Free paclitaxel loaded PEGylated-paclitaxel nanoparticles: preparation and comparison with other paclitaxel systems in vitro and in vivo.

Previously, PEGylated paclitaxel (PEG-PTX) was found not favorable as a polymer prodrug because of its poor antitumor efficiency. But surprisingly, it was found in our study that PEG-PTX could form a novel nanoparticle system with free PTX. To address how this system works, we compared PTX loaded PEG-PTX nanoparticles (PEG-PTX/PTX) with PTX loaded PEG-PLA micelles (PEG-PLA/PTX) or PTX injection available (Taxol(®)) in vitro and in vivo. Firstly, it was found that PEG-PTX/PTX was more stable in aqueous solution than PEG-PLA/PTX in terms of PTX crystal formation and drug release. Then it was demonstrated that coumarin loaded PEG-PTX nanoparticles had a much higher uptake in MCF-7 cells compared to coumarin loaded PEG-PLA micelles. The in vivo imaging study revealed that DIR or DID (near infrared fluorescent substances) loaded PEG-PTX nanoparticles distributed more in tumors in MCF-7 tumor bearing mice than DIR or DID loaded PEG-PLA micelles and solvent system of Taxol(®). In the efficacy study with MCF-7 tumor bearing mice, PEG-PTX/PTX showed significantly higher antitumor activity than PEG-PLA/PTX at the same PTX dosage. At the dose of 10mg free PTX per kg, PEG-PTX/PTX displayed similar efficacy as Taxol(®) but less toxicity evaluated by the loss of body weight. With the increase of free PTX to 15 mg/kg, PEG-PTX/PTX showed significantly better efficacy than Taxol(®). In conclusion, with favorable characteristics in stability, cellular uptake, cytotoxicity, biodistribution, safety and efficacy, PEG-PTX/PTX seems highly potential as a nanocarrier for PTX delivery.