PRNewswire - March 18, 2002

"PRO 542 showed important reductions in viral load in those patients who were most in need of new treatment options," said Jeffrey M. Jacobson, M.D., Director, AIDS Center, Mount Sinai School of Medicine, New York City and Principal Investigator of the PRO 542 study in adults. "Conventional therapy is unable to control HIV long-term due to mutation of the virus. All currently available HIV drugs inhibit just two enzymes involved in viral replication after infection has occurred. PRO 542 is a viral-entry inhibitor which may provide clinical advantages over the current armamentarium. This novel antibody-like fusion protein is designed to work against all strains of HIV and to minimize the emergence of viral resistance. PRO 542 may prove particularly valuable for salvage therapy of patients failing conventional drug regimens."

In clinical studies, PRO 542 was well tolerated and produced statistically significant (p=0.007) acute reductions in viral load across all seven patients who received a single 25 mg/kg intravenous infusion of the drug. These findings extend previous studies of four intravenous doses ranging to 10 mg/kg. In addition, an analysis of data from 22 adults treated with single-dose PRO 542 in a Phase I/II study identified a subgroup of patients who were the most highly responsive to therapy. These patients were failing conventional therapies and had evidence of advanced disease as measured by low numbers of CD4 T cells (<200 cells/mm3) and/or high viral loads (>100,000 copies/mL) before treatment with PRO 542. CD4 T cells are key components of the immune system and the major targets of HIV infection. The viral load reductions in these patients ranged from 0.4 to 0.8 log(10) copies/mL, were dose-dependent, and were sustained for two to four weeks.

Viruses that are broadly resistant to currently available antiretroviral medications represent a growing challenge for HIV therapy. A study presented at the most recent Interscience Conference on Antimicrobial Agents and Chemotherapy reported that in the U.S. approximately 78% of HIV-infected individuals harbor virus that is resistant to one or more classes of antiretroviral agents, thus reducing their treatment options. An estimated one million Americans will be infected with HIV by the end of 2002.

"We have identified a group of patients who were not responding to currently available therapies but who did exhibit a significant antiviral response to PRO 542," said Robert J. Israel, M.D., Vice President of Medical Affairs at Progenics. "These findings are being incorporated into our Phase II clinical program. The Company is also developing subcutaneous and intramuscular formulations of PRO 542 that may afford simplified dosing regimens."

PRO 542 is an antibody-like molecule which is designed to neutralize HIV by directly binding to gp120, a protein on the surface of the virus, thereby preventing HIV attachment to healthy cells within the immune system. Whereas current antiretroviral medications are active only against virus that has already infected immune system cells, PRO 542 is designed to neutralize HIV before the virus can enter and infect cells. In previously reported Phase I/II studies in HIV-infected patients, intravenously administered PRO 542 mediated dose-dependent and statistically significant reductions in plasma HIV RNA, a measure of HIV viral load. PRO 542 is currently in Phase II clinical testing.

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 expertise in immunology and molecular biology to develop biopharmaceuticals to fight viral diseases, such as human immunodeficiency virus (HIV) infection, and cancers, including malignant melanoma and prostate cancer. The Company is conducting Phase II clinical studies with methylnaltrexone, a compound designed to block the debilitating side effects of opioid 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.

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 on Progenics is available at http://www.progenics.com

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