Lubricant Blocks HPV Infection in Mice
Researchers have moved one step closer to developing a topical
microbicide that can prevent infection by human papillomaviruses
(HPVs), the most common sexually transmitted infection in the U.S.
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Irish moss, a major source of carrageenan. Image
courtesy of Department of Fisheries and Oceans Canada. |
There are more than 100 types of HPVs, over 30 of which are passed
between people through sexual conduct. Most HPV infections don't
cause noticeable symptoms and go away on their own, but some HPV
types can cause cervical cancers or genital warts. Women can reduce
their risk of HPV infection by using condoms, but the method isn't
100% effective. A recently approved vaccine prevents infections
by 4 HPV types that together cause about 70% of cervical cancers
and 90% of genital warts worldwide. Vaccines targeting other HPV
types are also under development. However, a topical microbicide,
a compound that could block HPV infection in the first place, would
be a useful addition to the arsenal of anti-HPV weapons.
Dr. John Schiller and his colleagues at NIH's National Cancer
Institute (NCI) had previously found, using cells growing in the
laboratory, that an inexpensive gelling agent called carrageenan
could block HPV from infecting its target cells. Carrageenan is
extracted primarily from red algae and used in a wide variety of
cosmetic and food products, ranging from sexual lubricants to infant
feeding formulas. Having identified a compound that could block
HPV in the laboratory, the researchers set out to develop a mouse
model to test whether it could block infection in the body.
The team developed an HPV "pseudovirus" composed of
the two proteins that form the virus's coat and a "reporter" gene
inside to replace the virus genome. Such pseudoviruses are thought
to carry out the early phases of infection much like the virus
itself does. As the researchers reported online on July 1, 2007,
in Nature Medicine, the pseudovirus they created was able
to infect the mouse genital tract.
Having established a model system, the researchers next tested
to see whether compounds used in vaginal products affect susceptibility
to infection. They found that a widely used vaginal spermicide,
nonoxynol-9 (N-9), greatly increased the rate of infection. They
then tested 2 commercial carrageenan-containing lubricants and
found that they blocked infection. Carrageenan prevented HPV infection
in the presence of N-9 as well.
These results raise the possibility that over-the-counter vaginal
contraceptives containing N-9 may raise the risk for genital HPV
infection in women. In contrast, carrageenan may serve as an effective
topical HPV microbicide. The compound is currently being studied
as a candidate topical microbicide against HIV. Carrageenan is
considerably more active against HPV in the laboratory. Schiller
and his colleagues are now planning a clinical trial to see if
it can block HPV as effectively in the human body.
—by Harrison Wein, Ph.D.
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