CHARACTERIZATION OF POLY(GLYCOLIDE-CO-D,L-LACTIDE) POLY(D,L-LACTIDE) MICROSPHERES FOR CONTROLLED-RELEASE OF GM-CSF/

Purpose. This study describes the preparation and characterization of a controlled release formulation of granulocyte-macrophage colony-stim ulating factor (GM-CSF) encapsulated in poly(glycolide-co-D,L-lactide) (PLGA) and poly(D,L-lactide) (PLA) microspheres. Methods. GM-CSF was encapsulated in PLGA/PLA microspheres by a novel silicone oil based ph ase separation process. Several different blends of PLGA and low molec ular weight PLA were used to prepare the microspheres. The microsphere s and the encapsulated GM-CSF were extensively characterized both in v itro and in vivo. Results. Steady release of GM-CSF was achieved over a period of about one week without significant ''burst'' of protein fr om the microspheres. Analysis of microsphere degradation kinetics by g el permeation chromatography (GPC) indicated that low molecular weight PLA enhanced the degradation of the PLGA and thereby affected release kinetics. GM-CSF released from the microspheres was found to be biolo gically active and physically intact by bioassay and chromatographic a nalysis. Analysis of serum from mice receiving huGM-CSF indicated that the GM-CSF was biologically active and that a concentration of greate r than 10 ng/mL was maintained for a period lasting at least nine days . MuGM-CSF was not detected following in vivo administration of muGM-C SF microspheres. The tissues of mice receiving muGM-CSF microspheres w ere characterized by infiltration of neutrophils, and macrophages whic h were in significant excess of those found in mice administered with placebo controls (i.e. microspheres without GM-CSF).Conclusions. This study demonstrates the influence of formulation parameters on the enca psulation of GM-CSF in PLGA/PLA microspheres and its controlled releas e in biologically active form. The intense local tissue reaction in mi ce to muGM-CSF microspheres demonstrates the importance of the mode of delivery on the pharmacologic activity of GM-CSF.