THE INTERACTION OF PLASMID DNA WITH POLYAMIDOAMINE DENDRIMERS - MECHANISM OF COMPLEX-FORMATION AND ANALYSIS OF ALTERATIONS INDUCED IN NUCLEASE SENSITIVITY AND TRANSCRIPTIONAL ACTIVITY OF THE COMPLEXED DNA

The application of synthetic vectors for gene transfer has potential a dvantages over virus-based systems. However, little is known about the mechanisms involved in binding of synthetic materials to DNA and the nature of the DNA complexes that result from this interaction. Polyami doamine (PAMAM) dendrimers are unique polymers with defined spherical structure. Dendrimers bind DNA to form complexes that efficiently tran sfect cells in vitro. We examined the formation of DNA/dendrimer compl exes and found it based entirely on charge interaction. Electronmicros copic examination of the complexes indicated that the majority of the plasmid DNA is contracted into isolated toroids, but also revealed lar ger, irregular aggregates of polymer and DNA. The binding of plasmid D NA to dendrimer appears to alter the secondary and tertiary structure, but does not fragment the DNA or alter its primary structure. Complex ed DNA is protected against degradation by either specific nucleases o r cellular extracts containing nuclease activity. While the initiation of transcription in vitro from promoters (for either T7 polymerase or eukaryotic RNA polymerase II) in dendrimer-complexed DNA is inhibited , elongation of the RNA transcript and translation do not appear to be affected. These resemble alterations of the DNA function when complex ed with naturally-occurring polycations like non-acetylated histones, However, DNA complexed to dendrimer appears to maintain transcriptiona l activity while histone complexes at similar charge ratios do not, Th ese results elucidate some aspects of the interaction between PAMAM de ndritic polymers and DNA, and could lead to improvements in the design of polymers or formation of DNA complexes that will increase the effi ciency of non-viral gene transfer. (C) 1997 Elsevier Science B.V.