Self-Assembled Amphiphilic Fluorinated Random Copolymers for the Encapsulation and Release of the Hydrophobic Combretastatin A-4 Drug.

Water-soluble amphiphilic random copolymers composed of tri(ethylene glycol) methacrylate (TEGMA) or poly(ethylene glycol) methyl ether methacrylate (PEGMA) and perfluorohexylethyl acrylate (FA) were synthesized by ARGET-ATRP, and their self-assembling and thermoresponsive behavior in water was studied by dynamic light scattering (DLS) and UV-vis spectroscopy. The copolymer ability to self-fold in single-chain nano-sized structures (unimer micelles) in aqueous solutions was exploited to encapsulate Combretastatin A-4 (CA-4), which is a very hydrophobic anticancer drug. The cloud point temperature ( T cp ) was found to linearly decrease with increasing drug concentration in the drug/copolymer system. Moreover, while CA-4 was preferentially incorporated into the unimer micelles of TEGMA- ran -FA, the drug was found to induce multi-chain, submicro-sized aggregation of PEGMA- ran -FA. Anyway, the encapsulation efficiency was very high (≥81%) for both copolymers. The drug release was evaluated in PBS aqueous solutions both below and above T cp for TEGMA- ran -FA copolymer and below T cp , but at two different drug loadings, for PEGMA- ran -FA copolymer. In any case, the release kinetics presented similar profiles, characterized by linear trends up to ≈10-13 h and ≈7 h for TEGMA- ran -FA and PEGMA- ran -FA, respectively. Then, the release rate decreased, reaching a plateau. The release from TEGMA- ran -FA was moderately faster above T cp than below T cp , suggesting that copolymer thermoresponsiveness increased the release rate, which occurred anyway by diffusion below T cp . Cytotoxicity tests were carried out on copolymer solutions in a wide concentration range (5-60 mg/mL) at 37 °C by using Balb/3T3 clone A31 cells. Interestingly, it was found that the concentration-dependent micro-sized aggregation of the amphiphilic random copolymers above T cp caused a sort of "cellular asphyxiation" with a loss of cell viability clearly visible for TEGMA- ran -FA solutions ( T cp below 37 °C) with higher copolymer concentrations. On the other hand, cells in contact with the analogous PEGMA- ran -FA ( T cp above 37 °C) presented a very good viability (≥75%) with respect to the control at any given concentration.