Virus sialidase

Further Developments of Influenza Virus Sialidase Inhibitors. 123... 

An overview of the role of the virus-associated glycoprotein sialidase (neuraminidase) and some of the most recent developments towards the discovery of anti-influenza drugs based on the inhibition of influenza virus sialidase is provided in this chapter. 

Influenza virus sialidase (Fig. 2) is a tetrameric glycoprotein consisting of four identical subnnits (Colman and Ward 1985), and acts as a glycohydrolase that removes a-ketosidically linked terminal AT-acetylneuraminic acid residues from gly-coconjugates. 

Fig. 3 Sialidase inhibitor Neu5Ac2en 4 bound in the active site of influenza A virus sialidase (from PDB structure IfSb (Smith et al, 2001)), Left Stick model of 4 surrounded by some important active site residues. Right Electrostatic potential surface rendering of the active site (blue -positive, red - negative), (Amino acid numbering for influenza A/N2 sialidase is used throughout this review)...

Neu5Ac2en 4, a micromolar inhibitor of influenza virus sialidase 4 x 10 M (A/N2)] (Holzer et al. 1993), was first identified as a very good inhibitor in the late 1960s (Meindl and Tuppy 1969). A series of C-5 modified Neu5Ac2en derivatives provided the first improved in vitro inhibitors compared with the parent compound 4. The replacement of the C-5 A-acetyl moiety with a A-trifluoroacetyl group resulted in the most potent inhibitor of this series, 2-deoxy-2,3-didehydro-A-trifluoroacetylneuraminic acid 10 [A] 8 x 10 M (A/Nl)] (Meindl et al. 1974). While these C-5 modified compounds were also very effective in cell culture assays (Palese et al. 1974a Palese and Compans 1976), none, including the parent... 

Fig. 5 Key interactions of 4-deoxy-4-guanidino-Neu5Ac2en (zanamivir) 12 with the active site of influenza A virus sialidase [Figure generated from crystal strucmre data (PDB - Innc) using LIGPLOT (Wallace et al. 1995)]. To the right is shown zanamivir 12 in the same orientation...

The discovery of the potent in vitro sialidase inhibitory activity and in vivo efficacy of zanamivir 12, and the increasing availability of 3D structural data for influenza virus sialidases in the 1990s, particularly with Neu5Ac and various inhibitors bound into the active site, provided a platform for further drug discovery efforts targeting... 

Analysis of Potential Binding Interactions within the Influenza Virus Sialidase Active Site... 

An interesting feature of the influenza virus sialidase active site that offers the potential for developing inhibitors specific for N1 sialidases, including avian influenza A/H5N1 virus sialidase, has recently been revealed by X-ray crystallography. The... 

Compound 34 (BCZ-1812, RWJ-270201, peramivir) showed selective inhibition of influenza virus sialidases over bacterial and mammalian sialidases (Babu et al. 2000 Bantia et al. 2001 Sidwell and Smee 2002). Successful inhibition of influenza virus infectivity in vitro (Smee et al. 2001) and upon oral administration in vivo [mice (Bantia et al. 2001) and ferrets, reviewed in Sidwell and Smee 2002] led to human clinical trials of orally administered peramivir (Barroso et al. 2005). While orally administrated peramivir successfully completed animal studies and Phase I and Phase II clinical trials, in which the compound was showing neither major side effects nor toxicity (Sidwell and Smee 2002), preliminary results of the Phase III trials (June 2002) demonstrated no statistically significant difference in the primary efficacy endpoint, possibly due to low bioavailability (Barroso et al. 2005). 

Fig. 8 Superimposition of inhibitors and key active site residues in influenza A virus sialidase cyclopentane-based inhibitor peramivir 34 (brown carbons, PDB - 117f), Neu5Ac2en 4 (green carbons, PDB - lf8b). Note the overlap of the carboxyl and acetamido-methyl groups of the inhibitors, and the alternative conformations of the side-chain of Glu276. To the right is shown peramivir 34 oriented as in the crystal structure...

Table 2 Sensitivity of influenza virus sialidase variants isolated in the clinical setting to sialidase inhibitors in sialidase assays ...

Smith PW, Sollis SL, Howes PD, Cherry PC, Starkey ID, Cobley KN, Weston H, Scicinski J, Merritt A, Whittington A, Wyatt P, Taylor N, Green D, BetheU R, Madar S, Fenton RJ, Motley PJ, Pateman T, Beresford A (1998) Dihydropyrancarboxamides related to zanamivir a new series of inhibitors of influenza virus sialidases. 1. Discovery, synthesis, biological activity, and structure-activity relationships of 4-guanidino- and 4-amino H-pyran-6-carboxamides. J Med Chem 41 787-797... 

India, medicinal research in, 22 (1985) 243 Influenza virus sialidase, inhibitors of, 36 (1999) 1... 

Carbon-carbon bond lyases, used in the reverse, synthetic direction have also enjoyed significant application in the pharmaceutical industry. For example 7/-acetyl-D-neuraminic acid (NANA), an intermediate in the chemoenzymatic synthesis of the influenza virus sialidase inhibitor zanamavir, may be synthesized using NANA aldolase. 

The internal, sialyl residue of GM, is not completely resistant to some sialidases, so long as the oligosaccharide chain is bound to the ceramide part of GM, it is slowly cleaved by C. perfringens sialidase in the presence of bile salts.77 57 3511 Surprisingly, it is a relatively good substrate for the A. ureafaciens sialidase.360 Rapid hydrolysis of GM, sialic acid has also been observed with Sendai virus sialidase, in contrast to the enzymes from NDV or influenza viruses.361 Susceptibility towards mammalian sialidases has also been reported.362 However, it... 

---