Preparation of Fluorescently Labeled pH-Sensitive Micelles for Controlled Drug Release

In this paper, novel pH-sensitive amphiphilic diblock copolymers [mPEG-b-PDPA(n) (n = 100-200, polymerization degree; PEG is polyethylene glycol and PDPA is polydiphenylamine)] with and without a fluorescent group (fluorescein isothiocyanate, FITC) were synthesized by atom transfer radical polymerization (ATRP). The copolymers were used to prepare micelles by solvent evaporation to act as drug carriers. The micelles were spherical with a uniform diameter of 180-240 nm (0.3 mg.mL(-1)). The model drug doxorubicin (DOX) could be encapsulated into the micelles with a high loading efficiency of about 11% (w, mass fraction). The micelles were stable at pH 7.4 and became looser upon the protonation of the PDPA block in a weakly acidic environment. The release of DOX accelerated when the micelles were exposed to weakly acidic conditions, and the amount released reached 80% after 2-3 h. Cell toxicity assays of the micelles were carried out using human cancer cells (Huh7), and the micelles showed good cytocompatibility. The micelles labeled with FITC displayed high cell transfection efficiency. As a result, micelles labeled with fluorescent groups may open up new perspectives for real-time tracking of drug delivery and/or distribution during chemotherapy.