PRNewswire - Aprl 9, 2001

In mice treated with PRO 140, initially high HIV concentrations became unde- tectable for up to nine days after a single dose of the experimental drug. PRO 140 is a monoclonal antibody that belongs to a new class of drugs designed to block HIV from entering and infecting cells, a therapeutic approach not exploited by currently approved HIV therapies. The scientific results were presented today at the 14th International Conference on Antiviral Research in Seattle.

"Today's findings represent an important first demonstration of the in vivo potency of PRO 140," said William C. Olson, Ph.D., Vice President of Research and Development at Progenics. "Future studies will explore the magnitude and duration of viral suppression attainable with multiple doses of PRO 140 used alone and in combination with other agents."

The Company believes that a large body of experimental evidence supports PRO 140 as a promising therapeutic candidate. In previous laboratory studies:

-- PRO 140 potently blocked each of 17 HIV isolates that are typical of those associated with person-to-person transmission of the virus and with the asymptomatic phase of infection.

-- PRO 140 was shown to be effective at protecting both primary T cells and macrophages, the immune system cells that are the major targets for HIV infection.

-- HIV did not develop resistance to PRO 140 despite continued exposure to the drug for 40 weeks, a period during which emergence of resistance is usually observed for other classes of anti-viral agents.

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 140 is designed to bind to a portion of the CCR5 receptor and block HIV entry while having no apparent effect on the normal function of CCR5.

While HIV normally infects only humans, investigators at the Scripps Research Institute 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 of more than 10,000 copies/ml in the blood. When the mice were treated with PRO 140, viral concentrations rapidly decreased more than 20-fold to undetectable levels (<400 copies/ml, the lower limit of detection for the assay) and remained undetectable for up to nine days. Infected mice given a control antibody maintained uniformly high HIV concentrations.

A single dose of PRO 140 was highly effective in reducing HIV viral loads in these animals," said Dennis R. Burton, Ph.D., Professor of Immunology at the Scripps Research Institute, La Jolla, CA, and one of the study's authors. Previously, Dr. Burton had used this mouse model of HIV infection to test other antibodies that effectively blocked HIV in vitro. "Interestingly, we found that PRO 140 was much more effective than other antibodies we've tested in this model. These findings highlight the promise of CCR5-targeting therapies in general and PRO 140 in particular," Burton added.

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 optimized for prolonged use in patients.

Progenics Pharmaceuticals, Inc., Tarrytown, NY, is a biopharmaceutical company focusing on the development and commercialization of products for the treatment and prevention of viral, cancer, and other 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, such as malignant melanoma and prostate cancer. The Company has initiated Phase II clinical trials of its lead HIV product, PRO 542, a viral-entry inhibitor. The Company is developing follow-on product candidates in HIV infection: PRO 367 has completed a Phase I study, PRO 140 is preparing to commence Phase I/II trials, and a lead therapeutic candidate has been selected from a novel class of anti-HIV compounds known as sulfated CCR5 peptides. The Company is also engaged in programs to discover and develop small-molecule HIV therapeutics that target the fusion co-receptors of the virus and other programs focusing on HIV attachment and fusion. The Company is developing cancer immunotherapies based on PSMA (prostate specific membrane antigen) technology. The Company's most clinically advanced product, GMK, is a cancer vaccine in a pivotal Phase III clinical trial for the treatment of malignant melanoma. Progenics is also prepared to commence Phase II trials with a second cancer vaccine, MGV, with broad application to a variety of cancers. The Company is also developing a novel small-molecule antioxidant, dehydroascorbic acid (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 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.

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

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