Phosphorus-carrying cascade molecules: inner architecture to biomedical applications

Cascade molecules are nearly uniform-sized macromolecules of small molecules or linear polymer cores built around symmetric branching units. A wide range of biological properties can be achieved with phosphorus-containing dendrimers, depending on their terminal functions, ranging from biomaterials to imaging, drug delivery, and acting as a drug by themselves. This feature article presents significant examples of phosphorus-containing dendrimers used to develop biochips, support cell cultures, carry or deliver biomacromolecules and drugs, bioimaging, and combinational benefits. Because of the thermal stability, ferrocene function, and physical and chemical properties of phosphorus, dendrimers show greater rigidity, mobility, and strength. These dendrimers will be discussed as having a favorable effect on cell growths, especially on neuronal cells, as well as human immune cells like natural killer cells and monocytes, which have a crucial part in preventing cancerous and viral infections. Several phosphorus dendrimers are effective as drugs by themselves (drug per se) and show their activity against neurodegenerative diseases, cancer, inflammation, ocular hypertension, and transmissible spongiform encephalopathies (TSEs) in both in vivo and in vitro. The present review discusses the synthetic route, fabrications, and biomedical applications of phosphorus-containing dendrimers. The toxicity of these dendrimers was also reported.

Low-Generation Cationic Phosphorus Dendrimers: Novel Approach to Tackle Drug-Resistant S. aureus In Vitro and In Vivo

The incessant, global increase in antimicrobial resistance (AMR) is a very big challenge for healthcare systems. AMR is predicted to grow at an alarming pace, with a dramatic increase in morbidity, mortality, and a 100 trillion US$ loss to the global economy by 2050. The mortality rate caused by methicillin-resistant S. aureus (MRSA) is much higher as compared to infections caused by drug-susceptible S. aureus. Additionally, there is a big paucity of therapeutics available for treatment of serious infections caused by MRSA. Thus, the discovery and development of novel therapies is an urgent, unmet medical need. In this context, we synthesized AE4G0, a low-generation cationic-phosphorus dendrimer expressing potent antimicrobial activity against S. aureus and Enterococcus sp., and demonstrating a broad selectivity index against eukaryotic cells. AE4G0 exhibits concentration-dependent, bactericidal activity and synergizes with gentamicin, especially against gentamicin-resistant MRSA NRS119. Fluorescence and scanning electron microscopy demonstrate that treatment with AE4G0 led to the utter destruction of S. aureus ATCC 29213 without inducing resistance, despite repeated exposure. When tested in vivo, AE4G0 demonstrates significant efficacy against S. aureus ATCC 29213, alone and in combination with gentamicin against gentamicin-resistant S. aureus NRS119 in the murine skin model of infection. Taken together, AE4G0 demonstrates the potential to be translated as a novel therapeutic option for the treatment of topical, drug-resistant S. aureus infections.

Dendriplex-Impregnated Hydrogels With Programmed Release Rate

Hydrogels are biocompatible matrices for local delivery of nucleic acids; however, functional dopants are required to provide efficient delivery into cells. In particular, dendrimers, known as robust nucleic acid carriers, can be used as dopants. Herein, we report the first example of impregnating neutral hydrogels with siRNA-dendrimer complexes. The surface chemistry of dendrimers allows adjusting the release rate of siRNA-containing complexes. This methodology can bring new materials for biomedical applications.

Safe Polycationic Dendrimers as Potent Oral In Vivo Inhibitors of Mycobacterium tuberculosis: A New Therapy to Take Down Tuberculosis

