Oct. 14, 2004 -- A new chemical is showing early effectiveness in blocking sexual transmission of the AIDS virus in animals, giving researchers some hope that they may have found a new method of HIV prevention in humans, according to a study released Thursday.
The chemical, known as PSC-RANTES, reliably prevented transmission of a variant of HIV when it was first applied to the vaginas of female rhesus monkeys. This is early proof that the compound could be a useful topical agent in preventing heterosexual HIV transmission, long considered a goal of anti-AIDS pharmaceutical research, investigators say.
Researchers treated female rhesus monkeys with PSC-RANTES shortly before exposing them to SHIV, a simian version of HIV that gives monkeys AIDS. Twenty-five animals got varying doses of the compound, while five got a treatment containing no active chemical for comparison.
Four of five monkeys in the comparison group later showed signs of SHIV infection, while those that got the strongest dose of PSC-RANTES all remained uninfected.
"With more drug, you got more protection," says Michael M. Lederman, MD, a researcher at Case Western Reserve University who lead the international study, published today in the online version of the journal Science.
HIV, like other viruses, must penetrate and take over cells in order to replicate and cause infection. Scientists know that HIV accomplishes this by binding to a series of receptors on the surface of immune system cells, then later destroying those cells, eventually disabling the immune system.
PSC-RANTES is a version of a naturally occurring chemical that acts as a signal carrier between cells in the body. The drug apparently works by causing receptors normally on the surface of immune cells to move inside, making them inaccessible to viruses.
Approximately 850,000 Americans and 40 million persons are infected with HIV worldwide, according to the World Health Organization. Women now constitute the majority of new infections, and finding a way to prevent male-to-female HIV transmissions is considered a major goal of anti-AIDS efforts.
Several other topical vaginal treatments are in development, including one called PRO 2000, which is set for a large-scale test in four African countries next year. None has yet gained regulatory approval for widespread use by women.
More Work Remains
Lederman says PSC-RANTES could be an advance since it specifically acts against known HIV receptors to prevent transmission. "This work gives us a single molecule to target," he told reporters at a science conference sponsored by the American Medical Association.
But he stresses that more work is needed before PSC-RANTES proves useful in humans. Researchers are still unsure what dose of the drug is needed to prevent transmission in people and whether it will remain effective when combined with gels or creams in a pharmaceutical product.
"There are a lot of things that need to be done before we go into human studies," he says.
The chemical's patent is owned by Gryphon Therapeutics, a San-Francisco-based pharmaceutical company. The company did not respond to calls requesting comment.