Polyamidoamine dendrimers surface-engineered with biomimetic phosphorylcholine as potential drug delivery carriers

Recent advances of zwitterionic based topological polymers for biomedical applications

Zwitterionic polymers, comprising hydrophilic anionic and cationic groups with the same total number of positive and negative charges on the same monomer residue, have received increasing attention due to their...

A reduction-responsive drug delivery with improved stability: disulfide crosslinked micelles of small amiphiphilic molecules

Micelles self-assembled from small amphiphilic molecules are unstable in biological fluids, and thus are poor drug carriers. In contrast, amphiphilic polymer micelles can encapsulate hydrophobic drugs in their core to greatly enhance their aqueous solubility and extend their retention time in blood circulation owing to their hydrophilic shell. However, the major disadvantages of conventional polymer micelles are the heterogeneity of the amphiphilic polymer structure and premature drug leakage. Thus, herein, to address these shortcomings, disulfide crosslinked micelles composed of a small amphiphilic molecule, di-lipoyl-glycerophosphorylcholine (di-LA-PC), were developed as redox-responsive drug carriers. Specifically, di-LA-PC was synthesized and self-assembled to form crosslinked micelles under catalysis by dithiothreitol. The disulfide crosslinked micelles maintained high stability in a simulated physiological environment, but rapidly disassembled under reductive conditions. Furthermore, paclitaxel (PTX), as a model drug, was encapsulated in the core of the crosslinked micelles with a high loading content of 8.13%. The in vitro release studies indicated that over 80% of PTX was released from the micelles in the reductive environment, whereas less than 20% PTX was released without reduction in the 68 h test. Benefiting from their nanoscale characteristics, the PTX-loaded micelles showed efficient cellular internalization and effectively induced the death of cancer cells, as revealed in the MTT, apoptosis and cell cycle tests. Moreover, pharmacokinetic studies demonstrated that the crosslinked micelles prolonged the circulation of the incorporated PTX in the bloodstream and increased its accumulation in the tumor tissue via the EPR effect. Finally, the PTX-loaded micelles displayed prominent in vivo anti-tumor activity in a 4T1 xenograft tumor model. In summary, the di-LA-PC crosslinked micelle platform possesses excellent stability, high loading capacity and reduction-responsive release profile, which may have applications in the delivery of PTX and other anti-cancer drugs.

Biocompatible Dendrimer-Encapsulated Palladium Nanoparticles for Oxidation of Morin

Development of highly efficient catalysts to expedite the degradation of organic dyes has been drawing great attention. The aggregation of catalysts reduces the accessibility of catalytic centers for organic dyes and therefore decreases their catalytic ability. Herein, we report a facile method to prepare highly biocompatible and stable dendrimer-encapsulated palladium nanoparticles (Pd n -G5MCI NPs), which exhibit high catalytic efficiency for oxidation of morin. The biocompatible dendrimers were prepared via surface modification of G5 polyamidoamine (G5 PAMAM) dendrimers using maleic anhydride and l-cysteine. Then, they were incubated with disodium tetrachloropalladate, followed by reduction using sodium borohydride to generate Pd n -G5MCI NPs. Transmission electron microscopy results demonstrated that palladium nanoparticles (Pd NPs) inside Pd n -G5MCI had small diameters (1.77-2.35 nm) and monodisperse states. Dynamic light scattering results confirmed that Pd n -G5MCI NPs had good dispersion and high stability in water. Furthermore, MTT results demonstrated that Pd n -G5MCI NPs had high biocompatibility. More importantly, Pd n -G5MCI NPs successfully catalyzed the decomposition of H2O2 to the hydroxyl radical (•OH), and the generated •OH quickly oxidized morin. This reaction kinetics followed pseudo-first-order kinetics. Apparent rate constant (k app) is an important criterion for evaluating the catalytic rate. The concentrations of Pd n -G5MCI NPs and H2O2 were positively correlated with k app, whereas the correlation between the concentration of morin and k app was negative. The prepared Pd n -G5MCI NPs have great potential to catalyze the degradation of organic dyes in bio-related systems in the future.

