Mak Eunice Chiu-Lam, Chen Ziyong, Lee Lawrence Cho-Cheung, Yan Liang-Liang, Yam Vivian Wing-Wah, Lo Kenneth Kam-Wing
Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong, P. R. China.
Institute of Molecular Functional Materials and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China.
JACS Au. 2025 Jun 10;5(6):2825-2836. doi: 10.1021/jacsau.5c00413. eCollection 2025 Jun 23.
Site-specific bioconjugation techniques are extensively utilized in biological and biomedical fields to precisely label biomolecules with luminescent tags for direct visualization of their intracellular dynamics or with cytotoxic agents for the development of novel anticancer therapeutics. In this work, a series of cyclometalated iridium-(III) polypyridine complexes featuring a thioester moiety was designed as novel phosphorogenic probes for labeling N-terminal cysteine (N-Cys)-containing biomolecules. These thioester complexes were weakly emissive in solutions due to the presence of a low-lying nonradiative distorted triplet intraligand (IL) state localized on the thioester unit, as elucidated by computational analyses. However, their emission intensities and singlet oxygen (O)-photosensitization efficiencies substantially increased upon reaction with l-Cys due to the conversion of the quenching thioester moiety to a nonquenching amide unit. Additionally, the thioester complexes exhibited high selectivity toward N-Cys and displayed significantly enhanced reactivity due to the electron-withdrawing iridium-(III) polypyridine moiety. The remarkable aminothiol-induced emission and O-photosensitization turn-on of the thioester complexes were exploited for the development of intracellular Cys sensors and Cys-activatable photosensitizers for cancer-targeted photodynamic therapy. Furthermore, one of the thioester complexes was selected to react with various N-Cys-modified tumor-targeting peptides, yielding photofunctional iridium-(III)-peptide conjugates with high O generation efficiencies. These conjugates retained the tumor-targeting capabilities of the original peptides and showed high specificity for MDA-MB-231 cells compared to MCF-7 and HEK-293 cells, resulting in selective photocytotoxicity toward this triple-negative breast cancer cell line. We believe that our design approach will inspire the development of novel luminogenic thioester-based reagents for bioconjugation, bioimaging, and therapeutic applications.
位点特异性生物共轭技术在生物学和生物医学领域被广泛应用，用于用发光标签精确标记生物分子，以直接观察其细胞内动态，或与细胞毒性剂结合用于开发新型抗癌疗法。在这项工作中，设计了一系列具有硫酯部分的环金属化铱（III）多吡啶配合物，作为用于标记含N端半胱氨酸（N-Cys）生物分子的新型发光探针。计算分析表明，由于硫酯单元上存在低能非辐射扭曲三重态配体内（IL）态，这些硫酯配合物在溶液中发射较弱。然而，由于淬灭性硫酯部分转化为非淬灭性酰胺单元，它们与l-Cys反应后发射强度和单线态氧（O）光敏化效率大幅提高。此外，硫酯配合物对N-Cys表现出高选择性，并且由于吸电子的铱（III）多吡啶部分而显示出显著增强的反应性。硫酯配合物显著的氨基硫醇诱导发射和O光敏化开启特性被用于开发细胞内Cys传感器和用于癌症靶向光动力疗法的Cys可激活光敏剂。此外，选择一种硫酯配合物与各种N-Cys修饰的肿瘤靶向肽反应，产生具有高O生成效率的光功能铱（III）-肽共轭物。这些共轭物保留了原始肽的肿瘤靶向能力，与MCF-7和HEK-293细胞相比，对MDA-MB-231细胞具有高特异性，从而导致对这种三阴性乳腺癌细胞系的选择性光细胞毒性。我们相信，我们的设计方法将激发用于生物共轭、生物成像和治疗应用的新型基于硫酯的发光试剂的开发。
