Low molecular weight polyethyleneimine modified by 2-aminoimidazole achieving excellent gene transfection efficiency

[Display omitted] •Designing the 2-aminoimidazole based imidazolyl and guanidyl.•Studying the interaction between DNA and the 2-aminoimidazole systematically.•Synthesizing a novel polymer by modifying 2-aminoimidazole to polyethyleneimine.•Improving the transfection efficiency and remain the low cytotoxicity. The transfection efficiency and cytotoxicity of polyethyleneimine (PEI), as a non-viral vector, increase with molecular weight. Low molecular weight PEI, such as branched PEI1800 (Mw ~ 1800 kDa), has negligible transfection efficiency but low cytotoxicity. Given the low efficiency of PEI1800, a variety of modifications were explored. A structure-integrated group of guanidyl and imidazolyl, 2-aminoimidazole was designed (Scheme 1). To verify the molecular interaction between 2-aminoimidazole and gene, molecular docking experiment, 1H NMR, FTIR and isothermal titration calorimetry (ITC) measurement were carried out. Studies confirmed that 2-aminoimidazole form double hydrogen bonds with phosphate group, which enhanced the thermodynamic interaction between 2-aminoimidazole and gene. Hence, we synthesized 2-aminoimidazole modified PEI1800, and as controls, guanidyl and imidazolyl modified PEI1800 were synthesized respectively. As expected, the results showed that 2-aminoimidazole modified PEI1800 could condense DNA into a higher positively charged complex with 116 ~ 120 nm in diameter and improve the cellular uptake. EGFP assay and luciferase assay showed that 2-aminoimidazole modified PEI1800 exhibited much better transfection than PEI1800, guanidyl modified PEI1800, imidazolyl modified PEI1800 both in HEK 293 T cells and SGC-7901 cells. Besides, MTT assay showed 2-aminoimidazole modified PEI1800 exhibited better biocompatibility than PEI25 K. These results highlight the critical role that 2-aminoimidazole played in non-viral gene delivery.