Lysosome‐Targeted Bioprobes for Sequential Cell Tracking from Macroscopic to Microscopic Scales

Abstract Longitudinal tracking of living cells is crucial to understanding the mechanism of action and toxicity of cell‐based therapeutics. To quantify the presence of administered cells in the host tissue without sacrifice of animals, labeling of the target cells with a nontoxic and stable contrast agent is a prerequisite. However, such long‐term live cell tracking is currently limited by the lack of fluorophores with steady optical and physicochemical properties in the near‐infrared (NIR) window. Herein, for the first time, the design of fixable cell‐tracking NIR fluorophores (CTNFs) with high optical properties, excellent cell permeation and retention, and high stability against chemical treatments is reported. Efficient cellular labeling and tracking of CTNFs using intraoperative optical fluorescence imaging by following the fate of NIR‐labeled cells from the time of injection into animals to ex vivo cellular analysis after resection of the target tissue is demonstrated. Due to the lipophilic cationicity and primary amine docking group, CTNF126 outperforms the other tested fluorophores with rapid diffusion into the cytoplasmic membrane and sequestration inside the lysosomes, which prevents cellular efflux and improves cellular retention. Thus, CTNF126 will be useful to track cells in living organisms for the mechanism of action at the single cell level.