Redox-Responsive Micelles Self-assembled from Multi-block Copolymer for Delivery of siRNA

Using double hydrogen bonds as the guide and double disulfide bond as the connecting unit, the redox-responsive amphiphilic cationic multi-block copolymer PEG₂₀₀₀-PLA₃₀₀₀-PEI₁₂₀₀-PLA₃₀₀₀-PEG₂₀₀₀ was synthesized and self-assembled into micelles for delivery of short-interfering ribonucleic acid (siRNA). The copolymer was characterized by Nuclear Magnetic Resonance (NMR), Gel Permeation Chromatography (GPC), Confocal Laser Scanning Microscope (CLSM) and Transmission Electron Microscope (TEM). The micellar particles were observed by Dynamic Light Scattering (DLS). The size of blank micelles was (32±0.1)nm and the Zeta potential was (46.9±0.7)mV. The size of siRNA-loaded micelles was (35±0.3)nm and the Zeta potential was (27.2±1.1)mV. The micelles observed by TEM were spherical. The Critical Micelle Concentration (CMC) of self-assembled micelles was determined with 1, 6-two phenyl-1, 3, 5-hexene (DPH) as a UV molecular probe, which was 0.052 mg/mL and indicated that the micelles could be stable in dilute solutions. The micellar particles kept stable under the environment of 37℃ for 18 d, as reflected by DLS results. The micellar particles could be destructed by dithiothreitol (DTT), confirming that reductive environment could trigger gene release. MTT assay results demonstrated that the blank micelles had low cytotoxicity and good biocompatibility even the mass concentration was up to 100 μg/mL. Gel retardation assay results demonstrated that in redox environment (Glutathione, GSH), disulfide bonds in the polyplexes could be cleaved and most of siRNA could be released. The CLSM results confirmed the delivery of siRNA from the nanomicellar particles into the SGC7901 cells. The reduction-responsive cationic copolymers provided a platform for constructing gene delivery system toward cancer therapy.