Columnar Mesophases of the Complexes of DNA with Low-Generation Poly(amido amine) Dendrimers

Superhelical DNA liquid crystals from dendrimer-induced DNA compaction

Electrostatic compaction of double stranded DNA induced by a positively charged poly(amidoamine) (PAMAM) dendrimer of generation four (G4) was found to produce two unique types of DNA mesophases, in which the DNA bent into superhelices packed in a tetragonal or hexagonal lattice. The structure formed at a lower dendrimer charge density was three-dimensionally (3D) ordered, as characterized by the P4₁2₁2 space group with a 4₁ screw axis in a tetragonal arrangement, showing that the weakly bent DNA superhelices with a pitch length of ca. 5.0 nm possessed both identical handedness and phase conservation. The 3D ordered structure transformed into a 2D mesophase at a higher dendrimer charge density, wherein the strongly bent superhelices with a pitch length of ca. 4.0 nm organized in a hexagonal lattice without lateral coherence of helical trajectory. The counterion valency of the protonic acid that is used to charge the dendrimer was found to influence the phase diagram. Under a given dendrimer charge density, the complex with a multivalent acid-protonated dendrimer tended to form structures with less curved DNA, attesting that the driving force of charge matching was reduced by increasing the counterion valency of the dendrimer.

Tuning DNA Condensation with Zwitterionic Polyamidoamine (zPAMAM) Dendrimers

Cationic dendrimers are promising vectors for non-viral gene due to their well-defined size and chemistry. We have synthesized a series of succinylated fourth generation (G4) PAMAM dendrimers to control the DNA packaging in dendriplexes, allowing us to probe the role of charge on DNA packaging. The self-assembly of DNA induced by these zwitterionic PAMAM (zPAMAM) was investigated using small-angle x-ray scattering (SAXS). We demonstrate that changing the degree of modification in zPAMAM-DNA significantly alters the packing density of the resulting dendriplexes. Salt sensitivities and pH dependence on the inter-DNA spacing were also examined. The swelling and stability to salt is reduced with increasing degree of PAMAM modification. Lowering the pH leads to significantly tighter hexagonal DNA packaging. In combination, these results show zPAMAM is an effective means to modulate nucleic acid packaging in a deterministic manner.

Recent progress in gene therapy to deliver nucleic acids with multivalent cationic vectors

Due to the potential use as transfecting agents of nucleic acids (DNA or RNA), multivalent cationic non-viral vectors have received special attention in the last decade. Much effort has been addressed to synthesize more efficient and biocompatible gene vectors able to transport nucleic acids into the cells without provoking an immune response. Among them, the mostly explored to compact and transfect nucleic acids are: (a) gemini and multivalent cationic lipids, mixed with a helper lipid, by forming lipoplexes; and (b) cationic polymers, polycations, and polyrotaxanes, by forming polyplexes. This review is focused on the progress and recent advances experimented in this area, mainly during the present decade, devoting special attention to the lipoplexes and polyplexes, as follows: (a) to its biophysical characterization (mainly electrostatics, structure, size and morphology) using a wide variety of experimental methods; and (b) to its biological activity (transfection efficacy and cytotoxicity) addressed to confirm the optimum formulations and viability of these complexes as very promising gene vectors of nucleic acids in nanomedicine.

Rapid Exchange Between Free and Bound States in RNA-Dendrimer Polyplexes: Implications on the Mechanism of Delivery and Release

A combination of solution NMR, dynamic light scattering (DLS), and fluorescence quenching assays were employed to obtain insights into the dynamics and structural features of a polyplex system consisting of HIV-1 transactivation response element (TAR) and PEGylated generation 5 poly(amidoamine) dendrimer (G5-PEG). NMR chemical shift mapping and (13)C spin relaxation based dynamics measurements depict the polyplex system as a highly dynamic assembly where the RNA, with its local structure and dynamics preserved, rapidly exchanges ( Collapse

Key Words

• therapeutic rna delivery
• pamam
• pegylation
• tar
• dls
• nmr spin relaxation

