Market Overview

Acceleron Announces Initiation of PULSAR Phase 2 Trial of Sotatercept in Pulmonary Arterial Hypertension


PULSAR trial expands Acceleron's pipeline into pulmonary disease

Acceleron Pharma Inc. (NASDAQ:XLRN), a leading biopharmaceutical company
in the discovery and development of TGF-beta therapeutics to treat
serious and rare diseases, today announced the initiation of the PULSAR
Phase 2 trial of sotatercept for the treatment of patients with
pulmonary arterial hypertension (PAH), a chronic and life-changing
disease that can lead to heart failure.

"There is a real need for new treatment options that have the potential
to improve survival for PAH patients," said David Badesch, M.D., the
Director of the Pulmonary Hypertension Program at the University of
Colorado and Chair of the PULSAR Trial Steering Committee. "Based on its
novel mechanism and preclinical results, sotatercept, particularly in
combination with standard-of-care therapies, could be an important
advancement in the future treatment of PAH. I look forward to the
results of the trial."

"The initiation of the PULSAR trial is an important milestone in our
newly expanded research and development efforts in pulmonary disease,"
said Habib Dable, Chief Executive Officer of Acceleron. "We believe that
treatment with sotatercept could restore a vital signaling pathway that
is known to be deficient in PAH patients. This is an extremely important
trial, as we hope to bring an innovative medicine to the thousands of
patients who are suffering from PAH."

The Company plans to report preliminary results from the 6-month primary
treatment period of the PULSAR Phase 2 trial in the first half of 2020.

About the PULSAR Trial

The PULSAR Phase 2 trial is a randomized, double-blind,
placebo-controlled study designed to evaluate the efficacy and safety of
sotatercept in PAH patients. The primary endpoint of the trial is the
change from baseline in pulmonary vascular resistance (PVR) over a
24-week treatment period. The key secondary endpoint is change from
baseline in six-minute walk distance (6MWD). A total of 90 patients will
be randomized 1:1:1 into three treatment arms with standard-of-care
vasodilator therapies in combination with sotatercept or placebo.
Following the 6-month double-blind treatment period, participants in the
trial will be eligible to enroll into the 18-month extension period.

For additional information about this clinical trial, please visit,
identifier NCT03496207.

About Sotatercept

Sotatercept acts as a ligand trap for members of the transforming growth
factor-beta superfamily, including those directly involved in the BMP
pathway proven critical for maintaining healthy pulmonary vasculature.
In multiple preclinical studies in PAH, sotatercept significantly
decreased pulmonary vessel muscularization, improved pulmonary arterial
pressures, and decreased indicators of right heart failure. Sotatercept
is currently being evaluated in the PULSAR Phase 2 trial in PAH.

About Pulmonary Arterial Hypertension (PAH)

Pulmonary Arterial Hypertension (PAH) is a rare, chronic, and rapidly
progressing disorder characterized by the narrowing of small pulmonary
arteries and elevated blood pressure in the pulmonary circulation. PAH
results in significant and progressive strain on the right side of the
heart, often leading to limited physical activity, heart failure, and
reduced life expectancy. The 5-year survival rate for patients with PAH
is approximately 57%. Available therapies primarily act by promoting the
dilation of pulmonary vessels without addressing the underlying cause of
the disease. As a result, PAH often progresses rapidly for many patients
despite standard-of-care treatment. A growing body of research has
implicated imbalances in BMP and TGF-beta signaling as a primary driver
of PAH in all forms of the disease.

About Acceleron

Acceleron is a Cambridge-based, clinical-stage biopharmaceutical company
dedicated to the discovery, development, and commercialization of
therapeutics to treat serious and rare diseases. The Company's
leadership in the understanding of TGF-beta biology and protein
engineering generates innovative compounds that engage the body's
ability to regulate cellular growth and repair.

Acceleron focuses its research and development efforts in hematologic,
neuromuscular, and pulmonary diseases. In hematology, the Company and
its global collaboration partner, Celgene, are developing luspatercept
for the treatment of chronic anemia in myelodysplastic syndromes,
beta-thalassemia, and myelofibrosis. Acceleron is also advancing its
neuromuscular franchise with two distinct Myostatin+ agents, ACE-083 and
ACE-2494, and a pulmonary program with sotatercept in pulmonary arterial

For more information, please visit
Follow Acceleron on Social Media: @AcceleronPharma and

Forward-Looking Statements

This press release contains forward-looking statements about the
Company's strategy, future plans and prospects, including statements
regarding the development of the Company's compounds, the timeline for
clinical development and regulatory approval of the Company's compounds
and the expected timing for reporting of data from ongoing clinical
trials. The words "anticipate," "believe," "could," "estimate,"
"expect," "goal," "intend," "may," "plan," "potential," "project,"
"should," "target," "will," "would," and similar expressions are
intended to identify forward-looking statements, although not all
forward-looking statements contain these identifying words.

Actual results could differ materially from those included in the
forward-looking statements due to various risks and uncertainties,
including, but not limited to, that preclinical testing of the Company's
compounds and data from clinical trials may not be predictive of the
results or success of ongoing or later clinical trials, that the
development of the Company's compounds will take longer and/or cost more
than planned, that the Company or its collaboration partner, Celgene,
will be unable to successfully complete the clinical development of the
Company's compounds, that the Company or Celgene may be delayed in
initiating, enrolling or completing any clinical trials, and that the
Company's compounds will not receive regulatory approval or become
commercially successful products. These and other risks and
uncertainties are identified under the heading "Risk Factors" included
in the Company's most recent Annual Report on Form 10-K, and other
filings that the Company has made and may make with the SEC in the

The forward-looking statements contained in this press release are based
on management's current views, plans, estimates, assumptions and
projections with respect to future events, and the Company does not
undertake and specifically disclaims any obligation to update any
forward-looking statements.

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