Acceleron Highlights Phase 3 Studies, New Clinical Results and Research Strategies at Research and Development Day Event

Acceleron Pharma Inc.

, a clinical stage biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutic candidates that regulate cellular growth and repair, today announced the phase 3 clinical trial designs for the luspatercept program in myelodysplastic syndromes ("MEDALIST" study) and beta-thalassemia ("BELIEVE" study), phase 1 preliminary results from the ACE-083 program, and its new IntelliTrap™ drug discovery platform. "We are extremely excited to present the plans for Acceleron's first phase 3 clinical trials, the unprecedented increases in muscle mass demonstrated in the ACE-083 phase 1 clinical trial supporting its advancement into phase 2 trials next year and our new IntelliTrap™ drug discovery platform which is already generating promising new therapeutic candidates such as ACE-2494," said John Knopf, Ph.D., Chief Executive Officer of Acceleron. "Acceleron is making great strides across its entire pipeline from our late stage phase 3 programs to our highly productive discovery organization and I am proud of the tremendous progress we are making." Luspatercept Phase 3 Clinical Trials in Myelodysplastic Syndromes (MDS) and Beta-Thalassemia Acceleron announced that the phase 3 MDS trial will be a double-blind, randomized, placebo-controlled study of luspatercept in 210 very low to intermediate risk MDS patients (the "MEDALIST" study). The primary endpoint is the proportion of patients that become red blood cell transfusion independent (≥ 8 weeks) during the first 24 weeks of the study. The phase 3 beta-thalassemia trial will be a double-blind, randomized, placebo-controlled study of luspatercept in 300 regularly transfused beta-thalassemia patients (the "BELIEVE" study). The primary endpoint is the proportion of patients with ≥ 33% reduction in transfusion burden from weeks 13 to 24 compared to the 12 weeks preceding treatment. Both the MEDALIST and BELIEVE studies are planned to begin by the end of the year. ACE-083 Phase 1 Preliminary Results Acceleron reported positive top-line data from the phase 1 randomized, double-blind, placebo-controlled, dose-ranging study in healthy volunteers. ACE-083 is designed to selectively increase muscle mass and strength in the muscles in which the drug is administered. The results showed a dose dependent increase in muscle volume, assessed by MRI, with the highest dose level generating a 14% increase in volume of the injected muscle, the rectus femoris, in the thigh. Based on these exciting results, Acceleron announced it intends to advance ACE-083 into a phase 2 clinical trial in patients with facioscapulohumeral muscular dystrophy in mid-2016. IntelliTrap™ Drug Discovery Platform Acceleron introduced its new IntelliTrap™ drug discovery platform from which it is creating a large and diverse library of new, selective therapeutic candidates targeting the TGF-beta superfamily. This platform has already generated several new therapeutic candidates including ACE-2494, a systemic muscle therapeutic and the first clinical candidate to emerge from this platform. Acceleron aims to initiate its first clinical trial of ACE-2494 by the end of 2016. A replay of the live webcast of the Research and Development Day event will be accessible from the "Investors & Media" section of the company's website, www.acceleronpharma.com.