Erythropoietin loaded microspheres prepared from biodegradable LPLG-PEO-LPLG triblock copolymers: protein stabilization and in-vitro release properties

Biodegradable microspheres containing recombinant human Erythrupoietin (EPO ) were prepared from ABA triblock copolymers. consisting of hydrophobic pol y(L-lactic-co-glycolic acid) A blocks and hydrophilic polyethylenoxide (PEO ) B blocks. Different polymer compositions were studied for the microencaps ulation of EPO using a modified double-emulsion process (W/O/W). The encaps ulation efficiency for EPO, ranging from 72% to 99% was quite acceptable. T he formation of high molecular weight EPO aggregates, however, was higher t han in poly(D,L-lactide-co-glycolide) (PLG) microparticles. Using different excipients with known protein stabilizing properties, such as Bovine Serum Albumin (BSA), Poly-L-Histidine (PH), Poly-L-Arginine (PA) or a combinatio n of PA with Dextran 40 (D40), the EPO aggregate content was significantly reduced to <5% of the encapsulated EPO. In contrast to PLG, ABA triblockcop olymers containing >7 mol % PEG, allowed a continuous release of EPO from m icrospheres for up to 2 weeks under in-vitro conditions. The release profil e was comparable to FITC-Dextran 40 kDa (FD 40) loaded microspheres in the initial release phase, while EPO release was leveling off at later time poi nts. BSA additionally prolonged the EPO release, while blends of PLG and PE O did not generate continuous EPO release profiles. LPLG-PEO-LPLG triblock- copolymers (35 mol % PEG; 30 kDa) in combination with 5% BSA yielded both a n acceptable level of EPO aggregates and a continuous release profile under in-vitro conditions for up to 2 weeks. The formation of EPO aggregates at later time points is probably induced by acidic cleavage products of the bi odegradable polymer and requires further optimization of the ABA polymer co mposition. (C) 1998 Elsevier Science BN. All rights reserved.