The long-term treatment of tuberculosis (TB) sometimes leads to nonadherence to treatment, resulting in multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis. Inadequate bioavailability of the drug is the main factor for therapeutic failure, which leads to the development of drug-resistant cases. Therefore, there is an urgent need to design and develop novel antimycobacterial agents minimizing the period of treatment and reducing the propagation of resistance at the same time. Here, we report the development of original and noncytotoxic polycationic phosphorus dendrimers essentially of generations 0 and 1, but also of generations 2-4, with pyrrolidinium, piperidinium, and related cyclic amino groups on the surface, as new antitubercular agents active per se, meaning with intrinsic activity. The strategy is based on the phenotypic screening of a newly designed phosphorus dendrimer library (generations 0-4) against three bacterial strains: attenuated Mycobacterium tuberculosis H37Ra, virulent M. tuberculosis H37Rv, and Mangora bovis BCG. The most potent polycationic phosphorus dendrimers 1G0,_HCl and 2G0,_HCl are active against all three strains with minimum inhibitory concentrations (MICs) between 3.12 and 25.0 μg/mL. Both are irregularly shaped nanoparticles with highly mobile branches presenting a radius of gyration of 7 Å, a diameter of maximal 25 Å, and a solvent-accessible surface area of dominantly positive potential energy with very localized negative patches arising from the central N₃P₃ core, which steadily interacts with water molecules. The most interesting is 2G0,_HCl, showing relevant efficacy against single-drug-resistant (SDR) M. tuberculosis H37Rv, resistant to rifampicin, isoniaid, ethambutol, or streptomycin. Importantly, 2G0,_HCl displayed significant in vivo efficacy based on bacterial counts in lungs of infected Balb/C mice at a dose of 50 mg/kg oral administration once a day for 2 weeks and superior efficacy in comparison to ethambutol and rifampicin. This series of polycationic phosphorus dendrimers represents first-in-class drugs to treat TB infection, could fulfill the clinical candidate pipe of this high burden of infectious disease, and play a part in addressing the continuous demand for new drugs.

Synthesis, Internalization and Visualization of N-(4-Carbomethoxy) Pyrrolidone Terminated PAMAM [G5:G3-TREN] Tecto(dendrimers) in Mammalian Cells

Tecto(dendrimers) are well-defined, dendrimer cluster type covalent structures. In this article, we present the synthesis of such a PAMAM [G5:G3-(TREN)]-N-(4-carbomethoxy) pyrrolidone terminated tecto(dendrimer). This tecto(dendrimer) exhibits nontraditional intrinsic luminescence (NTIL; excitation 376 nm; emission 455 nm) that has been attributed to three fluorescent components characterized by different fluorescence lifetimes. Furthermore, it has been shown that this PAMAM [G5:G3-(TREN)]-N-(4-carbomethoxy) pyrrolidone terminated tecto(dendrimer) is able to form a polyplex with double stranded DNA, and is nontoxic for HeLa and HMEC-1 cells up to a concentration of 10 mg/mL, even though it accumulates in endosomal compartments as demonstrated by its unique NTIL emission properties. Many of the above features would portend the proposed use of this tecto(dendrimer) as an efficient transfection agent. Quite surprisingly, transfection activity could not be demonstrated in HeLa cells, and the possible reasons are discussed in the article.

Phosphorus Dendrimers as Nanotools against Cancers

This review concerns the use of dendrimers, especially of phosphorhydrazone dendrimers, against cancers. After the introduction, the review is organized in three main topics, depending on the role played by the phosphorus dendrimers against cancers: (i) as drugs by themselves; (ii) as carriers of drugs; and (iii) as indirect inducer of cancerous cell death. In the first part, two main types of phosphorus dendrimers are considered: those functionalized on the surface by diverse organic derivatives, including known drugs, and those functionalized by diverse metal complexes. The second part will display the role of dendrimers as carriers of anticancer “drugs”, which can be either small molecules or anticancer siRNAs, or the combination of both. In the third part are gathered a few examples of phosphorhydrazone dendrimers that are not cytotoxic by themselves, but which under certain circumstances induce a cytotoxic effect on cancerous cells. These examples include a positive influence on the human immune system and the combination of bioimaging with photodynamic therapy properties.

Morpholino-functionalized phosphorus dendrimers for precision regenerative medicine: osteogenic differentiation of mesenchymal stem cells

A novel bioactive macromolecule based on morpholino-functionalized phosphorus dendrimers (generation 2, G2-Mor⁺) was developed for osteogenic differentiation of mesenchymal stem cells (MSCs). Interestingly, through in vitro tests, it was shown that G2-Mor⁺ dendrimer can strongly promote the transformation of MSCs into osteoblasts, which implies the potential application of phosphorus dendrimers in bone regeneration for precision regenerative medicine.

Phosphorus dendrimers functionalised with nitrogen ligands, for catalysis and biology

Phosphorus dendrimers (dendrimers having one phosphorus atom at each branching point) possess versatile properties, depending on the type of their terminal functions.

