Self-assembly of pH-responsive fluorinated dendrimer-based particulates for drug delivery and noninvasive imaging

Controlling the Morphology in Electrostatic Self-Assembly via Light

Electrostatic self-assembly of macroions is an emerging area with great potential in the development of nanoscale functional objects, where photo-irradiation responsiveness can either elevate or suppress the self-assembly. The ability to control the size and shape of macroion assemblies would greatly facilitate the fabrication of desired nano-objects that can be harnessed in various applications such as catalysis, drug delivery, bio-sensors, and actuators. Here, we demonstrate that a polyelectrolyte with a size of 5 nm and multivalent counterions with a size of 1 nm can produce well-defined nanostructures ranging in size from 10-1000 nm in an aqueous environment by utilizing the concept of electrostatic self-assembly and other intermolecular non-covalent interactions including dipole-dipole interactions. The pH- and photoresponsiveness of polyelectrolytes and azo dyes provide diverse parameters to tune the nanostructures. Our findings demonstrate a facile approach to fabricating and manipulating self-assembled nanoparticles using light and neutron scattering techniques.

Self-Assembled DNA-Protein Hybrid Nanospheres: Biocompatible Nano-Drug-Carriers for Targeted Cancer Therapy

We developed hybrid nanospheres comprised of two of the most important biomolecules in nature, DNA and proteins, which have excellent biocompatibility, high drug payload capacity, in vivo imaging ability, and in vitro/in vivo cancer targeting capability. The synthesis can be done in a facile one-pot assembly system that includes three steps: step-growth polymerization of two DNA oligomers, addition of streptavidin to assemble spherical hybrid nanostructures, and functionalization of hybrid nanospheres with biotinylated aptamers. To test the feasibility of cancer targeting and drug-loading capacity of the hybrid nanospheres, MUC1-specific aptamers (MA3) were conjugated to nanosphere surfaces (apt-nanospheres), and doxorubicin (Dox) was loaded into nanospheres by DNA intercalation. The successful construction of nanospheres and apt-nanospheres was confirmed by agarose gel electrophoresis and dynamic light scattering (DLS). Their uniform spherical morphology was confirmed by transmission electron microscopy (TEM). Fluorescence spectra of nanospheres demonstrated high Dox-loading capability and slow-release characteristics. In vitro MUC1-specific binding of the apt-nanospheres was confirmed by flow cytometry and confocal microscopy. Dox-loaded apt-nanospheres significantly increased cytotoxicity of the MUC1-positive cancer cells due to aptamer-mediated selective internalization, as shown via cell viability assays. Apt-nanospheres could also be imaged in vivo through the synthesis of hybrid nanospheres using fluorescent dye-conjugated DNA strands. Finally, in vivo specific targeting ability of apt-nanospheres was confirmed in a MUC1-positive 4T1 tumor-bearing mouse model, whereas apt-nanospheres did not cause any sign of systemic toxicity in normal mice. Taken together, our self-assembled DNA-streptavidin hybrid nanospheres show promise as a biocompatible cancer targeting material for contemporary nanomedical technology.

A Multifunctional Contrast Agent for 19F-Based Magnetic Resonance Imaging

Magnetic resonance imaging, MRI, relying on ¹⁹F nuclei has attracted much attention, because the isotopes exhibit a high gyromagnetic ratio (comparable to that of protons) and have 100% natural abundance. Furthermore, due to the very low traces of intrinsic fluorine in biological tissues, fluorine labeling allows easy visualization in vivo using ¹⁹F-based MRI. However, one of the drawbacks of the available fluorine tracers is their very limited solubility in water. Here, we detail the design and preparation of a set of water-compatible fluorine-rich polymers as contrast agents that can enhance the effectiveness of ¹⁹F-based MRI. The agents are synthesized using the nucleophilic addition reaction between poly(isobutylene-alt-maleic anhydride) copolymer and a mixture of amine-appended fluorine groups and polyethylene glycol (PEG) blocks. This allows control over the polymer architecture and stoichiometry, resulting in good affinity to water solutions. We further investigate the effects of introducing additional segmental mobility to the fluorine moieties in the polymer, by inserting a PEG linker between the moieties and the polymer backbone. We find that controlling the polymer stoichiometry and introducing additional segmental mobility enhance the NMR signals and narrow the peak profile. In particular, we assess the impact of the PEG linker on T₂* and T₁ relaxation times, using a series of gradient-recalled echo images with varying echo times, TE, or recovery time, TR, respectively. We find that for equivalent concentrations, the PEG linker greatly increases T₂*, while maintaining high T₁ values, as compared to polymers without this linker. Phantom images collected from these compounds show bright signals over a background with high intensities.

