Novel Anti Influenza Agents to Target Drug-Induced Resistance: Mechanism-based Neuraminidase Inhibitors
Lead Research Organisation:
University of Bath
Department Name: Pharmacy and Pharmacology
Abstract
Our research is focused on trying to develop an improved class of anti-virals for the treatment of influenza viruses, including the highly pathogenic avian H5N1 (Bird Flu) influenza virus. The compounds we will be developing are designed to overcome some of the problems associated with the current influenza drugs, Relenza and Tamiflu. Unfortunately, the clinical usefulness of Relenza is reduced by the fact that it cannot be administered orally and, most alarmingly, drug-induced resistance to Tamiflu has already been observed in some patients infected with the H5N1 virus.
Relenza and Tamiflu act by preventing the release of newly formed virus particles from infected cells. They do this by blocking the action of a particular enzyme known as a neuraminidase, and hence, are referred to as neuraminidase inhibitors. If the neuraminidase is blocked (inhibited), newly formed virus particles remain attached to the surface of already infected cells, and are unable to escape to infect further cells. The compounds we are developing are also neuraminidase inhibitors, but inhibit the enzyme in a very different way to Relenza and Tamiflu. By inhibiting the neuraminidase in a different way, we believe that; i). resistance to our compounds is much less likely to develop, and ii). it should also be possible to introduce chemical features into these inhibitors that will allow them to be administered orally. Ultimately, we hope to show that our neuraminidase inhibitors are suitable targets for the treatment of influenza, and they should also give us a much better understanding of how influenza viruses develop resistance to anti-viral drugs.
Relenza and Tamiflu act by preventing the release of newly formed virus particles from infected cells. They do this by blocking the action of a particular enzyme known as a neuraminidase, and hence, are referred to as neuraminidase inhibitors. If the neuraminidase is blocked (inhibited), newly formed virus particles remain attached to the surface of already infected cells, and are unable to escape to infect further cells. The compounds we are developing are also neuraminidase inhibitors, but inhibit the enzyme in a very different way to Relenza and Tamiflu. By inhibiting the neuraminidase in a different way, we believe that; i). resistance to our compounds is much less likely to develop, and ii). it should also be possible to introduce chemical features into these inhibitors that will allow them to be administered orally. Ultimately, we hope to show that our neuraminidase inhibitors are suitable targets for the treatment of influenza, and they should also give us a much better understanding of how influenza viruses develop resistance to anti-viral drugs.
Technical Summary
The recent emergence of the highly pathogenic H5N1 strain of avian influenza now circulating in Asia, EU and Africa has increased concerns that a new, and devastating, influenza pandemic may be imminent. Antiviral drugs represent the first line of defence for pandemic outbreaks, and governments are currently stockpiling the influenza neuraminidase inhibitors Relenza? (Zanamivir) and Tamiflu? (Oseltamivir) in preparedness. These inhibitors prevent the release of newly formed virions by blocking the action of the neuraminidase (sialidase) enzyme, which normally removes sialic acid from receptors on the surface of infected cells to allow virus release. These neuraminidase inhibitors are highly potent and specific inhibitors against all known influenza A and B strains, including the avian H5N1 virus. There are, however, several problems associated with Relenza and Tamiflu. Unfortunately, as Relenza is only delivered to the respiratory tract, its usefulness is limited if the pandemic influenza strain spreads to other organs, and, more alarmingly, drug-induced resistance to Tamiflu has already been observed in clinical isolates from H5N1 infected patients. As such, there is an urgent need to develop new and improved classes of anti-virals for the treatment of influenza.
We have recently filed a provisional patent application for the use of fluorinated sialic acid analogues as ?mechanism-based? neuraminidase inhibitors for the treatment of influenza. These novel compounds are known to covalently inhibit influenza neuraminidases by specifically targeting amino acid residues essential for catalytic activity and, as such, drug-induced resistance is less likely to evolve in response to these compounds. We propose to synthesise a series of modified fluoro-sialic acids as ?mechanism-based? inhibitors of influenza neuraminidases, incorporating structural features designed to improve the pharmacokinetic properties and inhibitory activities of our original inhibitors. We will then perform detailed kinetic analyses of their inhibitory activity against purified influenza neuraminidases, and potent inhibitors will then be tested for efficacy towards a panel of wild-type influenza viruses and viruses with known neuraminidase mutations that confer drug resistance to Relenza or Tamiflu. Finally, we will attempt to generate resistance to selected mechanism-based inhibitors by in vitro passaging of influenza viruses in cell cultures. This will help us to evaluate the susceptibility of this class of inhibitor to drug-induced resistance, and should provide a greater understanding of the mechanisms associated with drug resistance in influenza.
We have recently filed a provisional patent application for the use of fluorinated sialic acid analogues as ?mechanism-based? neuraminidase inhibitors for the treatment of influenza. These novel compounds are known to covalently inhibit influenza neuraminidases by specifically targeting amino acid residues essential for catalytic activity and, as such, drug-induced resistance is less likely to evolve in response to these compounds. We propose to synthesise a series of modified fluoro-sialic acids as ?mechanism-based? inhibitors of influenza neuraminidases, incorporating structural features designed to improve the pharmacokinetic properties and inhibitory activities of our original inhibitors. We will then perform detailed kinetic analyses of their inhibitory activity against purified influenza neuraminidases, and potent inhibitors will then be tested for efficacy towards a panel of wild-type influenza viruses and viruses with known neuraminidase mutations that confer drug resistance to Relenza or Tamiflu. Finally, we will attempt to generate resistance to selected mechanism-based inhibitors by in vitro passaging of influenza viruses in cell cultures. This will help us to evaluate the susceptibility of this class of inhibitor to drug-induced resistance, and should provide a greater understanding of the mechanisms associated with drug resistance in influenza.