pH-titratable superparamagnetic iron oxide for improved nanoparticle accumulation in acidic tumor microenvironments

Tumor-selective catalytic nanomedicine by nanocatalyst delivery

Tumor cells metabolize in distinct pathways compared with most normal tissue cells. The resulting tumor microenvironment would provide characteristic physiochemical conditions for selective tumor modalities. Here we introduce a concept of sequential catalytic nanomedicine for efficient tumor therapy by designing and delivering biocompatible nanocatalysts into tumor sites. Natural glucose oxidase (GOD, enzyme catalyst) and ultrasmall Fe₃O₄ nanoparticles (inorganic nanozyme, Fenton reaction catalyst) have been integrated into the large pore-sized and biodegradable dendritic silica nanoparticles to fabricate the sequential nanocatalyst. GOD in sequential nanocatalyst could effectively deplete glucose in tumor cells, and meanwhile produce a considerable amount of H₂O₂ for subsequent Fenton-like reaction catalyzed by Fe₃O₄ nanoparticles in response to mild acidic tumor microenvironment. Highly toxic hydroxyl radicals are generated through these sequential catalytic reactions to trigger the apoptosis and death of tumor cells. The current work manifests a proof of concept of catalytic nanomedicine by approaching selectivity and efficiency concurrently for tumor therapeutics.The specific metabolism of cancer cells may allow for selective tumor therapeutics. Here, the authors show that a suitable combination of an enzyme and iron nanoparticles loaded on dendritic silica induces apoptosis of cancer cells in response to the glucose-reliant and mild acidic microenvironment.

One-pot synthesis of nanochain particles for targeting brain tumors

To synthesize multi-component nanochains, we developed a simple 'one-pot' synthesis, which exhibited high yield and consistency. The nanochains particles consist of parent nanospheres chemically linked into a higher-order, chain-like assembly. The one-pot synthesis is based on the addition of two types of parent nanospheres in terms of their surface chemical functionality (e.g., decorated with PEG-NH₂ or PEG-COOH). By reacting the two types of parent nanospheres at a specific ratio (∼2 : 1) for a short period of time (∼30 min) under rigorous stirring, nanochains were formed. For example, we show the synthesis of iron oxide nanochains with lengths of about 125 nm consisting of 3-5 constituting nanospheres. The chain-like shaped nanoparticle possessed a unique ability to target and rapidly deposit on the endothelium of glioma sites via vascular targeting. To target and image invasive brain tumors, we used iron oxide nanochains with the targeting ligand being the fibronectin-targeting peptide CREKA. Overexpression of fibronectin is strongly associated with the perivascular regions of glioblastoma multiforme and plays a critical role in migrating and invasive glioma cells. In mice with invasive glioma tumors, 3.7% of the injected CREKA-targeted nanochains was found in gliomas within 1 h. Notably, the intratumoral deposition of the nanochain was ∼2.6-fold higher than its spherical variant. Using MR imaging, the precise targeting of nanochains to gliomas provided images with the exact topology of the disease including their margin of infiltrating edges and distant invasive sites.

Cu2+-Loaded Polydopamine Nanoparticles for Magnetic Resonance Imaging-Guided pH- and Near-Infrared-Light-Stimulated Thermochemotherapy

Cancer multimodal treatment by combining the effects of different theranostics agents can efficiently improve treatment efficacy and reduce side effects. In this work, we demonstrate the theranostics nanodevices on the basis of Cu²⁺-loaded polydopamine nanoparticles (CuPDA NPs), which are able to offer magnetic resonance imaging (MRI)-guided thermochemotherapy (TCT). Systematical studies reveal that after Cu²⁺ ions loading, the molar extinction coefficient of PDA NPs is greatly enhanced by 4 times, thus improving the performance in photothermal therapy. Despite Cu²⁺ ions being toxic, the release of Cu²⁺ is mainly stimulated in acidic environment. Once the NPs deposit in the slightly acidic tumor microenvironment (pH ≈ 6.5-6.8), the release rate boosts ∼30%, which effectively avoids the systematic toxicity during chemotherapy. Meanwhile, due to the increment of the electron-proton dipole-dipole interaction correlation time τ_C, the spin-lattice relaxation time (T₁) for PDA NPs is found to be shortened by Cu²⁺ loading, which boosts the longitudinal relaxivity (r₁). Hence, CuPDA NPs can be used as T₁-weighted contrast agent in MRI. In addition, due to the naturally existing DA in the human body with stealth effect, CuPDA NPs have an outstanding tumor retention rate as high as 8.2% ID/g. Further in vitro and in vivo tests indicate that CuPDA NPs possess long blood circulation time, good photothermal and physiological stability, and biocompatibility, which are potential nanodevices for MRI-guided TCT with minimal side effects.

Interactions of Renal-Clearable Gold Nanoparticles with Tumor Microenvironments: Vasculature and Acidity Effects

The success of nanomedicines in the clinic depends on our comprehensive understanding of nano-bio interactions in tumor microenvironments, which are characterized by dense leaky microvasculature and acidic extracellular pH (pHe ) values. Herein, we investigated the accumulation of ultrasmall renal-clearable gold NPs (AuNPs) with and without acidity targeting in xenograft mouse models of two prostate cancer types, PC-3 and LNCaP, with distinct microenvironments. Our results show that both sets of AuNPs could easily penetrate into the tumors but their uptake and retention were mainly dictated by the tumor microvasculature and the enhanced permeability and retention effect over the entire targeting process. On the other hand, increased tumor acidity indeed enhanced the uptake of AuNPs with acidity targeting, but only for a limited period of time. By making use of simple surface chemistry, these two effects can be synchronized in time for high tumor targeting, opening new possibilities to further improve the targeting efficiencies of nanomedicines.

