The deletion of a phenylalanine at position 508 (p.Phe508del) in the CFTR anion channel is the most prevalent variant in people with Cystic Fibrosis (CF). This variant impairs folding and stability of the CF transmembrane conductance regulator (CFTR) protein, resulting in its defective trafficking and premature degradation. Over the last years, therapeutic accomplishments have been attained in developing small molecules that partially correct p.Phe508del-CFTR defects; however, the mechanism of action (MoA) of these compounds has only started to be uncovered. In this study, we employed biochemical, fluorescence microscopy, and functional assays to examine the efficacy and properties of PTI-801, a newly developed p.Phe508del-CFTR corrector. To exploit its MoA, we assessed PTI-801 effects in combination with low temperature, genetic revertants of p.Phe508del-CFTR (the p.Val510Asp, p.Gly550Glu, p.Arg1070Trp, and 4RK) and other correctors. Our results demonstrated that PTI-801 rescues p.Phe508del-CFTR processing, PM trafficking, and channel function (upon agonist stimulation) with greater correction effects in combination with ABBV-2222, FDL-169, VX-661, or VX-809, but not with VX-445. Although PTI-801 exhibited no potentiator activity on low temperature- and corrector-rescued p.Phe508del-CFTR, this compound displayed similar behavior to that of VX-445 on genetic revertants. Such evidence associated with the lack of additivity when PTI-801 and VX-445 were combined indicates that they share a common binding site to correct p.Phe508del-CFTR defects. Despite the high efficacy of PTI-801 in combination with ABBV-2222, FDL-169, VX-661, or VX-809, these dual corrector combinations only partially restored p.Phe508del-CFTR conformational stability, as shown by the lower half-life of the mutant protein compared to that of WT-CFTR. In summary, PTI-801 likely shares a common MoA with VX-445 in rescuing p.Phe508del-CFTR, thus being a feasible alternative for the development of novel corrector combinations with greater capacity to rescue mutant CFTR folding and stability.

中文翻译：

---

PTI-801 (posenacaftor) 与 VX-445 (elexacaftor) 具有共同的机制来拯救 p.Phe508del-CFTR


CFTR 阴离子通道中 508 位苯丙氨酸 (p.Phe508del) 的缺失是囊性纤维化 (CF) 患者中最常见的变异。这种变异会损害 CF 跨膜电导调节蛋白 (CFTR) 的折叠和稳定性，导致其运输缺陷和过早降解。在过去的几年里，在开发部分纠正 p.Phe508del-CFTR 缺陷的小分子方面取得了治疗成就；然而，这些化合物的作用机制 (MoA) 才刚刚被揭示。在这项研究中，我们采用生化、荧光显微镜和功能测定来检查 PTI-801（一种新开发的 p.Phe508del-CFTR 校正剂）的功效和特性。为了利用其 MoA，我们结合低温、p.Phe508del-CFTR 基因回复体（p.Val510Asp、p.Gly550Glu、p.Arg1070Trp 和 4RK）和其他校正子评估了 PTI-801 的效果。我们的结果表明，PTI-801 与 ABBV-2222、FDL-169、VX-661 或 VX-809 联合使用可挽救 p.Phe508del-CFTR 加工、PM 运输和通道功能（激动剂刺激后），具有更大的校正效果。但不适用于 VX-445。尽管 PTI-801 对低温和校正剂拯救的 p.Phe508del-CFTR 没有表现出增效剂活性，但该化合物对遗传回复体表现出与 VX-445 相似的行为。这些与 PTI-801 和 VX-445 组合时缺乏加和性相关的证据表明它们共享一个共同的结合位点来纠正 p.Phe508del-CFTR 缺陷。尽管 PTI-801 与 ABBV-2222、FDL-169、VX-661 或 VX-809 结合使用具有高效能，但这些双校正剂组合仅部分恢复了 p.1。Phe508del-CFTR 构象稳定性，如与 WT-CFTR 相比突变蛋白的半衰期较短所示。总之，PTI-801 可能与 VX-445 在拯救 p.Phe508del-CFTR 方面具有共同的 MoA，因此是开发具有更大能力拯救突变 CFTR 折叠和稳定性的新型校正剂组合的可行替代方案。