PRNewswire - December 11, 2000

The development programs for PRO 542 and PRO 140 were described in an invited talk delivered by William C. Olson, Ph.D., Senior Director of Research and Development at Progenics. Included in the presentation were new findings on the sequence of molecular events that enable PRO 542, PRO 140 and certain other entry inhibitors to produce significantly enhanced or "synergistic" antiviral activity when used in combination in vitro. These insights are being used to design optimized preclinical animal and clinical studies to explore the combination use of these agents. The Company also presented new preclinical results on PRO 140, which examined the binding of the agent to selected cells and molecules having known biological functions in man. The experiments demonstrated that PRO 140 had minimal cross-reactivity with these targets, suggesting that it does not interfere with normal biological functions and may be well tolerated when tested in man.

"We are pleased to share our discoveries relating to viral entry and the progress we have made in the development of PRO 542 and PRO 140, with this distinguished group of academic, clinical and pharmaceutical researchers," said Dr. Olson. "Like the other participants in this conference, we believe that entry inhibitors are an exciting new class of anti-HIV therapeutics which may represent the next major advance in the treatment of HIV infection."

PRO 542 is a hybrid protein that incorporates the HIV binding region of CD4 into a human antibody-like molecule. PRO 542 directly neutralizes HIV by preventing the attachment of the viral surface glycoprotein gp120 to CD4, the primary cellular receptor for the virus. PRO 542 is currently in Phase II clinical testing. In single dose studies in HIV-infected adults, PRO 542 mediated dose-dependent reductions in plasma HIV RNA, a measure of HIV "viral load." In patients receiving the highest dose, statistically significant decreases in HIV RNA were observed, and infectious virus in plasma was reduced to undetectable levels for prolonged periods. In a separate study in HIV-infected children, all six subjects treated with weekly doses of PRO 542 experienced viral load decreases ranging to 30-fold. Three of six patients showed sustained reductions in viral loads that persisted for as long as 14 days post-treatment. There have been no serious drug-related adverse events reported in any of the trials. Progenics has a collaboration with Genzyme Transgenics Corporation (Framingham, MA) to develop transgenic animals for cost-effective production of PRO 542.

PRO 140 is a monoclonal antibody against CCR5, a co-receptor required for HIV entry. PRO 140 broadly and potently blocks HIV infection at concentrations that do not affect CCR5's normal function. It has been shown that HIV-infected individuals who express a defective CCR5 gene experience a milder, slower course of disease, providing clinical proof-of-concept for CCR5-directed therapies. Progenics has a collaboration with Protein Design Labs (Fremont, CA) to develop a humanized PRO 140 antibody.

The entry inhibitor category includes attachment inhibitors, co-receptor inhibitors, and fusion inhibitors. PRO 542 and PRO 140 are attachment and co-receptor inhibitors, respectively. T-20 is a fusion inhibitor being developed by Trimeris, Inc. and F. Hoffmann-La Roche Ltd. Progenics recently reported that the triple combination of PRO 542, PRO 140 and T-20 demonstrated significantly enhanced or synergistic activity in blocking HIV entry into cells.

Progenics Pharmaceuticals, Inc. is a biopharmaceutical company focusing on the development and commercialization of products for the treatment and prevention of cancer, viral, and other life-threatening diseases. The Company's lead HIV product, PRO 542, has completed two Phase I/II clinical trials, and two follow-on HIV products, PRO 367 and PRO 140, are preparing to commence Phase I/II trials. Progenics also has collaborations with F. Hoffmann-La Roche Ltd in the area of HIV fusion co-receptors, and with American Home Products and Pharmacopeia, Inc. focusing on HIV attachment and fusion. The Company's most advanced product, GMK, is a cancer vaccine in pivotal Phase III clinical trials for the treatment of malignant melanoma.

The Company is also prepared to commence Phase II trials with a second cancer vaccine, MGV, with broad application to a variety of cancers. GMK and MGV are the subject of a collaboration with Bristol-Myers Squibb Company. The Company, with Cytogen Corporation, has formed a joint venture focusing on the development of cancer immunotherapies based on PSMA (Prostate Specific Membrane Antigen) technology. The Company is also developing a novel small-molecule antioxidant, DHA, 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 Progenics uses the words "anticipates," "plans," "expects" and similar expressions, the Company is identifying forward-looking statements. Such forward-looking statements involve risks and uncertainties which may cause Progenics' 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 appeared 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 Progenics' Annual Report on Form 10-K for the fiscal year ended December 31, 1999 and other periodic filings with the Securities and Exchange Commission. In particular, Progenics cannot assure you that any of the Company's programs will result in a commercial product. Progenics 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.

Additional information on Progenics is available at http://www.progenics.com This release is available on the Internet at http://www.noonanrusso.com

Contact: Ronald J. Prentki, President of Progenics Pharmaceuticals, Inc., 914-789-2800, rprentki@progenics.com; or Renee Connolly, Media, of Noonan/Russo Communications, Inc., 212-696-4455, ext. 227, renee@noonanrusso.com, for Progenics Pharmaceuticals, Inc.

SOURCE Progenics Pharmaceuticals, Inc. Web Site: http://www.noonanrusso.com http://www.progenics.com

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