A hepatitis C drug developed by Danish company Santaris Pharma is creating excitement in the medical community. In preliminary testing done on chimpanzees chronically infected with the hepatitis C virus, SPC3649 dramatically reduced virus levels with no toxic side effects. Drug resistance, a common problem with currently available hepatitis C treatments, was not an issue. The results were reported in this week's online version of Science. Unlike current therapies, SPC3649 does not target the virus directly. The hepatitis C virus mutates continually, causing patients to develop resistance to therapy. Instead, SPC3649 inhibits a short RNA (microRNA) molecule called miR-122 that is crucial for the replication of the virus. In the animal study, four subjects were given weekly 5 mg or 1 mg doses of SPC3649 over a period of 12 weeks. Virus levels dropped 350 percent in animals that were given the larger dose. The drug remained effective for up to several months after treatment. SPC3649 is the first microRNA-targeted drug to be advanced to human clinical trials. The Los Angeles Times reports that microRNA has been shown to regulate gene activity within cells. The hepatitis C virus is the only virus known to use miR-122 to replicate. The World Health Organization estimates that 170 million people worldwide have chronic hepatitis C, which puts patients at risk for liver diseases like cirrhosis and liver cancer. Other companies developing treatments for hepatitis C include Monogram Biosciences, Sinovac Biotechnology, Idenix Pharmaceuticals and Novelos Therapeutics.