Janus Dendrimers as Nanocarriers of Ibuprofen, Chlorambucil and their Anticancer Activity

BACKGROUND

Janus Dendrimer represents a novel class of synthetic nanocarriers. Since it is possible to introduce multiple drugs and target moieties, this helps the designing of new biocompatible forms with pharmacological activities comprised of different drugs with tailor-made functionalities, such as anticancer and nonsteroidal anti-inflammatory, which could improve the anticancer activity with less toxicity.

AIMS

This study aimed to determine the anticancer activity of the Janus dendrimers formed by two dendrons. One dendron conjugates with chlorambucil, and the other dendron conjugates with Ibuprofen.

METHODS

The cytotoxicity of the drug carriers was determined by the sulforhodamine B (SRB) assay for three cell lines. PC-3 (human prostatic adenocarcinoma), HCT-15 (human colorectal adenocarcinoma), MFC-7 (human breast cancer) and the COS-7 African green monkey kidney (used as a control) cell lines were seeded into 96-well plates at a density of 5x103 cells/well and cultured for 24 h before use. All the obtained compounds were characterized by 1H and 13C NMR one and two dimensions, UVvis, FTIR, MALDI-TOF, Electrospray mass, and FAB+. Microscopic images were taken in an Inverted microscope Nikon, Diaphot 300, 10x4 in culture medium.

RESULTS

Janus dendrimers (G1 and G2) were synthesized via an azide-alkyne click-chemistry reaction attaching on one face dendrons with ibuprofen molecules and, on the other face, attached a chlorambucil- derivative. The IC50 behavior of the conjugates of the first and second generations showed anticancer activity against PC-3, HCT-15, and MFC-7 cell lines. The second generation was more active against PC-3, HCT-15 and MFC-7 with IC50 of 3.8±0.5, 3.0±0.2 and 3.7 ± 1.1 mM, respectively.

CONCLUSION

The new Janus dendrimers with anticancer chlorambucil and nonsteroidal antiinflammatory Ibuprofen can improve the anticancer activity of chlorambucil with less toxicity.

FUTURE PROSPECTS

Now, we are working on the synthesis of new Janus dendrimers using the most effective and fine methods. Moreover, we hope that we shall be able to obtain different generations that are more selective against cancer cells.

Innovative Strategy for Truly Reversible Capture of Polluting Gases-Application to Carbon Dioxide

This paper consists of a deep analysis and data comparison of the main strategies undertaken for achieving truly reversible capture of carbon dioxide involving optimized gas uptakes while affording weakest retention strength. So far, most strategies failed because the estimated amount of CO2 produced by equivalent energy was higher than that captured. A more viable and sustainable approach in the present context of a persistent fossil fuel-dependent economy should be based on a judicious compromise between effective CO2 capture with lowest energy for adsorbent regeneration. The most relevant example is that of so-called promising technologies based on amino adsorbents which unavoidably require thermal regeneration. In contrast, OH-functionalized adsorbents barely reach satisfactory CO2 uptakes but act as breathing surfaces affording easy gas release even under ambient conditions or in CO2-free atmospheres. Between these two opposite approaches, there should exist smart approaches to tailor CO2 retention strength even at the expense of the gas uptake. Among these, incorporation of zero-valent metal and/or OH-enriched amines or amine-enriched polyol species are probably the most promising. The main findings provided by the literature are herein deeply and systematically analysed for highlighting the main criteria that allow for designing ideal CO2 adsorbent properties.

Dendrimer-Based Coatings on a Photonic Crystal Surface for Ultra-Sensitive Small Molecule Detection

We propose and demonstrate dendrimer-based coatings for a sensitive biochip surface that enhance the high-performance sorption of small molecules (i.e., biomolecules with low molecular weights) and the sensitivity of a label-free, real-time photonic crystal surface mode (PC SM) biosensor. Biomolecule sorption is detected by measuring changes in the parameters of optical modes on the surface of a photonic crystal (PC). We describe the step-by-step biochip fabrication process. Using oligonucleotides as small molecules and PC SM visualization in a microfluidic mode, we show that the PAMAM (poly-amidoamine)-modified chip's sorption efficiency is almost 14 times higher than that of the planar aminosilane layer and 5 times higher than the 3D epoxy-dextran matrix. The results obtained demonstrate a promising direction for further development of the dendrimer-based PC SM sensor method as an advanced label-free microfluidic tool for detecting biomolecule interactions. Current label-free methods for small biomolecule detection, such as surface plasmon resonance (SPR), have a detection limit down to pM. In this work, we achieved for a PC SM biosensor a Limit of Quantitation of up to 70 fM, which is comparable with the best label-using methods without their inherent disadvantages, such as changes in molecular activity caused by labeling.