Exploiting the Fluxionality of Lanthanide Complexes in the Design of Paramagnetic Fluorine Probes

Fluorine-19 MRI is increasingly being considered as a tool for biomolecular imaging, but the very poor sensitivity of this technique has limited most applications. Previous studies have long established that increasing the sensitivity of ¹⁹F molecular probes requires increasing the number of fluorine nuclei per probe as well as decreasing their longitudinal relaxation time. The latter is easily achieved by positioning the fluorine atoms in close proximity to a paramagnetic metal ion such as a lanthanide(III). Increasing the number of fluorine atoms per molecule, however, is only useful inasmuch as all of the fluorine nuclei are chemically equivalent. Previous attempts to achieve this equivalency have focused on designing highly symmetric and rigid fluorinated macrocyclic ligands. A much simpler approach consists of exploiting highly fluxional lanthanide complexes with open coordination sites that have a high affinity for phosphated and phosphonated species. Computational studies indicate that Ln^III-TREN-MAM is highly fluxional, rapidly interconverting between at least six distinct isomers. In neutral water at room temperature, Ln^III-TREN-MAM binds two or three equivalents of fluorinated phosphonates. The close proximity of the ¹⁹F nuclei to the Ln^III center in the ternary complex decreases the relaxation times of the fluorine nuclei up to 40-fold. Advantageously, the fluorophosphonate-bound lanthanide complex is also highly fluxional such that all ¹⁹F nuclei are chemically equivalent and display a single ¹⁹F signal with a small LIS. Dynamic averaging of fluxional fluorinated supramolecular assemblies thus produces effective ¹⁹F MR systems.

Co-delivery of gefitinib and hematoporphyrin by aptamer-modified fluorinated dendrimer for hypoxia alleviation and enhanced synergistic chemo-photodynamic therapy of NSCLC

Although epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs)-based molecular targeted therapy are proved to be effective in the treatment of non-small cell lung cancer (NSCLC) with EGFR mutation, its efficacy is limited by the acquired drug resistance. The combination of EGFR-TKIs with photodynamic therapy (PDT) has been explored to combat NSCLC with promising synergistic results. However, hypoxic tumor microenvironment is associated with the development of EGFR-TKIs resistance and severely limits the efficacy of PDT. Here, we synthesized an aptamer modified fluorinated dendrimer (APF) as a drug carrier and prepared nanocomplexes APFHG by encapsulation of gefitinib (Gef) and hematoporphyrin (Hp). APF has good oxygen-carrying capacity, high drug entrapment efficiency, and could release Gef and Hp in response to intracellular pH. APF can specifically recognize EGFR-positive NSCLC cells and effectively improve the tumor hypoxic microenvironment due to the targeting effect of aptamer and the good oxygen-carrying capacity of the fluorinated dendrimer. Under the laser irradiation, APFHG can significantly increase the production of the intracellular reactive oxygen species and produce a synergistic therapeutic effect in inhibition of cellular growth and induction of cell cycle arrest and apoptosis on both Gef-sensitive and Gef-resistant EGFR-mutant NSCLC cells through PDT/molecular targeted therapy. This work indicates that fluorinated dendrimer could be a potent drug delivery platform to overcome hypoxia-related resistance and the co-delivery of EGFR-TKI and photosensitizer by the fluorinated dendrimer could be a promising therapeutic approach for reversal of EGFR-TKIs resistance in EGFR mutation-positive NSCLC.

Emergence of cationic polyamine dendrimersomes: design, stimuli sensitivity and potential biomedical applications

For decades, self-assembled lipid vesicles have been widely used in clinics as nanoscale delivery systems for various biomedical applications, including treatment of various diseases. Due to their core-shell architecture and versatile nature, they have been successfully used as carriers for the delivery of a wide range of therapeutic cargos, including drugs and nucleic acids, in cancer treatment. Recently, surface-modified polyamine dendrimer-based vesicles, or dendrimersomes, have emerged as promising alternatives to lipid vesicles for various biomedical applications, due to their ease of synthesis, non-immunogenicity, stability in circulation and lower size polydispersity. This mini-review provides an overview of the recent advances resulting from the use of biomimetic hydrophobically-modified polyamine-based dendrimersomes towards biomedical applications, focusing mainly on the two most widely used polyamine dendrimers, namely polyamidoamine (PAMAM) and poly(propylene imine) (PPI) dendrimers.

19F-nanoparticles: Platform for in vivo delivery of fluorinated biomaterials for 19F-MRI

Fluorine-19 (¹⁹F) magnetic resonance imaging (MRI) features one of the most investigated and innovative techniques for quantitative and unambiguous cell tracking, providing information for both localization and number of cells. Because of the relative insensitivity of the MRI technique, a high number of magnetically equivalent fluorine atoms are required to gain detectable signals. However, an increased amount of ¹⁹F nuclei induces low solubility in aqueous solutions, making fluorine-based probes not suitable for in vivo imaging applications. In this context, nanoparticle-based platforms play a crucial role, since nanoparticles may carry a high payload of ¹⁹F-based contrast agents into the relevant cells or tissues, increase the imaging agents biocompatibility, and provide a highly versatile platform. In this review, we present an overview of the ¹⁹F-based nanoprobes for sensitive ¹⁹F-MRI, focusing on the main nanotechnologies employed to date, such as fluorine and theranostic nanovectors, including their design and applications.

