Bioreducible Polycations as Shuttles for Therapeutic Nucleic Acid and Protein Transfection

Abstract

Significance: Nucleic acids such as gene-encoding DNAs, gene-silencing small interfering RNAs, or recombinant proteins addressing intracellular molecular targets present a major new therapeutic modality, provided efficient solutions for intracellular delivery can be found. The different physiological redox environments inside and outside the cell can be utilized for optimizing the involved transport processes. Recent Advances: Intracellular delivery of nucleic acids or proteins requires dynamic carriers that discriminate between different cellular locations. Bioreducible cationic polymers can package their therapeutic cargo stably in the extracellular environment, but sense the reducing intracellular cytosolic environment. Based on disulfide cleavage, carriers are degraded into biocompatible fragments and release the cargo in functional form. Disulfide linkages between oligocations, between the carrier and the cargo, or spatial caging of complexed cargo by disulfides have been pursued, with polymers or precise sequence-defined peptides and oligomers. Critical Issues: A quantitative knowledge of the bioreductive capacities within different biological compartments and the involved cellular reduction processes would be greatly helpful for improved carriers with disulfides cleaved within the right compartment at the right time. Future Directions: Novel designs of multifunctional nanocarriers will incorporate macromolecular disulfide entry mechanisms previously optimized by natural evolution of toxins and viruses. In addition to extracellular stabilization and intracellular disassembly, tuned disulfides will contribute to deshielding at the cell surface, or translocation from intracellular compartments to the cytosol. Antioxid. Redox Signal. 21, 804-817.

How to Tackle the Challenge of siRNA Delivery with Sequence‐Defined Oligoamino Amides

“…Polyplex stabilization via disulfide bond formation between cysteines can be reversed in the bioreductive environment of the cytosol with ≈100−1000‐fold higher intracellular glutathione (GSH) levels . To further evaluate the influence of crosslinking by bioreducible disulfide bridges, several structures including 2‐arm, 3‐arm, and t‐shaped oligomers were synthesized containing a twin disulfide‐forming cysteine–arginine–cysteine (CRC) motif .…”

A review of the developments of characteristics of PEI derivatives for gene delivery applications

“…Biological media have a redox environment that seriously affects the sustainability of cellular homeostasis as well as the redox potential gradient between extra and intra cellular and/or subcellular organelles. The redox potential gradient between the oxidizing extracellular space and the reducing environment of intracellular compartments has attracted a great deal of interest in studies carried out in the field of gene delivery systems . From these studies, it is well known that employing gene carriers that rely on the redox potential gradient results in more selectivity and, hence, lower immune system response.…”

“…From these studies, it is well known that employing gene carriers that rely on the redox potential gradient results in more selectivity and, hence, lower immune system response. Among the gene carriers, redox‐stimuli responsive, or bioreducible, polymers offer particular characteristics, such as excellent DNA condensing ability as well as high structure flexibility . The most attractive approach to achieving the redox‐response ability of these polymers is integrating disulfide bonds into the backbone or side chains of the polymers.…”

Tumoral gene silencing by receptor-targeted combinatorial siRNA polyplexes

“…These oligomers provide excellent nucleic acid binding ability, endosomal buffering capacity, and site-specific positioning of multiple functionalities. Further studies have been undertaken to optimize such cationic carriers by systematic variation of the topology [31], inclusion of small chemical delivery motifs such as buffering histidines [32], fatty acids [33], tyrosine trimers [10], disulfide-forming units [34], targeting ligands [35][36][37][38][39][40][41][42] and combinations of such elements [43]. Accordingly, this strategy of a step-by-step optimization resulted in a library of >1000 oligomers which included precise siRNA carriers.…”