“The first step of the complicated process of an HIV infection of women is the diffusion of the virus from the sperm into the vaginal tissue. Exactly this first step we want to stop,” says professor Patrick Kiser at the chair of bioengineering at the Utah University. In order to achieve that, the scientists have developed a gel thwarting the movement of the AIDS-virus in the vaginal milieu. The whole thing works like some sort of swimming pool: The moment the swimmer hits the water it will turn into some kind of gluey pulp.
The virus turns into a pillar of salt when contacting the gel
Kiser’s gel consists of two main components: Phenyl boronic acid and salicylhydroxyamid. In normal, slightly acidly vaginal milieu the chemical compounds between those two substances are in some kind of steady-state: They are connected and open again which entails that the gel keeps its gel-like consistence as long as it gets applied and no sexual intercourse took place. But when the slightly alkaline sperm gets into the game and increases the pH-value to more than 7, the situation changes. Suddenly the molecular bridges between the two gel components get a lot more solid, the gel gets hard and crumbly. On a molecular level it results in some kind of lattice structure with pores of 30 to 50 nanometers diameter. On the other hand the HI-Virus has a diameter of about 100 nanometers, thus it is significantly larger. In short: The virus present in the man’s sperm should – regarded strictly physically – quasi tangle up in a doughy, close-meshed and drying gel. In such a milieu it is hardly possible for the semen also to succeed in making the long way into the uterus. They get stuck as well. The scientists now were able to show in a study that this actually is happening. They published the results in the journal Advanced Functional Materials. They marked HI-Viruses with flourescent dyes and observed under a microscope how they reacted during contact with the gel respectively with sperm plus gel. The scientists were able to show that the viruses were not only mechanically stopped but they also interacted chemically with the polymeres.
Up to now only negative studies available for humans
In a next step a virostatic agent like Tenofovir will be added to the gel. “Thus the HI-Virus would have yet another obstacle to get over before it could enter the body”, explains Kiser whose works are financed by the NIH (National Institutes of Health) and the Bill & Melinda Gates Foundation. Now caution is required though. The experience made so far with antimicrobial effective preparations for application in the vagina weren’t so good. For example the preparation Carraguard was tested on 6000 women in South Africa over a period of three years. Data was available beginning of 2008: A comparison between verum- and placebo group showed no difference regarding the rate of HIV infections. The gel contained Carrageenan, a stabilizer also used in the cosmetic industry which intercepted HIV in animal experiments but did not under the obviously more difficult conditions of human sexual intercourse. Another phase-III study with antimicrobial effective cellulose sulphate with 1300 women in Africa and India was even stopped prematurely because the infection rate in the verum group was higher than in the placebo group. In a second study with the same preparation was no difference between the groups when the study was stopped.
Gel before sex requires good compliance
The new gel from Utah could work nevertheless, for one reason – amongst other – because it irritates the vaginal tissue less than its predecessor. Namely one of the hypotheses causing the failure of the African-Indian study was that the tissue showed slight signs of inflammation as a result of the application – a fact in turn making it easier for the HI-Virus to pass through the mucous membrane. Another factor of the preliminary examinations will be relevant for the new gel as well when it appears in upcoming clinical studies: The compliance appears to be not particularly high in this form of application. Data on this issue delivered the Carraguard study: Only an average of every second time the gel was applied prior to the sexual intercourse. Only ten percent of the women stated that they applied it every time.