Dendrimers in Medicine: Therapeutic Concepts and Pharmaceutical Challenges

Dendrimers in combination with natural products and analogues as anti-cancer agents

For the first time, an overview of dendrimers in combination with natural products and analogues as anti-cancer agents is presented. This reflects the development of drug delivery systems, such as dendrimers, to tackle cancers. The most significant advantages of using dendrimers in nanomedicine are their high biocompatibility, good water solubility, and their entry - with or without encapsulated, complexed or conjugated drugs - through an endocytosis process. This strategy has accelerated over the years in order to develop nanosystems as nanocarriers, to decrease the intrinsic toxicity of anti-cancer agents, to decrease the drug side effects, to increase the efficacy of the treatment, and consequently to improve patient compliance.

Ionic liquid syntheses via click chemistry: expeditious routes toward versatile functional materials

The application of click reaction (e.g. CuAAC, thiol–X, oxime formation and nucleophilic ring opening) has recently begun to draw attention for efficient and robust synthesis of new functional ionic liquids, requiring minimal purification.

New bow-tie cationic carbosilane dendritic system with a curcumin core as an anti-breast cancer agent

A water soluble “bow-tie” cationic carbosilane dendrimer with curcumin in the core displays antioxidant and antitumoral activities against breast cancer cells.

Dendrimers in combination with natural products and analogues as anti-cancer agents

Overview of the use of dendrimers in combination with encapsulated and conjugated natural products and analogues as anti-cancer agents.

Dendrimers in combination with natural products and analogues as anti-cancer agents

Overview of the use of dendrimers in combination with encapsulated and conjugated natural products and analogues as anti-cancer agents.

Enzyme-sensitive cytotoxic peptide–dendrimer conjugates enhance cell apoptosis and deep tumor penetration

Cytotoxic peptide conjugated PAMAM dendrimers with MMP2-sensitive PEG for efficient tumor penetration, cellular internalization and mitochondria disruption.

Prevention of Synaptic Alterations and Neurotoxic Effects of PAMAM Dendrimers by Surface Functionalization

One of the most studied nanocarriers for drug delivery are polyamidoamine (PAMAM) dendrimers. However, the alterations produced by PAMAM dendrimers in neuronal function have not been thoroughly investigated, and important aspects such as effects on synaptic transmission remain unexplored. We focused on the neuronal activity disruption induced by dendrimers and the possibility to prevent these effects by surface chemical modifications. Therefore, we studied the effects of fourth generation PAMAM with unmodified positively charged surface (G4) in hippocampal neurons, and compared the results with dendrimers functionalized in 25% of their surface groups with folate (PFO₂₅) and polyethylene glycol (PPEG₂₅). G4 dendrimers significantly reduced cell viability at 1 µM, which was attenuated by both chemical modifications, PPEG₂₅ being the less cytotoxic. Patch clamp recordings demonstrated that G4 induced a 7.5-fold increment in capacitive currents as a measure of membrane permeability. Moreover, treatment with this dendrimer increased intracellular Ca²⁺ by 8-fold with a complete disruption of transients pattern, having as consequence that G4 treatment increased the synaptic vesicle release and frequency of synaptic events by 2.4- and 3-fold, respectively. PFO₂₅ and PPEG₂₅ treatments did not alter membrane permeability, total Ca²⁺ intake, synaptic vesicle release or synaptic activity frequency. These results demonstrate that cationic G4 dendrimers have neurotoxic effects and induce alterations in normal synaptic activity, which are generated by the augmentation of membrane permeability and a subsequent intracellular Ca²⁺ increase. Interestingly, these toxic effects and synaptic alterations are prevented by the modification of 25% of PAMAM surface with either folate or polyethylene glycol.

