The U.S. drug company AbbVie is scuttling its $54 billion acquisition of the British drugmaker Shire in light of new U.S. tax regulations. When announced in July, the deal would have allowed AbbVie to reincorporate in the U.K. and considerably lower its tax rate. However, last month, the U.S. Treasury Department announced new rules that would make such transactions, known as inversions, less lucrative. AbbVie’s board will now recommend that its shareholders vote against the purchase. Shire says it is considering the situation. It recently reminded AbbVie that AbbVie must pay a $1.6 billion breakup fee if it cancels the deal.