The hepatitis C virus (HCV) NS4B RNA binding inhibitor clemizole is highly synergistic with HCV protease inhibitors.
BACKGROUND
We recently identified a compound, clemizole hydrochloride, that inhibits NS4B's RNA binding and hepatitis C virus (HCV) replication. Although significant, clemizole's antiviral effect is moderate (50% effective concentration of 8 microM against an HCV genotype 2a clone). We hypothesized that the combination of clemizole with other anti-HCV agents can increase the antiviral effect over that achieved with each drug alone and could also decrease the emergence of viral resistance.


METHODS
Luciferase reporter-linked HCV replication assays were used to study the antiviral effects of drug combinations that included clemizole. Data were analyzed using Loewe additivity and Bliss independence models for synergy, and resistance studies were performed using HCV colony formation assays.


RESULTS
Clemizole's antiviral effect was highly synergistic with the HCV protease inhibitors SCH503034 and VX950, without toxicity. In contrast, combinations of clemizole with either interferon, ribavirin, or the nucleoside (NM283) and nonnucleoside (HCV796) HCV polymerase inhibitors were additive. Furthermore, combination of clemizole with SCH503034 decreased the frequency of drug-resistant mutants, compared with treatment with either drug alone. Finally, no cross-resistance to clemizole of SCH503034-resistant mutants (or vice versa) was observed.


CONCLUSIONS
Clemizole can yield high-level synergy with the protease inhibitor class. Inclusion of clemizole in future anti-HCV cocktails can represent an attractive paradigm for increasing current virologic response rates.
Einav
Shirit
S
Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, California 94305-5187, USA.
Sobol
Hadas D
HD
Gehrig
Elizabeth
E
Glenn
Jeffrey S
JS
D000998:Antiviral Agents / Q000494:pharmacology*; D001562:Benzimidazoles / Q000494:pharmacology*; D002460:Cell Line; D024882:Drug Resistance, Viral; D004357:Drug Synergism; D016174:Hepacivirus / Q000187:drug effects*; D006801:Humans; D011480:Protease Inhibitors / Q000494:pharmacology*; D054334:Viral Regulatory and Accessory Proteins; D014779:Virus Replication
D000998:Antiviral Agents; D001562:Benzimidazoles; D011480:Protease Inhibitors; D054334:Viral Regulatory and Accessory Proteins; C084582:clemizole