Mast Therapeutics has entered into a definitive agreement to acquire Aires Pharmaceuticals, a privately-held, clinical stage pharmaceutical company developing therapies to treat pulmonary vascular disorders such as pulmonary arterial hypertension and pulmonary hypertension due to heart failure. Aires' lead product, AIR001, is an intermittently nebulized formulation of nitrite and has Orphan Drug status with the FDA and the EMA for the treatment of pulmonary arterial hypertension.

"The acquisition of Aires will enhance our pipeline with a phase II asset with more than 120 exposures and which is a strategic complement to our lead program, MST-188," said Brian M. Culley, CEO of Mast Therapeutics.

"Nitrite has demonstrable beneficial properties, including vasodilation and the reduction of inflammation and undesirable cell growth. These are important therapeutic objectives and an ideal complement to MST-188 and its ability to improve blood flow and seal cellular membranes," said Culley. “In addition, we intend to investigate the hypothesis that AIR001 positively affects mitochondrial activity and myocyte energetics. With this acquisition, and the initiation of our phase II trial of MST-188 for the treatment of acute limb ischemia later this quarter, we are taking additional steps towards building a sustainable company with a valuable pipeline addressing significant unmet needs in both specialized and major markets.”

"Our estimated costs for AIR001 will change as we refine our development strategy over the next few months, but Aires is expected to contribute approximately $3 million of net cash at the closing of the merger," he said.

Aires would become a wholly-owned subsidiary of Mast Therapeutics in exchange for shares of Mast common stock representing approximately 6% of Mast's outstanding common stock, 80% of which would be subject to a six-month holdback for certain indemnification claims of Mast. There are no milestone obligations payable to Aires.  The acquisition is expected to close in February 2014.