Preparation and Characterization of Electrostatically Crosslinked Polymer⁻Liposomes in Anticancer Therapy.

Yi-Ting Chiang,Sih-Ying Lyu,Chun-Liang Lo,Yu-Han Wen

doi:10.3390/ijms19061615

Abstract

pH-sensitive polymer–liposomes can rapidly release their payloads. However, it is difficult to simultaneously achieve stability and pH-responsiveness in the polymer–liposomes. In this study, stable and pH-sensitive crosslinked polymer–liposomes were fabricated through electrostatic interactions. The pH-sensitive copolymer methoxy poly(ethylene glycol)-block-poly(methacrylic acid)-cholesterol (mPEG-b-P(MAAc)-chol) and crosslinking reagent poly(ethylene glycol) with end-capped with lysine (PEG-Lys2) were synthesized and characterized. At physiological conditions, the pH-sensitive copolymers were anionic and interacted electrostatically with the cationic crosslinker PEG-Lys2, forming the electrostatically-crosslinked polymer–liposomes and stabilizing the liposomal structure. At pH 5.0, the carboxylic groups in mPEG-b-P(MAAc)-chol were neutralized, and the liposomal structure was destroyed. The particle size of the crosslinked polymer–liposomes was approximately 140 nm and the polymer–liposomes were loaded with the anticancer drug doxorubicin. At pH 7.4, the crosslinked polymer–liposomes exhibited good stability with steady particle size and low drug leakage, even in the presence of fetal bovine serum. At pH 5.0, the architecture of the crosslinked polymer–liposomes was damaged following rapid drug release, as observed by using transmission electron microscopy and their apparent size variation. The crosslinked polymer–liposomes were pH-sensitive within the endosome and in the human breast cancer cells MDA-MB-231, as determined by using confocal laser scanning microscopy. The intracellular drug release profiles indicated cytotoxicity in cancer cells. These results indicated that the highly-stable and pH-sensitive electrostatically-crosslinked polymer–liposomes offered a potent drug-delivery system for use in anticancer therapies.

Highlights

Liposomes have been employed in the pharmaceutical industries and approved for use as an anticancer therapy by the US Food and Drug Administration (FDA) for decades [1]
The liposomes were composed of phospholipids, pH-responsive copolymer (mPEG-b-P(MAAc)-chol), and crosslinkers (poly(ethylene glycol) end-capped with lysine (PEG-Lys2))
The copolymer Methoxy poly(ethylene glycol) (mPEG)-b-P(MAAc)40-chol was synthesized by free radical polymerization using the macroinitiator methoxy poly(ethylene glycol) modified with 4,4 -azobis-(4-cyanopetanoic acid), as previously reported [21]

Summary

Introduction

Liposomes have been employed in the pharmaceutical industries and approved for use as an anticancer therapy by the US Food and Drug Administration (FDA) for decades [1]. The most challenging limitation of the PEGylated liposomes is the slow drug release profiles [8]; in tumor cells or tissues, this may lead to a reduction in the anticancer efficiency of the PEGylated liposomes [9]. To facilitate anticancer drug release in cancer cells or lesions, polymers with the ability to respond to the tumor environments; for example, pH-responsive or temperature-sensitive polymers, were designed and incorporated into the liposomal systems [10,11,12]. Lee et al developed and fabricated a polymer-caged liposomal system to achieve both stability and pH-responsiveness for drug delivery. They prepared a pH-responsive poly(acrylic acid) liposomal system with crosslinkers inserted into the polymer–liposome complex, which formed covalent bonds to stabilize the liposomal structures [31]. The covalently crosslinked polymer–liposomes possessed high stability and pH-responsiveness, their elimination was difficult, owing to the higher molecular weight of the polymer molecular [32]

Methods

Results

Discussion

Conclusion