CHARACTERIZATION OF INHIBITION OF M(2) ION-CHANNEL ACTIVITY BY BL-1743, AN INHIBITOR OF INFLUENZA-A VIRUS

The influenza A virus M(2) integral membrane protein has ion channel a ctivity that can be inhibited by the antiviral drug amantadine, Recent ly, a spirene-containing compound, BL-1743 {2-[3-azaspiro (5,5)undecan ol]-2-imidazoline}, that inhibits influenza virus growth was identifie d (S. Kurtz, G. Luo, K. M. Hahnenberger, C. Brooks, O. Gecha, K. Ingal ls, K-I. Numata, and M. Krystal, Antimicrob. Agents Chemother, 33:2204 -2209, 1995), We have examined the ability of BL-1743 to inhibit the M (2) ion channel when expressed in oocytes of Xenopus laevis, BL-1743 i nhibition is complete as far as can be measured by electrophysiologica l methods and is reversible, with a reverse reaction rate constant of 4.0 x 10(-3) s(-1). In contrast, amantadine inhibition is irreversible within the time frame of the experiment, However, BL-1743 inhibition and amantadine inhibition have similar properties, The majority of iso lated influenza viruses resistant to BL-1743 are also amantadine resis tant, In addition, all known amino acid changes which result in amanta dine resistance also confer BL-1743 resistance, However, one BL-1743-r esistant virus isolated, designated M(2)-I35T, contained the change Il e-35-->Thr. This virus is >70-fold more resistant to BL-1743 and only 10-fold more resistant to amantadine than the wild-type virus. When th e ion channel activity of M(2)-I35T was examined in oocytes, it was fo und that M(2)-I35T is BL-1743 resistant but is reversibly inhibited by amantadine, These findings suggest that these two-drugs interact diff erently with the M(2) protein transmembrane pore region.