The drugmaker Shire wants AbbVie to stick with its roughly $55 billion acquisition bid, and it is reminding its U.S. counterpart of the hefty breakup fee it will receive if things don't work out. Shire's U.S.-traded shares shed about a quarter of their value before markets opened Wednesday and a day after AbbVie Inc. disclosed that it was reconsidering a deal it had fought for weeks to put together.