Acceleron Pharma's ACE-011 Increases Bone Mineral Density and Bone Strength in Preclinical Studies in Non-Human Primates.

CAMBRIDGE, Mass. -- Acceleron Pharma, Inc., a biopharmaceutical company developing novel therapeutics that modulate the growth of tissues including bone and muscle, today announced that ACE-011 improved bone microarchitecture, increased bone mineral density and bone mechanical strength. The results from the oral presentation titled "ACE-011, A Soluble Activin Receptor Type IIA Fusion Protein, Increases BMD and Improves Microarchitecture in Cynomolgus Monkeys" were presented at The American Society for Bone and Mineral Research (ASBMR) 29th Annual Meeting held in Honolulu, Hawaii, USA, September 16 - 19, 2007.

In this study, two groups of cynomolgus monkeys were treated for 3 months with ACE-011 or placebo. Effects on markers of bone formation and bone resorption were similar to the effects recently reported in the ACE-011 phase 1 clinical study. Statistically significant increases in BMD in the femurs and vertebrae were observed. Bone mineral density in the distal femur increased by nearly 15% compared to placebo-treated animals due to improvement in the trabecular architecture. These changes in bone microarchitecture translated to 23-46% improvement in mechanical strength.

"We are very excited by these results and the consistency with which the improvements in the microarchitecture have translated to improved bone strength in all preclinical models from rodents to primates. We look forward to extending these studies and continuing our R&D efforts to improve clinical outcomes in patients suffering from bone loss," said Jasbir Seehra, Ph.D., Chief Scientific Officer at Acceleron.

About ACE-011

ACE-011, a protein therapeutic based on the activin receptor type IIA, is a novel bone forming agent that is expected to begin phase 2 clinical trials in Q4 2007. In numerous preclinical models of bone loss, ACE-011 demonstrated beneficial effects on both trabecular and cortical bone. ACE-011 increased bone mineral density, improved bone architecture, increased the mineral apposition and bone formation rates and improved bone mechanical strength. These effects have been demonstrated in therapeutic models of bone loss in which ACE-011 stimulated bone formation - a significant unmet medical need that is underserved by current treatments for bone loss.

About Acceleron Pharma

Acceleron is a privately held biopharmaceutical company committed to discover, develop, manufacture and commercialize novel biotherapeutics that modulate the growth of bone, muscle, fat and the vasculature to treat musculoskeletal, metabolic and cancer-related diseases. Acceleron's scientific approach takes advantage of its unique insight into the regenerative powers of two protein families: the Growth and Differentiation Factors (GDFs) and Bone Morphogenetic Proteins (BMPs). ACE-011, a novel bone forming agent, is the company's lead program, and is being developed to reverse bone loss in diseases such as cancer-related bone loss. In addition, the company is advancing through preclinical development product candidates that increase muscle mass, control angiogenesis and inhibit fat accumulation. Acceleron utilizes proven biotherapeutic technologies and capitalizes on the company's internal GMP manufacturing capability to rapidly and efficiently advance its therapeutic programs. The investors in Acceleron are Advanced Technology Ventures, Flagship Ventures, OrbiMed Advisors, Polaris Ventures, Sutter Hill Ventures and Venrock.