LOS ALAMOS, N.M., Feb. 19, 2013 /PRNewswire-USNewswire/ -- A study by researchers from Los Alamos National Laboratory and a multinational team reveals how daclatasvir, a direct-acting antiviral agent in development for the treatment of hepatitis C virus (HCV), targets one of its proteins and causes the fastest viral decline ever seen with anti-HCV drugs – within 12 hours of treatment. Chronic infection with hepatitis C virus affects about 150 million people worldwide. It is the leading cause of cirrhosis, liver cancer and liver transplants and results in some 350,000 deaths worldwide every year. The team's work reveals that daclatasvir has two primary modes of action against HCV and also provides a more accurate estimate of the HCV half-life. Until 2011, treatment options were limited and offered modest effectiveness; fewer than half of treated patients were fully cured of the virus. In the last decade, active research on understanding the mechanisms of HCV replication resulted in the discovery of direct acting antivirals targeting all stages of the viral replication process. The new mathematical analysis of the rapid viral decline observed after one dose of daclatasvir reveals that the drug blocks two stages of the viral lifecycle and that the HCV half-life in serum is four times shorter than previously thought according to a study published in Proceedings of the National Academy of Sciences USA. The NS5A protein within the hepatitis virus is a specific target for drug development. The first NS5A inhibitor, daclatasvir, developed by Bristol Myers Squibb, showed one of the most potent effects in combating HCV; one dose led to a thousand-fold decrease in viral levels within about 12 hours. Oddly, however NS5A has no known enzymatic functions making it difficult to understand its mode of action and design optimal drug combinations.