WebMD Medical News
Daniel J. DeNoon
Louise Chang, MD
Jan. 21, 2009 -- Small anti-herpes RNA molecules applied to the vagina
protect mice against new herpes simplex virus type 2 (HSV-2) infections for one
The preventive treatment uses small interfering RNA (siRNA) molecules. These
tiny bits of genetic material are designed to switch off specific genes.
The herpes treatment uses two siRNAs. One keeps vaginal cells from producing
a molecule that the herpes virus uses to infect cells. The other siRNA targets
a viral gene required for herpes reproduction.
"One of the attractive features of the compound we developed is that it
creates in the tissue a state that's resistant to infection, even if applied up
to a week before sexual exposure," Harvard researcher Judy Lieberman, PhD,
says in a news release. "This aspect has a real practicality to it. If we
can reproduce these results in people, this could have a powerful impact on
HSV-2 is the main cause of genital herpes. It's considered a sexually
transmitted infection, although mother-to-infant transmission occurs during the
Researchers have long believed that herpes and HIV could be prevented by
vaginal application of antiviral agents. But such "vaginal
microbicides," even if effective, must be safe, non-messy, and long-lasting
to be of real use to women.
Lieberman's team came up with an earlier version of their topical siRNA but
found that the formulation they used actually encouraged herpes infection.
Their current, two-pronged siRNA treatment avoids this problem -- at least in
However, the same target they used in mouse vaginal cells -- a molecule
called nectin-1 -- is also found on human vaginal cells. Blocking nectin-1
doesn't seem to harm mice. It may not harm humans, either, as the molecule
seems to be needed during development but not during adult life.
That suggests the drug might not be safe during pregnancy. But if it works
in sexually active adults, it would still be an enormous benefit to human
health. An estimated 536 million people worldwide are infected with HSV-2. And
HSV-2 infection makes it easier for a person to get infected with HIV.
Lieberman and colleagues suggest their siRNA approach might also work
Their study appears in the Jan. 22 issue of Cell Host &
SOURCES:Wu, Y. Cell Host & Microbe, Jan. 22, 2009; vol 5: pp 1-11.News release, Harvard Medical School.
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