PRNewswire - December 18, 2001

"PRO 140 was highly effective in controlling HIV replication in vivo. Viral levels within the blood became undetectable in all animals treated, and the rate of virus reduction was dose-dependent," said William C. Olson, Ph.D., Progenics' Vice President of Research and Development and lead author of the presentation. "In animals receiving multiple doses of PRO 140, HIV was kept at bay for approximately one month, with no evidence of emergence of viral resistance. These results strengthen our earlier in vitro findings that resistance to PRO 140 does not develop rapidly."

In a separate session, John P. Moore, Ph.D., Professor of Microbiology and Immunology at Weill Medical College of Cornell University, reviewed the latest research on HIV entry inhibitors, including Progenics' PRO 542 and PRO 140, in a plenary lecture entitled HIV-1 Entry into Cells: A Target for Antivirals, Vaccines and Vaginal Microbicides. "HIV infection is a multi-step process that affords various promising targets for therapy, including viral entry," said Dr. Moore. "An emerging body of evidence indicates that entry inhibitors may play an important role in HIV therapy, especially in patients that are resistant to current antiretrovirals and in need of new therapeutic options."

Unlike existing AIDS drugs that work inside the cell and target viral enzymes involved in viral replication, PRO 542 and PRO 140 inhibit entry of HIV into host cells before the virus begins its replication process. For HIV to enter and infect human cells, it must interact sequentially with two receptors, CD4 and CCR5, normally present on the outer membrane of certain immune system cells. PRO 542 directly neutralizes HIV, thereby preventing the attachment of the virus to CD4. PRO 140 is a monoclonal antibody that binds to CCR5 and blocks HIV entry while having no apparent effect on the normal function of CCR5.

While HIV normally infects only humans, scientists at the Scripps Research Institute in San Diego used SCID mice to model human viral infection. SCID (severe combined immunodeficiency) mice lack an immune system; therefore, when researchers transplanted human immune system cells into the mice, the cells proliferated and were not rejected. The mice were then exposed to HIV directly isolated from infected patients. The virus was able to infect the human cells within the mice, to replicate, and to reach steady state concentrations ranging to nearly 30,000 copies/ml in the blood. When the mice were treated with PRO 140, viral concentrations decreased more than 70-fold to undetectable levels (<400 copies/ml, the lower limit of detection for the assay). Infected mice given a control antibody maintained uniformly high HIV concentrations.

Progenics has a development and license agreement with Protein Design Labs, Inc. to develop a humanized version of PRO 140 that retains the antibody's antiviral activity but which is less immunogenic and therefore may be better tolerated for prolonged use in patients.

Progenics Pharmaceuticals, Inc. of Tarrytown, NY, is a biopharmaceutical company focusing on the development and commercialization of innovative therapeutic products to treat the unmet medical needs of patients with debilitating conditions and life-threatening diseases. The Company applies its immunological expertise to develop biopharmaceuticals to fight viral diseases, such as human immunodeficiency virus (HIV) infections, and cancers, including malignant melanoma and prostate cancer. The Company is preparing to initiate Phase IIb clinical studies with methylnaltrexone, a compound designed to block the debilitating side effects of opioid-based analgesics without interfering with pain palliation. The Company has initiated Phase II clinical trials with its lead HIV product, PRO 542, a viral-entry inhibitor and is in preclinical development with PRO 140 and other follow-on product candidates in HIV infection. Progenics' most clinically advanced product, GMK, is a cancer vaccine in Phase III clinical trials for the treatment of malignant melanoma. MGV, a therapeutic vaccine for multiple cancers is also in clinical development. The Company is developing cancer immuno therapies based on PSMA (prostate specific membrane antigen) technology. Dehydro ascorbic acid (DHA), a novel small-molecule antioxidant, is the subject of preclinical studies to treat stroke and other disorders.

This press release contains forward-looking statements. Any statements contained herein that are not statements of historical fact may be forward-looking statements. When the Company uses the words "anticipates," "plans," "expects" and similar expressions, they are identifying forward-looking statements. Such forward-looking statements involve risks and uncertainties, which may cause the Company's actual results, performance or achievements to be materially different from those expressed or implied by forward-looking statements. Such factors include, among others, the uncertainties associated with product development, the risk that clinical trials will not commence when or proceed as planned, the risks and uncertainties associated with dependence upon the actions of the Company's corporate, academic and other collaborators and of government regulatory agencies, the risk that products that appear promising in early clinical trials do not demonstrate efficacy in larger-scale clinical trials, the uncertainty of future profitability and other factors set forth more fully in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2000 and other periodic filings with the Securities and Exchange Commission to which investors are referred for further information. In particular, the Company cannot assure you that any of the their programs will result in a commercial product. The Company does not have a policy of updating or revising forward-looking statements, and thus it should not be assumed that the Company's silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements.

Editor's Note: Additional information is available at http://www.progenics.com

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