Biotechnology Switzerland based Actelion (SIX: ATLN), Europe largest biotech company, went on the defensive last Friday after one of its investors, Elliot Associates hedge fund, sent a letter to the firm's directors (which came into the public domain), saying that chairman Robert Cawthorn should resign and the chief executive Jean-Paul Clozel should step down from the board, and calling for the formation of a strategic committee to explore the company's options on rumored takeover approaches. 7 February 2011