PRESS RELEASE: Actelion: Additional macitentan -2-

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-2 of 3- 17 May 2013 15:36:00 UTC  PRESS RELEASE: Actelion: Additional macitentan (Opsumit) data in pulmonary arterial hypertension presented at ATS

Actelion Pharmaceuticals Ltd / Additional macitentan (Opsumit) data in pulmonary arterial hypertension presented at ATS . Processed and transmitted by Thomson Reuters ONE. The issuer is solely responsible for the content of this announcement.

ALLSCHWIL/BASEL, SWITZERLAND - 17 May 2013 - Actelion (SIX: ATLN) today announced that further data for its investigational drug macitentan (Opsumit(R) ) will be presented at the American Thoracic Society (ATS) International Congress, Philadelphia, USA.

An oral presentation providing additional data from the SERAPHIN trial will be given by Richard Channick, MD., Director of the Pulmonary and Thromboendarterectomy Program at Massachusetts General Hospital. The presentation will be held on 20 May from 14:00 to 16:00.

A poster providing quality of life results from the SERAPHIN trial will be presented by Sanjay Mehta MD, FRCPC, FCCP, Professor of Medicine at Western University and Director of the Southwest Ontario Pulmonary Hypertension Clinic at the London Health Sciences Center in London, Canada.

In the context of presenting the quality of life data, a poster will be presented by Deborah McCollister RN, BSN, Research Instructor at the University of Colorado Denver, Colorado. The poster describes Actelion's efforts to develop a disease specific assessment tool for patient reported outcomes PAH-SYMPACT, the Pulmonary Arterial Hypertension-Symptoms And Impact (PAH-SYMPACT(TM)).

Macitentan is currently under review for approval at the Food and Drug Administration (FDA) in the United States (US), at the European Medicines Agency (EMA) in Europe and other countries.

As a supplement to the ATS conference Actelion will host a symposium with Richard Channick, MD. The program entitled: "Emerging Developments and Insights in Pulmonary Arterial Hypertension: How We Think, How We Practice." will be hosted at Millennium Hall, Loews Philadelphia Hotel on Tuesday 21 May between 18:30 and 21:00.

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NOTES TO THE EDITOR

RELATED ATS 2013 ABSTRACTS:

ORAL PRESENTATION

Macitentan Reduces PAH-related Hospitalizations: Results From The Randomized Controlled SERAPHIN Trial

Richard N. Channick*, Marion Delcroix, Nazzareno Galiè, Hossein-Ardeschir Ghofrani, Elke Hunsche, Pavel Jansa, Franck-Olivier Le Brun, Sanjay Mehta, Camilla Mittelholzer, Loïc Perchenet, Tomás Pulido, Bhagavatula Sastry, Olivier Sitbon, Rogério Souza, Adam Torbicki, Lewis J. Rubin, Gérald Simonneau

Oral presentation: May 20th, 14.00-16.00

Abstract reference: A3527

POSTER PRESENTATIONS

Macitentan Improves Health-Related Quality Of Life In Pulmonary Arterial Hypertension: Results From The Randomized Controlled SERAPHIN Trial

Sanjay Mehta*, Richard N. Channick, Marion Delcroix, Nazzareno Galiè, Hossein-Ardeschir Ghofrani, Elke Hunsche, Pavel Jansa, Franck-Olivier Le Brun, Camilla Mittelholzer, Loïc Perchenet, Tomás Pulido, Bhagavatula Sastry, Olivier Sitbon, Rogério Souza, Adam Torbicki, Lewis J. Rubin, Gérald Simonneau

Poster presentation: May 20th, 08.15-16.30

Abstract reference A3269

Development Of The Pulmonary Arterial Hypertension-Symptoms And Impact (PAH-SYMPACT) Questionnaire: A New Disease-Specific Patient-Reported Outcome Instrument For PAH