Reduction-Sensitive Fluorinated-Pt(IV) Universal Transfection Nanoplatform Facilitating CT45-Targeted CRISPR/dCas9 Activation for Synergistic and Individualized Treatment of Ovarian Cancer

Compared to traditional clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) system, CRISPR/dead Cas9 (dCas9) system can precisely regulate endogenous gene expression without damaging the host gene, representing a greater potential for cancer therapy. Cancer/testis antigen 45 (CT45) is proved to enhance platinum-based chemosensitivity for individualized ovarian cancer therapy. However, the development of a single nanocarrier codelivering CRISPR/dCas9 system and chemotherapeutics for synergistic cancer therapy still faces challenges. Herein, a reduction-sensitive fluorinated-Pt(IV) universal transfection nanoplatform (PtUTP-F) is developed for the CT45-targeted CRISPR/dCas9 activation to achieve synergistic and individualized treatment of ovarian cancer. Overcoming multiple physiological barriers, PtUTP-F condensed gene can efficiently transfect into different cells including 293T cells, A2780, SKOV3, A549, and A2780/cisplatin (DDP) cancer cells, which is superior to Lipofectamine 6000. With the responsive release of gene and Pt(II) in the intracellular reducing microenvironment, PtUTP-F/dCas9-CT45 can generate CRISPR/dCas9 activation of CT45 expression for protein phosphatase 4C (PP4C) activity inhibition to hinder the DNA repair pathway and thus enhances the sensitivity to Pt(II) drugs for individualized A2780 tumor therapy. The PtUTP-F not only represents a powerful nanoplatform for CRISPR/dCas9 system delivery but also initiates a novel strategy for synergistic and individualized treatment of CRISPR/dCas9-based gene therapy with chemotherapy.

Theranostic Applications of Nanomaterials in the Field of Cardiovascular Diseases

A large percentage of people are being exposed to mortality due to cardiovascular diseases. Convention approaches have not provided satisfactory outcomes in the management of these diseases. To overcome the limitations of conventional approaches, nanomaterials like nanoparticles, nanotubes, micelles, lipid based nanocarriers, dendrimers, carbon based nano-formulations represent the new aspect of diagnosis and treatment of cardiovascular diseases. The unique inherent properties of the nanomaterials are the major reasons for their rapidly growing demand in the field of medicine. Profound knowledge in the field of nanotechnology and biomedicine is needed for the notable translation of nanomaterials into theranostic cardiovascular applications. In this review, the authors have summarized different nanomaterials which are being extensively used to diagnose and treat the diseases such as coronary heart disease, myocardial infarction, atherosclerosis, stroke and thrombosis.

Engineered non-invasive functionalized dendrimer/dendron-entrapped/complexed gold nanoparticles as a novel class of theranostic (radio)pharmaceuticals in cancer therapy

Nanomedicine represents a very significant contribution in current cancer treatment; in addition to surgical intervention, radiation and chemotherapeutic agents that unfortunately also kill healthy cells, inducing highly deleterious and often life-threatening side effects in the patient. Of the numerous nanoparticles used against cancer, gold nanoparticles had been developed for therapeutic applications. Inter alia, a large variety of dendrimers, i.e. soft artificial macromolecules, have turned up as non-viral functional nanocarriers for entrapping drugs, imaging agents, and targeting molecules. This review will provide insights into the design, synthesis, functionalization, and development in biomedicine of engineered functionalized hybrid dendrimer-tangled gold nanoparticles in the domain of cancer theranostic. Several aspects are highlighted and discussed such as 1) dendrimer-entrapped gold(0) hybrid nanoparticles for the targeted imaging and treatment of cancer cells, 2) dendrimer encapsulating gold(0) nanoparticles (Au DENPs) for the delivery of genes, 3) Au DENPs for drug delivery applications, 4) dendrimer encapsulating gold radioactive nanoparticles for radiotherapy, and 5) dendrimer/dendron-complexed gold(III) nanoparticles as technologies to take down cancer cells.

Fluoropolymers in biomedical applications: state-of-the-art and future perspectives

Biomedical applications of fluoropolymers in gene delivery, protein delivery, drug delivery, ¹⁹F MRI, PDT, anti-fouling, anti-bacterial, cell culture, and tissue engineering.

The effects of fluoroalkyl chain length and density on siRNA delivery of bioreducible poly(amido amine)s

Fluorination is an attractive strategy for the improvement of transfection efficiency of nucleic acid delivery vectors. Bioreducible poly(amido amine)s (bPAAs) are an important class of biomaterials exhibited to effectively deliver multiple nucleic acids. However, still, the effects of fluoroalkyl chain length and density of bPAA on siRNA delivery are unveiled. Here, we synthesized bPAAs and grafted with different chain lengths and densities of fluorocarbon compounds. Furthermore, we prepared a library of complexes of fluorinated bPAA and siRNA, and investigated the effects of fluorination on the siRNA delivery in vitro and in vivo. We found that all the synthesized bPAAs readily formed complexes with siRNA and the fluorinated complexes considerably achieved improved gene silencing efficacies both in vitro and in vivo. Dramatically, the gene silencing efficacy was increased with increasing fluorine contents. Heptafluorobutyric anhydride (HF) modified bPAAs achieved better gene silencing efficacy when compared with bPAAs fluorinated by trifluoroacetic anhydride (TF) and pentafluoropropionic anhydride (PF) providing the evidence for choosing of best one among fluorocarbon compounds. In addition, a combination of fluorination with bioreducibility enables efficient and safe siRNA delivery.

