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

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.

AB5 Derivatives of Cyclotriphosphazene for the Synthesis of Dendrons and Their Applications

AB5 compounds issued from the reactivity of hexachlorocyclotriphosphazene are relatively easy to obtain using two ways: either first the reaction of one chloride with one reagent, followed by the reaction of the five remaining Cl with another reagent, or first the reaction of five chlorides with one reagent, followed by the reaction of the single remaining Cl with another reagent. This particular property led to the use of such compounds as core for the synthesis of dendrons (dendritic wedges), using the five functions for growing the dendritic branches. The single function can be used for the synthesis of diverse types of dendrimers (onion peel, dumbbell-shape, Janus), for covalent or non-covalent grafting to solid surfaces, providing nanomaterials, for grafting a fluorophore, especially for studying biological mechanisms, or for self-associations to get micelles. All these properties are reviewed in this paper.

Phosphorus dendrimers as powerful nanoplatforms for drug delivery, as fluorescent probes and for liposome interaction studies: A concise overview

Gene therapy is a new and promising tool to treat many severe diseases and the silencing of proteins is the safest and the most efficient tool to treat diseases because it does not induce changes in human genome and avoids a huge problem encompassing insertional mutagenesis. Using small RNAs to switch on/off target proteins is limited due to existence of some barriers for them in the human body (blood RNAses, serum albumins, cell walls, etc). For therapeutic applications they need the efficient and non-toxic carrier which will deliver them into cell cytoplasm. Within the huge range of carriers available, dendrimers can be underlined as new promising efficient carriers. This review summarizes several findings in phosphorus dendrimers based on in vitro and in vivo studies. As a result, we can conclude that advantages of phosphorus dendrimers are strong interaction with siRNA/DNA and formation of small and compact positively charged complexes of high and fast penetration into cells; efficient release of siRNA/pDNA in endosomes due to "proton sponge" effect; possibility of their modification including addition of fluorescent probes - in this case fluorescent dendrimer can be used both as a gene carrier and a tracer of delivery into cells. Additional benefit of using fluorescent phosphorus dendrimers is their ability to monitor the macrophage physiological status in vitro and in vivo.

Fluorescent Phosphorus Dendrimers: Towards Material and Biological Applications

Fluorescent derivatives of phosphorhydrazone dendrimers are reviewed. Diverse types of fluorophores have been used, such as pyrene, naphthol, anthracene, dansyl, diketone, phthalocyanine, maleimide, julolidine, rhodamine, fluorescein, or fluorene derivatives. The fluorescent groups can be located either as terminal groups on the surface, at the core, linked to the core (off-center), or to the branches of the dendritic structure. After fundamental research on their synthesis, these compounds have been used in the fields of catalysis, nanomaterials, OLEDs, sensors and biology/nanomedicine, in particular for monitoring transfection, or for their anti-inflammatory or anti-cancer properties.

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

Different types of two-photon absorbing (TPA) fluorophores have been synthesized and specifically functionalized to be incorporated in the structure of phosphorus dendrimers (highly branched macromolecules). The TPA fluorophores were included in the periphery as terminal functions, in the core, or in the branches of the dendrimer structures, respectively. Also the functionalization in two compartments (core and surface, or branches and surface) was achieved. The consequences of the location of the fluorophores on the fluorescence and TPA properties have been studied. Several of these TPA fluorescent dendrimers have water-solubilizing functions as terminal groups, and fluorophores at the core or in the branches. They have been used as fluorescent tools in biology for different purposes, such as tracers for imaging blood vessels of living animals, for determining the phenotype of cells, for deciphering the mechanism of action of anticancer compounds, and for safer photodynamic therapy.

Cytotoxicity of Dendrimers

Drug delivery systems are molecular platforms in which an active compound is packed into or loaded on a biocompatible nanoparticle. Such a solution improves the activity of the applied drug or decreases its side effects. Dendrimers are promising molecular platforms for drug delivery due to their unique properties. These macromolecules are known for their defined size, shape, and molecular weight, as well as their monodispersity, the presence of the void space, tailorable structure, internalization by cells, selectivity toward cells and intracellular components, protection of guest molecules, and controllable release of the cargo. Dendrimers were tested as carriers of various molecules and, simultaneously, their toxicity was examined using different cell lines. It was discovered that, in general, dendrimer cytotoxicity depended on the generation, the number of surface groups, and the nature of terminal moieties (anionic, neutral, or cationic). Higher cytotoxicity occurred for higher-generation dendrimers and for dendrimers with positive charges on the surface. In order to decrease the cytotoxicity of dendrimers, scientists started to introduce different chemical modifications on the periphery of the nanomolecule. Dendrimers grafted with polyethylene glycol (PEG), acetyl groups, carbohydrates, and other moieties did not affect cell viability, or did so only slightly, while still maintaining other advantageous properties. Dendrimers clearly have great potential for wide utilization as drug and gene carriers. Moreover, some dendrimers have biological properties per se, being anti-fungal, anti-bacterial, or toxic to cancer cells without affecting normal cells. Therefore, intrinsic cytotoxicity is a comprehensive problem and should be considered individually depending on the potential destination of the nanoparticle.

Use of Polyamidoamine Dendrimers in Brain Diseases

Polyamidoamine (PAMAM) dendrimers are one of the smallest and most precise nanomolecules available today, which have promising applications for the treatment of brain diseases. Each aspect of the dendrimer (core, size or generation, size of cavities, and surface functional groups) can be precisely modulated to yield a variety of nanocarriers for delivery of drugs and genes to brain cells in vitro or in vivo. Two of the most important criteria to consider when using PAMAM dendrimers for neuroscience applications is their safety profile and their potential to be prepared in a reproducible manner. Based on these criteria, features of PAMAM dendrimers are described to help the neuroscience researcher to judiciously choose the right type of dendrimer and the appropriate method for loading the drug to form a safe and effective delivery system to the brain.

