Renewed excitement over signs that RG-101, a microRNA-122 antagonist from Regulus Therapeutics Inc., could shorten the duration of several direct-acting antiviral (DAA) treatment regimens for hepatitis C virus (HCV) to as little as four weeks boosted company shares (NASDAQ:RGLS) briefly on Friday before giving way to concerns about whether the cure it delivers will persist over time, sending shares down 11 percent to close at $7.23.