Potent Anti-Influenza Activity through Two Distinct Endonuclease Polymerase Acidic-Targeted Degradation Pathways.

The spread of the influenza virus has caused devastating pandemics and huge economic losses worldwide. Antiviral drugs with diverse action modes are urgently required to overcome the challenges of viral mutation and drug resistance, and targeted protein degradation strategies constitute excellent candidates for this purpose. Herein, the first degradation of the influenza virus polymerase acidic (PA) protein using small-molecule degraders developed by hydrophobic tagging (HyT) technology to effectively combat the influenza virus was reported. The SAR results revealed that compound 19b with Boc2-(L)-Lys demonstrated excellent inhibitory activity against A/WSN/33/H1N1 (EC50 = 0.015 µM) and amantadine-resistant strain (A/PR/8/H1N1), low cytotoxicity, high selectivity, substantial degradation ability, and good drug-like properties. Mechanistic studies demonstrated that the proteasome system and autophagic lysosome pathway were the potential drivers of these HyT degraders. Thus, this study provides a powerful tool for investigating the targeted degradation of influenza virus proteins and for antiviral drug development.

Low antiviral resistance in Influenza A and B viruses isolated in Mexico from 2010 to 2023.

The most widely used class of antivirals available for Influenza treatment are the neuraminidase inhibitors (NAI) Oseltamivir and Zanamivir. However, amino acid (AA) substitutions in the neuraminidase may cause reduced inhibition or high antiviral resistance. In Mexico, the current state of knowledge about NAI susceptibility is scarce, in this study we report the results of 14 years of Influenza surveillance by phenotypic and genotypic methods. A total of 255 isolates were assessed with the NAI assay, including Influenza A(H1N1)pdm09, A(H3N2) and Influenza B (IBV). Furthermore, 827 sequences contained in the GISAID platform were analyzed in search of relevant mutations.Overall, five isolates showed highly reduced inhibition or reduced inhibition to Oseltamivir, and two showed reduced inhibition to Zanamivir in the NAI assays. Additionally, five A(H1N1)pdm09 sequences from the GISAID possessed AA substitutions associated to reduced inhibition to Oseltamivir and none to Zanamivir. Oseltamivir resistant A(H1N1)pdm09 harbored the H275Y mutation. No genetic mutations were identified in Influenza A(H3N2) and IBV. Overall, these results show that in Mexico the rate of NAI resistance is low (0.6%), but it is essential to continue the Influenza surveillance in order to understand the drug susceptibility of circulating strains.

In Vivo Immune-Modulatory Activity of Lefamulin in an Influenza Virus A (H1N1) Infection Model in Mice.

Lefamulin is a first-in-class systemic pleuromutilin antimicrobial and potent inhibitor of bacterial translation, and the most recent novel antimicrobial approved for the treatment of community-acquired pneumonia (CAP). It exhibits potent antibacterial activity against the most prevalent bacterial pathogens that cause typical and atypical pneumonia and other infectious diseases. Early studies indicate additional anti-inflammatory activity. In this study, we further investigated the immune-modulatory activity of lefamulin in the influenza A/H1N1 acute respiratory distress syndrome (ARDS) model in BALB/c mice. Comparators included azithromycin, an anti-inflammatory antimicrobial, and the antiviral oseltamivir. Lefamulin significantly decreased the total immune cell infiltration, specifically the neutrophils, inflammatory monocytes, CD4+ and CD8+ T-cells, NK cells, and B-cells into the lung by Day 6 at both doses tested compared to the untreated vehicle control group (placebo), whereas azithromycin and oseltamivir did not significantly affect the total immune cell counts at the tested dosing regimens. Bronchioalveolar lavage fluid concentrations of pro-inflammatory cytokines and chemokines including TNF-α, IL-6, IL-12p70, IL-17A, IFN-γ, and GM-CSF were significantly reduced, and MCP-1 concentrations were lowered (not significantly) by lefamulin at the clinically relevant 'low' dose on Day 3 when the viral load peaked. Similar effects were also observed for oseltamivir and azithromycin. Lefamulin also decreased the viral load (TCID50) by half a log10 by Day 6 and showed positive effects on the gross lung pathology and survival. Oseltamivir and lefamulin were efficacious in the suppression of the development of influenza-induced bronchi-interstitial pneumonia, whereas azithromycin did not show reduced pathology at the tested treatment regimen. The observed anti-inflammatory and immune-modulatory activity of lefamulin at the tested treatment regimens highlights a promising secondary pharmacological property of lefamulin. While these results require confirmation in a clinical trial, they indicate that lefamulin may provide an immune-modulatory activity beyond its proven potent antibacterial activity. This additional activity may benefit CAP patients and potentially prevent acute lung injury (ALI) and ARDS.