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.

Rational design of novel, fluorescent, tagged glutamic acid dendrimers with different terminal groups and in silico analysis of their properties

Dendrimers are hyperbranched polymers with a multifunctional architecture that can be tailored for the use in various biomedical applications. Peptide dendrimers are particularly relevant for drug delivery applications due to their versatility and safety profile. The overall lack of knowledge of their three-dimensional structure, conformational behavior and structure-activity relationship has slowed down their development. Fluorophores are often conjugated to dendrimers to study their interaction with biomolecules and provide information about their mechanism of action at the molecular level. However, these probes can change dendrimer surface properties and have a direct impact on their interactions with biomolecules and with lipid membranes. In this study, we have used computer-aided molecular design and molecular dynamics simulations to identify optimal topology of a poly(l-glutamic acid) (PG) backbone dendrimer that allows incorporation of fluorophores in the core with minimal availability for undesired interactions. Extensive all-atom molecular dynamic simulations with the CHARMM force field were carried out for different generations of PG dendrimers with the core modified with a fluorophore (nitrobenzoxadiazole and Oregon Green 488) and various surface groups (glutamic acid, lysine and tryptophan). Analysis of structural and topological features of all designed dendrimers provided information about their size, shape, internal distribution and dynamic behavior. We have found that four generations of a PG dendrimer are needed to ensure minimal exposure of a core-conjugated fluorophore to external environment and absence of undesired interactions regardless of the surface terminal groups. Our findings suggest that NBD-PG-G4 can provide a suitable scaffold to be used for biophysical studies of surface-modified dendrimers to provide a deeper understanding of their intermolecular interactions, mechanisms of action and trafficking in a biological system.

Cyclotriphosphazene, an old compound applied to the synthesis of smart dendrimers with tailored properties

The versatile reactivity of hexachlorocyclotriphosphazene (N3P3Cl6) has been developed for the synthesis of specifically engineered dendrimers. Dendrimers are hyperbranched macromolecules built by concentric layers constituted of associated monomeric units. Many of the properties of dendrimers depend on the type of their surface (terminal) functions, which are generally all identical. For some specific purposes, it is desirable to have one function that is different at the level of the core. Hexachlorocyclotriphosphazene offers the possibility to differentiate the reactivity of one (or more) Cl from the others, for producing specifically engineered dendritic tools. These specific reactions on N3P3Cl6 have produced highly dense dendrimers, Janus dendrimers (two faces), tools for functionalizing materials, with uses as catalysts, as chemical sensors, for trapping CO2, for the culture of cells, or for imaging biological events. These properties will be emphasized in this review.

Bifunctional Phosphorus Dendrimers and Their Properties

Dendrimers are hyperbranched and monodisperse macromolecules, generally considered as a special class of polymers, but synthesized step-by-step. Most dendrimers have a uniform structure, with a single type of terminal function. However, it is often desirable to have at least two different functional groups. This review will discuss the case of bifunctional phosphorus-containing dendrimers, and the consequences for their properties. Besides the terminal functions, dendritic structures may have also a function at the core, or linked off-center to the core, or at the core of dendrons (dendritic wedges). Association of two dendrons having different terminal functions leads to Janus dendrimers (two faces). The internal structure can also possess functional groups on one layer, or linked to one layer, or on several layers. Finally, there are several ways to have two types of terminal functions, besides the case of Janus dendrimers: either each terminal function bears two functions sequentially, or two different functions are linked to each terminal branching point. Examples of each type of structure will be given in this review, as well as practical uses of such sophisticated structures in the fields of fluorescence, catalysis, nanomaterials and biology.

The specific functionalization of cyclotriphosphazene for the synthesis of smart dendrimers

Hexachlorocyclotriphosphazene is an old compound which affords very new properties in the field of dendrimers. Indeed, it can be used as a branching point for the rapid synthesis of highly dense dendrimers, but also for the synthesis of dendrimers having precisely one function different from all the others. These types of dendrimers are useful in the field of materials, affording highly reusable catalysts, chemical sensors, or supports for cell cultures. However, the most developed uses concern fluorescence. These dendrimers have been used for in vivo imaging, and for trying to elucidate biological mechanisms, in particular for anti-inflammatory dendrimers. This review will display important examples in the field.

Mechanism of cationic phosphorus dendrimer toxicity against murine neural cell lines

The purpose of this manuscript is to study the toxic responses against murine embryonic hippocampal cells (mHippoE-18) and neuroblastoma cells (N2a) to treatment with cationic phosphorus dendrimers (CPD). Two low generations of CPD--generation 2 (G2) and generation 3 (G3)--were applied to cell cultures to monitor events leading to either apoptosis or necrosis. These processes were analyzed using several bioassays, which included the detection of reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨm) alterations, morphology changes, apoptotic and dead cells, cytochrome c (Cyt c) release, caspase 3 activity, DNA fragmentation, as well as changes in cell cycle phases distribution. The results showed that CPD became highly cytotoxic at concentrations above 1 μM and at 0.7 μM in the case of G3 for mHippoE-18 cells. The toxicity was manifested by a pronounced decrease in cell viability, which is correlated with disturbances in cellular activities, such as massive ROS generation. The breakdown of cellular processes leads mainly to the necrotic cell death. Our findings are of high importance in the context of further biomedical studies on CPD.

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.