Anti-poliovirus activity of protease inhibitor AG-7404, and assessment of in vitro activity in combination with antiviral capsid inhibitor compounds

• Antivirals are needed to treat immunodeficient chronic poliovirus excretors.
• Picornavirus protease inhibitor AG-7404 is active against 45 poliovirus strains.
• AG-7404 acts synergistically with either of two poliovirus capsid inhibitors.

The National Research Council has recommended that at least one, preferably two, polio antiviral drugs be developed as a supplement to the tools currently available for control of polio outbreaks post-eradication. The primary application of such drugs is expected to be the resolution of chronic poliovirus excretion in persons with primary immunodeficiency disorders. We have assessed the in vitro activity of AG-7404 (also known as “compound 1”), an inhibitor of picornaviral 3C protease, against a large panel of programmatically important poliovirus strains and its activity in combination with two poliovirus capsid inhibitors, V-073 and BTA798. AG-7404 was active against all viruses in this panel, with EC50 values ranging from 0.080 to 0.674 μM. Similarly, BTA798 was active against all viruses in this panel, with EC50 values ranging from 0.003 to 0.591 μM. By comparison, values for V-073 were 0.003–0.126 μM. BTA798 was active against V-073-resistant variants with an alanine to valine change in VP3 at position 24. However, BTA798 was inactive against the V-073-resistant strains with amino acid substitutions at VP1 amino acids 194 (equivalent to 192 in type 3) and 236. As expected from its different mechanism of action, AG-7404 was fully active against all V-073-resistant variants, with EC50 values ranging from 0.218 to 0.819 μM, compared to values of 0.202–0.407 μM for the V-073-susceptible parental strains. In vitro drug combination experiments demonstrated synergy between AG-7404 and either V-073 or BTA798, whereas the combination of the two capsid inhibitors acted additively.