A reexamination of active and passive tumor targeting by using rod-shaped gold nanocrystals and covalently conjugated peptide ligands

A novel amphiphilic fluorescent probe BODIPY–O-CMC–cRGD as a biomarker and nanoparticle vector

Fluorescent probes have been demonstrated to be promising candidates as biomarkers and biological carriers. Our study focuses on the development of a novel amphiphilic fluorescent probe with good photostability, high water solubility, excellent specificity and promising loading capability for tumor diagnosis and treatment. At first, BODIPY dye and O-carboxymethyl chitosan were prepared via a chemical reaction. Then, the prepared BODIPY dye and cRGD were bonded to O-carboxymethyl chitosan successively via an acylation reaction. Finally, we obtained the desired amphiphilic fluorescent probe: BODIPY–O-CMC–cRGD, which was based on the fluorescence resonance energy transfer (FRET) principle for selective visualization of tumors in vitro. Through a series of experiments, we found that this fluorescent probe possessed better fluorescence characteristics and tumor targeting properties. Simultaneously, by self-assembly, the amphiphilic probe encapsulated the other flexible structure of BODIPY2 and the rigid structure of porphyrin, which formed distinct nanoparticles with different particle sizes. Hence, we could observe different phagocytosis processes of the two nanoparticles in the tumor cells via the fluorescence of dyes by confocal laser scanning microscopy. Therefore, the results suggest that the fluorescent probe has advantages in tumor detection, and the constructed tumor-specific nanoparticles show high clinical potential to be utilized not only in visual and precise diagnosis but also in excellent drug delivery for tumor treatment. Henceforth, we will prepare new targeted and visualized pharmaceuticals by replacing BODIPY2 and porphyrin with antineoplastic drugs for future tumor treatment.

The amphipathic fluorescence probe, BODIPY–O-CMC–cRGD, can be applied in visualized diagnoses and as drug delivery vehicles of visualized therapies in the future.

Particle morphology: an important factor affecting drug delivery by nanocarriers into solid tumors

INTRODUCTION

Efficient delivery of drugs by nanoparticles deep into solid tumors is the precondition of valid cancer therapy. Despite profound understanding of the delivery of spherical nanoparticles into solid tumor attained, insufficient attention was paid to anisotropic particles. Actually, owing to their structural asymmetry, some non-spherical particles exhibit significant advantages over their spherical counterparts.

AREAS COVERED

This review will focus on particles with different shapes (discoidal particle, nanorod, filamentous particle, single-walled carbon nanotube) and the influence of their morphological characteristics (size, aspect ratio, rigidity) on the process of drug delivery to solid tumor in view of systemic circulation, transport from circulation system to tumor tissue, intratumoral transport and uptake by tumor cells, on the basis of introduction of challenges for drug delivery to solid tumor. In addition, the morphological characteristics will be briefly introduced to provide an understanding of anisotropic particle morphology.

EXPERT OPINION

Anisotropic particles exhibit desirable properties such as enhanced circulation time and efficient tumor penetration that could serve as an enlightenment in the exploitation of novel non-spherical nanocarriers to clinical therapy. Yet, current understanding of how anisotropic particles interact with organism is insufficient, which restricts the biomedical application of anisotropic particles. Further work is desired for the development of practical fabrication of anisotropic particles, quantitative analysis of particle morphology, as well as profound understanding of new targeting mechanism and intratumoral penetration of anisotropic particles.

Synthesis and Bioevaluation of Iodine-131 Directly Labeled Cyclic RGD-PEGylated Gold Nanorods for Tumor-Targeted Imaging

Introduction

Radiolabeled gold nanoparticles play an important role in biomedical application. The aim of this study was to prepare iodine-131 (¹³¹I)-labeled gold nanorods (GNRs) conjugated with cyclic RGD and evaluate its biological characteristics for targeted imaging of integrin α_vβ₃-expressing tumors.

Methods

HS-PEG₍₅₀₀₀₎-COOH molecules were applied to replace CTAB covering the surface of bare GNRs for better biocompatibility, and c(RGDfK) peptides were conjugated onto the carboxyl terminal of GNR-PEG-COOH via EDC/NHS coupling reactions. The nanoconjugate was characterized, and ¹³¹I was directly tagged on the surface of GNRs via AuI bonds for SPECT/CT imaging. We preliminarily studied the characteristics of the probe and its feasibility for tumor-targeting SPECT/CT imaging.

Results

The [¹³¹I]GNR-PEG-cRGD probe was prepared in a simple and rapid manner and was stable in both PBS and fetal bovine serum. It targeted selectively and could be taken up by tumor cells mainly via integrin α_vβ₃-receptor-mediated endocytosis. In vivo imaging, biodistribution, and autoradiography results showed evident tumor uptake in integrin α_vβ₃-expressing tumors.

Conclusions

These promising results showed that this smart nanoprobe can be used for angiogenesis-targeted SPECT/CT imaging. Furthermore, the nanoprobe possesses a remarkable capacity for highly efficient photothermal conversion in the near-infrared region, suggesting its potential as a multifunctional theranostic agent.

Platelet-Facilitated Photothermal Therapy of Head and Neck Squamous Cell Carcinoma

Here, we present a platelet-facilitated photothermal tumor therapy (PLT-PTT) strategy, in which PLTs act as carriers for targeted delivery of photothermal agents to tumor tissues and enhance the PTT effect. Gold nanorods (AuNRs) were first loaded into PLTs by electroporation and the resulting AuNR-loaded PLTs (PLT-AuNRs) inherited long blood circulation and cancer targeting characteristics from PLTs and good photothermal property from AuNRs. Using a gene-knockout mouse model, we demonstrate that the administration of PLT-AuNRs and localizing laser irradiation could effectively inhibit the growth of head and neck squamous cell carcinoma (HNSCC). In addition, we found that the PTT treatment augmented PLT-AuNRs targeting to the tumor sites and in turn, improved the PTT effects in a feedback manner, demonstrating the unique self-reinforcing characteristic of PLT-PTT in cancer therapy.

