Poly(ethylene glycol)-b-poly(ε-caprolactone) Micelles Containing Chemically Conjugated and Physically Entrapped Docetaxel: Synthesis, Characterization, and the Influence of the Drug on Micelle Morphology

Docetaxel (DTX), a chemotherapeutic agent, was coupled to the hydrophobic block of poly(ethylene glycol)-b-poly(epsilon-caprolactone) (PEG-b-PCL) copolymers synthesized by metal free ring-opening polymerization. Synthesis of the copolymers and the copolymer drug conjugate (PEG-b-PCL-DTX) were confirmed by H-1 NMR and GPC analyses. The PEG-b-PCL-DTX conjugates had a similar to 1:3 drug/copolymer ratio (w/w) and a low critical micelle concentration in aqueous solution (14 mg/L). Encapsulation of DTX in PEG-b-PCL-DTX micelles resulted in an 1840-fold increase in the aqueous solubility of the drug. Release of physically encapsulated DTX from PEG-b-PCL-DTX micelles was slower than drug release from PEG-b-PCL micelles due to the improved compatibility between DTX and the micelle core. Core-conjugated DTX was released over the course of one week indicating that PEG-b-PCL-DTX micelles have the capacity for sustained drug release in the absence of physically encapsulated drug. Importantly, conjugation of DTX to the core-forming block had a profound effect on the morphology of the copolymer aggregates.