Worm-like Polymeric Complex Micelle As Gene Delivery Carrier: Self-assemble, Characterization And Colloidal Stabilities

Synthetic polyelectrolyte-mediated gene therapy has been highlighted over past two decades,and gained ever-growing attractions to the pharmaceutical industry as promising genedelivery carrier concerning their clinical safety, and simple preparation liable to large-scaleproduction. Synthetic polymeric carriers are biocompatible compounds that are capable ofassociating genetic materials electrostatically, compacting them into nanometer-scalecomplexes that protect encapsulated genetic materials and facilitate them to be internalizedinto cells. Currently, substantial cationic polymeric systems in development have beenreported, such as polylysine (PLys), polyethylenimine (PEI), or polyamidoamine (PAMAM).These cationic polyelectrolytes functionalized with amine groups can package negative-charged nucleic acid into nanoscale particles via electrostatic interactions, thereby promotingsystemic transgene efficiency and facilitating their cellular uptake, on the other hand, facilechemical modification allowed prepared polymeric carriers encompass a string of biologicalbarriers towards safe and efficient transfection, e.g. tertiary amino groups in PEI providesuccessful endosome escape capacities, thus leading to enhanced transfection efficiency.The main hurdles in utilizing above polycation/pDNA complexes (polyplexes) in systemicdelivery are their aggregation, instability, toxicity and their propensity to be captured by themononuclear phagocyte system. These negative profiles were attributable to their non-stealthsurface characters of polyplexes, noting that the surface net charge of the complex isremarkable high in positive charge, inducing aggregation with charged components in theblood circulation, leadingly failure in systemic gene therapy. In this regard, hydrophilic andbiocompatible poly (ethylene glycol) was conjugated to cationic segment (PEGylation),forming distinct core-shell architecture of polyplex micelle, outer hydrophilic PEG shellshielding inner plasmid DNA/polycation complex core, leadingly possesses goodbiocompatibility and stealth behavior in physiological environment. PEGylation of cationicpolyplex has been demonstrated to be an effective approach in prolonging micelle circulationperiod in the blood stream and dramatically lowering the cytotoxic level of cationicpolyelectrolytes. This study aims to distinguish the individual functions of ionic and nonionic segments on theircolloidal stabilities in physiological milieu, including assessment of their resistance to saltdissociation, protein absorption, anionic species substitution and enzymatic digestion. In thisregard, we synthesized an intensively studied block copolymer PEG-b-PEI, at weight ratios of75/25and50/50, but kept entire PEG molecular weight at12,000Dalton, followed by polyplexmicelle preparation with pDNA. A class of biophysical properties was characterized to directlycorrelate how the cationic attributes of polyplex micelle influence their colloidal stabilities,which is of great importance to fully understand underlying mechanism of polyelectrolytemediated polyplex micelle towards further rational polymeric gene carrier design.Overall, cationic segment is responsible to condense plasmid DNA (pDNA), therebyelongation of cationic segment allowed the prepared polymeric micelle with more collapsedstructure and superior capacity in stabilizing electrostatic-based PEI/pDNA complex core,which was affirmed in examining their resistance to salt dissociation and anionic speciessubstitution. However, elongation of cationic segment was accompanied with less number ofblock copolymer (PEG) associating with pDNA according to stoichiometric ratio, thus led toinsufficient PEG shielding effect against protein absorption and enzymatic digestion. Insummary, it is required to fine-tune cationic and PEG segments in the block copolymer forrational synthetic gene carrier design toward highly stabilized polymeric gene delivery system.In conclusion, we have demonstrated the attributes of ionic segment PEI and non-ionicsegment PEG in enhancing colloidal stabilities in physiological environment. Overall, cationicsegment is responsible to condense plasmid DNA, thereby elongation of cationic segmentallowed the prepared polymeric micelle, more collapsed structure and superior capacity instabilizing electrostatic-based complex core, which is evident in test their resistance to saltdissociation and anionic species substitution. However, elongation of cationic segment wasaccompanied with less number of block copolymer (PEG) associating with pDNA according tostoichiometric ratio, thus led to insufficient PEG shielding effect against protein absorptionand enzymatic digestion. In summary, it is required to fine-tune cationic segment length and PEG quantity for rational synthetic gene carrier design toward highly stabilized polymericgene delivery system.