Design of biocompatible dendrimers for cancer diagnosis and therapy: current status and future perspectives

LSO:Ce Inorganic Scintillators Are Biocompatible With Neuronal and Circuit Function

Optogenetics is widely used in neuroscience to control neural circuits. However, non-invasive methods for light delivery in brain are needed to avoid physical damage caused by current methods. One potential strategy could employ x-ray activation of radioluminescent particles (RPLs), enabling localized light generation within the brain. RPLs composed of inorganic scintillators can emit light at various wavelengths depending upon composition. Cerium doped lutetium oxyorthosilicate (LSO:Ce), an inorganic scintillator that emits blue light in response to x-ray or ultraviolet (UV) stimulation, could potentially be used to control neural circuits through activation of channelrhodopsin-2 (ChR2), a light-gated cation channel. Whether inorganic scintillators themselves negatively impact neuronal processes and synaptic function is unknown, and was investigated here using cellular, molecular, and electrophysiological approaches. As proof of principle, we applied UV stimulation to 4 μm LSO:Ce particles during whole-cell recording of CA1 pyramidal cells in acute hippocampal slices from mice that expressed ChR2 in glutamatergic neurons. We observed an increase in frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), indicating activation of ChR2 and excitation of neurons. Importantly, LSO:Ce particles did not affect survival of primary mouse cortical neurons, even after 24 h of exposure. In extracellular dendritic field potential recordings, no change in the strength of basal glutamatergic transmission was observed during exposure to LSO:Ce microparticles. However, the amplitude of the fiber volley was slightly reduced with high stimulation. Additionally, there was a slight decrease in the frequency of sEPSCs in whole-cell voltage-clamp recordings from CA1 pyramidal cells, with no change in current amplitudes. The amplitude and frequency of spontaneous inhibitory postsynaptic currents were unchanged. Finally, long term potentiation (LTP), a synaptic modification believed to underlie learning and memory and a robust measure of synaptic integrity, was successfully induced, although the magnitude was slightly reduced. Together, these results show LSO:Ce particles are biocompatible even though there are modest effects on baseline synaptic function and long-term synaptic plasticity. Importantly, we show that light emitted from LSO:Ce particles is able to activate ChR2 and modify synaptic function. Therefore, LSO:Ce inorganic scintillators are potentially viable for use as a new light delivery system for optogenetics.

High-Performance Worm-like Mn-Zn Ferrite Theranostic Nanoagents and the Application on Tumor Theranostics

Previous reports from our team revealed the significant potential advantage of Mn-Zn ferrite nanoparticles (NPs) in magnetic resonance imaging (MRI), whereas anisotropic NPs reportedly increased the blood circulation time of nanocarriers. Thus, anisotropic Mn-Zn ferrite displayed a huge potential in cancer synchronous diagnosis and treatment, that is, enhanced MRI observation was performed simultaneously when drug-targeted delivery therapy was applied to the tumor. Here, we developed three shaped Mn-Zn ferrite (Mn_0.63Zn_0.37Fe₂O₄) MNPs used as cancer theranostic nanoagents and compared the effect of the three shaped MNPs on cancer theranostics. Compared to the monodisperse sphere MNPs (S-MNPs-PPR) and clustering MNPs (C-MNPs-PPR), worm-like Mn-Zn ferrite MNPs (W-MNPs-PPR) achieved better results in T₂-weighted MRI and achieved more sustained drug release than S-MNPs-PPR and more complete drug release than C-MNPs-PPR in vitro. Additionally, polyethylene glycol (PEG) coating and RGD modification encouraged the three shaped MNPs to evade the recruitment of macrophages more easily and to target the integrin-enriched endothelial cells instead. Meanwhile, W-MNPs-PPR coupled with Paclitaxel (PTX) exhibited more delivery of PTX in the integrin-enriched cells than the other two shaped MNPs, and the content of PTX was far more than that of the wild-type Taxol control group. What is more, in vivo results demonstrated that PTX-coated W-MNPs-PPR not only gained good dual-mode imaging in the tumor (MRI and fluorescence images) but also achieved longer blood circulation time and more PTX-targeted delivery to the tumor, as well as more efficiency in tumor cell killing, which make the simultaneous diagnosis and treatment of tumors to be conducted. Therefore, our works further revealed the importance of the NP shape on its functionality and ultimately provided an alternative and efficient worm-like theranostic nanoagent for tumor theranostics.