Cube-shaped theranostic paclitaxel prodrug nanocrystals with surface functionalization of SPC and MPEG-DSPE for imaging and chemotherapy

As one of nanomedicine delivery systems (NDSs), drug nanocrystals exhibited an excellent anticancer effect. Recently, differences of internalization mechanisms and subcellular localization of both drug nanocrystals and small molecular free drug have drawn much attention. In this paper, paclitaxel (PTX) as a model anticancer drug was directly labeled with 4-chloro-7-nitro-1, 2, 3-benzoxadiazole (NBD-Cl) (a drug-fluorophore conjugate Ma et al. (2016) and Wang et al. (2016) [1,2] (PTX-NBD)). PTX-NBD was synthesized by nucleophilic substitution reaction of PTX with NBD-Cl in high yield and characterized by fluorescence, XRD, ESI-MS, and FT-IR analysis. Subsequently, the cube-shaped PTX-NBD nanocrystals were prepared with an antisolvent method followed by surface functionalization of SPC and MPEG-DSPE. The obtained specific shaped PTX-NBD@PC-PEG NCs had a hydrodynamic particle size of ∼50nm, excellent colloidal stability, and a high drug-loading content of ∼64%. Moreover, in comparison with free PTX-NBD and the sphere-shaped PTX-NBD nanocrystals with surface functionalization of SPC and MPEG-DSPE (PTX-NBD@PC-PEG NSs), PTX-NBD@PC-PEG NCs remarkably reduced burst release and improved cellular uptake efficiency and in vitro cancer cell killing ability. In a word, the work highlights the potential of theranostic prodrug nanocrystals based on the drug-fluorophore conjugates for cell imaging and chemotherapy.

Polymer decorated gold nanoparticles in nanomedicine conjugates

Noble metal, especially gold nanoparticles and their conjugates with biopolymers have immense potential for disease diagnosis and therapy on account of their surface plasmon resonance (SPR) enhanced light scattering and absorption. Conjugation of noble metal nanoparticles to ligands specifically targeted to biomarkers on diseased cells allows molecular-specific imaging and detection of disease. The development of smart gold nanoparticles (AuNPs) that can deliver therapeutics at a sustained rate directly to cancer cells may provide better efficacy and lower toxicity for treating cancer tumors. We highlight some of the promising classes of targeting systems that are under development for the delivery of gold nanoparticles. Nanoparticles designed for biomedical applications are often coated with polymers containing reactive functional groups to conjugate targeting ligands, cell receptors or drugs. Using targeted nanoparticles to deliver chemotherapeutic agents in cancer therapy offers many advantages to improve drug/gene delivery and to overcome many problems associated with conventional radiotherapy and chemotherapy. The targeted nanoparticles were found to be effective in killing cancer cells which were studied using various anticancer assays. Cell morphological analysis shows the changes occurred in cancer cells during the treatment with AuNPs. The results determine the influence of particle size and concentration of AuNPs on their absorption, accumulation, and cytotoxicity in model normal and cancer cells. As the mean particle diameter of the AuNPs decreased, their rate of absorption by the intestinal epithelium cells increased. These results provide important insights into the relationship between the dimensions of AuNPs and their gastrointestinal uptake and potential cytotoxicity. Furthermore gold nanoparticles efficiently convert the absorbed light into localized heat, which can be exploited for the selective laser photothermal therapy of cancer. We also review the emerging technologies for the fabrication of targeted gold colloids as imagining agents.

Combined photothermal-chemotherapy of breast cancer by near infrared light responsive hyaluronic acid-decorated nanostructured lipid carriers

In this study, a novel type of hyaluronic acid (HA)-decorated nanostructured lipid carrier (NLC) was prepared and investigated as a light-triggered drug release and combined photothermal-chemotherapy for cancer treatment. Polyhedral gold nanoparticles (Au NPs) with an average size of 10 nm were synthesized and co-encapsulated with doxorubicin (DOX) in the matrix of NLCs with a high drug loading efficiency (above 80%). HA decoration was achieved by the electrostatic interaction between HA and CTAB on the NLC surface. A remarkable temperature increase was observed by exposing the Au NP-loaded NLCs to an NIR laser, which heated the samples sufficiently (above 40 °C) to kill tumor cells. The entrapped DOX exhibited a sustained, stepwise NIR laser-triggered drug release pattern. The biocompatibility of the NLCs was investigated by MTT assay and the cell viability was maintained above 85%, even at high concentrations. The intracellular uptake of free DOX and entrapped DOX, observed by confocal microscopy, revealed two distinct uptake mechanisms, i.e. passive diffusion and endocytosis, respectively. In particular, internalization of the HA-Au-DOX-NLCs was more extensively enhanced than the Au-DOX-NLCs, which was attributed to HA-CD44 receptor-mediated endocytosis. Meanwhile, the internalized NLCs successfully escaped from the lysosomes, increasing the intracellular DOX. The HA-Au-DOX-NLCs IC₅₀ value decreased from 2.3 to 0.6 μg ml^-1 with NIR irradiation at 72 h, indicating the excellent synergistic antitumor effect of photothermal-chemotherapy. The photothermal ablation was further confirmed by a live/dead cell staining assay. Thus, a combined photothermal-chemotherapy approach has been proposed as a promising strategy for cancer treatment.

Bridging Bio-Nano Science and Cancer Nanomedicine

The interface of bio-nano science and cancer medicine is an area experiencing much progress but also beset with controversy. Core concepts of the field-e.g., the enhanced permeability and retention (EPR) effect, tumor targeting and accumulation, and even the purpose of "nano" in cancer medicine-are hotly debated. In parallel, considerable advances in neighboring fields are occurring rapidly, including the recent progress of "immuno-oncology" and the fundamental impact it is having on our understanding and the clinical treatment of the group of diseases collectively known as cancer. Herein, we (i) revisit how cancer is commonly treated in the clinic and how this relates to nanomedicine; (ii) examine the ongoing debate on the relevance of the EPR effect and tumor targeting; (iii) highlight ways to improve the next-generation of nanomedicines; and (iv) discuss the emerging concept of working with (and not against) biology. While discussing these controversies, challenges, emerging concepts, and opportunities, we explore new directions for the field of cancer nanomedicine.

Targeting Strategies for the Combination Treatment of Cancer Using Drug Delivery Systems

Cancer cells have characteristics of acquired and intrinsic resistances to chemotherapy treatment-due to the hostile tumor microenvironment-that create a significant challenge for effective therapeutic regimens. Multidrug resistance, collateral toxicity to normal cells, and detrimental systemic side effects present significant obstacles, necessitating alternative and safer treatment strategies. Traditional administration of chemotherapeutics has demonstrated minimal success due to the non-specificity of action, uptake and rapid clearance by the immune system, and subsequent metabolic alteration and poor tumor penetration. Nanomedicine can provide a more effective approach to targeting cancer by focusing on the vascular, tissue, and cellular characteristics that are unique to solid tumors. Targeted methods of treatment using nanoparticles can decrease the likelihood of resistant clonal populations of cancerous cells. Dual encapsulation of chemotherapeutic drug allows simultaneous targeting of more than one characteristic of the tumor. Several first-generation, non-targeted nanomedicines have received clinical approval starting with Doxil® in 1995. However, more than two decades later, second-generation or targeted nanomedicines have yet to be approved for treatment despite promising results in pre-clinical studies. This review highlights recent studies using targeted nanoparticles for cancer treatment focusing on approaches that target either the tumor vasculature (referred to as 'vascular targeting'), the tumor microenvironment ('tissue targeting') or the individual cancer cells ('cellular targeting'). Recent studies combining these different targeting methods are also discussed in this review. Finally, this review summarizes some of the reasons for the lack of clinical success in the field of targeted nanomedicines.