Effect of Haoqin Qingdan Tang on influenza A virus through the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway.

OBJECTIVE: Influenza, a viral respiratory illness, leads to seasonal epidemics and occasional pandemics. Given the rising resistance and adverse reactions associated with anti-influenza drugs, Traditional Chinese Medicine (TCM) emerges as a promising approach to counteract the influenza virus. Specifically, Haoqin Qingdan Tang (HQQDT), a TCM formula, has been employed as an adjuvant treatment for influenza in China. However, the active compounds and underlying mechanisms of HQQDT remain unknown. AIM: The aim of this study was to investigate HQQDT's antiviral and anti-inflammatory activities in both in vivo and in vitro, and further reveal its active ingredients and mechanism. METHODS: In vivo and in vitro experiments were conducted to verify the antiviral and anti-inflammatory activities of HQQDT. Subsequently, the active ingredients and mechanism of HQQDT were explored through combining high performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (HPLC-Q-TOF-MS) analysis and network pharmacology. Finally, the examinations of cell cytokines and signaling pathways aimed to elucidate the predicted mechanisms. RESULTS: The results indicated that HQQDT exhibited inhibitory effects on influenza viruses A/PR/8/34 (H1N1), A/HK/1/68 (H3N2), and A/California/4/2009 (H1N1) in vitro. Furthermore, HQQDT enhanced the survival rate of influenza-infected mice, reduced the lung index and lung virus titer, and mitigated lung tissue damage in vivo. The proinflammatory cytokine expression levels upon influenza virus infection in PR8-induced A549 cells or mice were suppressed by HQQDT, including IL-6, IL-1ß, CCL2, CCL4, IP-10, interferon ß1 (IFN-ß1), the interferon regulatory factor 3 (IRF3), and hemagglutinin (HA). Twenty-two active components of HQQDT against influenza were identified using HPLC-Q-TOF-MS analysis. Based on network pharmacological predictions, the JAK/STAT signaling pathway is considered the most relevant for HQQDT's action against influenza. Finally, western blot assays revealed that HQQDT regulated the protein level of the JAK/STAT signaling pathway in PR8-infected A549 cells and lung tissue. CONCLUSION: These findings verified the antiviral and anti-inflammatory effects of HQQDT through JAK-STAT signaling pathway in influenza infections, laying the foundation for its further development.

Insights into the mechanism of action of pterostilbene against influenza A virus-induced acute lung injury.

