Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, which can lead to the development of liver cirrhosis and hepatocellular carcinoma. Current therapy of patients with chronic HCV infection includes treatment with IFN␣ in combination with ribavirin. Because most treated patients do not resolve the infection, alternative treatment is essential. RNA interference (RNAi) is a recently discovered antiviral mechanism present in plants and animals that induces double-stranded RNA degradation. Using a selectable subgenomic HCV replicon cell culture system, we have shown that RNAi can specifically inhibit HCV RNA replication and protein expression in Huh-7 cells that stably replicate the HCV genome, and that this antiviral effect is independent of IFN. These results suggest that RNAi may represent a new approach for the treatment of persistent HCV infection.H epatitis C virus (HCV), a member of the Flaviviridae family of viruses, is a major cause of chronic hepatitis and hepatocellular carcinoma (1, 2). Viral clearance during acute HCV infection is usually associated with a multispecific CD4 ϩ and CD8 ϩ T cell response, which is weak or undetectable in subjects who do not control the infection (3-5). Importantly, most chronically infected patients fail to resolve HCV infection after combination therapy with .The HCV genome is a positive-stranded Ϸ9.6-kb RNA molecule consisting of a single ORF, which is flanked by 5Ј and 3Ј UTR. The HCV 5Ј UTR contains a highly structured internal ribosome entry site (8-13). The HCV ORF encodes a single polyprotein that is 3,008-3,037 aa in length and is posttranslationally modified to produce at least ten different proteins: core, envelope proteins E1 and E2, p7, and nonstructural proteins NS2, NS3, NS4A, NS4B, NS5A, and NS5B (1,13,14). Despite considerable advances in the understanding of the function of these proteins, the basic mechanism(s) of HCV replication still remain unclear because of the absence of a tissue culture system that can sustain productive virus infection (1). The recent development of subgenomic and full-length HCV replicons that replicate and express HCV proteins in stably transfected human hepatoma cell-derived Huh-7 cells has facilitated the analysis of the role of cellular pathways required in HCV replication and the efficacy of antiviral drugs (15-19). For example, by using HCV replicons, the antiviral effects of IFN␣ and IFN␥ have been clearly demonstrated (20-23). Although IFN treatment can efficiently inhibit HCV replication in cultured Huh-7 cells, Ͼ60% of patients treated with IFN do not eliminate the virus (24)(25)(26)(27)(28). This suggests that HCV may be able to induce a state of IFN resistance in the infected liver. In keeping with this notion, HCV E2 and NS5A proteins have been demonstrated to interfere with the IFN-induced signaling pathway by interacting with protein kinase R (PKR) and inhibiting its kinase activity (29-32). Thus, alternative approaches to the treatment of chronic HCV infection seem to be warranted. Double-s...

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Differences in botulinum neurotoxin manufacturing, formulation, and potency evaluation can impact dose and biological activity, which ultimately affect duration of action. The potency of different labeled vials of incobotulinumtoxinA (Xeomin®; 50 U, 100 U, or 200 U vials; incobotA) versus onabotulinumtoxinA (BOTOX®; 100 U vial; onabotA) were compared on a unit-to-unit basis to assess biological activity using in vitro (light-chain activity high-performance liquid chromatography (LCA-HPLC) and cell-based potency assay (CBPA)) and in vivo (rat compound muscle action potential (CMAP) and mouse digit abduction score (DAS)) assays. Using LCA-HPLC, incobotA units displayed approximately 54% of the protease activity of label-stated equivalent onabotA units. Lower potency, reflected by higher EC50, ID50, and ED50 values (pooled mean ± SEM), was displayed by incobotA compared to onabotA in the CBPA (EC50: incobotA 7.6 ± 0.7 U/mL; onabotA 5.9 ± 0.5 U/mL), CMAP (ID50: incobotA 0.078 ± 0.005 U/rat; onabotA 0.053 ± 0.004 U/rat), and DAS (ED50: incobotA 14.2 ± 0.5 U/kg; onabotA 8.7 ± 0.3 U/kg) assays. Lastly, in the DAS assay, onabotA had a longer duration of action compared to incobotA when dosed at label-stated equivalent units. In summary, onabotA consistently displayed greater biological activity than incobotA in two in vitro and two in vivo assays. Differences in the assay results do not support dose interchangeability between the two products.