Jack Nguyen

Triple Combination of Amantadine, Ribavirin, and Oseltamivir Is Highly Active and Synergistic against Drug Resistant Influenza Virus Strains In Vitro

The rapid emergence and subsequent spread of the novel 2009 Influenza A/H1N1 virus (2009 H1N1) has prompted the World Health Organization to declare the first pandemic of the 21st century, highlighting the threat of influenza to public health and healthcare systems. Widespread resistance to both classes of influenza antivirals (adamantanes and neuraminidase inhibitors) occurs in both pandemic and seasonal viruses, rendering these drugs to be of marginal utility in the treatment modality. Worldwide, virtually all 2009 H1N1 and seasonal H3N2 strains are resistant to the adamantanes (rimantadine and amantadine), and the majority of seasonal H1N1 strains are resistant to oseltamivir, the most widely prescribed neuraminidase inhibitor (NAI). To address the need for more effective therapy, we evaluated the in vitro activity of a triple combination antiviral drug (TCAD) regimen composed of drugs with different mechanisms of action against drug-resistant seasonal and 2009 H1N1 influenza viruses. Amantadine, ribavirin, and oseltamivir, alone and in combination, were tested against amantadine- and oseltamivir-resistant influenza A viruses using an in vitro infection model in MDCK cells. Our data show that the triple combination was highly synergistic against drug-resistant viruses, and the synergy of the triple combination was significantly greater than the synergy of any double combination tested (P<0.05), including the combination of two NAIs. Surprisingly, amantadine and oseltamivir contributed to the antiviral activity of the TCAD regimen against amantadine- and oseltamivir-resistant viruses, respectively, at concentrations where they had no activity as single agents, and at concentrations that were clinically achievable. Our data demonstrate that the TCAD regimen composed of amantadine, ribavirin, and oseltamivir is highly synergistic against resistant viruses, including 2009 H1N1. The TCAD regimen overcomes baseline drug resistance to both classes of approved influenza antivirals, and thus may represent a highly active antiviral therapy for seasonal and pandemic influenza.

Triple combination of oseltamivir, amantadine, and ribavirin displays synergistic activity against multiple influenza virus strains in vitro.

ABSTRACT The recurring emergence of influenza virus strains that are resistant to available antiviral medications has become a global health concern, especially in light of the potential for a new influenza virus pandemic. Currently, virtually all circulating strains of influenza A virus in the United States are resistant to either of the two major classes of anti-influenza drugs (adamantanes and neuraminidase inhibitors). Thus, new therapeutic approaches that can be rapidly deployed and that will address the issue of recurring resistance should be developed. We have tested double and triple combinations of the approved anti-influenza drugs oseltamivir and amantadine together with ribavirin against three influenza virus strains using cytopathic effect inhibition assays in MDCK cells. We selected A/New Caledonia/20/99 (H1N1) and A/Sydney/05/97 (H3N2) as representatives of the wild-type versions of the predominant circulating seasonal influenza virus strains and A/Duck/MN/1525/81 (H5N1) as a representative of avian influenza virus strains. Dose-response curves were generated for all drug combinations, and the degree of drug interaction was quantified using a model that calculates the synergy (or antagonism) between the drugs in double and triple combinations. This report demonstrates that a triple combination of antivirals was highly synergistic against influenza A virus. Importantly, the synergy of the triple combination was 2- to 13-fold greater than the synergy of any double combination depending on the influenza virus subtype. These data support the investigation of a novel combination of oseltamivir, amantadine, and ribavirin as an effective treatment for both seasonal and pandemic influenza virus, allowing the efficient use of the existing drug supplies.

Modeling amantadine treatment of influenza A virus in vitro

We analyzed the dynamics of an influenza A/Albany/1/98 (H3N2) viral infection, using a set of mathematical models highlighting the differences between in vivo and in vitro infection. For example, we found that including virion loss due to cell entry was critical for the in vitro model but not for the in vivo model. Experiments were performed on influenza virus-infected MDCK cells in vitro inside a hollow-fiber (HF) system, which was used to continuously deliver the drug amantadine. The HF system captures the dynamics of an influenza infection, and is a controlled environment for producing experimental data which lend themselves well to mathematical modeling. The parameter estimates obtained from fitting our mathematical models to the HF experimental data are consistent with those obtained earlier for a primary infection in a human model. We found that influenza A/Albany/1/98 (H3N2) virions under normal experimental conditions at 37 degrees C rapidly lose infectivity with a half-life of approximately 6.6+/-0.2 h, and that the lifespan of productively infected MDCK cells is approximately 13 h. Finally, using our models we estimated that the maximum efficacy of amantadine in blocking viral infection is approximately 74%, and showed that this low maximum efficacy is likely due to the rapid development of drug resistance.

