ICAAC: Monoclonal Antibody Blocks HIV Entry

September 19, 2007

CHICAGO -- An antibody that blocks HIV entry to its target T-lymphocytes was found to be well tolerated and effective in the first study to test its activity in humans.

CHICAGO, Sept. 19 -- An antibody that blocks HIV entry to its target T-lymphocytes was found to be well tolerated and effective in the first study to test its activity in humans.

In a placebo-controlled, randomized study, the monoclonal antibody PRO 140 had a prolonged, potent, and dose-dependent antiviral effect, Jeffrey Jacobson, M.D., of Drexel University in Philadelphia, reported at the Interscience Conference on Anti-microbial Agents and Chemotherapy here.

At the same time, there were no serious drug-related adverse effects and no dose-limiting toxicities, Dr. Jacobson said.

"It's pretty clean, dramatic, and consistent data," Dr. Jacobson said.

The antibody blocks the CCR5 receptor and, in that respect, is similar to several small-molecule drugs now on the market and in the pipeline, including maraviroc (Selzentry) and vicriviroc, Dr. Jacobson said.

But it binds to a different part of the CCR5 receptor, allowing for the normal biological activity of the receptor while preventing HIV entry, he said.

The different binding site also opens the possibility of using PRO 140 and other CCR5 inhibitors at the same time, potentially improving the therapeutic response.

Indeed, Dr. Jacobson said, there is in vitro data showing that the small-molecule CCR5 blockers and PRO 140 have "synergy" in preventing HIV infection.

In this first human study of 39 patients, the researchers tested three doses of PRO 140 - 0.5, 2.0 and 5.0 milligrams, administered intravenously -- against placebo for efficacy, tolerability, pharmacodynamics, and pharmacokinetic data.

The antibody was administered once and produced a quick and prolonged reduction in viral load starting within five days.

Indeed, at day five of the study, some patients on the drug had already seen a reduction by a factor of 10 and by day 10, the average reduction was close to a factor of 1,000 (1.76 log10 copies of viral RNA per milliliter of plasma.)

The difference from placebo was significant for all three doses, at P