BACKGROUND: Severe respiratory system illness caused by influenza A virus infection is associated with excessive inflammation and abnormal apoptosis in alveolar epithelial cells (AEC). However, there are limited therapeutic options for influenza-associated lung inflammation and apoptosis. Pterostilbene (PTE, trans-3,5-dimethoxy-4-hydroxystilbene) is a dimethylated analog of resveratrol that has been reported to limit influenza A virus infection by promoting antiviral innate immunity, but has not been studied for its protective effects on virus-associated inflammation and injury in AEC. PURPOSE: Our study aimed to investigate the protective effects and underlying mechanisms of PTE in modulating inflammation and apoptosis in AEC, as well as its effects on macrophage polarization during influenza virus infection. STUDY DESIGN AND METHODS: A murine model of influenza A virus-mediated acute lung injury was established by intranasal inoculation with 5LD50 of mouse-adapted H1N1 viruses. Hematoxylin and eosin staining, immunofluorescence, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, western blotting, Luminex and flow cytometry were performed. RESULTS: PTE effectively mitigated lung histopathological changes and injury induced by H1N1 viruses in vivo. These beneficial effects of PTE were attributed to the suppression of inflammation and apoptosis in AEC, as well as the modulation of M1 macrophage polarization. Mechanistic investigations revealed that PTE activated the phosphorylated AMP-activated protein kinase alpha (P-AMPKα)/sirtui1 (Sirt1)/PPARγ coactivator 1-alpha (PGC1α) signal axis, leading to the inhibition of nuclear factor kappa-B (NF-κB) and p38 mitogen-activated protein kinase (MAPK) signaling induced by H1N1 viruses, thereby attenuating inflammation and apoptosis in AEC. PTE also forced activation of the P-AMPKα/Sirt1/PGC1α signal axis in RAW264.7 cells, counteracting the activation of phosphorylated signal transducer and activator of transcription 1 (P-STAT1) induced by H1N1 viruses and the augment of P-STAT1 activation in RAW264.7 cells with interferon-gamma (IFN-γ) pretreatment before viral infection, thereby reducing H1N1 virus-mediated M1 macrophage polarization as well as the enhancement of macrophages into M1 phenotypes elicited by IFN-γ pretreatment. Additionally, the promotion of the transition of macrophages towards the M2 phenotype by PTE was also related to activation of the P-AMPKα/Sirt1/PGC1α signal axis. Moreover, co-culturing non-infected AEC with H1N1 virus-infected RAW264.7 cells in the presence of PTE inhibited apoptosis and tight junction disruption, which was attributed to the suppression of pro-inflammatory mediators and pro-apoptotic factors in an AMPKα-dependent manner. CONCLUSION: In conclusion, our findings suggest that PTE may serve as a promising novel therapeutic option for treating influenza-associated lung injury. Its ability to suppress inflammation and apoptosis in AEC, modulate macrophage polarization, and preserve alveolar epithelial cell integrity highlights its potential as a therapeutic agent in influenza diseases.

Interaction and antiviral treatment of coinfection between SARS-CoV-2 and influenza in vitro.

BACKGROUND: The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has lasted for three years. Coinfection with seasonal influenza may occur resulting in more severe diseases. The interaction between these two viruses for infection and the effect of antiviral treatment remains unclear. METHODS: A SARS-CoV-2 and influenza H1N1 coinfection model on Calu-3 cell line was established, upon which the simultaneous and sequential coinfection was evaluated by comparing the viral load. The efficacy of molnupiravir and baloxavir against individual virus and coinfection were also studied. RESULTS: The replication of SARS-CoV-2 was significantly interfered when the influenza virus was infected simultaneously or in advance (p < 0.05). On the contrary, the replication of the influenza virus was not affected by the SARS-CoV-2. Molnupiravir monotherapy had significant inhibitory effect on SARS-CoV-2 when the concentration reached to 6.25 µM but did not show any significant anti-influenza activity. Baloxavir was effective against influenza within the dosage range and showed significant effect of anti-SARS-CoV-2 at 16 µM. In the treatment of coinfection, molnupiravir had significant effect for SARS-CoV-2 from 6.25 µM to 100 µM and inhibited H1N1 at 100 µM (p < 0.05). The tested dosage range of baloxavir can inhibit H1N1 significantly (p < 0.05), while at the highest concentration of baloxavir did not further inhibit SARS-CoV-2, and the replication of SARS-CoV-2 significantly increased in lower concentrations. Combination treatment can effectively inhibit influenza H1N1 and SARS-CoV-2 replication during coinfection. Compared with molnupiravir or baloxavir monotherapy, combination therapy was more effective in less dosage to inhibit the replication of both viruses. CONCLUSIONS: In coinfection, the replication of SARS-CoV-2 would be interfered by influenza H1N1. Compared with molnupiravir or baloxavir monotherapy, treatment with a combination of molnupiravir and baloxavir should be considered for early treatment in patients with SARS-CoV-2 and influenza coinfection.

Design, synthesis, docking, and antiviral evaluation of some novel pyrimidinone-based α-aminophosphonates as potent H1N1 and HCoV-229E inhibitors.