Peptide ligand-modified nanomedicines for targeting cells at the tumor microenvironment

Since their initial discovery more than 30years ago, tumor-homing peptides have become an increasingly useful tool for targeted delivery of therapeutic and diagnostic agents into tumors. Today, it is well accepted that cells at the tumor microenvironment (TME) contribute in many ways to cancer development and progression. Tumor-homing peptide-decorated nanomedicines can interact specifically with surface receptors expressed on cells in the TME, improve cellular uptake of nanomedicines by target cells, and impair tumor growth and progression. Moreover, peptide ligand-modified nanomedicines can potentially accumulate in the target tissue at higher concentrations than would small conjugates, thus increasing overall target tissue exposure to the therapeutic agent, enhance therapeutic efficacy and reduce side effects. This review describes the most studied peptide ligands aimed at targeting cells in the TME, discusses major obstacles and principles in the design of ligands for drug targeting and provides an overview of homing peptides in ligand-targeted nanomedicines that are currently in development for cancer therapy and diagnosis.

Fusion of gelonin and anti-insulin-like growth factor-1 receptor (IGF-1R) affibody for enhanced brain cancer therapy

Owing to the extraordinary potency in inhibiting protein translation that could eventually lead to apoptosis of tumor cells, ribosome-inactivating proteins (RIPs) such as gelonin have been considered attractive drug candidates for cancer therapy. However, due to several critical obstacles (e.g., severe toxicity issues caused by a lack of selectivity in their mode of action and the low cytotoxicity via poor cellular uptake, etc.), clinical application of RIPs is yet far from being accomplished. To overcome these challenges, in the present study, we engineered gelonin fusion proteins with anti-insulin-like growth factor-1 receptor (IGF-1R) affibody ("IAFF") via the genetic recombinant method and the SpyCatcher/SpyTag-mediated conjugation method. To this end, recombinant gelonin-anti-IGF-1R affibody (rGel-IAFF), gelonin-SpyCatcher (Gel-SpyCatcher) and SpyTag-IAFF fusion proteins were produced from the E. coli expression system, and gelonin-IAFF conjugate was synthesized by mixing Gel-SpyCatcher and SpyTag-IAFF. After preparation of both rGel-IAFF and Gel-IAFF conjugate, their components' functionality was characterized in vitro. Our assay results confirmed that, while both Gel-IAFF and Gel-SpyCatcher retained equipotent N-glycosidase activity to that of gelonin, IAFF was able to selectively bind to IGF-1R overexpressed U87 MG brain cancer cells over low expression LNCaP cells. The results of cellular analyses showed that rGel-IAFF and Gel-IAFF conjugate both exhibited a greater cell uptake in the U87 MG cells than gelonin, but not in the LNCaP cells, yielding a significantly augmented cytotoxicity only in the U87 MG cells. Remarkably, rGel-IAFF and Gel-IAFF conjugate displayed 22- and 5.6-fold lower IC₅₀ values (avg. IC₅₀: 180 and 720 nM, respectively) than gelonin (avg. IC₅₀: 4000 nM) in the U87 MG cells. Overall, the results of the present research demonstrated that fusion of gelonin with IAFF could provide an effective way to enhance the anti-tumor activity, while reducing the associated toxicity of gelonin.

Improving gold nanorod delivery to the central nervous system by conjugation to the shuttle Angiopep-2

AIM

To improve the in vivo delivery of gold nanorods (GNRs) to the central nervous system of rats, these gold nanoparticles were conjugated to Angiopep-2, a shuttle peptide that can cross the blood-brain barrier.

MATERIALS & METHODS

GNRs were synthesized and modified using polyethylene glycol and Angiopep-2 (GNR-PEG-Angiopep-2). The physicochemical properties, in vitro cytotoxicity and ex vivo biodistribution of the conjugate were examined.

RESULTS

GNR-PEG-Angiopep-2 was stable over the following days, and the different concentrations that were tested did not affect the viability of microvascular endothelial cells. The conjugation of Angiopep-2 to GNRs enhanced the endocytosis of these particles (in vitro) and the accumulation in brains (in vivo), when compared with GNRs modified only with PEG.

CONCLUSION

This study provides evidence that Angiopep-2 improves the delivery of GNRs to the brain parenchyma. This property is highly relevant for future applications of GNRs as platforms for photothermal and theranostic purposes.

In vitro microfluidic models of tumor microenvironment to screen transport of drugs and nanoparticles

Advances in nanotechnology have enabled numerous types of nanoparticles (NPs) to improve drug delivery to tumors. While many NP systems have been proposed, their clinical translation has been less than anticipated primarily due to failure of current preclinical evaluation techniques to adequately model the complex interactions between the NP and physiological barriers of tumor microenvironment. This review focuses on microfluidic tumor models for characterization of delivery efficacy and toxicity of cancer nanomedicine. Microfluidics offer significant advantages over traditional macroscale cell cultures by enabling recapitulation of tumor microenvironment through precise control of physiological cues such as hydrostatic pressure, shear stress, oxygen, and nutrient gradients. Microfluidic systems have recently started to be adapted for screening of drugs and NPs under physiologically relevant settings. So far the two primary application areas of microfluidics in this area have been high-throughput screening using traditional culture settings such as single cells or multicellular tumor spheroids, and mimicry of tumor microenvironment for study of cancer-related cell-cell and cell-matrix interactions. These microfluidic technologies are also useful in modeling specific steps in NP delivery to tumor and characterize NP transport properties and outcomes by systematic variation of physiological conditions. Ultimately, it will be possible to design drug-screening platforms uniquely tailored for individual patient physiology using microfluidics. These in vitro models can contribute to development of precision medicine by enabling rapid and patient-specific evaluation of cancer nanomedicine. WIREs Nanomed Nanobiotechnol 2017, 9:e1460. doi: 10.1002/wnan.1460 For further resources related to this article, please visit the WIREs website.