Improved large-scale synthesis and characterization of small and medium generation PAMAM dendrimers

Dendrimers are promising polymers for biomedical applications; however, most dendrimer formulations have failed to move from laboratory science to upscaled products for preclinical testing or GMP production. This publications reports on an improved large-scale PAMAM dendrimer synthesis that is suitable to manufacture large amounts of highly pure and monodisperse dendrimers of generations G0–G5. Furthermore, an extended analytical guideline how to characterize PAMAM dendrimers with NMR, HPLC, SEC-MALS, ESI, MALDI, UV–vis, fluorescence, and IR spectroscopy is provided.

Convergent dendrimer synthesis by olefin metathesis and studies toward glycoconjugation

The synthesis of novel hyperbranched monodisperse linear dendrimers, based on 2,2-bis-(hydroxymethyl)-propionic acid (bis-MPA), has been achieved by convergent metathesis-mediated coupling between the alkene-terminated focal point of bis-MPA dendrons. On their surface, dendrimers present 4, 8 and 16 functional groups. Glycodendrimers exposing multiple saccharide moieties have also been obtained. To the best of our knowledge, this is the first example of the use of metathesis for focal point coupling.

Exploring the in vivo toxicity of nanoparticles

Toxicological tests of a xenobiotic play a key role to determine the safety of the new compound before it reaches the market. In this review article, we describe the main types of toxicological studies that can be performed in vivo to detect a possible undesired effect of a xenobiotic with especial emphasis on the data available for the different types of nanoparticles. The different procedures described in this review allow to obtain valuable information about the possible toxic effects of a xenobiotic to minimize the possible risks for patients once the compound has been approved for therapeutic use.

Modified PAMAM dendrimer with 4-carbomethoxypyrrolidone surface groups-its uptake, efflux, and location in a cell

Traditional amine terminated PAMAM dendrimers may be readily surface engineered by a facile one-pot conversion with dialkyl itaconate esters into 4-carbomethoxypyrrolidone terminated PAMAM (G=0-4) dendrimers. These terminated dendrimers are uniquely characterized by exhibiting blue fluorescence emissions (λ_exc=370nm, λ_maxem=440nm). Thanks to this property they can be directly analyzed by confocal microscopy and flow cytometry without additional fluorescence labeling, treatment of dendrimers with chemicals or adjusting pH. These intrinsically fluorescent dendrimers were shown to be very effective for assessing important biological cell features such as cellular entry, intracellular trafficking/localization and efflux properties. For example, all tested cell lines (e.g., B14, BRL-3A, and mHippoE-18) rapidly accumulated PAMAM-pyrrolidone dendrimer. The BRL-3A cell line exhibited both cytoplasmic and nuclear localization patterns; whereas in B14 cells and mHippoE-18 cells, the blue dendrimer fluorescence could only be detected in intracellular endosome-like structures. The dendrimer was observed to be released from all three cell lines during the first 24h; however, efflux was substantially slower from the B-14 cell line. The highest efflux rate was observed for the mHippoE-18 cells. This first successful biological experiment opens a broad spectrum of using these dendrimers as new bioimaging agents for extensive biological cell characterizations.

Nanoparticle cellular uptake by dendritic wedge peptides: achieving single peptide facilitated delivery

Significant efforts are being undertaken to optimize the cargo carrying capacity and especially the cellular delivery efficiency of functionalized nanoparticles for applications in biological research and pharmacological delivery. One approach to increasing nanoparticle surface cargo display capacity is to decrease the number of moieties required for mediating cellular delivery by improving their efficiency. We describe a series of multivalent cell penetrating peptide (CPP) dendrimers that facilitate rapid cellular delivery of prototypical nanoparticle-semiconductor quantum dots (QDs). The modular CPP dendrimers were assembled through an innovative convergent oxime ligation strategy between (Arg₉)_n motifs and a dendritic QD-coordination scaffold. Dendrimeric peptides sequentially incorporate a terminal (His)₆ motif for metal-affinity QD coordination, a Pro₉ spacer, a branching poly-lysine scaffold, and wedged display of (Arg₉)_n binding motifs with n = 1×, 2×, 4×, 8×, 16× multivalency. QD dendrimer display capacity was estimated using structural simulations and QD-(Arg₉)_1-16 conjugates characterized by dynamic light scattering along with surface plasmon resonance-based binding assays to heparan sulfate proteoglycan surfaces. Cellular uptake via endocytosis was confirmed and peptide delivery kinetics investigated as a function of QD-(Arg₉)_1-16 conjugate exposure time and QD assembly ratio where cellular viability assays reflected no overt cytotoxicity. The ability of single dendrimer conjugates to facilitate cellular uptake was confirmed for QD-(Arg₉)_2-16 repeats along with the ability to deliver >850 kDa of protein cargo per QD. Minimizing the number of CPPs required for cellular uptake is critical for expanding nanoparticle cargo carrying capacity and can allow for inclusion of additional sensors, therapeutics and contrast agents on their surface.

