A powerful virus-stopping gel intended to stop the sexual spread of AIDS to women appears to be highly effective in the first testing on monkeys, according to a preliminary study.
The substance, called PMPA, totally stopped transmission of SIV, the monkey version of the AIDS virus, when applied protectively to the animals’ vaginas.
“We don’t know how this will translate to human beings, but we see the results as very promising and worth pursuing,” said Dr. Roberta Black of the National Institute of Allergy and Infectious Diseases, which financed the study.
If it works as researchers hope, the gel could be applied vaginally by women before intercourse - or perhaps afterward - to block the AIDS virus.
Finding a vaginal anti-AIDS compound is an important research goal. It would be used in circumstances when condoms are not available or not wanted, said Dr. Zeda Rosenberg of the national allergy institute.
“For women to have a woman-controlled method is very important so they can protect themselves,” she said.
Animal research suggests PMPA may be twice as effective as the spermicide nonoxynol-9, which also kills HIV.
Serious questions remain, however, because many medicines look impressive in the test tube or in lab animals but fail when tried on humans. Among other things, PMPA’s developers will have to show that it does not cause irritation, which is a drawback of nonoxynol-9.
“The biggest issue is safety. This would obviously be used in healthy young people, and it has to be very safe,” said Dr. Norbert Bischofberger of Gilead Sciences Inc. of Foster City, Calif.
Bischofberger presented the results today at the Ninth International Conference on Anti-viral Research in Fukushima, Japan.
PMPA short for (R)-9-(2-phosphonylmethoxypropyl)adenine - works by blocking reverse transcriptase, one of the enzymes the AIDS virus uses to make copies of itself. Its action is similar to AZT, but it appears to be more potent and 100 times less toxic.
So far, scientists have studied PMPA only in macaque monkeys, which are susceptible to the simian immunodeficiency virus. The virus is a relative of HIV, the human AIDS virus, and causes an AIDS-like fatal illness in monkeys.
Researchers at the University of California at Davis tested PMPA gel on six monkeys. Four received the gel, while two did not, and all were exposed to high levels of SIV. The four receiving the gel stayed healthy, while the other two became infected.
PMPA also shows promise as a way to prevent infection when people are exposed to HIV through cuts or needle jabs.
In November, Dr. Che-Chung Tsai and others from the University of Washington reported that injections of PMPA prevented infection when given up to 24 hours after monkeys had been inoculated with SIV. Tsai conducted his research at the UW’s Medical Lake field station.
While no one knows if PMPA gel will work as well in people as in primates, Tsai noted that SIV and HIV are closely related and monkey and human vaginas are anatomically similar.
“That convinces me this is a very promising result,” he said.