GS-621763 is an orally bioavailable prodrug form of the antiviral nucleotide analog GS-443902, which is also an active metabolite of remdesivir .1,2 Upon intestinal absorption, GS-621763 is metabolized into the intermediate metabolite GS-441524 , which is then further metabolized to the active nucleotide triphosphate GS-443902 in cells where it induces RNA chain termination and inhibits viral polymerases.2 It reduces the cytopathic effect of respiratory syncytial virus (RSV) in infected HEp-2 cells (EC50 = 0.26 ?M), as well as reduces viral titers in Vero E6 cells infected with various clinical isolates of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; EC50s = 0.11-0.73 ?M). GS-621763 (10 mg/kg) inhibits viral transmission in ferrets infected with the SARS-CoV-2 variant of concern (VOC) P.1, also known as the gamma variant.2
1.Mackman, R.L., Hui, H.C., Perron, M., et al.Prodrugs of a 1'-CN-4-aza-7,9-dideazaadenosine C-nucleoside leading to the discovery of remdesivir (GS-5734) as a potent inhibitor of respiratory syncytial virus with efficacy in the african green monkey model of RSVJ. Med. Chem.64(8)5001-5017(2021) 2.Cox, R.M., Wolf, J.D., Lieber, C.M., et al.Oral prodrug of remdesivir parent GS-441524 is efficacious against SARS-CoV-2 in ferretsNat. Commun.12(1)6415(2021)