John M. Layman

Influence of polycation molecular weight on poly(2-dimethylaminoethyl methacrylate)-mediated DNA delivery in vitro.

Establishing clear structure-property-transfection relationships is a critical step in the development of clinically relevant polymers for nonviral gene therapy. In this study, we determined the influence of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) molecular weight on cytotoxicity, DNA binding, and in vitro plasmid DNA delivery efficiency in human brain microvascular endothelial cells (HBMEC). Conventional free radical polymerization was used to synthesize PDMAEMA with weight-average molecular weights ranging from 43,000 to 915,000 g/mol. MTT and LDH assays revealed that lower molecular weight PDMAEMA (M(w) = 43,000 g/mol) was slightly less toxic than higher molecular weights (M(w) > 112,000 g/mol) and that the primary mode of toxicity was cellular membrane destabilization. An electrophoretic gel shift assay revealed that all PDMAEMA molecular weights completely bound with plasmid DNA. However, heparin competitive binding experiments revealed that higher molecular weight PDMAEMA (M(w) = 915,000 g/mol) had a greater binding affinity toward plasmid DNA than lower molecular weight PDMAEMA (M(w) = 43,000 g/mol). The molecular weight of PDMAEMA was found to have a dramatic influence on transfection efficiency, and luciferase reporter gene expression increased as a function of increasing molecular weight. However, cellular uptake of polyplexes was determined to be insensitive to PDMAEMA molecular weight. In addition, our data did not correlate polyplex size with transfection efficiency. Collectively, our data suggested that the intracellular fate of the polyplexes, which involves endosomal release and DNase resistance, is more important to overall transfection efficiency than barriers to entry, such as polyplex size.

Protonatable Ionenes for Nucleic Acid Complexation

Novel tboc-protected ionenes with M(w) exceeding 30 kDa were prepared from the step-growth polymerization of tert-butyl bis[3-(dimethylamino)propyl]carbamate and 1,12-dibromododecane. The protected ionenes yielded pH-sensitive, protonatable ionenes with pK(a) approximately 6.6 for the conjugate acid of the protonated secondary amine. Polyplexes of the protected and deprotected ionenes, whose cytotoxicity for endothelial cells was analyzed using the MTT assay, efficiently complex plasmid DNA. Polyplexes destabilized cellular membranes as revealed using the lactate dehydrogenase assay at high concentrations. The polyplexes were successfully transfected into HBMECs at mass ratios 2, 4, 8, 12, and 16 (polymer/DNA) at polyplex concentrations less than 10 microg . mL(-1).