Benzinga's Top #PreMarket Losers

bluebird bio Inc BLUE fell 31.02 percent to $57.71 in pre-market trading on mixed sickle cell data results presented at the ASH 2015. Global Blood Therapeutics Inc GBT shares tumbled 12.42 percent to $40.00 in pre-market trading after the company reported positive GBT440 Phase 1/2 data. Chipotle Mexican Grill, Inc. CMG shares dipped 9.04 percent to $510.00 in pre-market trading. Chipotle reported Friday that the recent e Coli incident had an adverse impact on financial and operating results during the fourth quarter. Cowen & Company downgraded Chipotle from Outperform to Market Perform and lowered the price target from $775.00 to $515.00. Chesapeake Energy Corporation CHK shares fell 3.30 percent to $4.40 in pre-market trading after dropping 6.67 percent on Friday. Relypsa Inc RLYP shares declined 2.88 percent to $28.30 in pre-market trading after surging 2.69 percent on Friday.