Extracellular matrix remodeling in vivo for enhancing tumor-targeting efficiency of nanoparticle drug carriers using the pulsed high intensity focused ultrasound

Dense and stiff extracellular matrix (ECM) in heterogeneous tumor tissues can inhibit deep penetration of nanoparticle drug carriers and decreases their therapeutic efficacy. Herein, we suggest the ECM remodeling strategy by the pulsed high intensity focused ultrasound (Pulsed-HIFU) technology for enhanced tumor-targeting of nanoparticles. First, we clearly observed that the tumor-targeting efficacy and tissue penetration of intravenously injected Cy5.5-labled glycol chitosan nanoparticles (Cy5.5-CNPs) were greatly inhibited in tumor tissue containing high collagen and hyaluronan contents in ECM-rich A549 tumor-bearing mice, compared to in ECM-less SCC7. When collagenase or hyaluronidase was treated by intra-tumoral injection, the amount of collagen and hyaluronan decreased in ECM-rich A549 tumor tissues and more Cy5.5-CNPs penetrated inside the tumor tissue, confirmed using non-invasive optical imaging. Finally, in order to break down the stiff ECM structure, ECM-rich A549 tumor tissues were treated with the relatively low power of Pulse-HIFU (20W/cm²), wherein acute tissue damage was not observed. As we expected, the A549 tumor tissues showed the remodeling of ECM structure after non-invasive Pulsed-HIFU exposure, which resulted in the increased blood flow, decreased collagen contents, and enhanced penetration of CNP_S. Importantly, the tumor targeting efficiency in Pulsed-HIFU-treated A549 tumor tissues was 2.5 times higher than that of untreated tumor tissues. These overall results demonstrate that ECM remodeling and disruption of collagen structure by Pulse-HIFU is promising strategy to enhance the deep penetration and enhanced tumor targeting of nanoparticles in ECM-rich tumor tissues.

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.

Current Multistage Drug Delivery Systems Based on the Tumor Microenvironment

The development of traditional tumor-targeted drug delivery systems based on EPR effect and receptor-mediated endocytosis is very challenging probably because of the biological complexity of tumors as well as the limitations in the design of the functional nano-sized delivery systems. Recently, multistage drug delivery systems (Ms-DDS) triggered by various specific tumor microenvironment stimuli have emerged for tumor therapy and imaging. In response to the differences in the physiological blood circulation, tumor microenvironment, and intracellular environment, Ms-DDS can change their physicochemical properties (such as size, hydrophobicity, or zeta potential) to achieve deeper tumor penetration, enhanced cellular uptake, timely drug release, as well as effective endosomal escape. Based on these mechanisms, Ms-DDS could deliver maximum quantity of drugs to the therapeutic targets including tumor tissues, cells, and subcellular organelles and eventually exhibit the highest therapeutic efficacy. In this review, we expatiate on various responsive modes triggered by the tumor microenvironment stimuli, introduce recent advances in multistage nanoparticle systems, especially the multi-stimuli responsive delivery systems, and discuss their functions, effects, and prospects.

Imaging the Tumor Microenvironment

The tumor microenvironment consists of tumor, stromal, and immune cells, as well as extracellular milieu. Changes in numbers of these cell types and their environments have an impact on cancer growth and metastasis. Non-invasive imaging of aspects of the tumor microenvironment can provide important information on the aggressiveness of the cancer, whether or not it is metastatic, and can also help to determine early response to treatment. This chapter provides an overview on non-invasive in vivo imaging in humans and mouse models of various cell types and physiological parameters that are unique to the tumor microenvironment. Current clinical imaging and research investigation are in the areas of nuclear imaging (positron emission tomography (PET) and single photon emission computed tomography (SPECT)), magnetic resonance imaging (MRI) and optical (near infrared (NIR) fluorescence) imaging. Aspects of the tumor microenvironment that have been imaged by PET, MRI and/or optical imaging are tumor associated inflammation (primarily macrophages and T cells), hypoxia, pH changes, as well as enzymes and integrins that are highly prevalent in tumors, stroma and immune cells. Many imaging agents and strategies are currently available for cancer patients; however, the investigation of novel avenues for targeting aspects of the tumor microenvironment in pre-clinical models of cancer provides the cancer researcher with a means to monitor changes and evaluate novel treatments that can be translated into the clinic.

Mesoporous carbon nanomaterials in drug delivery and biomedical application

Recent development of nano-technology provides highly efficient and versatile treatment methods to achieve better therapeutic efficacy and lower side effects of malignant cancer. The exploration of drug delivery systems (DDSs) based on nano-material shows great promise in translating nano-technology to clinical use to benefit patients. As an emerging inorganic nanomaterial, mesoporous carbon nanomaterials (MCNs) possess both the mesoporous structure and the carbonaceous composition, endowing them with superior nature compared with mesoporous silica nanomaterials and other carbon-based materials, such as carbon nanotube, graphene and fullerene. In this review, we highlighted the cutting-edge progress of carbon nanomaterials as drug delivery systems (DDSs), including immediate/sustained drug delivery systems and controlled/targeted drug delivery systems. In addition, several representative biomedical applications of mesoporous carbon such as (1) photo-chemo synergistic therapy; (2) delivery of therapeutic biomolecule and (3) in vivo bioimaging are discussed and integrated. Finally, potential challenges and outlook for future development of mesoporous carbon in biomedical fields have been discussed in detail.