Mesoporous organosilicas with thiol functionalised pores: multifunctional dendrimers as sacrificial building block and template

The synthesis of multifunctional poly(amidoamine) (PAMAM)-based dendrimers containing a cleavable disulfide linker within each arm of the dendrimer, together with condensable triethoxysilyl groups on the periphery of the dendrimer, is described. The dendrimers were mixed with 1,4-bis(triethoxysilyl)benzene and subsequently transformed into silsesquioxane gels or periodic mesoporous organosilicas (PMOs) to generate materials with dendrimers covalently embedded within the interior of the silsesquioxane networks. Subsequent treatment of the gels with dithiothreitol enabled the core of the dendrimers to be selectively cleaved at the disulfide site, thus generating thiol functions localised within the pores. The effect of different dendrimer generations on the reactivity of the pendant thiol functions was probed by impregnation with gold salts, which were reduced to obtain gold nanoparticles within the pore networks of the gels and PMOs. The gels yielded polydisperse gold nanoparticles (2 to 70 nm) with dimensions modulated by the generation of the dendrimer, together with well-defined gold/thiolate clusters with Au⋯S distances of 2.3 Å. Such clusters were also observed in the PMO system, together with monodispersed gold nanoparticles with diameters comparable to that of the organised pores in the PMO. The role of surface functionalisation in controlling the formation of gold clusters and/or nanoparticles is discussed.

Review of photoresponsive and glycoside dendrimers in biomaterials and sensors applications

Dendrimers are branched molecules with well-defined lengths, shapes, molecular weights, and monodispersity in comparison to linear polymers.

Controlled Anchoring of (Phenylureido)sulfonamide-Based Receptor Moieties: An Impact of Binding Site Multiplication on Complexation Properties

The repetition of urea-based binding units within the receptor structure does not only lead to monomer properties multiplication. As confirmed by spectroscopic studies, UV-Vis and ¹H-NMR in classical or competitive titration mode, the attachment to a carrier allocates the active moieties to mutual positions predetermining the function of the whole receptor molecule. Bivalent receptors form self-aggregates. Dendritic receptors with low dihydrogen phosphate loadings offer a cooperative complexation mode associated with a positive dendritic effect. In higher dihydrogen phosphate concentrations, the dendritic branches act independently and the binding mode changes to 1:1 anion: complexation site. Despite the anchoring, the dendritic receptors retain the superior efficiency and selectivity of a monomer, paving the way to recyclable receptors, desirable for economic and ecological reasons.

Recent Advances in Preclinical Research Using PAMAM Dendrimers for Cancer Gene Therapy

Carriers of genetic material are divided into vectors of viral and non-viral origin. Viral carriers are already successfully used in experimental gene therapies, but despite advantages such as their high transfection efficiency and the wide knowledge of their practical potential, the remaining disadvantages, namely, their low capacity and complex manufacturing process, based on biological systems, are major limitations prior to their broad implementation in the clinical setting. The application of non-viral carriers in gene therapy is one of the available approaches. Poly(amidoamine) (PAMAM) dendrimers are repetitively branched, three-dimensional molecules, made of amide and amine subunits, possessing unique physiochemical properties. Surface and internal modifications improve their physicochemical properties, enabling the increase in cellular specificity and transfection efficiency and a reduction in cytotoxicity toward healthy cells. During the last 10 years of research on PAMAM dendrimers, three modification strategies have commonly been used: (1) surface modification with functional groups; (2) hybrid vector formation; (3) creation of supramolecular self-assemblies. This review describes and summarizes recent studies exploring the development of PAMAM dendrimers in anticancer gene therapies, evaluating the advantages and disadvantages of the modification approaches and the nanomedicine regulatory issues preventing their translation into the clinical setting, and highlighting important areas for further development and possible steps that seem promising in terms of development of PAMAM as a carrier of genetic material.