Rational design and facile fabrication of biocompatible triple responsive dendrimeric nanocages for targeted drug delivery

Multi-responsive polymeric nanoparticles have shown great promise in the sufficient site-specific delivery of drugs in heterogeneous and complicated biological microenvironments, but without great success due to many problems such as sophisticated manufacture process, high cost and cytotoxicity. In this work, a novel triple responsive dendrimeric nanocage (TDN) is fabricated through co-assembling and cross-linking of lipoic acid modified low generation dendrimers with lipoic acid modified polyethylene glycols (PEGs). This nanocage exhibits improved drug loading capacity (about 2 times higher) at a lower temperature and stimuli-responsive drug release profile upon the stimulation of temperature, acid pH and reducing agent. More importantly, the nanocage promotes drug internalization, conduces endosomal escape, and realizes intracellular controlled drug release. Furthermore, the nanocage significantly improves the pharmacokinetics and biodistribution of antitumor drugs, confirming the potent in vivo therapeutic effect with reduced side effects. The rational design and facile fabrication of multi-responsive dendrimeric nanocages provide a "proof-of-concept" for precise targeted drug delivery, and may have great potential for clinical use in the future.

Surface Functionalization of Cotton Fabric with Fluorescent Dendrimers, Spectral Characterization, Cytotoxicity, Antimicrobial and Antitumor Activity

Poly(propylenimine) dendrimers from first and third generations modified with 1,8-naphthalimide units and their Zn(II) complexes have been investigated by absorption and fluorescence spectroscopy. These dendrimers have been deposited on a cotton cloth by the extraction method, producing yellow-colored textile materials. They have been characterized by defining their color coordinates L*a*b*, XYZ and xy. The antimicrobial activity of dendrimers has been investigated in vitro against model gram-positive and gram-negative bacteria and yeasts. Being deposited onto the surface of cotton fabric, the studied dendrimers reduced bacterial growth and prevented the formation of bacterial biofilm. Anticancer and cytotoxicity activities have also been performed against HeLa and Lep-3 human tumor cell lines as model systems.

Nanocarriers and Their Loading Strategies

Nanocarriers are of paramount significance for drug delivery and nanomedicine technology. Given the imperfect systems and nonideal therapeutic effects, there are works to be done in synthesis as much as in biological studies, if not more so. Building the foundation of synthesis would offer more tools and deeper insights for exploring the biological systems with extreme complexity. This review aims at a broad-scope summary and classification of nanocarriers for drug delivery, with focus on the synthetic strategy and structural implications. The nanocarriers are divided into four categories according to the loading principle: molecular-level loading, surface loading, matrix loading, and cavity loading systems. Making comparisons across diverse nanocarrier systems would make it easier to see the fundamental characteristics, from where the weakness can be addressed and the strengths combined. The systematic comparisons may also inspire new ideas and methods.

Current advances in development of new docetaxel formulations

INTRODUCTION

Docetaxel (DTX) is one of the most important chemotherapeutic agents and has been widely used for treatment of various types of cancers. However, the clinical chemotherapy of DTX gives many undesirable side effects due to the usage of organic solvent in the injection and its low selectivity for tumor cells. With the evolution of pharmaceutical technologies, great efforts have been paid to develop new DTX formulations to overcome these problems.

AREAS COVERED

This review provided an overview of the preparation and activities of new DTX formulations, which were classified by administration methods, including injection, oral, transdermal and rectal administration. Besides, up to date information of the clinical status of new DTX formulations was summarized. We also discussed the challenges and perspectives of the future development of DTX formulations.

EXPERT OPINION

There have been numerous studies on new DTX-based formulations in recent years, and many of them exhibited significantly enhanced anti-tumor and targeting activity compared with DTX in preclinical studies. However, only a few entered clinical trials, and none has been approved into market. The clinical translation of experimental drug faces many hurdles, including the limited knowledge of nanomedicine and oncology, safety issues, controllable and reproducible production.

Intracellular GSH-responsive camptothecin delivery systems

Smart GSH-responsive camptothecin delivery systems for treatment of tumors and real-time monitoring in vivo and in vitro were described.

Superparamagnetic iron oxides as MPI tracers: A primer and review of early applications

Magnetic particle imaging (MPI) has recently emerged as a non-invasive, whole body imaging technique that detects superparamagnetic iron oxide (SPIO) nanoparticles similar as those used in magnetic resonance imaging (MRI). Based on tracer "hot spot" detection instead of providing contrast on MRI scans, MPI has already proven to be truly quantitative. Without the presence of endogenous background signal, MPI can also be used in certain tissues where the endogenous MRI signal is too low to provide contrast. After an introduction to the history and simplified principles of MPI, this review focuses on early MPI applications including MPI cell tracking, multiplexed MPI, perfusion and tumor MPI, lung MPI, functional MPI, and MPI-guided hyperthermia. While it is too early to tell if MPI will become a mainstay imaging technique with the (theoretical) sensitivity that it promises, and if it can successfully compete with SPIO-based ¹H MRI and perfluorocarbon-based ¹⁹F MRI, it provides unprecedented opportunities for exploring new nanoparticle-based imaging applications.

Linear PVA–DTPA–Gd conjugate for magnetic resonance imaging

In this study, we report the preparation and characterization of the PVA–DTPA–Gd conjugate as a potential MRI contrast agent (CA). The r₁ value and the r₂/r₁ ratio were about 5.6 mM⁻¹ s⁻¹ and 1.31, respectively. In vitro toxicity studies not only demonstrated that the polymeric system possessed good biocompatibility, but also proved that the conjugate could be an attractive candidate for CA.