Hierarchical Targeting Strategy for Enhanced Tumor Tissue Accumulation/Retention and Cellular Internalization

Targeted delivery of therapeutic agents is an important way to improve the therapeutic index and reduce side effects. To design nanoparticles for targeted delivery, both enhanced tumor tissue accumulation/retention and enhanced cellular internalization should be considered simultaneously. So far, there have been very few nanoparticles with immutable structures that can achieve this goal efficiently. Hierarchical targeting, a novel targeting strategy based on stimuli responsiveness, shows good potential to enhance both tumor tissue accumulation/retention and cellular internalization. Here, the recent design and development of hierarchical targeting nanoplatforms, based on changeable particle sizes, switchable surface charges and activatable surface ligands, will be introduced. In general, the targeting moieties in these nanoplatforms are not activated during blood circulation for efficient tumor tissue accumulation, but re-activated by certain internal or external stimuli in the tumor microenvironment for enhanced cellular internalization.

Multicomponent, peptide-targeted glycol chitosan nanoparticles containing ferrimagnetic iron oxide nanocubes for bladder cancer multimodal imaging

While current imaging modalities, such as magnetic resonance imaging (MRI), computed tomography, and positron emission tomography, play an important role in detecting tumors in the body, no single-modality imaging possesses all the functions needed for a complete diagnostic imaging, such as spatial resolution, signal sensitivity, and tissue penetration depth. For this reason, multimodal imaging strategies have become promising tools for advanced biomedical research and cancer diagnostics and therapeutics. In designing multimodal nanoparticles, the physicochemical properties of the nanoparticles should be engineered so that they successfully accumulate at the tumor site and minimize nonspecific uptake by other organs. Finely altering the nano-scale properties can dramatically change the biodistribution and tumor accumulation of nanoparticles in the body. In this study, we engineered multimodal nanoparticles for both MRI, by using ferrimagnetic nanocubes (NCs), and near infrared fluorescence imaging, by using cyanine 5.5 fluorescence molecules. We changed the physicochemical properties of glycol chitosan nanoparticles by conjugating bladder cancer-targeting peptides and loading many ferrimagnetic iron oxide NCs per glycol chitosan nanoparticle to improve MRI contrast. The 22 nm ferrimagnetic NCs were stabilized in physiological conditions by encapsulating them within modified chitosan nanoparticles. The multimodal nanoparticles were compared with in vivo MRI and near infrared fluorescent systems. We demonstrated significant and important changes in the biodistribution and tumor accumulation of nanoparticles with different physicochemical properties. Finally, we demonstrated that multimodal nanoparticles specifically visualize small tumors and show minimal accumulation in other organs. This work reveals the importance of finely modulating physicochemical properties in designing multimodal nanoparticles for bladder cancer imaging.

T1-Weighted MR imaging of liver tumor by gadolinium-encapsulated glycol chitosan nanoparticles without non-specific toxicity in normal tissues

Herein, we have synthesized Gd(iii)-encapsulated glycol chitosan nanoparticles (Gd(iii)-CNPs) for tumor-targeted T1-weighted magnetic resonance (MR) imaging. The T1 contrast agent, Gd(iii), was successfully encapsulated into 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-modified CNPs to form stable Gd(iii)-encapsulated CNPs (Gd(iii)-CNPs) with an average particle size of approximately 280 nm. The stable nanoparticle structure of Gd(iii)-CNPs is beneficial for liver tumor accumulation by the enhanced permeation and retention (EPR) effect. Moreover, the amine groups on the surface of Gd(iii)-CNPs could be protonated and could induce fast cellular uptake at acidic pH in tumor tissue. To assay the tumor-targeting ability of Cy5.5-labeled Gd(iii)-CNPs, near-infrared fluorescence (NIRF) imaging and MR imaging were used in a liver tumor model as well as a subcutaneous tumor model. Cy5.5-labeled Gd(iii)-CNPs generated highly intense fluorescence and T1 MR signals in tumor tissues after intravenous injection, while DOTAREM®, the commercialized control MR contrast agent, showed very low tumor-targeting efficiency on MR images. Furthermore, damaged tissues were found in the livers and kidneys of mice injected with DOTAREM®, but there were no obvious adverse effects with Gd(iii)-CNPs. Taken together, these results demonstrate the superiority of Gd(iii)-CNPs as a tumor-targeting T1 MR agent.

