The NS4B protein is a key player in HCV replication. Disrupting NS4B function thus represents an attractive new anti-HCV strategy. Combining clemizole with other anti-HCV agents could increase the antiviral effect achieved with 1 active drug alone and decrease emergence of viral resistance.

In vitro: Although significant, clemizole’s antiviral effect was moderate (50% effective concentration of 8 mM against a HCV genotype 2a clone). Clemizole’s antiviral effect was highly synergistic with the HCV protease inhibitors VX950 and SCH503034, without toxicity. In contrast, clemizole combinations with either interferon, ribavirin, or the nucleoside (NM283) and nonnucleoside (HCV796) HCV polymerase inhibitors were additive [1].

In vivo: Clemizole had an unexpectedly short plasma half-life; it was very rapidly biotransformed into a glucuronide (M14) and a dealkylated metabolite (M12) and into a variety of lesser metabolites in C57BL/6J mice [2].

Clinical trial: The purpose of a study was to test the hypothesis that clemizole hydrochloride was safe and well tolerated when administered to subjects who were infected with hepatitis C virus and had not yet received treatment. This clinical study would also examine how the virus and body respond to clemizole hydrochloride.

References:
[1] Einav S, Sobol HD, Gehrig E, Glenn JS.  The hepatitis C virus (HCV) NS4B RNA binding inhibitor clemizole is highly synergistic with HCV protease inhibitors. J Infect Dis. 2010;202(1):65-74.
[2] Nishimura T, Hu Y, Wu M, Pham E, Suemizu H, Elazar M, Liu M, Idilman R, Yurdaydin C, Angus P, Stedman C, Murphy B, Glenn J, Nakamura M, Nomura T, Chen Y, Zheng M, Fitch WL, Peltz G.  Using chimeric mice with humanized livers to predict human drug metabolism and a drug-drug interaction. J Pharmacol Exp Ther. 2013;344(2):388-96. doi: 10.1124/jpet.112.198697. Epub 2012 Nov 8.