Effects of Double Combinations of Amantadine,Oseltamivir, and Ribavirin on Influenza A (H5N1) Virus Infections in Cell Culture and in Mice

An amantadine-resistant influenza A/Duck/MN/1525/81 (H5N1) virus was developed from the low-pathogenic North American wild-type (amantadine-sensitive) virus for studying treatment of infections in cell culture and in mice. Double combinations of amantadine, oseltamivir (or the cell culture-active form, oseltamivir carboxylate), and ribavirin were used. Amantadine-oseltamivir carboxylate and amantadine-ribavirin combinations showed synergistic interactions over a range of doses against wild-type virus in Madin-Darby canine kidney (MDCK) cell culture, but oseltamivir carboxylate-ribavirin combinations did not. Primarily additive interactions were seen with oseltamivir carboxylate-ribavirin combinations against amantadine-resistant virus. The presence of amantadine in drug combinations against the resistant virus did not improve activity. The wild-type and amantadine-resistant viruses were lethal to mice by intranasal instillation. The resistant virus infection could not be treated with amantadine up to 100 mg/kg body weight/day, whereas the wild-type virus infection was treatable with oral doses of 10 (weakly effective) to 100 mg/kg/day administered twice a day for 5 days starting 4 h prior to virus exposure. Drug combination studies showed that treatment of the amantadine-resistant virus infection with amantadine-oseltamivir or amantadine-ribavirin combinations was not significantly better than using oseltamivir or ribavirin alone. In contrast, the oseltamivir-ribavirin (25- and 75-mg/kg/day combination) treatments produced significant reductions in mortality. The wild-type virus infection was markedly reduced in severity by all three combinations (amantadine, 10 mg/kg/day combined with the other compounds at 20 or 40 mg/kg/day) compared to monotherapy with the three compounds. Results indicate a lack of benefit of amantadine in combinations against amantadine-resistant virus, but positive benefits in combinations against amantadine-sensitive virus.The effective treatment of influenza virus infections remains a public health priority. In the 2007-2008 influenza season there was a rise in the number of infected individuals, due to two of the vaccine virus strains being suboptimally matched with viruses circulating in nature (2). The afflicted individuals would have benefited from antiviral drug treatment. The threat of emerging highly pathogenic avian influenza A (H5N1) viruses for which no vaccines exist is also a concern (29). Recent data indicate the widespread viral resistance to the antiviral drug amantadine (6, 11) and the growing frequency of resistance to the other widely used antiviral drug oseltamivir (5, 19). Certain clades of highly pathogenic H5N1 viruses are resistant to amantadine, whereas other clades are not (3, 15).Highly pathogenic H5N1 virus infections of humans have a high human mortality rate, exceeding 60% (18). Such severe infections are difficult to treat with oseltamivir (4). Thus, there is a need for more potent therapy, as well as for treatment that may decrease the frequency of the emergence of drug-resistant viruses (14). Combination chemotherapy with the right medications may be the answer to both problems. Investigators over the years have studied various compounds in combination in vitro (10, 13, 14, 21, 26) and in mouse models (8, 16, 17, 20, 22, 26, 28) against the H1N1, H3N2, H5N1, and H9N2 strains of influenza viruses. These include the testing of M2 channel blockers amantadine and rimantadine; the neuraminidase inhibitors oseltamivir carboxylate, peramivir, and zanamivir; and the nucleoside analog ribavirin (an inhibitor of influenza virus RNA polymerase [7]). Since the M2 channel blockers, neuraminidase inhibitors, and ribavirin all have separate modes of antiviral action, various combinations of these inhibitors have been more beneficial than monotherapy in treating infections in cell culture and in mice. Due to the widespread occurrence of viruses that are resistant to amantadine, a recent study has focused on the treatment of amantadine-resistant influenza virus infections (17).We have developed a mouse model using a low-pathogenic North American strain, influenza A/Duck/MN/1525/81 (H5N1) virus for antiviral drug testing. The virus causes a severe lethal respiratory infection in mice that is treatable by antiviral therapy (25). The experimental influenza A/Duck mouse infection model described in the present set of experiments is not optimal, as it does not fully reflect the type of pathogenesis of the highly pathogenic avian influenza H5N1 viruses. The low-pathogenic A/Duck virus does not contain the multibasic amino acid R-X-R/K-R motif in the hemagglutinin protein, whereas the highly pathogenic avian viruses do (8). Having this motif allows for the highly pathogenic viruses to be proteolytically activated by ubiquitous subtilisin-like cellular proteases, favoring systemic spread in vivo beyond the respiratory tract, causing multiorgan failure. Indeed, Ilyushina et al. demonstrated spread of highly pathogenic H5N1 virus strains to other organs besides the lungs with a mouse model (16, 17). A high virus titer (approximately 10⁴ cell culture 50% infective doses [CCID₅₀] per mouse) is required to induce lethality with the wild-type A/Duck virus, compared to 1 to 4 PFU of A/Vietnam or A/Turkey viruses (16, 17). Thus, the highly pathogenic viruses are more virulent in mice. The A/Duck virus is sensitive to neuraminidase inhibitors (27) and to the RNA polymerase inhibitors ribavirin and T-705 (25, 27). It is also sensitive to inhibition by amantadine in vitro, as reported herein.For these studies we also developed an amantadine-resistant A/Duck virus that is lethal to mice. Treatment of infections caused by this virus was compared with the treatment of wild-type virus infections, using the drugs amantadine, oseltamivir (or the cell culture-active form oseltamivir carboxylate), and ribavirin. The results with mice correlate with recent reports by Ilyushina et al. (16, 17) using highly pathogenic H5N1 amantadine-sensitive and amantadine-resistant viruses. In those studies, amantadine-oseltamivir and oseltamivir-ribavirin combinations were evaluated, but not amantadine-ribavirin combinations. An advantage to using the A/Duck virus mouse model is that studies can be conducted in a low-containment laboratory.To our knowledge, the present investigation represents the first report of the use of amantadine and ribavirin in combination in vitro against an amantadine-resistant H5N1 virus and of oseltamivir carboxylate and ribavirin in combination against either sensitive or resistant H5N1 viruses in vitro. This is also the first report of treatment of an H5N1 virus infection in mice with the combination of amantadine plus ribavirin.     

