Blended Block Polycation Micelles Enhance Antisense Oligonucleotide Delivery

Abstract

Nucleic acid-based medicines and vaccines are becoming an important part of our therapeutic toolbox. One key genetic medicine is antisense oligonucleotides (ASOs), which are short single-stranded nucleic acids that downregulate protein production by binding to mRNA. However, ASOs cannot enter the cell without a delivery vehicle. Diblock polymers containing cationic and hydrophobic blocks self-assemble into micelles that have shown improved delivery compared to linear nonmicelle variants. Yet synthetic and characterization bottlenecks have hindered rapid screening and optimization. In this study, we aim to develop a method to increase throughput and discovery of new micelle systems by mixing diblock polymers together to rapidly form new micelle formulations. We synthesized diblocks containing an n-butyl acrylate block chain extended with cationic moieties amino ethyl acrylamide (A), dimethyl amino ethyl acrylamide (D), or morpholino ethyl acrylamide (M). These diblocks were then self-assembled into homomicelles (A100, D100, and M100)), mixed micelles comprising 2 homomicelles (MixR%+R′%), and blended diblock micelles comprising 2 diblocks blended into one micelle (BldR%R′%) and tested for ASO delivery. Interestingly, we observed that mixing or blending M with A (BldA50M50 and MixA50+M50) did not improve transfection efficiency compared to A100; however, when M was mixed with D, there was a significant increase in transfection efficacy for the mixed micelle MixD50+M50 compared to D100. We further examined mixed and blended D systems at different ratios. We observed a large increase in transfection and minimal change in toxicity when M was mixed with D at a low percentage of D incorporation in mixed diblock micelles (i.e., BldD20M80) compared to D100 and MixD20+M80. To understand the cellular mechanisms that may result in these differences, we added proton pump inhibitor Bafilomycin-A1 (Baf-A1) to the transfection experiments. Formulations that contain D decreased in performance in the presence of Baf-A1, indicating that micelles with D rely on the proton sponge effect for endosomal escape more than micelles with A. This result supports our conclusion that M is able to modulate transfection of D, but not with A. This research shows that polymer blending in a manner similar to that of lipids can significantly boost transfection efficiency and is a facile way to increase throughput of testing, optimization, and successful formulation identification for polymeric nucleic acid delivery systems.

Cinchona Alkaloid Polymers Demonstrate Highly Efficient Gene Delivery Dependent on Stereochemistry, Methoxy Substitution, and Length

“…Additionally, polyplexes often have a net positive charge, which aids in the internalization of genetic material into cells via interactions with the negatively charged cell membrane . Despite these advantages, the main problems associated with polymer-based gene delivery systems are low efficiency when compared to viruses as well as instances of high cytotoxicity. − Our work offers fundamental insight into how structural parameters, such as stereochemistry and chain length, can affect efficiency and toxicity to aid in the rational design of polymer-based systems. − …”

Predictive design of multimonomeric polyelectrolytes enables lung-specific gene delivery

“…We believe that the multimonomeric polyelectrolytes, with carefully tailored APMAm, TMAEMA, and PhHPMA compositions such as in PNP6, can exploit similar design principles as nanocarriers without exhaustive formulation efforts. Further strategies, such as blending polymers for bioenhancement 67,68 or bioconjugation to adopt endosomolytic agents, 68,69 can then be carried out to selectively increase targeted delivery to cells of interest.…”