In this study, we report the preparation and characterization of the PVA–DTPA–Gd conjugate as a potential MRI contrast agent (CA).

Click inspired synthesis of hexa and octadecavalent peripheral galactosylated glycodendrimers and their possible therapeutic applications

Click inspired glycodendrimers comprising a rigid hexapropargyloxy benzene core with peripheral β-d-galactopyranosidic units were developed and evaluated for their therapeutic potential.

Recent developments in the construction of metallacycle/metallacage-cored supramolecular polymers via hierarchical self-assembly

Supramolecular polymers have received considerable attention during the last few decades due to their scientific value in polymer chemistry and profound implications for future developments of advanced materials. Discrete supramolecular coordination complexes (SCCs) with well-defined size, shape, and geometry have been widely employed to construct hierarchical systems by coordination-driven self-assembly with the spontaneous formation of metal-ligand bonds, which results in the formation of well-defined two-dimensional (2D) metallacycles or three-dimensional (3D) metallacages with high functionalities. The incorporation of discrete SCCs into supramolecular polymers by the orthogonal combination of metal-ligand coordination and other noncovalent interactions or covalent bonding could further facilitate the construction of novel supramolecular polymers with hierarchical architectures and multiple functions including controllable uptake and release of guest molecules, providing a flexible platform for the development of smart materials. In this review, the recent progress in metallacycle/metallacage-cored supramolecular polymers that were constructed by the combination of metal-ligand interactions and other orthogonal interactions (including hydrophobic or hydrophilic interactions, hydrogen bonding, van der Waals forces, π-π stacking, electrostatic interactions, host-guest interactions and covalent bonding) has been discussed. In addition, the potential applications of metallacycle/metallacage-cored supramolecular polymers in the areas of light emitting, sensing, bio-imaging, delivery and release, etc., are also presented.

Dendrimers for pulmonary delivery: current perspectives and future challenges

Dendrimers and dendrimer-based delivery systems are potential biomedicines in the rapidly growing field of nanomedicine.

Bioconjugation in Drug Delivery: Practical Perspectives and Future Perceptions

For the past three decades, pharmaceutical research has been mainly converging to novel carrier systems and nanoparticulate colloidal technologies for drug delivery, such as nanoparticles, nanospheres, vesicular systems, liposomes, or nanocapsules to impart novel functions and targeting abilities. Such technologies opened the gate towards more sophisticated and effective multi-acting platform(s) which can offer site-targeting, imaging, and treatment using a single multifunctional system. Unfortunately, such technologies faced major intrinsic hurdles including high cost, low stability profile, short shelf-life, and poor reproducibility across and within production batches leading to harsh bench-to-bedside transformation.Currently, pharmaceutical industry along with academic research is investing heavily in bioconjugate structures as an appealing and advantageous alternative to nanoparticulate delivery systems with all its flexible benefits when it comes to custom design and tailor grafting along with avoiding most of its shortcomings. Bioconjugation is a ubiquitous technique that finds a multitude of applications in different branches of life sciences, including drug and gene delivery applications, biological assays, imaging, and biosensing.Bioconjugation is simple, easy, and generally a one-step drug (active pharmaceutical ingredient) conjugation, using various smart biocompatible, bioreducible, or biodegradable linkers, to targeting agents, PEG layer, or another drug. In this chapter, the different types of bioconjugates, the techniques used throughout the course of their synthesis and characterization, as well as the well-established synthetic approaches used for their formulation are presented. In addition, some exemplary representatives are outlined with greater emphasis on the practical tips and tricks of the most prominent techniques such as click chemistry, carbodiimide coupling, and avidin-biotin system.

Hydrazide-integrated carbazoles: synthesis, computational, anticancer and molecular docking studies

Novel carbazolylmethylene isonictinohydrazides have been synthesized as anticancer agents against pancreatic cancer cells.

Dendrimer- and copolymer-based nanoparticles for magnetic resonance cancer theranostics

Cancer theranostics is one of the most important approaches for detecting and treating patients at an early stage. To develop such a technique, accurate detection, specific targeting, and controlled delivery are the key components. Various kinds of nanoparticles have been proposed and demonstrated as potential nanovehicles for cancer theranostics. Among them, polymer-like dendrimers and copolymer-based core-shell nanoparticles could potentially be the best possible choices. At present, magnetic resonance imaging (MRI) is widely used for clinical purposes and is generally considered the most convenient and noninvasive imaging modality. Superparamagnetic iron oxide (SPIO) and gadolinium (Gd)-based dendrimers are the major nanostructures that are currently being investigated as nanovehicles for cancer theranostics using MRI. These structures are capable of specific targeting of tumors as well as controlled drug or gene delivery to tumor sites using pH, temperature, or alternating magnetic field (AMF)-controlled mechanisms. Recently, Gd-based pseudo-porous polymer-dendrimer supramolecular nanoparticles have shown 4-fold higher T1 relaxivity along with highly efficient AMF-guided drug release properties. Core-shell copolymer-based nanovehicles are an equally attractive alternative for designing contrast agents and for delivering anti-cancer drugs. Various copolymer materials could be used as core and shell components to provide biostability, modifiable surface properties, and even adjustable imaging contrast enhancement. Recent advances and challenges in MRI cancer theranostics using dendrimer- and copolymer-based nanovehicles have been summarized in this review article, along with new unpublished research results from our laboratories.