Dendritic fibrous nanosilica-supported dendritic IL/Ru(ii) as photocatalysts for the dicarbofunctionalization of styrenes with carbon dioxide and amines

The effectual utilization of heterogeneous catalysts from nano sources through chemical moderation for the α-aminomethylcarboxylation of alkenes with carbon dioxide and amines is an attractive area to study. Dendritic fibrous nanosilica (DFNS) is a cost-effective, resistant, plenteous, and reproducible source with dandelion-like fibrous anatomy. The present paper is a report on an easy method to provide a family of new DFNS-supported dendritic imidazolium IL/Ru(ii) heterogeneous catalysts DFNS/IL/Ru (1-3) with high ionic density from DFNS. A positive dendritic effect was perceived in the chemical stabilization performance of CO2. DFNS/IL/Ru(ii) was appropriately identified by UV-vis spectroscopy, XPS, SEM, TEM, FT-IR spectroscopy, and TGA. It was discovered that DFNS/IL/Ru(ii) has high catalytic activity for the synthesis of quinoline-2-one through the annulation of ortho-heteroaryl anilines and CO2. DFNS/IL/Ru (3) could be reutilized ten continuous times with no notable reduction in the catalytic activity. Notably, the coveted quinoline-2-one was prepared on a multi-gram scale by deploying DFNS/IL/Ru (3) as a green heterogeneous catalyst. Owing to the attendance of the zwitterionic liquid functional groups on the exterior layer of the bio-based DFNS/IL/Ru (3) catalyst, DFNS/IL/Ru (3) expressed the highest catalytic activity. This approach provides highly functional γ-amino acids in proper yields with great selective power. This paper announces the first nanocatalyst for this transformation, comprising the DFNS-supported Ru N-heterocyclic carbine complex.

Dendritic Macromolecular Architectures: Dendrimer-Based Polyion Complex Micelles

Polymeric micelles are nanoassemblies that are formed by spontaneous arrangement of amphiphilic block copolymers in aqueous solutions at critical micelle concentration (CMC). They represent an effective system for drug delivery of, for instance, poorly water-soluble anticancer drugs. Then, the development of polyion complexes (PICs) were emphasized. The morphology of these complexes depends on the topology of the polyelectrolytes used and the way they are assembled. For instance, ionic-hydrophilic block copolymers have been used for the preparation of PIC micelles. The main limitation in the use of PIC micelles is their potential instability during the self-assembly/disassembly processes, influenced by several parameters, such as polyelectrolyte concentration, deionization associated with pH, ionic strength due to salt medium effects, mixing ratio, and PIC particle cross-linking. To overcome these issues, the preparation of stable PIC micelles by increasing the rigidity of their dendritic architecture by the introduction of dendrimers and controlling their number within micelle scaffold was highlighted. In this original concise Review, we will describe the preparation, molecular characteristics, and pharmacological profile of these stable nanoassemblies.

Effects of pH on the Formation of PIC Micelles from PAMAM Dendrimers

Dendrimer-based PIC micelles are novel nanostructures from the assembly of dendrimers with polyion-neutral diblock copolymers. Because of the branched and three-dimensional structure of dendrimers, understanding the electrostatic assembly is challenging yet essential for manipulating the formation and property of the PIC micelles. Herein, we present the pH effects on the assembly of amine-terminated PAMAM dendrimers with PSS₉₂-b-PEO₁₁₃ diblock copolymers. The step-wise protonation of primary and tertiary amine groups of PAMAM allows us to manipulate the number of the positive charges by tuning pH. We find that the assembly based on the surface charges of PAMAM from G2 to G7 at pH 7 leads to well-defined micelles with high stability against salt. At pH 3, both the interior and surface charges contribute to the assembly, and the formed micelles are sensitive to ionic strength, namely, increasing salt concentration results in the formation of elongated (G2-G5) or bigger (G7) aggregates. Our study reveals the pH manipulation on the assembly of PAMAM dendrimers with linear polyelectrolytes and displays new findings that shall be helpful for understanding the assembly of asymmetric polyelectrolytes, as well as for designing new PIC micelles and functional soft nanocarriers.

Mitochondrial delivery of microRNA mimic let-7b to NSCLC cells by PAMAM-based nanoparticles

Many biological mechanisms including cellular metabolism and cell death are regulated by mitochondria known as powerhouse of the cell. Recently, let-7b, a tumour-suppressor microRNA has been detected in mitochondria of human cells targeting several mitochondrial-encoded respiratory chain genes. Triphenylphosphonium cation (TPP) is one of the major classes of mitochondriotropics that possess the ability of specifically targeting the mitochondria. PAMAM dendrimers are one of the most available agents in gene delivery due to their well-defined and beneficial features such as large density of surface functional groups. Hyaluronic acid (HA), a natural polysaccharide has been demonstrated to have the abilities such as good biocompatibility and targeting CD44 overexpressed receptors on non-small cell lung cancer (NSCLC) cells. In this research, let-7b-PAMAM (G5)-TPP and let-7b-PAMAM (G5)-TPP-HA nano-carriers were designed to deliver let-7b miRNA mimic to NSCLC cells' mitochondria as a novel way of cancer cells inhibition. Nano-carriers were capable of being successfully taken up by A549 cells and localised in mitochondria environment. Let-7b loaded nanoparticles reduced cell viability and induced apoptosis significantly. Expression of genes involved in mitochondrial oxidative function was decreased resulting in nanoparticles effect on mitochondria. Application of mitochondria targeted-miRNA delivery systems could regulate cellular functions to inhibit lung cancer.