Efficacy of Combined Therapy with Amantadine, Oseltamivir, and Ribavirin In Vivo against Susceptible and Amantadine-Resistant Influenza A Viruses

The limited efficacy of existing antiviral therapies for influenza – coupled with widespread baseline antiviral resistance – highlights the urgent need for more effective therapy. We describe a triple combination antiviral drug (TCAD) regimen composed of amantadine, oseltamivir, and ribavirin that is highly efficacious at reducing mortality and weight loss in mouse models of influenza infection. TCAD therapy was superior to dual and single drug regimens in mice infected with drug-susceptible, low pathogenic A/H5N1 (A/Duck/MN/1525/81) and amantadine-resistant 2009 A/H1N1 influenza (A/California/04/09). Treatment with TCAD afforded >90% survival in mice infected with both viruses, whereas treatment with dual and single drug regimens resulted in 0% to 60% survival. Importantly, amantadine had no activity as monotherapy against the amantadine-resistant virus, but demonstrated dose-dependent protection in combination with oseltamivir and ribavirin, indicative that amantadines activity had been restored in the context of TCAD therapy. Furthermore, TCAD therapy provided survival benefit when treatment was delayed until 72 hours post-infection, whereas oseltamivir monotherapy was not protective after 24 hours post-infection. These findings demonstrate in vivo efficacy of TCAD therapy and confirm previous reports of the synergy and broad spectrum activity of TCAD therapy against susceptible and resistant influenza strains in vitro.

Triple Combination Antiviral Drug (TCAD) Composed of Amantadine, Oseltamivir, and Ribavirin Impedes the Selection of Drug-Resistant Influenza A Virus

Widespread resistance among circulating influenza A strains to at least one of the anti-influenza drugs is a major public health concern. A triple combination antiviral drug (TCAD) regimen comprised of amantadine, oseltamivir, and ribavirin has been shown to have synergistic and broad spectrum activity against influenza A strains, including drug resistant strains. Here, we used mathematical modeling along with three different experimental approaches to understand the effects of single agents, double combinations, and the TCAD regimen on resistance in influenza in vitro, including: 1) serial passage at constant drug concentrations, 2) serial passage at escalating drug concentrations, and 3) evaluation of the contribution of each component of the TCAD regimen to the suppression of resistance. Consistent with the modeling which demonstrated that three drugs were required to suppress the emergence of resistance in influenza A, treatment with the TCAD regimen resulted in the sustained suppression of drug resistant viruses, whereas treatment with amantadine alone or the amantadine-oseltamivir double combination led to the rapid selection of resistant variants which comprised ∼100% of the population. Furthermore, the TCAD regimen imposed a high genetic barrier to resistance, requiring multiple mutations in order to escape the effects of all the drugs in the regimen. Finally, we demonstrate that each drug in the TCAD regimen made a significant contribution to the suppression of virus breakthrough and resistance at clinically achievable concentrations. Taken together, these data demonstrate that the TCAD regimen was superior to double combinations and single agents at suppressing resistance, and that three drugs at a minimum were required to impede the selection of drug resistant variants in influenza A virus. The use of mathematical modeling with multiple experimental designs and molecular readouts to evaluate and optimize combination drug regimens for the suppression of resistance may be broadly applicable to other infectious diseases.

Combination therapy with amantadine, oseltamivir and ribavirin for influenza A infection: safety and pharmacokinetics

BACKGROUND Antiviral resistance among influenza A viruses is associated with high morbidity and mortality in immunocompromised hosts. However, treatment strategies for drug-resistant influenza A are not established. A triple-combination antiviral drug (TCAD) regimen consisting of amantadine (AMT), oseltamivir (OSL) and ribavirin (RBV) demonstrated good efficacy in an animal model. METHODS We first analysed the pharmacokinetics (PKs) of TCAD therapy in healthy volunteers. We then performed a pilot study of TCAD therapy in patients undergoing chemotherapy or haematopoietic cell transplantation. AMT (75 mg), OSL (50 mg) and RBV (200 mg) were administered three times a day for 10 days. The safety and PKs of TCAD therapy were monitored. RESULTS The PKs of TCAD therapy in healthy volunteers was shown to be similar to the PKs of each drug individually from a single dose. In the pilot study, six immunocompromised patients received TCAD therapy and one patient received OSL monotherapy. All but one patient completed 10 days of TCAD therapy without side effects; one patient receiving TCAD was withdrawn from the study because of respiratory failure and ultimately recovered. Viral load was decreased after TCAD therapy, despite the presence of either AMT- or OSL-resistant virus in two cases. One patient with 2009 influenza A/H1N1 receiving OSL monotherapy developed confirmed OSL resistance during treatment. CONCLUSIONS TCAD therapy had similar PKs to each individual antiviral during monotherapy following a single dose and can be administered safely in immunocompromised patients.

