Interpreting the Rich Behavior of Ternary DNA-PEI-Fe(III) Complexes

In silico study of PEI-PEG-squalene-dsDNA polyplex formation: the delicate role of the PEG length in the binding of PEI to DNA

Biocompatible hydrophilic polyethylene glycol (PEG) is widely used in biomedical applications, such as drug or gene delivery, tissue engineering or as an antifouling component in biomedical devices. Experimental studies have shown that the size of PEG can weaken polycation-polyanion interactions, like those between branched polyethyleneimine (b-PEI) and DNA in gene carriers, but details of its cause and underlying interactions on the atomic scale are still not clear. To better understand the interaction mechanisms in the formation of polyplexes between b-PEI-PEG based carriers and DNA, we have used a combination of in silico tools and experiments on three multicomponent systems differing in PEG MW. Using the PEI-PEG-squalene-dsDNA systems of the same size, both in the all-atom MD simulations and in experimental in-gel electrophoresis measurements, we found that the binding between DNA and the vectors is highly influenced by the size of PEG, with the binding efficiency increasing with a shorter PEG length. The mechanism of how PEG interferes with the binding between PEI and DNA is explained using a two-step MD simulation protocol that showed that the DNA-vector interactions are influenced by the PEG length due to the hydrogen bond formation between PEI and PEG. Although computationally demanding we find it important to study molecular systems of the same size both in silico and in a laboratory and to simulate the behaviour of the carrier prior to the addition of bioactive molecules to understand the molecular mechanisms involved in the formation of the polyplex.

A zipped-up tunable metal coordinated cationic polymer for nanomedicine

Incorporating metal elements into polymers is a feasible means to fabricate new materials with multiple functionalities. In this work, a metal coordinated cationic polymer (MCCP) was developed. Ferric ions were incorporated into the polyethyleneimine-β-cyclodextrin (PC) polymer chain via coordination to produce a zipped-up polymer with a micro-ordered and macro-disordered topological structure. By varying the metal concentration, a tunable superstructure could be formed on the nano-templates via the "zipping" effect. In addition, the physicochemical properties of the assembly of MCCPs and nucleic acids were tailored by tuning the composition of the metal ions and polymers. The loading efficiency of Rhodamine-B by MCCPs was enhanced. The in vitro and in vivo results showed that the hybrid materials could be adjusted to deliver nucleic acids or small molecules with good performance and acquired the capacity of generating reactive oxygen species in tumor cells. Thus, the tunable and multifunctional MCCP system has great potential in nanomedicine and biomaterial science.

Compaction of DNA using C12EO4 cooperated with Fe(3.)

Nonionic surfactant, tetraethylene glycol monododecyl ether (C12EO4), cannot compact DNA because of its low efficiency in neutralizing the negative charges of the phosphate groups of DNA. It is also well-known that nonionic surfactants as a decompaction agent can help DNA be released from cationic surfactant aggregates. Herein, with the "bridge" Fe(3+) of C12EO4, we found that C12EO4 can efficiently compact DNA molecules into globular states with a narrow size distribution, indicating that the cooperative Fe(3+) can transform C12EO4 molecules from decompaction agents to compaction ones. The mechanism of the interaction of DNA and C12EO4 by "bridge" Fe(3+) is that the Fe(3+)-C12EO4 complexes act as multivalent ions by cooperative and hydrophobic interaction. The improved colloidal-stability and endosome escape effect induced by C12EO4 would provide the potential applications of nonionic surfactant in the physiological characteristics of DNA complexes. Cell viability assay demonstrates that Fe(3+)-C12EO4 complexes possess low cytotoxicity, ensuring good biocompatibility. Another advantage of this system is that the DNA complexes can be de-compacted by glutathione in cell without any other agents. This suggests the metal ion-nonionic surfactant complexes as compaction agent can act as the potential delivery tool of DNA in future nonviral gene delivery systems.

Computational and experimental approaches for investigating nanoparticle-based drug delivery systems

Most therapeutic agents suffer from poor solubility, rapid clearance from the blood stream, a lack of targeting, and often poor translocation ability across cell membranes. Drug/gene delivery systems (DDSs) are capable of overcoming some of these barriers to enhance delivery of drugs to their right place of action, e.g. inside cancer cells. In this review, we focus on nanoparticles as DDSs. Complementary experimental and computational studies have enhanced our understanding of the mechanism of action of nanocarriers and their underlying interactions with drugs, biomembranes and other biological molecules. We review key biophysical aspects of DDSs and discuss how computer modeling can assist in rational design of DDSs with improved and optimized properties. We summarize commonly used experimental techniques for the study of DDSs. Then we review computational studies for several major categories of nanocarriers, including dendrimers and dendrons, polymer-, peptide-, nucleic acid-, lipid-, and carbon-based DDSs, and gold nanoparticles. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.

Combining polyethylenimine and Fe(III) for mediating pDNA transfection

BACKGROUND

The potential use of Fe(III) ions in biomedical applications may predict the interest of its combination with pDNA-PEI polyplexes. The present work aims at assessing the impact of this metal on pDNA complex properties.

METHODS

Variations in the formation of complexes were imposed by using two types of biological buffers at different salt conditions. The incorporation of pDNA in complexes was characterised by gel electrophoresis and dynamic light scattering. Transfection efficiency and cytotoxicity were evaluated in HeLa and HUH-7 cell lines, supported by flow cytometry assays.

RESULTS

Fe(III) enhances pDNA incorporation in the complex, irrespective of the buffer used. Transfection studies reveal that the addition of Fe(III) to complexes at low ionic strength reduces gene transfection, while those prepared under high salt content do not affect or, in a specific case, increase gene transfection up to 5 times. This increase may be a consequence of a favoured interaction of polyplexes with cell membrane and uptake. At low salt conditions, results attained with chloroquine indicate that the metal may inhibit polyplex endosomal escape. A reduction on the amount of PEI (N/P 5) formed at intermediary ionic strength, complemented by Fe(III), reduces the size of complexes while maintaining a transfection efficiency similar to that obtained to N/P 6.

CONCLUSIONS

Fe(III) emerges as a good supporting condensing agent to modulate pDNA-PEI properties, including condensation, size and cytotoxicity, without a large penalty on gene transfection.

GENERAL SIGNIFICANCE

This study highlights important aspects that govern pDNA transfection and elucidates the benefits of incorporating the versatile Fe(III) in a gene delivery system.