Dialkyl/aryl aminophosphonates, 3a-g and 4a-e were synthesized using the LiClO4 catalyzed Kabachnic Fields-type reaction straightforwardly and efficiently. The synthesized phosphonates structures were characterized using elemental analyses, FT-IR, 1H NMR, 13C NMR, and MS spectroscopy. The new compounds were subjected to in-silico molecular docking simulations to evaluate their potential inhibition against Influenza A Neuraminidase and RNA-dependent RNA polymerase of human coronavirus 229E. Subsequently, the compounds were further tested in vitro using a cytopathic inhibition assay to assess their antiviral activity against both human Influenza (H1N1) and human coronavirus (HCoV-229E). Diphenyl ((2-(5-cyano-6-oxo-4-phenyl-1,6-dihydropyrimidin-2-yl) hydrazinyl) (furan-2-yl) methyl) phosphonate (3f) and diethyl ((2-(5-cyano-6-oxo-4-phenyl-1,6-dihydropyrimidin-2-yl) hydrazinyl) (1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl) methyl) phosphonate (4e) were demonstrated direct inhibition activity against Influenza A Neuraminidase and RNA-dependent RNA polymerase. This was supported by their highly favorable binding energies in-silico, with top-ranked values of -12.5 kcal/mol and -14.2 kcal/mol for compound (3f), and -13.5 kcal/mol and -9.89 kcal/mol for compound (4e). Moreover, they also displayed notable antiviral efficacy in vitro against both viruses. These compounds demonstrated significant antiviral activity, as evidenced by selectivity indices (SI) of 101.7 and 51.8, respectively against H1N1, and 24.5 and 5.1 against HCoV-229E, respectively.

Safety and efficacy of onradivir in adults with acute uncomplicated influenza A infection: a multicentre, double-blind, randomised, placebo-controlled, phase 2 trial.

BACKGROUND: Onradivir (ZSP1273) is a novel anti-influenza A virus inhibitor. Preclinical studies show that onradivir can inhibit influenza A H1N1 and H3N2 replication and increase the survival rate of infected animals. In this study, we aimed to evaluate the safety and efficacy of three onradivir dosing regimens versus placebo in outpatients with acute uncomplicated influenza A virus infection. METHODS: We did a multicentre, double-blind, randomised, placebo-controlled, phase 2 trial at 20 clinical sites in China. Eligible participants were adults (18-65 years) with an influenza-like illness screened by rapid antigen testing at the first clinical visit, had the presence of a fever (axillary temperature ≥38·0°C), and had the presence of at least one moderate systemic and one respiratory symptom within 48 h of symptom onset. Patients were excluded if they were pregnant, allergic to onradivir, or had received any influenza antiviral medication within 7 days before enrolment. Participants were randomly assigned (1:1:1:1) into four groups by an interactive web response system: onradivir 200 mg twice per day group, onradivir 400 mg twice per day group, onradivir 600 mg once per day group, and a matching placebo group. A 5-day oral treatment course was initiated within 48 h after symptoms onset. The primary outcome was the time to alleviate influenza symptoms in the modified intention-to-treat population. Safety was a secondary outcome. We evaluated the patients' self-assessed severity of seven influenza symptoms on a 4-point ordinal scale, and the treatment-emergent adverse events in all patients. This trial is registered with ClinicalTrials.gov, number NCT04024137. FINDINGS: Between Dec 7, 2019, and May 18, 2020, a total of 205 patients were screened; of whom, 172 (84%) were randomly assigned to receive onradivir (n=43 in the 200 mg twice per day group; n=43 in the 400 mg twice per day group; and n=43 in the 600 mg once per day group), or placebo (n=42). Median age was 22 years (IQR 20-26). All three onradivir groups showed decreased median time to alleviate influenza symptoms (46·92 h [IQR 24·00-81·38] in the 200 mg twice per day group, 54·87 h [23·67-110·62] in the 400 mg twice per day group, and 40·05 h [17·70-65·82] in the 600 mg once per day) compared with the placebo group (62·87 h [36·40-113·25]). The median difference between the onradivir 600 mg once per day group and the placebo group was -22·82 h (p=0·0330). The most frequently reported treatment-emergent adverse event was diarrhoea (71 [42%] of 171), ranging from 33-65% of the patients in onradivir-treated groups compared with 10% in the placebo group; no serious adverse events were observed. INTERPRETATION: Onradivir showed a safety profile comparable to placebo, as well as higher efficacy than placebo in ameliorating influenza symptoms and lowering the viral load in adult patients with uncomplicated influenza infection, especially the onradivir 600 mg once per day regimen. FUNDING: National Multidisciplinary Innovation Team Project of Traditional Chinese Medicine, National Natural Science Foundation of China, Guangdong Science and Technology Foundation, Guangzhou Science and Technology Planning Project, Emergency Key Program of Guangzhou Laboratory, Macao Science and Technology Development Fund, and Guangdong Raynovent Biotech.

