title: Effect of polymer structure on micelles formed between siRNA and cationic block copolymer comprising thiols and amidines.
abstract: Small interfering RNA (siRNA) has great therapeutic potential for the suppression of proteins associated with disease, but delivery methods are needed for improved efficacy. Here, we investigated the properties of micellar siRNA delivery vehicles prepared with poly(ethylene glycol)-block-poly(l-lysine) (PEG-b-PLL) comprising lysine amines modified to contain amidine and thiol functionality. Lysine modification was achieved using 2-iminothiolane (2-IT) [yielding PEG-b-PLL(N2IM-IM)] or dimethyl 3,3'-dithiobispropionimidate (DTBP) [yielding PEG-b-PLL(MPA)], with modifications aimed to impart disulfide cross-linking ability without compromising cationic charge. These two lysine modification reagents resulted in vastly different chemistry contained in the reacted block copolymer, which affected micelle formation behavior and stability along with in vitro and in vivo performance. Amidines formed with 2-IT were unstable and rearranged into a noncharged ring structure lacking free thiol functionality, whereas amidines generated with DTBP were stable. Micelles formed with siRNA and PEG-b-PLL(N2IM-IM) at higher molar ratios of polymer/siRNA, while PEG-b-PLL(MPA) produced micelles only near stoichiometric molar ratios. In vitro gene silencing was highest for PEG-b-PLL(MPA)/siRNA micelles, which were also more sensitive to disruption under disulfide-reducing conditions. Blood circulation was most improved for PEG-b-PLL(N2IM-IM)/siRNA micelles, with a circulation half-life 3× longer than naked siRNA. Both micelle formulations are promising for siRNA delivery applications in vitro and in vivo.
authors.affiliation: Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, Japan.
authors.forename: R James
authors.initials: RJ
authors.lastname: Christie
authors.forename: Kanjiro
authors.initials: K
authors.lastname: Miyata
authors.forename: Yu
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Takahiro
authors.initials: T
authors.lastname: Nomoto
authors.forename: Daniel
authors.initials: D
authors.lastname: Menasco
authors.forename: Tzai Chung
authors.initials: TC
authors.lastname: Lai
authors.forename: Matthew
authors.initials: M
authors.lastname: Pennisi
authors.forename: Kensuke
authors.initials: K
authors.lastname: Osada
authors.forename: Shigeto
authors.initials: S
authors.lastname: Fukushima
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Nishiyama
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Yamasaki
authors.forename: Kazunori
authors.initials: K
authors.lastname: Kataoka
mesh_terms: D000578:Amidines / Q000737:chemistry; D000818:Animals; D002412:Cations; D004339:Drug Compounding / Q000379:methods*; D016503:Drug Delivery Systems / Q000379:methods*; D004355:Drug Stability; D005260:Female; D020868:Gene Silencing / Q000187:drug effects; D017930:Genes, Reporter; D006207:Half-Life; D008156:Luciferases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D008239:Lysine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D009682:Magnetic Resonance Spectroscopy; D008546:Melanoma, Experimental / Q000188:drug therapy / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D008823:Micelles; D018715:Microscopy, Video; D011092:Polyethylene Glycols / Q000138:chemical synthesis / Q000378:metabolism / Q000493:pharmacokinetics; D034741:RNA, Small Interfering / Q000378:metabolism / Q000493:pharmacokinetics; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014407:Tumor Cells, Cultured
chemical_list: D000578:Amidines; D002412:Cations; D008823:Micelles; D034741:RNA, Small Interfering; D013438:Sulfhydryl Compounds; C092361:poly(ethylene glycol) lysine copolymer; D011092:Polyethylene Glycols; D008156:Luciferases; D008239:Lysine