Combination Therapy With Neuraminidase and Polymerase Inhibitors in Nude Mice Infected With Influenza Virus

Influenza B Virus: Target and acting mechanism of antiviral drugs

The influenza B virus is one of the causes of seasonal influenza, which has a long history of existence in various populations. Adolescents, children, pregnant women, the elderly, as well as patients with major diseases such as high blood pressure, diabetes, and cancer, and those with low immunity are more susceptible to infection by the influenza virus. During the influenza seasons, the influenza B virus can cause significant harm and economic burden. At present, neuraminidase inhibitors, hemagglutinin inhibitors and RNA polymerase inhibitors are the main antiviral drugs that are used in the clinical treatment of influenza B. Due to the repeated use of antiviral drugs in recent years, the emergence of resistant strains of the influenza virus exacerbated. By combining anti-viral drugs with different mechanisms of action or using a combination of traditional Chinese medicine and chemical drugs, the problem of reduced drug sensitivity can be improved. This article introduces the drug targets of the influenza B virus and the mechanism of virus resistance. It also emphasizes the clinically used antiviral drugs and their mechanisms of action, thereby providing a reference basis for the development of new anti-influenza drugs.

Efficacy of favipiravir against influenza virus resistant to both baloxavir and neuraminidase inhibitors

OBJECTIVES

Widespread resistance of influenza viruses to neuraminidase (NA) inhibitor or polymerase inhibitor, baloxavir, is a major public health concern. The amino acid mutations R152K in NA and I38T in polymerase acidic (PA) are responsible for resistance to NA inhibitors and baloxavir, respectively.

METHODS

We generated recombinant A(H1N1)pdm09 viruses possessing NA-R152K, PA-I38T or both mutations by using a plasmid-based reverse genetics system, characterized their virological properties in vitro and in vivo, and examined whether oseltamivir, baloxavir and favipiravir are effective against these mutant viruses.

RESULTS

The three mutant viruses showed similar or superior growth kinetics and virulence to those of wild-type virus. Although oseltamivir and baloxavir blocked the replication of the wild-type virus in vitro, oseltamivir and baloxavir failed to suppress the replication of the NA-R152K and PA-I38T viruses in vitro, respectively. Mutant virus possessing both mutations grew in the presence of oseltamivir or baloxavir in vitro. Baloxavir treatment protected mice from lethal infection with wild-type or NA-R152K virus, but failed to protect mice from lethal infection with PA-I38T or PA-I38T/NA-R152K virus. Favipiravir treatment protected mice from lethal infection with all viruses tested, whereas oseltamivir treatment did not protect at all.

CONCLUSIONS

Our findings indicate that favipiravir should be used to treat patients with suspected baloxavir-resistant virus infection.

The combined effect of oseltamivir and favipiravir on influenza a virus evolution in patients hospitalized with severe influenza

Our previous study shows favipiravir and oseltamivir combination therapy may accelerate clinical recovery compared to oseltamivir monotherapy in severe influenza, but its effect on virological evolution and resistance mutation against oseltamivir is still unknown. In this study, we collected longitudinal respiratory samples from influenza patients who underwent combination therapy and applied them to next generation sequencing of the whole genome of the influenza A virus (IAV). We also included a cohort untreated with any antivirals to serve as the control. In total, 62 samples from 19 patients treated with combination therapy and 20 samples from 20 patients untreated were successfully sequenced. The nucleotide diversity in the whole genome of IAV in the combination group showed no difference compared to that in the control group (P > 0.05). Moreover, we observed 174 kinds of nonsynonymous nucleotide substitutions in patients with combination therapy, mostly in NA (n = 44) and HA (n = 43). Of them, the G→A transition was the dominant variant type (27%) and 46/174 (26%) was reported to have biological effects, such as increased pathogenicity and polymerase activity. Among the 29 mutations conferring reduction in oseltamivir sensitivity we investigated, H275Y was the only mutation detected in the 4 samples from 1 of 19 patients and demonstrated increasing frequency during the treatment. Mutations conferring favipiravir resistance were not observed. Our studies showed combination therapy of favipiravir and oseltamivir has little effect on virus nucleotide diversity, nor prevents the increase of oseltamivir-resistant variants.

