Bioenvision Completes New Drug Application for Clofarabine.

Business Editors/Health/Medical Writers

EDINBURGH, Scotland--(BUSINESS WIRE)--April 2, 2004

Bioenvision, Inc. (AMEX:BIV) has announced the completion of a New Drug Application (NDA) to the U.S. Food and Drug Administration (FDA) for clofarabine for the treatment of refractory or relapsed acute leukaemia in children.

Bioenvision's North American development partner, ILEX Oncology, Inc. (Nasdaq:ILXO), submitted the first part of the "rolling" NDA in October 2003, after clofarabine was granted fast-track designation in refractory and relapsed paediatric leukaemia. The completed NDA package has been submitted by ILEX to the FDA on schedule.

The filing was based on data from two pivotal Phase II trials in acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML) which will be presented at the 40th American Society of Clinical Oncology annual meeting in June.

"The completion of this filing is a major milestone in the development and progression of a vital leukaemia treatment through the regulatory process," said Dr. Christopher B. Wood, Chairman and CEO of Bioenvision. "Clofarabine continues to deliver strong results in clinical trials involving children with very poor prognosis, and no remaining therapeutic options, and stands to represent an important future tool for physicians to manage the disease.

Commenting on the research that formed the basis of the filing, Sima Jeha, MD, Director, Developmental Therapeutics, Division of Leukemia/Lymphoma, St. Jude Children's Research Hospital, Memphis, and lead clofarabine investigator said: "In the clofarabine clinical trials, I have been able to offer hope to many children with very limited time left and no remaining therapeutic options. Pediatric patients and their families usually have to wait a long time before a novel treatment option is available to them and I'm encouraged to be part of an effort that has made children a priority in the oncology arena."

Bioenvision is currently conducting further clinical studies with clofarabine throughout Europe, in refractory/relapsed paediatric acute leukaemia and in adult acute myeloid leukaemia.

Bioenvision holds worldwide rights to clofarabine outside of North America. The FDA previously granted clofarabine an orphan drug designation for the treatment of adult and paediatric ALL and AML. In the U.S., orphan drug status guarantees seven years of market exclusivity following the FDA's marketing approval. In Europe, clofarabine was granted an 'Orphan Medicinal Product' designation by the European Agency for the Evaluation of Medicinal Products (EMEA) as a treatment for ALL and AML. Obtaining this designation provides European marketing exclusivity for 10 years.

About Clofarabine

Bioenvision, Inc. granted ILEX Oncology, Inc. (Nasdaq:ILXO) the right to develop clofarabine in the United States and Canada. Bioenvision is entitled to milestone payments tied to the development of the compound and is entitled to royalties on North American sales. Bioenvision is developing clofarabine exclusively in the rest of the world. Bioenvision originally obtained clofarabine development and commercialization rights under patents held by Southern Research Institute.

Clofarabine is a second-generation purine nucleoside analogue. Nucleoside analogues are antimetabolites that affect DNA synthesis. Clofarabine was rationally designed to combine many of the favorable properties of the two most commonly used nucleoside analogs, fludarabine and cladribine, but is reported to have greater potency at damaging the DNA of Leukemia cells than these other agents. (Blood, "Mitochondrial Toxicity of Deoxyadenoside Analogs", November 15, 2000, Volume 96, Number 10). In a single center Phase II study of clofarabine in adult patients with refractory AML, 42% of the patients had a complete response rate (CR) and a further 13% had a partial response (CRp).

About Bioenvision

Bioenvision's (Amex:BIV) primary focus is the development and distribution of compounds and technologies for the treatment of cancer. Bioenvision has a broad pipeline of products for the treatment of cancer, including: clofarabine (in co-development with ILEX Oncology, Inc.), Modrenal(R) (for which Bioenvision has obtained regulatory approval for marketing in the United Kingdom for the treatment of post-menopausal breast cancer following relapse to initial hormone therapy), and other products in clinical trials. Bioenvision is also developing anti-infective technologies, including the OLIGON technology; an advanced biomaterial that has been incorporated into various FDA approved medical devices. For more information on Bioenvision please visit our Web site at www.bioenvision.com.

About ILEX

Founded in 1994 as an oncology drug development company, ILEX is strategically positioned to become a product-driven biopharmaceutical company, focused primarily in oncology. ILEX has a marketed product, CAMPATH(R) in the United States and MABCAMPATH(R) in the European Union, and is advancing an innovative and diversified pipeline of compounds focused on the treatment of cancer. The ILEX pipeline comprises product candidates at various stages of clinical development, including cytotoxic and cytostatic agents with novel mechanisms of action, monoclonal antibodies, angiogenesis inhibitors and signal transduction inhibitors. ILEX maintains a core competency in oncology drug development, with locations in San Antonio, Texas, and Guildford, England. ILEX also conducts research in angiogenesis inhibition, cell signaling, medicinal chemistry and nuclear receptor biology at its laboratories in Boston, Mass., and Geneva, Switzerland. In February 2004, ILEX announced its agreement to merge with Genzyme Corporation, a global biotechnology company. The merger, subject to ILEX stockholder approval and other customary conditions, is expected to close in mid-2004.

Certain statements contained herein are "forward-looking" statements (as such term is defined in the Private Securities Litigation Reform Act of 1995). Because these statements include risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Specifically, factors that could cause actual results to differ materially from those expressed or implied by such forward-looking statements include, but are not limited to: risks associated with preclinical and clinical developments in the biopharmaceutical industry in general and in Bioenvision's compounds under development in particular; the potential failure of Bioenvision's compounds under development to prove safe and effective for treatment of disease; uncertainties inherent in the early stage of Bioenvision's compounds under development; failure to successfully implement or complete clinical trials; failure to receive marketing clearance from regulatory agencies for our compounds under development; acquisitions, divestitures, mergers, licenses or strategic initiatives that change Bioenvision's business, structure or projections; the development of competing products; uncertainties related to Bioenvision's dependence on third parties and partners; and those risks described in Bioenvision's filings with the SEC. Bioenvision disclaims any obligation to update these forward-looking statements.