Medarex And PharmAthene Announce New Therapeutic Data for Anthrax Anti-Toxin, Valortim

- Data Presentation at 48th ICAAC / IDSA 46th Annual Meeting -

PRINCETON, N.J. and ANNAPOLIS, Md., October 28, 2008 /PRNewswire-FirstCall/ -- Medarex, Inc. , a leading monoclonal antibody company, and PharmAthene, Inc. , a biodefense company developing medical countermeasures against biological and chemical threats, today announced results from a pilot study showing that the anthrax anti-toxin, Valortim(R) (MDX-1303), enhanced survival as compared to a control group in a therapeutic animal model known as the New Zealand White (NZW) rabbit model. Valortim is a fully human monoclonal antibody generated by Medarex's UltiMAb(R) technology that is being co-developed by the two companies for potential use as an anti- toxin therapeutic to prevent and treat inhalation anthrax.

The data were presented in an oral presentation entitled "Therapeutic Efficacy of MDX-1303, an Anti-toxin Monoclonal Antibody, for Inhalation Anthrax in the New Zealand White (NZW) Rabbit Model" at the 48th ICAAC/ IDSA 46th Annual Meeting by Israel Lowy, M.D., Ph.D., Senior Director of Clinical Science and Infectious Diseases at Medarex.

David P. Wright, President & Chief Executive Officer of PharmAthene, commented, "Mounting evidence from a number of animal studies suggests that Valortim may be efficacious as both a prophylactic and therapeutic for inhalation anthrax infection. Based on these results, we believe that Valortim is ideally positioned for procurement consideration in the Strategic National Stockpile, and we look forward to working collaboratively with the Department of Health and Human Services to fulfill a critical need in the Nation's arsenal to combat the threat of anthrax."

"We are pleased to have been able to refine this model for therapeutic intervention in anthrax infection, further defining the potential efficacy of Valortim in anthrax disease," commented Dr. Lowy. "Animal modeling for therapeutic intervention in anthrax infection (in contrast to post-exposure prophylaxis) has been challenging because of the variability in onset time to disease after exposure and the rapidity of disease progression once symptoms are manifest. We used a rapid approach to identify animals with active disease, and our results showed that the animals designated for treatment proved to have bacteria circulating in their blood, supporting the accuracy of the approach and that Valortim had impressive activity in this setting. This study, along with others being conducted by our partner PharmAthene, may help to define an optimal and reproducible approach to evaluate therapeutic agents for anthrax disease in general, as well as Valortim in particular."

Details of the study

The pilot study, funded by the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health (NIH), was designed to attempt to refine the New Zealand White (NZW) rabbit model as a predictive therapeutic model for anthrax inhalation disease, and to assess the efficacy of Valortim in this model. In the study, 32 adult NZW rabbits were exposed by aerosol to Ames anthrax spores. Beginning 12 hours post-exposure, animals were evaluated hourly for changes in temperature, and every 6 hours blood samples were collected to assess bacteremia and protective antigen in blood. Samples were analyzed for protective antigen via a rapid electrochemiluminescent immunoassay (ECL), and bacteremia was evaluated by 24- hour culture. A significant increase in body temperature and/or a positive ECL were used to identify an active infection that required therapeutic intervention, and animals were then treated with either Valortim or saline (control).

In this study, 94 percent (30/32) of the animals were subsequently shown to be bacteremic at the time of treatment. Twelve of the NZW rabbits were treated with an intravenous (IV) 10 mg/kg dose of Valortim, 8 were treated with a 20 mg/kg IV dose of Valortim, and 12 were treated with IV saline in the control group. Study findings showed that 100 percent (8/8) of the 20 mg/kg Valortim-treated animals survived compared to 83 percent (10/12) in the 10 mg/kg Valortim-treated group and 8 percent (1/12) in the control group.

About Valortim

Valortim (MDX-1303) is a fully human monoclonal antibody designed to protect against and treat anthrax infection, including inhalation anthrax, the most lethal form of illness in humans caused by the Bacillus anthracis bacterium. The investigational antibody is designed to target a protein component known as the anthrax protective antigen (PA) of the lethal toxin complex produced by the bacterium. The anthrax protective antigen is believed to initiate the onset of the illness by attaching to cells in the infected person, and then is believed to facilitate the entry of additional destructive toxins into the cells. Valortim is designed to target anthrax protective antigen and protect the cells from damage by the anthrax toxins.

As previously presented, Valortim has been administered intravenously and intramuscularly to healthy human volunteers in a completed Phase 1 study, was well tolerated at doses as high as 20 mg/kg (IV), and was not immunogenic. Pharmacokinetic analysis suggested that doses as low as 1 mg/kg resulted in circulating levels of antibody after a month, with a similar potency for neutralizing anthrax toxin in vitro as was seen with serum obtained from subjects who had been vaccinated with anthrax vaccine.

Preclinical studies suggest that Valortim has the potential to provide significant protection against anthrax infection when administered prophylactically post-exposure (prior to the emergence of symptoms of anthrax infection) and also may increase survival when administered therapeutically (once symptoms become evident).

