Evaluation of generations 2, 3 and 4 arginine modified PAMAM dendrimers for gene delivery

Generation 4 polyamidoamine dendrimers is a novel candidate of nano-carrier for gene delivery agents in breast cancer treatment

Polyamidoamine dendrimer (PAMAM-D) is a new gene vector developed in recent years. In this study, we successfully prepared G4PAMAM and detected its unique structure by NMR, FITR and TEM. We revealed that G4PAMAM could bind to human erythrocytes and BSA through electrostatic interaction respectively, and caused haemolysis and reduced bioavailability. However, G4PAMAM-VEGF-ASODN (antisense oligodeoxynucleotides) complex could prevent G4PAMAM from binding to the erythrocytes and BSA and remained stable as a conjugate, therefore the toxicity of the complex was reduced. Meanwhile, we showed that G4PAMAM could be used as a gene vector to deliver AODNs into breast cancer MDA-MB-231 cells without significant cell toxicity, and it enhanced cellular uptake of ODNs. In vivo experiment of human breast tumor xenograft mice model, G4PAMAM also showed more efficiency of accumulating VEGF-ASODN to inhibit the tumor vascularization of breast tumor tissue than naked AODN. Furthermore, G4PAMAM could protect DNA in cytoplasm from digestion of restriction enzymes, which was important to become an effective tool in gene research and therapy.

Dendritic Guanidines as Efficient Analogues of Cell Penetrating Peptides

The widespread application of cell penetrating agents to clinical therapeutics and imaging agents relies on the ability to prepare them on a large scale and to readily conjugate them to their cargos. Dendritic analogues of cell penetrating peptides, with multiple guanidine groups on their peripheries offer advantages as their high symmetry allows them to be efficiently synthesized, while orthogonal functionalities at their focal points allow them to be conjugated to cargo using simple synthetic methods. Their chemical structures and properties are also highly tunable as their flexibility and the number of guanidine groups can be tuned by altering the dendritic backbone or the linkages to the guanidine groups. This review describes the development of cell-penetrating dendrimers based on several different backbones, their structure-property relationships, and comparisons of their efficacies with those of known cell penetrating peptides. The toxicities of these dendritic guanidines are also reported as well as their application towards the intracellular delivery of biologically significant cargos including proteins and nanoparticles.

PAMAM dendrimers — diverse biomedical applications. Facts and unresolved questions

In this mini-review a number of novel outcomes, originating from studies in the field of PAMAM dendrimers, are presented and discussed. Owing to the multi-disciplinary nature of dendrimer chemistry it seems important to focus on the relevant topical research of PAMAM dendrimers, including their function, toxicity, surface modifications, and also possible new applications of these spherical polymers. We also consider the possibilities of specific functionalisation of PAMAM dendrimers — both novel ideas and those that have already been reported; as well as their cell-mediated effects (toxic and non-toxic). Then the reactivity of dendrimers’ terminal groups, and their anticipated protective role against modifications of biomacromolecules, are discussed with regard to future developments in biomedical research.

Oligoarginine-PEG-lipid particles for gene delivery

Cell-penetrating peptides (CPPs) are small peptides that can facilitate the uptake of macromolecular drugs, such as proteins or nucleic acids, into mammalian cells. Cytosolic delivery of CPPs could be beneficial to bypass conventional endocytosis in order to avoid degradation in the lysosomes. Oligoarginine conjugates have characteristics similar to CPPs in terms of cell translocation and are used in the intracellular delivery of plasmid DNA. In these cases, oligoarginine length and/or charge are important factors in the cellular uptake of oligoarginine alone. The arginine moiety of oligoarginine-modified particles may also be a decisive factor for vectors to deliver plasmid DNA. Oligoarginine-PEG-lipids can form self-assembled particles and modify the surface of lipid- and polymer-based particles. This review focuses on the influence of: i) oligoarginine-modified particles such as micelles, liposomes and polymer-based particles; ii) the morphology of oligoarginine-PEG-lipid complexed with plasmid DNA by decreasing the charge ratio; and iii) the oligoarginine length in the complex on its cellular uptake, transfection efficiency and uptake mechanism. The oligoarginine length of oligoarginine-modified particle complexed with plasmid DNA governs the cellular uptake pathway that determines the destiny of intracellular trafficking and finally transfection efficiency. The new aspects of surface-functionalized particle vectors with oligoarginine are discussed.