Resistance profiles for the investigational neuraminidase inhibitor AV5080 in influenza A and B viruses.

Neuraminidase inhibitors (NAIs) are recommended for influenza treatment and prevention worldwide. The most widely prescribed NAI is oral oseltamivir, while inhaled zanamivir is less commonly used. Using phenotypic neuraminidase (NA) enzymatic assays and molecular modeling approaches, we examined the ability of the investigational orally-dosed NAI AV5080 to inhibit viruses of the influenza A(H1N1)pdm09, A(H3N2), A(H5N1), and A(H7N9) subtypes and the influenza B/Victoria- and B/Yamagata-lineages containing NA substitutions conferring oseltamivir or zanamivir resistance including: NA-R292K, NA-E119G/V, NA-H274Y, NA-I122L/N, and NA-R150K. Broadly, AV5080 showed enhanced in vitro efficacy when compared with oseltamivir and/or zanamivir. Reduced AV5080 inhibition was determined for influenza A viruses with NA-E119G and NA-R292K, and for B/Victoria-lineage viruses with NA-I122N/L and B/Yamagata-lineage virus with NA-R150K. Molecular modeling suggested loss of the short hydrogen bond to the carboxyl group of AV5080 affected inhibition of NA-R292K viruses, whereas loss of the salt bridge with the guanidine group of AV5080 affected inhibition of NA-E119G. The resistance profiles and predicted binding modes of AV5080 and zanamivir are most similar, but dissimilar to those of oseltamivir, in part because of a guanidine moiety compensatory binding effect. Overall, our data suggests that AV5080 is a promising orally-dosed NAI that exhibited similar or superior in vitro efficacy against viruses with reduced or highly reduced inhibition phenotypes with respect to currently approved NAIs.

Rational design and optimization of acylthioureas as novel potent influenza virus non-nucleoside polymerase inhibitors.

Evidence suggests that rapidly evolving virus subvariants risk rendering current vaccines and anti-influenza drugs ineffective. Hence, exploring novel scaffolds or new targets of anti-influenza drugs is of great urgency. Herein, we report the discovery of a series of acylthiourea derivatives produced via a scaffold-hopping strategy as potent antiviral agents against influenza A and B subtypes. The most effective compound 10m displayed subnanomolar activity against H1N1 proliferation (EC50 = 0.8 nM) and exhibited inhibitory activity toward other influenza strains, including influenza B virus and H1N1 variant (H1N1, H274Y). Additionally, druggability evaluation revealed that 10m exhibited favorable pharmacokinetic properties and was metabolically stable in liver microsome preparations from three different species as well as in human plasma. In vitro and in vivo toxicity studies confirmed that 10m demonstrated a high safety profile. Furthermore, 10m exhibited satisfactory antiviral activity in a lethal influenza virus mouse model. Moreover, mechanistic studies indicated that these acylthiourea derivatives inhibited influenza virus proliferation by targeting influenza virus RNA-dependent RNA polymerase. Thus, 10m is a potential lead compound for the further exploration of treatment options for influenza.

Impact of Baloxavir Resistance-Associated Substitutions on Influenza Virus Growth and Drug Susceptibility.

