Certain protein kinase inhibitors, now in clinical development against cancer, unexpectedly have been found to block the dengue virus, for which no pharmacological treatment exists. Using immunofluorescent imaging techniques, HMS researchers discovered that inhibitors of c-Src protein kinases prevented the assembly of dengue virus particles in primate and mosquito cells. The findings were reported in the Feb. 27 Proceedings of the National Academy of Sciences.
Transmitted by mosquitoes and related to the West Nile virus, dengue virus can cause head and joint aches symptomatic of dengue fever. This condition sometimes progresses to the deadly dengue hemorrhagic fever, or dengue shock syndrome. A report last year indicated that dengue virus, whose mechanism of infecting cells remains unclear, annually afflicts 50 to 100 million people with dengue fever and causes 250,000 to 500,000 cases of the more severe shock syndrome.
With expanding mosquito habitats and increasing cases of the severe form of dengue fever, Priscilla Yang, HMS assistant professor of microbiology and molecular genetics, and postdoctoral researcher Justin Chu wondered whether molecules directed at cellular targets could be used to combat the virus.
“We wanted to pick a third-world disease, a less studied virus,” Yang said. To have a head start on finding a treatment, the researchers used drugs already in development.
“There are lots of molecules in clinical development as kinase inhibitors,” Yang said. “They are known to be orally bioavailable, but not to be toxic.”
But which kinase inhibitor to choose? To whittle down the possibilities, Yang and Chu first developed an immunofluorescent imaging assay to detect the amount of dengue infection in cells incubated with the virus. The assay measured dengue-virus envelope protein, a viral-encapsulating molecule. Three days after cotreatment with the virus and mycophenolic acid (an immunosuppressive agent that is known to also inhibit dengue virus in vitro), the number of positively stained cells showed a dose-dependent decrease in the viral envelope protein. Satisfied that their assay could detect inhibition of dengue, the researchers went on to co-incubate with the virus non-cytotoxic concentrations of 120 different kinase inhibitors.
“We found several hits, including Src kinases,” Yang said. The c-Src protein kinase inhibitors dasatinib and AZD0530 showed particularly strong inhibitory effects on the virus. Yang and Chu went on to demonstrate that silencing c-Src protein prevented the replication of the dengue virus in human hepatoma cells and that the inhibitors’ virus-blocking abilities were due to their inhibition of viral-particle assembly. The results indicate that host-cell factors such as protein kinases are viable antiviral drug targets.
Because dengue virus belongs to the Flavivirus genus, which includes West Nile virus and tick-borne encephalitis, it is possible that Src kinase treatment could be effective against other types of viral infection.