Chemistry of Mesoporous Organosilica in Nanotechnology: Molecularly Organic-Inorganic Hybridization into Frameworks

Organic-inorganic hybrid materials aiming to combine the individual advantages of organic and inorganic components while overcoming their intrinsic drawbacks have shown great potential for future applications in broad fields. In particular, the integration of functional organic fragments into the framework of mesoporous silica to fabricate mesoporous organosilica materials has attracted great attention in the scientific community for decades. The development of such mesoporous organosilica materials has shifted from bulk materials to nanosized mesoporous organosilica nanoparticles (designated as MONs, in comparison with traditional mesoporous silica nanoparticles (MSNs)) and corresponding applications in nanoscience and nanotechnology. In this comprehensive review, the state-of-art progress of this important hybrid nanomaterial family is summarized, focusing on the structure/composition-performance relationship of MONs of well-defined morphology, nanostructure, and nanoparticulate dimension. The synthetic strategies and the corresponding mechanisms for the design and construction of MONs with varied morphologies, compositions, nanostructures, and functionalities are overviewed initially. Then, the following part specifically concentrates on their broad spectrum of applications in nanotechnology, mainly in nanomedicine, nanocatalysis, and nanofabrication. Finally, some critical issues, presenting challenges and the future development of MONs regarding the rational synthesis and applications in nanotechnology are summarized and discussed. It is highly expected that such a unique molecularly organic-inorganic nanohybrid family will find practical applications in nanotechnology, and promote the advances of this discipline regarding hybrid chemistry and materials.

Functional nanoparticles for magnetic resonance imaging

Nanoparticle-based magnetic resonance imaging (MRI) contrast agents have received much attention over the past decade. By virtue of a high payload of magnetic moieties, enhanced accumulation at disease sites, and a large surface area for additional modification with targeting ligands, nanoparticle-based contrast agents offer promising new platforms to further enhance the high resolution and sensitivity of MRI for various biomedical applications. T ₂ * superparamagnetic iron oxide nanoparticles (SPIONs) first demonstrated superior improvement on MRI sensitivity. The prevailing SPION attracted growing interest in the development of refined nanoscale versions of MRI contrast agents. Afterwards, T ₁ -based contrast agents were developed, and became the most studied subject in MRI due to the positive contrast they provide that avoids the susceptibility associated with MRI signal reduction. Recently, chemical exchange saturation transfer (CEST) contrast agents have emerged and rapidly gained popularity. The unique aspect of CEST contrast agents is that their contrast can be selectively turned 'on' and 'off' by radiofrequency saturation. Their performance can be further enhanced by incorporating a large number of exchangeable protons into well-defined nanostructures. Besides activatable CEST contrast agents, there is growing interest in developing nanoparticle-based activatable MRI contrast agents responsive to stimuli (pH, enzyme, etc.), which improves sensitivity and specificity. In this review, we summarize the recent development of various types of nanoparticle-based MRI contrast agents, and have focused our discussions on the key advantages of introducing nanoparticles in MRI. WIREs Nanomed Nanobiotechnol 2016, 8:814-841. doi: 10.1002/wnan.1400 For further resources related to this article, please visit the WIREs website.

Mesoporous manganese silicate coated silica nanoparticles as multi-stimuli-responsive T1-MRI contrast agents and drug delivery carriers

A novel kind of monodisperse mesoporous manganese silicate coated silica nanoparticle (MMSSN) as a highly efficient T1-weighted MRI contrast agent (CA) and drug carrier for cancer diagnosis and chemotherapy has been constructed by a modified "SiO2 sacrifice and in situ silicate growth" approach under a relatively low hydrothermal temperature and alkali-free condition. The mesoporous manganese silicate shell provides a large specific surface area and abundant exposed Mn paramagnetic centers to water molecules, which endows the MMSSNs with extraordinarily high longitudinal relaxivity. Meanwhile, the MMSSNs presented an efficient pH/redox-responsive T1-MRI feature based on the significant enhancement of relaxation rate (r1) stimulated by mild acidic environment or reducing agent (GSH) both in vitro and in vivo. Furthermore, the mesoporous structure and negatively charged pore surface of the manganese silicate shell enable the MMSSNs to attain anti-cancer drug (DOX) storage and a pH-responsive release, which is suitable for on-demand drug release for the chemotherapy of tumors. Therefore, the mesoporous manganese silicate-based nanomaterial is a promising candidate as T1-MRI CAs and anticancer-drug delivery carriers for the theranostics of tumor in an intelligent and on-demand manner.

STATEMENT OF SIGNIFICANCE

MRI is one of the most frequently used imaging techniques in daily clinics for cancer diagnosis. Using contrast agents (CAs) in MRI can afford much clearer and enlarged images of detectable organs. Gadolinium (Gd(3+))-based T1-positive CAs are widely used but associated with the risk of nephrogenic systemic fibrosis. To achieve much safer CAs, various Mn(2+)-based T1-positive CAs have been reported, such as MnO or core-shell MnOx-based nanoparticles. However, the efficiency of these CAs is still lower. Herein, we report a novel kind of mesoporous manganese silicate coated silica nanoparticle as CA and anti-cancer drug carrier. Results obtained from this study, especially the pH/redox-responsive T1-MRI feature are helpful for us to further design efficient MnSiO3-based materials for clinical MRI applications.

An affinity triggered MRI nanoprobe for pH-dependent cell labeling

The pH-sensitive affinity pair composed by neutravidin and iminobiotin was used to develop a multilayered Magnetic Resonance Imaging (MRI) nanoprobe responsive to the acidic pH of tumor microenvironment.

Efficient free radical generation against cancer cells by low-dose X-ray irradiation with a functional SPC delivery nanosystem

SPC@HMSNs–PAA can provide oxygen, which induce overproduction of radicals to kill cancer cells even under low energy X-ray irradiation.