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.

Highly biocompatible zwitterionic dendrimer-encapsulated platinum nanoparticles for sensitive detection of glucose in complex medium

The sensitive detection of glucose using zwitterionic dendrimer-encapsulated platinum nanoparticles was not affected by proteins.

Enhanced glucose detection using dendrimer encapsulated gold nanoparticles benefiting from their zwitterionic surface

The application of ultrasmall gold nanoparticles as enzyme mimics has been drawing great attention. Herein, we developed zwitterionic dendrimer encapsulated gold nanoparticles (Au-G5MC NPs) for highly sensitive and simple colorimetric detection of glucose. Au-G5MC NPs showed peroxidase-like property, which could efficiently catalyze oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂, producing a blue color product (oxTMB). This peroxidase-like reaction follows a typical Michaelis-Menten kinetics. The K_m towards TMB exhibited a lower value (0.194 mM) than that of horseradish peroxidase (HRP, 0.434 mM). Furthermore, the peroxidase-like properties of Au-G5MC NPs enable colorimetric detection of the concentration of glucose with high selectivity. The linear concentration range of this method was from 14 μM to 166 μM with the detection limit down to 3.8 μM. More importantly, the detection was not interfered by proteins due to the single zwitterionic layer on the Au-G5MC NPs surface. These excellent properties are attributed to the ultrasmall size of gold nanoparticles and high stability of Au-G5MC NPs in complex medium. This catalytic system might have great potential applications for glucose detection in medical diagnostics and biochemistry in the future.

Engineering Polyzwitterion and Polydopamine Decorated Doxorubicin-Loaded Mesoporous Silica Nanoparticles as a pH-Sensitive Drug Delivery

Multifunctional drug carriers have great applications in biomedical field. In this study, we introduced both polydopamine (PDA) and zwitterionic polymer of poly(3-(3-methacrylamidopropyl-(dimethyl)-ammonio)propane-1-sulfonate) (PSPP) onto the surface of mesoporous silica nanoparticles (MSNs) to develop a novel nanoparticle (MSNs@PDA-PSPP), which was employed as a new kind of drug carrier for the delivery of doxorubicin (DOX). The PDA coating, as a gatekeeper, could endow the drug carrier with pH-sensitive drug release performance. The outermost PSPP layer would make the drug carrier possess protein resistance performance. The chemical structure and properties were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS) and thermogravimetric analysis (TGA). MSNs@PDA-PSPP could keep good colloidal stability within 72 h in phosphate buffered saline (PBS) and protein solutions. Meanwhile, MSNs@PDA-PSPP exhibited a high drug loading for DOX. In vitro drug release experiments suggested MSNs-DOX@PDA-PSPP exhibited pH-dependent drug release behaviors. Besides, MSNs@PDA-PSPP had no cytotoxicity to human hepatocellular carcinoma cells (HepG2 cells) even at a concentration of 125 µg/mL. More importantly, cellular uptake and in vitro anticancer activity tests suggested that MSNs-DOX@PDA-PSPP could be taken up by HepG2 cells and DOX could be successfully released and delivered into the cell nuclei. Taken together, MSNs@PDA-PSPP have great potential in the biomedical field.

Highly stable and biocompatible zwitterionic dendrimer-encapsulated palladium nanoparticles that maintain their catalytic activity in bacterial solution

This study offers a method for constructing an artificial enzyme (Pd_n-G5MC), which maintains its catalytic efficiency in bacterial solution.

Stimuli-responsive nanocarriers for intracellular delivery

The emergence of different nanoparticles (NPs) has made a significant revolution in the field of medicine. Different NPs in the form of metallic NPs, dendrimers, polymeric NPs, carbon quantum dots and liposomes have been functionalized and used as platforms for intracellular delivery of biomolecules, drugs, imaging agents and nucleic acids. These NPs are designed to improve the pharmacokinetic properties of the drug, improve their bioavailability and successfully surpass physiological or pathological obstacles in the biological system so that therapeutic efficacy is achieved. In this review I present some of the current approaches used in intracellular delivery systems, with a focus on various stimuli-responsive nanocarriers, including cell-penetrating peptides, to highlight their various biomedical applications.