The mechanism of lauric acid-modified protein nanocapsules escape from intercellular trafficking vesicles and its implication for drug delivery

Protein nanocapsules have exhibited promising potential applications in the field of protein drug delivery. A major issue with various promising nano-sized biotherapeutics including protein nanocapsules is that owing to their particle size they are subject to cellular uptake via endocytosis, and become entrapped and then degraded within endolysosomes, which can significantly impair their therapeutic efficacy. In addition, many nano-sized biotherapeutics could be also sequestered by autophagosomes and degraded through the autolysosomal pathway. Thus, a limiting step in achieving an effective protein therapy is to facilitate the endosomal escape and auto-lysosomal escape to ensure cytosolic delivery of the protein drugs. Here, we prepared a protein nanocapsule based on BSA (nBSA) and the BSA nanocapsules modified with a bilayer of lauric acid (LA-nBSA) to investigate the escape effects from the endosome and autophagosome. The size distribution of nBSA and LA-nBSA analyzed using DLS presents a uniform diameter centered at 10 nm and 16 nm. The data also showed that FITC-labeled nBSA and LA-nBSA were taken up by the cells mainly through Arf-6-dependent endocytosis and Rab34-mediated macropinocytosis. In addition, LA-nBSA could efficiently escape from endosomal before the degradation in endo-lysosomes. Autophagy could also sequester the LA-nBSA through p62 autophagosome vesicles. These two types of nanocapsules underwent different intracellular destinies and lauric acid (LA) coating played a vital role in intracellular particle retention. In conclusion, the protein nanocapsules modified with LA could enhance the protein nanocapsules escape from intercellular trafficking vesicles, and protect the protein from degradation by the lysosomes.

Multifunctional Dendrimer-Entrapped Gold Nanoparticles Conjugated with Doxorubicin for pH-Responsive Drug Delivery and Targeted Computed Tomography Imaging

Novel theranostic nanocarriers exhibit a desirable potential to treat diseases based on their ability to achieve targeted therapy while allowing for real-time imaging of the disease site. Development of such theranostic platforms is still quite challenging. Herein, we present the construction of multifunctional dendrimer-based theranostic nanosystem to achieve cancer cell chemotherapy and computed tomography (CT) imaging with targeting specificity. Doxorubicin (DOX), a model anticancer drug, was first covalently linked onto the partially acetylated poly(amidoamine) dendrimers of generation 5 (G5) prefunctionalized with folic acid (FA) through acid-sensitive cis-aconityl linkage to form G5·NHAc-FA-DOX conjugates, which were then entrapped with gold (Au) nanoparticles (NPs) to create dendrimer-entrapped Au NPs (Au DENPs). We demonstrate that the prepared DOX-Au DENPs possess an Au core size of 2.8 nm, have 9.0 DOX moieties conjugated onto each dendrimer, and are colloid stable under different conditions. The formed DOX-Au DENPs exhibit a pH-responsive release profile of DOX because of the cis-aconityl linkage, having a faster DOX release rate under a slightly acidic pH condition than under a physiological pH. Importantly, because of the coexistence of targeting ligand FA and Au core NPs as a CT imaging agent, the multifunctional DOX-loaded Au DENPs afford specific chemotherapy and CT imaging of FA receptor-overexpressing cancer cells. The constructed DOX-conjugated Au DENPs hold a promising potential to be utilized for simultaneous chemotherapy and CT imaging of various types of cancer cells.

Stimuli-Responsive Therapeutic Metallodrugs

The success of platinum-based anticancer agents has motivated the exploration of novel metal-based drugs for several decades, whereas problems such as drug-resistance and systemic toxicity hampered their clinical applications and efficacy. Stimuli-responsiveness of some metal complexes offers a good opportunity for designing site-specific prodrugs to maximize the therapeutic efficacy and minimize the side effect of metallodrugs. This review presents a comprehensive and up-to-date overview on the therapeutic stimuli-responsive metallodrugs that have appeared in the past two decades, where stimuli such as redox, pH, enzyme, light, temperature, and so forth were involved. The compounds are classified into three major categories based on the nature of stimuli, that is, endo-stimuli-responsive metallodrugs, exo-stimuli-responsive metallodrugs, and dual-stimuli-responsive metallodrugs. Representative examples of each type are discussed in terms of structure, response mechanism, and potential medical applications. In the end, future opportunities and challenges in this field are tentatively proposed. With diverse metal complexes being introduced, the foci of this review are pointed to platinum and ruthenium complexes.

