Influence of Polymer Backbone Architecture and Amino Group Density on the Cytotoxicity and Transfection Performance of Cationic Block Copolymer Polyplexes

The development of efficient and biocompatible polymeric vectors remains a cornerstone of successful gene therapy. In this study, we developed a versatile polymeric platform for nucleic acid delivery by synthesizing a series of cationic block copolymers based on polyaspartamide or polyglutamide backbones and polyethylene glycol (PEG) segments. Block copolymer precursors were synthesized via ring-opening polymerization. The degrees of polymerization were confirmed via 1H NMR spectroscopy, followed by functionalization with diethylenetriamine, spermine, or spermidine. Cytotoxicity was evaluated using the WST-1 assay in HEK293 and SH-SY5Y cells. Cytotoxicity profiling identified N3-PEG114-b-pAsp(DET)62 as the least cytotoxic polymer among the tested derivatives in both cell lines. The polyplexes enhanced reporter gene expression compared with naked plasmid DNA, and an N/P ratio of 15 was selected for subsequent comparative experiments. In SH-SY5Y neuroblastoma cells, the material obtained following the dopamine-modification procedure exhibited a 1.78-fold increase in reporter fluorescence and a 1.75-fold increase in the percentage of GFP-positive cells compared with the corresponding unmodified formulation. These findings establish the engineered block copolymers as highly adaptable, low-toxicity, and efficient candidates for targeted nucleic acid delivery and support the potential of dopamine functionalization for enhancing delivery to dopamine-receptor-expressing cells.