Studies in macaques have for the first time shown that an intravaginal ring laced with an anti-HIV drug can block transmission of HIV during sexual intercourse. Researchers at the Population Council who demonstrated the product are now refining drug concentrations and contents of the ring and hope to begin human trials within 18 to 24 months.
Previous studies with vaginal microbicides to block HIV have produced mixed results, with at least one showing some protection and another showing none. Those studies have been based on gels containing the drugs and have shared some limitations -- particularly patient compliance. Some women have seemed unwilling or unable to apply the gels long enough before intercourse for them to be effective. Researchers speculate that an intravaginal ring would eliminate that problem by being implanted for periods of at least three months, perhaps longer. That would provide the first true protection for women who have no other means of defense against the virus.
Researchers at the Population Council in New York have developed an intravaginal ring composed of ethylene vinyl acetate impregnated with a proprietary non-nucleoside reverse transcriptase inhibitor called MIV-150. That drug interferes with an enzyme the virus needs to replicate. A team led by the Population Council's Thomas M. Zydowsky inserted the rings into 17 macaques and placebo rings into another 16, then exposed the animals to a single dose of SHIV, a virus containing genes from HIV and SIV, its monkey equivalent. The team reported in the journal Science Translational Medicine that two of the 17 animals fitted with the microbicide contracted HIV, compared to 11 of the 16 fitted with a placebo.
"This proof-of-concept study confirms that the investment in vaginal rings as a delivery system for HIV prevention is paying off," said Naomi Rutenberg, the council's vice president and director of its HIV and AIDS Program.
Previous studies have shown that adding the antiviral agent zinc acetate to MIV-150 increases the drug's activity against HIV and prevents other STDs, such as herpes simplex virus-2. The team hopes eventually to incorporate a variety of antiviral agents so that the ring can provide broad-spectrum protection.
A human trial of an intravaginal ring containing a different anti-HIV drug, called dapivirine, is now being conducted by the Microbicides Trial Network and International Partnership for Microbicides. Not date for results has been announced.
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