Development of self-assembling peptide nanovesicle with bilayers for enhanced EGFR-targeted drug and gene delivery

Development of rational vectors for efficient drug and gene delivery is crucial for cancer treatment. In this study, epidermal growth factor receptor (EGFR)-binding peptide amphiphile (PA) were used as the primary bilayer skeleton material to construct ultra-stable self-assembling peptide nanovesicle (SPV). The resulted EGFR-targeted SPV (ESPV) could efficiently encapsulate therapeutic cargos (drugs or small interfering RNAs [siRNAs]) or labelled fluorescent cargo (quantum dots [QDs]) and exhibited excellent affinity for EGFR-positive cancer cells. Moreover, ESPV could deliver more drug or plasmid DNA to tumour sites and promote gene expression (a three-fold ratio of ESPVs vs cationic liposomes). Notably, the individual delivery or co-delivery of doxorubicin (DOX) and the acetylcholinesterase (AChE) gene via the ESPVs resulted in excellent drug/gene delivery both in vitro and in vivo and exerted a significant growth-suppressing effect on a liver cancer xenograft. This nanoscale, targeted cargo-packaging technology may provide a new strategy for the design of highly targeted cancer therapy vectors.

A simple method for the synthesis of porous polymeric vesicles and their application as MR contrast agents

Because of their low membrane permeability the use of polymeric vesicles in certain drug delivery and molecular imaging applications and as bioreactors is less than ideal. Here, we report a simple method to prepare porous polymeric vesicles that possess high membrane permeability. Specifically, porous vesicles were produced from the aqueous assembly of the diblock copolymer PEG-PBD, and the triblock copolymer PEG-PPO-PEG. It was found that PEG-PPO-PEG-doped polymersomes exhibited improved membrane permeability to molecules less than 5 kDa. Further, these porous vesicles retained molecules ≥10 kDa within their aqueous interiors with no significant leakage. To demonstrate its application, highly efficient magnetic resonance contrast agents were produced from porous polymersomes by encapsulating macromolecules labeled with gadolinium. Due to a fast water exchange rate with surrounding bulk water, these paramagnetic porous polymersomes exhibited higher r₁ relaxivity compared with Gd-encapsulated vesicles with no pores. Due to their simplicity, the porous polymersomes prepared with this method are expected to have additional useful applications.

Clearance Pathways and Tumor Targeting of Imaging Nanoparticles

A basic understanding of how imaging nanoparticles are removed from the normal organs/tissues but retained in the tumors is important for their future clinical applications in early cancer diagnosis and therapy. In this review, we discuss current understandings of clearance pathways and tumor targeting of small-molecule- and inorganic-nanoparticle-based imaging probes with an emphasis on molecular nanoprobes, a class of inorganic nanoprobes that can escape reticuloendothelial system (RES) uptake and be rapidly eliminated from the normal tissues/organs via kidneys but can still passively target the tumor with high efficiency through the enhanced permeability permeability and retention (EPR) effect. The impact of nanoparticle design (size, shape, and surface chemistry) on their excretion, pharmacokinetics, and passive tumor targeting were quantitatively discussed. Synergetic integration of effective renal clearance and EPR effect offers a promising pathway to design low-toxicity and high-contrast-enhancement imaging nanoparticles that could meet with the clinical translational requirements of regulatory agencies.

Dual-Enzyme-Loaded Multifunctional Hybrid Nanogel System for Pathological Responsive Ultrasound Imaging and T2-Weighted Magnetic Resonance Imaging

A dual-enzyme-loaded multifunctional hybrid nanogel probe (SPIO@GCS/acryl/biotin-CAT/SOD-gel, or SGC) has been developed for dual-modality pathological responsive ultrasound (US) imaging and enhanced T2-weighted magnetic resonance (MR) imaging. This probe is composed of functionalized superparamagnetic iron oxide particles, a dual enzyme species (catalase and superoxide dismutase), and a polysaccharide cationic polymer glycol chitosan gel. The dual-modality US/MR imaging capabilities of the hybrid nanogel for responsive US imaging and enhanced T2-weighted MR imaging have been evaluated both in vitro and in vivo. These results show that the hybrid nanogel SGC can exhibit efficient dual-enzyme biocatalysis with pathological species for responsive US imaging. SGC also demonstrates increased accumulation in acidic environments for enhanced T2-weighted MR imaging. Further research on these nanogel systems may lead to the development of more efficient US/MR contrast agents.

A "Smart" ¹²⁸Xe NMR Biosensor for pH-Dependent Cell Labeling

Here we present a "smart" xenon-129 NMR biosensor that undergoes a peptide conformational change and labels cells in acidic environments. To a cryptophane host molecule with high Xe affinity, we conjugated a 30mer EALA-repeat peptide that is α-helical at pH 5.5 and disordered at pH 7.5. The (129)Xe NMR chemical shift at room temperature was strongly pH-dependent (Δδ = 3.4 ppm): δ = 64.2 ppm at pH 7.5 vs δ = 67.6 ppm at pH 5.5, where Trp(peptide)-cryptophane interactions were evidenced by Trp fluorescence quenching. Using hyper-CEST NMR, we probed peptidocryptophane detection limits at low-picomolar (10(-11) M) concentration, which compares favorably to other NMR pH reporters at 10(-2)-10(-3) M. Finally, in biosensor-HeLa cell solutions, peptide-cell membrane insertion at pH 5.5 generated a 13.4 ppm downfield cryptophane-(129)Xe NMR chemical shift relative to pH 7.5 studies. This highlights new uses for (129)Xe as an ultrasensitive probe of peptide structure and function, along with potential applications for pH-dependent cell labeling in cancer diagnosis and treatment.

