'Molecular condom' developed - could make a microbicide more effective

Researchers in America have developed a “molecular condom” that could be capable of rapidly releasing an anti-HIV microbicide in the vagina. They believe that this could make a microbicide 90% effective.

In a paper published in the December 11^th edition of the Journal of Pharmaceutical Sciences, investigators from the university of Utah describe the laboratory development of a gel that can be inserted into the vagina daily and is activated on exposure to semen, releasing large and small molecules with a similar structure to HIV entry inhibitors. The investigators believe that their findings are an important advance in research into HIV microbicides as the study of microbicide delivery had previously received “scant attention.”

Microbicides are seen as an emergent key HIV prevention technology and as a tool that will provide women with greater control over their sexual health. Several microbicides are currently being investigated in clinical trials and use either anti-HIV drugs to prevent infection with the virus, or maintain an acidic environment in the vagina that is capable of neutralising HIV.

Research has so far focused on the development of an effective microbicide, largely neglecting how the drug would be best delivered. Therefore investigators from Utah conducted laboratory research to see if they could identify a long-lasting substance capable of effectively and durably delivering an antiretroviral microbicide.

Investigators at the university of Utah designed a water-based gel (hydrogel) that was sensitive to both body temperature and pH (acidity or alkalinity) in the vagina. The hope was to develop a “smart semen-triggered vaginal microbiocidal vehicle.”

The substance developed by the investigators can be inserted into the vagina daily in a liquid form. At body temperature it becomes a gel that coats tissue, but on exposure to semen, it once again becomes a liquid, capable of releasing an anti-HIV drug. The liquid has been designed so it does not dehydrate vaginal cells, which can involve a risk of infections, increasing the risk of infection with HIV.

Although the investigators have yet to test the actual release of an anti-HIV drug from the gel, they have conducted tests using large and small molecules to simulate an HIV entry inhibitor. They found that in the thick gel tested in the laboratory, 49% of the small molecule drug was released within five minutes and 81% within an hour. Tests also showed that 48% of the large molecule was available within 30 minutes of exposure to semen and 66% within 90 minutes. But the investigators emphasise that gel tested in the laboratory was considerably thicker than the concentration in the vagina, meaning that the antiretroviral would “all be released within a few minutes.”

The Utah investigators are hopeful that their “molecular condom” will have a much higher level of efficacy than that envisaged for the first-generation microbicides. These are expected to become available within the next five years and to be between 50% - 60% effective. With such a level of efficacy, and with use by 20% of women in 73 resource-limited countries, it is estimated that 2.5 million new HIV infections would be prevented over three years. The US investigators believe that their method of microbicide delivery could provide an efficacy rate of 90%.