Inhibition of influenza virus infections in immunosuppressed mice with orally administered peramivir (BCX-1812)

Synergistic PA and HA mutations confer mouse adaptation of a contemporary A/H3N2 influenza virus

The mouse is the most widely used animal model for influenza virus research. However, the susceptibility of mice to seasonal influenza virus depends on the strain of mouse and on the strain of the influenza virus. Seasonal A/H3N2 influenza viruses do not replicate well in mice and therefore they need to be adapted to this animal model. In this study, we generated a mouse-adapted A/H3N2 virus (A/Switzerland/9715293/2013 [MA-H3N2]) by serial passaging in mouse lungs that exhibited greater virulence compared to the wild-type virus (P0-H3N2). Seven mutations were found in the genome of MA-H3N2: PA(K615E), NP(G384R), NA(G320E) and HA(N122D, N144E, N246K, and A304T). Using reverse genetics, two synergistically acting genes were found as determinants of the pathogenicity in mice. First, the HA substitutions were shown to enhanced viral replication in vitro and, second, the PA-K615E substitution increased polymerase activity, although did not alter virus replication in vitro or in mice. Notably, single mutations had only limited effects on virulence in vitro. In conclusion, a co-contribution of HA and PA mutations resulted in a lethal mouse model of seasonal A/H3N2 virus. Such adapted virus is an excellent tool for evaluation of novel drugs or vaccines and for study of influenza pathogenesis.

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.

A pharmacologically immunosuppressed mouse model for assessing influenza B virus pathogenicity and oseltamivir treatment

Immunocompromised patients are highly susceptible to influenza virus infections. Although neuraminidase inhibitor (NAI) therapy has proved effective in these patients, the treatment regimens require optimization, which can be partly addressed via animal models. Here, we describe a pharmacologically immunosuppressed mouse model for studying the pathogenesis of influenza B viruses and evaluating the efficacy of antiviral treatment. We modeled clinical regimens for dexamethasone and cyclophosphamide to immunosuppress BALB/c mice that were then inoculated with B/Phuket/3073/2013 (Yamagata lineage) or B/Brisbane/60/2008 (BR/08, Victoria lineage) virus. Although both viruses caused morbidity and mortality in immunosuppressed mice, BR/08 was more virulent, consistently inducing greater morbidity and 100% lethality in mice inoculated with at least 10³ TCID₅₀/mouse. The replication of both viruses was prolonged in the lungs of immunosuppressed mice, but the extent of pulmonary inflammation in these mice was markedly less than that in immunocompetent animals. Most of the examined cytokines, including IFN-γ, IL-1β, and RANTES, were significantly decreased in the lungs of immunosuppressed mice, as compared to immunocompetent animals, until at least 10 days post-infection. Treatment with the NAI oseltamivir for 8 or 16 days increased the mean survival time and reduced virus spread in the lungs of immunosuppressed mice challenged with a lethal dose of BR/08 but did not completely provide protection or decrease the virus titers. Our data suggests that the synergy of the viral load and aberrant immune responses is a key contributor to the severity of infection, as well as the limited efficacy of oseltamivir, which in immunosuppressed mice curtails virus release without clearing infected cells.

Emergence of Oseltamivir-Resistant H7N9 Influenza Viruses in Immunosuppressed Cynomolgus Macaques

Antiviral compounds (eg, the neuraminidase inhibitor oseltamivir) are invaluable for the treatment of individuals infected with influenza A viruses of the H7N9 subtype (A[H7N9]), which have infected and killed hundreds of persons. However, oseltamivir treatment often leads to the emergence of resistant viruses in immunocompromised individuals. To better understand the emergence and properties of oseltamivir-resistant A(H7N9) viruses in immunosuppressed individuals, we infected immunosuppressed cynomolgus macaques with an A(H7N9) virus and treated them with oseltamivir. Disease severity and mortality were higher in immunosuppressed than in immunocompetent animals. Oseltamivir treatment at 2 different doses reduced A(H7N9) viral titers in infected animals, but even high-dose oseltamivir did not block viral replication sufficiently to suppress the emergence of resistant variants. Some resistant variants were not appreciably attenuated in cultured cells, but an oseltamivir-resistant A(H7N9) virus did not transmit among ferrets. These findings are useful for the control of A(H7N9) virus infections in clinical settings.

