Acceleron Pharma Presents Preclinical Study Results for ACE-041 at the AACR 100th Annual Meeting 2009

First detailed introduction of Acceleron’s lead anti-angiogenesis drug candidate

CAMBRIDGE, Mass.--(BUSINESS WIRE)--Acceleron Pharma, Inc., a biopharmaceutical company developing novel therapeutics that modulate the growth of tissues including bone, muscle, red blood cells and vasculature, today announced that it will present results from preclinical studies of its anti-angiogenesis program, ACE-041, at the American Association for Cancer Research (AACR) 100th Annual Meeting 2009 in Denver, Colorado, April 18-22, 2009.

“INHIBITION OF ALK1 SIGNALING USING RAP-041, A NOVEL SOLUBLE ALK1-FC COMPOUND, PREVENTS ENDOTHELIAL CORD FORMATION IN VITRO AND INHIBITS ANGIOGENESIS IN VIVO”

ACE-041 is a protein therapeutic that works by blocking signaling through Activin receptor-like kinase 1 (ALK1), a receptor in the Growth and Differentiation Factor (GDF) protein family necessary for angiogenesis.

The ACE-041 results will be presented at AACR at the following times and locations:

• “RAP-041, A SOLUBLE ACTIVIN RECEPTOR-LIKE KINASE 1 (ALK1) FUSION PROTEIN, IS A NOVEL ANTI-ANGIOGENIC AGENT THAT PREVENTS TUMOR GROWTH IN AN ORTHOTOPIC MODEL OF BREAST CANCER” (Angiogenesis Inhibitors II – Poster 25); Exhibit Hall B-F, Sunday April 19^th, 8:00 AM – 12:00 PM
• “INHIBITION OF ALK1 SIGNALING USING RAP-041, A NOVEL SOLUBLE ALK1-FC COMPOUND, PREVENTS ENDOTHELIAL CORD FORMATION IN VITRO AND INHIBITS ANGIOGENESIS IN VIVO” (Angiogenesis Inhibitors I - Poster 18); Exhibit Hall B-F, Sunday April 19^th, 8:00 AM – 12:00 PM

About ACE-041

ACE-041, a protein therapeutic based on the Activin receptor-like kinase 1 (ALK1) receptor, is a novel anti-angiogenic agent. ACE-041 blocks signaling through ALK1, thereby preventing vessel formation. In preclinical models, systemic administration of ACE-041 inhibits VEGF and FGF-induced angiogenesis, even though ACE-041 does not bind to VEGF or FGF. The ability of ACE-041 to inhibit multiple angiogenic factors may provide benefit to patients suffering from hematologic and solid tumors. A Phase 1 study of ACE-041 in cancer patients is planned to begin in the middle of 2009.

About Acceleron

Acceleron is a privately held biopharmaceutical company committed to discover, develop, manufacture and commercialize novel biotherapeutics that modulate the growth of bone, muscle, red blood cells, 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 the Growth and Differentiation Factor (GDF) family of proteins. ACE-011 is currently being studied in a Phase 2 clinical trial in multiple myeloma patients with osteolytic bone disease. ACE-031 is currently being studied in a Phase 1 clinical trial in healthy volunteers. In addition, the company is advancing new product candidates that increase muscle mass, control angiogenesis, inhibit fat accumulation and increase hemoglobin. 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, Bessemer Ventures, Flagship Ventures, MPM BioEquities, OrbiMed Advisors, Polaris Ventures, QVT Financial, Sutter Hill Ventures and Venrock. For more information, visit www.acceleronpharma.com.