Drugs Are Found to Block HIV In Monkeys
Tuesday, February 10, 2009
AIDS researchers who were gathered in Montreal yesterday heard encouraging results from studies of three strategies for preventing HIV infection using pharmaceuticals, particularly in women.
Two experiments in monkeys showed that antiretroviral (ARV) drugs, given by mouth or by vaginal gel, were highly effective in blocking infection by the virus that causes AIDS.
A third study, in 3,100 women in the United States and Africa, showed a small amount of protection from a vaginal gel that acts by binding up the AIDS virus and preventing it from invading cells.
Many experts believe that, short of a vaccine, a virus-blocking substance that could be inserted in the vagina or rectum before sexual activity would be the most important tool in fighting the AIDS pandemic. Numerous topical microbicides have been tried, but none have worked, and two have actually increased the risk of infection.
"The field of microbicide gels is now moving into a new generation," said Walid Heneine, a virologist at the U.S. Centers for Disease Control and Prevention, who led one of the monkey studies.
Microbicides can be applied without the knowledge of sexual partners. They are seen as being especially important in cultures where the subservient status of women makes it difficult for them to insist on abstinence or condom use, the two proven methods of preventing infection through sexual contact. In sub-Saharan Africa, nearly 60 percent of HIV-positive people are women.
The gel used in the human study reduced the risk of infection by 30 percent over the course of about two years, an effect that did not reach the level of statistical significance. The women -- from the United States, South Africa, Malawi, Zambia and Zimbabwe -- also used condoms in about three-quarters of their sexual encounters.
A study by British and African researchers that is testing the same microbicide in 9,400 women may have interim results later this year.
Although this result was marginal, the substance, called PRO 2000/5, may ultimately prove useful to women who are monogamous, are married to high-risk men and do not want to use condoms because they want to conceive, the lead researcher said.
"This could be a niche product for a group of women who have no other option," said Salim Abdool Karim of Durban, South Africa. He spoke at a news conference at the 16th Conference on Retroviruses and Opportunistic Infections, the annual mid-winter AIDS meeting in North America.
In the first monkey study, researchers gave rhesus macaques oral doses of a compound containing two ARV drugs, tenofovir and emtricitabine (which is sold under the name Truvada). The medicine was administered at different intervals, both before and after the animals were rectally exposed to the AIDS virus once a week for three months.
When the first dose was given either one or three days before contact with the virus, five out of six animals were protected. When it was given seven days before exposure, four in six animals were protected. When the dose was two hours before exposure, however, only three in six were protected.