GlaxoSmithKline could be among the suitors for United Therapeutics, the Evening Standard reported.
The Justice Department is investigating the company's charitable contributions for kickbacks and false claims.
Alexion Pharmaceuticals, United Therapeutics and Gilead Sciences were among the biotech stock movers in premarket trading on July 27.
Novocure, United Therapeutics and Kite Pharma were among the biotech stock movers in early trading Monday.
Credit Suisse initiated United Therapeutics with an 'underperform' rating.