GlaxoSmithKline and Myogen, Inc. entered a two-part collaboration in Pulmonary Arterial Hypertension (PAH). Myogen licensed commercialisation rights for ambrisentan, Myogen's selective endothelin receptor antagonist (ERA) currently in Phase 3 development to GlaxoSmithKline in all territories outside of the United States. Filing for marketing approval in the US and Europe is expected later this year.

Simultaneously, GlaxoSmithKline and Myogen entered into a distribution agreement whereby Myogen will be responsible for the marketing and distribution of GSK's Flolan (epoprostenol sodium) a life-saving medicine for many patients, used in the treatment of PAH, in the United States.

Andrew Witty, President, Pharma Europe GlaxoSmithKline said, "Myogen's innovative approach to collaboration on ambrisentan has provided both companies with a potentially rewarding opportunity by giving GlaxoSmithKline access to a product candidate in an indication we know very well. At the same time, Myogen will be able to establish a commercial presence in the PAH market in the United States."

Under the terms of the ambrisentan license agreement, Myogen will receive an upfront payment of $20 million and, subject to the achievement of specific milestones, will be eligible to receive up to an additional $80 million in milestone payments. In addition, Myogen will also receive stepped royalties on product sales with an estimated average royalty in the mid-20% range, which reflect the late stage development status and market potential of ambrisentan. Myogen will be responsible for the continued clinical development of ambrisentan. GlaxoSmithKline will be responsible for all regulatory and commercial expenses in its licensed territories. The companies will share the costs of certain additional clinical development activities for ambrisentan.

Under the terms of the Flolan distribution agreement, Myogen will build a commercial support team and field sales organisation beginning in the second quarter of 2006 dedicated to the marketing and distribution of Flolan in the United States. The distribution agreement is a three-year agreement with an option to renew upon mutual consent.

Ambrisentan is an investigational drug being developed as a once-daily oral therapy for patients with PAH and has been granted orphan drug designation for the treatment of PAH in both the United States and European Union. In December, Myogen announced positive top-line results from the ARIES-2 trial, the first pivotal trial evaluating ambrisentan in PAH. Top-line results of a second important trial (ARIES-1) are expected to be announced in April 2006, with FDA and EMEA filing targeted for Q4 this year.