Hybrid polypeptide micelles loading indocyanine green for tumor imaging and photothermal effect study.

Indocyanine green (ICG) is a near-infrared (NIR) fluorescence dye for extensive applications; however, it is limited for further biological application due to its poor aqueous stability in vitro, concentration-dependent aggregation, rapid elimination from the body, and lack of target specificity. To overcome its limitations, ICG was encapsulated in the core of a polymeric micelle, which self-assembled from amphiphilic PEG-polypeptide hybrid triblock copolymers of poly(ethylene glycol)-b-poly(l-lysine)-b-poly(l-leucine) (PEG-PLL-PLLeu), with PLLeu as the hydrophobic core and PEG as the hydrophilic shell. The ICG was associated with the hydrophobic core via hydrophobic interaction and also the hydrophilic heads through electrostatic attractive interaction. Compared with free ICG, PEG-PLL-PLLeu-ICG micelles significantly improved quantum yield and fluorescent stability. The cellular uptake experiments showed that PEG-PLL-PLLeu-ICG micelles have a high cellular uptake rate. And the in vivo experiments revealed the excellent passive tumor targeting ability and long circulation time of PEG-PLL-PLLeu-ICG. The above results indicated the broad prospects of PEG-PLL-PLLeu-ICG application in the fields of tumor diagnosis and imaging. In addition, temperature measurements under NIR laser irradiation and in vitro photothermal ablation studies proved the potential application of PEG-PLL-PLLeu-ICG in tumor photothermal therapy.