Triphosphates of the Two Components in DESCOVY and TRUVADA are Inhibitors of the SARS-CoV-2 Polymerase

Steffen Jockusch; Chuanjuan Tao; Xiaoxu Li; Thomas K. Anderson; Minchen Chien; Shiv Kumar; James J. Russo; Robert Kirchdoerfer; Jingyue Ju

Although potential drug candidates have been designed to target nearly every stage of the viral infection, 2 no effective drug is currently approved to treat COVID-19. RdRp in coronaviruses is a precise and welldefined drug target; the active site of the RdRp is highly conserved among different positive-sense RNA viruses and shares common structural features in these viruses. 4 RdRps, including the coronavirus polymerase, have low fidelity, 5 which enables them to recognize a variety of modified nucleotide analogues as substrates. Such nucleotide and nucleoside analogues may inhibit further RNA-polymerase catalyzed RNA replication and are therefore important candidate anti-viral agents. [6] [7] [8] [9] In our previous studies, we used molecular analysis to design and select nucleotide analogues as potential inhibitors of the SARS-CoV-2 RdRp, 10, 11 with particular focus on two key properties: (1) their similarity in size and structure to natural nucleotides, including their ability to bind within the active site of the polymerase and (2) their ability to terminate polymerase reactions due either to (a) the presence of blocking groups on the 3'-OH or (b) the presence of chemical modification groups at nearby positions on the sugar ring. Based on these criteria, we previously tested the active triphosphate forms of Sofosbuvir, Alovudine and AZT with the RdRps of both SARS-CoV and SARS-CoV-2. These three triphosphates, 2'-F,Me-UTP, 3'-F-dTTP and 3'-N3-dTTP, all demonstrated the ability to be incorporated by these two coronavirus RdRps, and to block further incorporation. 10, 11 We also demonstrated the ability of the active triphosphate form of tenofovir, tenofovir diphosphate (TFV-DP), to inhibit the SARS-CoV-2 RdRp. 11 Tenofovir prodrugs are often used in combination with the drug emtricitabine as anti-viral medications. We report here that the active triphosphate forms of both tenofovir and emtricitabine are inhibitors of the SARS-CoV-2 RdRp catalyzed reaction in side-by-side experiments.