Synthesis and characterization of chemically condensed oligoethylenimine containing beta-aminopropionamide linkages for siRNA delivery

Polyethylenimines (PEI) are often inefficient in gene knockdown experiments with small interfering RNA (siRNA), presumably due to the strong complexing properties. A more efficient and potentially degradable oligoethylenimine-based carrier was synthesized by the condensation of 800 molecular weight PEI oligomers with hexanedioldiacrylate. Reaction conditions were chosen such that Michael reaction occurs followed by complete N-acylation of all residual ester bonds resulting in beta-aminopropionamide linkage sites and an average molecular weight of 30,000. Based on NMR analysis, these conditions produced 38% tertiary amides and 62% secondary amides, with about 2% residual carboxylate, presumably from hydrolysis. The ionizable equivalent weight of the carrier increased to 51, compared to a value of 43 for standard PEI. Sensible in vitro knockdown of the luciferase gene in stably transfected HUH7 cells, up to 80% in comparison to non-specific siRNA, demonstrated its suitability for siRNA delivery.