Lysosome-controlled efficient ROS overproduction against cancer cells with a high pH-responsive catalytic nanosystem

Excess reactive oxygen species (ROS) have been proved to damage cancer cells efficiently. ROS overproduction is thus greatly desirable for cancer therapy. To date, ROS production is generally uncontrollable and outside cells, which always bring severe side-effects in the vasculature. Since most ROS share a very short half-life and primarily react close to their site of formation, it would be more efficient if excess ROS are controllably produced inside cancer cells. Herein, we report an efficient lysosome-controlled ROS overproduction via a pH-responsive catalytic nanosystem (FeOx-MSNs), which catalyze the decomposition of H2O2 to produce considerable ROS selectively inside the acidic lysosomes (pH 5.0) of cancer cells. After a further incorporation of ROS-sensitive TMB into the nanosystem (FeOx-MSNs-TMB), both a distinct cell labeling and an efficient death of breast carcinoma cells are obtained. This lysosome-controlled efficient ROS overproduction suggests promising applications in cancer treatments.

Real-time monitoring of arsenic trioxide release and delivery by activatable T(1) imaging

Delivery of arsenic trioxide (ATO), a clinical anticancer drug, has drawn much attention to improve its pharmacokinetics and bioavailability for efficient cancer therapy. Real-time and in situ monitoring of ATO behaviors in vivo is highly desirable for efficient tumor treatment. Herein, we report an ATO-based multifunctional drug delivery system that efficiently delivers ATO to treat tumors and allows real-time monitoring of ATO release by activatable T1 imaging. We loaded water-insoluble manganese arsenite complexes, the ATO prodrug, into hollow silica nanoparticles to form a pH-sensitive multifunctional drug delivery system. Acidic stimuli triggered the simultaneous release of manganese ions and ATO, which dramatically increased the T1 signal (bright signal) and enabled real-time visualization and monitoring of ATO release and delivery. Moreover, this smart multifunctional drug delivery system significantly improved ATO efficacy and strongly inhibited the growth of solid tumors without adverse side effects. This strategy has great potential for real-time monitoring of theranostic drug delivery in cancer diagnosis and therapy.

High molecular weight chitosan derivative polymeric micelles encapsulating superparamagnetic iron oxide for tumor-targeted magnetic resonance imaging

Magnetic resonance imaging (MRI) contrast agents based on chitosan derivatives have great potential for diagnosing diseases. However, stable tumor-targeted MRI contrast agents using micelles prepared from high molecular weight chitosan derivatives are seldom reported. In this study, we developed a novel tumor-targeted MRI vehicle via superparamagnetic iron oxide nanoparticles (SPIONs) encapsulated in self-aggregating polymeric folate-conjugated N-palmitoyl chitosan (FAPLCS) micelles. The tumor-targeting ability of FAPLCS/SPIONs was demonstrated in vitro and in vivo. The results of dynamic light scattering experiments showed that the micelles had a relatively narrow size distribution (136.60±3.90 nm) and excellent stability. FAPLCS/SPIONs showed low cytotoxicity and excellent biocompatibility in cellular toxicity tests. Both in vitro and in vivo studies demonstrated that FAPLCS/SPIONs bound specifically to folate receptor-positive HeLa cells, and that FAPLCS/SPIONs accumulated predominantly in established HeLa-derived tumors in mice. The signal intensities of T2-weighted images in established HeLa-derived tumors were reduced dramatically after intravenous micelle administration. Our study indicates that FAPLCS/SPION micelles can potentially serve as safe and effective MRI contrast agents for detecting tumors that overexpress folate receptors.

Tumor extracellular acidity activated “off–on” release of bortezomib from a biocompatible dendrimer

A nanoparticle with a specific response to tumor extracellular acidity provides a new option in the design of tumor-targeted delivery systems.

Nanogel Carrier Design for Targeted Drug Delivery

Polymer-based nanogel formulations offer features attractive for drug delivery, including ease of synthesis, controllable swelling and viscoelasticity as well as drug loading and release characteristics, passive and active targeting, and the ability to formulate nanogel carriers that can respond to biological stimuli. These unique features and low toxicity make the nanogels a favorable option for vascular drug targeting. In this review, we address key chemical and biological aspects of nanogel drug carrier design. In particular, we highlight published studies of nanogel design, descriptions of nanogel functional characteristics and their behavior in biological models. These studies form a compendium of information that supports the scientific and clinical rationale for development of this carrier for targeted therapeutic interventions.

Break-up of two-dimensional MnO2 nanosheets promotes ultrasensitive pH-triggered theranostics of cancer

Chemically exfoliated two-dimensional MnO2 nanosheets are successfully modified with amino-polyethylene glycol as a theranostic platform for ultrasensitive stimuli-responsive theranostics of cancer. The highly dispersed MnO2 nanosheets exhibit a unique break-up in the mildly acidic microenvironment of tumor tissues, which could substantially enhance their in vitro and in vivo performances in T1 -weighted magnetic resonance imaging. Such a pH-triggered breaking-up behavior could further promote the fast release of loaded anticancer drugs for concurrent pH-responsive drug release and circumvent the multidrug resistance of cancer cells.