A biocompatible and cathepsin B sensitive nanoscale system of dendritic polyHPMA-gemcitabine prodrug enhances antitumor activity markedly

In an attempt to improve the therapeutic indices of gemcitabine (GEM), a prodrug was designed by conjugating GEM with a stimuli-responsive dendritic polyHPMA copolymer (dendritic polyHPMA-GEM) and synthesized using the one-pot method of RAFT polymerization. The prodrug with dendritic architectures was able to aggregate and form stable nanoscale systems in the order of 46 nm. The high molecular weight (HMW, 168 kDa) dendritic prodrug could biodegrade into segments of low molecular weight (LMW, 29 kDa) for excretion. The prodrug demonstrates enzyme-responsive drug release features; over 95% GEM was released from the carrier in the presence of cathepsin B within 3 h. Investigation of the cellular mechanism underlying the dendritic prodrug suggests that cytotoxicity is associated with cellular uptake and cell apoptosis. The prodrug shows good hemocompatibility and in vivo biosafety. In particular, the dendritic polymer prodrug displays high accumulation within tumors and markedly improved in vivo antitumor activity in the 4T1 murine breast cancer model compared to free GEM. The in vivo antitumor activities are characterized by a marked suppression in tumor volumes indicating much higher tumor growth inhibition (TGI, 83%) than that in GEM treatment (TGI, 36%). In addition, some tumors were eliminated. The tumor xenograft immunohistochemistry study clearly indicates that tumor apoptosis occurs through antiangiogenic effects. These results suggest that the stimuli-responsive dendritic polymer-gemcitabine has great potential as an efficient anticancer agent.

Near Infrared Boron Dipyrromethene Nanoparticles for Optotheranostics

Boron dipyrromethene (BODIPY) is a class of important emerging fluorescent dyes. Due to their unique chemical and optical properties, near infrared (NIR)-emitting BODIPY dyes containing nanoparticles have recently been developed for a wide array of cutting-edge cancer optotheranostic applications. These nanoparticles not only have robust photostability and tunable photophysical properties, but they can also be flexibly tailored to a multitude of functional uses. Based on these outstanding characteristics, such nanoparticles have shown great promise in diagnosis as biological sensors, as well as in their utilization in advanced imaging and photomedicine for cancer treatment. In particular, here, this study first discusses their use as photoswitchable fluorescence probes toward in vitro single-molecule imaging. Second, this study takes a look at their opportunities for photoacoustic imaging utilization. Third, approaches are discussed to construct new NIR-absorbing BODIPY nanoparticles for photodynamic therapy (PDT). Fourth, this study delves into the new approach to use such nanoparticles as an emerging version of triplet-triplet annihilation upconversion (TTA-UC) and their biological uses, such as their photoactivation prodrug therapy (PAPT) for cancer. Finally, new biological sensors based on NIR BODIPY nanoparticles are introduced.

Super-silent FRET Sensor Enables Live Cell Imaging and Flow Cytometric Stratification of Intracellular Serine Protease Activity in Neutrophils

Serine proteases are released by neutrophils to act primarily as antimicrobial proteins but excessive and unbalanced serine protease activity results in serious host tissue damage. Here the synthesis of a novel chemical sensor based on a multi-branched fluorescence quencher is reported. It is super-silent, exhibiting no fluorescence until de-quenched by the exemplar serine protease human neutrophil elastase, rapidly enters human neutrophils, and is inhibited by serine protease inhibitors. This sensor allows live imaging of intracellular serine protease activity within human neutrophils and demonstrates that the unique combination of a multivalent scaffold combined with a FRET peptide represents a novel and efficient strategy to generate super-silent sensors that permit the visualisation of intracellular proteases and may enable point of care whole blood profiling of neutrophils.

The Future of Nanotechnology in Plant Pathology

Engineered nanoparticles are materials between 1 and 100 nm and exist as metalloids, metallic oxides, nonmetals, and carbon nanomaterials and as functionalized dendrimers, liposomes, and quantum dots. Their small size, large surface area, and high reactivity have enabled their use as bactericides/ fungicides and nanofertilizers. Nanoparticles can be designed as biosensors for plant disease diagnostics and as delivery vehicles for genetic material, probes, and agrichemicals. In the past decade, reports of nanotechnology in phytopathology have grown exponentially. Nanomaterials have been integrated into disease management strategies and diagnostics and as molecular tools. Most reports summarized herein are directed toward pathogen inhibition using metalloid/metallic oxide nanoparticles as bactericides/fungicides and as nanofertilizers to enhance health. The use of nanoparticles as biosensors in plant disease diagnostics is also reviewed. As global demand for food production escalates against a changing climate, nanotechnology could sustainably mitigate many challenges in disease management by reducing chemical inputs and promoting rapid detection of pathogens.

