Li_2021_Antimicrob.Agents.Chemother__AAC0060221

Remdesivir (RDV; GS-5734; Veklury(a)), the first FDA-approved antiviral to treat COVID-19, is a single diastereomer monophosphoramidate prodrug of an adenosine analogue. RDV is taken up in the target cells and metabolized in multiple steps to form the active nucleoside triphosphate (TP) (GS-443902), which in turn acts as a potent and selective inhibitor of multiple viral RNA polymerases. In this report, we profiled the key enzymes involved in the RDV metabolic pathway with multiple parallel approaches: (1) bioinformatic analysis of nucleoside/tide metabolic enzyme mRNA expression using public human tissue and lung single-cell RNAseq datasets; (2) protein and mRNA quantification of enzymes in human lung tissue and primary lung cells; (3) biochemical studies on the catalytic rate of key enzymes; (4) effects of specific enzyme inhibitors on the GS-443902 formation; and (5) the effects of these inhibitors on RDV antiviral activity against SARS-CoV-2 in cell culture. Our data collectively demonstrated that carboxylesterase 1 (CES1) and cathepsin A (CatA) are enzymes involved in hydrolyzing RDV to its alanine intermediate Met X, which is further hydrolyzed to the monophosphate form by histidine triad nucleotide-binding protein 1 (HINT1). The monophosphate is then consecutively phosphorylated to diphosphate and triphosphate by cellular phosphotransferases. Our data support the hypothesis that the unique properties of RDV prodrug not only allow lung-specific accumulation critical for the treatment of respiratory viral infection such as COVID-19, they also enable efficient intracellular metabolism of RDV and its Met X to monophosphate and successive phosphorylation to form the active TP in disease-relevant cells.