ROS-Response-Induced Zwitterionic Dendrimer for Gene Delivery

As one of the most promising therapeutic methods, gene therapy has been playing a more and more important role in treating disease due to its ultra-high therapy efficiency. Even if nonviral gene vectors represented by polycation, liposomal, dendrimers, and zwitterionic materials have made great progress in gene complexation, low immunogenicity, and biocompatibility, intracellular gene release with low toxicity is effectively still a bottleneck restricting the clinical application of gene therapy. We designed and synthesized a reactive oxygen species (ROS)-responsive dendrimer poly(amido amine)- N-(4-boronobenzyl)- N, N-diethyl-2-(propionyloxy)ethan-1-aminium (PAMAM-(B-DEAEP)₁₆) as a gene vector whose potential can vary from positive to negative under the elevated ROS (H₂O₂) in cancerous cells. Dynamic light scattering results showed that the zeta potential of PAMAM-(B-DEAEP)₁₆ decreased from +12.3 to -5 mV under 80 mM H₂O₂ in PBS buffer. The ¹H NMR results demonstrated that the intermediate status of PAMAM-(B-DEAEP)₁₆ was zwitterionic in ∼6 h because it consisted of the positive quaternary ammonium and negative carboxylic acid simultaneously before the ester bond was completely hydrolyzed. Gel retardation assay showed that PAMAM-(B-DEAEP)₁₆ can condense DNA at above N/P = 1; then, PAMAM-(B-DEAEP)₁₆ transfers to zwitterionic, which begins to continuously release DNA with the decrease in the positive charges and increase in the negative charges, and finally to negatively charged poly(amido amine)-propionic acid (PAMAM-PAc₁₆) in the 80 mM H₂O₂. Fluorescence-labeled Cy-5 DNA indicated that PAMAM-(B-DEAEP)₁₆ can enter into the cell completely in ∼4 h. The results showed that this compound we designed exhibited higher gene transfection efficiency and lower cytotoxicity than commercial PEI. This is the first time that the positively charged dendrimer was transferred to zwitterionic dendrimer under the stimuli of H₂O₂ and was successfully applied to gene delivery. Unlike all of the previous reports, we did not seek a compromise between the high gene transfection and low toxicity but find a new avenue to make the gene carrier not only have higher gene transfection efficiency but also exhibit lower toxicity by introducing stimuli-sensitive groups into the positively charged dendrimer to make it capable of adjusting the charge property according to the microenvironment. This study not only provides a good method to design materials for gene delivery but also opens a new perspective to understand the process of gene delivery.