Efficacy of oseltamivir therapy in ferrets inoculated with different clades of H5N1 influenza virus

Highly pathogenic H5N1 influenza viruses have infected an increasing number of humans in Asia, with high mortality rates and the emergence of multiple distinguishable clades. It is not known whether antiviral drugs that are effective against contemporary human influenza viruses will be effective against systemically replicating viruses, such as these pathogens. Therefore, we evaluated the use of the neuraminidase (NA) inhibitor oseltamivir for early postexposure prophylaxis and for treatment in ferrets exposed to representatives of two clades of H5N1 virus with markedly different pathogenicities in ferrets. Ferrets were protected from lethal infection with the A/Vietnam/1203/04 (H5N1) virus by oseltamivir (5 mg/kg of body weight/day) given 4 h after virus inoculation, but higher daily doses (25 mg/kg) were required for treatment when it was initiated 24 h after virus inoculation. For the treatment of ferrets inoculated with the less pathogenic A/Turkey/15/06 (H5N1) virus, 10 mg/kg/day of oseltamivir was sufficient to reduce the lethargy of the animals, significantly inhibit inflammation in the upper respiratory tract, and block virus spread to the internal organs. Importantly, all ferrets that survived the initial infection were rechallenged with homologous virus after 21 days and were completely protected from infection. Direct sequencing of the NA or HA1 gene segments in viruses isolated from ferret after treatment showed no amino acid substitutions known to cause drug resistance in conserved residues. Thus, early oseltamivir treatment is crucial for protection against highly pathogenic H5N1 viruses and the higher dose may be needed for the treatment of more virulent viruses.     

Comparison of efficacies of RWJ-270201, zanamivir, and oseltamivir against H5N1, H9N2, and other avian influenza viruses

The orally administered neuraminidase (NA) inhibitor RWJ-270201 was tested in parallel with zanamivir and oseltamivir against a panel of avian influenza viruses for inhibition of NA activity and replication in tissue culture. The agents were then tested for protection of mice against lethal H5N1 and H9N2 virus infection. In vitro, RWJ-270201 was highly effective against all nine NA subtypes. NA inhibition by RWJ-270201 (50% inhibitory concentration, 0.9 to 4.3 nM) was superior to that by zanamivir and oseltamivir carboxylate. RWJ-270201 inhibited the replication of avian influenza viruses of both Eurasian and American lineages in MDCK cells (50% effective concentration, 0.5 to 11.8 microM). Mice given 10 mg of RWJ-270201 per kg of body weight per day were completely protected against lethal challenge with influenza A/Hong Kong/156/97 (H5N1) and A/quail/Hong Kong/G1/97 (H9N2) viruses. Both RWJ-270201 and oseltamivir significantly reduced virus titers in mouse lungs at daily dosages of 1.0 and 10 mg/kg and prevented the spread of virus to the brain. When treatment began 48 h after exposure to H5N1 virus, 10 mg of RWJ-270201/kg/day protected 50% of mice from death. These results suggest that RWJ-270201 is at least as effective as either zanamivir or oseltamivir against avian influenza viruses and may be of potential clinical use for treatment of emerging influenza viruses that may be transmitted from birds to humans.     

Oseltamivir-ribavirin combination therapy for highly pathogenic H5N1 influenza virus infection in mice

We studied the effects of a neuraminidase inhibitor (oseltamivir) and an inhibitor of influenza virus polymerases (ribavirin) against two highly pathogenic H5N1 influenza viruses. In vitro, A/Vietnam/1203/04 virus (clade 1) was highly susceptible to oseltamivir carboxylate (50% inhibitory concentration [IC₅₀] = 0.3 nM), whereas A/Turkey/15/06 virus (clade 2.2) had reduced susceptibility (IC₅₀ = 5.5 nM). In vivo, BALB/c mice were treated with oseltamivir (1, 10, 50, or 100 mg/kg of body weight/day), ribavirin (37.5, 55, or 75 mg/kg/day), or the combination of both drugs for 8 days, starting 4 h before virus inoculation. Monotherapy produced a dose-dependent antiviral effect against the two H5N1 viruses in vivo. Three-dimensional analysis of the drug-drug interactions revealed that oseltamivir and ribavirin interacted principally in an additive manner, with several exceptions of marginal synergy or marginal antagonism at some concentrations. The combination of ribavirin at 37.5 mg/kg/day and oseltamivir at 1 mg/kg/day and the combination of ribavirin at 37.5 mg/kg/day and oseltamivir at 10 mg/kg/day were synergistic against A/Vietnam/1203/04 and A/Turkey/15/06 viruses, respectively. These optimal oseltamivir-ribavirin combinations significantly inhibited virus replication in mouse organs, prevented the spread of H5N1 viruses beyond the respiratory tract, and abrogated the cytokine response (P < 0.01). Importantly, we observed clear differences between the efficacies of the drug combinations against two H5N1 viruses: higher doses were required for the protection of mice against A/Turkey/15/06 virus than for the protection of mice against A/Vietnam/1203/04 virus. Our preliminary results suggest that oseltamivir-ribavirin combinations can have a greater or lesser antiviral effect than monotherapy, depending on the H5N1 virus and the concentrations used.     

