Alnylam Pharmaceuticals Inc. priced an underwritten public offering of 5 million common shares at $77.50 each.
The Cambridge, Mass.-based biopharmaceutical company expects to raise gross proceeds of about $387.5 million.
Underwriters have a 30-day overallotment option to buy up to 750,000 additional common shares.
Alnylam Pharmaceuticals plans to use the net proceeds for general corporate purposes, including commercialization of Onpattro in the U.S. and Europe. Onpattro, also known as patisiran, is a treatment for the polyneuropathy of hereditary transthyretin-mediated amyloidosis in adults. The rare, genetic, progressive disease is characterized by the formation of the protein called amyloid in the peripheral nerves, heart or gastrointestinal tract.
The offering is expected to close on or about Jan. 17, subject to customary closing conditions.
Barclays Capital Inc. is acting as sole book-running manager for the offering.