Enzon Acquires Global Rights from Natimmune for Oncology Product

Oct 3, 2005

Bridgewater, NJ and Copenhagen, Denmark - October 3, 2005 - Enzon Pharmaceuticals, Inc. (Nasdaq: ENZN) and the Danish biotech company, NatImmune A/S today announced that they have entered into a license agreement for NatImmune's lead development product, recombinant human Mannan-Binding Lectin (rhMBL), a protein therapeutic being developed for the prevention of severe infections in MBL-deficient individuals undergoing chemotherapy. Under the agreement, Enzon receives exclusive worldwide rights, excluding the Nordic countries, and is responsible for the development, manufacture, and marketing of rhMBL. NatImmune will receive an upfront payment of $10 million and is eligible to receive additional payments upon the successful completion of certain clinical development, regulatory, and sales-based milestones. NatImmune is also eligible to receive royalties from any future product sales of rhMBL by Enzon and retains certain rights to develop a non-systemic formulation for topical administration of MBL.

Mannan-Binding Lectin (MBL) is a naturally occurring human plasma protein that plays a key role in the immune system's first-line defense against infections. MBL binds to a wide range of invading organisms, including bacteria, fungi, viruses, and parasites and activates the lectin pathway of the complement system, an important defense mechanism of the immune system.

Numerous studies have found a strong correlation between MBL-deficiency and an increased susceptibility to infections in patients with a suppressed immune system, such as cancer patients undergoing treatment with chemotherapy. In addition, a number of publications have also highlighted the potentially important future role of MBL replacement therapy in preventing serious infections in other critical care areas associated with immunodeficiency.

"Today's announcement underscores our commitment to rebuilding our clinical pipeline with promising product development opportunities," said Jeffrey H. Buchalter, Enzon's chairman and chief executive officer. "Given the vital role MBL plays in the immune system, this compound represents an exciting opportunity for us to bring a substantial clinical advantage to patients who are susceptible to serious infections."

"We believe Enzon's extensive experience in developing and commercializing therapeutics for patients with cancer and other immunodeficiency disorders makes them an ideal partner to advance this high-potential therapeutic," said Dr. Martin Bonde NatImmune's chief executive officer. "Further, we will also work together to leverage Enzon's long-standing skills in developing optimized versions of protein-based therapeutics through PEGylation to potentially explore a next-generation compound."

In December 2004, NatImmune completed Phase 1 clinical trials that evaluated the safety and pharmacokinetic profile of single and multi dose intravenous administration of rhMBL in 28 MBL-deficient volunteers. Results from the Phase 1 trials demonstrated that rhMBL replacement therapy is safe and has an attractive pharmacokinetic profile. NatImmune has also completed a prospective correlation study of 250 hematological cancer patients that documented MBL-deficient patients have a significantly higher risk of severe infections following chemotherapy compared to patients with sufficient MBL levels. These results confirmed previous clinical correlation studies published in the Lancet in August 2001.

About Enzon

Enzon Pharmaceuticals, Inc. is a biopharmaceutical company dedicated to the development and commercialization of therapeutics to treat patients with cancer and other life-threatening diseases. Enzon's specialized sales force markets ABELCET®, ONCASPAR®, ADAGEN®, and DEPOCYT® in North America. In addition, Enzon also receives royalties on sales of PEG-INTRON®, marketed by Schering-Plough Corporation, and MACUGEN®, marketed by Eyetech Pharmaceuticals and Pfizer Inc. Enzon's product-driven strategy includes an extensive drug development program that leverages its proprietary technologies, including a next-generation PEGylation platform that utilizes linkers designed to release compounds at a controlled rate. Enzon complements its internal research and development efforts with strategic initiatives, such as partnerships designed to broaden its revenue base or provide access to promising new technologies or product development opportunities. Further information about Enzon and this press release can be found on the Company's web site at www.enzon.com.

About NatImmune

NatImmune A/S is a biotech company focused on the development of therapeutic proteins. Based in Symbion Science Park, the Company was founded in 2000 and has 22 employees. NatImmune's lead product, Mannan Binding Lectin (MBL), has completed Phase 1 clinical trials and is being developed under a global licensing agreement with the U.S. biopharmaceutical company, Enzon Pharmaceuticals, Inc. NatImmune has retained certain rights to develop a non-systemic formulation for the topical administration of MBL. In addition, the Company's pipeline also includes antibodies for the treatment of colorectal cancer (COU-I) and cardiovascular diseases (MASP-2). Further information about NatImmune can be found at the Company's web site at www.natimmune.com.

There are forward-looking statements contained herein that are not based on historical fact, including without limitation statements containing the words "believes," "may," "plans," "will," "estimate," "continue," "anticipates," "intends," "expects," and similar expressions. Such forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause actual results, events or developments to be materially different from the future results, events or developments discussed above. Such factors include, but are not limited to the timing of, success, and cost of clinical studies; the ability to obtain regulatory approval of products; and those described in Enzon's Form 10-K and Forms 10-Q on file with the United States Securities and Exchange Commission and NatImmune's publicly filed reports. These factors should be considered carefully and readers are cautioned not to place undue reliance on such forward-looking statements. All information in this press release is as of October 3, 2005 and Enzon and NatImmune undertake no duty to update this information.

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Contact:
Susan Mesco
Director, Investor Relations
908-541-8777