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MESH Headings

• Dendrimers/chemistry
• HIV-1/chemistry
• Magnetic Resonance Spectroscopy/methods
• Polyamines/chemistry
• Polyethylene Glycols/chemistry
• RNA/chemistry
• Response Elements/genetics
• Transfection/methods

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Grants

• R01 AI066975 NIAID NIH HHS
• P50 GM103297 NIGMS NIH HHS
• R01 AI087463-01 NIAID NIH HHS
• R01 EB005028 NIBIB NIH HHS
• R01EB005028 NIBIB NIH HHS
• R01 GM089846 NIGMS NIH HHS

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Affiliation(s)

Anisha Shakya Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
Casey A. Dougherty Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
Yi Xue Department of Biochemistry and Chemistry, Duke University Medical Center, Durham, NC 27710, USA
Hashim M. Al-Hashimi Department of Biochemistry and Chemistry, Duke University Medical Center, Durham, NC 27710, USA
Mark M. Banaszak Holl Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA

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Current progress in nanotechnology applications for diagnosis and treatment of kidney diseases

Significant progress has been made in nanomedicine, primarily in the form of nanoparticles, for theranostic applications to various diseases. A variety of materials, both organic and inorganic, have been used to develop nanoparticles with promise to achieve improved efficacy in medical applications as well as reduced systemic side effects compared to current standard of care medical practices. In particular, this article highlights the recent development and application of nanoparticles for diagnosing and treating nephropathologies.

Structural and dynamic properties of linker histone H1 binding to DNA

Found in all eukaryotic cells, linker histones H1 are known to bind to and rearrange nucleosomal linker DNA. In vitro, the fundamental nature of H1∕DNA interactions has attracted wide interest among research communities-from biologists to physicists. Hence, H1∕DNA binding processes and structural and dynamical information about these self-assemblies are of broad importance. Targeting a quantitative understanding of H1 induced DNA compaction mechanisms, our strategy is based on using small-angle x-ray microdiffraction in combination with microfluidics. The usage of microfluidic hydrodynamic focusing devices facilitates a microscale control of these self-assembly processes, which cannot be achieved using conventional bulk setups. In addition, the method enables time-resolved access to structure formation in situ, in particular, to transient intermediate states. The observed time dependent structure evolution shows that the H1∕DNA interaction can be described as a two-step process: an initial unspecific binding of H1 to DNA is followed by a rearrangement of molecules within the formed assemblies. The second step is most likely induced by interactions between the DNA and the H1's charged side chains. This leads to an increase in lattice spacing within the DNA∕protein assembly and induces a decrease in the correlation length of the mesophases, probably due to a local bending of the DNA.

Physicochemical and biological properties of self-assembled antisense/poly(amidoamine) dendrimer nanoparticles: the effect of dendrimer generation and charge ratio

To gain a deeper understanding of the physicochemical phenomenon of self-assembled nanoparticles of different generations and ratios of poly (amidoamine) dendrimer (PAMAM) dendrimer and a short-stranded DNA (antisense oligonucleotide), multiple methods were used to characterize these nanoparticles including photon correlation spectroscopy (PCS); zeta potential measurement; and atomic force microscopy (AFM). PCS and AFM results revealed that, in contrast to larger molecules of DNA, smaller molecules produce more heterodisperse and large nanoparticles when they are condensed with a cationic dendrimer. AFM images also showed that such nanoparticles were spherical. The stability of the antisense content of the nanoparticles was investigated over different charge ratios using polyacrylamide gel electrophoresis. It was clear from such analyses that much more than charge neutrality point was required to obtain stable nanoparticles. For cell uptake, self-assembled nanoparticles were prepared with PAMAM G5 and 5’-FITC labeled antisense and the uptake experiment was carried out in T47D cell culture. This investigation also shows that the cytotoxicity of the nanoparticles was dependent upon the generation and charge ratio of the PAMAM dendrimer, and the antisense concentration had no significant effect on the cytotoxicity.