Activities of oseltamivir and ribavirin used alone and in combination against infections in mice with recent isolates of influenza A (H1N1) and B viruses

Mouse models have been widely used for evaluating potential influenza virus inhibitors. However, the viral strains traditionally used in these models are fairly old and do not represent currently circulating viruses in nature. We developed two new lethal infection models in mice using mouse-adapted influenza A/New Caledonia/20/99 (H1N1) and influenza B/Sichuan/379/99 viruses. Both virus infections were used to study oral treatment with oseltamivir and ribavirin, both alone and in combination. Oral treatments were given twice daily for 5 days starting 4 h before infection in initial studies. Against influenza A, oseltamivir was active at 10, 20, and 40 mg/kg/day, protected 80-100% of mice from death and reduced lung consolidation - ribavirin was similarly effective at 20, 40, and 80 mg/kg/day. When treatments were initiated after virus challenge, delaying treatment with oseltamivir even 1 day caused it to be ineffective. Ribavirin prevented mortality by 50-80% when treatments were delayed 1-4 days after infection. The combination of the two drugs (oseltamivir at 20 mg/kg/day and ribavirin at 40 mg/kg/day) was no better than ribavirin alone. In contrast to what we observed with influenza A virus infections, oseltamivir and ribavirin showed similar dose-related antiviral activities against influenza B virus infections. The compounds both significantly increased survival when treatments started up to 4 days after infection, but ribavirin was more active than oseltamivir (50-80% survival compared to 30-40% survival, respectively, when starting treatments on days 2-4 after infection). By varying the doses of each drug that were used in combination (oseltamivir at 1.25, 2.5 and 5 mg/kg/day; ribavirin at 5, 10 and 20 mg/kg/day) certain dosage combinations were superior to either compound used alone as assessed by decreased mortality, lung virus titre, lung score and lung weight parameters. These activities differed from published results with older, more established virus strains as oseltamivir was less effective and ribavirin was more active than previously reported.     

Triple-combination antiviral drug for pandemic H1N1 influenza virus infection in critically ill patients on mechanical ventilation

A recent in vitro study showed that the three compounds of antiviral drugs with different mechanisms of action (amantadine, ribavirin, and oseltamivir) could result in synergistic antiviral activity against influenza virus. However, no clinical studies have evaluated the efficacy and safety of combination antiviral therapy in patients with severe influenza illness. A total of 245 adult patients who were critically ill with confirmed pandemic influenza A/H1N1 2009 (pH1N1) virus infection and were admitted to one of the intensive care units of 28 hospitals in Korea were reviewed. Patients who required ventilator support and received either triple-combination antiviral drug (TCAD) therapy or oseltamivir monotherapy were analyzed. A total of 127 patients were included in our analysis. Among them, 24 patients received TCAD therapy, and 103 patients received oseltamivir monotherapy. The 14-day mortality was 17% in the TCAD group and 35% in the oseltamivir group (P = 0.08), and the 90-day mortality was 46% in the TCAD group and 59% in the oseltamivir group (P = 0.23). None of the toxicities attributable to antiviral drugs occurred in either group of our study, including hemolytic anemia and hepatic toxicities related to the use of ribavirin. Logistic regression analysis indicated that the odds ratio for the association of TCAD with 90-day mortality was 0.58 (95% confidence interval, 0.24 to 1.42; P = 0.24). Although this study was retrospective and did not provide virologic outcomes, our results suggest that the treatment outcome of the triple combination of amantadine, ribavirin, and oseltamivir was comparable to that of oseltamivir monotherapy.     

Synergistic Effect of Nitazoxanide with Neuraminidase Inhibitors against Influenza A Viruses In Vitro

