Sienna Biopharmaceuticals Inc. has hired John Smither as chief financial officer, returning him to a position he previously held. Smither previously served as chief financial officer at Westlake Village-based Sienna from January 2016 to March 2017. Since then he has worked as an independent consultant in the biotech industry. Earlier in his career, he served as chief financial officer of Westlake Village-based Kythera Biopharmaceuticals Inc. until it was acquired by Allergan in October 2015 for $2.1 billion. From 1998 to 2007, Smither held various positions at Amgen Inc. in Thousand Oaks. Smither will succeed Richard Peterson, who has resigned for personal reasons, effective March 29. Shares of Sienna Biopharmaceuticals (SNNA) closed Wednesday up 14 cents, or a fraction of a percent, to $19.99 on the Nasdaq.