Novel Bioreducible Poly(amido amine)s for Highly Efficient Gene Delivery

Abstract

A series of novel bioreducible poly(amido amine)s containing multiple disulfide linkages (SS-PAAs) were\nsynthesized and evaluated as nonviral gene vectors. These linear SS-PAAs could be easily obtained by Michael-type polyaddition of various primary amines to the disulfide-containing cystamine bisacrylamide. The SS-PAA\npolymers are relatively stable in medium mimicking physiological conditions (pH 7.4, 150 mM PBS, 37 °C), but\nare rapidly degraded in the presence of 2.5 mM DTT, mimicking the intracellular reductive environment (pH 7.4,\n[R−SH] = 5 mM, 37 °C). The polymers efficiently condense DNA into nanoscaled (<200 nm) and positively\ncharged (>+20 mV) polyplexes that are stable under neutral conditions but are rapidly destabilized in a reductive\nenvironment, as was revealed by both dynamic light scatting measurement and agarose gel assays. Moreover,\nmost of the poly(amido amine)s possess buffer capacities in the pH range pH 7.4−5.1 that are even higher than\npolyethylenimine (pEI), a property that may favorably contribute to the endosomal escape of the polyplexes.\nPolyplexes of four of the seven SS-PAAs studied were able to transfect COS-7 cells in vitro with transfection\nefficiencies significantly higher than those of branched pEI, being one of the most effective polymeric gene\ncarriers reported to date. Importantly, also in the presence of serum, a high level of gene expression could be\nobserved when the incubation time was elongated from 1 h to 4 h. XTT assays showed that SS-PAAs and their\npolyplexes possess essentially no or only very low cytotoxicity at concentrations where the highest transfection\nactivity is observed. The results indicate that bioreducible poly(amido amine)s have excellent properties for the\ndevelopment of highly potent and nontoxic polymeric gene carriers.