43rd ICAAC
A meeting of the American Society for Microbiology

September 14-17, 2003, Chicago, IL


For more information on any presentation at the 43rd ICAAC contact Jim Sliwa, ASM Office of Communications at jsliwa@asmusa.org



EMBARGOED UNTIL:  Sunday, September 14, 11:30 a.m.

(Session 22, Paper V-287)

Terri Stoner
Northeastern Ohio Universities College of Medicine
Rootstown, OH,
Phone: 330-325-6142

Our research shows that the compound Indole-3-Carbinol (I3C) inhibits replication of HSV by interfering with cell cycle factors such as cyclin dependent kinases (cdks). Because I3C is derived from plants such as broccoli it has proven to be relatively nontoxic to cells. HSV is a common human virus that affects most humans and is capable of infecting virtually every organ of the human body. Infection can result in diseases ranging from minor illness such as cold sores to potentially life threatening illnesses such as encephalitis. Current drug therapies used to treat individuals infected with HSV generally target the DNA synthesizing mechanism of the virus. Acyclovir is the most widely used agent of this type. Other chemotherapeutic antivirals available are less effective and usually toxic. There is concern when treating patients with anti-HSV drugs like acyclovir that the virus will become resistant to these drugs. Therefore, there is increasing emphasis on the development of new antiviral agents that act in a manner other than attacking viral DNA. One potential candidate for a new anti-HSV agent is the compound, I3C. I3C has been previously isolated from broccoli and related vegetables and is relatively nontoxic. It is known that HSV replication requires the host cell machinery in order to replicate. Our research suggests that I3C may target specific host cell cycle factors that the virus needs in order to reproduce itself. This would include cdks, which play an essential role in the control of the cell cycle and are also utilized by HSV in order to replicate.

Research Summary:

This research includes testing drug toxicity in cell culture, measuring I3C anti-HSV activity by viral growth studies, and measuring cell cycle gene expression in the presence and absence of I3C. We have discovered that this relatively nontoxic compound found in certain foods inhibits HSV replication by at least 99.9% in vitro in tissue culture. This inhibition was found to be caused by the adverse effects of I3C on specific cell cycle factors such as cdks that are a part of the normal host cell machinery. Monkey kidney tissue culture cells required at least 12 hours of I3C pretreatment and human lung tissue culture cells required at least 36 hours of pretreatment prior to infection for viral inhibition to occur. The observed inhibition of HSV was not due to direct inactivation of the virus by the drug or cell toxicity.

Cdks are proteins that normally regulate the cell cycle at crucial points but they also play a role in HSV replication. It has long been known that HSV is connected to host cell functions and that replication is dependent on cdk activity as observed by more efficient replication in cycling cells. Previous studies have shown that host cell factors and cdks are a requirement for transcription of HSV genes or interact with HSV proteins. Known inhibitors of cdks disable the protein and deprive the virus an opportunity to replicate efficiently. Cdks phosphorylate proteins and control the cell transition from G1 to S or G2 to M. The p53 protein is another important factor of the cell cycle and it stops the cell cycle if there is DNA damage or if repair is necessary. The p21 protein is a cdk inhibitor of the cell cycle. The p21 protein can prevent the cell from entering the S phase of the cell cycle. Our results suggest that I3C may deny HSV the cell cycle factors it requires by manipulating p21 or p53.

Gene expression studies and RNA isolation results in our study support the mechanism described above. If specific cell cycle factors required by HSV can be disrupted by I3C then I3C may be a novel pharmacological inhibitor of HSV replication.