Mahuang Xixin Fuzi decoction protects the BALB/c-nude mice infected with influenza A virus by reducing inflammatory cytokines storm and weakly regulating SIgA immune response

ETHNOPHARMACOLOGICAL RELEVANCE

Mahuang Xixin Fuzi Decoction (MXF), as a classical prescription of traditional Chinese medicine (TCM), has been used to treat the immunocompromised individuals infected with influenza A virus (IAV).

AIM OF THE STUDY

The study aims to explore the regulatory of MXF on inflammation and secretory immunoglobulin A (SIgA) antibodies immune response in BALB/c-nude mice infected with IAV.

MATERIALS AND METHODS

The BALB/c-nude mice were infected with IAV, then different dosages of MXF were orally administrated to the mice. The weight, rectal temperature, spontaneous activity, spleen index, lung index, pathological changes of lung tissues, and the relative mRNA expression level of H1N1 M gene were measured for the purpose of valuing the antiviral effect of MXF. The expression levels of cytokines in lungs and immunoglobulin A (IgA) in serum of BALB/c-nude mice were determined with Cytometric Bead Array System (CBA). SIgA in bronchoalveolar lavage fluids (BALF) was detected with Enzyme-linked Immunosorbent Assay (ELISA). The mRNA and protein expression levels of B cell activating factor (BAFF), chemokine receptors 10 (CCR10), and polymeric immunoglobulin receptor (pIgR) in the lung tissues, which are related to the secretion of SIgA, were determined by using RT-PCR and Western blot.

RESULTS

MXF could alleviate the clinical features and reduce the severity of viral lung lesions, including improving the body weight, rectal temperature and spontaneous activity of nude mice infected with IAV, increasing spleen index, decreasing lung index, alleviating pathological damage, and decreasing the relative expression level of H1N1 M gene. Levels of pro-inflammatory cytokines, including interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interleukin-2 (IL-2), interleukin-12p70 (IL-12p70), and interleukin-17A (IL-17A) were also significantly decreased after treatment with MXF. Interferon-γ (IFN-γ), an antiviral cytokine, was significantly up-regulated in high dose MXF (3.12 g/kg) group. Moreover, after MXF treatment, the expressions of SIgA in BALF and IgA in serum were both at relatively low levels. And the mRNA and protein expressions of BAFF, CCR10, and pIgR were significantly decreased after treatment with MXF.

CONCLUSIONS

MXF has obviously protective effects on BALB/c-nude mice infected with IAV by inhibiting virus replication, calming inflammatory cytokine storm, and regulating SIgA immune response weakly.

Influenza polymerase inhibitor resistance: Assessment of the current state of the art - A report of the isirv Antiviral group

It is more than 20 years since the neuraminidase inhibitors, oseltamivir and zanamivir were approved for the treatment and prevention of influenza. Guidelines for global surveillance and methods for evaluating resistance were established initially by the Neuraminidase Inhibitor Susceptibility Network (NISN), which merged 10 years ago with the International Society for influenza and other Respiratory Virus Diseases (isirv) to become the isirv-Antiviral Group (isirv-AVG). With the ongoing development of new influenza polymerase inhibitors and recent approval of baloxavir marboxil, the isirv-AVG held a closed meeting in August 2019 to discuss the impact of resistance to these inhibitors. Following this meeting and review of the current literature, this article is intended to summarize current knowledge regarding the clinical impact of resistance to polymerase inhibitors and approaches for surveillance and methods for laboratory evaluation of resistance, both in vitro and in animal models. We highlight limitations and gaps in current knowledge and suggest some strategies for addressing these gaps, including the need for additional clinical studies of influenza antiviral drug combinations. Lessons learned from influenza resistance monitoring may also be helpful for establishing future drug susceptibility surveillance and testing for SARS-CoV-2.

Influenza Polymerase Inhibitors: Mechanisms of Action and Resistance

The influenza virus RNA-dependent RNA polymerase is highly conserved among influenza A, B, C, and D viruses. It comprises three subunits: polymerase basic protein 1 (PB1), polymerase basic protein 2 (PB2), and polymerase acidic protein (PA) in influenza A and B viruses or polymerase 3 protein (P3) in influenza C and D viruses. Because this polymerase is essential for influenza virus replication, it has been considered as a target for antiviral agents. Recently, several polymerase inhibitors that target each subunit have been developed. This review discusses the mechanism of action, antiviral activity, and emergence of resistance to three inhibitors approved for the treatment of influenza or in late-phase clinical trials: the PB1 inhibitor favipiravir, the PB2 inhibitor pimodivir, and the PA inhibitor baloxavir marboxil.