Significance of Ligand-Anchored Polymers for Drug Targeting in the Treatment of Colonic Disorders

Treatment of a variety of bowel diseases like Crohn's disease, ulcerative colitis, colonic cancers, colonic pathologies, and systemic delivery of drugs at the target sites can be done with the help of targeted drug delivery technique. Conventional colon specific drug delivery systems lack specificity and release significant amount of drug prior reaching the target site. Hence, efficient drug delivery system that ensures effective release of the drug at the colon is still a sought after research arena. Ligand anchored therapy is a strong and effective approach to execute drug delivery in selective target cells, for both, diagnostic, as well as therapeutic reasons. Compared to the regular drugs, such ligand anchored therapy provides added benefit of minimum toxicity and few side effects. Discovery of overexpressed receptors on diseased cells, as compared to healthy cells led to the emergence of active drug targeting. Further, drug resistance constitutes one of the major reasons of the failure of chemotherapy and presents a major obstacle for the effective treatment. The reason behind drug resistance is exposure of pathological cells/pathogens to sub-therapeutic levels of drugs due lack of specificity of therapeutics. Active targeting, specifically taken up by the target cells, can warrant exposure of pathological cells/pathogens to high drug load at the target and sparing non-target cells hence minimal damage to normal cells and least chance of drug resistance. Many ligands like antibodies, aptamers, peptides, folate, and transferrin have been discovered in the past few years. The design of nanocarriers can be incorporated with many different functions which enables functions like imaging and triggered intracellular drug release. The present review article focuses on advances in ligand anchored therapy and its significance on the progress of targeted nanocarriers. It will also establish novel concepts like multi-targeting and multi-functional nanocarriers for the treatment of colonic disorders.

Camptothecin-based dendrimersomes for gene delivery and redox-responsive drug delivery to cancer cells

Combination therapy involving chemotherapeutic drugs and genes is emerging as a promising strategy to provide a synergistic therapeutic effect, to overcome drug resistance while reducing the severe side effects associated with conventional chemotherapeutic drugs. However, the lack of nanomedicines able to simultaneously carry anti-cancer drugs and nucleic acids limits the application of this therapeutic strategy. To overcome this issue, we proposed to synthesize a pro-drug dendrimer by conjugating the PEGylated, positively charged generation 3-diaminobutyric polypropylenimine dendrimer to the anti-cancer drug camptothecin with a redox-sensitive disulphide linkage, and evaluate its efficacy to co-deliver the complexed DNA and camptothecin to cancer cells. This PEGylated pro-drug dendrimer was found to spontaneously self-assemble into cationic (∼3-5 mV) vesicles at pH 7.4, at a critical aggregation concentration of about 200 μg mL-1. These vesicles (dendrimersomes) became smaller (150-200 nm) with increasing dendrimer concentration and remained stable over 7 days. They were able to release about 70% of the conjugated camptothecin in presence of 50 mM glutathione (equivalent to the intracellular environment of tumor tissue). They could also condense more than 85% of the DNA at dendrimer : DNA weight ratios of 5 : 1 and higher. DNA condensation occurred instantly and was found to be stable for at least 24 h. This led to an enhanced cellular uptake of DNA (by up to 1.6-fold) and increased gene transfection (by up to 2.4-fold) in prostate cancer cells in comparison with the unmodified dendrimer. These novel dendrimersomes are therefore promising for single carrier-based combination cancer therapy.

Calcium phosphate nanocarriers for drug delivery to tumors: imaging, therapy and theranostics

Calcium phosphate (CaP) was engineered as a drug delivery nanocarrier nearly 50 years ago due to its biocompatibility and biodegradability. In recent years, several approaches have been developed for the preparation of size-controllable, stable and multifunctional CaP nanocarriers, and several targeting moieties have also been decorated on the surface of these nanocarriers for active targeting. The CaP nanocarriers have been utilized for loading probes, nucleic acids, anticancer drugs and photosensitizers for cancer imaging, therapy and theranostics. Herein, we reviewed the recent advances in the preparation strategies of CaP nanocarriers and the applications of these nanocarriers in tumor diagnosis, gene delivery, drug delivery and theranostics and finally provided perspectives.