Dendrimers Show Promise for siRNA and microRNA Therapeutics

The lack of an appropriate intracellular delivery system for therapeutic nucleic acids (TNAs) is a major problem in molecular biology, biotechnology, and medicine. A relatively new class of highly symmetrical hyperbranched polymers, called dendrimers, shows promise for transporting small TNAs into both cells and target tissues. Dendrimers have intrinsic advantages for this purpose: their physico-chemical and biological properties can be controlled during synthesis, and they are able to transport large numbers of TNA molecules that can specifically suppress the expression of single or multiple targeted genes. Numerous chemical modifications of dendrimers extend the biocompatibility of synthetic materials and allow targeted vectors to be designed for particular therapeutic purposes. This review summarizes the latest experimental data and trends in the medical application of various types of dendrimers and dendrimer-based nanoconstructions as delivery systems for short small interfering RNAs (siRNAs) and microRNAs at the cell and organism levels. It provides an overview of the structural features of dendrimers, indicating their advantages over other types of TNA transporters.

Hydrogels of Polycationic Acetohydrazone-Modified Phosphorus Dendrimers for Biomedical Applications: Gelation Studies and Nucleic Acid Loading

In this work, we report the assemblage of hydrogels from phosphorus dendrimers in the presence of biocompatible additives and the study of their interactions with nucleic acids. As precursors for hydrogels, phosphorus dendrimers of generations 1–3 based on the cyclotriphosphazene core and bearing ammonium or pyridinium acetohydrazones (Girard reagents) on the periphery have been synthesized. The gelation was done by the incubation of dendrimer solutions in water or phosphate-buffered saline in the presence of biocompatible additives (glucose, glycine or polyethylene glycol) to form physical gels. Physical properties of gels have been shown to depend on the gelation conditions. Transmission electron microscopy revealed structural units and well-developed network structures of the hydrogels. The hydrogels were shown to bind nucleic acids efficiently. In summary, hydrogels of phosphorus dendrimers represent a useful tool for biomedical applications.

Vibrational spectroscopic study of cationic phosphorus dendrimers with aminoethylpiperidine terminal groups

Two generations of phosphoric dendrimers with piperidine functional groups were synthesized for use in biology and medicine. Neutral samples are soluble in organic solvents but after protonation these dendrimers become water soluble and can be used for biological experiments. The FTIR and FT Raman spectra of two generations of dendrimers G_i constructed from the cyclotriphosphazene core, repeating units OC₆H₄CHNN(CH₃)P(S)< and aminoethylpiperidine end groups NH(CH₂)₂C₅NH₁₁ were recorded. The study of the IR spectra shows that the NH groups form hydrogen bonds. The calculation of the molecular structure and vibrational spectra of the first generation dendrimer was performed by the method of DFT. This molecule has flat, repeating units and a plane of symmetry passing through the core. The calculation of the distribution of potential energy made it possible to classify the bands in the experimental spectra of dendrimers. Amine groups are manifested in the form of a band of NH stretching vibrations at 3389 cm^-1 in the IR spectrum of G₁. NH⁺ stretching bands located at 2646 and 2540 cm^-1 in the IR spectrum of G₂. The stretching vibrations of NH⁺ groups are noticeably shifted to low frequencies due to the formation of a hydrogen bond with the chlorine atom. The line at 1575 cm^-1 in the Raman spectrum of G₁ is characteristic for repeating units.

Phosphorus dendrimers for nanomedicine

From biomaterials to imaging, and from drug delivery to drugs by themselves, phosphorus-containing dendrimers offer a large palette of biological properties, depending essentially on their types of terminal functions. The most salient examples of phosphorus dendrimers used for the elaboration of bio-chips and of supports for cell cultures, for imaging biological events, and for carrying and delivering drugs or biomacromolecules are presented in this feature article. Several phosphorus dendrimers can be considered also as drugs per se (by themselves) in particular to fight against cancers, neurodegenerative diseases, and inflammation, both in vitro and in vivo. Toxicity assays are also reported.

Which Dendrimer to Attain the Desired Properties? Focus on Phosphorhydrazone Dendrimers

Among the six Critical Nanoscale Design Parameters (CNDPs) proposed by Prof. Donald A. Tomalia, this review illustrates the influence of the sixth one, which concerns the elemental composition, on the properties of dendrimers. After a large introduction that summarizes different types of dendrimers that have been compared with PolyAMidoAMine (PAMAM) dendrimers, this review will focus on the properties of positively and negatively charged phosphorhydrazone (PPH) dendrimers, especially in the field of biology, compared with other types of dendrimers, in particular PAMAM dendrimers, as well as polypropyleneimine (PPI), carbosilane, and p-Lysine dendrimers.

Synthesis of dissymmetric phosphorus dendrimers using an unusual protecting group

We report the synthesis of neutral and polycationic dissymmetric phosphorus dendrimers bearing branches of different generations on the core.