The Role of Branch Cell Symmetry and Other Critical Nanoscale Design Parameters in the Determination of Dendrimer Encapsulation Properties

This article reviews progress over the past three decades related to the role of dendrimer-based, branch cell symmetry in the development of advanced drug delivery systems, aqueous based compatibilizers/solubilizers/excipients and nano-metal cluster catalysts. Historically, it begins with early unreported work by the Tomalia Group (i.e., The Dow Chemical Co.) revealing that all known dendrimer family types may be divided into two major symmetry categories; namely: Category I: symmetrical branch cell dendrimers (e.g., Tomalia, Vögtle, Newkome-type dendrimers) possessing interior hollowness/porosity and Category II: asymmetrical branch cell dendrimers (e.g., Denkewalter-type) possessing no interior void space. These two branch cell symmetry features were shown to be pivotal in directing internal packing modes; thereby, differentiating key dendrimer properties such as densities, refractive indices and interior porosities. Furthermore, this discovery provided an explanation for unimolecular micelle encapsulation (UME) behavior observed exclusively for Category I, but not for Category II. This account surveys early experiments confirming the inextricable influence of dendrimer branch cell symmetry on interior packing properties, first examples of Category (I) based UME behavior, nuclear magnetic resonance (NMR) protocols for systematic encapsulation characterization, application of these principles to the solubilization of active approved drugs, engineering dendrimer critical nanoscale design parameters (CNDPs) for optimized properties and concluding with high optimism for the anticipated role of dendrimer-based solubilization principles in emerging new life science, drug delivery and nanomedical applications.

Synthesis and Reactivity of Poly(propyleneimine) Dendrimers Functionalized with Cyclopentadienone N-Heterocyclic-Carbene Ruthenium(0) Complexes

Ligand design in metal chemistry is a fundamental step when pursuing compounds with specific reactivity. In this paper, the functionalization of the OH group in the lateral chain of the N-heterocyclic-carbene (NHC) ligand bound to a bis-carbonyl cyclopentadienone NHC ruthenium(0) complex allowed the decoration of five generations of poly(propyleneimine) (PPIs) dendrimers with up to 64 organometallic moieties. The coupling was achieved by employing carbonyldiimidazole and the formation of carbamate linkages between dendritic peripheral NH2 and lateral OH groups on ruthenium complexes. The synthetic procedure, chemical purification, and spectroscopic characterization of the five generations of dendrimers (3g1–5) are here described. The ruthenium-modified dendrimers were activated as catalysts in the transfer hydrogenation of the model compound 4-fluoroacetophenone in the presence of cerium ammonium nitrate as their mononuclear congeners. The catalytic activity, being similar for the five generations, shows a decrease if compared to mononuclear complexes. This detrimental effect might be ascribed to the –CH2NH– functionalization, largely present in dendrimer skeleton and that can compete with the hydrogen transfer mechanism, but also partially to a dendritic effect caused by steric encumbrance.

Structure-activity relationship of novel low-generation dendrimers for gene delivery

Structure-activity relationship (SAR) studies are very critical to design ideal gene vectors for gene delivery. However, It is difficult to obtain SAR information of low-generation dendrimers due to the lack of easy structural modification ways. Here, we synthesized a novel family of rigid aromatic backbone-based low-generation polyamidoamine (PAMAM) dendrimers. According to the number of primary amines, they were divided into two types: four-amine-containing PAMAM (DL1-DL5) and eight-amine-containing PAMAM (DL6-DL10). Due to the introduction of a rigid aromatic backbone, the low-generation PAMAM could be modified easier by different hydrophobic aliphatic chains. Several assays were used to study the interactions of the PAMAM dendrimers with plasmid DNA, and the results revealed that they not only had good DNA binding ability but also could efficiently condense DNA into spherical-shaped nanoparticles with suitable sizes and zeta potentials. The SAR studies indicated that the gene-transfection efficiency of the synthesized materials depended on not only the structure of their hydrophobic chains but also the number of primary amines. It was found that four-amine-containing PAMAM prepared from oleylamine (DL5) gave the best transfection efficiency, which was 3 times higher than that of lipofectamine 2000 in HEK293 cells. The cellular uptake mechanism mediated by DL5 was further investigated, and the results indicated that DL5/DNA complexes entered the cells mainly via caveolae and clathrin-mediated endocytosis. In addition, these low-generation PAMAMs modified with a single hydrophobic tail showed lower toxicity than lipofectamine 2000 in MC3T3-E1, MG63, HeLa, and HEK293 cells. These results reveal that such a type of low-generation polyamidoamines might be promising non-viral gene vectors, and also give us clues for the design of safe and high-efficiency gene vectors.

