In vitro activity: Vesatolimod (formerly known as GS-9620) is a novel potent, selective and orally bioactive small molecule agonist of Toll-like receptor 7 (TLR-7) with an EC50 of 291 nM. It has the potential for the treatment of chronic hepatitis B viral (HBV) infection. GS-9620 selectively induces IFN-α, cytokines and chemokines. The minimum effective concentrations for IFN-α induction were similar in pDCs and in PBMCs from HCV-positive donors. GS-9620 demonstrates an EC50 of 291 nM for human TLR7, which is 30-fold selectivity over TLR8 with EC50 of 9 μM.

Kinase Assay: Vesatolimod (GS-9620) rapidly internalizes into cells and preferentially localizes to and signals from endo-lysosomal compartments. To test this hypothesis, the kinetics of cellular uptake of the compound in Daudi cells using tritiated Vesatolimod (3H-GS-9620) is measured. The kinetics of 3H-GS-9620 accumulation is rapid, reaching concentration-dependent steady-state equilibrium in approximately thirty minutes. Measured intracellular concentration of 3H-Vesatolimod is 5-fold higher than the extracellular concentration of 3H-GS-9620 used to treat cells. Increases in intracellular 3H-Vesatolimod concentrations are roughly proportional with increasing concentrations of 3H-GS-9620.

Cell Assay: Daudi cells are incubated for indicated times with varying concentrations [3H]Vesatolimod (GS-9620) (0.7μCi/mL). Cell associated radioactivity is extracted with ice cold 80% ethanol and measured using liquid scintillation counting. The total amount of Vesatolimod in cells is calculated from a calibration curve for Vesatolimod (GS-9620) mass versus radioactivity. Cell volume is measured.