Pathogenicity and peramivir efficacy in immunocompromised murine models of influenza B virus infection

Influenza B viruses are important human pathogens that remain inadequately studied, largely because available animal models are poorly defined. Here, we developed an immunocompromised murine models for influenza B virus infection, which we subsequently used to study pathogenicity and to examine antiviral efficacy of the neuraminidase inhibitor peramivir. We studied three influenza B viruses that represent both the Yamagata (B/Massachusetts/2/2012 and B/Phuket/3073/2013) and Victoria (B/Brisbane/60/2008, BR/08) lineages. BR/08 was the most pathogenic in genetically modified immunocompromised mice [BALB scid and non-obese diabetic (NOD) scid strains] causing lethal infection without prior adaptation. The immunocompromised mice demonstrated prolonged virus shedding with modest induction of immune responses compared to BALB/c. Rather than severe virus burden, BR/08 virus-associated disease severity correlated with extensive virus spread and severe pulmonary pathology, stronger and persistent natural killer cell responses, and the extended induction of pro-inflammatory cytokines and chemokines. In contrast to a single-dose treatment (75 mg/kg/day), repeated doses of peramivir rescued BALB scid mice from lethal challenge with BR/08, but did not result in complete virus clearance. In summary, we have established immunocompromised murine models for influenza B virus infection that will facilitate evaluations of the efficacy of currently available and investigational anti-influenza drugs.

In Vitro Evaluation of Absorption Characteristics of Peramivir for Oral Delivery

BACKGROUND AND OBJECTIVE

Peramivir is a novel antiviral agent approved for the treatment of severe influenza. However, the development of oral formulation of peramivir has been severely hurdled by poor bioavailability (human, ≤3%). The present work aims to evaluate oral permeability characteristics of peramivir.

METHODS

In vitro gastrointestinal stability, metabolic stability in human intestinal S9 fraction and Caco-2 permeability were performed. The liquid chromatography with tandem mass spectrometric (LC-MS/MS) was used to quantify peramivir in buffer and biological sample. Using GastroPlus™ software, intestinal effective permeability coefficient (P _eff) of peramivir was estimated.

RESULTS

Our results indicated that peramivir maintained stability in pH 5.5 and 7.4 buffers, fasted state simulated gastric fluid and fasted state simulated intestinal fluid, and human intestinal S9 fractions. The apparent permeability coefficient (P _app) values of peramivir (10 μM) were 3.29 ± 0.73 × 10^-7 cm/s in a Caco-2 cell model. In vivo intestinal effective permeability coefficient (P _eff) was estimated to be 0.06 × 10^-4 cm/s. Furthermore, co-incubating with cyclosporine, mitoxantrone, rifampicin, or paroxetine, the apical (AP) to basolateral (BL) flux of peramivir decreased (p < 0.05). The efflux and influx of peramivir was not significantly affected with co-incubation with verapamil, MK-571, or diclofenac (p > 0.05).

CONCLUSIONS

These results revealed that carrier-mediated transports, including OATP1B (organic anion transport 1B) and OCT1 (organic cation transport 1), might be involved in the absorption of peramivir. In conclusion, our results provide insight into the poor oral bioavailability of peramivir. Peramivir can be classified as a BCS-III (high solubility/low permeability) and BDDCS-III high solubility/poor metabolism) drug. The oral bioavailability of peramivir primarily depends on its permeability across cell membranes. Both of passive and active transports are involved in the permeability of peramivir.

