ENZON/INEX SIGN COMMERCIALIZATION PACT FOR ONCOLOGY DRUG ONCO TCS.

Enzon Pharmaceuticals, Inc. (NASDAQ: ENZN) and Inex Pharmaceuticals Corporation (TSX: IEX) have formed a strategic partnership to develop and commercialize INEX's proprietary oncology product Onco TCS.

Under the terms of the agreement, Enzon receives the exclusive North American commercialization rights for Onco TCS for all indications. The lead indication is relapsed aggressive non-Hodgkin's lymphoma (NHL) for which INEX is in the process of submitting a "rolling" New Drug Application (NDA) to the United States Food and Drug Administration (FDA), which is expected to be completed during the first quarter of calendar year 2004.

The product is also in numerous phase II clinical trials for several other cancer indications, including first-line NHL. INEX receives a US$12 million up-front payment and will receive up to a US$20 million payment upon Onco TCS receiving approval from the FDA. Additional development milestones and sales based bonus payments could total US$43.75 million, of which US$10 million is payable upon annual sales first reaching US$125 million and US$15 million is payable upon annual sales first reaching US$250 million.

INEX will also receive a percentage of commercial sales of Onco TCS and this percentage will increase as sales reach certain predetermined thresholds. INEX has the option of complementing Enzon's sales efforts by co-promoting Onco TCS through the formation of a dedicated North American sales and medical science liaison force. The costs of building INEX's co-promotion force would be shared equally by both companies and Enzon will record all sales in the licensed territories.

Arthur Higgins, Enzon's chairman and chief executive officer, said, "This transaction is highly complementary to our R&D and manufacturing infrastructure, is an excellent fit with the therapeutic focus of our field force and most importantly, offers the potential to significantly increase Enzon's product revenues beginning as soon as fiscal 2005."

David Main, INEX's president and chief executive officer, said the agreement meets INEX's objectives for a commercialization partnership. "It rewards our company for successfully taking Onco TCS through clinical trials and through to an NDA, it gives us a strong partner dedicated to oncology with which to share costs of commercializing Onco TCS and expanding its potential uses. It also lets us benefit from future sales with a formula for capturing an increasing share of commercial sales."

"Enzon has expertise in the development, manufacturing and marketing of liposomal drugs and has the motivation to make Onco TCS sales an important part of its future," Main said. "This deal also provides a cost-effective means for us to build our own commercial infrastructure to work alongside Enzon's, which is important for our future growth strategy and pipeline activities."

Enzon and INEX will share equally the future development costs designed to obtain and maintain marketing approvals in North America for Onco TCS, while Enzon will pay all sales and marketing costs and certain other post-approval clinical development costs typically associated with commercialization activities. Enzon plans to market Onco TCS through its entire North American sales force of approximately 60 people, which currently markets ABELCET, ONCASPAR, and DEPOCYT to the oncology market.

INEX retains manufacturing rights and will initially manufacture and supply the drug and be reimbursed by Enzon. INEX and Enzon are discussing the potential of transferring manufacturing to Enzon's sterile injectable manufacturing facility in Indianapolis, Indiana where Enzon manufacturers its commercial drug ABELCET (Amphotericin B Lipid Complex Injection) and where MYOCET (liposome encapsulated doxorubicin citrate complex) is manufactured for Elan Corporation, plc.

The companies will also explore the acquisition and joint development of other cancer drugs.

About Onco

TCS Onco TCS is a proprietary drug comprised of the widely used off-patent cancer drug vincristine encapsulated in INEX's TCS (liposomal) drug delivery technology. The TCS technology provides prolonged blood circulation, tumor accumulation and extended drug release at the cancer site. These characteristics are designed to increase the effectiveness and reduce the side effects of the encapsulated drug. INEX has completed a pivotal phase II/III clinical trial treating relapsed aggressive NHL with Onco TCS. Currently, there is no effective treatment for patients with aggressive NHL that have relapsed following first-line and second-line treatment.

INEX's multi-center pivotal phase II/III trial treated 119 NHL patients who had not responded to their previous therapy or had responded and subsequently relapsed. After treatment with Onco TCS, an overall response rate of 25% was attained. The results of this pivotal trial were released in June 2003 and presented in December 2003 at the American Society of Hematology annual conference along with interim results from two ongoing phase II trials in relapsed Hodgkin's disease and relapsed B-cell lymphoma.

INEX has submitted two major sections of its "rolling" NDA to the FDA seeking marketing approval for Onco TCS as a treatment for relapsed aggressive NHL. The first section was submitted September 30, 2003 and included nonclinical, safety and pharmacology data. The second section was submitted December 3, 2003 and included data on manufacturing process, stability of the drug, composition of the drug and other chemistry and related information. INEX expects the third and final section, containing data from clinical trials, to be submitted during the first quarter of calendar year 2004.

A "rolling" NDA is a process used by the FDA to expedite the review of a drug intended for the treatment of a serious or life threatening condition and that demonstrates the potential to address an unmet medical need. This allows the FDA to begin to review sections of the NDA as they are submitted, as opposed to the normal approval process, which requires the entire NDA to be submitted at one time. In order to be eligible to submit a rolling NDA, a company will usually have been granted Fast Track designation by the FDA, which INEX received in August 2000.

Subject to acceptance of the full NDA for review, INEX expects to have a response from the FDA within six months. If approved, it is anticipated that Onco TCS could be introduced to the marketplace before the end of calendar year 2004 or early in 2005.

Although INEX has chosen to file an NDA for relapsed aggressive NHL as the first route to approval for Onco TCS, Enzon and INEX intend to develop Onco TCS for use as a stand-alone drug and/or in combination therapy for several cancers in which vincristine is now used. Onco TCS is being evaluated in several phase II clinical trials as a treatment for first-line NHL, relapsed small cell lung cancer, relapsed Hodgkin's disease, relapsed acute lymphoblastic leukemia, relapsed pediatric malignancies, relapsed NHL in combination with the approved cancer drug Rituxan (rituximab), and relapsed NHL in combination with the approved cancer drug etoposide.

About Non-Hodgkin's Lymphoma (NHL)

NHL is the fifth-leading cause of cancer deaths in the United States (23,400 estimated in 2003) and the sixth-leading cause of cancer deaths in Canada (2,800 estimated in 2003), according to estimates of the American Cancer Society and the Canadian Cancer Society. Approximately 53,400 and 6,400 new cases were diagnosed in the U.S. and Canada respectively in 2003.

NEX entered into the partnership with Enzon through agreements entered into by its wholly owned U.S. subsidiary, Inex Pharmaceuticals, Inc.

About Enzon

Enzon Pharmaceuticals is a biopharmaceutical company dedicated to the discovery, development and commercialization of therapeutics to treat life-threatening diseases. The company has developed or acquired a number of marketed products, including PEG-INTRON, marketed by Schering-Plough, and ABELCET, ONCASPAR, ADAGEN, and DEPOCYT, which are all marketed in North America by Enzon's hospital and oncology sales forces. Enzon's science-focused strategy includes an extensive drug development program that leverages the company's macromolecular engineering technology platforms, including PEG modification and single-chain antibody (SCA) technologies. Internal research and development efforts are complemented by strategic transactions that provide access to additional products, projects, and technologies. Enzon has several drug candidates in various stages of development, independently and with partners.

For more information, call 908/541-8678.