Dual stimuli-responsive rotaxane-branched dendrimers with reversible dimension modulation

With the aim of mimicking biological machines, in which the delicate arrangement of nanomechanical units lead to the output of specific functions upon the external stimulus, the construction of dual stimuli-responsive rotaxane-branched dendrimers was realized in this study. Starting from a switchable organometallic [2]rotaxane precursor, the employment of a controllable divergent approach allowed for the successful synthesis of a family of rotaxane-branched dendrimers up to the third generation with 21 switchable rotaxane moieties located on each branch. More importantly, upon the addition and removal of dimethylsulfoxide (DMSO) molecule or acetate anion as the external stimulus, the amplified responsiveness of the switchable rotaxane units endowed the resultant rotaxane-branched dendrimers the solvent- or anion-controlled molecular motions, thus leading to the dimension modulation. Therefore, we successfully constructed a family of rotaxane-branched dendrimers with dual stimuli-responsiveness that will be a privileged platform for the construction of dynamic supramolecular materials.

Mechanically interlocked molecules are extensively applied as artificial molecular machines but rotaxane-branched dendrimers are rarely explored because of synthetic challenges. Here the authors present the construction of dual stimuli-responsive rotaxane-branched dendrimer which can be stimulated by DMSO or acetate ions.

A biodegradable polyphosphoester-functionalized poly(disulfide) nanocarrier for reduction-triggered intracellular drug delivery

Stimuli-responsive and biodegradable polymeric carriers are of great importance for safe delivery and efficient release of chemotherapeutic agents. In this work, given the unique advantages of poly(disulfide)s and biodegradable polyphosphoesters, we designed and constructed a reduction-sensitive amphiphilic triblock copolymer poly(ethyl ethylene phosphate)-b-poly(disulfide)-b-poly(ethyl ethylene phosphate) (PEEP-PDS-PEEP) by combining thiol-disulfide polycondensation and ring-opening polymerization (ROP). The thiol-disulfide polycondensation between 1,6-hexanedithiol and 2,2'-dithiodipyridine yielded the linear telechelic pyridyl disulfide-terminated poly(disulfide)s, followed by the treatment with 2-mercaptoethanol to quantitatively produce dihydroxyl-terminated poly(disulfide)s, which was used to initiate the ROP reaction of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane, generating ABA-type amphiphilic triblock copolymers. The chemical structures of various polymers were thoroughly characterized and verified using nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy. The resultant amphiphilic PEEP-PDS-PEEP could self-assemble into spherical nanoparticles in aqueous solution as evidenced from dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. Hydrophobic anti-tumor drug doxorubicin (DOX) was used to study the encapsulation capacity of nanoparticles, the drug loading content (DLC) and drug loading efficiency (DLE) values were determined to be 11.2% and 31.5%, respectively. In vitro release studies indicated that DOX was released much faster under reductive conditions compared to physiological conditions, confirming their reduction-responsive release behavior owing to the scission of the poly(disulfide) segment and subsequent disintegration of nanoparticles. The cellular uptake study using a live cell imaging system demonstrated that this DOX-loaded nanoparticle can be internalized into HeLa cells and release DOX over time. Methyl thiazolyl tetrazolium (MTT) assay revealed the favorable cytocompatibility of a bare triblock copolymer toward both L929 and HeLa cells, whereas the DOX-loaded copolymer nanoparticles exhibited the lower inhibitory ability against HeLa and HepG2 cell proliferation than free DOX. This finding presents a strategy for the construction of biocompatible and reduction-responsive polymeric drug carriers.

Surface functionalized dendrimers as controlled-release delivery nanosystems for tumor targeting

Dendrimers are nano-sized and three-dimensional macromolecules with well-defined globular architecture and are widely used in various aspects such as drug and gene delivery owing to multivalent and host-guest entrapment properties. However, dendrimers like other nanomaterials have some disadvantages for example rapid clearance by reticuloendothelial system, toxicity due to interaction of amine terminated group with cell membrane, low transfection efficiency and lack of controlled release behavior, which reduce their therapeutic efficiency. To solve these problems, surface functionalization of dendrimers can be carried out. Surface functionalization not only mitigates this obstacle but also renders excessive specificity to dendrimer to improve efficiency of cancer therapy. Specific properties in cancer cell compared to normal cells such as overexpression of various receptors and difference in biological condition like pH, temperature and redox of tumor environment can be an appropriate strategy to increase site-specific targeting efficiency. Therefore, in this article we focus on numerous functionalization strategies, which are used in the modification of dendrimers through attachment of lipid, amino acid, protein/peptide, aptamer, vitamin, antibody. Moreover, increased biocompatibility, site-specific delivery based on various ligands, enhanced transfection efficiency, sustained and controlled release behavior based on stimuli responsiveness are benefits of functionalized dendrimer which we discuss in this review. Overall, these functionalized dendrimers can open a new horizon in the field of targeted drug and gene delivery.

