Using a cell-based replicon screen, we identified a class of compounds with a thiazolidinone core structure as inhibitors of hepatitis C virus (HCV) replication. The concentration of one such compound, BMS-824, that resulted in a 50% inhibition of HCV replicon replication was ϳ5 nM, with a therapeutic index of >10,000. The compound showed good specificity for HCV, as it was not active against several other RNA and DNA viruses. Replicon cells resistant to BMS-824 were isolated, and mutations were identified. A combination of amino acid substitutions of leucine to valine at residue 31 (L31V) and glutamine to leucine at residue 54 (Q54L) in NS5A conferred resistance to this chemotype, as did a single substitution of tyrosine to histidine at amino acid 93 (Y93H) in NS5A. To further explore the region(s) of NS5A involved in inhibitor sensitivity, genotype-specific NS5A inhibitors were used to evaluate a series of genotype 1a/1b hybrid replicons. Our results showed that, consistent with resistance mapping, the inhibitor sensitivity domain also mapped to the N terminus of NS5A, but it could be distinguished from the key resistance sites. In addition, we demonstrated that NS5A inhibitors, as well as an active-site inhibitor that specifically binds NS3 protease, could block the hyperphosphorylation of NS5A, which is believed to play an essential role in the viral life cycle. Clinical proof of concept has recently been achieved with derivatives of these NS5A inhibitors, indicating that small molecules targeting a nontraditional viral protein like NS5A, without any known enzymatic activity, can also have profound antiviral effects on HCV-infected subjects.Hepatitis C virus (HCV) is the major causative agent for non-A, non-B hepatitis worldwide, which affects more than 3% of the world population. HCV establishes chronic infections in a large percentage of infected individuals, increasing the risk for developing liver cirrhosis and, in some cases, hepatocellular carcinoma. Although the current standard of care for HCV infection involves the use of PEGylated interferon and ribavirin, a large proportion of patients fail to respond to this therapy, and treatment is associated with frequent and sometimes serious side effects (9). Given the limited efficacy of the current therapy, the development of safer and more effective therapies is of tremendous importance.HCV is a positive-strand RNA virus belonging to the family Flaviviridae. The HCV genome consists of a ϳ9.6-kb RNA with a large open reading frame encoding a polyprotein of ϳ3,010 amino acids. The polyprotein is cleaved co-and posttranslationally by both cellular and viral proteases into at least 10 different products (10, 11). The viral proteins required for RNA replication include NS3, NS4A, NS4B, NS5A, and NS5B (4, 19). NS3 consists of an amino-terminal protease domain required for the cleavage of the remaining nonstructural proteins and a carboxyl-terminal helicase/NTPase domain (8,11,30). NS4A serves as a cofactor for NS3 protease and helicase activities (8). NS4B is a...

Indole derivative 1 interferes with the interaction of the HIV surface protein gp120 with the host cell receptor CD4. The 4-fluoro derivative 2 exhibited markedly enhanced potency and was bioavailable in the rat, dog, and cynomolgus monkey when administered orally as a solution formulation. However, aqueous suspensions of 2 were poorly bioavailable, indicative of dissolution-limited absorption. The 7-azaindole derivative 3, BMS-378806, exhibited improved pharmaceutical properties while retaining the HIV-1 inhibitory profile of 2.

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