Perspectives on dendritic architectures and their biological applications: From core to cell

The challenges of medicine today include the increasing stipulation for sensitive and effective systems that can improve the pathological responses with a simultaneous reduction in accumulation and drug side effects. The demand can be fulfilled through the advancements in nanomedicine that includes nanostructures and nanodevices for diagnosing, treating, and prevention of various diseases. In this respect, the nanoscience provides various novel techniques with carriers such as micelles, dendrimers, particles and vesicles for the transportation of active moieties. Further, an efficient way to improve these systems is through stimuli a responsive system that utilizes supramolecular hyperbranched structures to meet the above criteria. The stimuli-responsive dendritic architectures exhibit spatial, temporal, convenient, effective, safety and controlled drug release in response to specific trigger through electrostatic interactions plus π stacking. The stimuli-responsive systems are capable of sequestering the drug molecules underneath a predefined set of conditions and discharge them in a different environment through either exogenous or endogenous stimulus. The incorporation of photoresponsive moieties at various components of dendrimer such as core, branches or at the peripheral end exaggerates its significance in various allied fields of nanotechnology which includes sensors, photoswitch, electronic widgets and in drug delivery systems. This is due to the light instigated geometrical modifications at the core or at the surface molecules which generates huge conformational changes throughout the hyperbranched structure. Further, numerous synthetic methodologies have been investigated for utilization of dendrimers in therapeutic drug delivery and its applicability towards stimuli responsive systems such as photo-instigated, thermal-instigated, and pH-instigated hyperbranched structures and their advancement in the field of nanomedicine. This paper highlights the fascinating theoretical advances and principal mechanisms of dendrimer synthesis and their ability to capture light that strengthens its applicability from radiant energy to medical photonics.

Biomimetics in drug delivery systems: A critical review

Today, the advanced drug delivery systems have been focused on targeted drug delivery fields. The novel drug delivery is involved with the improvement of the capacity of drug loading in drug carriers, cellular uptake of drug carriers, and the sustained release of drugs within target cells. In this review, six groups of therapeutic drug carriers including biomimetic hydrogels, biomimetic micelles, biomimetic liposomes, biomimetic dendrimers, biomimetic polymeric carriers and biomimetic nanostructures, are studied. The subject takes advantage of the biomimetic methods of productions or the biomimetic techniques for the surface modifications, similar to what accrues in natural cells. Moreover, the effects of these biomimetic approaches for promoting the drug efficiency in targeted drug delivery are visible. The study demonstrates that the fabrication of biomimetic nanocomposite drug carriers could noticeably promote the efficiency of drugs in targeted drug delivery systems.

Highly stable and biocompatible dendrimer-encapsulated gold nanoparticle catalysts for the reduction of 4-nitrophenol

The enhanced properties of dendrimer-encapsulated gold nanoparticles were attributed to the single zwitterionic layer on the new dendrimer template.

Stable and pH-responsive polyamidoamine based unimolecular micelles capped with a zwitterionic polymer shell for anticancer drug delivery

Zwitterionic dendrimer based unimolecular micelles for anticancer drug delivery were prepared, exhibiting excellent stability in complex biological media.

Recombinant invasive Lactococcus lactis can transfer DNA vaccines either directly to dendritic cells or across an epithelial cell monolayer