Deborah McCollister*, Shannon Kummer, David Badesch, Arthur Filusch, Elke Hunsche, René Schüler, Ingela Wiklund, Andrew Peacock

Poster presentation: May 20th, 08.15-16.30

Abstract reference: A3294

ABOUT MACITENTAN (OPSUMIT(R))

Macitentan (Opsumit(R)) is a novel dual endothelin receptor antagonist (ERA) that resulted from a tailored drug discovery process with the target to develop an ERA optimized for efficacy and safety [2]. Macitentan has a number of potentially key beneficial characteristics i.e., increased in vivo preclinical efficacy vs. existing ERAs resulting from sustained receptor binding [3] and physicochemical properties that allow an enhanced penetration into tissue [4]. The clinical pharmacology program indicated a low propensity of macitentan for drug-drug interactions [5,6,7]

ABOUT MACITENTAN (OPSUMIT(R)) SUBMISSIONS TO HEALTHCARE AUTHORITIES

On 22(nd) October 2012 Actelion announced that it had submitted a new drug application to the US Food and Drug Administration (FDA) seeking approval for macitentan (Opsumit(R)) in patients with pulmonary arterial hypertension.

On 22(nd) November 2012 Actelion announced that it had successfully submitted the Market Authorisation Application to the European Medicines Agency (EMA) and a validation letter had been received.

Regulatory review is also ongoing in Canada, Switzerland, Australia, Taiwan and Mexico.

ABOUT THE SERAPHIN STUDY

SERAPHIN (Study with an Endothelin Receptor Antagonist in Pulmonary arterial Hypertension to Improve cliNical outcome) was the largest and longest randomized, controlled study in PAH patients to include a clearly defined morbidity/mortality primary endpoint [1]. The pivotal Phase III study was designed to evaluate the efficacy and safety of macitentan (Opsumit(R)) - a novel dual endothelin receptor antagonist that resulted from a tailored drug discovery process - through the primary endpoint of time to first morbidity and all-cause mortality event in patients with symptomatic PAH.

Global enrollment was completed in December 2009 with a total of 742 patients. Patients were randomized 1:1:1 to receive two different doses of macitentan (3 mg and 10 mg once daily) or placebo. Patients were allowed to receive PAH background therapy throughout the study, either PDE-5 inhibitors or oral/inhaled prostanoids. This event-driven study was conducted in 151 centers from almost 40 countries in North and Latin America, Europe, Asia-Pacific and Africa and was completed in the first half of 2012, with 287 patients having an adjudicated event.

ABOUT PULMONARY ARTERIAL HYPERTENSION

Pulmonary arterial hypertension (PAH) is a chronic, life-threatening disorder characterized by abnormally high blood pressure in the arteries between the heart and lungs of an affected individual. The symptoms of PAH are non-specific and can range from mild breathlessness and fatigue during normal daily activity to symptoms of right heart failure and severe restrictions on exercise capacity and ultimately reduced life expectancy.

PAH is one group within the classification of pulmonary hypertension (PH). This group includes idiopathic PAH, heritable PAH and PAH caused by factors which include connective tissue disease, HIV infection and congenital heart disease.

The last decade has seen significant advances in the understanding of the pathophysiology of PAH, which has been paralleled with developments of treatment guidelines and new therapies. Drugs targeting the 3 pathways that have been established in the pathogenesis of PAH are endothelin receptor antagonists (ERAs), prostacyclins and phosphodiesterase-5 inhibitors. PAH treatments have transformed the prognosis for PAH patients from symptomatic improvements in exercise tolerance 10 years ago to delayed disease progression today. Improved disease awareness and evidence-based guidelines developed from randomized controlled clinical trial data have highlighted the need for early intervention, goal-oriented treatment and combination therapy.

Despite these advances in PAH, survival rates are unacceptably low and PAH remains incurable.

References

1. For a general discussion of a clinically meaningful outcome end-point, please see: Proceedings of the 4th world symposium on pulmonary hypertension. J Am Coll Cardiol 2009;54(1 Suppl).

