Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)¹. The rapid development of highly effective vaccines^2,3 against SARS-CoV-2 has altered the trajectory of the pandemic, and antiviral therapeutics⁴ have further reduced the number of COVID-19 hospitalizations and deaths. Coronaviruses are enveloped, positive-sense, single-stranded RNA viruses that encode various structural and non-structural proteins, including those critical for viral RNA replication and evasion from innate immunity⁵. Here we report the discovery and development of a first-in-class non-covalent small-molecule inhibitor of the viral guanine-N7 methyltransferase (MTase) NSP14. High-throughput screening identified RU-0415529, which inhibited SARS-CoV-2 NSP14 by forming a unique ternary S-adenosylhomocysteine (SAH)-bound complex. Hit-to-lead optimization of RU-0415529 resulted in TDI-015051 with a dissociation constant (K_d) of 61 pM and a half-maximal effective concentration (EC₅₀) of 11 nM, inhibiting virus infection in a cell-based system. TDI-015051 also inhibited viral replication in primary small airway epithelial cells and in a transgenic mouse model of SARS CoV-2 infection with an efficacy comparable with the FDA-approved reversible covalent protease inhibitor nirmatrelvir⁶. The inhibition of viral cap methylases as an antiviral strategy is also adaptable to other pandemic viruses.

2019 冠状病毒病 （COVID-19） 由严重急性呼吸系统综合症冠状病毒 2 （SARS-CoV-2）¹ 引起。针对 SARS-CoV-2 的高效疫苗^2,3 的快速开发改变了大流行的轨迹，而抗病毒疗法⁴ 进一步减少了 COVID-19 住院和死亡人数。冠状病毒是有包膜的正义单链 RNA 病毒，编码各种结构和非结构蛋白，包括对病毒 RNA 复制和逃避先天免疫至关重要的蛋白⁵。在这里，我们报道了病毒鸟嘌呤-N7 甲基转移酶 （MTase） NSP14 的同类首创非共价小分子抑制剂的发现和开发。高通量筛选确定了 RU-0415529，它通过形成独特的三元 S-腺苷同型半胱氨酸 （SAH） 结合复合物来抑制 SARS-CoV-2 NSP14。RU-0415529 的苗头化合物到先导化合物优化导致 TDI-015051 的解离常数 （K_d） 为 61 pM，半数最大有效浓度 （EC₅₀） 为 11 nM，抑制了基于细胞的系统中的病毒感染。TDI-015051 还抑制原代小气道上皮细胞和 SARS CoV-2 感染转基因小鼠模型中的病毒复制，其疗效与 FDA 批准的可逆共价蛋白酶抑制剂 nirmatrelvir⁶ 相当。抑制病毒帽甲基化酶作为一种抗病毒策略也适用于其他大流行性病毒。