** Shares of drug developer Gritstone bio fall 29.4% to 14 cents premarket
** Company files for Chapter 11 bankruptcy
** GRTS lists both estimated assets and liabilities at $100 million to $500 million - court filing
** "During its financial restructuring process, Gritstone intends to operate in the ordinary course and remains committed to advancing its clinical programs" - company
** Up to last close, stock down 90.3% YTD
(Reporting by Puyaan Singh)
((Puyaan.Singh@thomsonreuters.com;))