Acceleron and Celgene Announce Interim Clinical Data for Sotatercept Demonstrating Dose Dependent Increases in Hemoglobin in

  Acceleron and Celgene Announce Interim Clinical Data for Sotatercept
  Demonstrating Dose Dependent Increases in Hemoglobin in Patients with End
  Stage Renal Disease on Hemodialysis

Business Wire

CAMBRIDGE, Mass. -- April 23, 2014

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 its
collaboration partner, Celgene Corporation, presented interim data
demonstrating dose dependent increases in hemoglobin in patients with end
stage renal disease (ESRD) on hemodialysis. The data are from an ongoing phase
2a study of sotatercept and were presented at the National Kidney Foundation
2014 Spring Clinical Meeting in Las Vegas, NV.

The phase 2a clinical trial of sotatercept is designed as a randomized,
placebo-controlled, dose escalation study to evaluate sotatercept for the
correction of anemia in patients with end stage renal disease on hemodialysis.
There are four sotatercept dose groups (0.3 mg/kg, 0.5 mg/kg, 0.7 mg/kg, or
0.7 mg/kg loading dose followed by 0.4 mg/kg). Highlights of the data from the
two lowest dose level cohorts (0.3 mg/kg and 0.5 mg/kg) are summarized below:

  *Hemoglobin increase ≥1.0 g/dL was achieved by 20%, 37% and 40% of patients
    in the placebo, sotatercept 0.3 mg/kg and sotatercept 0.5 mg/kg cohorts,
    respectively, in the first 28-day cycle following a single dose.
  *The mean peak hemoglobin increase in the first 28-day dose cycle was 0.1
    g/dL, 0.5 g/dL and 0.8 g/dL in patients in the placebo, sotatercept 0.3
    mg/kg and sotatercept 0.5 mg/kg cohorts, respectively.
  *Rescue therapy with erythropoietin, if hemoglobin levels fell to less than
    9 g/dL, was required in 40% of placebo patients, 13% of patients at
    sotatercept 0.3 mg/kg, and 0% of patients at sotatercept 0.5 mg/kg.

The poster (NKF Spring Clinical Meeting, poster #81) is available on the
Publications page of the Acceleron website (www.acceleronpharma.com).

About Sotatercept Clinical Trials in Patients with End Stage Renal Disease

The Phase 2a clinical trial of sotatercept is designed as a randomized,
placebo-controlled single dose and multi-dose, dose escalation study to
evaluate the pharmacokinetics, safety, efficacy, tolerability and
pharmacodynamics of sotatercept for the correction of anemia in patients with
end stage renal disease on hemodialysis. Eligible subjects are randomized to
one of two arms (sotatercept or placebo in a 3:1 ratio) in 4 sequential dose
groups (sotatercept 0.3 mg/kg, 0.5 mg/kg, 0.7 mg/kg, or 0.7 mg/kg loading dose
followed by 0.4 mg/kg). Each dose group will include up to 12 patients. For
additional information on this clinical trial, please visit
www.clinicaltrials.gov, identifier NCT01146574.

In December, 2013, Celgene initiated a phase 2b clinical trial of sotatercept
in patients with end stage renal disease (ESRD) who are on hemodialysis. This
phase 2 clinical trial is designed as a two-part study to assess the safety
and efficacy of sotatercept as a therapy to treat anemia and potentially to
control the adverse manifestations of chronic kidney disease mineral and bone
disorder (CKD-MBD). Part one of the study will enroll up to 60 patients and
part two of the study will enroll up to 230 patients. For additional
information on this clinical trial, please visit www.clinicaltrials.gov,
identifier NCT01999582.

About Chronic Kidney Disease

Chronic Kidney Disease (CKD) is a serious condition characterized by the
progressive loss of kidney function and is most often caused by diabetes or
high blood pressure. CKD is classified in five stages according to the degree
of kidney impairment. End Stage Renal Disease (ESRD), also known as kidney
failure, is the most advanced stage of CKD and a life-threatening condition in
which patients require a either kidney transplant or dialysis for survival.
Anemia, low levels of red blood cells, is a common secondary disorder to
Chronic Kidney Disease and worsens with progression of the disease.
Disturbance in mineral and bone metabolism, known as Chronic Kidney Disease
Mineral and Bone Disorder (CKD-MBD), is also a common complication in CKD
patients that affects almost all patients who are on dialysis. CKD-MBD can
lead to bone abnormalities and/or calcification in soft tissue, especially
blood vessels, and is associated with increased morbidity and mortality in CKD
patients.

About Sotatercept

Sotatercept is an activin receptor type IIA fusion protein that acts as a
ligand trap for members in the Transforming Growth Factor-Beta (TGF-β)
superfamily involved in the late stages of erythropoiesis (red blood cell
production). Sotatercept regulates 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. Acceleron and Celgene are jointly
developing sotatercept as part of a global collaboration. Sotatercept is
currently in multiple phase 2 clinical trials. 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
 
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