A smart "sense-act-treat" system: combining a ratiometric pH sensor with a near infrared therapeutic gold nanocage

Herein, we design a "sense-act-treat" system via the combination of a ratiometric pH sensor with a therapeutic gold nanocage. Our design could "sense" the tumor through two-state switching of fluorescence and further provide chemotherapy and hyperthermia for "treating" the tumor, showing the potential for future biomedical applications.

Tumor-targeting glycol chitosan nanoparticles as a platform delivery carrier in cancer diagnosis and therapy

A natural based polymer, chitosan has received widespread attention in drug delivery systems due to its valuable physicochemical and biological characteristics. In particular, hydrophobic moiety-conjugated glycol chitosan can form amphiphilic self-assembled glycol chitosan nanoparticles (GCNPs) and simultaneously encapsulate hydrophobic drug molecules inside their hydrophobic core. This GCNP-based drug delivery systems exhibit excellent tumor-homing efficacy, attributed to the long blood circulation and the enhanced permeability and retention effect; this tumor-targeting drug delivery results in improved therapeutic efficiency. In this review, we describe the requisite properties of GCNPs for cancer therapy as well as imaging for diagnosis, such as their basic characteristics, in vitro delivery efficiency and in vivo tumor-targeting ability.

Self-assembled glycol chitosan nanoparticles for disease-specific theranostics

Hydrophobically modified glycol chitosan (hGC) conjugates spontaneously form self-assembled nanoparticles (NPs) in aqueous conditions, and glycol chitosan NPs (CNPs) have been extensively studied for the past few decades. For disease-specific theranostics, CNPs could be simply modified with imaging agents, and the hydrophobic domains of hGC are available for encapsulation of various drugs. Based on the excellent physiochemical and biological properties, CNPs have been investigated for multimodal imaging and target specific drug delivery. In particular, a recent application of CNPs has shown great potential as an efficient theranostic system because the CNPs could be utilized for a disease-specific theranostic delivery system of different imaging agents and therapeutics, simultaneously. Furthermore, various therapeutic agents including chemo-drugs, nucleotides, peptides, and photodynamic chemicals could be simply encapsulated into the CNPs through hydrophobic or charge-charge interactions. Under in vivo conditions, the encapsulated imaging agents and therapeutic drugs have been successfully delivered to targeted diseases. In this article, the overall research progress on CNPs is reviewed from early works. The current challenges of CNPs to overcome in theranostics are also discussed, and continuous studies would provide more opportunities for early diagnosis of diseases and personalized medicine.

Progress in the characterization of bio-functionalized nanoparticles using NMR methods and their applications as MRI contrast agents

Significant progress has been made over the last three decades in the field of NMR, a technique which has proven to have a variety of applications in many scientific disciplines, including nanotechnology. Herein we describe how NMR enables the characterization of nanosystems at different stages of their formation and modification (raw materials, bare or functionalized nanosystems), even making it possible to study in vivo nanoparticle interactions, thereby importantly contributing to nanoparticle design and subsequent optimization. Furthermore, the unique characteristics of nanosystems can open up new prospects for site-targeted, more specific contrast agents, contributing to the development of certain nuclear magnetic resonance applications such as MRI.

Polymeric nanoparticles for molecular imaging

Conventional imaging technologies (X-ray computed tomography, magnetic resonance, and optical) depend on contrast agents to visualize a target site or organ of interest. The imaging agents currently used in clinics for diagnosis suffer from disadvantages including poor target specificity and in vivo instability. Consequently, delivery of low concentrations of contrast agents to region of interest affects image quality. Therefore, it is important to selectively deliver high payload of contrast agent to obtain clinically useful images. Nanoparticles offer multifunctional capabilities to transport high concentrations of imaging probes selectively to diseased site inside the body. Polymeric nanoparticles, incorporated with contrast agents, have shown significant benefits in molecular imaging applications. These materials possess the ability to encapsulate different contrast agents within a single matrix enabling multimodal imaging possibilities. The materials can be surface conjugated to target-specific biomolecules for controlling the navigation under in vivo conditions. The versatility of this class of nanomaterials makes them an attractive platform for developing highly sensitive molecular imaging agents. The research community's progress in the area of synthesis of polymeric nanomaterials and their in vivo imaging applications has been noteworthy, but it is still in the pioneer stage of development. The challenges ahead should focus on the design and fabrication of these materials including burst release of contrasts agents, solubility, and stability issues of polymeric nanomaterials.

Nanoprobes visualizing gliomas by crossing the blood brain tumor barrier

The difficulty in delineating the glioma margins in brain is a major obstacle for its completed resection, which leads to the disproportionately high recurrence and mortality. Besides the fast exertion rate, inadequate sensitivity and non-targeting specificity, the main reason leading to failure of small molecular probes to define gliomas is their incapability to efficiently cross the blood brain tumor barrier (BBTB). Nanoprobes (NPs) show promise to precisely delineate the geographically irregular tumor margins due to their tunable size/circulation lifetime that maximize their passive intratumoral accumulation and their convenience for surface modification that increases the BBTB transcytosis efficacy, imaging sensitivity and receptor targeting specificity. In this work, the characteristics of the BBTB are addressed from biological and physiological perspectives, strategies are presented to deliver NPs across the BBTB, recent developments of NPs are reviewed for glioma visualization and finally the difficulty and promise for clinical translation of NPs are described. Overall, NPs hold great potential for glioma imaging and treatment by pre-surgically delineating tumor margins and intra-operatively guiding tumor excision.

