Uncovering the key to latency may bring an end to oral herpes, researchers hope
One distinguishing characteristic of the herpevirus family of viruses is latency. Rather than being cleared by the body’s immune system, the herpes simplex virus establishes permanent residence in a nerve root called a ganglion. While the virus is in an active phase, the immune system is capable of responding, sending out antibodies to fight off infection. But when herpes goes into hiding during its latent (or inactive) phase in the ganglia, it remains beyond the immune system’s reach.
But what if we could bring the herpes simplex virus out of hiding? Researchers at Duke University in Durham, NC looked at that question and, in the process, have uncovered a new key to understanding latency and HSV-1.
In a joint statement, Professor Bryan Cullen and Jennifer Lin Umbach, Ph.D. of the Duke Department of Molecular Genetics and Microbiology and Center for Virology, commented on the impact of their research: “Our work provides, for the first time, a molecular understanding of how HSV-1 establishes a life-long latent infection in the nerve cells of the face, and how it reactivates from latency to cause cold sores . . . The work we have performed provides a basis for the development of anti-HSV-1 drugs that might be able to permanently clear HSV-1 from
patients.”
The Duke research team studied the one molecular product produced by the herpes simplex virus during its latent phase—latency associated transcript RNA or LAT RNA. They were able to demonstrate, in studies of mice, that LAT RNA is processed into microRNAs—single-strand RNA molecules. These microRNAs block the production of proteins that make the herpes virus turn on active viral replication. As long as there is a sufficient supply of microRNAs, the herpes virus will stay latent, or inactive.
The potential for treatment lies in learning how to tip the balance and regulate the production and supply of microRNA in order to activate the virus. “Inactive virus is completely untouchable by any treatment we have. Unless you activate the virus, you can’t kill it,” Cullen commented.
Cullen and his team are testing a new drug designed to very precisely bind to the microRNAs that keep the virus dormant. If it works, the virus would become activated and start replicating. Once the virus is active, a patient would then be treated with antiviral therapy to effectively kill the virus.“In principle, you could activate and then kill all of the virus in a patient,” Cullen said. “This would completely cure a person, and you would never get another cold sore.”
Interesting as this new discovery is, many years of research lie ahead before researchers can explore the possibility of development a new treatment. As Cullen and Lin commented, “We anticipate approximately 2 years of animal experiments in mice followed by approximately 1 year of toxicity studies in other animals, followed by small studies in healthy volunteers. After that, assuming things go well, this drug might proceed to clinical trials in HSV-1 infected individuals. It is very possible that the drug candidate might fall out at any of these stages, due to lack of effectiveness or some unanticipated side effect.”
While the Duke research team has focused on HSV-1, they hope that their work will translate into a better understanding of latency and HSV-2 as well. As Cullen and Lin indicated, “All our work so far has been on HSV-1 . . . but HSV-2 is quite closely related. We have begun work to see if the lessons we have learned in HSV-1 also apply to HSV-2, and should know this by the end of the year. If these lessons do hold, then we might hope to start animal trials for an anti-HSV-2 drug in early 2009. However, our initial data indicate that HSV-1 and HSV-2 will require distinct drug therapies.”