Baloxavir Marboxil Treatment of Nude Mice Infected With Influenza A Virus

BACKGROUND

Immunocompromised patients infected with influenza virus require prolonged treatment with neuraminidase inhibitors, because these patients are not able to eradicate the virus from the respiratory tract, leading to the emergence of drug-resistant mutant viruses.

METHODS

In this study, we examined the efficacy of baloxavir marboxil in nude mice that were immunologically deficient.

RESULTS

Daily treatment with a suboptimal dose of baloxavir marboxil increased the survival time of the virus-infected nude mice but did not clear the virus from their respiratory organs, resulting in gradual body weight loss after termination of treatment.

CONCLUSIONS

Despite the prolonged baloxavir marboxil treatment, few resistant mutants were detected.

Recent progress in chemical approaches for the development of novel neuraminidase inhibitors

Influenza virus is the main cause of an infectious disease called influenza affecting the respiratory system including the throat, nose and lungs. Neuraminidase inhibitors are reagents used to block the enzyme called neuraminidase to prevent the influenza infection from spreading. Neuraminidase inhibitors are widely used in the treatment of influenza infection, but still there is a need to develop more potent agents for the more effective treatment of influenza. Complications of the influenza disease lead to death, and one of these complications is drug resistance; hence, there is an urgent need to develop more effective agents. This review focuses on the recent advances in chemical synthesis pathways used for the development of new neuraminidase agents along with the medicinal aspects of chemically modified molecules, including the structure-activity relationship, which provides further rational designs of more active small molecules.

Effects of Different Drug Combinations in Immunodeficient Mice Infected with an Influenza A/H3N2 Virus

The prolonged treatment of immunosuppressed (IS) individuals with anti-influenza monotherapies may lead to the emergence of drug-resistant variants. Herein, we evaluated oseltamivir and polymerase inhibitors combinations against influenza A/H3N2 infections in an IS mouse model. Mice were IS with cyclophosphamide and infected with 3 × 10³ PFU of a mouse-adapted A/Switzerland/9715293/2013 (H3N2) virus. Forty-eight hours post-infection, the animals started oseltamivir, favipiravir or baloxavir marboxil (BXM) as single or combined therapies for 10 days. Weight losses, survival rates and lung viral titers (LVTs) were determined. The neuraminidase (NA) and polymerase genes from lung viral samples were sequenced. All untreated animals died. Oseltamivir and favipiravir monotherapies only delayed mortality (the mean day to death (MDD) of 21.4 and 24 compared to 11.4 days for those untreated) while a synergistic improvement in survival (80%) and LVT reduction was observed in the oseltamivir/favipiravir group compared to the oseltamivir group. BXM alone or in double/triple combination provided a complete protection and significantly reduced LVTs. Oseltamivir and BXM monotherapies induced the E119V (NA) and I38T (PA) substitutions, respectively, while no resistance mutation was detected with combinations. We found that the multiple dose regimen of BXM alone provided superior benefits compared to oseltamivir and favipiravir monotherapies. Moreover, we suggest the potential for drug combinations to reduce the incidence of resistance.

Optimizing T-705 (favipiravir) treatment of severe influenza B virus infection in the immunocompromised mouse model

BACKGROUND

Influenza B virus infections remain insufficiently studied and antiviral management in immunocompromised patients is not well defined. The treatment regimens for these high-risk patients, which have elevated risk of severe disease-associated complications, require optimization and can be partly addressed via animal models.

METHODS

We examined the efficacy of monotherapy with the RNA-dependent RNA polymerase inhibitor T-705 (favipiravir) in protecting genetically modified, permanently immunocompromised BALB scid mice against lethal infection with B/Brisbane/60/2008 (BR/08) virus. Beginning at 24 h post-infection, BALB scid mice received oral T-705 twice daily (10, 50 or 250 mg/kg/day) for 5 or 10 days.

