Sanguinarine and chelerythrine: two natural products for mitochondria-imaging with aggregation-induced emission enhancement and pH-sensitive characteristics

In this paper, two natural products: chelerythrine (Che) and sanguinarine (San) were systematically explored for aggregation-induced emission enhancement (AIEE) characteristics by a series of spectroscopic and theoretical experiments. After adding increasing amounts of H2O into CH3OH solutions of San and Che, typical AIEE behaviors could be observed; then, the enhanced fluorescence lifetime and nanoparticles were also monitored. Moreover, owing to the presence of two kinds of molecular conformations, the pH-sensitive behaviors of San and Che were displayed in CH3OH/H2O mixtures. Density functional theory indicated that J-aggregation was responsible for the AIEE behaviors of San and Che. Taking advantage of the unique AIEE characteristics, excellent cellular permeability and mitochondria-targeting ability of Che were displayed as a lipophilic cation. In addition, based on the remarkable anti-cancer activity in vitro, depolarization of the mitochondrial membrane potential and the morphological collapses of mitochondria caused by Che were observed, confirming that the aggregation of Che in mitochondria could result in mitochondrial dysfunction. Herein, San and Che are proposed to be AIEE dyes for promising mitochondria-imaging which enabled us to observe their anti-cancer effects directly. In conclusion, these natural products provided an innovative strategy for potential image-guided therapy of tumor cells.