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Prevention - Microbicides: HIV-blocking Gel For Women: New 'Molecular Condom' Meant To Prevent AIDS

09 Aug, 2009

ScienceDaily (Aug. 9, 2009) — University of Utah scientists developed a new kind of "molecular condom" to protect women from AIDS in Africa and other impoverished areas. Before sex, women would insert a vaginal gel that turns semisolid in the presence of semen, trapping AIDS virus particles in a microscopic mesh so they can't infect vaginal cells

 "The first step in the complicated process of HIV (human immunodeficiency virus) infection in a woman is the virus diffusing from semen to vaginal tissue. We want to stop that first step," says Patrick Kiser, an associate professor of bioengineering at the University of Utah's College of Engineering. "We have created the first vaginal gel designed to prevent movement of the AIDS virus. This is unique. There's nothing like it."

 "We did it to develop technologies that can enable women to protect themselves against HIV without approval of their partner," he adds. "This is important – particularly in resource-poor areas of the world like sub-Sahara Africa and south Asia where, in some age groups, as many as 60 percent of women already are infected with HIV. In these places, women often are not empowered to force their partners to wear a condom."

 A study testing the behavior of the new gel and showing how it traps AIDS-causing HIV particles will be published online later this week in the journal Advanced Functional Materials. Kiser is the senior author.

 "Due to cultural and socioeconomic factors, women often are unable to negotiate the use of protection with their partner," says Julie Jay, the study's first author and a University of Utah doctoral candidate in pharmaceutics and pharmaceutical chemistry.

 So the researchers developed a vaginal gel that a woman could insert a few hours before sex and "could detect the presence of semen and provide a protective barrier between the vaginal tissue and HIV," Jay says. "We wanted to build a gel that would stop HIV from interacting with vaginal tissue."

 Kiser estimates that if all goes well, human tests of the gel would start in three to five years, and the gel would reach the market in several more years. He and Jay want to incorporate an antiviral drug into the gel so it both blocks HIV movement and prevents the virus from replicating.

 A Rocky Road to Microbicides against AIDS
The effort to develop microbicides – intravaginal gels, rings and films – to prevent transmission of the AIDS virus has been halting. The few that have reached human clinical trials in Africa failed to prevent HIV transmission – either because they carried antiviral drugs that were not long-lived or strong enough, or because patients failed to use them. Some experimental microbicides increased the risk, possibly by irritating vaginal tissue and attracting immune cells that are targeted by the virus.

 In 2006, Kiser and colleagues published a study on their development of another "molecular condom" to be applied vaginally as a liquid, turn into a gel coating at body temperature, then, in the presence of semen, turn liquid and release an anti-HIV drug. 

Unfortunately, few antiviral drugs bind to and attack HIV in semen. And in Africa, high air temperatures prevent the gel from turning liquid so it could coat the vagina evenly, Kiser says.

The new "molecular condom" gel in the current study works in the opposite way. Like the old version, it changes in response to changes in pH – acidity or alkalinity – in the vagina caused by the introduction of semen during sex. But unlike the old gel, which became liquid at the higher (less acidic) pH of semen, the new "molecular condom" becomes a semisolid at the pH of semen, forming a mesh of "crosslinked" molecules.

 The new gel is applied as a gel, and then becomes more solid and impenetrable as changes in pH alter the strength of the bond between the gel's two key components, both of which are polymers, or long, chain-like molecules made of many smaller, repeating units: PBA, or phenylboronic acid, and SHA, or salicylhydroxamic acid.