Photodegradable coumarin-derived amphiphilic dendrons for DNA binding: Self-assembly and phototriggered disassembly in water and air-water interface

In this article, we demonstrate the self-assembly and photoresponive behavior of a novel coumarin-based amphiphilic dendron in both aqueous solution and air-water interface. The dendritic structure, namely C-IG₁, was composed of a lipophilic cholesterol and hydrophilic poly(amido amine) (PAMAM) dendron, and the amphiphilic counterpart is interconnected by a photolabile coumarin carbonate ester, enabling the photoinduced degradation of the amphiphiles in protic solvents via S_N1-like mechanism. A Nile red solubilization fluorescence assay suggests a low critical aggregation concentration for the micelle formation of C-IG₁ in aqueous solutions (3.9 × 10^-5 M); the Langmuir analysis further indicates that C-IG₁ possesses significant compressibility in air-water interface, eventually forming homogeneous monolayers with a final molecular area (A₀) of 36 Ų. Notably, the micelles and Langmuir monolayer are quite stable until photo-triggered dissociation based on the photocleavage of C-IG₁ amphiphile activated by 365-nm incident light. Moreover, the transition in interfacial morphology of the Langmuir monolayer during the assembly and photodegradation processes also can be visually analyzed by incorporating Nile red probes with in situ monitoring through fluorescence microscopy. The thin film deposited on a glass substrate by the Langmuir-Blodgett technique also shows a photoresponsive behavior based on the change in the contact angles of a water droplet on the surface upon light stimulation. The binding affinity of C-IG₁ and cyclic DNA determined by the fluorescence quenching analysis of the coumarin reporter suggests a ground-state macromolecular complexation process occurring through polyvalent interactions between the pseudodendrimers and biomacromolecules. The ethidium bromide displacement assay further indicates thus dendriplex formation at low nitrogen-to-phosphorous value (N/P < 1) and confirms that the decomplexation accompanied by DNA release can be achieved through an active phototriggered route under spatiotemporal control.

Topological Aspects of the Design of Nanocarriers for Therapeutic Peptides and Proteins

Supramolecular chemistry holds great potential for the design of versatile and safe carriers for therapeutic proteins and peptides. Nanocarriers can be designed to meet specific criteria for given application (exact drug, administration route, target tissue, etc.). However, alterations in the topology of formulation components can drastically change their activity. This is why the supramolecular topology of therapeutic nanoconstructions has to be considered. Herein, we discuss several topological groups used for the design of nanoformulations for peptide and protein delivery: modification of polypeptide chains by host-guest interactions; packaging of proteins and peptides into liposomes; complexation and conjugation with dendrimers. Each topological type has its own advantages and disadvantages, so careful design of nanoformulations is needed. Ideally, each case where nanomedicine is needed requires a therapeutic construction specially created for that taking into account features of the administration route, target tissue, or organ, properties of a drug, its bioavailability, etc. The wide number of studies in the field of protein delivery by supramolecular and nanocarriers for proteins and peptides evidence their increasing potential for different aspects of the innovative medicine. Although significant progress has been achieved in the field, there are several remaining challenges to be overcome in future.

Hydrogels composed of hyaluronic acid and dendritic ELPs: hierarchical structure and physical properties

Hydrogels that mimic the native extracellular matrix were prepared from hyaluronic acid (HA) and amine-terminated dendritic elastin-like peptides (denELPs) of generations 1, 2, and 3 (G1, 2, and 3) as crosslinking units. The physical properties of the hydrogels were investigated by rheology, scanning electron microscopy, swelling tests, small-angle X-ray scattering (SAXS), and model drug loading and release assays. Hydrogel properties depended on the generation number of the denELP, which contained structural segments based on the repeating GLPGL pentamer. Hydrogels with higher generation denELPs (G2 and 3) showed similar properties, but those prepared from G1 denELPs were rheologically weaker, had a larger mesh size, absorbed less model drug, and released the drug more quickly. Interestingly, most of the HA_denELP hydrogels studied here remained transparent upon gelation, but after lyophilization and addition of water retained opaque, "solid-like" regions for up to 4 d during rehydration. This rehydration process was carefully evaluated through time-course SAXS studies, and the phenomenon was attributed to the formation of pre-coacervates in the gel-forming step, which slowly swelled in water during rehydration. These findings provide important insights into the behavior of ELP-based hydrogels, in which physical crosslinking of the ELP domains can be controlled to tune mechanical properties, highlighting the potential of HA_denELP hydrogels as biomaterials.

