Discovery of New Inhibitors of Hepatitis C Virus NS3/4A Protease and Its D168A Mutant

Hepatitis
C virus (HCV) is a human pathogen with high morbidity.
The HCV NS3/4A protease is essential for viral replication and is
one of the top three drug targets. Several drugs targeting the protease
have been developed, but drug-resistant mutant strains emerged. Here,
we screened a library and synthesized a novel class of small molecules
based on a tryptophan derivative scaffold identified as HCV NS3/4A
protease inhibitors that are active against both wild type and mutant
form of the protease. Only the compounds with predicted binding poses
not affected by the most frequent mutations in the active site were
selected for experimental validation. The antiviral activities were
evaluated by replicon and enzymatic assays. Twenty-two compounds were
found to inhibit HCV with EC50 values ranging between 0.64
and 63 μM with compound 22 being the most active.
In protease assays, 22 had a comparable inhibition profile
for the common mutant HCV GT1b D168A and the wild-type enzyme. However,
in the same assay, the potency of the approved drug, simeprevir, decreased
5.7-fold for the mutant enzyme relative to the wild type. The top
three inhibitors were also tested against four human serine proteases
and were shown to be specific to the viral protease. The fluorescence-based
cell viability assay demonstrated a sufficient therapeutic range for
the top three candidates.