United Therapeutics Corp. has contemplated its license agreement with Arena Pharmaceuticals, Inc., acquiring exclusive, worldwide rights to develop and manufacture the Phase III investigational drug candidate ralinepag, a next-generation, oral, selective and potent prostacyclin receptor agonist in development for the treatment of pulmonary arterial hypertension (PAH).  United Therapeutics paid $800 million and Arena is also entitled to potential milestone payments of as much as $400 million b...