Baloxavir marboxil (baloxavir) is a recently FDA-approved influenza virus polymerase acidic (PA) endonuclease inhibitor. Several PA substitutions have been demonstrated to confer reduced susceptibility to baloxavir; however, their impacts on measurements of antiviral drug susceptibility and replication capacity when present as a fraction of the viral population have not been established. We generated recombinant A/California/04/09 (H1N1)-like viruses (IAV) with PA I38L, I38T, or E199D substitutions and B/Victoria/504/2000-like virus (IBV) with PA I38T. These substitutions reduced baloxavir susceptibility by 15.3-, 72.3-, 5.4-, and 54.5-fold, respectively, when tested in normal human bronchial epithelial (NHBE) cells. We then assessed the replication kinetics, polymerase activity, and baloxavir susceptibility of the wild-type:mutant (WT:MUT) virus mixtures in NHBE cells. The percentage of MUT relative to WT virus necessary to detect reduced baloxavir susceptibility in phenotypic assays ranged from 10% (IBV I38T) to 92% (IAV E199D). While I38T did not alter IAV replication kinetics or polymerase activity, IAV PA I38L and E199D MUTs and the IBV PA I38T MUT exhibited reduced replication levels and significantly altered polymerase activity. Differences in replication were detectable when the MUTs comprised ≥90%, ≥90%, or ≥75% of the population, respectively. Droplet digital PCR (ddPCR) and next-generation sequencing (NGS) analyses showed that WT viruses generally outcompeted the respective MUTs after multiple replication cycles and serial passaging in NHBE cells when initial mixtures contained ≥50% of the WT viruses; however, we also identified potential compensatory substitutions (IAV PA D394N and IBV PA E329G) that emerged and appeared to improve the replication capacity of baloxavir-resistant virus in cell culture. IMPORTANCE Baloxavir marboxil, an influenza virus polymerase acidic endonuclease inhibitor, represents a recently approved new class of influenza antivirals. Treatment-emergent resistance to baloxavir has been observed in clinical trials, and the potential spread of resistant variants could diminish baloxavir effectiveness. Here, we report the impact of the proportion of drug-resistant subpopulations on the ability to detect resistance in clinical isolates and the impact of substitutions on viral replication of mixtures containing both drug-sensitive and drug-resistant variants. We also show that ddPCR and NGS methods can be successfully used for detection of resistant subpopulations in clinical isolates and to quantify their relative abundance. Taken together, our data shed light on the potential impact of baloxavir-resistant I38T/L and E199D substitutions on baloxavir susceptibility and other biological properties of influenza virus and the ability to detect resistance in phenotypic and genotypic assays.

Optimization and SAR research at the benzoxazole and tetrazole rings of JNJ4796 as new anti-influenza A virus agents, part 2.

We have already reported the modification on the piperazine and phenyl rings of JNJ4796, a small-molecule fuse inhibitor targeting hemagglutinin (HA). In this study, we described the structure-activity relationship of the benzoxazole and tetrazole rings of JNJ4796. Many derivatives demonstrated good in vitro activity against IAV H1N1and Oseltamivir-resistant IAV H1N1 stains. Although compounds (R)-1e and (R)-1h exhibited excellent in vitro activity, high drug exposure level and low hERG inhibition, they displayed low oral efficacy. Excitedly, (R)-1a, a representative identified in our previous study, was found to show potent in vivo anti-IAV activity with the survival rates of 100%, 100% and 70% at 15, 5 and 1.67 mg/kg, respectively, comparable to JNJ4796. Currently, we are exploring different ways to ease its gastrointestinal response.

Dihydromaniwamycin E, a Heat-Shock Metabolite from Thermotolerant Streptomyces sp. JA74, Exhibiting Antiviral Activity against Influenza and SARS-CoV-2 Viruses.

Dihydromaniwamycin E (1), a new maniwamycin derivative featuring an azoxy moiety, has been isolated from the culture extract of thermotolerant Streptomyces sp. JA74 along with the known analogue maniwamycin E (2). Compound 1 is produced only by cultivation of strain JA74 at 45 °C, and this type of compound has been previously designated a "heat shock metabolite (HSM)" by our research group. Compound 2 is detected as a production-enhanced metabolite at high temperature. Structures of 1 and 2 are elucidated by NMR and MS spectroscopic analyses. The absolute structure of 1 is determined after the total synthesis of four stereoisomers. Though the absolute structure of 2 has been proposed to be the same as the structure of maniwamycin D, the NMR and the optical rotation value of 2 are in agreement with those of maniwamycin E. Therefore, this study proposes a structural revision of maniwamycins D and E. Compounds 1 and 2 show inhibitory activity against the influenza (H1N1) virus infection of MDCK cells, demonstrating IC50 values of 25.7 and 63.2 µM, respectively. Notably, 1 and 2 display antiviral activity against SARS-CoV-2, the causative agent of COVID-19, when used to infect 293TA and VeroE6T cells, with 1 and 2 showing IC50 values (for infection of 293TA cells) of 19.7 and 9.7 µM, respectively. The two compounds do not exhibit cytotoxicity in these cell lines at those IC50 concentrations.