Lactococcus lactis (L. lactis), a generally regarded as safe (GRAS) bacterium has recently been investigated as a mucosal delivery vehicle for DNA vaccines. Because of its GRAS status, L. lactis represents an attractive alternative to attenuated pathogens. Previous studies showed that eukaryotic expression plasmids could be delivered into intestinal epithelial cells (IECs) by L. lactis, or recombinant invasive strains of L. lactis, leading to heterologous protein expression. Although expression of antigens in IECs might lead to vaccine responses, it would be of interest to know whether uptake of L. lactis DNA vaccines by dendritic cells (DCs) could lead to antigen expression as they are unique in their ability to induce antigen-specific T cell responses. To test this, we incubated mouse bone marrow-derived DCs (BMDCs) with invasive L. lactis strains expressing either Staphylococcus aureus Fibronectin Binding Protein A (LL-FnBPA+), or Listeria monocytogenes mutated Internalin A (LL-mInlA+), both strains carrying a plasmid DNA vaccine (pValac) encoding for the cow milk allergen β-lactoglobulin (BLG). We demonstrated that they can transfect BMDCs, inducing the secretion of the pro-inflammatory cytokine IL-12. We also measured the capacity of strains to invade a polarized monolayer of IECs, mimicking the situation encountered in the gastrointestinal tract. Gentamycin survival assay in these cells showed that LL-mInlA+ is 100 times more invasive than L. lactis. The cross-talk between differentiated IECs, BMDCs and bacteria was also evaluated using an in vitro transwell co-culture model. Co-incubation of strains in this model showed that DCs incubated with LL-mInlA+ containing pValac:BLG could express significant levels of BLG. These results suggest that DCs could sample bacteria containing the DNA vaccine across the epithelial barrier and express the antigen.

Cell membrane-inspired polymeric micelles as carriers for drug delivery

Cell membrane-inspired polymeric micelles were designed as drug carriers for cancer therapy.

Recent advances in dendrimer-based nanovectors for tumor-targeted drug and gene delivery

Advances in the application of nanotechnology in medicine have given rise to multifunctional smart nanocarriers that can be engineered with tunable physicochemical characteristics to deliver one or more therapeutic agent(s) safely and selectively to cancer cells, including intracellular organelle-specific targeting. Dendrimers having properties resembling biomolecules, with well-defined 3D nanopolymeric architectures, are emerging as a highly attractive class of drug and gene delivery vector. The presence of numerous peripheral functional groups on hyperbranched dendrimers affords efficient conjugation of targeting ligands and biomarkers that can recognize and bind to receptors overexpressed on cancer cells for tumor-cell-specific delivery. The present review compiles the recent advances in dendrimer-mediated drug and gene delivery to tumors by passive and active targeting principles with illustrative examples.

Synthesis and characterization of dendritic star-shaped zwitterionic polymers as novel anticancer drug delivery carriers

In this work, a novel dendritic star-shaped zwitterionic polymer, polyamidoamine-graft-poly[3-dimethyl (methacryloyloxyethyl) ammonium propanesulfonate] (PAMAM-g-PDMAPS), was synthesized. PAMAM dendrimers (generation 2, G2) were firstly prepared and then converted into the PAMAM-Br macroinitiator with 2-bromoisobutyryl bromide for ATRP. Finally, ATRP of zwitterionic DMAPS was carried out to obtain the dendritic star-shaped polymers PAMAM-g-PDMAPS with different PDMAPS chain lengths. Fourier transform-infrared spectroscopy, (1)H NMR, dynamic laser light scattering (DLS), and TEM were used to characterize the polymers. Encapsulation of adriamycin (ADR) by PAMAM-g-PDMAPS nanoparticles and ADR release behavior from ADR-loaded PAMAM-g-PDMAPS nanoparticles were investigated in detail. PAMAM-g-PDMAPS polymers, even starting from low-generation PAMAM core (G2), were found to show high loading efficiency for ADR because ADR existed not only within G2 PAMAM cores but also in PDMAPS layers. The release profile of ADR from ADR-loaded PAMAM-g-PDMAPS nanoparticles was pH-sensitive and could be controlled by the length of PDMAPS chains. Cell viability studies indicated that ADR-loaded PAMAM-g-PDMAPS could effectively restrain the growth of HepG2 cells and even kill them, whereas PAMAM-g-PDMAPS exhibited nontoxicity. All these results demonstrated that dendritic star-shaped zwitterionic polymers PAMAM-g-PDMAPS are attractive candidates as anticancer drug delivery carriers.