2. Bolli MH et al. The Discovery of N-[5-(4-Bromophenyl)-6-[2-[(5-bromo-2-pyrimidinyl)oxy]ethoxy]-4-pyrimidin l]-N'-propylsulfamide (Macitentan), an Orally Active, Potent Dual Endothelin Receptor Antagonist. J Med Chem. 2012; 55:7849-61.

3. Gatfield J, Mueller Grandjean C, Sasse T, Clozel M, Nayler O (2012). Slow Receptor Dissociation Kinetics Differentiate Macitentan from Other Endothelin Receptor Antagonists in Pulmonary Arterial Smooth Muscle Cells. PLOS ONE 7(10): e47662. doi:10.1371/journal.pone.0047662

4. Iglarz M et al. Pharmacology of macitentan, an orally active tissue-targeting dual endothelin receptor antagonist. J Pharmacol Exp Ther. 2008;327(3):736-45.

5. Sidharta PN et al. Macitentan: Entry-into-humans study with a new endothelin receptor antagonist. Eur J Clin Pharmacol. 2011;67(10):977-84

6. Bruderer S et al. Absorption, distribution, metabolism, and excretion of macitentan, a dual endothelin receptor antagonist, in humans. Xenobiotica. 2012 Sep;42(9):901-10

7. Bruderer S et al. Effect of cyclosporine A and rifampin on the pharmacokinetics of macitentan, a tissue-targeting dual endothelin receptor antagonist. AAPS J. 2012;14(1):68-78.

Actelion Ltd

Actelion Ltd is a biopharmaceutical company with its corporate headquarters in Allschwil/Basel, Switzerland. Actelion's first drug Tracleer(R) (bosentan), an orally available dual endothelin receptor antagonist, has been approved as a therapy for pulmonary arterial hypertension. Actelion markets Tracleer through its own subsidiaries in key markets worldwide, including the United States (based in South San Francisco), the European Union, Japan, Canada, Australia and Switzerland. Actelion, founded in late 1997, is a leading player in innovative science related to the endothelium - the single layer of cells separating every blood vessel from the blood stream. Actelion's over 2,300 employees focus on the discovery, development and marketing of innovative drugs for significant unmet medical needs. Actelion shares are traded on the SIX Swiss Exchange (ticker symbol: ATLN) as part of the Swiss blue-chip index SMI (Swiss Market Index SMI(R)). (MORE TO FOLLOW) Dow Jones Newswires

   May 17, 2013 11:36 ET (15:36 GMT)- - 11 36 AM EDT 05-17-13

-3 of 3- 17 May 2013 15:36:00 UTC  PRESS RELEASE: Actelion: Additional macitentan -2-
For further information please contact:

Roland Haefeli

Senior Vice President, Head of Investor Relations & Public Affairs

Actelion Pharmaceuticals Ltd, Gewerbestrasse 16, CH-4123 Allschwil

+41 61 565 62 62

+1 650 624 69 36

www.actelion.com

The above information contains certain "forward-looking statements", relating to the company's business, which can be identified by the use of forward-looking terminology such as "estimates", "believes", "expects", "may", "are expected to", "will", "will continue", "should", "would be", "seeks", "pending" or "anticipates" or similar expressions, or by discussions of strategy, plans or intentions. Such statements include descriptions of the company's investment and research and development programs and anticipated expenditures in connection therewith, descriptions of new products expected to be introduced by the company and anticipated customer demand for such products and products in the company's existing portfolio. Such statements reflect the current views of the company with respect to future events and are subject to certain risks, uncertainties and assumptions. Many factors could cause the actual results, performance or achievements of the company to be materially different from any future results, performances or achievements that may be expressed or implied by such forward-looking statements. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those described herein as anticipated, believed, estimated or expected.

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Actelion Pharmaceuticals Ltd

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