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 RSV.

Mackman, Richard L; Hui, Hon C; Perron, Michel; Murakami, Eisuke; Palmiotti, Christopher; Lee, Gary; Stray, Kirsten; Zhang, Lijun; Goyal, Bindu; Chun, Kwon; Byun, Daniel; Siegel, Dustin; Simonovich, Scott; Du Pont, Venice; Pitts, Jared; Babusis, Darius; Vijjapurapu, Arya; Lu, Xianghan; Kim, Cynthia; Zhao, Xiaofeng; Chan, Julie; Ma, Bin; Lye, Diane; Vandersteen, Adelle; Wortman, Sarah; Barrett, Kimberly T; Toteva, Maria; Jordan, Robert; Subramanian, Raju; Bilello, John P; Cihlar, Tomas

A discovery program targeting respiratory syncytial virus (RSV) identified C-nucleoside 4 (RSV A2 EC50 = 530 nM) as a phenotypic screening lead targeting the RSV RNA-dependent RNA polymerase (RdRp). Prodrug exploration resulted in the discovery of remdesivir (1, GS-5734) that is >30-fold more potent than 4 against RSV in HEp-2 and NHBE cells. Metabolism studies in vitro confirmed the rapid formation of the active triphosphate metabolite, 1-NTP, and in vivo studies in cynomolgus and African Green monkeys demonstrated a >10-fold higher lung tissue concentration of 1-NTP following molar normalized IV dosing of 1 compared to that of 4. A once daily 10 mg/kg IV administration of 1 in an African Green monkey RSV model demonstrated a >2-log10 reduction in the peak lung viral load. These early data following the discovery of 1 supported its potential as a novel treatment for RSV prior to its development for Ebola and approval for COVID-19 treatment.