RESULTS

T-705 had a dose-dependent effect on survival after BR/08 challenge, resulting in 100% protection at the highest dosages. With the 5 day regimens, dosages of 50 or 250 mg/kg/day reduced the peak lung viral titres within the treatment window, but could not efficiently clear the virus after completion of treatment. With the 10 day regimens, dosages of 50 or 250 mg/kg/day significantly suppressed virus replication in the lungs, particularly at 45 days post-infection, limiting viral spread and pulmonary pathology. No T-705 regimen decreased virus growth in the nasal turbinates of mice, which potentially contributed to the viral dynamics in the lungs. The susceptibility of influenza B viruses isolated from T-705-treated mice remained comparable to that of viruses from untreated control animals.

CONCLUSIONS

T-705 treatment is efficacious against lethal challenge with BR/08 virus in immunocompromised mice. The antiviral benefit was greatest when longer T-705 treatment was combined with higher dosages.

Influenza virus polymerase inhibitors in clinical development

Purpose of review

We review antivirals inhibiting subunits of the influenza polymerase complex that are advancing in clinical development.

Recent findings

Favipiravir, pimodivir, and baloxavir are inhibitory in preclinical models for influenza A viruses, including pandemic threat viruses and those resistant to currently approved antivirals, and two (favipiravir and baloxavir) also inhibit influenza B viruses. All are orally administered, although the dosing regimens vary. The polymerase basic protein 1 transcriptase inhibitor favipiravir has shown inconsistent clinical effects in uncomplicated influenza, and is teratogenic effects in multiple species, contraindicating its use in pregnancy. The polymerase basic protein 2 cap-binding inhibitor pimodivir displays antiviral effects alone and in combination with oseltamivir in uncomplicated influenza, although variants with reduced susceptibility emerge frequently during monotherapy. Single doses of the polymerase acidic protein cap-dependent endonuclease inhibitor baloxavir are effective in alleviating symptoms and rapidly inhibiting viral replication in otherwise healthy and higher risk patients with acute influenza, although variants with reduced susceptibility emerge frequently during monotherapy. Combinations of newer polymerase inhibitors with neuraminidase inhibitors show synergy in preclinical models and are currently undergoing clinical testing in hospitalized patients.

Summary

These new polymerase inhibitors promise to add to the clinical management options and overall control strategies for influenza virus infections.

Triple combination therapy of favipiravir plus two monoclonal antibodies eradicates influenza virus from nude mice

Prolonged treatment of immunocompromised influenza patients with viral neuraminidase (NA) inhibitors is required, because the immune system of such patients fails to eradicate the viruses. Here, we attempted to eradicate influenza virus from the respiratory organs of nude mice, which is a model of immunocompromised hosts, by using combination therapy of the viral polymerase inhibitor favipiravir and monoclonal antibodies (mAbs) against the receptor-binding site (RBS) and stem of viral hemagglutinin (HA). Although monotherapy or combination therapy of two antivirals (two mAbs or favipiravir plus a mAb) suppressed virus replication, they failed to eradicate viruses from nude mice. In contrast, the triple combination therapy of favipiravir plus anti-Stem and anti-RBS mAbs completely stopped virus replication in nude mice, resulting in virus clearance. Triple combination approaches should be considered for the treatment of human immunocompromised patients with severe influenza.

Severe acute respiratory infection risk following glucocorticosteroid treatment in uncomplicated influenza-like illness resulting from pH1N1 influenza infection: a case control study

Background

Current studies regarding glucocorticosteroid treatment of influenza have only estimated risk of critical illness or death which can be easily confounded by timing of treatment administration. We used severe acute respiratory infection (sARI) as an endpoint and investigated risk associated with receiving glucocorticosteroids before sARI onset.

Methods

sARI cases were defined as influenza-like illness (ILI) with pH1N1 infection and respiratory distress. Controls were defined as pH1N1 cases other than sARI and randomly selected from the community. We compared glucocorticosteroids and other medications used before sARI onset using a matched case control study adjusted for age group as well as underlying disease. Time-dependent risk and dose responses at different time periods over the course of sARI cases were also examined.

Results

Of the sARI cases, 34% received glucocorticosteroids before sARI onset compared to 3.8% of controls during equivalent days (OR_M-H = 17,95%CI = 2.1–135). Receiving glucocorticosteroids before sARI onset increased risk of developing subsequent critical illness or death (OR_M-H = 5.7,95%CI = 1.6–20.2), and the OR_M-H increased from 5.7 to 8.5 for continued glucocorticosteroid use after sARI onset. However, only receiving glucocorticosteroids after sARI onset did not increase risk of severe illness (OR_M-H = 1.1,95%CI = 0.3–4.6). Each increase in glucocorticosteroids dose of 1 mg/kg/day before sARI onset resulted in an increase of 0.62 (R² = 0.87) in the pMEWS score at the time of sARI onset.

