To better understand the dynamics of hepatitis C virus and the antiviral effect of interferon-alpha-2b (IFN), viral decline in 23 patients during therapy was analyzed with a mathematical model. The analysis indicates that the major initial effect of IFN is to block virion production or release, with blocking efficacies of 81, 95, and 96% for daily doses of 5, 10, and 15 million international units, respectively. The estimated virion half-life (t1/2) was, on average, 2.7 hours, with pretreatment production and clearance of 10(12) virions per day. The estimated infected cell death rate exhibited large interpatient variation (corresponding t1/2 = 1.7 to 70 days), was inversely correlated with baseline viral load, and was positively correlated with alanine aminotransferase levels. Fast death rates were predictive of virus being undetectable by polymerase chain reaction at 3 months. These findings show that infection with hepatitis C virus is highly dynamic and that early monitoring of viral load can help guide therapy.

The nonstructural 5A (NS5A) protein is a target for drug development against hepatitis C virus (HCV). Interestingly, the NS5A inhibitor daclatasvir (BMS-790052) caused a decrease in serum HCV RNA levels by about two orders of magnitude within 6 h of administration. However, NS5A has no known enzymatic functions, making it difficult to understand daclatasvir's mode of action (MOA) and to estimate its antiviral effectiveness. Modeling viral kinetics during therapy has provided important insights into the MOA and effectiveness of a variety of anti-HCV agents. Here, we show that understanding the effects of daclatasvir in vivo requires a multiscale model that incorporates drug effects on the HCV intracellular lifecycle, and we validated this approach with in vitro HCV infection experiments. The model predicts that daclatasvir efficiently blocks two distinct stages of the viral lifecycle, namely viral RNA synthesis and virion assembly/ secretion with mean effectiveness of 99% and 99.8%, respectively, and yields a more precise estimate of the serum HCV half-life, 45 min, i.e., around four times shorter than previous estimates. Intracellular HCV RNA in HCV-infected cells treated with daclatasvir and the HCV polymerase inhibitor NM107 showed a similar pattern of decline. However, daclatasvir treatment led to an immediate and rapid decline of extracellular HCV titers compared to a delayed (6-9 h) and slower decline with NM107, confirming an effect of daclatasvir on both viral replication and assembly/secretion. The multiscale modeling approach, validated with in vitro kinetic experiments, brings a unique conceptual framework for understanding the mechanism of action of a variety of agents in development for the treatment of HCV.direct-acting antiviral agents | mathematical modeling | viral dynamics H epatitis C virus (HCV) infection is a major health burden affecting about 150 million people worldwide (1) and ∼4.1 million in the United States (2), where it is the primary cause of liver cirrhosis and liver cancer (1). Until 2011, the most advanced antiviral therapy was pegylated interferon-α (IFN-α) plus ribavirin (Peg-IFN/RBV), with a cure rate of 50% or less in patients infected with HCV genotype 1, the most prevalent in the Western world.To obtain higher cure rates, drug development has focused mainly on inhibiting the function of nonstructural (NS) viral proteins with known enzymatic functions, such as the NS3-4A protease and the NS5B polymerase. Through the use of an innovative screening approach to search for nonenzymatic targets, daclatasvir (BMS-790052) was identified as a potent NS5A inhibitor (3). The functions of the NS5A protein are not fully elucidated, although in vitro studies suggest an essential role of NS5A in both viral replication (4-7) and assembly/release of infectious particles (8-11). The efficacy of daclatasvir as an antiviral agent was confirmed in a single ascending-dose study in which a mean 3.3-log 10 reduction in viral load 24 h after drug administration was observed in patients receiving a 1...