Diastereoselective Synthesis of Symmetrical and Unsymmetrical Tetrahydropyridines Catalyzed by Bi(III) Immobilized on Triazine Dendrimer Stabilized Magnetic Nanoparticles

Unsymmetrical 1,2,5,6-tetrahydropyridine-3-carboxylates were obtained for the first time from a five-component Fe₃O₄@TDSN-Bi(III)-catalyzed reaction of aryl aldehydes, aryl amines, and ethyl acetoacetate. This magnetically separable catalyst enabled the selective incorporation of two different aryl amines or two different aryl aldehydes into the product, and provided excellent yields, short reaction times, mild reaction conditions, satisfactory catalyst recyclability, and low catalyst loading.

Biodegradable Poly(Amino Ester) with Aromatic Backbone as Efficient Nonviral Gene Delivery Vectors

The development of gene delivery vectors with high efficiency and biocompatibility is one of the critical points of gene therapy. Two biodegradable poly(amino ester)s were synthesized via ring-opening polymerization between low molecular weight (LMW) PEI and diepoxide. The molecular weights of poly(amino ester)s were measured by GPC. Agarose gel retardation assays showed that these materials have good DNA-binding ability and can retard the electrophoretic mobility of plasmid DNA (pDNA) at a weight ratio of 1. The formed polyplexes have proper sizes of around 200 nm and zeta-potential values of about 30-40 mV for cellular uptake. In vitro experiments revealed that polymer P2 gave higher transfection efficiency than PEI 25KDa and Lipofectamine 2000 with less toxicity, especially in 293 cells. Results demonstrate that such a type of degradable poly(amino ester) may serve as a promising non-viral gene vector.

Polyplex Evolution: Understanding Biology, Optimizing Performance

Polyethylenimine (PEI) is a gold standard polycationic transfectant. However, the highly efficient transfecting activity of PEI and many of its derivatives is accompanied by serious cytotoxic complications and safety concerns at innate immune levels, which impedes the development of therapeutic polycationic nucleic acid carriers in general and their clinical applications. In recent years, the dilemma between transfection efficacy and adverse PEI activities has been addressed from in-depth investigations of cellular processes during transfection and elucidation of molecular mechanisms of PEI-mediated toxicity and translation of these integrated events to chemical engineering of novel PEI derivatives with an improved benefit-to-risk ratio. This review addresses these perspectives and discusses molecular events pertaining to dynamic and multifaceted PEI-mediated cytotoxicity, including membrane destabilization, mitochondrial dysfunction, and perturbations of glycolytic flux and redox homeostasis as well as chemical strategies for the generation of better tolerated polycations. We further examine the effect of PEI and its derivatives on complement activation and interaction with Toll-like receptors. These perspectives are intended to lay the foundation for an improved understanding of interlinked mechanisms controlling transfection and toxicity and their translation for improved engineering of polycation-based transfectants.

Charge-reversible and pH-responsive biodegradable micelles and vesicles from linear-dendritic supramolecular amphiphiles for anticancer drug delivery

The linear-dendritic supramolecular amphiphiles could assemble into charge-reversible and pH-responsive biodegradable micelles and vesicles.