Reducing the cytotoxity of poly(amidoamine) dendrimers by modification of a single layer of carboxybetaine

The surface primary amines of generation five poly(amido amine) (G5 PAMAM) dendrimer were modified by different amounts of carboxybetaine acrylamide (CBAA). As a result, the fully modified molecules (CBAA-PAMAM-20, obtained from the 20:1 molar ratio of CBAA molecules to amino groups in modification solution) show excellent compatibility with protein and cells. CBAA-PAMAM-20 and fibrinogen (Fg) could coexist in solution without forming aggregation, indicating very weak interaction force between CBAA-PAMAM-20 and fibrinogen. CBAA-PAMAM-20 exhibits almost undetectable hemolytic activity, while other partially modified ones cause severe hemolysis and fibrinogen aggregation. Furthermore, the membrane of human umbilical vascular endothelial cell (HUVEC) remains intact after 24 h incubation with CBAA-PAMAM-20. The cytotoxicity assay of HUVEC cells and KB cells also showed that the CBAA-PAMAM-20 was not cytotoxic up to a 2 mg/mL concentration (>90% cell viability). In short, a thin compact layer of zwitterionic carboxybetaine could reduce the cytotoxicity of PAMAM through minimizing the interaction with protein and cell membranes, which suggest that the carboxybetaine-coated PAMAM could be a useful platform for biocompatible carriers to load contrast agents and drugs.

Bioconjugates of PAMAM dendrimers with trans-retinal, pyridoxal, and pyridoxal phosphate

Background

Bioconjugates of a polyamidoamine (PAMAM) G3 dendrimer and an aldehyde were synthesized as carriers for vitamins A and B₆, and the bioavailability of these vitamins for skin nutrition was investigated.

Methods

Nuclear magnetic resonance (NMR) and ultraviolet-visible methods were used to characterize the structure of the bioconjugates and for monitoring release of pyridoxal (Pyr) and pyridoxal phosphate (PLP) from these bioconjugates in vitro. A skin model permeation of bioconjugates was also studied in a Franz chamber.

Results

A transdermal G3 PAMAM dendrimer was used to synthesize bioconjugates with trans-retinal (Ret), pyridoxal (Pyr), or PLP. These nanomolecules, containing up to four covalently linked Ret, Pyr, or PLP (G3^4Ret, G3^4Pyr, and G3^4PLP), were able to permeate the skin, as demonstrated in vitro using a model skin membrane. PLP and Pyr bound to a macromolecular vehicle were active cofactors for glutamic pyruvic transaminase, as shown by ¹H NMR spectral monitoring of the progress of the L-alanine + α-ketoglutarate → glutamic acid + pyruvic acid reaction.

Conclusion

PAMAM-PLP, PAMAM-Pyr, and PAMAM-Ret bioconjugates are able to permeate the skin. PLP and Pyr are available as cofactors for glutamic pyruvic transaminase.

Study of interaction energies between the PAMAM dendrimer and nonsteroidal anti-inflammatory drug using a distributed computational strategy and experimental analysis by ESI-MS/MS

The structure of a dendrimer exhibits a large number of internal and superficial cavities, which can be exploited, to capture and deliver small organic molecules, enabling their use in drug delivery. Structure-based modeling and quantum mechanical studies can be used to accurately understand the interactions between functionalized dendrimers and molecules of pharmaceutical and industrial interest. In this study, we implemented a Metropolis Monte Carlo algorithm to calculate the interaction energy of dendrimer-drug complexes, which can be used for in silico prediction of dendrimer-drug affinity. Initially, a large-scale sampling of different dendrimer-drug conformations was generated using Euler angles. Then, each conformation was distributed on different nodes of a GRID computational system, where its interaction energy was calculated by semiempirical quantum mechanical methods. These energy calculations were performed for four different nonsteroidal anti-inflammatory drugs, each showing different affinities for the PAMAM-G4 dendrimer. The affinities were also characterized experimentally by using Cooks' kinetic method to calculate PAMAM-drug dissociation constants. The quantitative structure-activity relationship between the interaction energies and dissociation constants showed statistical correlations with r(2) > 0.9.