The activation chain of the broad-spectrum antiviral bemnifosbuvir at atomic resolution

Bemnifosbuvir (AT-527) and AT-752 are guanosine analogues currently in clinical trials against several RNA viruses. Here we show that these drugs require a minimal set of 5 cellular enzymes for activation to their common 5'-triphosphate AT-9010, with an obligate order of reactions. AT-9010 selectively inhibits essential viral enzymes, accounting for broad spectrum antiviral potency. Functional and structural data at atomic resolution decipher N6-purine deamination compatible with metabolic activation by human ADALP1. Crystal structures of human HINT1, ADALP1, GUK1, and NDPK at 2.09, 2.44, 1.76, and 1.9 A resolution, respectively, with cognate precursors of AT-9010 illuminate the activation pathway from the orally available bemnifosbuvir to AT-9010, pointing to key drug-protein contacts along the activation pathway. Our work provides a framework to integrate the design of antiviral nucleotide analogues, confronting requirements and constraints associated with activation enzymes along the 5'-triphosphate assembly line.