Medarex Announces New Primate Data on Anthrax Monoclonal Antibody

Medarex has announced that Valortim, a fully human monoclonal antibody product candidate being developed for the prevention and treatment of anthrax infection, has been shown to have a therapeutic effect in a new primate model of established inhalation anthrax infection.

The new model, which is being developed at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), seeks to improve on existing therapeutic models for anthrax by closely monitoring the disease process to establish the presence of anthrax bacteremia -- bacteria in the bloodstream -- and determine the optimal window for therapeutic intervention. In addition, the new model uses the African green monkey, which, based on research data, USAMRIID believes follows a similar disease course as is expected in humans exposed to aerosolized Bacillus anthracis spores. This new animal model has not yet been validated under the FDA Animal Effectiveness Rule, Medarex said.

In the pilot study conducted at USAMRIID, adult African Green monkeys were exposed to aerosolized anthrax spores, and blood samples were collected at regular intervals beginning at 24 hours postexposure. The samples were closely monitored for evidence of bacteremia both by culture and by use of a rapid assay designed to detect protective antigen. Protective antigen is one of the toxins produced by B. anthracis, and its presence in the blood is being evaluated as a surrogate marker for symptomatic anthrax disease. Once bacteremia was detected by the rapid assay, animals were administered either Valortim or placebo by intravenous injection. In the study, 50 percent of the Valortim-treated animals survived compared with none of the placebo-treated animals.

Valortim is designed to target a protein component known as the anthrax protective antigen 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, according to Medarex.