19F MRI of Polymer Nanogels Aided by Improved Segmental Mobility of Embedded Fluorine Moieties

Using fluorinated probes for 19F MRI imaging is an emerging field with potential utility in cellular imaging and cell tracking in vivo, which complements conventional 1H MRI. An attractive feature of 19F-based imaging is that this is a bio-orthogonal nucleus and the naturally abundant isotope is NMR active. A significant hurdle however in the 19F MRI arises from the tendency of organic macromolecules, with multiple fluorocarbon substitutions, to aggregate in the aqueous phase. This aggregation results in significant loss of sensitivity, because the T2 relaxation times of these aggregated 19F species tend to be significantly lower. In this report, we have developed a strategy to covalently trap nanoscopic states with an optimal degree of 19F substitutions, followed by significant enhancement in T2 relaxation times through increased segmental mobility of the side chain substituents facilitated by the stimulus-responsive elements in the polymeric nanogel. In addition to NMR relaxation time based evaluations, the ability to obtain such signals are also evaluated in mouse models. The propensity of these nanoscale assemblies to encapsulate hydrophobic drug molecules and the availability of surfaces for convenient introduction of fluorescent labels suggest the potential of these nanoscale architectures for use in multimodal imaging and therapeutic applications.

Nuclear singlet multimers (NUSIMERs) with long-lived singlet states

Magnetic resonance (NMR) is a powerful tool in chemical analysis, structure determination and in medical diagnostics. Developing novel biological sensors for this field holds promise to better investigate protein structures or target diseases more efficiently. Herein, we explore nuclear spin singlet states in dendritic macromolecules as a platform molecule to develop stimuli responsive probes. We have developed a nuclear singlet multimer (NUSIMER) based on a generation 5 poly(amidoamine) dendrimer (PAMAM) which contains on average about 90 accessible nuclear spin singlet states with lifetimes up to 10-fold longer than the T 1 relaxation times (up to 10 seconds T s vs. T 1 < 0.5 seconds) in a single molecule. We demonstrate little influence on the singlet lifetime in phosphate buffer (H2O) and a high viscosity gel environment in the presence of paramagnetic oxygen. Additionally, we demonstrate an increase in singlet lifetime upon the release of a protective chemical moiety from the NUSIMER following a stimulus, whereby no change in longitudinal relaxation time is observed. The robustness and change in singlet lifetime of the NUSIMER holds promise for the development of a novel type of biosensors.

Phenylboronic acid-modified polyamidoamine-mediated delivery of short GC rich DNA for hepatocarcinoma gene therapy

Phenylboronic acid was introduced on the surface of polyamidoamine to construct a derivative PP, which was further used as a tumor-targeting carrier for realizing the delivery of short GC rich DNA (GCD).

Redox-sensitive, cholesterol-bearing PEGylated poly(propylene imine)-based dendrimersomes for drug and gene delivery to cancer cells

Stimuli-responsive nanocarriers have attracted increased attention as materials that can facilitate drug and gene delivery in cancer therapy. The present study reports the development of redox-sensitive dendrimersomes comprising disulfide-linked cholesterol-bearing PEGylated dendrimers, which can be used as drug and gene delivery systems. Two disulfide-linked cholesterol-bearing PEGylated generation 3 diaminobutyric polypropylenimine dendrimers have been successfully synthesized via an in situ two-step reaction. They were able to spontaneously self-assemble into stable, cationic, nanosized vesicles (or dendrimersomes) with lower critical aggregation concentration values for high-cholesterol-bearing vesicles. These dendrimersomes were able to entrap both hydrophilic and hydrophobic dyes, and they also showed a redox-responsive sustained release of the entrapped guests in the presence of a glutathione concentration similar to that of a cytosolic reducing environment. The high-cholesterol-bearing dendrimersomes were found to have a higher melting enthalpy, increased adsorption tendency on mica surface, entrapping ability for a larger amount of hydrophobic drugs, and increased resistance to redox-responsive environments in comparison with their low-cholesterol counterpart. In addition, both dendrimersomes were able to condense more than 85% of the DNA at all the tested ratios for the low-cholesterol vesicles, and at dendrimer : DNA weight ratios of 1 : 1 and higher for the high-cholesterol vesicles. These vesicles resulted in an enhanced cellular uptake of DNA, by up to 15-fold when compared with naked DNA with low-cholesterol vesicles. As a result, they increased the gene transfection on the PC-3 prostate cancer cell line, with the highest transfection being obtained with low-cholesterol vesicle complexes at a dendrimer : DNA weight ratio of 5 : 1 and high-cholesterol vesicle complexes at a dendrimer : DNA weight ratio of 10 : 1. These transfection levels were about 5-fold higher than those observed when treated with naked DNA. These cholesterol-bearing PEGylated dendrimer-based vesicles are, therefore, promising as redox-sensitive drugs and gene delivery systems for potential applications in combination cancer therapies.

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.

Low molecular weight PEI-based fluorinated polymers for efficient gene delivery

Fluorinated biomaterials have been reported to have promising features as non-viral gene carriers. In this study, a series of fluorinated polymeric gene carriers were synthesized via Michael addition from low molecular weight polyethyleneimine (PEI) and fluorobenzoic acids (FBAs)-based linking compounds with different numbers of fluorine atoms. The structure-activity relationship (SAR) of these materials was systematically investigated. SAR studies showed that fluorine could screen the positive charge of these polymers. However, this shielding effect of fluorine would endow fluorinated polymers with good balance between DNA condensation and release. In vitro transfection results suggested that these fluorinated polymers could mediate efficient gene delivery. Flow cytometry and confocal microscopy studies demonstrated that more efficient cell uptake could be achieved by fluorinated materials with more fluorine atoms. Cytotoxicity assays showed that these fluorinated materials exhibited very low cytotoxicity even at high mass ratios. This study demonstrates that FBA-based fluorinated biopolymers have the potential for practical application.

