The oligoadenylate synthetase (OAS)–RNase L system is an IFN-inducible antiviral pathway activated by viral infection. Viral double-stranded (ds) RNA activates OAS isoforms that synthesize the second messenger 2-5A, which binds and activates the pseudokinase-endoribonuclease RNase L. In cells, OAS activation is tamped down by ADAR1, an adenosine deaminase that destabilizes dsRNA. Mutation of ADAR1 is one cause of Aicardi-Goutières syndrome (AGS), an interferonopathy in children. ADAR1 deficiency in human cells can lead to RNase L activation and subsequent cell death. To evaluate RNase L as a possible therapeutic target for AGS, we sought to identify small-molecule inhibitors of RNase L. A 500-compound library of protein kinase inhibitors was screened for modulators of RNase L activity in vitro. We identified ellagic acid (EA) as a hit with 10-fold higher selectivity against RNase L compared with its nearest paralog, IRE1. SAR analysis identified valoneic acid dilactone (VAL) as a superior inhibitor of RNase L, with 100-fold selectivity over IRE1. Mechanism-of-action analysis indicated that EA and VAL do not bind to the pseudokinase domain of RNase L despite acting as ATP competitive inhibitors of the protein kinase CK2. VAL is nontoxic and functional in cells, although with a 1,000-fold decrease in potency, as measured by RNA cleavage activity in response to treatment with dsRNA activator or by rescue of cell lethality resulting from self dsRNA induced by ADAR1 deficiency. These studies lay the foundation for understanding novel modes of regulating RNase L function using small-molecule inhibitors and avenues of therapeutic potential.

寡腺苷酸合成酶（OAS）-RNase L系统是由病毒感染激活的IFN诱导型抗病毒途径。病毒双链（ds）RNA激活了OAS亚型，该亚型合成了第二个信使2-5A，后者结合并激活了假激酶-核糖核酸内切酶RNaseL。在细胞中，OAS激活被ADAR1抑制，这是一种使dsRNA稳定的腺苷脱氨酶。ADAR1突变是儿童心律失常性心律失常综合征（AGS）的原因之一。人细胞中的ADAR1缺乏会导致RNase L活化和随后的细胞死亡。为了评估RNase L作为AGS的可能治疗靶标，我们寻求鉴定RNase L的小分子抑制剂。筛选了500种蛋白激酶抑制剂的化合物文库，用于体外RNase L活性的调节剂。我们将鞣花酸（EA）鉴定为对RNase L的选择性比其最接近的同源物IRE1高10倍的命中。SAR分析表明，瓦尼酸双内酯（VAL）是RNase L的优良抑制剂，选择性比IRE1高100倍。作用机理分析表明，尽管EA和VAL充当蛋白激酶CK2的ATP竞争性抑制剂，但它们并未与RNase L的假激酶结构域结合。VAL在细胞中无毒且无功能，尽管效价降低了1000倍，如通过响应dsRNA激活剂处理的RNA裂解活性或通过挽救由ADAR1缺乏引起的自身dsRNA导致的细胞杀伤力来衡量。这些研究为了解使用小分子抑制剂调节RNase L功能的新模式和治疗潜力奠定了基础。