Intracellular Ca²⁺ leak from cardiac ryanodine receptor (RyR2) is an established mechanism of sudden cardiac death (SCD), whereby dysregulated Ca²⁺ handling causes ventricular arrhythmias. We previously discovered the RyR2-selective inhibitor ent-(+)-verticilide (ent-1), a 24-membered cyclooligomeric depsipeptide that is the enantiomeric form of a natural product (nat-(-)-verticilide). Here, we examined its 18-membered ring-size oligomer (ent-verticilide B1; "ent-B1") in RyR2 single channel and [³H]ryanodine binding assays, and in Casq2^–/– cardiomyocytes and mice, a gene-targeted model of SCD. ent-B1 inhibited RyR2 single channels and RyR2-mediated spontaneous Ca²⁺ release in Casq2^–/– cardiomyocytes with sub-micromolar potency. ent-B1 was a partial RyR2 inhibitor, with maximal inhibitory efficacy of less than 50%. ent-B1 was stable in plasma, with a peak plasma concentration of 1460 ng/ml at 10 minutes and half-life of 45 minutes after intraperitoneal administration of 3 mg/kg in mice. In vivo, ent-B1 significantly reduced catecholamine-induced ventricular arrhythmias in Casq2^–/– mice in a dose-dependent manner. Hence, we have identified a novel chemical entity – ent-B1 – that preserves the mechanism of action of a hit compound and shows therapeutic efficacy. These findings strengthen RyR2 as an antiarrhythmic drug target and highlight the potential of investigating the mirror-image isomers of natural products to discover new therapeutics.

心脏兰尼碱受体 (RyR2) 的细胞内 Ca ²⁺泄漏是心源性猝死 (SCD) 的既定机制，其中 Ca ²⁺处理失调会导致室性心律失常。我们之前发现了 RyR2 选择性抑制剂ent- (+)-verticilide ( ent -1)，一种 24 元环寡聚缩肽，是天然产物 ( nat -(-)-verticilide ) 的对映体形式。在这里，我们在 RyR2 单通道和 [ ³ H]ryanodine 结合测定中以及在Casq2 ^–/–心肌细胞和小鼠中检查了其 18 元环大小寡聚物（ent -verticilide B1；“ ent -B1”） ， SCD 的目标模型。ent -B1 以亚微摩尔浓度抑制Casq2 ^–/–心肌细胞中RyR2 单通道和 RyR2 介导的自发 Ca ²⁺释放。 ent -B1是RyR2的部分抑制剂，最大抑制效力低于50%。ent -B1在血浆中稳定，小鼠腹腔注射3mg/kg后10分钟血浆峰浓度为1460ng/ml，半衰期为45分钟。在体内，ent -B1以剂量依赖性方式显着减少Casq2 ^–/–小鼠中儿茶酚胺诱导的室性心律失常。因此，我们发现了一种新的化学实体——ent - B1——它保留了热门化合物的作用机制并显示出治疗功效。这些发现加强了 RyR2 作为抗心律失常药物靶点的地位，并强调了研究天然产物的镜像异构体以发现新疗法的潜力。