Based: Cambridge, MA
Founded: 2004
Website: www.acceleronpharma.com
CEO: John Knopf

The Scoop: These days it's rare to see a fledgling developer ramp up a large staff and eagerly grab on to new office space. But Acceleron has big plans, and it intends to have the brain power needed to make them a reality. The biotech has struck major market deals with Shire and Celgene and has ambitious long-term goals that include launching specialty commercial operations as it lays a path to gain approvals on new drugs to treat rare diseases. And Acceleron's ability to positively influence muscle and bone development has far-reaching implications that extend well past the orphan drug arena.

What Makes It Fierce: When the New York Times recently went looking for examples of the most promising new therapies in the pipeline for muscle loss, Acceleron was ranked right alongside Pfizer and Amgen for its work on a new drug that blocks myostatin, a protein known to inhibit muscle development and a key obstacle for anyone facing the debilitating effects of muscle erosion.

Acceleron's lead drug--ACE-031--is a fusion protein that combines the human activin receptor type IIB with a section of antibody, capturing myostatin and other proteins that inhibit the growth and strength of muscles. Just days after garnering fast track and orphan drug status for Duchenne Muscular Dystrophy, Shire inked a $498 million pact for the ex-North American rights to the therapy.

Acceleron's Phase IIa clinical trial for DMD got underway in May as researchers hit a key milestone in determining if ACE-031 can build muscle and increases strength.

"We could have partnered 31 a long time ago," says CEO John Knopf. "We wanted just the right sort of deal." Shire has been ambitious about tackling orphan diseases and fits the description of an ideal partner for Acceleron, which has been smart about forging partnerships that can help fuel the biotech through to the next stage of development. The pact also leaves Acceleron with U.S. marketing rights, pointing it directly down the path to commercialization work.

Late last year Alkermes paid out $10 million for a deal to license Acceleron's Medifusion technology for a pair of development programs. But that pales in comparison to the $50 million upfront that Celgene paid to partner up on ACE-011 for bone loss--a deal that included a package of more than $1.8 billion in milestones covering three indications. Acceleron keeps co-promotion rights in the U.S. as another possible springboard into commercial activities. Its third program, ACE-041, is a protein therapeutic that binds to a member of the GDF family necessary for angiogenesis.

Acceleron has 140 staffers, large by private biotech standards. But Knopf insists that when you're doing everything from discovery work through manufacturing, that's still "lean and mean."

Venture backers: Advanced Technology Ventures, Bessemer Venture Partners, Flagship Ventures, MPM Capital, OrbiMed Advisors, Polaris Venture Partners, Sutter Hill Ventures and Venrock Associates.