Conclusions

Early glucocorticosteroid treatment increased risk of sARI and subsequent critical illness or death; however, only receiving glucocorticosteroids after sARI onset did not increase risk of severe illness.

Neuraminidase inhibitor resistance in influenza: a clinical perspective

PURPOSE OF REVIEW

Neuraminidase inhibitors (NAIs), including oseltamivir, zanamivir, and peramivir, is the main class of antiviral available for clinical use. As such, development of resistance toward these agents is of great clinical and public health concern.

RECENT FINDINGS

At present, NAI resistance remains uncommon among the circulating viruses (oseltamivir <3.5%, zanamivir <1%). Resistance risk is slightly higher in A(H1N1) than A(H3N2) and B viruses. Resistance may emerge during drug exposure, particularly among young children (<5 years), the immunocompromised, and individuals receiving prophylactic regimens. H275Y A(H1N1) variant, showing high-level oseltamivir resistance, is capable of causing outbreaks. R294K A(H7N9) variant shows reduced inhibition across NAIs. Multi-NAI resistance has been reported in the immunocompromised.

SUMMARY

These findings highlight the importance of continuous surveillance, and assessment of viral fitness and transmissibility of resistant virus strains. Detection can be challenging, especially in a mix of resistant and wild-type viruses. Recent advances in molecular techniques (e.g. targeted mutation PCR, iART, ddPCR, pyrosequencing, next-generation sequencing) have improved detection and our understanding of viral dynamics. Treatment options available for oseltamivir-resistant viruses are limited, and susceptibility testing of other NAIs may be required, but non-NAI antivirals (e.g. polymerase inhibitors) that are active against these resistant viruses are in late-stage clinical development.

Adult influenza A (H3N2) with reduced susceptibility to baloxavir or peramivir cured after switching anti-influenza agents

We describe two adults with A/H3N2 influenza with (patient 1), and without (patient 2) polymerase acidic (PA) subunit I38 T substitution during the same season. Patient 1 had a reduced clinical response to baloxavir, a cap-dependent endonuclease inhibitor (CEI), but was cured by peramivir, a neuraminidase inhibitor. Baloxavir was clinically effective for patient 2, for whom peramivir had been ineffective. Susceptibility to baloxavir can be decreased by a PA unit mutation, but response to treatment can be increased by switching and/or combination with a neuraminidase inhibitor, even though CEI are clinically effective against influenza in adults.

Antivirals targeting the polymerase complex of influenza viruses

Current influenza antivirals have limitations with regard to their effectiveness and the potential emergence of resistance. Encouragingly, several new compounds which inhibit the polymerase of influenza viruses have recently been shown to have enhanced pre-clinical and clinical effectiveness compared to the neuraminidase inhibitors, the mainstay of influenza antiviral therapy over the last two decades. In this review we focus on four compounds which inhibit polymerase function, baloxavir marboxil, favipiravir, pimodivir and AL-794 and discuss their clinical and virological effectiveness, their propensity to select for resistance and their potential for future combination therapy with the most commonly used neuraminidase inhibitor, oseltamivir.

Predicting Host Immune Cell Dynamics and Key Disease-Associated Genes Using Tissue Transcriptional Profiles

Motivation: Immune cell dynamics is a critical factor of disease-associated pathology (immunopathology) that also impacts the levels of mRNAs in diseased tissue. Deconvolution algorithms attempt to infer cell quantities in a tissue/organ sample based on gene expression profiles and are often evaluated using artificial, non-complex samples. Their accuracy on estimating cell counts given temporal tissue gene expression data remains not well characterized and has never been characterized when using diseased lung. Further, how to remove the effects of cell migration on transcript counts to improve discovery of disease factors is an open question. Results: Four cell count inference (i.e., deconvolution) tools are evaluated using microarray data from influenza-infected lung sampled at several time points post-infection. The analysis finds that inferred cell quantities are accurate only for select cell types and there is a tendency for algorithms to have a good relative fit (R 2 ) but a poor absolute fit (normalized mean squared error; NMSE), which suggests systemic biases exist. Nonetheless, using cell fraction estimates to adjust gene expression data, we show that genes associated with influenza virus replication and increased infection pathology are more likely to be identified as significant than when applying traditional statistical tests.

