Reductive triblock copolymer micelles with a dynamic covalent linkage deliver antimiR-21 for gastric cancer therapy

A reductive tri-block copolymer PEG-SS-PLA-SS-PEI with a double disulphide linkage in the backbone directed by H-bonding association was synthesized and self-assembled into cationic polymeric nanomicellar particles for in vivo antimiRNA delivery with an average diameter of 68 nm and a zeta potential of approximately 39 mV. The chemical structure of the copolymer was well characterized by 1H NMR and GPC. The cationic polymeric nanomicellar particles could be unpacked in an intracellular reductive environment (GSH) leading to the release of encapsulated antimiRNA. MTT assays in vitro showed no significant cytotoxicity of SGC7901 gastric cancer cells incubated with PEG-SS-PLA-SS-PEI micelles. The in vitro study indicated that the micelle-based antimiR-21 delivery system could effectively facilitate cellular uptake and greatly down-regulate the expression level of miR-21 in SGC7901 cell lines, which was comparable to Lipofectamine™ 2000. The down regulation of miR-21 remarkably induced apoptosis, suppressed the tumor cell migration and invasion, and increased the expression of target genes such as phosphatase and tensin homolog deleted on chromosome ten (PTEN) and Programmed Cell Death Protein 4 (PDCD4). More importantly, the in vivo systemic administration of the micelles/antimiR-21 complex in a gastric cancer model significantly inhibited tumor growth and increased the expression of target genes. The nanoparticle based on the PEG-SS-PLA-SS-PEI copolymer would be a safe and efficient carrier for delivery of therapeutic antimiRNA, which shows a prospective therapy method in gastric cancer.