Delaying Anticancer Drug Delivery by Self-Assembly and Branching Effects of Minimalist Dendron-Drug Conjugates

Self-assembly of a covalently-bound lipophilic drug to a dendronic scaffold for making organic nanoparticles is reported as a proof of concept in nanovectorization. A minimalist structural approach with a small PEG-dendron conjugated to paclitaxel (PTX), incorporating safe succinic and gallic acids, is efficient to provide the expected anticancer bioactivity, but also significantly retards and targets intracellular delivery of PTX in 2D and 3D lung cancer cell cultures. A branching effect of dendrons is crucial, when compared to linear PTX conjugates. Transmission electron microscopy (TEM) and dynamic light-scattering (DLS) studies indicate the formation of stable, low-disperse nanoparticles at 10^-5  m in H₂ 0, which could also be responsible for the biological effects. An ultrasensitive LC-MS/MS method was used for the determination of intracellular PTX concentration over time, along with the survival rates of cancer cells. Similarly, cell survival assays were successfully correlated to a 3D cell culture with spheroids for mimicking tumors, when treated with PTX conjugates. Our work opens the way to a full evaluation program required for new chemical entities.

Poly (amidoamine) (PAMAM) dendrimer mediated delivery of drug and pDNA/siRNA for cancer therapy

Poly (amidoamine) (PAMAM) dendrimers are well-defined, highly branched macromolecules with numerous active amine groups on the surface. Because of their unique properties, PAMAM dendrimers have steadily grown in popularity in drug delivery, gene therapy, medical imaging and diagnostic application. This review focuses on the recent developments on the application in PAMAM dendrimers as effective carriers for drug and gene (pDNA, siRNA) delivery in cancer therapy, including: a) PAMAM for anticancer drug delivery; b) PAMAM and gene therapy; c) PAMAM used in overcoming tumor multidrug resistance; d) PAMAM used for hybrid nanoparticles; and e) PAMAM linked or loaded in other nanoparticles.

A triple modality BSA-coated dendritic nanoplatform for NIR imaging, enhanced tumor penetration and anticancer therapy

Functional theranostic systems for drug delivery capable of concurrent near-infrared (NIR) fluorescence imaging, active tumor targeting and anticancer therapies are desired for concise cancer diagnosis and treatment. Dendrimers with controllable size and surface functionalities are good candidates for such platforms. However, integration of active targeting ligands and imaging agents separately on the surface or encapsulation of the imaging agents in the inner core of the dendrimers will result in a more complex composition or reduced drug loading efficiency. Herein, we reported a PAMAM-based theranostic system, with a simple integrin-specific imaging ligand prepared from two motifs. One motif is a NIR carbocyanine fluorescent dye (Cyp) for precise in vivo monitoring of the system and identification of tumor or cancer cells, and the other is a novel tumor-penetrating cyclic peptide (CRGDKGPDC, abbreviated iRGD). BSA was non-covalently bonded with Cyp to reduce NIR agent fluorescence-quenching aggregates and enhance imaging signals. The chemotherapy effect of these dendritic systems was achieved by encapsulating paclitaxel into the hydrophobic interior of the dendrimers. In vitro and in vivo targeting and penetrating studies revealed that a significantly high amount of the dendritic systems was endocytosed by HepG2 cells and enhanced accumulation and penetration at tumor sites. Our safety evaluation showed that masking of cationic-end groups of PAMAM to neutral or anionic groups has resulted in decreased or even zero-toxicity. The preliminary antitumor efficacy of the dendritic system was evaluated. In vitro and in vivo studies confirmed that paclitaxel-encapsulated functionalized PAMAM can efficiently kill HepG2 cancer cells. In conclusion, our functionalized theranostic dendritic system could be a promising nanocarrier to effectively deliver drugs to deep tumor regions for anticancer therapy.

Tuning Spin-Spin Interactions in Radical Dendrimers

Two generations of polyphosphorhydrazone (PPH) dendrimers were synthesized and fully functionalized with TEMPO radicals via acrylamido or imino group linkers to evaluate the impact of the linker substitution on the radical-radical interactions. A drastic change in the way that the radicals interacted among them was observed by EPR and CV studies: while radicals in Gn -imino-TEMPO dendrimers presented a strong spin-spin interaction, in the Gn -acrylamido-TEMPO ones they acted mainly as independent radicals. This shows that these interactions could be tuned by the solely substitution of the radical linker, opening the perspective of controlling and modulating the extension of these interactions depending on each application. The chemical properties of the linker strongly influence the spin-spin exchange between pendant radicals.