How to study dendriplexes II: Transfection and cytotoxicity

This paper reviews different techniques for analyzing the transfection efficiencies and cytotoxicities of dendriplexes-complexes of nucleic acids with dendrimers. Analysis shows that three plasmids are mainly used in transfection experiments: plasmid DNA encoding luciferase from the firefly Photinus pyralis, beta-galactosidase, or green fluorescent protein. The effective charge ratio of transfection does not directly correlate with the charge ratio obtained from gel electrophoresis, zeta-potential or ethidium bromide intercalation data. The most popular cells for transfection studies are human embryonic kidney cells (HEK293), mouse embryonic cells (NIH/3T3), SV40 transformed monkey kidney fibroblasts (COS-7) and human epithelioid cervical carcinoma cells (HeLa). Cellular uptake is estimated using fluorescently-labeled dendrimers or nucleic acids. Transfection efficiency is measured by the luciferase reporter assay for luciferase, X-Gal staining or beta-galactosidase assay for beta-galactosidase, and confocal microscopy for green fluorescent protein. Cytotoxicity is determined by the MTT test and lactate dehydrogenase assays. On the basis of the papers reviewed, a standard essential set of techniques for characterizing dendriplexes was constructed: (1) analysis of size and shape of dendriplexes in dried/frozen state by electron or atomic force microscopy; (2) analysis of charge/molar ratio of complexes by gel electrophoresis or ethidium bromide intercalation assay or zeta-potential measurement; (3) analysis of hydrodynamic diameter of dendriplexes in solution by dynamic light scattering. For the evaluation of transfection efficiency the essential techniques are (4) luciferase reporter assay, beta-galactosidase assay or green fluorescent protein microscopy, and (5) cytotoxicity by the MTT test. All these tests allow the transfection efficiencies and cytotoxicities of different kinds of dendrimers to be compared.

Controlled delivery of antisense oligonucleotides: a brief review of current strategies

Antisense therapy has been investigated extensively over the past two decades, either experimentally for gene functional research or clinically as therapeutic agents owing to the conceptual simplicity, ease of design and low cost. The concept of this therapeutic approach is promising because short antisense oligonucleotides (ASOs) can be delivered into target cells for specific hybridisation with target mRNA, resulting in the inhibition of the expression of pathogenic genes. However, the efficient delivery of the ASO molecules into target cells remains challenging; this bottleneck together with several other technical hurdles need to be overcome before this approach becomes effective and widely adopted. A variety of vectors such as lipids, polymers, peptides and nanoparticles have been explored. This review outlines the recent advances of the non-viral ASO delivery strategies. Several recent scientific studies, including authors' contributions, have been selected to highlight the technical aspects of ASO delivery.

Acetylation of PAMAM dendrimers for cellular delivery of siRNA

Background

The advancement of gene silencing via RNA interference is limited by the lack of effective short interfering RNA (siRNA) delivery vectors. Rational design of polymeric carriers has been complicated by the fact that most chemical modifications affect multiple aspects of the delivery process. In this work, the extent of primary amine acetylation of generation 5 poly(amidoamine) (PAMAM) dendrimers was studied as a modification for the delivery of siRNA to U87 malignant glioma cells.

Results

PAMAM dendrimers were reacted with acetic anhydride to obtain controlled extents of primary amine acetylation. Acetylated dendrimers were complexed with siRNA, and physical properties of the complexes were studied. Dendrimers with up to 60% of primary amines acetylated formed ~200 nm complexes with siRNA. Increasing amine acetylation resulted in reduced polymer cytotoxicity to U87 cells, as well as enhanced dissociation of dendrimer/siRNA complexes. Acetylation of dendrimers reduced the cellular delivery of siRNA which correlated with a reduction in the buffering capacity of dendrimers upon amine acetylation. Confocal microscopy confirmed that escape from endosomes is a major barrier to siRNA delivery in this system.

Conclusion

Primary amine acetylation of PAMAM dendrimers reduced their cytotoxicity to U87 cells, and promoted the release of siRNA from dendrimer/siRNA complexes. A modest fraction (approximately 20%) of primary amines of PAMAM can be modified while maintaining the siRNA delivery efficiency of unmodified PAMAM, but higher degrees of amine neutralization reduced the gene silencing efficiency of PAMAM/siRNA delivery vectors.

Synthesis and characterization of polyamidoamine dendrimer-coated multi-walled carbon nanotubes and their application in gene delivery systems

With the aim of improving the amount and delivery efficiency of genes taken by carbon nanotubes into human cancer cells, different generations of polyamidoamine dendrimer modified multi-walled carbon nanotubes (dMNTs) were fabricated, and characterized by high-resolution transmission electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis, revealing the presence of dendrimer capped on the surface of carbon nanotubes. The dMNTs fully conjugated with FITC-labeled antisense c-myc oligonucleotides (asODN), those resultant asODN-dMNTs composites were incubated with human breast cancer cell line MCF-7 cells and MDA-MB-435 cells, and liver cancer cell line HepG2 cells, and confirmed to enter into tumor cells within 15 min by laser confocal microscopy. These composites inhibited the cell growth in time- and dose-dependent means, and down-regulated the expression of the c-myc gene and C-Myc protein. Compared with the composites of CNT-NH(2)-asODN and dendrimer-asODN, no. 5 generation of dendrimer-modified MNT-asODN composites exhibit maximal transfection efficiencies and inhibition effects on tumor cells. The intracellular gene transport and uptake via dMNTs should be generic for the mammalian cell lines. The dMNTs have potentials in applications such as gene or drug delivery for cancer therapy and molecular imaging.