l-Serine-modified polyamidoamine dendrimer as a highly potent renal targeting drug carrier

Effective delivery of drug carriers selectively to the kidney is challenging because of their uptake by the reticuloendothelial system in the liver and spleen, which limits effective treatment of kidney diseases and results in side effects. To address this issue, we synthesized l-serine (Ser)-modified polyamidoamine dendrimer (PAMAM) as a potent renal targeting drug carrier. Approximately 82% of the dose was accumulated in the kidney at 3 h after i.v. injection of ¹¹¹In-labeled Ser-PAMAM in mice, while i.v. injection of ¹¹¹In-labeled unmodified PAMAM, l-threonine modified PAMAM, and l-tyrosine modified PAMAM resulted in kidney accumulations of 28%, 35%, and 31%, respectively. Single-photon emission computed tomography/computed tomography (SPECT/CT) images also indicated that ¹¹¹In-labeled Ser-PAMAM specifically accumulated in the kidneys. An intrakidney distribution study showed that fluorescein isothiocyanate-labeled Ser-PAMAM accumulated predominantly in renal proximal tubules. Results of a cellular uptake study of Ser-PAMAM in LLC-PK1 cells in the presence of inhibitors [genistein, 5-(N-ethyl-N-isopropyl)amiloride, and lysozyme] revealed that caveolae-mediated endocytosis, micropinocytosis, and megalin were associated with the renal accumulation of Ser-PAMAM. The efficient renal distribution and angiotensin-converting enzyme (ACE) inhibition effect of captopril (CAP), an ACE inhibitor, was observed after i.v. injection of the Ser-PAMAM-CAP conjugate. These findings indicate that Ser-PAMAM is a promising renal targeting drug carrier for the treatment of kidney diseases. Thus, the results of this study demonstrate efficient renal targeting of a drug carrier via Ser modification.

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.

Negative dendritic effect on enzymatic hydrolysis of dendrimer conjugates

The “negative dendritic effect” observed during enzymatic hydrolysis of dendrimer conjugates can be positively exploited for tailored, generation-dependent drug release.

Engineering dendrimers to produce dendrimer dipole excitation based terahertz radiation sources suitable for spectrometry, molecular and biomedical imaging

Two critical nanoscale design parameters (CNDPs); namely, surface chemistry and interior compositions of poly(amidoamine) (PAMAM) dendrimers were systematically engineered to produce unique hyperpolarizable, electro-optical substrates. These electro-optically active dendritic films were demonstrated to produce high quality, continuous wave terahertz radiation when exposed to a suitable pump laser that could be used for spectrometry and molecular imaging. These dendrimer based dipole excitation (DDE) terahertz sources were used to construct a working spectrometer suitable for many practical applications including THz imaging and analysis of encapsulated hydrogen species in fullerenes.

Polymer-Nucleic Acid Interactions

Gene therapy is an important therapeutic strategy in the treatment of a wide range of genetic disorders. Polymers forming stable complexes with nucleic acids (NAs) are non-viral gene carriers. The self-assembly of polymers and nucleic acids is typically a complex process that involves many types of interaction at different scales. Electrostatic interaction, hydrophobic interaction, and hydrogen bonds are three important and prevalent interactions in the polymer/nucleic acid system. Electrostatic interactions and hydrogen bonds are the main driving forces for the condensation of nucleic acids, while hydrophobic interactions play a significant role in the cellular uptake and endosomal escape of polymer-nucleic acid complexes. To design high-efficiency polymer candidates for the DNA and siRNA delivery, it is necessary to have a detailed understanding of the interactions between them in solution. In this chapter, we survey the roles of the three important interactions between polymers and nucleic acids during the formation of polyplexes and summarize recent understandings of the linear polyelectrolyte-NA interactions and dendrimer-NA interactions. We also review recent progress optimizing the gene delivery system by tuning these interactions.

