Utilization of pillar[5]arene-based ICT probes embedded into proteins for live-cell imaging and traceable drug delivery

Three protein microenvironment-sensitive pillar[5]arene-based fluorescent probes (3/4/5C-B) were designed and synthesized based on intramolecular charge transfer (ICT) mechanism. Unlike the majority of micromolecular ICT probes, the aforementioned probes displayed differentiated sensitivity to multiple proteins. The 7-(diethylamino)coumarin-3-formic acid (DCCA) group in the probes was essential for their sensitivity. The presence of a pillar[5]arene group was also crucial as they benefit 3/4/5C-B form complexes with the proteins, although it changed the electron density distribution of the DCCA group. 3/4/5C-B exhibited favorable carrier ability for regorafenib (REG). 4C-B had the best spatial structure for complexation. The 3/4/5C-B-REG complexes would assemble into high drug-loading fluorescent nanoparticles in a physiological environment (pH = 7.4). Such nanoparticles exhibited pH-triggered enrichment ability, which rapidly enriched REG in the acidic environment (pH = 6.0). Moreover, the complexation between 3/4/5C-B and REG maintained the live-cell membrane imaging property of the probes and the excellent targeted anticancer activity of the drug.