HOW TO OVERCOME RESISTANCE OF INFLUENZA-A VIRUSES AGAINST ADAMANTANE DERIVATIVES

We tested two approaches to overcoming resistance of influenza A virus es against adamantane derivatives. First, adamantane derivatives that interfere with the ion channel function of the variant M2 protein of a mantadine-resistant viruses may prevent drug resistance, if they are u sed in mixture with amantadine. Second, amantadine acts on the M2 prot ein (at low concentrations) and indirectly on the hemagglutinin (at co ncentrations at least 100 times higher). Identifying and using a drug that reacted with both targets at the same concentration might reduce development of resistance, since, in this case, two mutations, one in each target protein would be necessary at once. Such a double mutation is assumed to be a rare event. We evaluated forty adamantane derivati ves and two related compounds to determine whether they interfered wit h plaque formation by influenza A strains, including A/Singapore/1/57 (H2N2). Variants resistant to drugs that interfered at low concentrati ons (approximate to 1 mu g/ml; e.g. amantadine) were cross-resistant w ith each other, but were sensitive to those agents effective at high c oncentrations (8 mu g/ml; e.g. memantine). The former group of compoun ds act on the ion channel; the corresponding escape mutants tested had amino acid replacements at positions 27, 30 or 31 of the M2 protein. Hemagglutinin was the indirect target of the latter group of compounds . Variants resistant to these agents lacked amino acid replacements wi thin the ion channel of the M2 protein and the mutants tested had amin o acid replacements in the hemagglutinin. Although we failed to identi fy compounds that interacted with the ion channel of amantadine-resist ant variants and inhibited their replication, we were able to construc t at least two compounds that interfered with both the ion channel and the hemagglutinin at about the same concentration. After passage in t he presence of these compounds, we either failed to obtain any drug-re sistant mutants or those obtained had amino acid replacements in the i on channel of the M2 protein and the hemagglutinin. (C) 1998 Elsevier Science B.V. All rights reserved.