The inhibition of the RNA polymerase activity of influenza virus A by pyrophosphate analogues

Synthesis and evaluation of l-rhamnose 1C-phosphonates as nucleotidylyltransferase inhibitors

We report the synthesis of a series of phosphonates and ketosephosphonates possessing an L-rhamnose scaffold with varying degrees of fluorination. These compounds were evaluated as potential inhibitors of α-D-glucose 1-phosphate thymidylyltransferase (Cps2L), the first enzyme in Streptococcus pneumoniae L-rhamnose biosynthesis, and a novel antibiotic target. Enzyme-substrate and enzyme-inhibitor binding experiments were performed using water-ligand observed binding via gradient spectroscopy (WaterLOGSY) NMR for known sugar nucleotide substrates and selected phosphonate analogues. IC50 values were measured and Ki values were calculated for inhibitors. New insights were gained into the binding promiscuity of enzymes within the prokaryotic L-rhamnose biosynthetic pathway (Cps2L, RmlB-D) and into the mechanism of inhibition for the most potent inhibitor in the series, L-rhamnose 1C-phosphonate.

Development of antivirals against influenza

Morbidity and mortality due to influenza virus infections remain a major problem throughout the world. Yearly, medical costs and loss of productivity resulting from influenza infection are estimated to be in the range of 12 dollars bn in the USA. The predicted increases in the elderly and immune-deficient populations will make influenza an even greater threat in the future. Despite the availability of vaccines, they have been least effective in these high-risk populations. Coupled with the requirement for routine revaccination, the need for effective antiviral agents is illustrated. The currently approved drugs, amantadine, rimantadine and ribavirin (in some countries), have limitations. They are only inhibitory against influenza A viruses, are prone to adverse reactions and quickly give rise to resistant virus. This review examines current drug therapies, antivirals in development and possible future opportunities for anti-influenza drugs.

Antiviral effects of phosphonoformate (PFA, foscarnet sodium)

This article describes the antiviral properties of foscarnet (trisodium phosphonoformate) at the enzyme level as well as in cell cultures and in vivo. The mechanism of action against herpesvirus DNA polymerases and reverse transcriptases is outlined. Clinical studies using topical foscarnet against mucocutaneous herpes simplex virus infections are presented. The clinical use of intravenous foscarnet against severe viral infections caused by cytomegalovirus, hepatitis B virus and human immunodeficiency virus is discussed.

Potential targets for antiviral chemotherapy

Serendipity and random screening have been successful in producing effective antiviral agents. The increase in our knowledge of the basic biochemistry of viral replication and of virus-host interrelationships has revealed not only an understanding of the targets upon which existing antiviral agents exert their inhibitory effect, but also has uncovered new potential targets. The hope is that such molecular understanding will afford the synthesis of compounds with selective antiviral activity. A review of various viral targets which are potentially susceptible to attack, and a few approaches for development of antiviral agents are presented.

The antiviral activity of tetrazole phosphonic acids and their analogues

5-(Phosphonomethyl)-1H-tetrazole and a number of related tetrazoles have been prepared and their effects on the replication of Herpes Simplex Viruses-1 and -2 have been investigated as well as their abilities to inhibit the DNA polymerases induced by these viruses and the RNA transcriptase activity of influenza virus A. Contrary to an earlier report, 5-(phosphonomethyl)-1H-tetrazole was not an efficient inhibitor of the replication of HSV-1 and HSV-2 in tissue culture. Analogues of 5-(phosphonomethyl)-1H-tetrazole were also devoid of significant antiviral activity. Only 5-(phosphonomethyl)-1H-tetrazole and 5-(thiophosphonomethyl)-1H-tetrazole inhibited the influenza virus transcriptase, and both were more effective as inhibitors than phosphonoacetic acid under the same conditions. The DNA polymerases induced by HSV-1 and HSV-2 were inhibited slightly by 5-(phosphonomethyl)-1H-tetrazole and to a lesser extent by its N-ethyl analogue and 3-(phosphonomethyl)-1H-1,2,4-triazole. None of these compounds were as effective as phosphonoacetic acid. 5-(Thiophosphonomethyl)-1H-tetrazole was a better inhibitor of the DNA polymerase induced by HSV-1 than 5-(phosphonomethyl)-1H-tetrazole.

Metal chelators as potential antiviral agents

Metal-chelating compounds can inhibit virus-induced enzymes in infected cells by coordinating with metal ions at their active sites. Consideration of the coordinating properties of ligands can explain the antiviral activity of these compounds. The antiviral actions of a number of compounds (e.g., thiosemicarbazones, pyrophosphate analogues, beta-diketones, cyclic polyethers and flavanoids) are discussed in the light of their metal-chelating properties.

Thio-analogues of inorganic pyrophosphate inhibit the replication of influenza virus A in vitro

Mono- and bisthiopyrophosphate can inhibit the replication of influenza virus A/X49 in Madin-Darby canine kidney (MDCK) cells at concentrations at which no cytotoxic effect is observed after 3 days. The thiopyrophosphate analogues inhibit the RNA transcriptase activity of this virus possibly by chelating with an essential metal ion in the transcriptase complex. [31P]NMR spectroscopy indicates that bisthiopyrophosphate coordinates to zinc through sulphur and magnesium through oxygen which may influence the inhibitory properties of this compound with metal-containing enzymes.

Mode of interference of trisodium phosphonoformate (INN: foscarnet sodium), with influenza virus mRNA synthesis

Foscarnet has previously been shown to inhibit influenza RNA polymerase activity. In this report the mode of inhibition of foscarnet has been investigated by enzyme-kinetic procedures and product analysis. Foscarnet shows noncompetitive inhibition with respect to ATP, CTP, and UTP, and a mixed inhibition with respect to GTP. In the presence of foscarnet the initiation of the mRNA synthesis can still occur, but the elongation is inhibited. The block of mRNA formation by foscarnet seems to occur after the synthesis of the 12-nucleotide-long conserved sequence found at the 5 prime end of the viral message.