Synthesis of Electroneutralized Amphiphilic Copolymers with Peptide Dendrons for Intramuscular Gene Delivery

The Interaction Mechanism of Intramuscular Gene Delivery Materials with Cell Membranes

It has been confirmed that skeletal muscle cells have the capability to receive foreign plasmid DNA (pDNA) and express functional proteins. This provides a promisingly applicable strategy for safe, convenient, and economical gene therapy. However, intramuscular pDNA delivery efficiency was not high enough for most therapeutic purposes. Some non-viral biomaterials, especially several amphiphilic triblock copolymers, have been shown to significantly improve intramuscular gene delivery efficiency, but the detailed process and mechanism are still not well understood. In this study, the molecular dynamics simulation method was applied to investigate the structure and energy changes of the material molecules, the cell membrane, and the DNA molecules at the atomic and molecular levels. From the results, the interaction process and mechanism of the material molecules with the cell membrane were revealed, and more importantly, the simulation results almost completely matched the previous experimental results. This study may help us design and optimize better intramuscular gene delivery materials for clinical applications.

The Progress of Non-Viral Materials and Methods for Gene Delivery to Skeletal Muscle

Since Jon A. Wolff found skeletal muscle cells being able to express foreign genes and Russell J. Mumper increased the gene transfection efficiency into the myocytes by adding polymers, skeletal muscles have become a potential gene delivery and expression target. Different methods have been developing to deliver transgene into skeletal muscles. Among them, viral vectors may achieve potent gene delivery efficiency. However, the potential for triggering biosafety risks limited their clinical applications. Therefore, non-viral biomaterial-mediated methods with reliable biocompatibility are promising tools for intramuscular gene delivery in situ. In recent years, a series of advanced non-viral gene delivery materials and related methods have been reported, such as polymers, liposomes, cell penetrating peptides, as well as physical delivery methods. In this review, we summarized the research progresses and challenges in non-viral intramuscular gene delivery materials and related methods, focusing on the achievements and future directions of polymers.

Synthetic promoter for efficient and muscle-specific expression of exogenous genes

Synthetic promoters (SPs) have many advantages over their natural counterparts, especially with regard to transcriptional activity and tissue specificity. Here, we report a new strategy to construct SPs for efficient and muscle-specific gene expression. First, 19 nucleic acid motifs classified to 3 kinds of transcriptional regulatory elements were rationally selected. A recombinant promoter library was constructed by randomly assembling these motifs. Second, the transcriptional activities of ~1200 SPs were screened by intramuscular expression of several reporter genes in different cell lines for activity higher than that of the cytomegalovirus (CMV) promoter, with SP-301 finally identified as the strongest. A single intramuscular injection of mice with an SP-301 plasmid expressing mouse growth hormone releasing hormone accelerated mouse growth significantly over 24 days. Third, the muscle specificity of SP-301 was confirmed in transgenic mice. Finally, in comparison with the CMV promoter, SP-301 accelerated translocation and increased the level of plasmid in the nuclei of myoblast cells to a greater extent than in non-muscle cells. Altogether, the study has provided a more rational strategy to construct efficient and tissue-specific promoters, with the promoter SP-301 exhibiting promising potential for establishing an intramuscular gene expression system for therapeutic applications.

Synthesis and Characterization of Phosphorus- and Carborane-Containing Polyoxanorbornene Block Copolymers

Grubbs-catalyzed ring-opening metathesis polymerization (ROMP) of carborane- and phosphonate-containing monomers has been used for the generation of hybrid block copolymers. Molecular weights with Mn of 50,000 g/mol were readily obtained with polydispersity index values, Đ, between 1.03⁻1.08. Reaction of the phospha ester and carborane substituted oxanorbornene block copolymer with trimethylsilyl bromide led to a new polymer with phosphonic acid functionalities. In application studies, the phospha-carborane functionalized block polymer was tested as heat resistance material. Thermal stability was investigated by thermal gravimetric analysis (TGA) and microscale combustion calorimetry (MCC) analysis. Thermal treatment and ceramic yield under air were directly correlated to the carborane content of the block copolymer. However, phosphorus content in the polymer was more crucial for the char residues when heated under nitrogen atmosphere. The peak heat release rate (PHRR) increased as the number of phosphonate functionalities increased. However, corresponding phosphonic acid derivatives featured a lower heat release rate and total heat release. Moreover, the phosphonic acid functionalities of the block copolymer offer efficient chelating capabilities for iron nanoparticles, which is of interest for applications in biomedicine in the future. The complexation with iron oxide nanoparticles was studied by transmission electron microscopy (TEM) and inductively coupled plasma mass spectrometry (ICP⁻MS).

Engineering the Aromaticity of Cationic Helical Polypeptides toward "Self-Activated" DNA/siRNA Delivery

The development of potent yet nontoxic membrane-penetrating materials is in high demand for effective intracellular gene delivery. We have recently developed α-helical polypeptides which afford potent membrane activities to facilitate intracellular DNA delivery via both endocytosis and the nonendocytic "pore formation" mechanism. Endocytosis will cause endosomal entrapment of the DNA cargo, while excessive "pore formation" would cause appreciable cytotoxicity. Additionally, helical polypeptides with stiff, rodlike structure suffer from low siRNA binding affinity. To address such critical issues, we herein incorporated various aromatic domains (benzyl, naphthyl, biphenyl, anthryl, and pyrenyl) into the side-chain terminals of guanidine-rich, helical polypeptides, wherein the flat-rigid shape, π-electronic structures of aromatic motifs "self-activated" the membrane-penetrating capabilities of polypeptides to promote intracellular gene delivery. Benzyl (Bn)- and naphthyl (Naph)-modified polypeptides demonstrated the highest DNA uptake level that outperformed the unmodified polypeptide, P2, by ∼4 fold. More importantly, compared with P2, Bn- and Naph-modified polypeptides allowed more DNA cargos to be internalized via the nonendocytic pathway, which significantly bypassed the endosomal entrapment and accordingly enhanced the transfection efficiency by up to 42 fold, outperforming PEI 25k as the commercial reagent by 3-4 orders of magnitude. The aromatic modification also improved the siRNA condensation capability of polypeptides, achieving notably enhanced gene-silencing efficiency against tumor necrosis factor-α to treat acute hepatic inflammation. Furthermore, we revealed that aromaticity-augmented membrane activity was accompanied by comparable or even significantly reduced "pore formation" capability, thus leading to diminished cytotoxicity at high concentrations. This study therefore provides a promising approach to manipulate the membrane activities and penetration mechanisms of polycations, which overcomes the multiple critical barriers preventing effective and safe gene delivery.

Recent development of synthetic nonviral systems for sustained gene delivery

Sustained gene delivery is of particular importance today because it circumvents the need for repeated therapeutic administration and provides spatial and temporal control of the release profile. Better understanding of the genetic basis of diseases and advances in gene therapy have propelled significant research on biocompatible gene carriers for therapeutic purposes. Varied biodegradable polymer-based architectures have been used to create new compositions with unique properties suitable for sustained gene delivery. This review presents the most recent advances in various polymeric systems: hydrogels, microspheres, nanospheres and scaffolds, having complex architectures to encapsulate and deliver functional genes. Through the recombination of different existing polymer systems, the multicomplex systems can be further endowed with new properties for better-targeted biomedical applications.