Be Active or Not: the Relative Contribution of Active and Passive Tumor Targeting of Nanomaterials

Malignant tumor (cancer) remains as one of the deadliest diseases throughout the world, despite its overall mortality drops. Nanomaterials (NMs) have been widely studied as diagnostic and/or therapeutic agents for tumors. A feature of NMs, compared to small molecules, is that NMs can be concentrated passively in tumors through enhanced permeability and retention (EPR) effect. In the meantime, NMs can be engineered to target toward tumor specific markers in an active manner, e.g., receptor-mediated targeting. The relative contribution of the EPR effect and the receptor-mediated targeting to NM accumulation in tumor tissues has not been clearly defined yet. Here, we tackle this fundamental issue by reviewing previous studies. First, we summarize the current knowledge on these two tumor targeting strategies of NMs, and on how NMs arrive to tumors from blood circulation. We then demonstrate that contribution of the active and passive effects to total accumulation of NMs in tumors varies with time. Over time, the receptor-mediated targeting contributes more than the EPR effect with a ratio of 3 in the case of urokinase-type plasminogen activator receptor (uPAR)-mediated targeting and human serum albumin (HSA)-mediated EPR effect. Therefore, this review highlights the dynamics of active and passive targeting of NMs on their accumulation at tumor sites, and is valuable for future design of NMs in cancer diagnosis and treatment.

DNA origami/gold nanorod hybrid nanostructures for the circumvention of drug resistance

We herein demonstrate that DNA origami can work as a multifunctional platform integrating a chemotherapeutic drug (doxorubicin), gold nanorods and a tumour-specific aptamer MUC-1, to realize the effective circumvention of drug resistance. Doxorubicin (DOX) was loaded efficiently onto DNA origami through base pair intercalation and surface-modified gold nanorods (AuNRs) were assembled onto the DNA origami through DNA hybridization. Due to the active targeting effect of the assembled aptamers, the multifunctional nanostructures achieved increased cellular internalization of DOX and AuNRs. Upon near-infrared (NIR) laser irradiation, the P-glycoprotein (multidrug resistance pump) expression of multidrug resistant MCF-7 (MCF-7/ADR) cells was down-regulated, achieving the synergistically chemotherapeutic (DOX) and photothermal (AuNRs) effects.

A multifunctional organosilica cross-linker for the bio-conjugation of gold nanorods

We report on the use of organosilica shells to couple gold nanorods to functional peptides and modulate their physiochemical and biological profiles. In particular, we focus on the case of cell penetrating peptides, which are used to load tumor-tropic macrophages and implement an innovative drug delivery system for photothermal and photoacoustic applications. The presence of organosilica exerts subtle effects on multiple parameters of the particles, including their size, shape, electrokinetic potential, photostability, kinetics of endocytic uptake and cytotoxicity, which are investigated by the interplay of colorimetric methods and digital holographic microscopy. As a rule of thumb, as the thickness of organosilica increases from none to ∼30nm, we find an improvement of the photophysical performances at the expense of a deterioration of the biological parameters. Therefore, detailed engineering of the particles for a certain application will require a careful trade-off between photophysical and biological specifications.

18F-FDG PET/CT-based early treatment response evaluation of nanoparticle-assisted photothermal cancer therapy

Within the field of nanoparticle-assisted photothermal cancer therapy, focus has mostly been on developing novel heat-generating nanoparticles with the right optical and dimensional properties. Comparison and evaluation of their performance in tumor-bearing animals are commonly assessed by changes in tumor volume; however, this is usually a late-occurring event. This study implements 2-deoxy-2-[F-18]fluoro-D-glucose positron emission tomography imaging to perform early evaluation of the treatment outcome of photothermal therapy. Silica-gold nanoshells (NS) are administered intravenously to nude mice bearing human neuroendocrine tumor xenografts and the tumors are irradiated by a near-infrared laser. The animals are positron emission tomography scanned with 2-deoxy-2-[F-18]fluoro-D-glucose one day before and one day after treatment. Using this setup, a significant decrease in tumor uptake of 2-deoxy-2-[F-18]fluoro-D-glucose is found already one day after therapy in the group receiving NS and laser treatment compared to control animals. At this time point no change in tumor volume can be detected. Moreover, the change in tumor uptake, is used to stratify the animals into responders and non-responders, where the responding group matched improved survival. Overall, these findings support the use of 2-deoxy-2-[F-18]fluoro-D-glucose positron emission tomography imaging for preclinical and clinical evaluation and optimization of photothermal therapy.

Galectin-1-based tumour-targeting for gold nanostructure-mediated photothermal therapy

PURPOSE

To demonstrate delivery of Au nanocages to cells using the galectin-1 binding peptide anginex (Ax) and to demonstrate the value of this targeting for selective in vitro photothermal cell killing.

MATERIALS AND METHODS

Au nanocages were synthesised, coated with polydopamine (PDA), and conjugated with Ax. Tumour and endothelial cell viability was measured with and without laser irradiation. Photoacoustic (PA) mapping and PA flow cytometry were used to confirm cell targeting in vitro and in tissue slices ex vivo.

RESULTS

Cell viability was maintained at ≥50% at 100 pM suggesting low toxicity of the nanocage alone. Combining the targeted construct (25 pM) with low power 808 nm laser irradiation for 10-20 min (a duration previously shown to induce rapid and sustained heating of Au nanocages [AuNC] in solution), resulted in over 50% killing of endothelial and tumour cells. In contrast, the untargeted construct combined with laser irradiation resulted in negligible cell killing. We estimate approximately 6 × 10⁴ peptides were conjugated to each nanocage, which also resulted in inhibition of cell migration. Binding of the targeted nanocage reached a plateau after three hours, and cell association was 20-fold higher than non-targeted nanocages both in vitro and ex vivo on tumour tissue slices. A threefold increase in tumour accumulation was observed in preliminary in vivo studies.

CONCLUSIONS

These studies demonstrate Ax's potential as an effective targeting agent for Au-based theranostics to tumour and endothelial cells, enabling photothermal killing. This platform further suggests potential for multimodal in vivo therapy via next-generation drug-loaded nanocages.

Self-Assembly of Gold Nanoparticles Shows Microenvironment-Mediated Dynamic Switching and Enhanced Brain Tumor Targeting

Inorganic nanoparticles with unique physical properties have been explored as nanomedicines for brain tumor treatment. However, the clinical applications of the inorganic formulations are often hindered by the biological barriers and failure to be bioeliminated. The size of the nanoparticle is an essential design parameter which plays a significant role to affect the tumor targeting and biodistribution. Here, we report a feasible approach for the assembly of gold nanoparticles into ~80 nm nanospheres as a drug delivery platform for enhanced retention in brain tumors with the ability to be dynamically switched into the single formulation for excretion. These nanoassemblies can target epidermal growth factor receptors on cancer cells and are responsive to tumor microenvironmental characteristics, including high vascular permeability and acidic and redox conditions. Anticancer drug release was controlled by a pH-responsive mechanism. Intracellular L-glutathione (GSH) triggered the complete breakdown of nanoassemblies to single gold nanoparticles. Furthermore, in vivo studies have shown that nanospheres display enhanced tumor-targeting efficiency and therapeutic effects relative to single-nanoparticle formulations. Hence, gold nanoassemblies present an effective targeting strategy for brain tumor treatment.