The emergence of drug-resistant influenza A virus (IAV) strains represents a serious threat to global human health and underscores the need for novel approaches to anti-influenza chemotherapy. Combination therapy with drugs affecting different IAV targets represents an attractive option for influenza treatment. We have previously shown that the thiazolide anti-infective nitazoxanide (NTZ) inhibits H1N1 IAV replication by selectively blocking viral hemagglutinin maturation. Herein we investigate the anti-influenza activity of NTZ against a wide range of human and avian IAVs (H1N1, H3N2, H5N9, H7N1), including amantadine-resistant and oseltamivir-resistant strains, in vitro. We also investigate whether therapy with NTZ in combination with the neuraminidase inhibitors oseltamivir and zanamivir exerts synergistic, additive, or antagonistic antiviral effects against influenza viruses. NTZ was effective against all IAVs tested, with 50% inhibitory concentrations (IC₅₀s) ranging from 0.9 to 3.2 μM, and selectivity indexes (SIs) ranging from >50 to >160, depending on the strain and the multiplicity of infection (MOI). Combination therapy studies were performed in cell culture-based assays using A/Puerto Rico/8/1934 (H1N1), A/WSN/1933 (H1N1), or avian A/chicken/Italy/9097/1997 (H5N9) IAVs; dose-effect analysis and synergism/antagonism quantification were performed using isobologram analysis according to the Chou-Talalay method. Combination index (CI) analysis indicated that NTZ and oseltamivir combination treatment was synergistic against A/Puerto Rico/8/1934 (H1N1) and A/WSN/1933 (H1N1) IAVs, with CI values ranging between 0.39 and 0.63, independently of the MOI used. Similar results were obtained when NTZ was administered in combination with zanamivir (CI = 0.3 to 0.48). NTZ-oseltamivir combination treatment was synergistic also against the avian A/chicken/Italy/9097/1997 (H5N9) IAV (CI = 0.18 to 0.31). Taken together, the results suggest that regimens that combine neuraminidase inhibitors and nitazoxanide exert synergistic anti-influenza effects.     

Recurrence and persistence of fever in children who developed amantadine-resistant influenza viruses after treatment

In recent years, a dramatic increase of amantadine-resistant influenza A has occurred globally, but limited data have been available on the clinical course of patients developed amantadine-resistant viruses. We compared fever reduction between patients who developed resistance or remained sensitive in a pediatric clinic in Niigata, Japan, from 2000 to 2006. A total of 2,802 clinical samples were collected from patients who visited the pediatric outpatient clinic with influenza like illness during the seven influenza epidemic seasons. Patients were divided into 4 groups and analyzed for the fever reduction after amantadine treatment: emerged amantadine-resistant (n = 15); amantadine-sensitive (n = 35); patients administered no antiviral drugs (n = 42); and oseltamivir-treated patients (n = 320), which served as references. All 4 groups showed alleviation of fever up to day 3. The amantadine-resistant group had a significant recurrence of fever on day 4 and/or 5, and as a consequence, the course of illness was prolonged. Considering the pattern of fever, recurrent and persistent patterns were found significantly at higher rates in children with emerged resistant virus compared to other groups, and the age tended to be younger in amantadine-resistant compared to amantadine-sensitive group (3.9 +/- 3.0 vs 6.7 +/- 4.1 years old, n.s.). Therefore, we concluded that younger children were prone to develop amantadine-resistance after treatment and showed a significant recurrence of fever on day 4 and/or 5, and the course of illness was consequently prolonged.     

Efficacy of orally administered T-705 on lethal avian influenza A (H5N1) virus infections in mice

T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) was inhibitory to four strains of avian H5N1 influenza virus in MDCK cells, with the 90% effective concentrations ranging from 1.3 to 7.7 microM, as determined by a virus yield reduction assay. The efficacy was less than that exerted by oseltamivir carboxylate or zanamivir but was greater than that exerted by ribavirin. Experiments with mice lethally infected with influenza A/Duck/MN/1525/81 (H5N1) virus showed that T-705 administered per os once, twice, or four times daily for 5 days beginning 1 h after virus exposure was highly inhibitory to the infection. Dosages from 30 to 300 mg/kg of body weight/day were well tolerated; each prevented death, lessened the decline of arterial oxygen saturation (SaO(2)), and inhibited lung consolidation and lung virus titers. Dosages from 30 to 300 mg/kg/day administered once or twice daily also significantly prevented the death of the mice. Oseltamivir (20 mg/kg/day), administered per os twice daily for 5 days, was tested in parallel in two experiments; it was only weakly effective against the infection. The four-times-daily T-705 treatments at 300 mg/kg/day could be delayed until 96 h after virus exposure and still significantly inhibit the infection. Single T-705 treatments administered up to 60 h after virus exposure also prevented death and the decline of SaO(2). Characterization of the pathogenesis of the duck influenza H5N1 virus used in these studies was undertaken; although the virus was highly pathogenic to mice, it was less neurotropic than has been described for clinical isolates of the H5N1 virus. These data indicate that T-705 may be useful for the treatment of avian influenza virus infections.     

Treatment of mannan-enhanced influenza B virus infections in mice with oseltamivir, ribavirin and viramidine

