Synthesis and evaluation of cholesterol-grafted PEGylated peptides with pH-triggered property as novel drug carriers for cancer chemotherapy

Multifunctional core/shell micelles were self-assembled from triblock copolymers poly(ethylene glycol) methyl ether-b-peptide-g-cholesterol (mPEG-b-P-g-Chol) and used as the doxorubicin delivery carriers for cancer chemotherapy. The copolymers were designed and synthesized successfully based on peptides containing histidine residues (pH-trigger) with different topological structures. The peptides were modified by mPEG (hydrophilic) and cholesterol motifs (hydrophobic) on the terminus, resulting in pH-sensitive amphiphilic copolymers. The critical micelle concentrations (CMCs) of the micelles were determined as 4.79, 2.50 and 1.86mg/L for the linear, Y-shape and fork-shape copolymers, respectively, demonstrating the formation of micelle even at low concentration. The pKb values of three copolymers were found to be around 6.1-6.3 by potentiometric titration test, showing the satisfied pH-sensitivity. The average diameter and zeta potential of blank micelles were 170nm and +20mV at pH 7.4, and increased to 250nm and +35mV at pH 5.0. DOX was loaded into the core of polymeric micelles by dialysis method, and the drug loading capacity slightly increased when the copolymer topological structure changed from linear to Y- and fork-shape. The drug release rate from the system was obviously influencing by the pH values according to the results of in vitro DOX release experiment. Moreover, to investigate the structure-property relationship, the drug release mechanism was preliminarily explored by the semi-empirical equations. Toxicity test showed that three copolymers had bare toxicity whereas the DOX-loaded micelles remained high cytotoxicity for tumor cells. The results indicate the synthesized copolymers might be a potential hydrophobic drug delivery carrier for cancer targeting therapy with controlled drug release.