Triphenylquinoline (TPQ)-Based Dual-State Emissive Probe for Cell Imaging in Multicellular Tumor Spheroids

Insufficient
intratumoral penetration and limited stroma distribution
of the imaging probes or theranostics can lead to a poor-quality diagnosis
or therapeutic resistance. Multicellular tumor spheroids can recapitulate
the physiological environment of tumor tissues with the extracellular
matrix and is thus a better in vitro tumor model to evaluate the imaging
performance and barrier penetration capability of advanced cancer
imaging probes. In this Article, we designed and synthesized a series
of quinoline-based fluorophores with strong emissions in both solution
and solid states. The quinoline core can be constructed via a one-pot
iron-catalysis reaction. Optical properties and single crystal structures
of these quinoline derivatives were tuned by varying the substitutes
at the 6-position of the quinoline core. The twisted intramolecular
charge transfer effect can enhance the fluorescent efficiency, resulting
in the high quantum yield of TPQ-TPA in both solution
(70%) and solid (48%) states (TPQ, triphenylquinoline; TPA, triphenylamine).
In addition, TPQ-TPA exhibited a good biocompatibility
and can deeply penetrate into 3D tumor spheroids within 12 h. The
results indicated that quinoline can be a new fluorescent scaffold,
and the employment of quinoline-based probes will provide a new platform
for biological applications.