Carrageenan Inhibits the Entry of HPV

18/07/06 Researchers have discovered a potent inhibitor of the human papilloma viruses (HPV), particularly those types that cause cervical cancer and genital warts, according to a study published in PLoS Pathogens. The inhibitor is found in commercially available products, including many food products.

In laboratory tests, carrageenan, a compound derived from red algae, prevented HPV infection by both genital wart and cancer-causing types. "We were floored by how much better it worked than anything else we have tested. It's effective at 100-fold lower concentration than the next best inhibitor we've found," said Dr. John Schiller, senior investigator at the National Cancer Institute.

Normally, HPV attacks cells by attaching to proteins on their surface and then chemically manipulating access to the cells. Carrageenan thwarts this process by attaching to HPV and preventing its entry into cells.

Christopher Buck, lead author of the study and post-doctoral fellow at the National Cancer Institute, searched for candidate inhibitory compounds by looking for substances that were structurally similar to a key cell surface component involved in HPV infection.

"When carrageenan came up to be the clear winner, Chris started to search for products that might contain it," said Schiller. "It quickly became clear that it is widely used as a thickening agent in many foods and topically applied products. So he decided to search for sexual lubricants that might contain it as the gelling agent and came up with several. Although carrageenan was identified in a systematic screen, the serendipity that this seaweed-derived compound is already used in over-the-counter products for genital application is really quite amazing."

In spite of these promising results, it is not realistic to suggest that people rush out to buy carrageenan-containing products to prevent HPV infections. "Our results do not prove that carrageenans will work as a practical HPV topical microbicide," Schiller said. "The potent inhibition of infection of cells in dishes, coupled with the fact that carrageenan-based products are already in use for genital application, are promising, but we will need to do a well controlled clinical trial before use of any of these products as an HPV inhibitor could be recommended."

Such a product, if identified or developed, could complement the HPV vaccine recently approved by the Food and Drug Administration, according to Schiller, who also contributed to the initial development of the HPV vaccine.

This vaccine is virtually 100% effective against some HPV strains, but it doesn't prevent infections against every strain and its cost -- about $360 for the three necessary doses -- could be prohibitive, especially for women in developing countries.

"An effective HPV microbicide could reduce the burden of HPV-related genital disease in women," Schiller said. About 10,000 American women are diagnosed with cervical cancer each year, and about 250,000 women worldwide die from the disease annually.