Self-Assembled Thermoresponsive Polymeric Nanogels for 19F MR Imaging

Magnetic resonance imaging using fluorinated contrast agents (¹⁹F MRI) enables to achive highcontrast in images due to the negligible fluorine background in living tissues. In this pilot study, we developed new biocompatible, temperature-responsive, and easily synthesized polymeric nanogels containing a sufficient concentration of magnetically equivalent fluorine atoms for ¹⁹F MRI purposes. The structure of the nanogels is based on amphiphilic copolymers containing two blocks, a hydrophilic poly[ N-(2-hydroxypropyl)methacrylamide] (PHPMA) or poly(2-methyl-2-oxazoline) (PMeOx) block, and a thermoresponsive poly[ N(2,2difluoroethyl)acrylamide] (PDFEA) block. The thermoresponsive properties of the PDFEA block allow us to control the process of nanogel self-assembly upon its heating in an aqueous solution. Particle size depends on the copolymer composition, and the most promising copolymers with longer thermoresponsive blocks form nanogels of suitable size for angiogenesis imaging or the labeling of cells (approximately 120 nm). The in vitro ¹⁹F MRI experiments reveal good sensitivity of the copolymer contrast agents, while the nanogels were proven to be noncytotoxic for several cell lines.

In vivo drug tracking with 19F MRI at therapeutic dose

Tracking drugs with 19F MRI would be beneficial for developing theranostics and optimizing drug therapy. To this end, a fluorinated dendritic amphiphile with high 19F MRI sensitivity and biocompatibility has been developed for 19F MRI tracking of doxorubicin (DOX)-loaded liposomes in mice, which may provide an effective platform to in vivo trace various drugs with 19F MRI.

Fluorine Meets Amine: Reducing Microenvironment-Induced Amino-Activatable Nanoprobes for 19F-Magnetic Resonance Imaging of Biothiols

¹⁹F-magnetic resonance imaging (MRI) is of great significance for noninvasive imaging and detection of various diseases. However, the main obstacle in the application of ¹⁹F-MRI agents stems from the unmet signal sensitivity due to the poor water solubility and restricted mobility of segments with high number of fluorine atoms. Herein, we report a kind of intracellular reducing microenvironment-induced amino-activatable ¹⁹F-MRI nanoprobe, which can be used for specific imaging of biothiols. In principle, the nanoprobe has an initial architecture of hydrophobic core, where the trifluoromethyl-containing segments are compactly packed and ¹⁹F NMR/MRI signals are quenched ("OFF" state). Upon encountering sulfydryl, the strong electron-withdrawing 2,4-dinitrobenzenesulfonyl groups are excised to recover secondary amino groups, whose p K_a is proved to be 7.21. As a consequence, the molecular weight loss of the hydrophobic segment and the protonation of amino groups induce significant disturbance of hydrophilic/hydrophobic balance, leading to the disassembly of the nanoprobes and regain of spin-spin relaxation and ¹⁹F NMR/MRI signals ("ON" state, T₂ up to 296 ± 5.3 ms). This nanoprobe shows high sensitivity and selectivity to biothiols, enabling intracellular and intratumoral imaging of glutathione. Our study not only provides a new nanoprobe candidate for biothiols imaging in vivo but also a promising strategy for the molecular design of real water-soluble and highly sensitive ¹⁹F-MRI nanoprobes.

Fluorinated Paramagnetic Complexes: Sensitive and Responsive Probes for Magnetic Resonance Spectroscopy and Imaging

Fluorine magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) of chemical and physiological processes is becoming more widespread. The strength of this technique comes from the negligible background signal in in vivo¹⁹F MRI and the large chemical shift window of ¹⁹F that enables it to image concomitantly more than one marker. These same advantages have also been successfully exploited in the design of responsive ¹⁹F probes. Part of the recent growth of this technique can be attributed to novel designs of ¹⁹F probes with improved imaging parameters due to the incorporation of paramagnetic metal ions. In this review, we provide a description of the theories and strategies that have been employed successfully to improve the sensitivity of ¹⁹F probes with paramagnetic metal ions. The Bloch-Wangsness-Redfield theory accurately predicts how molecular parameters such as internuclear distance, geometry, rotational correlation times, as well as the nature, oxidation state, and spin state of the metal ion affect the sensitivity of the fluorine-based probes. The principles governing the design of responsive ¹⁹F probes are subsequently described in a "how to" guide format. Examples of such probes and their advantages and disadvantages are highlighted through a synopsis of the literature.

A pH-responsive nanoprobe for turn-on 19F-magnetic resonance imaging

A pH-responsive MRI nanoprobe was developed by partially replacing organic linkers in ZIF-8, which displays pH-responsive in vivo¹⁹F MRI ability.

