Metal-Coordinated Histidine-Functionalized Redox-Responsive Polyethyleneimine as a Smart Gene Delivery Vector

Despite significant advancements in gene delivery and CRISPR technology, several challenges remain. Chief among these are overcoming serum inhibition and achieving high transfection efficiency with minimal cytotoxicity. To address these issues, there is a need for novel vectors that exhibit lower toxicity, maintain stability in serum-rich environments, and effectively deliver plasmids of various sizes across diverse cell types. In this study, to convert common polyethylenimine (PEI_1.8k) into high-performance DNA delivery vectors, an innovative multifunctional vector was constructed based on histidine linked to PEI_1.8k by redox-responsive disulfide bonds. Apart from highly efficient transfection of both small and large plasmids into HEK 293T (Human Embryonic Kidney 293T cells) with negligible cytotoxicity, PEI_1.8k-S-S-His showed great transfection potential even at low plasmid doses (0.5 µg), as well as at serum concentrations ranging from 5 to 30% into HEK 293T cells, and achieved excellent plasmid transfection into NIH/3T3 (Mouse Embryonic Fibroblast cells), and MCF7 (Human Breast Cancer cells). Additionally, several metals were tested (Co, Cu, Cd, Ni, Zn, and Mn) to promote the plasmid packaging functionality and improve transfection efficiency. We observed that, in comparison to PEI_1.8k-S-S-His, the manganese-functionalized nanocarrier (PEI_1.8k-S-S-His-Mn) could transfect a large plasmid with equal efficiency (~ 30%) into MSCs (Mesenchymal Stem Cells). Interestingly, PEI_1.8k-S-S-His-Mn showed higher transfection efficiency with the small plasmid (~ 90%) and the large one (~ 80%) into HEK 293T cells, even better than its backbone. We propose that the presence of metal-coordinated His ligand, redox-responsive S-S bonds, and the cationic polymer can synergistically provide robust DNA binding, efficient endosomal disruption, tolerance of serum protein adsorption, and low cytotoxicity. These new vectors could be promising for gene delivery and may be therapeutically relevant.