pH-sensitive degradable chimaeric polymersomes for the intracellular release of doxorubicin hydrochloride

pH-sensitive degradable chimaeric polymersomes were developed based on asymmetric poly(ethylene glycol)-b-poly(2,4,6-trimethoxybenzylidene-1,1,1-tris( hydroxymethyl)ethane methacrylate)-b-poly(acrylic acid) (PEG-PTTMA-PAA) triblock copolymers for active loading as well as triggered intracellular release of hydrophilic doxorubicin hydrochloride (DOX center dot HCl). PEG-PTTMA-PAA copolymers were readily prepared with M-n (PAA) ranging from 1.5, 2.1 to 2.7 kg/mol by sequential reversible addition-fragmentation chain transfer (RAFT) copolymerization of 2,4,6-trimethoxybenzylidene-1,1,1-tris(hydroxymethyl)ethane methacrylate (TTMA) and acrylic acid (AA) using PEG-CPADN (M-n (PEG) = 5.0 kg/mol; CPADN: 4-cyanopentanoic acid dithionaphthalenoate) as a macro-RAFT agent. PEG-PTTMA-PAA copolymers formed mono-disperse polymersomes with average sizes of 63.9-112.1 nm, which decreased with increasing M-n PAA. The polymersomal structure was confirmed by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Notably, the acetals in polymersomes while sufficiently stable at pH 7.4 were prone to rapid hydrolysis at mildly acidic pHs of 4.0 and 5.0, which resulted in swelling and eventually disassembly of polymersomes. These chimaeric polymersomes could actively load DOX center dot HCI resulting in remarkably high drug loading contents (up to 15.9 wt.%) and loading efficiencies (up to 88.8%). The in vitro release studies showed that DOX center dot HCl was released from chimaeric polymersomes in a controlled and pH-dependent manner. CLSM observations revealed that these chimaeric polymersomes could efficiently deliver and release DOX center dot HCI into the nuclei of HeLa cells. MTT assays in HeLa cells demonstrated that DOX center dot HCl-loaded PEG-PTTMA-PAA polymersomes exhibited high anti-tumor activity with IC50 (inhibitory concentration to produce 50% cell death) of 1.48-1.67 mu g/mL, close to that of free DOX center dot HCI, while blank polymersomes were practically non-toxic up to a tested concentration of 2.0 mg/mL These pH-sensitive degradable chimaeric polymersomes have appeared to be a promising alternative to liposomes for tumor-targeted delivery of DOX center dot HCI. (C) 2012 Elsevier Ltd. All rights reserved.