Polyester-poly(ethylene glycol) nanoparticles loaded with the pure antiestrogen RU 58668: physicochemical and opsonization properties.

Purpose: The pure antiestrogen RU58668 (RU) was encapsulated within nanospheres (NS) and nanocapsules (NC) prepared from different polyester copolymers with poly(ethylene glycol) (PEG) chains. The influence of their physicochemical properties on drug release in vitro and their susceptibility to opsonization were evaluated.

Methods: RU-loaded PEG-bearing nanoparticles (NP) prepared by interfacial deposition of preformed polymer were characterized (size, zeta potential, percentage encapsulation and loading). In vitro release kinetics were studied in the presence of 10% fetal calf serum (FCS). Their opsonization in mouse serum was evaluated by silver staining of SDS-PAGE and Western blotting of desorbed proteins.

Results: The NS were smaller than NC and had a zeta potential close to zero and a higher percentage of loading. RU release from NS in vitro was reduced as compared with the dissolution profile of free RU in a serum-containing medium. Decreased opsonin adsorption at the surface of pegylated NS was observed.

Conclusion: Small nanoparticulate systems containing a high load of pure antiestrogen, showing reduced drug release, have been developed. Among the six nanosphere preparations containing RU, two show a size below 200 nm, and two others undergo reduced protein adsorption in the presence of serum, compatible with increased persistence in the blood.