A degradable hydrogel formed by dendrimer-encapsulated platinum nanoparticles and oxidized dextran for repeated photothermal cancer therapy

Hydrogels can be used to prolong the retention of photothermal agents in tumors to conduct repeated photothermal therapy (PTT) and thus reduce high-dose-induced toxicity, but the long-term retention of photothermal nanoparticles post-therapy still increases the risk of toxicity. In this work, we developed an injectable and degradable photothermal hydrogel to conduct repeated PTT. The hydrogel was composed of dendrimer-encapsulated platinum nanoparticles (DEPts) crosslinked aldehyde-modified dextran via imine bond formation. The hydrogel represented excellent photothermal effect and good biocompatibility. It was able to remain in tumors for a period of days to allow repeated PTT, leading to complete tumor regression. After treatment, the hydrogel was gradually degraded due to the decomposition of imine bonds. The study developed a practical photothermal hydrogel that allowed repeated PTT and reduced long-term retention-induced toxicity.

Nanoreactors for green catalysis

Sustainable and environmentally benign production are key drivers for developments in the chemical industrial sector, as protecting our planet has become a significant element that should be considered for every industrial breakthrough or technological advancement. As a result, the concept of green chemistry has been recently defined to guide chemists towards minimizing any harmful outcome of chemical processes in either industry or research. Towards greener reactions, scientists have developed various approaches in order to decrease environmental risks while attaining chemical sustainability and elegancy. Utilizing catalytic nanoreactors for greener reactions, for facilitating multistep synthetic pathways in one-pot procedures, is imperative with far-reaching implications in the field. This review is focused on the applications of some of the most used nanoreactors in catalysis, namely: (polymer) vesicles, micelles, dendrimers and nanogels. The ability and efficiency of catalytic nanoreactors to carry out organic reactions in water, to perform cascade reaction and their ability to be recycled will be discussed.

PAMAM-modified citric acid-coated magnetic nanoparticles as pH sensitive biocompatible carrier against human breast cancer cells

Denderimer-modified magnetic nanoparticles are a promising drug delivery nanosystem which can improve the therapeutic efficacy of chemotherapy drugs and can also be beneficial as magnetic resonance (MR) images contrast agent. The present study introduces the preparation and characterization of the potential therapeutic efficiency of curcumin (CUR)-loaded denderimer-modified citric acid coated Fe₃O₄ NPs. Polyamidoamine (PAMAM, generation G₅) was used to encapsulate citric acid coated Fe₃O₄ nanoparticles. The successful preparation of CUR-loaded nanocarriers were confirmed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), and transmission electron microscopy (TEM) techniques. The loading capacity and encapsulation efficiency of CUR molecules were 12 ± 0.03% and 45.58 ± 0.41%, respectively. The anticancer effect of void CUR and CUR-loaded nanocarriers were compared to each other by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay on treated MCF-7 cell line. It can be concluded that application of nanoparticles can be more effective strategy for controlled and slow release of CUR in human breast cancer treatment.

Facile construction of organometallic rotaxane-terminated dendrimers using neutral platinum-acetylides as the main scaffold

We present the successful construction of a new family of organometallic rotaxane-terminated dendrimers using neutral platinum-acetylides as the main scaffold. The fourth generation dendrimer has 24 rotaxane moieties on the surface termini in a monodisperse manner.

Aptamer-integrated DNA nanoassembly: A simple and sensitive DNA framework to detect cancer cells

The development of powerful techniques to detect cancer cells at early stages plays a notable role in diagnosing and prognosing cancer patients and reducing mortality. This paper reports on a novel functional DNA nanoassembly capable of detecting cancer cells based on structural DNA nanotechnology. DNA nanoassemblies were constructed by the self-assembly of a DNA concatemer to a plenty of sticky-ended three-way junctions. While an aptamer moiety guided the nanoassembly to the target cancer cell, the peroxidase-mimicking DNAzymes embedded in the nanoassemblies were used as the sensing element to produce colorimetric signals. As proof-of-concept, as low as 175 cancer cells were detected by the assay, and color change was clearly distinguished by the naked eyes. The proposed system enjoys potential applications for point-of-care cancer diagnosis, with its excellent sensitivity and selectivity.

Toxicology of Engineered Nanoparticles: Focus on Poly(amidoamine) Dendrimers

Engineered nanomaterials are increasingly being developed for paints, sunscreens, cosmetics, industrial lubricants, tyres, semiconductor devices, and also for biomedical applications such as in diagnostics, therapeutics, and contrast agents. As a result, nanomaterials are being manufactured, transported, and used in larger and larger quantities, and potential impacts on environmental and human health have been raised. Poly(amidoamine) (PAMAM) dendrimers are specifically suitable for biomedical applications. They are well-defined nanoscale molecules which contain a 2-carbon ethylenediamine core and primary amine groups at the surface. The systematically variable structural architecture and the large internal free volume make these dendrimers an attractive option for drug delivery and other biomedical applications. Due to the wide range of applications, the Organisation for Economic Co-Operation and Development (OECD) have included them in their list of nanoparticles which require toxicological assessment. Thus, the toxicological impact of these PAMAM dendrimers on human health and the environment is a matter of concern. In this review, the potential toxicological impact of PAMAM dendrimers on human health and environment is assessed, highlighting work to date exploring the toxicological effects of PAMAM dendrimers.