Heptapeptide ligands against receptor-binding sites of influenza hemagglutinin toward anti-influenza therapy

The initial attachment of influenza virus to cells is the binding of hemagglutinin (HA) to the sialyloligosaccharide receptor; therefore, the small molecules that inhibit the sugar-protein interaction are promising as HA inhibitors to prevent the infection. We herein demonstrate that sialic acid-mimic heptapeptides are identified through a selection from a primary library against influenza virus HA. In order to obtain lead peptides, an affinity selection from a phage-displayed random heptapeptide library was performed with the HAs of the H1 and H3 strains, and two kinds of the HA-binding peptides were identified. The binding of the peptides to HAs was inhibited in the presence of sialic acid, and plaque assays indicated that the corresponding N-stearoyl peptide strongly inhibited infections by the A/Aichi/2/68 (H3N2) strain of the virus. Alanine scanning of the peptides indicated that arginine and proline were responsible for binding. The affinities of several mutant peptides with single-amino-acid substitutions against H3 HA were determined, and corresponding docking studies were performed. A Spearman analysis revealed a correlation between the affinity of the peptides and the docking study. These results provide a practicable method to design of peptide-based HA inhibitors that are promising as anti-influenza drugs.

A lethal disease model for hantavirus pulmonary syndrome in immunosuppressed Syrian hamsters infected with Sin Nombre virus

Sin Nombre virus (SNV) is a rodent-borne hantavirus that causes hantavirus pulmonary syndrome (HPS) predominantly in North America. SNV infection of immunocompetent hamsters results in an asymptomatic infection; the only lethal disease model for a pathogenic hantavirus is Andes virus (ANDV) infection of Syrian hamsters. Efforts to create a lethal SNV disease model in hamsters by repeatedly passaging virus through the hamster have demonstrated increased dissemination of the virus but no signs of disease. In this study, we demonstrate that immunosuppression of hamsters through the administration of a combination of dexamethasone and cyclophosphamide, followed by infection with SNV, results in a vascular leak syndrome that accurately mimics both HPS disease in humans and ANDV infection of hamsters. Immunosuppressed hamsters infected with SNV have a mean number of days to death of 13 and display clinical signs associated with HPS, including pulmonary edema. Viral antigen was widely detectable throughout the pulmonary endothelium. Histologic analysis of lung sections showed marked inflammation and edema within the alveolar septa of SNV-infected hamsters, results which are similar to what is exhibited by hamsters infected with ANDV. Importantly, SNV-specific neutralizing polyclonal antibody administered 5 days after SNV infection conferred significant protection against disease. This experiment not only demonstrated that the disease was caused by SNV, it also demonstrated the utility of this animal model for testing candidate medical countermeasures. This is the first report of lethal disease caused by SNV in an adult small-animal model.

Efficacy of repeated intravenous injection of peramivir against influenza A (H1N1) 2009 virus infection in immunosuppressed mice

The efficacy of intravenous peramivir against influenza A (H1N1) 2009 virus infection was evaluated in mice in which the immune system was suppressed by cyclophosphamide (CP) treatment. The mortality rate of the vehicle control group was 100%, and the mice lost 20% of their body weight on average by day 13 postinfection (p.i.). Repeated administration of peramivir (40 mg/kg of body weight once a day, given intravenously for 20 days), starting at 1 h p.i., significantly reduced mortality, body weight loss, viral titers, and cytokine production in infected mice compared with results for administration of vehicle (P < 0.01). In addition, repeated administration of peramivir, starting at 24 h, 48 h, or 72 h p.i., also resulted in increases in survival rates and reduction of viral titers in the lungs (P < 0.01). The mean days to death (MDD) of the vehicle group was 14.5 days, while in the groups treated with peramivir starting at 24 h, 48 h, and 72 h p.i., the MDDs were >23.0, 20.9, and 21.8 days, respectively. In comparison, repeated administration of oseltamivir phosphate (5 mg/kg twice a day, given orally for 20 days), starting at 24 h, 48 h, and 72 h p.i., also significantly prevented body weight loss, whereas no significant differences in mortality rates and viral titers in the lungs were observed compared with results for the vehicle group. These data indicated that repeated administration of peramivir was effective in promoting the survival and reducing virus replication in immunosuppressed mice infected with influenza A (H1N1) 2009 virus.

