** Shares of drug developer AnaptysBio ANAB.O fall 14% to $34.27, its worst day in over 3 weeks

** Co says it will halt development of its experimental drug rosnilimab for ulcerative colitis after the treatment failed to show enough benefit in a mid-stage clinical trial

** Ulcerative colitis is a chronic bowel disease that causes inflammation and ulcers in the digestive tract

** ANAB says rosnilimab was safe and well tolerated, but failed to improve symptoms after 12 weeks

** Halting trial expected to save at least $10 mln; Co to focus on testing drug in rheumatoid arthritis - ANAB

** Including session's move, stock up ~154% YTD

(Reporting by Sahil Pandey in Bengaluru)

((Sahil.Pandey@thomsonreuters.com))