Biodegradable self-assembling PEG-copolymer as vehicle for poorly water-soluble drugs

Purpose. To develop self-assembling systems increasing the solubility of poorly water-soluble drugs. Methods. Low molecular weight liquid biodegradable copolymers were synthesized by ring-opening polymerization using caprolactone (CAP) and trimethylenecarbonate (TMC) as monomers. Various initiators were evaluated. The emulsifying and self-assembling properties were investigated by a water titration method. The self-assembling systems were characterized for size, shape, isotropic behavior, cloud point, surface charge, and critical micellar concentration in order to optimize the polymer synthesis. Finally, the improvement of solubility of model drugs was assessed. Results. Only diblock monomethyl ether PEG-CAP/TMC copolymers synthesized with monomethyl ether polyethyleneglycol 550 to 2000 as initiator have shown self-assembling properties: upon dilution, these copolymers formed an isotropically clear solution with droplet sizes in the range of 20 to 100 nm. The hypothesis that these diblock polymers form micelles was confirmed by their low critical micellar concentration (10(-5) g/ml). The copolymers initated with mmePEG750 had a higher cloud point and better colloidal stability than those initiated with mmePEG 550. The solubility of the poorly water-soluble drugs was increased by 1 to 2 orders of magnitude. Good reproducibility was observed from batch to batch. Conclusions. The polyester diblock copolymer mmePEG750-CAP/ TMC forms spontaneously stable micelles in aqueous medium and increases the solubility of lipophilic drugs. They are very promising vehicles for the oral delivery of poorly water-soluble drugs.