Preclinical Evaluation of Amphihevir, a First-in-Class Clinical Hepatitis C Virus NS4B Inhibitor

Amphihevir, a benzofuran derivative, is the first reported hepatitis C virus (HCV) nonstructural protein 4B (NS4B) inhibitor that has advanced to clinical trials (currently in phase Ib trial [CTR20170632]). Here, we report the results of a preclinical study of its potency, toxicity, selectivity, drug metabolism and pharmacokinetics (DMPK), and safety profiles. Amphihevir displayed good antiviral activities against genotype 1a (50% effective concentration [EC(50)] of 0.34 nM) and genotype 1b (EC(50) of 1.97 nM) replicons and no cytotoxicity in 12 cell lines derived from animals and humans. Amphihevir was found to be inactive against other viruses, human kinases, and G protein-coupled receptors (GPCRs), which implies its good selectivity. A 9-day long-term treatment of genotype 1b replicons with amphihevir resulted in a 3.8 Log(10) decline of the hepatitis C viral RNA at a concentration of 25× EC(90). Drug resistance screening showed that mutations occurred at H94, F98, and V105 of NS4B, which mediated the resistance to amphihevir. This result suggests that NS4B is the main target of amphihevir. There was no cross-resistance between amphihevir and NS5A, NS3/4A, and NS5B inhibitors, suggesting that amphihevir in combination with other anti-hepatitis C virus drugs could be used to treat hepatitis C, as proven by studies of amphihevir and other hepatitis C virus inhibitors. Pharmacokinetic studies demonstrated that amphihevir has good oral bioavailability and appropriate half-life (t(1/2)) in rats and dogs, thereby supporting its use once per day. Finally, amphihevir showed good safety profiles in rats and dogs. The results shed light on the use of amphihevir as a potential treatment option for chronic hepatitis C patients.