About Anthrax

According to the Centers for Disease Control and Prevention, anthrax is an acute infectious disease caused by the spore-forming bacterium Bacillus anthracis. Anthrax most commonly occurs in hoofed mammals and can also infect humans. Symptoms of disease vary depending on how the disease is contracted, but usually occur within seven days after exposure. The serious forms of human anthrax are inhalation anthrax, cutaneous anthrax, and intestinal anthrax. Initial symptoms of inhalation anthrax infection may resemble a common cold. After several days, the symptoms may progress to severe breathing problems and shock. Inhalation anthrax is often fatal, even if treated by antibiotics. Currently, antibiotics are the only drugs available for therapeutic or prophylactic use for inhalation anthrax, and post-exposure prophylaxis is the only FDA-approved indication for such products. However, antibiotic therapy, while useful, is believed to be associated with a number of limitations, including: (1) lack of activity against the toxins produced by the B. anthracis bacteria (2) need for long-term dosing to achieve full protection, complicated by side effects and non-compliance (3) lack of efficacy when administered late in the anthrax disease cycle, and (4) lack of effectiveness against multi-drug resistant or genetically engineered strains of anthrax.

About Medarex

Medarex is a biopharmaceutical company focused on the discovery, development and potential commercialization of fully human antibody-based therapeutics to treat life-threatening and debilitating diseases, including cancer, inflammation, autoimmune disorders and infectious diseases. Medarex applies its UltiMAb(R) technology and product development and clinical manufacturing experience to generate, support and potentially commercialize a broad range of fully human antibody product candidates for itself and its partners. Over forty of these therapeutic product candidates derived from Medarex technology are in human clinical testing or have had INDs submitted for such trials, with the most advanced product candidates currently in Phase 3 clinical trials or the subject of regulatory applications for marketing authorization. Medarex is committed to building value by developing a diverse pipeline of antibody products to address the world's unmet healthcare needs. For more information about Medarex, visit its website at www.medarex.com.

About PharmAthene, Inc.

PharmAthene was formed to meet the critical needs of the United States and its allies by developing and commercializing medical countermeasures against biological and chemical weapons. PharmAthene's lead product development programs include:

-- SparVax(TM) - a second generation recombinant protective antigen (rPA) anthrax vaccine

-- Third generation rPA anthrax vaccine

-- Valortim(R) - a fully human monoclonal antibody for the prevention and treatment of anthrax infection

-- Protexia(R) - a novel bioscavenger for the prevention and treatment of morbidity and mortality associated with exposure to chemical nerve agents

 

    -- RypVax(TM) - a recombinant dual antigen vaccine for plague


    For more information about PharmAthene, please visit www.PharmAthene.com.

Statement on Cautionary Factors for Medarex

Except for the historical information presented herein, matters discussed herein may constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to certain risks and uncertainties that could cause actual results to differ materially from any future results, performance or achievements expressed or implied by such statements. Statements that are not historical facts, including statements preceded by, followed by, or that include the words "potential"; "believe"; "suggest"; "may"; or similar statements are forward-looking statements. Medarex disclaims, however, any intent or obligation to update these forward-looking statements, except as required by law. Risks and uncertainties include risks associated with the reliability of animal modelling, unforeseen safety issues resulting from the handling of Bacillus anthracis, unforeseen safety issues resulting from the administration of Valortim(R) (MDX-1303) in human subjects, uncertainties related to product manufacturing as well as risks detailed from time to time in Medarex's public disclosure filings with the U.S. Securities and Exchange Commission (SEC), including its Annual Report on Form 10-K for the fiscal year ended December 31, 2007 and its quarterly reports on Form 10-Q. Copies of Medarex's public disclosure filings are available from its investor relations department.

Statement on Cautionary Factors for PharmAthene

Except for the historical information presented herein, matters discussed may constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to certain risks and uncertainties that could cause actual results to differ materially from any future results, performance or achievements expressed or implied by such statements. Statements that are not historical facts, including statements preceded by, followed by, or that include the words "potential"; "believe"; "anticipate"; "intend"; "plan"; "expect"; "estimate"; "could"; "may"; "should"; or similar statements are forward-looking statements. PharmAthene disclaims, however, any intent or obligation to update these forward-looking statements. Risks and uncertainties include risk associated with the reliability of the results of the studies relating to human safety and possible adverse effects resulting from the administration of the Company's product candidates, unexpected funding delays and/or reductions or elimination of U.S. government funding for one or more of the Company's development programs, the award of government contracts to our competitors, unforeseen safety issues, unexpected determinations that these product candidates prove not to be effective and/or capable of being marketed as products, as well as risks detailed from time to time in PharmAthene's Form 10-K under the caption "Risk Factors" and in its other reports filed with the U.S. Securities and Exchange Commission (the "SEC"). In particular, the study described above constitutes non-clinical animal studies. Significant additional non-clinical animal studies, human clinical trials, and manufacturing development work remain to be completed. At this point there can be no assurance that Valortim(R) will be shown to be safe and effective and approved by regulatory authorities for use in humans. Copies of PharmAthene's public disclosure filings are available from its investor relations department and our website under the investor relations tab at www.PharmAthene.com.

Medarex(R), the Medarex logo and UltiMAb(R) are registered trademarks of Medarex, Inc. All rights are reserved. Valortim(R) is a trademark of PharmAthene, Inc. All rights are reserved.

CONTACT: Laura S. Choi, Investor Relations, +1-609-430-2880, x2216, orNichol Ochsner, Corporate Communications (media), +1-609-430-2880, x2214,both of Medarex, Inc., or Stacey Jurchison, Director, CorporateCommunications of PharmAthene, Inc., +1-410-269-2610, Cell,+1-410-474-8200, jurchisons@pharmathene.com

Web site: http://www.medarex.com/http://www.PharmAthene.com/

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Ticker Symbol: (NASDAQ-NMS:MEDX),(NYSE:PIP)

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Posted: October 2008

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