Amantadine improves cognitive outcome and increases neuronal survival after fluid percussion traumatic brain injury in rats

This study evaluated the effects of clinically relevant concentrations of amantadine (AMT) on cognitive outcome and hippocampal cell survival in adult rats after lateral fluid percussion traumatic brain injury (TBI). AMT is an antagonist of the N-methyl-D-aspartate-type glutamate receptor, increases dopamine release, blocks dopamine reuptake, and has an inhibitory effect on microglial activation and neuroinflammation. Currently, AMT is clinically used as an antiparkinsonian drug. Amantadine or saline control was administered intraperitoneally, starting at 1 h after TBI followed by dosing three times daily for 16 consecutive days at 15, 45, and 135 mg/kg/day. Terminal blood draws were obtained from TBI rats at the time of euthanasia at varying time points after the last amantadine dose. Pharmacokinetics analysis confirmed that the doses of AMT achieved serum concentrations similar to those observed in humans receiving therapeutic doses (100-400 mg/day). Acquisition of spatial learning and memory retention was assessed using the Morris water maze (MWM) on days 12-16 after TBI. Brain tissues were collected and stained with Cresyl-violet for long-term cell survival analysis. Treatment with 135mg/kg/day of AMT improved acquisition of learning and terminal cognitive performance on MWM. The 135-mg/kg/day dosing of AMT increased the numbers of surviving CA2-CA3 pyramidal neurons at day 16 post-TBI. Overall, the data showed that clinically relevant dosing schedules of AMT affords neuroprotection and significantly improves cognitive outcome after experimental TBI, suggesting that it has the potential to be developed as a novel treatment of human TBI.

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

ABSTRACT 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.

Rapid quantification of single-nucleotide mutations in mixed influenza A viral populations using allele-specific mixture analysis

Monitoring antiviral resistance in influenza is critical to public health epidemiology and pandemic preparedness activities. Effective monitoring requires methods to detect low-level resistance and to monitor the change in resistance as a function of time and drug treatment. Resistance-conferring single-nucleotide mutations in influenza virus are ideal targets for such methods. In the present study, fives sets of paired TaqMan allele-specific PCR (ASPCR) assays were developed and validated for quantitative single-nucleotide polymorphism (SNP) analysis. This novel method using Delta Ct is termed allele-specific mixture analysis (ASMA) or FluASMA. The FluASMA assays target L26F, V27A, A30T, and S31N mutations in the A/Albany/1/98 (H3N2) M2 gene and H275Y mutation in the A/New Caledonia/20/99 (H1N1) NA gene and have a limit of quantification of 0.25-0.50% mutant. The error for % mutant estimation was less than 10% in all FluASMA assays, with intra-run Delta Ct coefficient of variance (CoV) at <or=2% and inter-run Delta Ct CoV at <or=5%. Results from the current study demonstrate that FluASMA is a highly sensitive and quantitative SNP analysis method, even for minor mutant components (<1%).

Treatment of Oseltamivir-Resistant Influenza A (H1N1) Virus Infections in Mice With Antiviral Agents

Influenza A/Mississippi/03/2001 (H1N1) and A/Hong Kong/2369/2009 (H1N1) viruses containing the neuraminidase gene mutation H275Y (conferring resistance to oseltamivir) were adapted to mice and evaluated for suitability as models for lethal infection and antiviral treatment. The viral neuraminidases were resistant to peramivir and oseltamivir carboxylate but sensitive to zanamivir. Similar pattern of antiviral activity were seen in MDCK cell assays. Lethal infections were achieved in mice with the two viruses. Oral oseltamivir at 100 and 300mg/kg/day bid for 5day starting at -2h gave 30% and 60% protection from death, respectively, due to the A/Mississippi/03/2001 infection. Intraperitoneal treatments with zanamivir at 30 and 100mg/kg/day starting at -2h gave 60% and 90% protection, respectively. Neither compound at <300mg/kg/day protected mice when treatments began at +24h. Amantadine was effective at 10, 30, and 100mg/kg/day, rimantadine was protective at 10 and 30mg/kg/day (highest dose tested), and ribavirin was active at 30 and 75mg/kg/day, with survival ranging from 60-100% for oral treatments initiated at -2h. For treatments begun at +24h, amantadine was protective at 30 and 100mg/kg/day, rimantadine showed efficacy at 10 and 30mg/kg/day, and ribavirin was active at 75mg/kg/day, with 60-100% survival per group. In the A/Hong Kong/2369/2009 infection, oral oseltamivir at 100 and 300mg/kg/day starting at -2h gave 50% and 70% protection from death, respectively. These infection models will be useful to study newly discovered anti-influenza virus agents and to evaluate compounds in combination.