Presatovir (GS-5806) (GS-5806) is a novel, orally bioavailable RSV fusion inhibitor (mean EC50: 0.43 nM).

Presatovir exhibits potent activity against a wide range of RSV A and B clinical isolates (mean EC50: 0.43 nM) [1]. GS-5806 inhibits pre to post triggered conformational changes of RSV F protein, suggesting a possible mechanism for antiviral activity [2].

In a cotton rat model of RSV infection, Presatovir demonstrates dose-dependent (0-30 mg/kg) antiviral efficacy. Oral bioavailability in preclinical species ranges from 46 to 100%, with penetration of the compound into the lung tissue demonstrated in Sprague-Dawley rats. Multidose oral treatment of Presatovir appears safe in adults, and in healthy human volunteers experimentally infected with RSV, a potent antiviral effect and reduction in disease severity are observed in the high dose group [1].

GS-5806 is diluted in 100% DMSO. To conduct the cytopathic antiviral assay, 0.4 μL of 100×concentrated 3-fold serially diluted drug is added to 20 μL of cell culture medium in a 384-well plate. HEp-2 cells are then suspended in MEM plus 10% FBS at a density of 1×10^5 cells/mL, are infected in bulk with RSV A2 at a titer of approximately 1×10^4.5 tissue culture infectious doses/mL. Immediately following infection, 20 μL of RSV-infected cells are added to each well. The cells are then cultured for 4 days at 37 °C. Following this incubation, the cells are allowed to equilibrate to 25°C. The RSV-induced cytopathic effect is determined by adding 40 μL of Cell-Titer Glo viability reagent. Following a 10 min incubation at 25 °C, cell viability is determined [1].