pH-sensitive degradable hydrophobe modified 1.8 kDa branched polyethylenimine as “artificial viruses” for safe and efficient intracellular gene transfection

1.8 kDa branched polyethylenimine (PEI)_was modified with pH-sensitive degradable acetal containing hydrophobe, 2,4,6-trimethoxybenzylidene-tris(hydroxymethyl)ethane (TMB-THME), to enhance its DNA condensation under extracellular conditions as well as to achieve active DNA release inside cells. PEI-(TMBTHME)n conjugates in the amount of 1.8 kDa were prepared with varying degrees of substitution (DS) from 3.0, 5.7 to 10.1. Notably, dynamic light scattering (DLS) measurements showed that all three 1.8 kDa PEI-(TMB-THME)n conjugates could effectively condense DNA into nano-sized particles (189–197 nm) at N/P ratios ranging from 20/1 to 80/1. The surface charges of PEI-(TMB-THME)n polyplexes depending on DS and N/P ratios varied from +22 to +28 mV, which were comparable to or slightly higher than the unmodified 1.8 kDa PEI counterparts (∼+22 to +23 mV). Under a mildly acidic condition mimicking that of endosomes, interestingly, 1.8 kDa PEI-(TMB-THME)n polyplexes were quickly unpacked to release DNA because of the pH-induced acetal degradation that transforms hydrophobic modification into hydrophilic modification. MTT assays demonstrated that all PEI-(TMB-THME)n polyplexes displayed low cytotoxicity (>80%) to 293T, and HeLa cells at N/P ratios ranging from 20/1 to 60/1. The in vitro gene transfection studies showed that the transfection activity of 1.8 kDa PEI was significantly enhanced by modifications with TMB-THME, in which transfection efficiencies increased with increasing DS. For example, 1.8 kDa PEI-(TMB-THME)10.1 polyplexes displayed 250-fold and 80-fold higher transfection efficiencies than those of the unmodified 1.8 kDa PEI counterparts in 293T and HeLa cells, respectively, which were approximately 4-fold and 2-fold higher than that of 25 kDa PEI control. The superior transfection activity of 1.8 kDa PEI-(TMB-THME)10.1 polyplexes was also confirmed by confocal laser scanning microscopy (CLSM), which showed efficient delivery of DNA into the nuclei of 293T cells following 4 h transfection. Modification of low molecular weight PEI with pH-sensitive degradable hydrophobe has appeared to be highly promising in the development of “artificial viruses” for safe and efficient gene transfer. [graphic not available: see fulltext]