Mannan, a polysaccharide preparation from Saccharomyces cerevisiae, has previously been shown to enhance influenza virus replication in mice by inhibiting host defense collectins. The use of mannan in infections may serve to broaden the types of influenza viruses that can be studied in rodent infection models. When mannan was co-administered with influenza B/Sichuan/379/99 virus to mice, the animals died from the infection, whereas mice infected with only virus survived. Three types of influenza A (H1N1) and another influenza B (Hong Kong/330/01) virus infection were also enhanced by mannan, but not four types of influenza A (H3N2) viruses. Mannan was used at 0.16 or 0.5 mg/mouse for optimal disease-enhancing activity using influenza B/Sichuan/379/99 virus. Using this model, influenza B/Sichuan/379/99 infections were treated with oseltamivir, ribavirin or viramidine (the carboxamidine derivative of ribavirin). When oral gavage treatments started 4 h before virus and mannan challenge, oseltamivir was effective at 2.5, 5 and 10 mg/kg/day. Ribavirin was active at 20, 40 and 80 mg/kg/day. Viramidine was effective at 80 and 160 mg/kg/day but not at 40 mg/kg/day. Active drug doses improved lung consolidation scores and lung weights, with decreases in lung virus titres also noted. Arterial oxygen saturation values in treated groups were significantly better than those of the placebo group on days 7-11 of the infection. Oseltamivir (5 mg/kg/day) and ribavirin (40 mg/kg/day) were used alone and in combination to determine how late after infection they could be beneficially administered. Ribavirin alone was very effective (90-100% survival of mice) when treatments started as late as 3 days after infection. Forty percent survival was evident even when treatments started 4 days post-infection. Oseltamivir was active starting treatments 1 day after virus exposure, but lost considerable efficacy when treatments began after that time. The combination of ribavirin and oseltamivir appeared to be no better than ribavirin alone, due to the stronger beneficial effect of ribavirin in this model. The overall results demonstrate that mannan can be used to enhance certain non-lethal influenza virus infections sufficiently to allow antiviral studies.     

Effect of oral gavage treatment with ZnAL42 and other metallo-ion formulations on influenza A H5N1 and H1N1 virus infections in mice

Avian influenza H5N1 infections can cause severe, lethal human infections. Whether influenza A virus treatments effectively ameliorate avian influenza H5N1 human infections is uncertain. The research objective was to evaluate the efficacy of novel zinc and other metallo-ion formulations in two influenza A mouse models. Mice infected with influenza A/Duck/MN/1525/81 (H5N1) virus were treated orally 48 h before virus exposure and then twice daily for 13 days with ZnAL42. The optimal dosing regimen for ZnAL42 was achieved at 17.28 mg/kg 48 h prior to virus exposure, twice daily for 7 days. The survival rate was 80% compared with 10% in the untreated control group and a 100% survival rate with ribavirin (75 mg/kg/day, twice a day for 5 days, beginning 4 h before virus exposure). ZnAL42 treatment significantly lessened the decline in arterial oxygen saturation (SaO2; P < 0.001). This regimen was also well tolerated by the mice. Manganese and selenium formulations were not inhibitory to virus replication when given therapeutically. Mice were also infected with influenza A/NWS/33 (H1N1) virus and were treated 48 h before virus exposure with three dosages of ZnAL42 (8.64, 1.46 or 0.24 mg/kg/day). Treatment was by oral gavage twice daily for 13 days. The highest dose of ZnAL42 was significantly inhibitory to the virus infection as seen by prevention of deaths and lessening of decline in SaO2. The data suggest that the prophylactic use of ZnAL42 is effective against avian influenza H5N1 or H1N1 virus infection in mice and should be further explored as an option for treating human influenza virus infections.     

Effects of the Combination of Favipiravir (T-705) and Oseltamivir on Influenza A Virus Infections in Mice

