Acetal linked oligoethylenimines for use as pH-sensitive gene carriers

Two types of acid-degradable nonviral gene carriers, OEI-MK and OEI-BAA, were synthesized by polymerizing oligoethylenimine of 800 Da (OEI800) with the pH-sensitive acetone ketal cross-linker 2,2-bis(N-maleimidoethyloxy) propane (MK) or the 4-methoxybenzaldehyde bisacrylate acetal cross-linker 1,1-bis-(2-acryloyloxy ethoxy)-[4-methoxy-phenyl]methane) (BAA). Corresponding acid-insensitive counterparts (OEI-BM and LT-OEI-HD) were synthesized as well, representing control polymers. Kinetics of hydrolysis were measured and confirmed the pH-dependent degradation profile of the acetal functions, with short half-lives of 3 min at pH 5.0, and 5 h (OEI-MK) or 3.5 h (OEI-BAA) at physiological pH 7.4 and 37 degrees C. DNA polyplexes of a luciferase expression plasmid were tested for gene transfer efficiency and biocompatibility in two cell lines (B16F10 and Neuro2A). Polyplexes with acid-labile polymers showed an improved toxicity profile compared to those made with acid-stable polymer analogues. At low cation/plasmid (c/p) w/w ratios the transfection efficiency of pH-sensitive polymers was slightly reduced, but it became similar or superior to the efficiency of acid-stable polymers at higher c/p ratios. An improved in vivo biocompatibility of the acid-degradable polymers over the stable control polymers was confirmed by liver histology after systemic administration of polymers in Balb/c mice.