Alnylam Pharmaceuticals lines up space for expansion

Want to know which biotechnology companies have big expectations for the new drugs in their labs? Follow the real estate.

Two weeks after the Cambridge biotech Genzyme said it will move out of its 500 Kendall St. headquarters — known as Genzyme Center — when its lease expires in 2018, Alnylam Pharmaceuticals Inc. has negotiated a “right of first offer” on the signature office tower in the heart of Kendall Square’s biotechnology cluster.

The right to potentially occupy the 350,000-square-foot building was part of an agreement Alnylam signed with San Diego-based BioMed Realty Trust Inc., one of the nation’s largest developers of life sciences offices and labs, which owns a block of buildings in Kendall Square.

Under the agreement, disclosed in a regulatory filing last week, Alnylam also will lease 295,000 square feet of offices and labs at 675 West Kendall St., diagonally across from Genzyme Center, starting on May 1, 2018. That space is currently leased to Vertex Pharmaceuticals Inc., which last year moved to a new Boston campus and plans to sublease the Cambridge location to other tenants for the next three years.

Alnylam’s move signals the anticipated expansion of a company that has become a leader in the emerging technology known as RNA interference therapeutics, or RNAi, which fights diseases by silencing genes that cause the unwanted overproduction of proteins in human cells.

Last year, Genzyme, an arm of the French drug maker Sanofi SA, paid $700 million to take a 12 percent stake in Alnylam, with an option to buy as much as 30 percent of the company in the future. The deal also gave Genzyme the ability to tap into Alnylam’s robust pipeline of rare-disease drug candidates based on its RNAi technology. Genzyme plans to move about 950 employees now in Genzyme Center to a new headquarters being built at nearby 50 Binney St.