Favipiravir (T-705 [6-fluoro-3-hydroxy-2-pyrazinecarboxamide]) and oseltamivir were combined to treat influenza virus A/NWS/33 (H1N1), A/Victoria/3/75 (H3N2), and A/Duck/MN/1525/81 (H5N1) infections. T-705 alone inhibited viruses in cell culture at 1.4 to 4.3 μM. Oseltamivir inhibited these three viruses in cells at 3.7, 0.02, and 0.16 μM and in neuraminidase assays at 0.94, 0.46, and 2.31 nM, respectively. Oral treatments were given twice daily to mice for 5 to 7 days starting, generally, 24 h after infection. Survival resulting from 5 days of oseltamivir treatment (0.1 and 0.3 mg/kg/day) was significantly better in combination with 20 mg/kg of body weight/day of T-705 against the H1N1 infection. Treatment of the H3N2 infection required 50 mg/kg/day of oseltamivir for 7 days to achieve 60% protection; 25 mg/kg/day was ineffective. T-705 was ≥70% protective at 50 to 100 mg/kg/day but inactive at 25 mg/kg/day. The combination of inhibitors (25 mg/kg/day each) increased survival to 90%. The H5N1 infection was not benefited by treatment with oseltamivir (≤100 mg/kg/day for 7 days). T-705 was 30 to 70% protective at 25 to 100 mg/kg/day. Survival improved slightly with combination treatments. Increased activity was seen against H5N1 infection by starting treatments 2 h before infection. Oseltamivir was ineffective at ≤40 mg/kg/day. T-705 was 100% protective at 40 and 80 mg/kg/day and inactive at 20 mg/kg/day. Combining ineffective doses (20 mg/kg/day of T-705 and 10 to 40 mg/kg/day of oseltamivir) afforded 60 to 80% protection and improved body weights during infection. Thus, synergistic responses were achieved with low doses of T-705 combined with oseltamivir. These compounds may be viable candidates for combination treatment of human influenza infections.The emergence of swine influenza H1N1 virus infections in 2009 (2) highlights the need for effective antiviral therapy in a largely immune-naïve population. Treatment options for influenza are becoming more limited because viruses, including the 2009 swine H1N1 virus, are resistant to the antiviral drugs amantadine and rimantadine (3, 4, 11, 13, 20). Oseltamivir-resistant viruses are also becoming more common in the environment, particularly within the last 2 years (1, 5, 19). Thus, more potent and effective treatments are needed to combat these growing threats.More potent antiviral therapy can be achieved by using drugs in combination, as demonstrated in mouse models (10, 14-17, 24, 26, 27). Such treatment can slow down the emergence of drug-resistant viruses (12). The reported animal studies have primarily focused on the known-active antiviral agents amantadine, rimantadine, oseltamivir, peramivir, zanamivir, and ribavirin. The kinds of studies that can be performed have been limited based upon the number of active antiviral compounds that are available.In 2002, Furuta et al. reported a novel pyrazine molecule, T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide, now named favipiravir), as an inhibitor of influenza virus infections in cell culture and in mice (8). T-705 inhibits both influenza A and B viruses (8, 23, 29). The compound converts to nucleoside mono- (T-705 RMP [ribosylated, monophosphorylated]), di-, and triphosphate (T-705 RTP [ribosylated, triphosphorylated]) forms in cells (9). The mode of action of T-705 RTP is similar to that of ribavirin triphosphate as an inhibitor of influenza virus RNA polymerase (6, 9). Unlike ribavirin monophosphate, T-705 RMP is only weakly inhibitory to cellular inosine monophosphate (IMP) dehydrogenase (9, 28), and thus, it is less cytotoxic. These properties make T-705 a viable candidate for the treatment of influenza virus infections in humans. The compound is currently undergoing phase II clinical trials.The use of T-705 in combination with other antiviral substances has not been reported. The purpose of the present work was to evaluate whether the combination of T-705 with the widely used antiviral drug oseltamivir is more beneficial than either substance used alone against influenza virus infections in mice. We chose three mouse-adapted influenza viruses for these comparisons, A/NWS/33 (H1N1), A/Victoria/3/75 (H3N2), and A/Duck/MN/1525/81 (H5N1). The A/NWS and A/Victoria viruses are of seasonal origin and are confined to the respiratory tract following infection. The A/Duck virus is a low-pathogenicity avian virus from the United States that also does not spread beyond the respiratory tract of mice. The experimental influenza A/Duck mouse infection does not fully reflect the type of pathogenesis of the highly pathogenic avian influenza H5N1 viruses from the Old World. This is because the A/Duck virus lacks the multibasic amino acid R-X-R/K-R motif in the hemagglutinin protein, whereas the highly pathogenic avian H5N1 viruses contain it (7). This motif allows for the highly pathogenic viruses to be proteolytically activated by ubiquitous subtilisin-like cellular proteases, allowing the virus to spread in vivo beyond the respiratory tract and to cause multiorgan failure. Nevertheless, the A/Duck virus induces rapid, severe lung infections that are difficult to treat with conventional antiviral therapy. Using these three models, H1N1, H3N2, and H5N1, in mice, we were able to demonstrate the benefits of using oseltamivir and T-705 in combination to treat influenza virus infections.     

Amantadine resistance among porcine H1N1, H1N2, and H3N2 influenza A viruses isolated in Germany between 1981 and 2001

This study was designed to gain insight into amantadine susceptibility of porcine influenza A viruses isolated in Germany between 1981 and 2001. The 12 studied H1N1, H1N2, and H3N2 porcine influenza virus strains were isolated in chicken eggs and passaged once in MDCK cells. Plaque reduction assays were applied to examine virus susceptibility to amantadine. Genotyping was used to confirm drug resistance. In the results of these antiviral studies, only 3 of the 12 isolates were shown to be amantadine-susceptible. All resistant strains contained the AA substitutions G16E, S31N, and R77Q in the membrane protein 2 (M2). Additionally, L27A was detected in two H1N1 strains. S31N and/or L27A are well-known amino acid substitutions in M2 that confer amantadine resistance. The role of the pig as an intermediate host of avian and human influenza A viruses, the possible involvement of genetic reassortment, and the high incidence of naturally amantadine-resistant porcine influenza A viruses suggest a real risk of emergence of amantadine resistant human viruses. Therefore, drug susceptibility monitoring appears to be warranted for effective application of those drugs.     

Assessment of Antiviral Properties of Peramivir against H7N9 Avian Influenza Virus in an Experimental Mouse Model

The H7N9 influenza virus causes a severe form of disease in humans. Neuraminidase inhibitors, including oral oseltamivir and injectable peramivir, are the first choices of antiviral treatment for such cases; however, the clinical efficacy of these drugs is questionable. Animal experimental models are essential for understanding the viral replication kinetics under the selective pressure of antiviral agents. This study demonstrates the antiviral activity of peramivir in a mouse model of H7N9 avian influenza virus infection. The data show that repeated administration of peramivir at 30 mg/kg of body weight successfully eradicated the virus from the respiratory tract and extrapulmonary tissues during the acute response, prevented clinical signs of the disease, including neuropathy, and eventually protected mice against lethal H7N9 influenza virus infection. Early treatment with peramivir was found to be associated with better disease outcomes.     

