Scientists have long sought a vaginal gel that women could apply before sex to block HIV. Now they've found a new lead--a chemical specially designed to thwart the way HIV penetrates women's cells. The experimental drug isn't ready for human testing yet, but it provided potent protection to female monkeys exposed to large amounts of the simian version of HIV, researchers reported Thursday in the journal Science. The chemical prevented HIV from invading vaginal tissue by blocking its preferred cellular doorway, the first evidence that targeting that portal is sufficient to prevent infection.
HIV invades cells through receptor molecules on their surfaces; it prefers one called CCR5. Scientists have long known that people who lack CCR5 because of genetic mutations hardly ever become infected with HIV, and that the body harbors another molecule called RANTES that can block HIV by sticking to CCR5 first. Lead researcher Michael Lederman of Case Western Reserve University partnered with Swiss researchers who created a manmade RANTES version thousands of times more potent at blocking CCR5. They gave 30 monkeys a hormone to make them more vulnerable to HIV infection. Then they sprayed their vaginas with the new chemical, called PSC-RANTES, and 15 minutes later squirted in high doses of a monkey-human strain of AIDS virus. Monkeys who received the highest dose of PSC-RANTES were completely protected; a lower dose provided 80% protection. There were no detectable side effects.
PSC-RANTES costs a lot to manufacture, so the scientists are working on cheaper formulas and on a gel version that could stay in the vagina longer. More safety studies in animals are needed too. But "if we're lucky," a CCR5-blocking molecule might begin small safety studies in women in a year, Lederman said.
The Alliance for Microbicide Development reports that there are six microbicide products in Phase II or Phase III human tests, and dozens of others in early human trials or animal and laboratory tests. While most are being studied for their effectiveness in preventing vaginal HIV infections among women, some also are being evaluated to see if they can help prevent infections through anal sex in both men and women. (AP, with additional reporting by Advocate.com)