Acceleron Announces New Interim Phase 2 Sotatercept Clinical Data in Beta-Thalassemia to be Presented at 2013 American Society

  Acceleron Announces New Interim Phase 2 Sotatercept Clinical Data in
  Beta-Thalassemia to be Presented at 2013 American Society of Hematology
  Annual Meeting

55th American Society of Hematology (ASH) Annual Meeting and Exposition

Business Wire

CAMBRIDGE, Mass. -- December 2, 2013

Acceleron Pharma Inc. (NASDAQ:XLRN), a clinical stage biopharmaceutical
company focused on the discovery, development and commercialization of novel
protein therapeutics for cancer and rare diseases, today announced that data
in five abstracts for sotatercept and ACE-536, Acceleron’s programs to treat
red blood cell disorders, will be presented at the 55^th American Society of
Hematology (ASH) Annual Meeting and Exposition. The conference will take place
on December 7-10^th at the Ernest N. Morial Convention Center in New Orleans,
Louisiana.

Key information to be presented include new interim data from the ongoing
phase 2 clinical trial of sotatercept in patients with beta-thalassemia.
Initial interim data from the 0.5 mg/kg dose level will be presented in a
poster presentation by the first author Maria-Domenica Cappellini, M.D.,
University of Milan, Milan, Italy on Monday December 9^th from 6:00 – 8:00 PM
CST in Hall E of the convention center. Acceleron has previously provided
interim clinical data from the 0.1 mg/kg and 0.3 mg/kg dose levels in this
trial.

Additionally, preclinical data from both the sotatercept and ACE-536 programs
will be presented at the meeting. Both sotatercept and ACE-536 are being
jointly developed through a global collaboration with Celgene Corporation. The
presentations from Acceleron, Celgene and academic collaborators will take
place as follows:

Sotatercept Clinical Data

Abstract title: “A Phase 2a, Open-Label, Dose-Finding Study to Determine the
Safety and Tolerability of Sotatercept (ACE-011) in Adults with Beta
(β)-Thalassemia: Interim Results”
Abstract number: 3448
Session: 112. Thalassemia and Globin Gene Regulation: Poster III
Date: Monday, December 9, 2013
Time: 6:00 PM – 8:00 PM CST (Ernest N. Morial Convention Center, Hall E)

Sotatercept Preclinical Data

Abstract title: “Sotatercept Promotes Differentiation and Survival of
Erythroid Progenitors by Blocking Inhibitory Effects of TGFβ Superfamily
Members”
Abstract number: 944
Session: 101. Red Cells and Erythropoiesis, Structure and Function, Metabolism
and Survival, Excluding Iron: Poster I
Date: Saturday, December 7, 2013
Time: 5:30 PM – 7:30 PM CST (Ernest N. Morial Convention Center, Hall E)

Abstract title: “Sotatercept, an Activin Receptor-2a Ligand Trap, Modulates
Hepcidin Levels in Primary Human Hepatocytes”
Abstract number: 3441
Session: 102. Regulation of Iron Metabolism: Poster III
Date: Monday, December 9, 2013
Time: 6:00 PM – 8:00 PM CST (Ernest N. Morial Convention Center, Hall E)

Abstract title: “RAP-011 Efficiently Rescues Erythropoiesis in Zebrafish
Models of Diamond Blackfan Anemia”
Abstract number: 3702
Session: 508. Bone Marrow Failure: Poster III
Date: Monday, December 9, 2013
Time: 6:00 PM – 8:00 PM CST (Ernest N. Morial Convention Center, Hall E)

ACE- 536 Preclinical Data
Abstract title: “Modified Activin Receptor Type IIb-Fc Fusion Protein
(RAP-536) Decreases Anemia in a Murine Model of Myelodysplastic Syndrome and
Improves Overall Survival”
Abstract number: 749
Date: Monday, December 9, 2013
Session: 633. Myelodysplastic Syndromes: Basic and Clinical Insights
Time: Oral presentation at 7:15 PM CST (New Orleans Theater AB)

About Sotatercept and ACE-536

Sotatercept is an activin receptor type IIA fusion protein and ACE-536 is a
modified activin receptor type IIB fusion protein. Both molecules act as
ligand traps for members of the TGF-β superfamily involved in the late stages
of erythropoiesis (red blood cell production). Sotatercept and ACE-536
regulate late-stage erythrocyte (red blood cell) precursor cell
differentiation and maturation. This mechanism of action is distinct from that
of erythropoietin (EPO), which stimulates the proliferation of early-stage
erythrocyte precursor cells. Diseases like myelodysplastic syndromes (MDS) and
beta-thalassemia are characterized by “ineffective erythropoiesis,” in which
there is an over-production of early-stage erythrocyte precursors in the bone
marrow and premature apoptosis (cell death) of later-stage precursors.
Administration of EPO does not correct the underlying cause of the anemia
associated with ineffective erythropoiesis. By promoting the differentiation
of later-stage erythroid precursor cells into mature red blood cells,
sotatercept and ACE-536 address the ineffective erythropoiesis and therefore
have the potential to treat the anemia underlying both MDS and
beta-thalassemia. Acceleron and Celgene are jointly developing sotatercept and
ACE-536. Both molecules are currently in phase 2 clinical trials in patients
with beta-thalassemia and in patients with MDS. For more information, please
visit www.clinicaltrials.gov.

About Acceleron

Acceleron is a clinical stage biopharmaceutical company focused on the
discovery, development and commercialization of novel protein therapeutics for
cancer and rare diseases. The company is a leader in understanding the biology
of the Transforming Growth Factor-Beta (TGF-β) protein superfamily, a large
and diverse group of molecules that are key regulators in the growth and
repair of tissues throughout the human body, and in targeting these pathways
to develop important new medicines. Acceleron has built a highly productive
R&D platform that has generated innovative clinical and preclinical protein
therapeutic candidates with novel mechanisms of action. These protein
therapeutic candidates have the potential to significantly improve clinical
outcomes for patients with cancer and rare diseases.

For more information, please visit www.acceleronpharma.com.

Contact:

Acceleron Pharma
Steven Ertel, 617-649-9234
Senior Vice President and Chief Business Officer
or
Media:
Suda Communications LLC
Maureen L. Suda, 585-387-9248