Urolithin M5 from the Leaves of Canarium album (Lour.) DC. Inhibits Influenza Virus by Targeting Neuraminidase.

Ganlanye (GLY), the leaf of Canarium album (Lour.) DC., is a traditional Chinese medicinal herb for warm disease treatment. We found that its aqueous extract could inhibit the influenza A virus. To find and characterize anti-influenza virus phytochemicals from GLY, we performed (1) bioassay-guided isolation, (2) a cell and animal assay, and (3) a mechanism study. Bioassay-guided isolation was used to identify the effective components. Influenza virus-infected MDCK cell and BALB/c mouse models were employed to evaluate the anti-influenza virus activities. A MUNANA assay was performed to find the NA inhibitory effect. As a result, urolithin M5 was obtained from the crude extract of GLY. It inhibited influenza virus activities in vitro and in vivo by suppressing the viral NA activity. In the MDCK cell model, urolithin M5 could inhibit an oseltamivir-resistant strain. In a PR8-infected mouse model, 200 mg/kg/d urolithin M5 protected 50% of mice from death and improved lung edema conditions. GLY was recorded as a major traditional herb for warm disease treatment. Our study identified GLY as a potent anti-influenza herb and showed urolithin M5 as the active component. We first report the in vivo activity of urolithin M5 and support the anti-influenza application of GLY.

Discovery of Cyclic Diarylheptanoids as Inhibitors against Influenza A Virus from the Roots of Casuarina equisetifolia.

Four new cyclic diarylheptanoids, casuarinols A-C (1-3) and casuarinolide A (4), together with six known ones (5-10), were isolated from the roots of Casuarina equisetifolia. Structures were elucidated by extensive spectroscopic analysis, theoretical conformational, and electronic circular dichroism analyses. Casuarinol C (3) is a novel cyclic diarylheptanoid-aldehyde adduct. Casuarinolide A (4) represents the first structure of a seco-cyclic diarylheptanoid. Compounds 1-9 were evaluated for their anti-influenza A virus (IAV) activity against A/WSN/33 (H1N1). (-)-(M)-11-Oxo-3,12R,17-trihydroxy-9-ene-[7,0]-metacyclophane (5) displayed significant anti-IAV activity with an IC50 value of 8.64 ± 2.49 µM and a CC50 higher than 100 µM.

Discovery and pharmacodynamic evaluation of the novel butene lactone derivative M355 against influenza A virus in vitro and in vivo.

A new series of butene lactone derivatives were designed according to an influenza neuraminidase target and their antiviral activities against H1N1 infection of Madin-Darby canine kidney cells were evaluated. Among them, a compound that was given the name M355 was identified as the most potent against H1N1 (EC50 = 14.7 µM) with low toxicity (CC50 = 538.13 µM). It also visibly reduced the virus-induced cytopathic effect. Time-of-addition analysis indicated that H1N1 was mostly suppressed by M355 at the late stage of its infectious cycle. M355 inhibited neuraminidase in a dose-dependent fashion to a similar extent as oseltamivir, which was also indicated by a computer modeling experiment. In a mouse model, lung lesions and virus load were reduced and the expression of nucleoprotein was moderated by M355. The enzyme-linked immunosorbent assay and quantitative real-time polymerase chain reaction analyses revealed that the levels of interferon-γ, interferon regulatory factor-3, Toll-like receptor-3, tumor necrosis factor-α, interleukin (IL)-1ß, IL-6, and IL-8 were downregulated in the M355-treated groups, whereas the levels of IL-10 and IL-13 were upregulated. Similarly, IgG was found to be increased in infected mice plasma. These results demonstrate that M355 inhibit the expression of H1N1 in both cellular and animal models. Thus, M355 has the potential to be effective in the treatment of influenza A virus infection.