Biodegradable Polymersomes Containing An Ionizable Membrane For Intracellular Drug Delivery: Facile Preparation, Efficient Loading Of Proteins And Anticancer Drugs, And PH-Responsive Release

In this thesis, we investigated the biodegradable polymersomes containing an ionizablemembrane for efficient loading of protein and anticancer drugs as well as their endosomalpH responsive release. The polymersomes were prepared from poly（ethyleneglycol）-b-poly（trimethylene carbonate）（PEG-PTMC） block copolymer derivativescontaining acrylate, carboxylic acid and amine groups along PTMC block, which aredenoted as PEG-PTMC（AC）, PEG-PTMC（COOH） and PEG-PTMC（NH₂）, respectively.Notably, nano-sized polymersomes （95.1-111.6nm） were formed by directly dispersingthese copolymers in phosphate buffer at room temperature. Moreover, both FITC-labeledbovine serum albumin （FITC-BSA） and cytochrome C （FITC-CC） were readily loaded intoPEG-PTMC（COOH） and PEG-PTMC（NH₂） polymersomes with remarkably high loadinglevels. For example, protein loading efficiencies of86.4-94.5%and50.1-51.0%wereobserved for FITC-BSA at a theoretical loading content of50wt.%and FITC-CC at atheoretical loading content of20wt.%, respectively, likely due to presence of electrostaticand/or hydrogen bond interactions. Interestingly, in vitro release studies showed thatPEG-PTMC（COOH） and PEG-PTMC（NH₂） polymersomes had pH-responsive proteinrelease behaviors in which significantly faster protein release was observed at endosomalpH than at physiological pH. For instance, FITC-CC-loaded PEG-PTMC（COOH）polymersomes released88.0%FITC-CC in24h at pH5.4while only13.9%FITC-CC wasreleased in24h at pH7.4under otherwise the same conditions. MTT assays in MCF-7,and HeLa cells indicated that these polymersomes had low cytotoxicity. Furthermore,confocal laser scanning microscope （CLSM） observations revealed that FITC-CC loadedpolymersomes efficiently delivered proteins into MCF-7cells following24h incubation.Importantly, flow cytometry showed that CC-loaded polymersomes induced markedlyenhanced apoptosis in MCF-7cells as compared to free CC.Using the same principle, we explored the encapsulation of hydrophilic small molecularanticancer drugs, since these hydrophilic anticancer drugs like doxorubicin hydrochloridesuffers from short circulation time and low cell penetration resulting in low bioavailability. These hydrophilic anticancer drugs like doxorubicin hydrochloride cis-platin andmethotrexate are often ionizable under physiological conditions, and could be loaded intoPEG-PTMC（COOH） or PEG-PTMC（NH₂） polymersomes with very high efficiency （up to95%）. Interestingly, drug loaded polymersomes showed pH-responsive release behaviors.Moreover, these polymersomes could also load hydrophobic anticancer drug doxorubicinand curcumin into the hydrophobic membrane. Finally, we preliminarily studied thecoloading of protein and small molecular anticancer drugs. These novel membraneionizable biodegradable polymersomes have appeared as highly promising nanocarriers forefficient intracellular protein delivery and combination cancer therapy.