Bioreducible poly(amidoamine)s as carriers for intracellular protein delivery to intestinal cells

An effective intracellular protein delivery system was developed based on linear poly(amidoamine)s (PAAs) that form self-assembled cationic nanocomplexes with oppositely charged proteins. Two differently functionalized PAAs were synthesized by Michael-type polyaddition of 4-amino-1-butanol (ABOL) to cystamine bisacrylamide (CBA) and to bisacryloylpiperazine (BAP), yielding p(CBA-ABOL) and p(BAP-ABOL), respectively. These water-soluble PAAs efficiently condense human serum albumin (HSA) by self-assembly into stable nanoscaled and positively-charged complexes. The disulfide-containing p(CBA-ABOL)/HSA nanocomplexes exhibited high mucoadhesive properties and, while stable under neutral (extracellular) conditions, rapidly destabilized in a reductive (intracellular) environment due to the cleavage of the repetitive disulfide linkages in the CBA units of the polymer. Human-derived intestinal Caco-2/TC7 cells and HT29-MTX mucus secreting cells were exposed to these PAAs/HSA nanoparticles and the extent of their uptake and the localization within endosomal compartments were examined. The higher uptake of p(CBA-ABOL)/HSA than that of p(BAP-ABOL)/HSA suggests that the mucoadhesive properties of the p(CBA-ABOL) are beneficial to the uptake process. The transported HSA was located within early endosomes, lysosomes and the cytosol. The enhanced uptake of the p(CBA-ABOL)/HSA nanoparticles, observed in the presence of Cyclosporin A, a non-specific Multi Drug Resistance (MDR) blocker, indicates the possible efflux of these nanoparticles through MDR transporters. The results show that bioreducible PAAs have excellent properties for intracellular protein delivery, and should be applicative in oral protein delivery.