Influenza

Virus Research 103 (2004) 199–203

Molecular mechanisms of influenza virus resistance to neuraminidase inhibitors
Larisa V. Gubareva∗
Department of Internal Medicine, University of Virginia Health Sciences Center, P.O. Box 800473, Charlottesville, VA, USA

Abstract A wide use of inhibitors of influenza virus neuraminidase (NAIs) to control influenza in humans demands a better understanding ofthe mechanisms involved in the resistance emergence. In vitro studies demonstrate that both neuraminidase (NA) and hemagglutinin (HA) influence virus susceptibility to NAIs. Drug resistance conferred due to changes in the NA could be monitored in the NA inhibition assays. Zanamivir-selected viruses acquired the NA substitutions at residues 119 and 292; oseltamivir-selected—at 274 and 292;peramivir-selected—at 292; and A-315675-selected—at 119. The HA binding efficiency and therefore susceptibility to NAIs are affected by the amino acids forming the HA receptor-binding site, the location and number of oligosaccharide chains, and structure of the neuraminic acid-containing cellular receptors. The lack of suitable cell culture-based assays hampers the assessment of virus susceptibility inhumans. Emergence of the viruses with the NAI-induced substitutions in the NA is uncommon in drug-treated humans, however a compromised state of the immune system promotes emergence of drug resistance. In vivo, the zanamivir-selected mutant contained a substitution at 152 (B/NA); the oseltamivir-selected mutants—at residues 119 (A/N2), 198 (B/NA), 274 (A/N1), and 292 (A/N2). Substitutions in the NAwere often accompanied by impairment of virus infectivity and virulence in animal models. Because of complexity of mechanisms of virus resistance, further analysis of the viruses recovered from the drug-treated humans is warranted. © 2004 Elsevier B.V. All rights reserved.
Keywords: Drug resistance; Neuraminidase inhibitor; Immunocompromised patients

1. Introduction The HA of influenza A and Bviruses binds to neuraminic acid-containing receptors (Colman, 1989). The neuraminidase (NA) enzymatic activity promotes influenza virus dispersement within mucosal secretions of the respiratory tract and prevents progeny virions from self-aggregation by removing neuraminic (sialic) acids from oligosaccharide chains of receptors (Colman, 1989). NA inhibitors (NAI) are designed to limit influenza virusinfection by blocking the enzyme active site (Table 1). Two NAIs, inhaled zanamivir (RelenzaTM ) and oral oseltamivir (prodrug) (TamifluTM ) have been licensed for influenza treatment in several countries. Peramivir is undergoing clinical evaluation (Babu et al., 2000), and A-315677 (prodrug) is in pre-clinical phase of development (Kati et al., 2002) (Fig. 1). All four compounds are highly potentinhibitors of the NAs of influenza
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A and B viruses. Introduction of new antivirals into practice raises questions concerning the emergence of drug-resistant viruses, their transmissibility and virulence (Gubareva et al., 2000). These concerns demand elucidation of the molecular mechanisms of influenza virus resistance to NAI. In 1999, the global neuraminidase inhibitor susceptibility networkhas been established to address public heath and regulatory concerns regarding the potential emergence of drug resistance. The objectives of NISN are to examine data from the scientific literature and specific programs, make recommendations for resistance monitoring, conduct surveillance for resistance emergence via WNO Global Influenza Surveillance Network, and communicate this information toscientific community (Zambon and Hayden, 2001). 1.1. In vitro susceptibility of influenza viruses to neuraminidase inhibitors Soon after development of the first NAI zanamivir, it became apparent that susceptibility of influenza viruses

Tel.: +1-434-243-2705; fax: +1-434-982-0384. E-mail address: lvg9b@virginia.edu (L.V. Gubareva).

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