蚀斑减数试验的建立及在体外抗流感病毒药物敏感性试验中的应用

目的 建立PRA以评估奥司他韦(达菲)、金刚烷胺、利巴韦林和板蓝根4种药物的体外抗流感病毒作用.方法 建立PRA,选取临床分离的流感病毒株8株,其中甲型流感病毒3株,乙型流感病毒5株.病毒培养并接种,利用PRA测定奥司他韦、金刚烷胺、利巴韦林和板蓝根4种药物体外对流感病毒的IC_(50)值.结果 8株甲、乙型流感病毒临床分离株的PRA测定结果显示,奥司他韦对甲型流感病毒IC_(50)值为0.064-0.128 mg/L,金刚烷胺为0.5 mg/L,利巴韦林对甲型流感病毒不敏感(IC_(50)>8 mg/L),板蓝根无抗病毒作用;奥司他韦、金刚烷胺、利巴韦林和板蓝根对乙型流感病毒均未发现体外抗病毒作用.结论 奥司他韦和金刚烷胺对甲型流感病毒敏感,利巴韦林不敏感,板蓝根无抗病毒作用,该4种药物未发现体外抗乙型流感病毒作用.     

In Vitro System for Modeling Influenza A Virus Resistance under Drug Pressure

One of the biggest challenges in the effort to treat and contain influenza A virus infections is the emergence of resistance during treatment. It is well documented that resistance to amantadine arises rapidly during the course of treatment due to mutations in the gene coding for the M2 protein. To address this problem, it is critical to develop experimental systems that can accurately model the selection of resistance under drug pressure as seen in humans. We used the hollow-fiber infection model (HFIM) system to examine the effect of amantadine on the replication of influenza virus, A/Albany/1/98 (H3N2), grown in MDCK cells. At 24 and 48 h postinfection, virus replication was inhibited in a dose-dependent fashion. At 72 and 96 h postinfection, virus replication was no longer inhibited, suggesting the emergence of amantadine-resistant virus. Sequencing of the M2 gene revealed that mutations appeared at between 48 and 72 h of drug treatment and that the mutations were identical to those identified in the clinic for amantadine-resistant viruses (e.g., V27A, A30T, and S31N). Interestingly, we found that the type of mutation was strongly affected by the dose of the drug. The data suggest that the HFIM is a good model for influenza virus infection and resistance generation in humans. The HFIM has the advantage of being a highly controlled system where multiplicity parameters can be directly and accurately controlled and measured.Each year thousands of people die from human H1N1 and H3N2 influenza A virus epidemics (38). In 2009, a swine-origin influenza A (H1N1) virus caused a pandemic (8). Fortunately, this virus causes a mild disease that either resolves on its own or, if caught in time, is amenable to treatment with the currently available neuraminidase inhibitors, oseltamivir carboxylate and zanamivir (8). In the past, human H1N1, H2N2, and H3N2 influenza A viruses have caused pandemics leading to many more deaths (25). Neuraminidase inhibitors, such as oseltamivir carboxylate and zanamivir, and M2 ion channel blockers, such as the adamantane derivatives, amantadine, and rimantadine, have been effective for the prevention and treatment of human influenza A virus infections (19, 22, 30-32, 39). However, with more frequent use of these inhibitors, influenza viruses resistant to the adamantanes or oseltamivir carboxylate have emerged in the human population (4, 5, 9, 16, 20, 26, 32). Amantadine resistance is so widespread that adamantane is no longer recommended for the treatment of human influenza A virus infections (20), and resistance to oseltamivir carboxylate in the currently circulating H1N1 human influenza viruses is essentially 100% (32).We wished to employ our hollow-fiber infection model (HFIM) to determine whether when influenza virus was exposed to amantadine in this in vitro circumstance (i) mutations could be generated in the M2 gene and (ii) these mutations would mimic those seen clinically. In this way, we would provide some validation that the system can be employed to identify clinically relevant mutations early for the development of new drugs and to explore the spacing of doses and administration schedule to determine if emergence of resistance can be suppressed.Sequencing the M2 genes of progeny viruses obtained from individual viral plaques of viruses grown in the HFIM system in the presence of amantadine showed that most of the viruses contained mutations identical to those found in clinical isolates obtained from patients treated with amantadine (5).(Portions of this paper were presented previously [29a].)     

Rimantadine and oseltamivir demonstrate synergistic combination effect in an experimental infection with type A (H3N2) influenza virus in mice

We studied the combination effect of rimantadine hydrochloride and oseltamivir phosphate on mice infected with influenza A/Aichi/2/68 (H3N2) virus. Compounds were simultaneously administered in a 5-day-treatment course, starting 4 h before intranasal infection with 10 or 20 viral 50% mouse lethal doses. Initially, we tested combinations of oseltamivir (0.05, 0.1 and 0.2 mg/kg/day) and rimantadine (2.5, 5.0 and 7.5 mg/kg/day). Significant differences were recorded between combination-treated groups, and groups with separately applied compounds and the placebo group, such as: protection index of oseltamivir with 5.0 or 7.5 mg/kg rimantadine varied between 34-41% and 43-87%, respectively, whereas the individual effects of oseltamivir, 5 mg/kg of rimantadine and 7.5 mg/kg of rimantadine were 0-10%, 0% and 18.7-29.6%, respectively; mean survival time in combination-treated groups was lengthened by 3.1-6.9 days, in oseltamivir groups by 0-1.9 days, and in rimantadine groups by 0.8-1.3 days at 5 mg/kg and 2.6-3.2 days at 7.5 mg/kg. The three-dimensional method of Prichard and Shipman characterized the combination effect as synergistic. Further, we studied the activity of 0.05 mg/kg/day of oseltamivir combined with 5 mg/kg of rimantadine. Lung virus titre in Madin Darby canine kidney cells, lung index and consolidation score proved the high effectiveness of the combination. When compared with the placebo group, a 2.8 log10 lower titre of 50% cell culture infectious dose (CCID50) was recorded in the combination-treated group at 48-60 h post-infection (the peak of lung virus growth). This is in contrast to the 0.1-1.0 log10 and 1.1-1.4 log10 reduction in CCID50 titre observed in the oseltamivir and rimantadine groups, respectively. These data emphasize the high anti-influenza A potential of the combination.     