Anti-Inflammatory Effect of Anti-TNF-α SiRNA Cationic Phosphorus Dendrimer Nanocomplexes Administered Intranasally in a Murine Acute Lung Injury Model

Inflammation is an essential component of many lung diseases, including asthma, chronic obstructive pulmonary disease (COPD), or acute lung injury. Our purpose was to design efficient carriers for lung delivery of small interfering RNA (siRNA) targeting tumor necrosis factor (TNF-α) in an acute lung injury model. To achieve this goal, two different types of phosphorus-based dendrimers with either pyrrolidinium or morpholinium as terminal protonated amino groups were selected for their better biocompatibility compared to other dendrimers. Dendriplexes containing pyrrolidinium surface groups demonstrated a stronger siRNA complexation, a higher cellular uptake, and enhanced in vitro silencing efficiency of TNF-α in the lipopolysaccharide (LPS)-activated mouse macrophage cell line RAW264.7, compared to morpholinium-containing dendriplexes. The better performance of the pyrrolidium dendriplexes was attributed to their higher pK_a value leading to a stronger siRNA complexation and improved protection against enzymatic degradation resulting in a higher cellular uptake. The superior silencing effect of the pyrrolidinium dendriplexes, compared to noncomplexed siRNA, was confirmed in vivo in an LPS-induced murine model of short-term acute lung injury upon lung delivery via nasal administration. These data suggest that phosphorus dendriplexes have a strong potential in lung delivery of siRNA for treating inflammatory lung diseases.

Dendritic nanocarriers based on hyperbranched polymers

The use of hyperbranched polymers as an alternative to perfect dendrimers as nanocarrier systems for drugs, dyes and other guest molecules is covered. Different types of hyperbranched polymers are discussed with regard to aspects like synthesis, functionalisation and encapsulation properties but also their degradation.

Multifaceted glycodendrimers with programmable bioactivity through convergent, divergent, and accelerated approaches using polyfunctional cyclotriphosphazenes

The cyclotriphosphazene-based platform facilitates versatile synthesis of glycodendrimers active as inhibitors of two biomedically relevant lectins.

Multivalent glycoconjugate syntheses and applications using aromatic scaffolds

Glycan-protein interactions are of utmost importance in several biological phenomena. Although the variety of carbohydrate residues in mammalian cells is limited to less than a dozen different sugars, their spatial topographical presentation in what is now associated as the "glycocodes" provides the fundamental keys for specific and high affinity "lock-in" recognition events associated with a wide range of pathologies. Toward deciphering our understanding of these glycocodes, chemists have developed new creative tools that included dendrimer chemistry in order to provide monodisperse multivalent glycoconjugates. This review provides a survey of the numerous aromatic architectures generated for the multivalent presentation of relevant carbohydrates using covalent attachment or supramolecular self-assemblies. The basic concepts toward their controlled syntheses will be described using modern synthetic procedures with a particular emphasis on powerful organometallic methodologies. The large variety of dendritic aromatic scaffolds, together with a brief survey of their unique biophysical and biological properties will be critically reviewed. The distinctiveness of the resulting multivalent glycoarchitectures, encompassing glycoclusters, glycodendrimers and molecularly defined self-assemblies, in forming well organized cross-linked lattices with multivalent carbohydrate binding proteins (lectins) together with their photophysical, medical, and imaging properties will also be briefly highlighted. The topic will be presented in increasing order of aromatic backbone complexities and will end with fullerenes together with self-assembled nanostructures, thus complementing the various scaffolds described in this special thematic issue dedicated to multivalent glycoscience.

Biological properties of water-soluble phosphorhydrazone dendrimers

Dendrimers are hyperbranched and perfectly defined macromolecules, constituted of branches emanating from a central core in an iterative fashion. Phosphorhydrazone dendrimers constitute a special family of dendrimers, possessing one phosphorus atom at each branching point. The internal structure of these dendrimers is hydrophobic, but hydrophilic terminal groups can induce the solubility of the whole structure in water. Indeed, the properties of these compounds are mainly driven by the type of terminal groups their bear; this is especially true for the biological properties. For instance, positively charged terminal groups are efficient for transfection experiments, as drug carriers, as anti-prion agents, and as inhibitor of the aggregation of Alzheimer's peptides, whereas negatively charged dendrimers have anti-HIV properties and can influence the human immune system, leading to anti-inflammatory properties usable against rheumatoid arthritis. This review will give the most representative examples of the biological properties of water-soluble phosphorhydrazone dendrimers, organized depending on the type of terminal groups they bear.