Animal models for the study of influenza pathogenesis and therapy

Influenza A viruses causes a variety of illnesses in humans. The most common infection, seasonal influenza, is usually a mild, self-limited febrile syndrome, but it can be more severe in infants, the elderly, and immunodeficient persons, in whom it can progress to severe viral pneumonitis or be complicated by bacterial superinfection, leading to pneumonia and sepsis. Seasonal influenza also occasionally results in neurologic complications. Rarely, viruses that have spread from wild birds to domestic poultry can infect humans; such “avian influenza” can range in severity from mild conjunctivitis through the rapidly lethal disease seen in persons infected with the H5N1 virus that first emerged in Hong Kong in 1997. To develop effective therapies for this wide range of diseases, it is essential to have laboratory animal models that replicate the major features of illness in humans. This review describes models currently in use for elucidating influenza pathogenesis and evaluating new therapeutic agents.

An immunosuppressed Syrian golden hamster model for SARS-CoV infection

Several small animal models have been developed for the study of severe acute respiratory syndrome coronavirus (SARS-CoV) replication and pathogenesis. Syrian golden hamsters are among the best small animal models, though little clinical illness and no mortality are observed after virus infection. Cyclophosphamide was used to immunosuppress hamsters leading to a prolonged disease course and higher mortality after SARS-CoV infection. In addition, there was a significant weight loss, expanded tissue tropism, and increased viral pathology in the lung, heart, kidney, and nasal turbinate tissues. Infection with recombinant SARS-CoV viruses bearing disruptions in the gene 7 coding region showed no significant change in replication kinetics, tissue tropism, morbidity, or mortality suggesting that the ORF7a (7a) and ORF7b (7b) proteins are not required for virus replication in immunosuppressed hamsters. This modified hamster model may provide a useful tool for SARS-CoV pathogenesis studies, evaluation of antiviral therapy, and analysis of additional SARS-CoV mutants.

Efficacy and Tolerability of the Oral Neuraminidase Inhibitor Peramivir in Experimental Human Influenza: Randomized, Controlled Trials for Prophylaxis and Treatment

Objective

Oseltamivir is the only oral neuraminidase inhibitor currently available; we determined the tolerability and antiviral efficacy of oral peramivir for treatment and prophylaxis of experimental human influenza A and B.

Participants

288 susceptible, healthy volunteers (ages 18–45) were inoculated intranasally with A/Texas/36/ 91/H1N1 or B/Yamagata/16/88 virus in four randomized, double-blind, placebo-controlled trials. Interventions: For treatment dosing was initiated at 24 h after inoculation with peramivir doses ranging from 100–800 mg/day for 5 days. For prophylaxis dosing was initiated 24 h before inoculation and continued for 4 days with peramivir doses ranging from 50–800 mg/day.

Outcomes

The primary outcome measure for treatment was quantitative viral detection defined by the area under the curve (AUC) for nasal wash viral titres. For prophylaxis the primary outcome measure was the incidence of virus recovery.

Results

In influenza A treatment, peramivir 400 mg q24h and 200mg q12h, but not lower doses, resulted in significant reductions in viral titre AUC. In influenza B treatment, both 400 and 800/400 mg once daily dose groups reduced AUC values. In influenza A prophylaxis, the percentage of individuals with nasal viral shedding did not differ significantly in the placebo (58%), 50 mg (61%), 200 mg (37%) and 400 mg (31%) dose groups. In influenza B prophylaxis, shedding frequencies were similar in placebo (55%), 200 mg (41%), 400 mg (35%) and 800 mg (47%) dose groups. The drug was well tolerated in all four studies, with nausea and headache being the most common side effects. No drug-resistant variants were detected.

Conclusion

Early treatment with peramivir was associated with significant antiviral effects in experimentally induced influenza in humans. Prophylaxis did not significantly reduce viral shedding. The relatively low blood peramivir concentrations observed may explain the lack of more robust antiviral effects, and parenteral dosing should be studied.