A simultaneous one pot synthesis of two fractal structures via swapping two fractal reaction kinetic states

We introduce a new class of fractal reaction kinetics wherein two or more distinct fractal structures are synthesized as parts of a singular cascade reaction in a single chemical beaker. Two examples: sphere ↔ spiral & triangle ↔ square fractals, grow 10(6) orders from a single dendrimer (8 nm) to the visible scale.

Efficient Encapsulation of Fluorinated Drugs in the Confined Space of Water-Dispersible Fluorous Supraparticles

Fluorophobic-driven assemblies of gold nanomaterials were stabilized into water-dispersible fluorous supraparticles by the film-forming protein hydrophobin II. The strategy makes use of fluorous nanomaterials of different dimensions to engineer size and inner functionalization of the resulting confined space. The inner fluorous compartments allow efficient encapsulation and transport of high loadings of partially fluorinated drug molecules in water.

Calcium-Induced Morphological Transitions in Peptide Amphiphiles Detected by 19F-Magnetic Resonance Imaging

Misregulation of extracellular Ca²⁺ can indicate bone-related pathologies. New, noninvasive tools are required to image Ca²⁺ fluxes and fluorine magnetic resonance imaging (¹⁹F-MRI) is uniquely suited to this challenge. Here, we present three, highly fluorinated peptide amphiphiles that self-assemble into nanoribbons in buffered saline and demonstrate these nanostructures can be programmed to change ¹⁹F-NMR signal intensity as a function of Ca²⁺ concentration. We determined these nanostructures show significant reduction in ¹⁹F-NMR signal as nanoribbon width increases in response to Ca²⁺, corresponding to ¹⁹F-MR image intensity reduction. Thus, these peptide amphiphiles can be used to quantitatively image biologically relevant Ca²⁺ concentrations.

Dendrimer pre-treatment enhances the skin permeation of chlorhexidine digluconate: Characterisation by in vitro percutaneous absorption studies and Time-of-Flight Secondary Ion Mass Spectrometry

Skin penetration and localisation of chlorhexidine digluconate (CHG) within the skin have been investigated in order to better understand and optimise the delivery using a nano polymeric delivery system of this topically-applied antimicrobial drug. Franz-type diffusion cell studies using in vitro porcine skin and tape stripping procedures were coupled with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) to visualise the skin during various treatments with CHG and polyamidoamine dendrimers (PAMAM). Pre-treatment of the skin with PAMAM dendrimers significantly increased the amount and depth of permeation of CHG into the skin in vitro. The effect observed was not concentration dependant in the range 0.5-10mM PAMAM. This could be important in terms of the efficiency of treatment of bacterial infection in the skin. It appears that the mechanism of enhancement is due to the PAMAM dendrimer disrupting skin barrier lipid conformation or by occluding the skin surface. Franz-type diffusion cell experiments are complimented by the detailed visualisation offered by the semi-quantitative ToF-SIMS method which provides excellent benefits in terms of sensitivity and fragment ion specificity. This allows a more accurate depth profile of chlorhexidine permeation within the skin to be obtained and potentially affords the opportunity to map the co-localisation of permeants with skin structures, thus providing a greater ability to characterise skin absorption and to understand the mechanism of permeation, providing opportunities for new and more effective therapies.

Combining Fluorination and Bioreducibility for Improved siRNA Polyplex Delivery

Polycations are promising vectors for the delivery of siRNA therapeutics but they often suffer from toxicity and low in vivo delivery efficacy. This study tests the hypothesis that combining fluorination and bioreducibility of polycations will overcome problems with both the toxicity and delivery efficacy. To test the hypothesis, we synthesized bioreducible (RHB) and nonreducible (NHB) poly(amido amine)s. The RHB were additionally fluorinated using reaction with heptafluorobutyric anhydride to obtain F-RHB. We found that both RHB and F-RHB showed significantly reduced cytotoxicity compared with NHB, which allowed their safe use in a wider range of doses than NHB. All three synthesized polycations formed polyplexes with siRNA. F-RHB achieved the best siRNA silencing efficacy in multiple cell lines in vitro, which was at least in part because of fluorination-induced enhancement of cellular uptake and improved endosomal escape. Lastly, F-RHB showed greatly improved Luc silencing efficacy in tumors in vivo when compared with polyplexes based on RHB, NHB, as well as control poly(ethylenimine) (PEI). This study suggests that combining fluorination with bioreducibility of polycations is a promising strategy to the design of siRNA delivery vectors with improved toxicity and in vivo activity profiles.