Complexes between cationic pyridylphenylene dendrimers and ovine prion protein: do hydrophobic interactions matter?

MD simulation predicted the possible binding sites for the dendrimer interactions with protein while ITC data revealed both electrostatic and hydrophobic driving forces for the complexation.

Impact of Dendrimer Terminal Group Chemistry on Blockage of the Anthrax Toxin Channel: A Single Molecule Study

Nearly all the cationic molecules tested so far have been shown to reversibly block K⁺ current through the cation-selective PA₆₃ channels of anthrax toxin in a wide nM-mM range of effective concentrations. A significant increase in channel-blocking activity of the cationic compounds was achieved when multiple copies of positively charged ligands were covalently linked to multivalent scaffolds, such as cyclodextrins and dendrimers. Even though multivalent binding can be strong when the individual bonds are relatively weak, for drug discovery purposes we often strive to design multivalent compounds with high individual functional group affinity toward the respective binding site on a multivalent target. Keeping this requirement in mind, here we perform a single-channel/single-molecule study to investigate kinetic parameters of anthrax toxin PA₆₃ channel blockage by second-generation (G2) poly(amido amine) (PAMAM) dendrimers functionalized with different surface ligands, including G2-NH₂, G2-OH, G2-succinamate, and G2-COONa. We found that the previously reported difference in IC₅₀ values of the G2-OH/PA₆₃ and G2-NH₂/PA₆₃ binding was determined by both on- and off-rates of the reversible dendrimer/channel binding reaction. In 1 M KCl, we observed a decrease of about three folds in k o n and a decrease of only about ten times in t r e s with G2-OH compared to G2-NH₂. At the same time for both blockers, k o n and t r e s increased dramatically with transmembrane voltage increase. PAMAM dendrimers functionalized with negatively charged succinamate, but not carboxyl surface groups, still had some residual activity in inhibiting the anthrax toxin channels. At 100 mV, the on-rate of the G2-succinamate binding was comparable with that of G2-OH but showed weaker voltage dependence when compared to G2-OH and G2-NH₂. The residence time of G2-succinamate in the channel exhibited opposite voltage dependence compared to G2-OH and G2-NH₂, increasing with the cis-negative voltage increase. We also describe kinetics of the PA₆₃ ion current modulation by two different types of the "imperfect" PAMAM dendrimers, the mixed-surface G2 75% OH 25% NH₂ dendrimer and G3-NH₂ dendron. At low voltages, both "imperfect" dendrimers show similar rate constants but significantly weaker voltage sensitivity when compared with the intact G2-NH₂ PAMAM dendrimer.

Effect of anionic and cationic polyamidoamine (PAMAM) dendrimers on a model lipid membrane

In spite of the growing variety of biological applications of dendrimer-based nanocarriers, a major problem of their potential applications in bio-medicine is related to the disruption of lipid bilayers and the cytotoxicity caused by the aggregation processes involved onto cellular membranes. With the aim to study model dendrimer-biomembrane interaction, the self-assembly processes of a mixture of charged polyamidoamine (PAMAM) dendrimers and dipalmitoylphosphatidylcholine (DPPC) lipids were investigated by means of Zeta potential analysis, Raman and x-ray scattering. Zwitterionic DPPC liposomes showed substantially different behaviors during their interaction with negatively charged (generation G=2.5) sodium carboxylate terminated (COO^- Na⁺) dendrimers or positively charged (generation G=3.0) amino terminated (-NH₂) dendrimers. More specifically the obtained results evidence the sensitive interactions between dendrimer terminals and lipid molecules at the surface of the liposome, with an enhancement of the liposome surface zeta potential, as well as in the hydrophobic region of the bilayers, where dendrimer penetration produce a perturbation of the hydrophobic alkyl chains of the bilayers. Analysis of the SAXS structure factor with a suitable model for the inter-dendrimers electrostatic potential allows an estimation of an effective charge of 15 ǀeǀ for G=2.5 and 7.6 ǀeǀ for G=3.0 PAMAM dendrimers. Only a fraction (about 1/7) of this charge contributes to the linear increase of liposome zeta-potential with increasing PAMAM/DPPC molar fraction. The findings of our investigation may be applied to rationalize the effect of the nanoparticles electrostatic interaction in solution environments for the design of new drug carriers combining dendrimeric and liposomal technology.

