Abstract
Oligonucleotide therapeutics have gained considerable attention as a new class of molecular targeted drugs. The major issues in the therapeutic use of oligonucleotides are the rapid degradation of administered oligonucleotides and their low delivery efficiency to target tissues and cells. Although nuclease-resistant oligonucleotides with high potency have been developed, the current oligonucleotide delivery is limited to the liver, compromising the therapeutic application of oligonucleotides. To explore the oligonucleotide delivery beyond the liver, we have developed a series of nano-assemblies, so-called polyion complexes（PICs）, from anionic oligonucleotides and cationic polymers. Fine-tuning of the polymer/oligonucleotide structures provides a variety of PIC structures. For instance, a Y-shaped block copolymer comprising branched poly（ethylene glycol） （PEG） and polylysine（PLys） can form a PIC containing a single oligonucleotide molecule, termed unit PIC（uPIC）. Owing to both prolonged blood circulation and relatively smaller size（〜18 nm in diameter）, the uPIC successfully delivered the oligonucleotide payloads into pancreatic and brain tumor models. As for other PICs, micellar PICs（mPICs） can be obtained by mixing antisense oligonucleotides（ASOs） with linear block copolymers comprising PEG and PLys. Because the core of the mPIC is surrounded by PEG shell, ligand conjugation to the distal end of PEG can provide ligand-decorated mPICs. We constructed glucose-decorated mPICs（Glc-mPICs） for glucose transporter 1（GLUT1）-mediated ASO delivery to the brain. Indeed, Glc-mPIC showed enhanced cellular uptake by specific interaction with GLUT1. Furthermore, systemically administered Glc-mPIC efficiently accumulated in the brain tissue and exhibited significant knockdown of a target gene. We also successfully developed vesicular PICs（vPICs） containing oligonucleotides in the vesicular membrane. Optimization of the cationic functional group in the block copolymer provided stable vPICs even under physiological conditions. To investigate the therapeutic potential of this vPIC, we incorporated an effector enzyme, i.e., RNase H, in the aqueous cavity of the vPIC. Encapsulation of RNase H into the vPIC allowed the simultaneous delivery of RNase H and oligonucleotide to the target cells, leading to a cooperative gene knockdown effect. Overall, our approach can provide a promising nanoplatform for oligonucleotide delivery to intractable tumors and non-cancerous brain.
