Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, Maryland 21702, United States.
Laboratory for in Vivo Cellular and Molecular Imaging, ICMI-BEFY/MIMA, Vrije Universiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium.
J Am Chem Soc. 2023 Jul 12;145(27):14647-14659. doi: 10.1021/jacs.3c01765. Epub 2023 Jun 27.
Heptamethine indocyanines are invaluable probes for near-infrared (NIR) imaging. Despite broad use, there are only a few synthetic methods to assemble these molecules, and each has significant limitations. Here, we report the use of pyridinium benzoxazole (PyBox) salts as heptamethine indocyanine precursors. This method is high yielding, simple to implement, and provides access to previously unknown chromophore functionality. We applied this method to create molecules to address two outstanding objectives in NIR fluorescence imaging. First, we used an iterative approach to develop molecules for protein-targeted tumor imaging. When compared to common NIR fluorophores, the optimized probe increases the tumor specificity of monoclonal antibody (mAb) and nanobody conjugates. Second, we developed cyclizing heptamethine indocyanines with the goal of improving cellular uptake and fluorogenic properties. By modifying both the electrophilic and nucleophilic components, we demonstrate that the solvent sensitivity of the ring-open/ring-closed equilibrium can be modified over a wide range. We then show that a chloroalkane derivative of a compound with tuned cyclization properties undergoes particularly efficient no-wash live cell imaging using organelle-targeted HaloTag self-labeling proteins. Overall, the chemistry reported here broadens the scope of accessible chromophore functionality, and, in turn, enables the discovery of NIR probes with promising properties for advanced imaging applications.
七甲川菁染料是近红外（NIR）成像中非常有价值的探针。尽管应用广泛，但目前仅有少数几种方法可用于合成这些分子，而且每种方法都存在明显的局限性。在此，我们报告了使用吡啶苯并恶唑（PyBox）盐作为七甲川菁染料前体的方法。该方法产率高、操作简单，并可获得以前未知的发色团功能。我们应用该方法来合成分子，以解决 NIR 荧光成像中的两个突出目标。首先，我们采用迭代方法开发用于蛋白质靶向肿瘤成像的分子。与常见的 NIR 荧光团相比，优化后的探针增加了单克隆抗体（mAb）和纳米抗体缀合物的肿瘤特异性。其次，我们开发了具有环化七甲川菁染料的分子，以提高细胞摄取和荧光性质。通过修饰亲电和亲核部分，我们证明了开环/闭环平衡的溶剂敏感性可以在很宽的范围内进行调节。然后我们表明，经修饰的具有调控环化性质的化合物的氯代烷烃衍生物，通过靶向细胞器的 HaloTag 自标记蛋白，可实现特别高效的无冲洗活细胞成像。总的来说，这里报道的化学拓宽了可获得的发色团功能的范围，并进一步实现了具有有前景的成像应用性能的 NIR 探针的发现。
