Tampa, FL (Sept. 22, 2004) -- The compound in marijuana that produces a high, delta-9 tetrahydrocannbinol or THC, may block the spread of several forms of cancer causing herpes viruses, University of South Florida College of Medicine scientists report.

The findings, published Sept. 15 in the online journal BMC Medicine, could lead to the creation of antiviral drugs based on nonpsychoactive derivatives of THC.

The gamma herpes viruses include Kaposi's Sarcoma Associated Herpes virus, which is associated with an increased risk of cancer that is particularly prevalent in AIDS sufferers. Another is Epstein-Barr virus, which predisposes infected individuals to cancers such as Burkitt's lymphoma and Hodgkin's disease.

Once a person is infected, these viruses can remain dormant for long periods within white blood cells before they burst out and begin replicating. This reactivation of the virus boosts the number of cells infected thereby increasing the chances that the cells will become cancerous.

The USF team, led by virologist Peter Medveczky, MD, found that this sudden reactivation was prevented if infected cells were grown in the presence of THC. While cells infected with a mouse gamma herpes virus normally died when the virus was reactivated, these same cells survived when cultured in the laboratory along with the cannabinoid compound – further evidence that THC prevents viral reactivation.

Furthermore, the researchers showed that THC acts specifically on gamma herpes viruses. The chemical had no effect on another related virus, herpes simplex-1, which causes cold sores and genital herpes.

Small concentrations of THC were more potent and selective against gamma herpes viruses than the commonly used antiviral drugs acyclovir, gancicyclovir and foscamet, said Dr. Medveczky, a professor in the Department of Medical Microbiology and Immunology.

The USF researchers suggest that THC selectively inhibits the spread of gamma herpes viruses by targeting a gene these viruses all share called ORF50.

Dr. Medveczky emphasized that more studies are needed. "We have not evaluated the effect of THC in an animal model yet so we do not recommend people start using pot to prevent or treat cancers."

In fact, Dr. Meveczky said, THC has also been shown to suppress the immune system so smoking marijuana could "do more harm than good" to patients whose immune systems are often already weakened.