Stimuli-responsive dendrimers in drug delivery

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

Fe- and Ln-DOTAm-F12 Are Effective Paramagnetic Fluorine Contrast Agents for MRI in Water and Blood

A series of fluorinated macrocyclic complexes, M-DOTAm-F12, where M is La^III, Eu^III, Gd^III, Tb^III, Dy^III, Ho^III, Er^III, Tm^III, Yb^III, and Fe^II, was synthesized, and their potential as fluorine magnetic resonance imaging (MRI) contrast agents was evaluated. The high water solubility of these complexes and the presence of a single fluorine NMR signal, two necessary parameters for in vivo MRI, are substantial advantages over currently used organic polyfluorocarbons and other reported paramagnetic ¹⁹F probes. Importantly, the sensitivity of the paramagnetic probes on a per fluorine basis is at least 1 order of magnitude higher than that of diamagnetic organic probes. This increased sensitivity is due to a substantial-up to 100-fold-decrease in the longitudinal relaxation time (T₁) of the fluorine nuclei. The shorter T₁ allows for a greater number of scans to be obtained in an equivalent time frame. The sensitivity of the fluorine probes is proportional to the T₂/T₁ ratio. In water, the optimal metal complexes for imaging applications are those containing Ho^III and Fe^II, and to a lesser extent Tm^III and Yb^III. Whereas T₁ of the lanthanide complexes are little affected by blood, the T₂ are notably shorter in blood than in water. The sensitivity of Ln-DOTAm-F12 complexes is lower in blood than in water, such that the most sensitive complex in water, Ho^III-DOTAm-F12, could not be detected in blood. Tm^III yielded the most sensitive lanthanide fluorine probe in blood. Notably, the relaxation times of the fluorine nuclei of Fe^II-DOTAm-F12 are similar in water and in blood. That complex has the highest T₂/T₁ ratio (0.57) and the lowest limit of detection (300 μM) in blood. The combination of high water solubility, single fluorine signal, and high T₂/T₁ of M-DOTAm-F12 facilitates the acquisition of three-dimensional magnetic resonance images.

Cross-linked polymers with fluorinated bridges for efficient gene delivery

A new strategy for the construction of fluorinated cationic polymers for gene delivery was introduced.

Nucleobase-modified polyamidoamine-mediated miR-23b delivery to inhibit the proliferation and migration of lung cancer

The nucleobase analogue 2-amino-6-chloropurine was modified on the surface of polyamidoamine (PAMAM) to construct a derivative AP-PAMAM, and then it was used as a gene carrier for miR-23b delivery to achieve the anti-tumor effects.

pH-Sensitive stimulus-responsive nanocarriers for targeted delivery of therapeutic agents

In recent years miscellaneous smart micro/nanosystems that respond to various exogenous/endogenous stimuli including temperature, magnetic/electric field, mechanical force, ultrasound/light irradiation, redox potentials, and biomolecule concentration have been developed for targeted delivery and release of encapsulated therapeutic agents such as drugs, genes, proteins, and metal ions specifically at their required site of action. Owing to physiological differences between malignant and normal cells, or between tumors and normal tissues, pH-sensitive nanosystems represent promising smart delivery vehicles for transport and delivery of anticancer agents. Furthermore, pH-sensitive systems possess applications in delivery of metal ions and biomolecules such as proteins, insulin, etc., as well as co-delivery of cargos, dual pH-sensitive nanocarriers, dual/multi stimuli-responsive nanosystems, and even in the search for new solutions for therapy of diseases such as Alzheimer's. In order to design an optimized system, it is necessary to understand the various pH-responsive micro/nanoparticles and the different mechanisms of pH-sensitive drug release. This should be accompanied by an assessment of the theoretical and practical challenges in the design and use of these carriers. WIREs Nanomed Nanobiotechnol 2016, 8:696-716. doi: 10.1002/wnan.1389 For further resources related to this article, please visit the WIREs website.

(19)F Magnetic Resonance Imaging Signals from Peptide Amphiphile Nanostructures Are Strongly Affected by Their Shape

Magnetic resonance imaging (MRI) is a noninvasive imaging modality that provides excellent spatial and temporal resolution. The most commonly used MR probes face significant challenges originating from the endogenous (1)H background signal of water. In contrast, fluorine MRI ((19)F MRI) allows quantitative probe imaging with zero background signal. Probes with high fluorine content are required for high sensitivity, suggesting nanoscale supramolecular assemblies containing (19)F probes offer a potentially useful strategy for optimum imaging as a result of improved payload. We report here on supramolecular nanostructures formed by fluorinated peptide amphiphiles containing either glutamic acid or lysine residues in their sequence. We identified molecules that form aggregates in water which transition from cylindrical to ribbon-like shape as pH increased from 4.5 to 8.0. Interestingly, we found that ribbon-like nanostructures had reduced magnetic resonance signal, whereas their cylindrical counterparts exhibited strong signals. We attribute this drastic difference to the greater mobility of fluorinated tails in the hydrophobic compartment of cylindrical nanostructures compared to lower mobility in ribbon-like assemblies. This discovery identifies a strategy to design supramolecular, self-assembling contrast agents for (19)F MRI that can spatially map physiologically relevant changes in pH using changes in morphology.

Well-defined poly(vinylidene fluoride) (PVDF) based-dendrimers synthesized by click chemistry: enhanced crystallinity of PVDF and increased hydrophobicity of PVDF films

This study reports the preparation of a novel fluorinated dendrimer bearing PVDF branches by click chemistry and its characterization by several analytical methods.