A new pH responsive polymer based on inulin for siRNA Delivery

siRNA-based therapeutics hold great potential for treatment of cancer by targeting signalling pathways that promote tumor progression. However, many challenges, including rapid nuclease degradation and poor cellular uptake, need to be addressed in order to carry these molecules into clinical trials. The goal of the work was that to produce an inulin derivative, Inulin-g-imidazole-g-diethylenetriamine (INU-IMI-DETA), bearing diethylentriamine chains (DETA) and imidazole groups (IMI) with good potential as polymeric vector for siRNA. This because DETA and IMI groups are able respectively to give strong polycation properties to resulting copolymer and to improve endosomal escaping exploiting the proton sponge effect. Moreover, these polymer derivatives bearing diaminoethane side chains exhibit a peculiar two-step protonation behaviour that facilitates membrane destabilization at the acidic pH of late endo-lysosome. The experimental results showed that INU-IMI-DETA exhibited strong cationic characteristics, high solubility in the pH range 3-5, self aggregation triggered by pH increase and physiological salt concentration as well as a high buffering capacity in the endosomal pH range of 7.4-5.1. INU-IMI-DETA was tested as siRNA complexing and delivering agent and a specific two-step procedure was followed to obtain stable INU-IMI-DETA complex nanoaggregates (ICONs) into DPBS pH 7.4. This lead to produce siRNA loaded nanoparticles with minimized surface charge and suitable size for parenteral administration. In vitro studies on breast cancer cells, expressing luciferase gene, demonstrated that ICONs had no cytotoxic effect in a wide range of concentration and that are able to produce a satisfactory luciferase knockdown. Moreover, Bafilomycin A1 inhibited transfection, indicating that the copolymer favors the system escape from endolysosomal compartment.