Baloxavir marboxil, a novel cap-dependent endonuclease inhibitor potently suppresses influenza virus replication and represents therapeutic effects in both immunocompetent and immunocompromised mouse models

Baloxavir marboxil (BXM) is an orally available small molecule inhibitor of cap-dependent endonuclease (CEN), an essential enzyme in the initiation of mRNA synthesis of influenza viruses. In the present study, we evaluated the efficacy of BXM against influenza virus infection in mouse models. Single-day oral administration of BXM completely prevented mortality due to infection with influenza A and B virus in mice. Moreover, 5-day repeated administration of BXM was more effective for reducing mortality and body weight loss in mice infected with influenza A virus than oseltamivir phosphate (OSP), even when the treatment was delayed up to 96 hours post infection (p.i.). Notably, administration of BXM, starting at 72 hours p.i. led to significant decrease in virus titers of >2-log₁₀ reduction compared to the vehicle control within 24 hours after administration. Virus reduction in the lung was significantly greater than that observed with OSP. In addition, profound and sustained reduction of virus titer was observed in the immunocompromised mouse model without emergence of variants possessing treatment-emergent amino acid substitutions in the target protein. In our immunocompetent and immunocompromised mouse models, delayed treatment with BXM resulted in rapid and potent reduction in infectious virus titer and prevention of signs of influenza infection, suggesting that BXM could extend the therapeutic window for patients with influenza virus infection regardless of the host immune status.

Efficacy of laninamivir octanoate in mice with advanced inflammation stage caused by infection of highly lethal influenza virus

Four neuraminidase (NA) inhibitors and an RNA synthesis inhibitor were recently approved and are currently in clinical use for influenza. Among NA inhibitors, oseltamivir phosphate (OSE, Tamiflu^®) and zanamivir are approved worldwide, whereas peramivir and laninamivir octanoate (LAN, Inavir^®) are regionally approved for human use. Therefore, OSE has been used to treat infections of highly pathogenic influenza viruses, such as H5N1 and H7N9, which caused epidemic in southeast Asia and Egypt, and China, respectively. Generally, OSE is administered twice daily for 5 days by oral administration, and LAN once by inhalation for completing influenza therapy. In this study, we compared the efficacy of OSE and LAN administered according to the regimens in mice infected with highly lethal influenza viruses. The drugs were administered at the early and late stages of infection, which correspond to mild and severe inflammation in the lungs, respectively. Based on the drugs' regimens for human, a single administration of LAN at both stages of inflammation showed superior efficacy to repeated administration of OSE. LAN, as in OSE, could also be efficacious in treating severe influenza in humans.

Status of antiviral therapeutics against rabies virus and related emerging lyssaviruses

Rabies virus (RABV) constitutes a major social and economic burden associated with 60 000 deaths annually worldwide. Although pre-exposure and post-exposure treatment options are available, they are efficacious only when initiated before the onset of clinical symptoms. Aggravating the problem, the current RABV vaccine does not cross-protect against the emerging zoonotic phylogroup II lyssaviruses. A requirement for an uninterrupted cold chain and high cost of the immunoglobulin component of rabies prophylaxis generate an unmet need for the development of RABV-specific antivirals. We discuss desirable anti-RABV drug profiles, past efforts to address the problem and inhibitor candidates identified, and examine how the rapidly expanding structural insight into RABV protein organization has illuminated novel druggable target candidates and paved the way to structure-aided drug optimization. Special emphasis is given to the viral RNA-dependent RNA polymerase complex as a promising target for direct-acting broad-spectrum RABV inhibitors.

