Protease-responsive polymer vesicle by peptide-polymer hybrid

Abstract

Protease-sensitive polymer vesicles are a potential carriers for stimuli-responsive drug delivery. There are only few protease-sensitive polymer vesicles developed. This thesis aims to prepare protease-sensitive polymer vesicles for triggere-release. The factors that affect the cleavage-induced release have not been explored yet. In the first part, modular synthesis of protease-cleavable peptide-polymer hybrids is introduced to simplify the synthesis route and purification. Click reactions, using azide-alkyne and thiol-ene pairs, are employed to avoid protection and deprotection steps. Poly(ethylene glycol)-peptide-poly(caprolactone) and poly(ethylene glycol)-peptide-poly(methyl-caprolactone) were synthesized. In the second part, the peptide-polymer hybrids (PCL-AAAF-PEG and PMCL-AAAF-PEG) are self-assembled into vesicles and the release of carboxyfluorescein from the vesicles by the model protease, chymotrypsin, is studied. Despite the cleavage of hybrids from the vesicles by chymotrypsin, the release of carboxyfluorescein was limited. Osmotic force was proposed as the driving force to promote the protease-triggered release. In the third part, additional salt is added into the vesicles to increase the osmolarity to allow the study of effect of osmotic force on release of carboxyfluorescein from the vesicles. Despite of similar percentage of cleavage, about 20% cleavage on the vesicles, the release from poly(ethylene glycol)-peptide-poly(methyl-caprolactone) (PMCL-AAAF-PEG) vesicles but not poly(ethylene glycol)-peptide-poly(caprolactone) (PCL-AAAF-PEG) in hypotonic solution increase substantially. The release of carboxyfluorescein were 100% and 20% after 4 hours respectively. In the last part, a tumor-associated protease was used to demonstrate the possibility of triggered release from peptide-polymer vesicles. PEG-PVGLIGC-PMCL vesicles were prepared and rapid release was achieved from the hybrid vesicles by MMP-9. The leakage of carboxyfluorescein from PMCL-AAAF-PEG and PEG-PVGLIGC-PMCL vesicles was compared. It is found that the leakage from PMCL-AAAF-PEG (~5%) is less than PEG-PVGLIGC-PMCL (50%) after 24 hours. Also, the leakage in the presence of osmotic force is also less from the AAAF functionalized vesicles. The hydrophobicity of AAAF over PVGLIGC may have contributed to the membrane stability and the different behavior.

Date of Award	2015
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology