Enzon Initiates Phase I Clinical Trial for PEG-paclitaxel.

Business/Health & Technology Editors

PISCATAWAY, N.J.--(BUSINESS WIRE)--May 7, 2001

Enzon, Inc. (NASDAQ: ENZN) announced today the initiation of patient dosing in a Phase I clinical trial for PEG-paclitaxel.

The trial is designed to determine the safety, tolerability, and pharmacology of PEG-paclitaxel in patients with advanced solid tumors and lymphomas. Up to 40 patients will be enrolled in this study.

PEG-paclitaxel is a PEG modified version of paclitaxel formulated for ease of administration. Preclinical animal studies have demonstrated that PEG-paclitaxel can be dosed at higher levels than TAXOL(R) (paclitaxel), a leading cancer drug. The ability to dose PEG-paclitaxel at higher levels may allow increased efficacy when compared to TAXOL.

TAXOL is a powerful chemotherapeutic agent with delivery limitations. It is used to treat various types of cancers, including ovarian, breast, non-small cell lung, and AIDS-related Kaposi's sarcoma. In 2000, sales of TAXOL were reported to be approximately $1.6 billion.

Using Enzon's proprietary PEG technology, scientists at Enzon have modified paclitaxel through the chemical attachment of PEG using a linker designed to deteriorate over time, giving PEG-paclitaxel prodrug attributes. PEG-paclitaxel was designed to be delivered without the need for solubilizing agents or premedications. TAXOL, a commercial formulation of paclitaxel, contains the solubilizing agent CREMOPHOR(R) and patients are required to take premedications prior to treatment to reduce the potential for adverse reactions, which may be caused by CREMOPHOR.

To date, Enzon's PEG technology has been used to create three approved protein therapeutics, including PEG-INTRON(TM), currently marketed by Schering-Plough for the treatment of hepatitis C.PEG-paclitaxel is the second application of Enzon's PEG technology to deliver small organic chemical molecules. PROTHECAN(R), a PEG modified version of the topoisomerase inhibitor camptothecin, is currently in two Phase I clinical trials. PROTHECAN is expected to commence Phase II clinical trials in the near future.

Enzon is a biopharmaceutical company developing advanced therapeutics for life-threatening diseases through the application of its proprietary drug delivery and targeting technologies, PEG Modification, Pro Drug/Transport technology and Single-Chain Antigen-Binding (SCA(R)) protein technology. Three products are currently marketed which utilize Enzon's technology: PEG-INTRON marketed by Schering-Plough for hepatitis C, ONCASPAR(R) for Acute Lymphoblastic Leukemia (ALL), and ADAGEN(R) a treatment for a form of Severe Combined Immunodeficiency Disease (SCID), commonly known as the "Bubble Boy Disease." In addition to three approved products, Enzon has several products in various stages of clinical development by itself and with partners, including additional indications for PEG-INTRON with Schering-Plough. PEG-INTRON is in Phase III clinical trials conducted by Schering-Plough for the treatment of malignant melanoma and chronic myelogenous leukemia. Enzon develops and markets products on its own and through strategic alliances, which in addition to Schering-Plough Corporation, include Alexion Pharmaceuticals, Inc., Baxter Healthcare Corporation, Bristol-Myers Squibb Company, Eli Lilly & Company, and Aventis.

Except for the historical information herein, the matters discussed in this news release include forward-looking statements that may involve a number of risks and uncertainties. Actual results may vary significantly based upon a number of factors which are described in the Company's Form 10-K/A, Form 10-Q's and Form 8-Ks on file with the SEC, including without limitation, risks in obtaining and maintaining regulatory approval for indications and expanded indications, market acceptance of and continuing demand for Enzon's products and the impact of competitive products and pricing.

This release is also available at www.enzon.com