Biophysical and biological investigation of DNA nano-complexes with a non-toxic, biodegradable amine-modified hyperbranched polyester

Abstract Designed for gene therapy of chronic diseases, HBP–DEAPA 60 is a non-toxic biodegradable amine modified hyperbranched polyester. This candidate was chosen from a series of hyperbranched polymers for further characterization as it showed the best transfection efficiency and fastest degradation rate. HBP–DEAPA 60/DNA complexes were investigated with regard to stability, uptake and formation to gain a better insight into HBP–DEAPA 60/DNA complex properties. We investigated HBP–DEAPA 60/DNA complex uptake into A 549 cells by FACS and CLSM. Their stability was investigated by a heparin displacement assay as well as by DNAse I assay. Morphology was shown by AFM. HBP–DEAPA 60/DNA complex formation was further characterized in terms of thermodynamic parameters. We studied the conformation of DNA in nano-complexes via circular dichroism (CD) spectroscopy for different NP ratios. Thermodynamic studies showed that binding enthalpies were endothermic; the nano-complex formation was entropically driven. Although PEI/DNA and HBP–DEAPA 60/DNA complexes showed similar behavior with regard to uptake, heparin stability, DNA helicality and their entropically driven complex formation they differ in their binding constant K a and in their ability to protect the DNA from DNAse. Concerning K a and DNAse stability, HBP–DEAPA/DNA complexes should be further optimized. This shows that different characterization studies are necessary to fully characterize polyplex stability and properties.