Abnormality Detection in Correlated Gaussian Molecular Nano-Networks: Design and Analysis

A nano-abnormality detection scheme (NADS) in molecular nano-networks is studied. This is motivated by the fact that early detection of diseases such as cancer plays a crucial role in their successful treatment. The proposed NADS is in fact a two-tier network of sensor nano-machines (SNMs) in the first tier and a data-gathering node (DGN) at the sink. The SNMs detect the presence of competitor cells (abnormality) by variations in input and/or parameters of a nano-communications channel. The noise of SNMs as their nature suggest is considered correlated in time and space and herein assumed additive Gaussian. In the second step, the SNMs transmit micro-scale messages over a noisy micro-communications channel (MCC) to the DGN, where a decision is made upon fusing the received signals. We find an optimum design of detectors for each of the NADS tiers based on the end-to-end NADS performance. The detection performance of each SNM is analyzed by setting up a generalized likelihood ratio test. Next, taking into account the effect of the MCC, the overall performance of the NADS is analyzed in terms of probabilities of misdetection and false alarm. In addition, computationally efficient expressions to quantify the NADS performance are derived by providing, respectively, an approximation and an upper bound for the probabilities of misdetection and false alarm. This in turn enables formulating a design problem, where the optimized concentration of SNMs in a sample is obtained for a high probability of detection and a limited probability of false alarm. The results indicate that otherwise ignoring the spatial and temporal correlation of SNM noise in the analysis, leads to an NADS that noticeably underperforms in operations.The results indicate how effective fusion of the noisy observations collected from a number of SNMs with limited capabilities could provide an acceptable detection performance.

Biomedical Applications of Multifunctional Gold-Based Nanocomposites

Active application of gold nanoparticles for various diagnostic and therapeutic purposes started in recent decades due to the emergence of new data on their unique optical and physicochemical properties. In addition to colloidal gold conjugates, growth in the number of publications devoted to the synthesis and application of multifunctional nanocomposites has occurred in recent years. This review considers the application in biomedicine of multifunctional nanoparticles that can be produced in three different ways. The first method involves design of composite nanostructures with various components intended for either diagnostic or therapeutic functions. The second approach uses new bioconjugation techniques that allow functionalization of gold nanoparticles with various molecules, thus combining diagnostic and therapeutic functions in one medical procedure. Finally, the third method for production of multifunctional nanoparticles combines the first two approaches, in which a composite nanoparticle is additionally functionalized by molecules having different properties.

Harnessing supramolecular peptide nanotechnology in biomedical applications

The harnessing of peptides in biomedical applications is a recent hot topic. This arises mainly from the general biocompatibility of peptides, as well as from the ease of tunability of peptide structure to engineer desired properties. The ease of progression from laboratory testing to clinical trials is evident from the plethora of examples available. In this review, we compare and contrast how three distinct self-assembled peptide nanostructures possess different functions. We have 1) nanofibrils in biomaterials that can interact with cells, 2) nanoparticles that can traverse the bloodstream to deliver its payload and also be bioimaged, and 3) nanotubes that can serve as cross-membrane conduits and as a template for nanowire formation. Through this review, we aim to illustrate how various peptides, in their various self-assembled nanostructures, possess great promise in a wide range of biomedical applications and what more can be expected.

Synergistically enhanced selective intracellular uptake of anticancer drug carrier comprising folic acid-conjugated hydrogels containing magnetite nanoparticles

Targeted drug delivery has long been extensively researched since drug delivery and release at the diseased site with minimum dosage realizes the effective therapy without adverse side effects. In this work, to achieve enhanced intracellular uptake of anticancer drug carriers for efficient chemo-therapy, we have designed targeted multifunctional anticancer drug carrier hydrogels. Temperature-responsive poly(N-isopropylacrylamide) (PNIPAm) hydrogel core containing superparamagnetic magnetite nanoparticles (MNP) were prepared using precipitation polymerization, and further polymerized with amine-functionalized copolymer shell to facilitate the conjugation of targeting ligand. Then, folic acid, specific targeting ligand for cervical cancer cell line (HeLa), was conjugated on the hydrogel surface, yielding the ligand conjugated hybrid hydrogels. We revealed that enhanced intracellular uptake by HeLa cells in vitro was enabled by both magnetic attraction and receptor-mediated endocytosis, which were contributed by MNP and folic acid, respectively. Furthermore, site-specific uptake of the developed carrier was confirmed by incubating with several other cell lines. Based on synergistically enhanced intracellular uptake, efficient cytotoxicity and apoptotic activity of HeLa cells incubated with anticancer drug loaded hybrid hydrogels were successfully achieved. The developed dual-targeted hybrid hydrogels are expected to provide a platform for the next generation intelligent drug delivery systems.

Limiting the protein corona: A successful strategy for in vivo active targeting of anti-HER2 nanobody-functionalized nanostars

Gold nanoparticles hold great promise as anti-cancer theranostic agents against cancer by actively targeting the tumor cells. As this potential has been supported numerously during in vitro experiments, the effective application is hampered by our limited understanding and control of the interactions within complex in vivo biological systems. When these nanoparticles are exposed to a biological environment, their surfaces become covered with proteins and biomolecules, referred to as the protein corona, reducing the active targeting capabilities. We demonstrate a chemical strategy to overcome this issue by reducing the protein corona's thickness by blocking the active groups of the self-assembled monolayer on gold nanostars. An optimal blocking agent, 2-mercapto ethanol, has been selected based on charge and length of the carbon chain. By using a nanobody as a biological ligand of the human epidermal growth factor 2 receptor (HER2), the active targeting is demonstrated in vitro and in vivo in an experimental tumor model by using darkfield microscopy and photoacoustic imaging. In this study, we have established gold nanostars as a conceivable theranostic agent with a specificity for HER2-positive tumors.

Comparison of four methods for the biofunctionalization of gold nanorods by the introduction of sulfhydryl groups to antibodies

Introducing sulfhydryl groups to biomolecules to functionalize gold nanorods (GNRs) is an attractive method that involves the creation of a strong Au-S bond. Previously, we developed a facile method to functionalize GNR surfaces by thiolating antibodies using Traut's reagent. In the current study, we evaluated several methods for the introduction of thiol groups onto the surface of GNRs by using Traut's reagent, dithiotreitol (DTT), dithiolaromatic PEG6-CONHNH₂, and thiol-polyethylene glycolamine (SH-PEG-NH₂) combined with EDC reaction. We showed that the four above-mentioned thiolation methods can efficiently functionalize GNRs and simplify the functionalization procedures. The formed GNR-bioconjugates showed superior stability without compromising the biological activity. The GNR nanochip prepared with these four thiolated antibodies can detect human IgG targets with specificity. However, SH-PEG-NH₂ combined with EDC reaction may affect the amount of functionalized GNRs because of the efficiency of thiol moiety linkage to antibodies, thereby affecting the sensitivity of the GNR sensor. The introduction of a thiol group to antibodies by using Traut's reagent, DTT, and PEG6-CONHNH₂ allowed for direct immobilization onto the GNR surface, improved the efficacy of functionalized GNRs, and increased the sensitivity in response to target detection as a biosensor. Given that PEG6-CONHNH₂ modification requires glycosylated biomolecules, Traut's reagent and DTT thiolation are recommended as universal applications of GNR biofunctionalization and can be easily extended to other sensing applications based on other gold nanostructures or new biomolecules.

