Luspatercept Data Presented at the 13th International Symposium on Myelodysplastic Syndromes

Acceleron Pharma Inc. has announced preliminary data from the ongoing Phase II clinical trial of luspatercept in patients with lower risk myelodysplastic syndromes (MDS). The data showed that luspatercept increased hemoglobin levels and enabled many patients to become transfusion independent. The presentation was given by Uwe Platzbecker, University Hospital in Dresden, Germany in an oral session titled “Best of Clinical Trials II” at the MDS Foundation 13th International Symposium on MDS. Acceleron and its collaboration partner, Celgene Corporation, are jointly developing luspatercept.

“We are excited by the results in lower risk MDS patients, which confirm and extend our previous findings,” said Uwe Platzbecker, Professor of Hematology and Head of the MDS programme at the University Hospital in Dresden, Germany and co-ordinating principal investigator of the luspatercept PACE-MDS study. “Luspatercept may be useful early in the treatment of lower risk MDS patients, either as the initial treatment for anemia or in patients who do not respond or become refractory to treatment with erythropoiesis stimulating agents.”

Key preliminary data from the presentation:

• The ongoing Phase II clinical trial is fully enrolled and data from 44 of the 58 patients was available for efficacy analyses. 17 of these 44 patients were enrolled in the expansion cohort, using the planned Phase III dosing regimen, whose data had not been previously presented.

• Luspatercept was generally well-tolerated with the majority of adverse events (AE) being mild to moderate (grade 1 or 2). There were two possibly related serious adverse events of muscle pain and worsening of general condition.

• In the higher dose groups (0.75 to 1.75 mg/kg administered subcutaneously every 3 weeks):
     - 54% achieved the International Working Group (IWG) hematologic improvement-erythroid
       (HI-E) threshold of efficacy.
     - 36% of patients who received red blood cell transfusions during the 8 weeks prior to treatment in the study          achieved transfusion independence for at least 8 weeks during the study.

• Ring sideroblasts (RS) are a type of abnormal red blood cell (RBC) precursor cell in the bone marrow. These ring sideroblasts are associated with ineffective erythropoiesis and anemia. When at least 15% of the cells in an MDS patient’s bone marrow are ring sideroblasts, this patient is considered RS positive. At least 30% of all MDS patients are RS positive, and the proportion is likely even greater within the lower risk segment of all MDS patients.

• In the RS positive patients in the higher dose groups treated with luspatercept,
     - 63% achieved IWG HI-E
     - 39% achieved transfusion independence.