Department of Biomedical Sciences, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China.
Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China.
Eur J Med Chem. 2019 Oct 1;179:828-836. doi: 10.1016/j.ejmech.2019.06.082. Epub 2019 Jun 29.
A ferrocenyl boron dipyrromethene (BODIPY) has been developed and utilized as a dark quencher to construct a cathepsin B-responsive fluorescent probe and photosensitizer. The smart fluorescent probe and photosensitizer (Pc-FcQ) contains a zinc(II) phthalocyanine as the fluorescent and photosensitizing unit which is conjugated to the ferrocenyl BODIPY dark quencher via a cathepsin B-cleavable peptide substrate [Gly-Phe-Leu-Gly-Lys]. The photosensitizing properties of Pc-FcQ, including fluorescence and singlet oxygen generation, are significantly quenched through energy transfer to the BODIPY unit and subsequently by the photoinduced electron transfer from the nearby ferrocenyl moiety. Upon exposure of cathepsin B in human hepatocellular carcinoma HepG cells, the fluorescence emission of Pc-FcQ could be restored, indicating the cleavage of the peptide substrate and the separation of the phthalocyanine and ferrocenyl BODIPY unit. However, the intracellular fluorescence intensity of Pc-FcQ was largely diminished after the cells were pre-treated with cathepsin B inhibitor. Its intracellular fluorescence intensity was comparable to that of the control compound in which the peptide substrate was replaced by the non-cleavable one [Gly-Gly-Gly-Gly-Lys]. The singlet oxygen generation of Pc-FcQ was also examined in HepG2 cells as reflected by the cytotoxicity assay. The Pc-FcQ exhibited higher potency when compared with the non-cleavable analogue due to the cleavage of peptide substrate and the detachment of the BODIPY dark quencher from the phthalocyanine. The activation of the Pc-FcQ was also demonstrated in tumor-bearing nude mice. After intratumoral injection of Pc-FcQ, the fluorescence intensity at the tumor region increased gradually over 10 h as a result of the detachment of the dark quencher upon the action of cathepsin B. All the results suggest that this ferrocenyl BODIPY could serve as an efficient dark quencher and the resulting Pc-FcQ could act as the cathepsin B-responsive fluorescent probe and activatable photosensitizer.
开发并利用一种二茂铁基硼二吡咯甲川（BODIPY）作为暗猝灭剂来构建组织蛋白酶 B 响应型荧光探针和光动力剂。智能荧光探针和光动力剂（Pc-FcQ）包含一个锌（II）酞菁作为荧光和光敏单元，通过组织蛋白酶 B 可切割的肽底物 [Gly-Phe-Leu-Gly-Lys] 与二茂铁基 BODIPY 暗猝灭剂连接。Pc-FcQ 的光敏性质，包括荧光和单线态氧生成，通过能量转移到 BODIPY 单元并随后通过来自附近二茂铁部分的光致电子转移而显著猝灭。在人肝癌 HepG 细胞中暴露于组织蛋白酶 B 后，Pc-FcQ 的荧光发射可以恢复，表明肽底物的切割以及酞菁和二茂铁基 BODIPY 单元的分离。然而，在用组织蛋白酶 B 抑制剂预处理细胞后，Pc-FcQ 的细胞内荧光强度大大降低。其细胞内荧光强度与对照化合物（其中肽底物被不可切割的 [Gly-Gly-Gly-Gly-Lys] 取代）相当。通过细胞毒性测定也检查了 Pc-FcQ 的单线态氧生成。与不可切割的类似物相比，由于肽底物的切割和 BODIPY 暗猝灭剂从酞菁上的脱离，Pc-FcQ 表现出更高的效力。Pc-FcQ 的激活也在荷瘤裸鼠中得到了证明。在肿瘤内注射 Pc-FcQ 后，由于组织蛋白酶 B 的作用导致暗猝灭剂的脱离，肿瘤区域的荧光强度逐渐增加，超过 10 小时。所有结果表明，这种二茂铁基 BODIPY 可以作为有效的暗猝灭剂，所得的 Pc-FcQ 可以作为组织蛋白酶 B 响应型荧光探针和可激活的光敏剂。
