Roche and fellow Swiss pharmaceutical firm Actelion have teamed up to develop a series of drugs for autoimmune disorders targeting the S1P1 receptor, in a deal valued at up to $555 million.

Roche will make an upfront payment of $75 million for the initial rights to co-develop and market the S1P1 agonists. The lead compound is currently in Phase I clinical development.

Sphingosine-1-phospate (S1P) is a phospholipid released by platelets, mast and other cells thought to be involved in a variety of biological responses, such as lymphocyte migration, endothelial cell proliferation, blood vessel constriction, and heart rate modulation.

News of the deal is a boost for Actelion, which has been reaping the benefits of the launch of its Tracleer (bosentan) product for pulmonary artery hypertension, with sales topping $500 million last year, but is now facing competition in the PAH market from Pfizer's Revatio (sildenafil).