Self-assembly of gold nanorods coated with phospholipids: a coarse-grained molecular dynamics study

The self-assembly of phospholipid-coated gold nanorods (GNRs) was investigated by coarse-grained molecular dynamics simulations. We predict that in addition to the formation of deformed vesicles encapsulating GNRs with diverse orientations, the lipid-coated GNRs can form a semi-ring attached to an excess vesicle phase, a branch with excess vesicle phase, a ring phase, a branch phase, a stack phase, and a vortex phase. The morphologies of the lipid-GNR complexes depend on the lipid/GNR molar ratio and the interaction strength between the nanorod surface and the lipid head groups. At given lipid-nanorod interactions, removing the lipid induces a phase transition from an isolated ring or branch phase to an aggregated vortex or stack phase and vice versa. As the lipid-coated GNRs transit from an isolated phase to an aggregated phase, the structure of the lipid at the nanorod surface converts from a bilayer state to a non-bilayer state.

Early Development Challenges for Drug Products Containing Nanomaterials

The vast majority of drug product candidates in early development fail to progress to clinics. This is true for products containing nanomaterials just as for other types of pharmaceuticals. Early development pathways should therefore place high priority on experiments that help candidates fail faster and less expensively. Nanomedicines fail for many reasons, but some are more avoidable than others. Some of the points of failure are not considerations in the development of small molecules or biopharmaceuticals, and so may be unexpected, even to those with previous experience bringing drug products to the clinic. This article reviews experiments that have proven useful in providing "go/no-go" decision-making data for nanomedicines in early preclinical development. Of course, the specifics depend on the particulars of the drug product and the nanomaterial type, and not every product shares the same development pathway or the same potential points of failure. Here, we focus on challenges that differ from those in the development of traditional small molecule therapeutics, and on experiments that reveal deficiencies that can only be corrected by essentially starting over-altering the nanomedicine to an extent that all previous characterization and proof-of-concept testing must be repeated. Conducting these experiments early in the development process can save significant resources and time and allow developers to focus on derisked candidates with a greater likelihood of ultimate success.

Multifunctional gold-based nanocomposites for theranostics

Although Au-particle potential in nanobiotechnology has been recognized for the last 15 years, new insights into the unique properties of multifunctional nanostructures have just recently started to emerge. Multifunctional gold-based nanocomposites combine multiple modalities to improve the efficacy of the therapeutic and diagnostic treatment of cancer and other socially significant diseases. This review is focused on multifunctional gold-based theranostic nanocomposites, which can be fabricated by three main routes. The first route is to create composite (or hybrid) nanoparticles, whose components enable diagnostic and therapeutic functions. The second route is based on smart bioconjugation techniques to functionalize gold nanoparticles with a set of different molecules, enabling them to perform targeting, diagnostic, and therapeutic functions in a single treatment procedure. Finally, the third route for multifunctionalized composite nanoparticles is a combination of the first two and involves additional functionalization of hybrid nanoparticles with several molecules possessing different theranostic modalities. This last class of multifunctionalized composites also includes fluorescent atomic clusters with multiple functionalities.

Synergistic active targeting of dually integrin αvβ3/CD44-targeted nanoparticles to B16F10 tumors located at different sites of mouse bodies

Conventional enhanced permeation and retention (EPR) mediates the effects of many drugs, including the accumulation of nanocarriers at tumor sites, but its efficiency remains low. In this study, this limitation was overcome by developing a dual-targeting delivery system based on hyaluronan (HA, a major ligand of CD44) and tetraiodothyroacetic acid (tetrac, a specific ligand of αvβ3), which was exploited to carry docetaxel (DTX) for the synergistic active targeting to tumors. First, a tetrac-HA (TeHA) conjugate was synthesized and grafted onto the surfaces of solid lipid nanoparticles (SLNs) (TeHA-SLNs/DTX), with a high encapsulation efficiency of >91.6%. The resulting SLNs exhibited an approximately toroid morphology revealed using TEM. The cellular uptake and cytotoxicity of various formulations on CD44/αvβ3-enriched B16F10 cells were then assessed, and both results confirmed the selective uptake and high cytotoxicity of the TeHA-SLNs/DTX in a TeHA-dependent manner. In vivo imaging and vessel distribution tests revealed the efficiency of synergistic active targeting was higher than that of EPR-mediated passive targeting by the TeHA-SLNs to αvβ3-expressing tumor blood vessels and CD44-expressing tumor cells via selective targeting. Finally, in both xenograft tumor mice and in situ lung metastasis tumor mice, tumor growth was significantly inhibited by TeHA-SLNs/DTX. Therefore, TeHA-SLNs are an efficient system for the dual-targeted delivery of drugs to treat cancer in vivo.

Preparation and Photoacoustic Analysis of Cellular Vehicles Containing Gold Nanorods

Gold nanorods are attractive for a range of biomedical applications, such as the photothermal ablation and the photoacoustic imaging of cancer, thanks to their intense optical absorbance in the near-infrared window, low cytotoxicity and potential to home into tumors. However, their delivery to tumors still remains an issue. An innovative approach consists of the exploitation of the tropism of tumor-associated macrophages that may be loaded with gold nanorods in vitro. Here, we describe the preparation and the photoacoustic inspection of cellular vehicles containing gold nanorods. PEGylated gold nanorods are modified with quaternary ammonium compounds, in order to achieve a cationic profile. On contact with murine macrophages in ordinary Petri dishes, these particles are found to undergo massive uptake into endocytic vesicles. Then these cells are embedded in biopolymeric hydrogels, which are used to verify that the stability of photoacoustic conversion of the particles is retained in their inclusion into cellular vehicles. We are confident that these results may provide new inspiration for the development of novel strategies to deliver plasmonic particles to tumors.