Facile synthesis of stable, water soluble, dendron-coated gold nanoparticles

Upon reduction with sodium borohydride, diazonium tetrachloroaurate salts of triazine dendrons yield dendron-coated gold nanoparticles connected by a gold-carbon bond. These robust nanoparticles are stable in water and toluene solutions for longer than one year and present surface groups that can be reacted to change surface chemistry and manipulate solubility. Molecular modeling was used to provide insight on the hydration of the nanoparticles and their observed solubilties.

Stimuli-responsive dendrimers in drug delivery

Dendrimers have shown great promise as carriers in drug delivery due to their unique structures and superior properties. However, the precise control of payload release from a dendrimer matrix still presents a great challenge. Stimuli-responsive dendrimers that release payloads in response to a specific trigger could offer distinct clinical advantages over those dendrimers that release payloads passively. These smart polymers are designed to specifically release their payloads at targeted regions or at constant release profiles for specific therapies. They represent an attractive alternative to targeted dendrimers and enable dendrimer-based therapeutics to be more effective, more convenient, and much safer. The wide range of stimuli, either endogenous (acid, enzyme, and redox potentials) or exogenous (light, ultrasound, and temperature change), allows great flexibility in the design of stimuli-responsive dendrimers. In this review article, we will highlight recent advances and opportunities in the development of stimuli-responsive dendrimers for the treatment of various diseases, with emphasis on cancer. Specifically, the applications of stimuli-responsive dendrimers in drug delivery as well as their mechanisms are intensively reviewed.

Dendrimer-protein interactions versus dendrimer-based nanomedicine

Dendrimers are hyperbranched polymers belonging to the huge class of nanomedical devices. Their wide application in biology and medicine requires understanding of the fundamental mechanisms of their interactions with biological systems. Summarizing, electrostatic force plays the predominant role in dendrimer-protein interactions, especially with charged dendrimers. Other kinds of interactions have been proven, such as H-bonding, van der Waals forces, and even hydrophobic interactions. These interactions depend on the characteristics of both participants: flexibility and surface charge of a dendrimer, rigidity of protein structure and the localization of charged amino acids at its surface. pH and ionic strength of solutions can significantly modulate interactions. Ligands and cofactors attached to a protein can also change dendrimer-protein interactions. Binding of dendrimers to a protein can change its secondary structure, conformation, intramolecular mobility and functional activity. However, this strongly depends on rigidity versus flexibility of a protein's structure. In addition, the potential applications of dendrimers to nanomedicine are reviwed related to dendrimer-protein interactions.

Synthetic methodologies and spatial organization of metal chelate dendrimers and star and hyperbranched polymers

The synthetic methodologies, physico-chemical peculiarities, properties, and structure of metal chelate dendrimers and star and hyperbranched polymers are considered.

Low generation PAMAM-based nanomicelles as ROS-responsive gene vectors with enhanced transfection efficacy and reduced cytotoxicity in vitro

ROS-responsive cationic nanomicelles formed from amphiphilic PPS–SS–PAMAM_G2.0 conjugates exhibit high transfection efficacy and low cytotoxicity.

Exploring the Structural Properties of Positively Charged Peptide Dendrimers

We report a combined experimental and computational approach to study the structural behavior of positively charged peptide dendrimers. Third-generation dendrimers containing combinations of positive/neutral amino acid residues in the different dendrimer generations were synthesized and their overall size evaluated using diffusion NMR. Molecular dynamics simulations were performed to obtain a comprehensive description of the molecular-level phenomena substantiating the structural differences observed. Comparison of the results presented with previous findings reveals a striking charge-dependent tendency in these systems, where the simple number and placement of charged amino acids in the sequence allows an extensive control over the exhibited structural features. Indeed, we observe that peptide dendrimers bearing progressively higher amounts of charged residues are characterized by an increasing structural plasticity, with a myriad of conformational states equally accessible to them. On the other hand, dendrimers containing only small amounts of charged residues evidence, to some extent, a characteristic structural rigidity.

Exploring the Loading Capacity of Generation Six to Eight Dendronized Polymers in Aqueous Solution

Aspects of size, structural (im)perfection, inner density, and guest molecule loading capacity of dendronized polymers (DPs) of high generation (6≤g≤8) in aqueous solution are studied using electron paramagnetic resonance spectroscopy on amphiphilic, spin-labeled guest molecules. The results show that the interior of the charged DPs is strongly polar, especially in comparison to their lower generation (1-4) analogues. This is a direct sign that large amounts of water penetrate the DP surface, reflecting the structural (im)perfections of these high-generation DPs and much lower segmental densities than theoretically achievable. Images obtained with atomic force microscopy reveal that the high-generation DPs do not aggregate and give further insights into the structural imperfections. Electron paramagnetic resonance spectroscopic data further show that despite their structural imperfections, these DPs can bind and release large numbers of amphiphilic molecules. It is concluded that attention should be paid to their synthesis, for which a protocol needs to be developed that avoids the relatively large amount of defects generated in the direct conversion of a generation g=4 DP to a generation g=6 DP, which had to be used here.

