Tenofovir

Gel protects against HIV in animal model study

8^th August 08

Researchers at St George’s, University of London have shown that a gel containing a drug used to treat HIV patients protects animals from SIV infection, the simian form of the virus.

Researchers at St George’s, University of London have shown that a gel containing a drug used to treat HIV patients protects animals from SIV infection, the simian form of the virus.

In the experiment six animals were totally protected from SIV infection and another three partially protected by a gel containing the anti-HIV drug Tenofovir, when applied rectally, according to the study published in the August 2008 edition of the journal PLOS.

This study marks a significant step forward in research into microbicides – a substance designed to protect people from sexually transmitted infections, including HIV, when applied either in the vagina or the rectum. It is the first time that this type of HIV drug, which targets an enzyme made in cells infected with HIV and is usually used in treatment, has been tested in such a way.

One of the most encouraging findings of the study is that the researchers have identified a blood test that may predict how well the microbicide is absorbed by the cells in the rectal canal that are first exposed to HIV.

Furthermore, the team found that small pieces of tissue can be used to test for activity of the drug, therefore reducing the need for animal testing. “We are also investigating the activity of combinations of anti-HIV drugs using rectal biopsies,” said study author Professor Martin Cranage. “It is likely that combinations of anti-HIV drugs will offer highly significant levels of protection.”

The multi-centre study led by a team at St George’s, University of London, in collaboration with five other centres including the University of California Los Angeles and the Health Protection Agency (UK) is part of a National Institutes of Health (USA)-funded program investigating rectal microbicides.

The drugs used in the trial were supplied by the manufacturers of Tenofovir, Gilead Sciences, Inc.  

Guide to microbicides

-          A ‘microbicide’ is any substance that can substantially reduce transmission of sexually transmitted diseases when applied to the rectum or vagina. Like today’s spermicides, a microbicide could be produced in many forms including gels, creams, suppositories, films, lubes or for vaginal use, in the form of a sponge or ring that slowly releases the active ingredient over time.

-          How does it protect you against HIV? Some microbicides bind to the virus and prevent the virus from attaching and or fusing to the target cells in the body. In contrast, most antiretroviral drugs (used therapeutically) interfere with virus replication within the infected cell. This is the case with Tenofovir. The drug requires processing within a cell to become active. It is the cells in and associated with the rectum that take up the Tenofovir in the current trial. These cells, when they become infected, undergo what is known as abortive infection. They are pre-charged with active drug which interferes with virus replication by acting on a virus-specific enzyme called reverse transcriptase. 

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