Diffusion and Uptake of Tobacco Mosaic Virus as Therapeutic Carrier in Tumor Tissue: Effect of Nanoparticle Aspect Ratio

Nanoparticle-based technologies, including platforms derived from plant viruses, hold great promise for targeting and delivering cancer therapeutics to solid tumors by overcoming dose-limiting toxicities associated with chemotherapies. A growing body of data indicates advantageous margination and penetration properties of high aspect-ratio nanoparticles, which enhance payload delivery, resulting in increased efficacy. Our lab has demonstrated that elongated rod-shaped and filamentous macromolecular nucleoprotein assemblies from plant viruses have higher tissue diffusion rates than spherical particles. In this study, we developed a mathematical model to quantify diffusion and uptake of tobacco mosaic virus (TMV) in a spheroid system approximating a capillary-free segment of a solid tumor. Model simulations predict TMV concentration distribution with time in a tumor spheroid for different sizes and cell densities. From simulations of TMV concentration distribution, we can quantify the effect of TMV aspect ratio (e.g., nanorod length-to-width) with and without cellular uptake by modulated surface chemistry. This theoretical analysis can be applied to other viral or nonviral delivery systems to complement the experimental development of the next generation of nanotherapeutics.

Interrogating the Role of Receptor-Mediated Mechanisms: Biological Fate of Peptide-Functionalized Radiolabeled Gold Nanoparticles in Tumor Mice

To get a better insight on the transport mechanism of peptide-conjugated nanoparticles to tumors, we performed in vivo biological studies of bombesin (BBN) peptide functionalized gold nanoparticles (AuNPs) in human prostate tumor bearing mice. Initially, we sought to compare AuNPs with thiol derivatives of acyclic and macrocyclic chelators of DTPA and DOTA types. The DTPA derivatives were unable to provide a stable coordination of (67)Ga, and therefore, the functionalization with the BBN analogues was pursued for the DOTA-containing AuNPs. The DOTA-coated AuNPs were functionalized with BBN[7-14] using a unidentate cysteine group or a bidentate thioctic group to attach the peptide. AuNPs functionalized with thioctic-BBN displayed the highest in vitro cellular internalization (≈ 25%, 15 min) in gastrin releasing peptide (GRP) receptor expressing cancer cells. However, these results fail to translate to in vivo tumor uptake. Biodistribution studies following intravenous (IV) and intraperitoneal (IP) administration of nanoconjugates in tumor bearing mice indicated that the presence of BBN influences to some degree the biological profile of the nanoconstructs. For IV administration, the receptor-mediated pathway appears to be outweighed by the EPR effect. By contrast, in IP administration, it is reasoned that the GRPr-mediated mechanism plays a role in pancreas uptake.

Gold nanoparticle surface functionalization: mixed monolayer versus hetero bifunctional peg linker

To create a clinically relevant gold nanoparticle (AuNP) treatment, the surface must be functionalized with multiple ligands such as drugs, antifouling agents and targeting moieties. However, attaching several ligands of differing chemistries and lengths, while ensuring they all retain their biological functionality remains a challenge. This review compares the two most widely employed methods of surface co-functionalization, namely mixed monolayers and hetero-bifunctional linkers. While there are numerous in vitro studies successfully utilizing both surface arrangements, there is little consensus regarding their relative merits. Animal and preclinical studies have demonstrated the effectiveness of mixed monolayer functionalization and while some promising in vitro results have been reported for PEG linker capped AuNPs, any potential benefits of the approach are not yet fully understood.

Cell and nanoparticle transport in tumour microvasculature: the role of size, shape and surface functionality of nanoparticles

Through nanomedicine, game-changing methods are emerging to deliver drug molecules directly to diseased areas. One of the most promising of these is the targeted delivery of drugs and imaging agents via drug carrier-based platforms. Such drug delivery systems can now be synthesized from a wide range of different materials, made in a number of different shapes, and coated with an array of different organic molecules, including ligands. If optimized, these systems can enhance the efficacy and specificity of delivery compared with those of non-targeted systems. Emerging integrated multiscale experiments, models and simulations have opened the door for endless medical applications. Current bottlenecks in design of the drug-carrying particles are the lack of knowledge about the dispersion of these particles in the microvasculature and of their subsequent internalization by diseased cells (Bao et al. 2014 J. R. Soc. Interface 11, 20140301 (doi:10.1098/rsif.2014.0301)). We describe multiscale modelling techniques that study how drug carriers disperse within the microvasculature. The immersed molecular finite-element method is adopted to simulate whole blood including blood plasma, red blood cells and nanoparticles. With a novel dissipative particle dynamics method, the beginning stages of receptor-driven endocytosis of nanoparticles can be understood in detail. Using this multiscale modelling method, we elucidate how the size, shape and surface functionality of nanoparticles will affect their dispersion in the microvasculature and subsequent internalization by targeted cells.

Photosensitizer-loaded gold nanorods for near infrared photodynamic and photothermal cancer therapy

Despite the advancement of photodynamic therapy and photothermal therapy, the ability to form compact nanocomplex for combined photodynamic and photothermal cancer therapy under a single near infrared irradiation remains limited. In this work, we prepared an integrated sub-100 nm nanosystem for simultaneous near infrared photodynamic and photothermal cancer therapy. The nanosystem was formed by adsorption of silicon 2,3-naphthalocyanine dihydroxide onto gold nanorod followed by covalent stabilization with alkylthiol linked polyethylene glycol. The effects of alkylthiol chain length on drug loading, release and cell killing efficacy were examined using 6-mercaptohexanoic acid, 11-mercaptoundecanoic acid and 16-mercaptohexadecanoic acid. We found that the loading efficiency of silicon 2,3-naphthalocyanine dihydroxide increased and the release rate decreased with the increase of the alkylthiol chain length. We demonstrated that the combined near infrared photodynamic and photothermal therapy using the silicon 2,3-naphthalocyanine dihydroxide-loaded gold nanorods exhibit superior efficacy in cancer cell destruction as compared to photodynamic therapy and photothermal therapy alone. The nanocomplex stabilized with 16-mercaptohexadecanoic acid linked polyethylene glycol provided highest cell killing efficiency as compared to those stabilized with the other two stabilizers under low drug dose. This new nanosystem has potential to completely eradicate tumors via noninvasive phototherapy, preventing tumor reoccurrence and metastasis.

Gold nanoparticle surface functionalization: a necessary requirement in the development of novel nanotherapeutics

With several gold nanoparticle-based therapies currently undergoing clinical trials, these treatments may soon be in the clinic as novel anticancer agents. Gold nanoparticles are the subject of a wide ranging international research effort with preclinical studies underway for multiple applications including photoablation, diagnostic imaging, radiosensitization and multifunctional drug-delivery vehicles. These applications require an increasingly complex level of surface modification in order to achieve efficacy and limit off-target toxicity. This review will discuss the main obstacles in relation to surface functionalization and the chemical approaches commonly utilized. Finally, we review a range of recent preclinical studies that aim to advance gold nanoparticle treatments toward the clinic.