Fungal diseases: could nanostructured drug delivery systems be a novel paradigm for therapy?

Invasive mycoses are a major problem for immunocompromised individuals and patients in intensive care units. Morbidity and mortality rates of these infections are high because of late diagnosis and delayed treatment. Moreover, the number of available antifungal agents is low, and there are problems with toxicity and resistance. Alternatives for treating invasive fungal infections are necessary. Nanostructured systems could be excellent carriers for antifungal drugs, reducing toxicity and targeting their action. The use of nanostructured systems for antifungal therapy began in the 1990s, with the appearance of lipid formulations of amphotericin B. This review encompasses different antifungal drug delivery systems, such as liposomes, carriers based on solid lipids and nanostructure lipids, polymeric nanoparticles, dendrimers, and others. All these delivery systems have advantages and disadvantages. Main advantages are the improvement in the antifungal properties, such as bioavailability, reduction in toxicity, and target tissue, which facilitates innovative therapeutic techniques. Conversely, a major disadvantage is the high cost of production. In the near future, the use of nanosystems for drug delivery strategies can be used for delivering peptides, including mucoadhesive systems for the treatment of oral and vaginal candidiasis.

Dendrimers as a promising tool in ocular therapeutics: Latest advances and perspectives

Dendrimers have called the attention of scientists in the area of drug and gene delivery over the last two decades for their versatility, complexity and multibranching properties. Some strategies for optimizing drug pharmacokinetics and site-specific targeting using dendrimers have been proposed. Among them, those related to treating and managing ocular diseases are of special interest. Ocular therapies suffer from significant disadvantages, including frequent administration, poor penetration and/or rapid elimination. This review provides an overview of the recent and promising progress in the dendrimers field, focusing on both the anterior and posterior segments of the eye ocular targets, the use of dendrimers as a strategy for overcoming obstacles to the traditional treatment of ocular diseases and an outlook on future directions. Finally, a first approach to ocular safety with dendrimers is intended that accounts for the state-of-the-art science to date.

Recent insights into nanotechnology development for detection and treatment of colorectal cancer

The global incidence of colorectal cancer (CRC) is 1.3 million cases. It is the third most frequent cancer in males and females. Most CRCs are adenocarcinomas and often begin as a polyp on the inner wall of the rectum or colon. Some of these polyps become malignant, eventually. Detecting and removing these polyps in time can prevent CRC. Therefore, early diagnosis of CRC is advantageous for preventive and instant action interventions to decrease the mortality rates. Nanotechnology has been enhancing different methods for the detection and treatment of CRCs, and the research has provided hope within the scientific community for the development of new therapeutic strategies. This review presents the recent development of nanotechnology for the detection and treatment of CRC.

Carbon nanodots as molecular scaffolds for development of antimicrobial agents

We report the potential of carbon nanodots (CNDs) as a molecular scaffold for enhancing the antimicrobial activities of small dendritic poly(amidoamines) (PAMAM). Carbon nanodots prepared from sago starch are readily functionalized with PAMAM by using N-ethyl-N'-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). Electron microscopy images of these polyaminated CNDs show that they are approximately 30-60nm in diameter. Infrared and fluorescence spectroscopy analyses of the water-soluble material established the presence of the polyamidoaminated moiety and the intrinsic fluorescence of the nanodots. The polyaminated nanodots (CND-PAM1 and CND-PAM2) exhibit in vitro antimicrobial properties, not only to non-multidrug resistant bacteria but also to the corresponding Gram-negative multidrug bacteria. Their minimum inhibitory concentration (MIC) ranges from 8 to 64μg/mL, which is much lower than that of PAMAM G1 or the non-active PAMAM G0 and CNDs. Additionally, they show synergistic effect in combination with tetracycline or colistin. These preliminary results imply that CNDs can serve as a promising scaffold for facilitating the rational design of antimicrobial materials for combating the ever-increasing threat of antibiotic resistance. Moreover, their fluorescence could be pertinent to unraveling their mode of action for imaging or diagnostic applications.

