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One of the principal problems facing nucleic acid delivery systems using polyplexes is the instability of the complexes in the presence of proteins and high salt concentrations. We have used a cross-linking polymer to overcome this problem. Pendant thiol moieties have been incorporated into a PAA (polyamidoamine) homopolymer and a PEG [poly(ethylene glycol)]–PAA–PEG copolymer reported previously as a self-assembling system. When mixed with DNA, small monodisperse sterically stabilized particles are formed in quantitative yields. Optimization of the formulation resulted in nanoparticles which are stable in seawater. This cross-linked formulation has been successfully tested in both freshwater and estuarine field trials as a water tracer. Future work will develop these particles as a groundwater tracer and also for therapeutic applications of nucleic acid delivery. [ABSTRACT FROM AUTHOR]

An amphoteric bio-compatible and stealth-like poly (amidoamine) named ISA23 was obtained from 2,2-bis(acrylamido)acetic acid (BAC) and 2-methylpiperazine. The partial substitution of 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (Amino-TEMPO) for 2-methylpiperazine as co-monomer gave two new PAA-TEMPO conjugates based on ISA23: ISA23-TEMPO1 and ISA23-TEMPO2 with 10 and 40% TEMPO-carrying units per polymer chain, respectively. In this study, a thorough NMR characterization of ISA23 polymer together with NMR and ESR characterizations of the ISA23-TEMPO derivatives and a preliminary evaluation of their potential as NMR labels for imaging applications are reported. Relaxivity measurements performed on ISA23-TEMPO1 and ISA23-TEMPO2 showed relaxivities of 0.4 and 1.8 mM−1 s−1, respectively, indicating that the PAA-TEMPO adducts have a definite potential as NMR imaging contrast agents. This was confirmed by preliminary magnetic resonance imaging (MRI) determinations. [ABSTRACT FROM AUTHOR]