Organophosphorus chemistry for the synthesis of dendrimers

Dendrimers are multifunctional, hyperbranched and perfectly defined macromolecules, synthesized layer after layer in an iterative manner. Besides the nature of the terminal groups responsible for most of the properties, the nature of the internal structure, and more precisely of the branching points, is also of crucial importance. For more than 15 years, we have demonstrated that the presence of phosphorus atom(s) at each branching point of the dendrimeric structure is particularly important and highly valuable for three main reasons: (i) the versatility of phosphorus chemistry that allows diversified organochemistry for the synthesis of dendrimers; (ii) the use of 31P-NMR, which is a highly valuable tool for the characterization of dendrimers; (iii) some properties (in the fields of catalysis, materials, and especially biology), that are directly connected to the nature of the internal structure and of the branching points. This review will give an overview of the methods of synthesis of phosphorus-containing dendrimers, as well on the ways to graft phosphorus derivatives as terminal groups, with emphasis on the various roles played by the chemistry of phosphorus.

Dendrimers--revolutionary drugs for infectious diseases

Over recent years innovative nanomolecules in a form of dendrimers have been gaining increasing interest. These compounds can be designed and modified in many ways giving a molecule which meets required expectations. For this reason dendrimers are the object of intensive studies in many fields of nanoscience including one of the most thriving--biomedicine. Numerous studies provide evidence that some dendrimers exhibit activities against many species/strains of viruses, bacteria, fungi, and prions. These types of dendritic nanostructures which are distinguished by antipathogenic properties and low cytotoxicity to eukaryotic cells may be potentially applied in medicine as novel drugs for various infectious diseases, especially those which are persistent, marked by high mortality rate, or untreatable. Dendrimers can exert their effect via different mechanisms of action, which are, in most cases, related to multivalency of the nanomolecule. The application of dendrimers is likely to be a breakthrough in prevention and treatment of infectious diseases which still beset humanity and may significantly improve the quality of people's life.

Triazine dendrimers as drug delivery systems: from synthesis to therapy

The use of triazine dendrimers as drug delivery systems benefits from their synthetic versatility and well-defined structure. Triazine dendrimers can be designed and readily synthesized to display orthogonally functional surfaces that facilitate post-synthetic manipulation such as attachment of drug, PEGylation, and/or the installation of ligands or reporting groups. The synthesis is scalable, and large generations can be accessed. To date, triazine dendrimers have been probed for a variety of medicinal applications including drug delivery with an emphasis on cancer, nonviral DNA and RNA delivery systems, in sensing applications, and as bioactive materials. Specifically, triazine adducts with paclitaxel, camptothecin, brefeldin A, and desferrioxamine have been prepared and assessed. Paclitaxel constructs show promising activity in vivo. The use of these materials in fluorescence-based glucose sensors is being pursued. Glycosylated triazine dendrimers interfere with signal transduction in the Toll-4 receptor pathway.

High Cytotoxic Activity of Phosphonium Salts and Their Complementary Selectivity towards HeLa and K562 Cancer Cells: Identification of Tri-n-butyl-n-hexadecylphosphonium bromide as a Highly Potent Anti-HeLa Phosphonium Salt

Quaternary ammonium and phosphonium salts have been screened for their toxic effect on HeLa and K562 cancer cell lines, as well as on normal HUVEC cells. Tri-n-butyl-n-hexadecylphosphonium bromide, the first phosphonium salt with a halogen anion tested against HeLa cells, was 12 times more potent (IC50 <5 μm after 24 and 48 h) than the clinically used reference compound cisplatin and 17 times more potent than tri-n-hexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, which, to the best of our knowledge, is the first phosphonium salt to be evaluated in HeLa cells. However, it was inactive against K562 cells (24 and 48 h). According to a caspase-3/7 assay, its toxicity has not been connected with the induction of apoptosis. In contrast, triphenylalkylphosphonium iodides with shorter C1-5 alkyl chains were inactive against HeLa cells but very active against K562 cells (IC50=6-10 μm after 48 h). Phosphonium cations with halide counterions proved to be more potent than those with (CF3SO2)2N(-) as the anion, as in the anticancer agent NSC 747251, or other anions in molecules with similar alkyl chain lengths. On the other hand, a series of ammonium salts containing a short methylthiomethyl or methoxymethyl side chain revealed low cytotoxicity (IC50 >500 μm after 24 and 48 h) against both HeLa and K562 cancer cell lines as well as normal HUVEC cells, showing that the nontoxic N(+)CH2YMe (Y=S, O) structural motif in ammonium salts could be suitable for further optimization and development, especially in transfection experiments.