Targeting and retention enhancement of quantum dots decorated with amino acids in an invertebrate model organism

The use of quantum dots (QDs) in biological imaging applications and targeted drug delivery is expected to increase. However, the efficiency of QDs in drug targeting needs to be improved. Here, we show that amino acids linked to CdTe QDs significantly increased the targeted transfer efficiency and biological safety in the invertebrate model Bombyx mori. Compared with bare QDs530, the transfer efficiency of Ala- and Gly-conjugated QDs (QDs530-Ala and QDs530-Gly) in circulatory system increased by 2.6 ± 0.3 and 1.5 ± 0.3 times, and increased by 7.8 ± 0.9 and 2.9 ± 0.2 times in target tissue silk glands, respectively, after 24 h of QDs exposure. Meanwhile, the amount of conjugated QDs decreased by (68.4 ± 4.4)% and (46.7 ± 9.1)% in the non-target tissue fat body, and the speed at which they entered non-target circulating blood cells significantly decreased. The resultant QDs530-Ala revealed a better structural integrity in tissues and a longer retention time in hemolymph than that of QDs530 after exposure via the dorsal vessel. On the other hand, QDs530-Ala significantly reduced the toxicity to hemocytes, silk gland, and fat body, and reduced the amount of reactive oxygen species (ROS) in tissues.

Dose-Dependent Therapeutic Distinction between Active and Passive Targeting Revealed Using Transferrin-Coated PGMA Nanoparticles

The paradigm of using nanoparticle-based formulations for drug delivery relies on their enhanced passive accumulation in the tumor interstitium. Nanoparticles with active targeting capabilities attempt to further enhance specific delivery of drugs to the tumors via interaction with overexpressed cellular receptors. Consequently, it is widely accepted that drug delivery using actively targeted nanoparticles maximizes the therapeutic benefit and minimizes the off-target effects. However, the process of nanoparticle mediated active targeting initially relies on their passive accumulation in tumors. In this article, it is demonstrated that these two tumor-targeted drug delivery mechanisms are interrelated and dosage dependent. It is reported that at lower doses, actively targeted nanoparticles have distinctly higher efficacy in tumor inhibition than their passively targeted counterparts. However, the enhanced permeability and retention effect of the tumor tissue becomes the dominant factor influencing the efficacy of both passively and actively targeted nanoparticles when they are administered at higher doses. Importantly, it is demonstrated that dosage is a pivotal parameter that needs to be taken into account in the assessment of nanoparticle mediated targeted drug delivery.

Hyperthermia using nanoparticles--Promises and pitfalls

An ever-increasing body of literature affirms the physical and biological basis for sensitisation of tumours to conventional therapies such as chemotherapy and radiation therapy by mild temperature hyperthermia. This knowledge has fuelled the efforts to attain, maintain, measure and monitor temperature via technological advances. A relatively new entrant in the field of hyperthermia is nanotechnology which capitalises on locally injected or systemically administered nanoparticles that are activated by extrinsic energy sources to generate heat. This review describes the kinds of nanoparticles available for hyperthermia generation, their activation sources, their characteristics, and the unique opportunities and challenges with nanoparticle-mediated hyperthermia.

Crossing the barrier: treatment of brain tumors using nanochain particles

Despite advancements in surgery and radiotherapy, the aggressive forms of brain tumors, such as gliomas, are still uniformly lethal with current therapies offering only palliation complicated by significant toxicities. Gliomas are characteristically diffuse with infiltrating edges, resistant to drugs and nearly inaccessible to systemic therapies due to the brain-tumor barrier. Currently, aggressive efforts are underway to further understand brain-tumor's microenvironment and identify brain tumor cell-specific regulators amenable to pharmacologic interventions. While new potent agents are continuously becoming available, efficient drug delivery to brain tumors remains a limiting factor. To tackle the drug delivery issues, a multicomponent chain-like nanoparticle has been developed. These nanochains are comprised of iron oxide nanospheres and a drug-loaded liposome chemically linked into a 100-nm linear, chain-like assembly with high precision. The nanochain possesses a unique ability to scavenge the tumor endothelium. By utilizing effective vascular targeting, the nanochains achieve rapid deposition on the vascular bed of glioma sites establishing well-distributed drug reservoirs on the endothelium of brain tumors. After reaching the target sites, an on-command, external low-power radiofrequency field can remotely trigger rapid drug release, due to mechanical disruption of the liposome, facilitating widespread and effective drug delivery into regions harboring brain tumor cells. Integration of the nanochain delivery system with the appropriate combination of complementary drugs has the potential to unfold the field and allow significant expansion of therapies for the disease where success is currently very limited. WIREs Nanomed Nanobiotechnol 2016, 8:678-695. doi: 10.1002/wnan.1387 For further resources related to this article, please visit the WIREs website.

Specific detection of CD133-positive tumor cells with iron oxide nanoparticles labeling using noninvasive molecular magnetic resonance imaging

Background

The use of ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles to visualize cells has been applied clinically, showing the potential for monitoring cells in vivo with magnetic resonance imaging (MRI). USPIO conjugated with anti-CD133 antibodies (USPIO-CD133 Ab) that recognize the CD133 molecule, a cancer stem cell marker in a variety of cancers, was studied as a novel and potent agent for MRI contrast enhancement of tumor cells.

Materials and methods

Anti-CD133 antibodies were used to conjugate with USPIO via interaction of streptavidin and biotin for in vivo labeling of CD133-positive cells in xenografted tumors and N-ethyl-N-nitrosourea (ENU)-induced brain tumors. The specific binding of USPIO-CD133 Ab to CD133-positive tumor cells was subsequently detected by Prussian blue staining and MRI with T2-weighted, gradient echo and multiple echo recombined gradient echo images. In addition, the cellular toxicity of USPIO-CD133 Ab was determined by analyzing cell proliferation, apoptosis, and reactive oxygen species production.

Results

USPIO-CD133 Ab specifically recognizes in vitro and labels CD133-positive cells, as validated using Prussian blue staining and MRI. The assays of cell proliferation, apoptosis, and reactive oxygen species production showed no significant differences in tumor cells with or without labeling of USPIO-CD133 Ab. In vivo imaging of CD133-positive cells was demonstrated by intravenous injection of USPIO-CD133 Ab in mice with HT29 xenografted tumors. The MRI of HT29 xenografts showed several clusters of hypotensive regions that correlated with CD133 expression and Prussian blue staining for iron. In rat, brain tumors induced by transplacental ENU mutagenesis, several clusters of hypointensive zones were observed in CD133-expressing brain tumors by MRI and intravenously administered USPIO-CD133 Ab.

Conclusion

Combination of USPIO-CD133 Ab and MRI is valuable in recognizing CD133-expressing tumor cells in vitro, extracellularly labeling for cell tracking and detecting CD133-expressing tumors in xenografted tumors as well as ENU-induced rat brain tumors.