Supramolecular association of recombinant human growth hormone with hydrophobized polyhydroxyethylaspartamides.

Abstract The protein delivery properties of polymer supramolecular assemblies were investigated by using recombinant human growth hormone (rh-GH) and two polyhydroxyethylaspartamide (PHEA) derivatives: (a) PHEA-C 16 obtained by PHEA random grafting with hexadecylalkylamine; (b) PHEA-PEG 5000 -C 16 obtained by PHEA random co-grafting with hexadecylalkylamine and 5 kDa poly(ethylene glycol). The two polymers possessed similar self-assembling properties: critical micelle concentration (CMC) and particle size. The protein loading (protein/polymer, w/w, %) was 12.1 ± 1.3% and 8.5 ± 0.4% with PHEA-C 16 and PHEA-PEG 5000 -C 16 , respectively. The rh-GH/polymer association constant calculated by Scatchard analysis was 1.87 × 10 5  M −1 with PHEA-C 16 and 0.27 × 10 5  M −1 with PHEA-PEG 5000 -C 16 . The Klotz analysis showed that 5 PHEA-C 16 and 9 PHEA-PEG 5000 -C 16 polymer chains associated with one protein molecule. The protein dissociation from the PHEA-C 16 and PHEA-PEG 5000 -C 16 supramolecular complexes was complete in about 350–450 and 450–550 h, respectively. With both polymers, the protein release was faster as the protein/polymer ratio increased. Pharmacokinetic studies were performed by subcutaneous administration to rats of protein/polymer solutions at different w/w ratios (1:75 and 1:150). Both polymer formulations slowed the protein absorption. The protein bioavailability increased as the protein/polymer complex stability decreased and the protein/polymer w/w ratio increased indicating that efficient protein delivery can be achieved by proper polymer choice and formulation composition.