Combination Therapy with Oseltamivir and Favipiravir Delays Mortality but Does Not Prevent Oseltamivir Resistance in Immunodeficient Mice Infected with Pandemic A(H1N1) Influenza Virus

Immunosuppressed individuals can shed influenza virus for prolonged periods of time, leading to the frequent emergence of antiviral resistance. We evaluated the benefits of oseltamivir and favipiravir combination therapy compared to single antiviral agents and monitored the emergence of drug-resistant variants in a pharmacologically immunosuppressed mouse model infected with the A(H1N1) pandemic influenza virus. C57BL/6 mice were immunosuppressed with cyclophosphamide and infected with a lethal dose of pandemic influenza A(H1N1) virus. Forty-eight hours post-infection, mice were treated with oseltamivir (20 mg/kg), favipiravir (20 or 50 mg/kg) or both agents BID for 5 or 10 days. Body weight losses, survival rates, lung viral titers, cytokine levels and emergence of resistant viruses were evaluated. Treatment of immunosuppressed mice with high (50 mg/kg) but not low (20 mg/kg) doses of favipiravir in combination with oseltamivir (20 mg/kg) significantly delayed mortality and reduced lung viral titers compared to treatment with a single drug regimen with oseltamivir but did not prevent the emergence of oseltamivir-resistant H275Y neuraminidase variants. Combination therapy with oseltamivir and favipiravir should be considered for evaluation in clinical trials.

Neutralizing Anti-Hemagglutinin Monoclonal Antibodies Induced by Gene-Based Transfer Have Prophylactic and Therapeutic Effects on Influenza Virus Infection

Hemagglutinin (HA) of influenza virus is a major target for vaccines. HA initiates the internalization of the virus into the host cell by binding to host sialic acid receptors; therefore, inhibition of HA can significantly prevent influenza virus infection. However, the high diversity of HA permits the influenza virus to escape from host immunity. Moreover, the vaccine efficacy is poor in some high-risk populations (e.g., elderly or immunocompromised patients). Passive immunization with anti-HA monoclonal antibodies (mAbs) is an attractive therapy; however, this method has high production costs and requires repeated inoculations. To address these issues, several methods for long-term expression of mAb against influenza virus have been developed. Here, we provide an overview of methods using plasmid and viral adeno-associated virus (AAV) vectors that have been modified for higher expression of neutralizing antibodies in the host. We also examine two methods of injection, electro-transfer and hydrodynamic injection. Our results show that antibody gene transfer is effective against influenza virus infection even in immunocompromised mice, and antibody expression was detected in the serum and upper respiratory tract. We also demonstrate this method to be effective following influenza virus infection. Finally, we discuss the perspective of passive immunization with antibody gene transfer for future clinical trials.

Impact of R152K and R368K neuraminidase catalytic substitutions on in vitro properties and virulence of recombinant A(H1N1)pdm09 viruses

Neuraminidase (NA) mutations conferring resistance to NA inhibitors (NAIs) are expected to occur at framework or catalytic residues of the NA enzyme. Numerous clinical and in vitro reports already described NAI-resistant A(H1N1)pdm09 variants harboring various framework NA substitutions. By contrast, variants with NA catalytic changes remain poorly documented. Herein, we investigated the effect of R152K and R368K NA catalytic mutations on the NA enzyme properties, in vitro replicative capacity and virulence of A(H1N1)pdm09 recombinant viruses. In NA inhibition assays, the R152K and R368K substitutions resulted in reduced inhibition [10- to 100-fold increases in IC₅₀ vs the wild-type (WT)] or highly reduced inhibition (>100-fold increases in IC₅₀) to at least 3 approved NAIs (oseltamivir, zanamivir, peramivir and laninamivir). Such resistance phenotype correlated with a significant reduction of affinity observed for the mutants in enzyme kinetics experiments [increased Km from 20 ± 1.77 for the WT to 200.8 ± 10.54 and 565.2 ± 135 μM (P < 0.01) for the R152K and R368K mutants, respectively]. The R152K and R368K variants grew at comparable or even higher titers than the WT in both MDCK and ST6GalI-MDCK cells. In experimentally-infected C57BL/6 mice, the recombinant WT and the R152K and R368K variants induced important signs of infection (weight loss) and resulted in mortality rates of 87.5%, 37.5% and 100%, respectively. The lung viral titers were comparable between the three infected groups. While the NA mutations were stable, an N154I substitution was detected in the HA2 protein of the R152K and R368K variants after in vitro passages as well as in lungs of infected mice. Due to the multi-drug resistance phenotypes and conserved fitness, the emergence of NA catalytic mutations accompanied with potential compensatory HA changes should be carefully monitored in A(H1N1)pdm09 viruses.