A polymer gel that blocks viral particles could one day provide a way for women to protect themselves against HIV infection. The gel reacts with semen to form a tight mesh that blocks the movement of virus particles. The material, which is still in early development, could eventually be combined with antiviral gels currently in clinical trials to provide a dual defense against HIV.
Viral blockade: A gel, shown here stained blue, forms tendril structures at pH 7.4. The red dots are 100 nanometer particles, about the same size as HIV, which are trapped in these structures.
Scientists have been working on microbicide gels for HIV for more than a decade. This type of prophylactic, which women could use without relying on their partners, is of particular interest in areas such as Sub-Saharan Africa, where HIV-infection rates are high and use of condoms is relatively low. But development has been slow–a number of products have failed clinical trials.
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Most of the topical microbicides being tested for HIV prevention contain antiviral drugs designed to block replication of the virus once it infects a cell. The new gel, which is being developed by Patrick Kiser and colleagues at the University of Utah, in Salt Lake City, acts at the first stage of infection–when the virus moves from semen to the surface of vaginal tissue.
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“This research stresses improvement not in the drugs but in the vehicle used to deliver the drugs,” says Ian McGowan, a physician and scientist at the University of Pittsburgh Medical Center who was not involved in the research. “That’s a relatively neglected area, and the technology is quite exciting.”
Kiser and colleagues developed a gel from two polymers–PBA (phenylboronic acid) and SHA (salicylhydroxamic acid)–that can be spread around the vagina prior to intercourse. With the introduction of semen, the vagina reaches a higher pH level, causing molecules in the gel to bind together, creating a finer mesh that prevents HIV particles from passing through. “The idea is to use the trigger of semen to activate the gel and create a more effective barrier,” says Kiser.
In research published this week in the journal of Advanced Functional Materials, researchers showed in lab tests that the gel can block the movement of HIV particles, and that it appears safe when tested in human vaginal cells. The next step is to test the gel on human tissue collected from women who have had hysterectomies to show that it can prevent infection.
“It’s a very interesting approach to take advantage of normal vaginal physiology and alter it to inhibit HIV transmission,” says Craig Hoesley, an infectious-disease specialist at the University of Alabama, in Birmingham. But this might also prove troublesome. McGowan points out that the change in pH after intercouse can be variable, so researchers need to show that the gel can react under different chemical conditions.
Kiser and his team ultimately want to combine this type of gel with an antiviral drug in order to block both the movement of HIV and its replication. But extensive testing, including safety testing, remains to be done. For example, for use in Sub-Saharan Africa, the gel must be stable at different temperatures. “We will also need to see if it is compatible with antiviral drugs,” says McGowan.