Engineering cytochrome-modified silica nanoparticles to induce programmed cell death

A low native membrane permeability and ineffective access to the cellular cytosol, together with aggressive proteolytic degradation, often severely hampers the practical application of any therapeutic protein or antibody. Through engineering the charging profile of mesoporous silica nanoparticles, cellular uptake and subsequent subcellular distribution can be controlled. We show herein that programmed cell death can subsequently be induced across a population of cancer cells with remarkable efficacy on conjugating a specific caspase-cascade-activating cytochrome to such cytosol-accessing particles.

A pH-responsive polymer/mesoporous silica nano-container linked through an acid cleavable linker for intracellular controlled release and tumor therapy in vivo

This paper proposes a pH-responsive polymer/mesoporous silica nano-container linked through an acid cleavable linker for intracellular controlled release and tumor therapy in vivo. In this system, the poly(acrylic acid) homopolymer (PAA), as a nanoscopic cap, is grafted onto the MSN through an acid cleavable linker (PAA-ACL-MSN). Doxorubicin (DOX), as a model drug, is used to assess the drug release behaviors and tumor therapy. At neutral pH, the linker is intact, resulting in blockage of pores and package of DOX. By the degradation of the linker at acidic pH, the grafted PAA is removed, which gives rise to uncapping and the subsequent pH-responsive controlled release of DOX. In vitro studies using a nasopharyngeal carcinoma cell line (HNE-1) prove that DOX loaded PAA-ACL-MSN (DOX@PAA-ACL-MSN) is endocytosed and demonstrates efficient operation at lysosomal pH, leading to significant cytotoxicity. As a preliminary tumor therapy in vivo, the progressive tumor development and inhibition following DOX@PAA-ACL-MSN treatment is monitored using bioluminescence imaging. By the examination of cell proliferation in tumor tissues and the comparison of body weight, it is revealed that the DOX@PAA-ACL-MSN is superior to free DOX in terms of therapeutic efficacy and side effects due to the enhanced permeability and retention effects and lower pH in tumor areas. We believe that this developed MSN based delivery system will provide a promising nanodevice for tumor therapy.

A computational framework for identifying design guidelines to increase the penetration of targeted nanoparticles into tumors

Targeted nanoparticles are increasingly being engineered for the treatment of cancer. By design, they can passively accumulate in tumors, selectively bind to targets in their environment, and deliver localized treatments. However, the penetration of targeted nanoparticles deep into tissue can be hindered by their slow diffusion and a high binding affinity. As a result, they often localize to areas around the vessels from which they extravasate, never reaching the deep-seeded tumor cells, thereby limiting their efficacy. To increase tissue penetration and cellular accumulation, we propose generalizable guidelines for nanoparticle design and validate them using two different computer models that capture the potency, motion, binding kinetics, and cellular internalization of targeted nanoparticles in a section of tumor tissue. One strategy that emerged from the models was delaying nanoparticle binding until after the nanoparticles have had time to diffuse deep into the tissue. Results show that nanoparticles that are designed according to these guidelines do not require fine-tuning of their kinetics or size and can be administered in lower doses than classical targeted nanoparticles for a desired tissue penetration in a large variety of tumor scenarios. In the future, similar models could serve as a testbed to explore engineered tissue-distributions that arise when large numbers of nanoparticles interact in a tumor environment.

Gd-labeled glycol chitosan as a pH-responsive magnetic resonance imaging agent for detecting acidic tumor microenvironments

Neoplastic lesions can create a hostile tumor microenvironment with low extracellular pH. It is commonly believed that these conditions can contribute to tumor progression as well as resistance to therapy. We report the development and characterization of a pH-responsive magnetic resonance imaging contrast agent for imaging the acidic tumor microenvironment. The preparation included the conjugation of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid 1-(2,5-dioxo-1-pyrrolidinyl) ester (DOTA-NHS) to the surface of a water-soluble glycol chitosan (GC) polymer, which contains pH-titrable primary amines, followed by gadolinium complexation (GC-NH2-GdDOTA). GC-NH2-GdDOTA had a chelate-to-polymer ratio of approximately1:24 and a molar relaxivity of 9.1 mM(-1) s(-1). GC-NH2-GdDOTA demonstrated pH-dependent cellular association in vitro compared to the control. It also generated a 2.4-fold enhancement in signal in tumor-bearing mice 2 h postinjection. These findings suggest that glycol chitosan coupled with contrast agents can provide important diagnostic information about the tumor microenvironment.

In vivo anti-cancer efficacy of magnetite nanocrystal--based system using locoregional hyperthermia combined with 5-fluorouracil chemotherapy

We present an approach for synchronizing hyperthermia and thermal-responsive local drug release. The targeting probe has a magnetite nanocrystal (Fe₃O₄@PSMA) core and a polynucleotide shell that carries 5-fluorouracil (5-FU) and anti-human epidermal growth factor receptor 2 (anti-HER2) antibody for cancer cell-specific targeting. The targeting nanocrystals play as an important role to relay the externally delivered radiofrequency energy for tumor hyperthermia. Locoregional heat then triggers a drug release from the oligonucleotide carrier as it directly damages tumor cells. Cell viability assays and pathological examinations show that this synchronization is significantly more efficacious in both in vitro and in vivo models than hyperthermia or chemotherapy alone. Prominent tumor remission in vivo was achieved through radiofrequency synchronization of hyperthermia and chemotherapy after the nanoparticle had been intravenously injected.