Multifunctional TK-VLPs nanocarrier for tumor-targeted delivery

Virus-like particles (VLPs) have been exploited for various biomedical applications, such as the monitoring, prevention, diagnosis and therapy of disease. In this study, a novel multifunctional VLPs nanocarrier (TK-VLPs) was prepared and used for tumor-targeted delivery. The SPR and cell uptake results indicated that the TK peptide is a "bi-functional ligand" with high affinity for Caco-2, HRT-18 and HUVEC cells through the integrin α6β1 and integrin αvβ3 receptors. The results of the direct immunofluorescence, SDS-PAGE and western blot assays demonstrated that the TK-VLPs were successfully prepared using the baculovirus expression system. Confocal laser scanning microscopy and the flow cytometry analysis validated that the TK-VLPs could target to Caco-2, HRT-18 and HUVEC cells. An in vivo study further confirmed that the TK-VLPs could target and efficiently deliver fluorescein to tumor cells and the tumor vasculature in mice bearing subcutaneous tumors. TK-VLPs-DOX displayed a uniform, spherical shape and an average size of approximately 28nm. The results of the cell uptake and cytotoxicity assays indicated that TK-VLPs-DOX could enhance the selectivity for colorectal cancer cells. Together, our studies provide strong evidence that TK-VLPs could target colon tumor cells and tumor angiogenesis with enhanced permeability and retention effects, suggesting that the TK-VLPs are a multifunctional nanocarrier with potential applications in a colon tumor-targeted drug delivery system.

Synthesis, photophysical, electrochemical, and DSSC application of novel donor–acceptor triazole bridged dendrimers with a triphenylamine core and benzoheterazole as a surface unit

Triazole bridged novel donor–acceptor dendrimers were synthesized via click chemistry. Lower generation dendrimers when used as additives exhibit better current-generating capacity and power conversion efficiency in DSSCs.

Facile and Efficient Synthesis of Carbosiloxane Dendrimers via Orthogonal Click Chemistry Between Thiol and Ene

A combination of a thiol-Michael addition reaction and a free radical mediated thiol-ene reaction is employed as a facile and efficient approach to carbosiloxane dendrimer synthesis. For the first time, carbosiloxane dendrimers are constructed rapidly by an orthogonal click strategy without protection/deprotection procedures. The chemoselectivity of these two thiol-ene click reactions leads to a design of a new monomer containing both electron-deficient carbon-carbon double bonds and unconjugated carbon-carbon double bonds. Siloxane bonds are introduced as the linker between these two kinds of carbon-carbon double bonds. Starting from a bifunctional thiol core, the dendrimers are constructed by iterative thiol-ene click reactions under different but both mild reaction conditions. After simple purification steps the fifth dendrimer with 54 peripheral functional groups is obtained with an excellent overall yield in a single day. Furthermore, a strong blue glow is observed when the dendrimer is excited by a UV lamp.

Recent advances in vaccine delivery

The field of vaccination is moving from the use of attenuated or inactivated pathogens to safer but less immunogenic protein and peptide antigens, which require stronger adjuvant compositions. Antigen delivery carriers appear to play an important role in vaccine development, providing not only antigen protection and controlled release but also an intrinsic adjuvant potential. Among them, carriers based on polymers and lipids are the most representative ones. Patent applications in this area have disclosed, either the design and preparation methods for new biocompatible antigen delivery systems or the application of the previously developed systems for the delivery of novel antigens. Some of them have also reported the use of these technologies for modern therapeutic vaccination approaches.