Human Genome Science Inc. said it is on track to deliver doses of its ABthrax, a monoclonal antibody for treating anthrax exposure next year, after the drug yielded positive results in two animal studies.

Results showed that a single dose of ABthrax (raxibacumab), administered without concomitant antibiotics, improved survival rates by up to 64 percent in animals that were symptomatic for anthrax disease as a result of inhalation exposure to massively lethal doses of anthrax spores. That survival benefit was seen in two animal species, as required for establishing bioterrorism drugs.

ABthrax is designed specifically to target anthrax toxins and is in development under a contract with the Biomedical Advance Research and Development Authority. The drug aims to treat the toxins produced by the anthrax bacteria - considered the cause of most anthrax-related deaths - rather than targeting the Bacillis anthracis bacteria. Currently marketed antibiotics can kill those bacteria, but they aren't able to tackle the toxins.

In one of the animal studies, three groups of monkeys were exposed by inhalation to anthrax spores and treated with ABthrax or placebo after they began showing clinical signs of anthrax disease. After 28 days, 64.3 percent of monkeys in the single high-dose ABthrax group survived and 50 percent in the low-dose ABthrax group survived, compared to none in the placebo group.

A separate study aimed at measuring the 14-day survival rate in rabbits also showed statistically significant survival benefit over placebo. All ABthrax-treated rabbits that survived in both studies were rapidly cleared of anthrax toxin and bacteria following intravenous administration of a single dose of the drug, while all the placebo-treated animals remained bacteremic or toxemic and died.

In June 2006, the federal government agreed to pay HGS $165 million under a contract to supply ABthrax to the Strategic National Stockpile. That order calls for 20,000 courses of the therapeutic, which must first receive licensure under an emergency use authorization, expected in 2008. To date, the company has met all of its milestones under that contract. (See BioWorld Today, June 21, 2006.)

The company also completed a second safety study of ABthrax in human volunteers, and results so far have indicated that the drug generally is safe and well tolerated. One more human trial is needed for licensure.

"We have manufactured conformance lots of ABthrax and are currently producing ABthrax for delivery to the stockpile," James David, executive vice president and general counsel at HGS, said in a press release. "We have more work to do, but our interactions with [the Department of Health and Human Services], FDA and [the Centers for Disease Control and Prevention] continue to be positive."

Shares of HGS (NASDAQ:HGSI) rose 44 cents Tuesday to close at $10.98.

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