Biological properties of new viologen-phosphorus dendrimers

Some biological properties of eight dendrimers incorporating both phosphorus linkages and viologen units within their cascade structure or at the periphery were investigated for the first time. In particular cytotoxicity, hemotoxicity, and antimicrobial and antifungal activity of these new macromolecules were examined. Even if for example all these species exhibited good antimicrobial properties, it was demonstrated that their behavior strongly depends on several parameters as their size and molecular weight, the number of viologen units and the nature of the terminal groups.

Synthesis of a fluorescent cationic phosphorus dendrimer and preliminary biological studies of its interaction with DNA

The synthesis of a water-soluble phosphorus-containing dendrimer possessing a fluorophore (maleimide-type) linked to the core is described. This dendrimer is found brightly fluorescent in CH(2)Cl(2), but poorly fluorescent in water. The cytotoxicity of this compound is relatively low towards HeLa and A549 cells, and less toxic after 48 hours than after 24 hours. Association of this dendrimer with plasmid DNA (BACE-GFP) analyzed with circular dichroism (CD) indicates a possible disturbing of the helical B-type structure of DNA. The strength of this association (a "dendriplex") with BACE-GFP (also with HygEGFP) was measured by electrophoresis.

Triazine dendrimers as nonviral gene delivery systems: effects of molecular structure on biological activity

A family of generation 1, 2, and 3 triazine dendrimers differing in their core flexibility was prepared and evaluated for their ability to accomplish gene transfection. Dendrimers and dendriplexes were analyzed by their physicochemical and biological properties such as condensation of DNA, size, surface charge, morphology of dendriplexes, toxic and hemolytic effects, and ultimately transfection efficiency in L929 and MeWo cells. Flexibility of the backbone was found to play an important role with generation 2 dendrimer displaying higher transfection efficiencies than 25 kDa poly(ethylene imine) or SuperFect at a lower cytotoxicity level. This result is surprising, as PAMAM dendrimers require generations 4 or 5 to become effective transfection reagents. The ability to delineate effects of molecular structure and generation of triazine dendrimers with biological properties provides valuable clues for further modifying this promising class of nonviral delivery system.

Designing dendrimers for ocular drug delivery

New series of phosphorus-containing dendrimers, having one quaternary ammonium salt as core and carboxylic acid terminal groups have been synthesized from generation 0 (3 carboxylic acid terminal groups) to generation 2 (12 carboxylic acid terminal groups). These dendrimers react with the neutral form of carteolol (an ocular anti-hypertensive drug used to treat glaucoma) to afford ion pair (saline) species. The solubility in water of these charged dendrimers depends on the generation considered: generation 0 (3 carteolol) is well soluble, whereas generation 1 (6 carteolol) and generation 2 (12 carteolol) are poorly soluble. These dendrimers have been tested in vivo, as vehicle for ocular drug delivery of carteolol to rabbits.

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.

Polycationic triazine-based dendrimers: effect of peripheral groups on transfection efficiency

A panel of eight, second generation triazine dendrimers differing in the number of amines, guanidines, hydroxyls and aliphatic groups on the periphery was synthesized and assayed for gene transfer in an attempt to correlate the effects of surface functionality on transfection efficiency. The physicochemical and biological properties of the dendrimers and dendriplexes, such as condensation of DNA, size, surface charge and morphology of dendriplexes, toxicity and ultimately transfection efficiency in MeWo cells, were analyzed. The results from an ethidium bromide exclusion assay showed that the complexation efficiency of the dendrimers with DNA is moderately affected by surface groups. Increasing the number of surface amines, reducing the number of surface hydroxyl groups, or replacing the amine moiety with guanidines all help strengthen the complex formed. Results from dynamic light scattering and zeta potential analyses indicate that the smallest particles correlate with complexes that exhibit the highest zeta potentials. Cytotoxicity was low for all compounds, particularly for the G2-5 dendrimer containing alkyl groups on the periphery, indicating the benefit of incorporating such neutral functionality onto the surface of the triazine dendrimers. Within this panel, the highest transfection efficiency was observed for the dendrimers that formed the smallest complexes, suggesting that this physicochemical property is an accurate predictor for determining which dendrimers will show high transfection efficiency.