A Simple Zn2+ Complex-Based Composite System for Efficient Gene Delivery.

Zhe Zhang,Changlin Liu,Dan Zhao,Xianggao Meng,Yanjie Zhao,Dan Zhang,Li Wang,Dariush Hinderberger

doi:10.1371/journal.pone.0158766

Abstract

Metal complexes might become a new type of promising gene delivery systems because of their low cytotoxicity, structural diversity, controllable aqua- and lipo-solubility, and appropriate density and distribution of positive charges. In this study, Zn2+ complexes (1–10) formed with a series of ligands contained benzimidazole(bzim)were prepared and characterized. They were observed to have different affinities for DNA, dependent on their numbers of positive charges, bzim groups, and coordination structures around Zn2+. The binding induced DNA to condensate into spherical nanoparticles with ~ 50 nm in diameter. The cell transfection efficiency of the DNA nanoparticles was poor, although they were low toxic. The sequential addition of the cell-penetrating peptide (CPP) TAT(48–60) and polyethylene glycol (PEG) resulted in the large DNA condensates (~ 100 nm in diameter) and the increased cellular uptake. The clathrin-mediated endocytosis was found to be a key cellular uptake pathway of the nanoparticles formed with or without TAT(48–60) or/and PEG. The DNA nanoparticles with TAT(48–60) and PEG was found to have the cell transfection efficiency up to 20% of the commercial carrier Lipofect. These results indicated that a simple Zn2+-bzim complex-based composite system can be developed for efficient and low toxic gene delivery through the combination with PEG and CPPs such as TAT.

Highlights

Nucleic acid delivery mediated by the nonviral carriers including cationic lipids and organic polymers provides a major contribution to development of gene therapy [1,2,3], the inorganic systems designed for efficient nucleic acid delivery have attracted great interest [4,5,6,7].Of inorganic carriers, metal complexes might become one of the promising nonviral gene carriers, because of their low cytotoxicicty, structural diversity, controllable aqua- and lipo-solubility, and appropriate density and distribution of positive charges
The data showed that the affinities of the complexes for the DNA are at a micromolar scale with an exception of 8 whose DNA affinity is higher than those of the other Zn2+ complexes (Table 1), indicating that the DNA binding of the complexes is dependent on their numbers of positive charges and bzim groups, as well as coordination geometries of Zn2+ [40,41,42,43,44,45,46]
The sequential addition of TAT(48–60) and 8 led to the conversion of DNA into nanoparticles with a diameter of ~ 50 nm under the conditions tested (Fig 3B), indicating that 8 and TAT(48–60)could cooperatively promote DNA condensation, but the DNA condensation is mainly dependent on the addition of 8, because 8 was added to the DNA condensation reaction following this peptide, and the DNA nanoparticles formed with and without TAT(48–60) had the almost same diameters (Figs 2A and 3B).The introduction of polyethylene glycol (PEG) converted these DNA nanoparticles into spherical and compact condensates whose diameters were ~ 100 nm, and the large nanoparticles did not conglomerate and change their profiles and sizes with prolonging incubation time in the buffer used (Fig 3C). This increase in diameters of the DNA condensates indicated that PEG binds only at surfaces of the nanoparticles. These results revealed that (1) the complex provides a pivotal contribution to the condensation of DNA compared with the cell-penetrating peptide (CPP) and PEG, (2) the co-presence of 8 and TAT(48–60) results in the formation of loose and irregular DNA condensates compared with those formed only with 8 (Fig 2A) likely because of the electrostatic repulsion among these DNA-bound TAT(48–60) molecules with multiple positive charges, and (3) the DNA condensates formed in the composite system containing PEG are more compact, larger and more stable than those formed in the DNA condensationsystems only containing either 8 or 8 and TAT(48–60) in the buffer tested

Summary

Introduction

Nucleic acid delivery mediated by the nonviral carriers including cationic lipids and organic polymers provides a major contribution to development of gene therapy [1,2,3], the inorganic systems designed for efficient nucleic acid delivery have attracted great interest [4,5,6,7].Of inorganic carriers, metal complexes might become one of the promising nonviral gene carriers, because of their low cytotoxicicty, structural diversity, controllable aqua- and lipo-solubility, and appropriate density and distribution of positive charges.The metal complexes are a promoting agent in efficient nucleic acid condensation. The mono- and multi-nuclear Ni(II) and Ru(II) complexes with polypyridines were reported to be an effectively promoting agent in DNA condensation under neutral and acidic conditions [22,23,24,25,26]. The spherically nanosized coordination compoundPd12L24, which possesses 24 positive charges and mimics a histone octamer in size and charge density, triggers a stepwise condensation process of DNA in a manner similar to that of the natural system [27]. These metal complexes promote DNA packing mainly via neutralizing the negative charges on DNA surfaces [28]

Methods

Results

Conclusion