Mechanisms of action of novel influenza A/M2 viroporin inhibitors derived from hexamethylene amiloride

The increasing prevalence of influenza viruses with resistance to approved antivirals highlights the need for new anti-influenza therapeutics. Here we describe the functional properties of hexamethylene amiloride (HMA)–derived compounds that inhibit the wild-type and adamantane-resistant forms of the influenza A M2 ion channel. For example, 6-(azepan-1-yl)- N -carbamimidoylnicotinamide ( 9 ) inhibits amantadine-sensitive M2 currents with 3- to 6-fold greater potency than amantadine or HMA (IC 50 = 0.2 vs. 0.6 and 1.3 µ M, respectively). Compound 9 competes with amantadine for M2 inhibition, and molecular docking simulations suggest that 9 binds at site(s) that overlap with amantadine binding. In addition, tert -butyl 4′-(carbamimidoylcarbamoyl)-2′,3-dinitro-[1,1′-biphenyl]-4-carboxylate ( 27 ) acts both on adamantane-sensitive and a resistant M2 variant encoding a serine to asparagine 31 mutation (S31N) with improved efficacy over amantadine and HMA (IC 50 = 0.6 µ M and 4.4 µ M, respectively). Whereas 9 inhibited in vitro replication of influenza virus encoding wild-type M2 (EC 50 = 2.3 µ M), both 27 and tert -butyl 4′-(carbamimidoylcarbamoyl)-2′,3-dinitro-[1,1′-biphenyl]-4-carboxylate ( 26 ) preferentially inhibited viruses encoding M2(S31N) (respective EC 50 = 18.0 and 1.5 µ M). This finding indicates that HMA derivatives can be designed to inhibit viruses with resistance to amantadine. Our study highlights the potential of HMA derivatives as inhibitors of drug-resistant influenza M2 ion channels.