Special Issue: "Functional Dendrimers"

This special issue entitled “Functional Dendrimers” focuses on the manipulation of at least six “critical nanoscale design parameters” (CNDPs) of dendrimers including: size, shape, surface chemistry, flexibility/rigidity, architecture and elemental composition. These CNDPs collectively define properties of all “functional dendrimers”. This special issue contains many interesting examples describing the manipulation of certain dendrimer CNDPs to create new emerging properties and, in some cases, predictive nanoperiodic property patterns (i.e., dendritic effects). The systematic engineering of CNDPs provides a valuable strategy for optimizing functional dendrimer properties for use in specific applications.

Solvatochromism of dye-labeled dendronized polymers of generation numbers 1-4: comparison to dendrimers

Two series of dendronized polymers (DPs) of generations g = 1-4 with different levels of dendritic substitution (low and high) and a solvatochromic probe at g = 1 level are used to study their swelling behavior in a collection of solvents largely differing in polarity as indicated by the Kamlet-Taft parameters. This is done by measuring the UV-Vis spectra of all samples in all solvents and determining the longest wavelength absorptions (λmax). The λmax values fall into a range defined by the extreme situations, when the solvatochromic probe is either fully surrounded by solvent or completely shielded against it. The former situation is achieved in a model compound and the latter situation is believed to be reached when in a poor solvent the dendritic shell around the backbone is fully collapsed. We observe that solvent penetration into the interior of the DPs decreases with increasing g and does so faster for the more highly dendritically substituted series than for the less highly substituted one. Interestingly, the swelling of the more highly substituted DP series already at the g = 4 level has decreased to approximately 20% of that at the g = 1 level which supports an earlier proposal that high g DPs can be viewed as nano-sized molecular objects. Furthermore, when comparing these two DP series with a g = 1-6 series of dendrimers investigated by Fréchet et al. it becomes evident that even the less substituted series of DPs is much less responsive to solvent changes as assessed by the solvatochromic probe than the dendrimers, suggesting the branches around the (polymeric) core in DPs to be more densely packed compared to those in dendrimers, thus, establishing a key difference between these two dendritic macromolecules.

Nanoparticle Effects on Human Platelets in Vitro: A Comparison between PAMAM and Triazine Dendrimers

Triazine and PAMAM dendrimers of similar size and number of cationic surface groups were compared for their ability to promote platelet aggregation. Triazine dendrimers (G3, G5 and G7) varied in molecular weight from 8 kDa-130 kDa and in surface groups 16-256. PAMAM dendrimers selected for comparison included G3 (7 kDa, 32 surface groups) and G6 (58 kDa, 256 surface groups). The treatment of human platelet-rich plasma (PRP) with low generation triazine dendrimers (0.01-1 µM) did not show any significant effect in human platelet aggregation in vitro; however, the treatment of PRP with larger generations promotes an effective aggregation. These results are in agreement with studies performed with PAMAM dendrimers, where large generations promote aggregation. Triazine dendrimers promote aggregation less aggressively than PAMAM dendrimers, a factor attributed to differences in cationic charge or the formation of supramolecular assemblies of dendrimers.

Bioactive cell-like hybrids coassembled from (glyco)dendrimersomes with bacterial membranes

A library of amphiphilic Janus dendrimers including two that are fluorescent and one glycodendrimer presenting lactose were used to construct giant dendrimersomes and glycodendrimersomes. Coassembly with the components of bacterial membrane vesicles by a dehydration-rehydration process generated giant cell-like hybrid vesicles, whereas the injection of their ethanol solution into PBS produced monodisperse nanometer size assemblies. These hybrid vesicles contain transmembrane proteins including a small membrane protein, MgrB, tagged with a red fluorescent protein, lipopolysaccharides, and glycoproteins from the bacterium Escherichia coli. Incorporation of two colored fluorescent probes in each of the components allowed fluorescence microscopy to visualize and demonstrate coassembly and the incorporation of functional membrane channels. Importantly, the hybrid vesicles bind a human galectin, consistent with the display of sugar moieties from lipopolysaccharides or possibly glycosylated membrane proteins. The present coassembly method is likely to create cell-like hybrids from any biological membrane including human cells and thus may enable practical application in nanomedicine.