An Indianapolis plant that manufactures specialty drugs has been sold by its parent company as part of a deal that could be worth more than $300 million.

New Jersey-based Enzon Pharmaceuticals Inc. said Friday that it closed the sale of its specialty pharmaceutical business to the Italian-owned Sigma-Tau Group. The sale included the plant and several Enzon drugs produced at the facility.

The operations at 6925 Guion Road manufacture four drugs: Oncaspar, for leukemia; DepoCyt, for meningitis; Abelcet, for fungal infection; and Adegen, for the “bubble boy disease” immune disorder.

Enzon may be entitled to an additional $27 million based on the achievement of certain milestones, in addition to royalties of up to 10 percent on profit through 2014.

The plant employs about 100 workers, and the manufacturing operations will remain in Indianapolis, Sigma Tau spokesman Marc Tewey said.

The plant and its products that treat rare diseases are a "nice addition" to Sigma Tau, which focuses on orphan drugs, Tewey said. Orphan drugs, as they're known in the pharmaceutical industry, treat diseases that afflict fewer than 200,000 patients in the United States.

The plant also contracts with outside companies to manufacture their drugs, and Tewey said Sigma Tau will attempt to expand that outside business. 

Enzon announced in August 2008 that it might sell the plant, or one or all of its products, as part of a strategic review of its specialty pharmaceutical business.

Billionaire shareholder Carl Icahn has pressed the company to unload assets or sell itself in order to increase value to shareholders.

Enzon stock has languished near $10 a share since 2006. The shares opened Monday morning at $9.97.