( LUCCA ITALY ­ May 14 2007-Accel...)Accelreon Pharma's ACE-031Shown to Increase Muscle Mass in,Preclinical Studies,Health

LUCCA, ITALY, ­ May 14, 2007-Acceleron Pharma, Inc., a biopharmaceutical company developing therapeutics for the treatment of musculoskeletal, metabolic and cancer-related diseases, today announced results of a preclinical study with ACE-031 that demonstrated the ability of the compound to increase muscle mass and strength in normal mice and in murine models of muscular dystrophy. ACE-031 inhibits negative regulators of muscle to increase muscle mass and strength as a potential treatment for neuromuscular diseases and cancer-related muscle loss. The data was presented on Sunday, May 13 at the Gordon Research Conference on Myogenesis in Lucca, Italy. ³

Acceleron is encouraged by the significant outcomes and positive data generated by ACE-031 spanning numerous preclinical models of muscle loss², said Jas Seehra, Ph.D., Chief Scientific Officer of Acceleron. ³ACE-031 and related Acceleron compounds consistently demonstrate substantial increases in skeletal muscle mass and strength.² ACE-031, a protein therapeutic based on the activin receptor type IIB (ActRIIB), is the first of several compounds Acceleron is developing for the treatment of diseases involving the loss of muscle mass, strength and function. ActRIIB binds to myostatin (GDF-8) and other negative regulators of muscle mass and strength. Over-expression of myostatin has been shown to cause a loss in muscle mass and strength, and inhibition of myostatin results in the selective increase in skeletal muscle mass and strength. In preclinical models, ACE-031 increased skeletal muscle mass and strength in disease models of amyotrophic lateral sclerosis (ALS), muscular dystrophy, glucocorticoid-induced muscle loss and age-related muscle loss (sarcopenia).

ACE-031 offers the potential for an entirely new type of therapy for the treatment of various muscle wasting conditions. ³The clinical potential of ACE-031 to selectively increase skeletal muscle will offer
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