title: Poly(l-histidine) based triblock copolymers: pH induced reassembly of copolymer micelles and mechanism underlying endolysosomal escape for intracellular delivery.
abstract: Various poly(l-histidine) based amphiphilic copolymers have been developed for intracellular drug delivery due to the pH responsive properties and the escape from endolysosomal pathway. However, the pH induced reassembly of copolymer micelles and the assumed endolysosome membrane rupture during the copolymer facilitated endolysosomal escape have never been elucidated. To address these issues, a series of poly(ethylene glycol)-poly(d,l-lactide)-poly(l-histidine) (mPEG-PLA-PHis) with different degrees of polymerization of PLA and PHis block were synthesized. The self-assembly and reassembly behaviors of the copolymers were characterized using transmission electron microscopy (TEM), (1)H NMR, fluorescence probe technique, and dynamic light scattering (DLS). The copolymers self-assembled into micelles with PLA and unprotonated PHis blocks as hydrophobic core and PEG as hydrophilic shell at neutral pH. The changes in TEM images, (1)H NMR spectrum of PHis peak, pyrene fluorescene spectrum, and particle size as well as size distribution over the pH range from pH 8.5 to 4.5 suggest that the copolymer micelles reassembled into micelles with PLA as hydrophobic core and protonated PHis and PEG as hydrophilic shell under acidic environment. The pH induced reassembly triggered the incoporated doxorubicin (DOX) release, as indicated by the in vitro accelerated drug release and enhanced cytotoxicity. The integrity of endolysosome membrane during the copolymer facilitated DOX endolysosomal escape was observed by confocal laser scan microscopy (CLSM) and further evaluated by hemolysis test and calculation of the critical size of endolysosomal membrane. The results indicate that the endolysosomal membrane remained intact during the copolymer facilitated endolysosomal escape of DOX. It is more reasonable to ascribe the PHis based copolymer facilitation endolysosomal escape to the "proton sponge" hypothesis without rupturing the endolysosomal membrane.
authors.affiliation: School of Pharmacy, Shenyang Pharmaceutical University , P.O. Box 42, Wenhua Road 103, Shenyang, Liaoning Province 110016, P.R. China.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Zhang
authors.forename: Dawei
authors.initials: D
authors.lastname: Chen
authors.forename: Shuang
authors.initials: S
authors.lastname: Ba
authors.forename: Jia
authors.initials: J
authors.lastname: Zhu
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Hong
authors.forename: Xiuli
authors.initials: X
authors.lastname: Zhao
authors.forename: Haiyang
authors.initials: H
authors.lastname: Hu
authors.forename: Mingxi
authors.initials: M
authors.lastname: Qiao
mesh_terms: D000818:Animals; D016503:Drug Delivery Systems / Q000379:methods*; D006639:Histidine / Q000008:administration & dosage / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000187:drug effects* / Q000378:metabolism; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D061986:MCF-7 Cells; D008297:Male; D008823:Micelles; D011108:Polymers / Q000008:administration & dosage / Q000737:chemistry* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D008823:Micelles; D011108:Polymers; C033223:polyhistidine; D006639:Histidine