A single intravenous (IV) dose of the HIV entry inhibitor PRO 140 reduced virus by nearly 100-fold for up to 10 days in a small phase IIa study, according to a study presented at the 49th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in San Francisco and reported by the National AIDS Treatment Advocacy Project (NATAP).

PRO 140 is a monoclonal antibody. Monoclonal antibodies are artificially created antibodies that can attach to viruses, bacteria or even human cells. Pro 140 attaches to a CD4 cell receptor called CCR5, which HIV uses to enter and infect CD4 cells.

In study 2301, presented at ICAAC, researchers compared two single doses of PRO 140 with a placebo, all given by IV. Ten HIV-positive volunteers received 5 milligrams per kilogram of body weight (mg/kg) of PRO 140 as a single dose; 10 received a 10 mg/kg single dose of PRO 140; and 11 received a single dose of a placebo.

After dosing, all of the volunteers receiving either dose of PRO 140 had at least a 10-fold reduction in HIV. Twenty percent of those who got the 5 mg/kg dose had a 100-fold drop in virus, and nearly 60 percent in the 10 mg/kg group had a 100-fold drop. None of the patients in the placebo group had either a 10- or a 100-fold drop in virus.

PRO 140 proved quite long-lasting. The maximum drop in virus occurred about 10 days after the single dose of either 5 mg/kg or 10 mg/kg and did not return to pretreatment levels for about 60 days.

Side effects were minimal, and there was no significant difference in side effects between either of the two doses or the placebo. The company developing PRO 140, Progenics, stated that it will continue development and that it anticipates the drug can be self-administered.