Evaluation of AT-752, a double prodrug of a guanosine nucleotide analog with in vitro and in vivo activity against dengue and other flaviviruses.

Every year millions of people worldwide are infected with dengue virus (DENV), with a significant number developing severe life-threatening disease. There are currently no broadly indicated vaccines or therapeutics available for treatment of DENV infection. Here, we show that AT-281, the free base of AT-752, an orally available double prodrug of a guanosine nucleotide analog, was a potent inhibitor of DENV serotypes 2 and 3 in vitro, requiring concentrations of 0.48 and 0.77 μM, respectively, to inhibit viral replication by 50% (EC50) in Huh-7 cells. AT-281 was also a potent inhibitor of all other flaviviruses tested with EC50 values ranging from 0.19 to 1.41 μM. Little to no cytotoxicity was observed for AT-281 at concentrations up to 170 μM. After oral administration of AT-752, substantial levels of the active triphosphate metabolite AT-9010 were formed in vivo in peripheral blood mononuclear cells of mice, rats and monkeys. Furthermore, AT-9010 competed with guanosine triphosphate in RNA template-primer elongation assays with DENV-2 RNA polymerase, which is essential for viral replication, with incorporation of AT-9010 resulting in termination of RNA synthesis. In AG129 mice infected with DENV D2Y98P, treatment with AT-752 significantly reduced viremia and morbidity and increased survival. The demonstrated in vitro and in vivo activity of AT-752 suggest that it is a promising compound for the treatment of dengue virus infection, and is currently under evaluation in clinical studies.