Comparison of the anti-influenza virus activity of RWJ-270201 with those of oseltamivir and zanamivir

We have recently reported an influenza virus neuraminidase inhibitor, RWJ-270201 (BCX-1812), a novel cyclopentane derivative discovered through structure-based drug design. In this paper, we compare the potency of three compounds, RWJ-270201, oseltamivir, and zanamivir, against neuraminidase enzymes from various subtypes of influenza. RWJ-270201 effectively inhibited all tested influenza A and influenza B neuraminidases in vitro, with 50% inhibitory concentrations of 0.09 to 1.4 nM for influenza A neuraminidases and 0.6 to 11 nM for influenza B neuraminidases. These values were comparable to or lower than those for oseltamivir carboxylate (GS4071) and zanamivir (GG167). RWJ-270201 demonstrated excellent selectivity (>10,000-fold) for influenza virus neuraminidase over mammalian, bacterial, or other viral neuraminidases. Oral administration of a dosage of 1 mg/kg of body weight/day of RWJ-270201 for 5 days (beginning 4 h preinfection) showed efficacy in the murine model of influenza virus infection as determined by lethality and weight loss protection. RWJ-270201 administered intranasally at 0.01 mg/kg/day in the murine influenza model demonstrated complete protection against lethality, whereas oseltamivir carboxylate and zanamivir at the same dose demonstrated only partial protection. In the delayed-treatment murine influenza model, oral administration of a 10-mg/kg/day dose of RWJ-270201 or oseltamivir (GS4104, a prodrug of GS4071) at 24 h postinfection showed significant protection against lethality (P < 0.001 versus control). However, when the treatment was delayed for 48 h, no significant protection was observed in either drug group. No drug-related toxicity was observed in mice receiving 100 mg/kg/day of RWJ-270201 for 5 days. These efficacy and safety profiles justify further consideration of RWJ-270201 for the treatment and prevention of human influenza.     

In vitro and in vivo activities of anti-influenza virus compound T-705

T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) has been found to have potent and selective inhibitory activity against influenza virus. In an in vitro plaque reduction assay, T-705 showed potent inhibitory activity against influenza A, B, and C viruses, with 50% inhibitory concentrations (IC(50)s) of 0.013 to 0.48 microg/ml, while it showed no cytotoxicity at concentrations up to 1,000 microg/ml in Madin-Darby canine kidney cells. The selectivity index for influenza virus was more than 2,000. It was also active against a neuraminidase inhibitor-resistant virus and some amantadine-resistant viruses. T-705 showed weak activity against non-influenza virus RNA viruses, with the IC(50)s being higher for non-influenza virus RNA viruses than for influenza virus, and it had no activity against DNA viruses. Orally administered T-705 at 100 mg/kg of body weight/day (four times a day) for 5 days significantly reduced the mean pulmonary virus yields and the rate of mortality in mice infected with influenza virus A/PR/8/34 (3 x 10(2) PFU). These results suggest that T-705 may be a compound that is useful and highly selective against influenza virus infections and that has a mode of action different from those of commercially available drugs, such as amantadine, rimantadine, and neuraminidase inhibitors.     

In vivo prophylactic activity of QR-435 against H3N2 influenza virus infection

BACKGROUND: Prophylaxis against influenza infection can take several forms, none of which is totally effective at preventing the spread of the disease. QR-435, an all-natural compound of green-tea extract and other agents, has been developed to protect against a range of viral infections, including the influenza subtype H3N2. METHODS: Several different QR-435 formulations were tested against the two influenza A H3N2 viruses (A/Sydney/5/97 and A/Panama/2007/99) in the ferret model. Most experiments included negative (phosphate-buffered saline) and positive (oseltamivir 5 mg/kg, twice daily) controls. QR-435 and the control were administered 5 minutes after intranasal delivery of the virus as prophylaxis against infection resulting from exposure to infected but untreated ferrets and for prevention of transmission from infected and treated ferrets to untreated animals. Effects of QR-435 on seroconversion, virus shedding, and systemic sequelae of infection (weight loss, fever, reduced activity) were evaluated. RESULTS: QR-435 prevented transmission and provided prophylaxis against influenza virus H3N2. Prophylaxis with QR-435 was significantly more than with oseltamivir in these experiments. Optimal in vivo efficacy of QR-435 requires a horseradish concentration of at least 50% of that in the original formulation, and the benefits of this preparation appear to be dose dependent. CONCLUSIONS: QR-435 is effective for both prevention of H3N2 viral transmission and prophylaxis. These preclinical results warrant further evaluation of its prophylactic properties against avian influenza virus infection in humans.