Enzon Files PEG Patent Infringement Lawsuit Against Roche

Enzon Files PEG Patent Infringement Lawsuit Against Roche

Enzon Issued New Branched PEG Patent

PISCATAWAY, N.J. - September 5, 2000. Enzon, Inc. (NASDAQ:ENZN) announced today that it has filed a lawsuit in Federal Court in New Jersey against Hoffmann-LaRoche, Inc. and Roche Laboratories, Inc. (Roche) for infringement of Enzon's new U.S. Patent 6,113,906 ('906), by Roche's "PEGASYS," a pegylated alpha interferon-2a product.

This new Enzon patent, which has composition of matter claims directed to "branched PEG," a unique form of Enzon's high-molecular-weight pegylation technology, was issued by the U.S. Patent and Trademark Office on September 5, 2000; Foreign patent applications corresponding to this U.S. patent are now pending.

Enzon's new '906 patent issued from the same family as Enzon's earlier U.S. Patent 5,643,575, which Enzon is currently asserting against Shearwater Polymers, Inc. (Shearwater), in federal court in Alabama. In the Alabama case, Shearwater asserted that the '575 patent is invalid on a number of grounds, including certain articles authored by Yamasaki and colleagues. The Yamasaki articles were considered by the U.S. Patent and Trademark Office during prosecution of the application for Enzon's new '906 patent, which was issued in spite of these references.

Enzon licenses a different pegylation technology to Schering-Plough Corporation for use with PEG-INTRON™ (peginterferon alfa-2b), which is currently undergoing FDA review for the treatment of hepatitis C. In May 2000, Schering-Plough received marketing authorization in the European Union for PEGINTRON™ for the treatment of hepatitis C. Under the Company's licensing agreement with Schering-Plough, Enzon is entitled to royalties on worldwide sales of PEG-INTRON and milestone payments.

Pegylation involves the chemical combination of polyethylene glycol (PEG) with protein and small molecule drugs to increase their circulation time in the body and decrease their immunogenicity. Enzon has several U.S. and foreign patent applications and issued patents covering this technology.

"We are very pleased to add this new patent to our portfolio and plan to vigorously pursue this case against Roche's infringement of our intellectual property rights," stated Peter G. Tombros, Enzon's president and chief executive officer.

"Schering-Plough fully supports Enzon's efforts to defend their new PEG patent against infringement," said Thomas C. Lauda, executive vice president, Schering-Plough Pharmaceuticals.

Enzon currently sells two FDA-approved products that utilize its earlier pegylation technology; ONCASPAR, which is used to treat acute lymphoblastic leukemia, and ADAGEN, a treatment for a form of severe combined immunodeficiency disease.

Enzon is a biopharmaceutical company developing and commercializing enhanced therapeutics for life-threatening diseases through the application of its proprietary technologies, PEG Modification or PEG and Single-Chain Antibody (SCA®) technology. Enzon's research activities are focused on applying its technologies to enhance performance of compounds with known therapeutic efficacy. In addition to two FDA approved products, Enzon has several products in various stages of clinical development by itself and with its partners. Enzon develops and markets products on its own and through its alliance partners, which in addition to Schering-Plough include Alexion Pharmaceuticals, Baxter Healthcare, Bristol-Myers Squibb, Eli Lilly, and Aventis S.A.

Contact:
Kenneth J. Zuerblis, Vice President, Finance and Chief Financial Officer
732-980-4717

Noonan/Russo Communications, Inc.
212-696-4455
Lisa Fern, Media Relations x353
Matthew Knight, Media Relations x271

Certain statements made in this press release related to patent litigations, potential government approvals, market potential, commercialization and sales revenues of medical products and biologics, as well as their therapeutic applications and outcomes, are forward-looking and are made pursuant to the safe harbor provisions of the Securities Litigation Reform Act of 1995. Such statements involve risks and uncertainties, and the ultimate outcome of the matters described in these statements may differ materially from those set forth in these statements. In addition, the economic, competitive, governmental, technological and other factors identified in the Company's filings with the Securities and Exchange Commission could affect such results.