MR molecular imaging of HER‐2 in a murine tumor xenograft by SPIO labeling of anti‐HER‐2 affibody

In vivo molecular imaging is a rapidly growing research area both for basic and clinical science. Non‐invasive imaging of in vivo conditions at the molecular level increases understanding of the biological characteristics of normal and diseased tissues without the need for invasive surgical procedures. Among the various imaging modalities, magnetic resonance imaging (MRI) has garnered interest as a molecular imaging modality due to its high spatial resolution. Here, we have demonstrated that the combined use of HER‐2 targeting affibody, a small 7 kDa molecule that behaves similarly to antibodies, and superparamagnetic iron oxide (SPIO) can non‐invasively image HER‐2 expressing cells or tissues both in vitro and in vivo by MRI. This preliminary study demonstrates that affibody‐SPIO is a feasible, target‐specific contrast agent for in vivo MR molecular imaging. Copyright © 2010 John Wiley & Sons, Ltd.     

Superparamagnetic iron oxide nanoparticles for in vivo molecular and cellular imaging

In the last decade, the biomedical applications of nanoparticles (NPs) (e.g. cell tracking, biosensing, magnetic resonance imaging (MRI), targeted drug delivery, and tissue engineering) have been increasingly developed. Among the various NP types, superparamagnetic iron oxide NPs (SPIONs) have attracted considerable attention for early detection of diseases due to their specific physicochemical properties and their molecular imaging capabilities. A comprehensive review is presented on the recent advances in the development of in vitro and in vivo SPION applications for molecular imaging, along with opportunities and challenges. Copyright © 2015 John Wiley & Sons, Ltd.     

Increased transverse relaxivity in ultrasmall superparamagnetic iron oxide nanoparticles used as MRI contrast agent for biomedical imaging

Synthesis of a contrast agent for biomedical imaging is of great interest where magnetic nanoparticles are concerned, because of the strong influence of particle size on transverse relaxivity. In the present study, biocompatible magnetic iron oxide nanoparticles were synthesized by co‐precipitation of Fe²⁺ and Fe³⁺ salts, followed by surface adsorption with reduced dextran. The synthesized nanoparticles were spherical in shape, and 12 ± 2 nm in size as measured using transmission electron microscopy; this was corroborated with results from X‐ray diffraction and dynamic light scattering studies. The nanoparticles exhibited superparamagnetic behavior, superior T₂ relaxation rate and high relaxivities (r₁ = 18.4 ± 0.3, r₂ = 90.5 ± 0.8 s^?1 mM^?1, at 7 T). MR image analysis of animals before and after magnetic nanoparticle administration revealed that the signal intensity of tumor imaging, specific organ imaging and whole body imaging can be clearly distinguished, due to the strong relaxation properties of these nanoparticles. Very low concentrations (3.0 mg Fe/kg body weight) of iron oxides are sufficient for early detection of tumors, and also have a clear distinction in pre‐ and post‐enhancement of contrast in organs and body imaging. Many investigators have demonstrated high relaxivities of magnetic nanoparticles at superparamagnetic iron oxide level above 50 nm, but this investigation presents a satisfactory, ultrasmall, superparamagnetic and high transverse relaxivity negative contrast agent for diagnosis in pre‐clinical studies. Copyright © 2016 John Wiley & Sons, Ltd.     

Magnetic resonance nanoparticles for cardiovascular molecular imaging and therapy

Molecular vascular imaging represents a novel tool that promises to change the current medical paradigm of ‘see and treat’ to a ‘detect and prevent’ strategy. Nanoparticle agents, such as superparamagnetic nanoparticles and perfluorocarbon nanoparticle emulsions, have been developed for noninvasive imaging, particularly for magnetic resonance imaging. Designed to target specific epitopes in tissues, these agents are beginning to enter clinical trials for cardiovascular applications. The delivery of local therapy with these nanoparticles, using mechanisms such as contact-facilitated drug delivery, is in the advanced stages of preclinical research. Ultimately, combined diagnostic and therapeutic nanoparticle formulations may allow patients to be characterized noninvasively and segmented to receive custom-tailored therapy. This review focuses on recent developments of nanoparticle technologies with an emphasis on cardiovascular applications of magnetic resonance imaging.     

In vivo visualization of transplanted pancreatic islets by MRI: comparison between in vivo,histological and electron microscopy findings

The aim of the work was to compare in vivo MRI visualization of pancreatic islets labeled with clinical‐grade superparamagnetic iron oxide (SPIOs) contrast agents with ex vivo examination of liver tissue in an experimental model of marginal mass transplantation in rats. Seven hundred IEq (Islet Equivalent) from Wistar rats, labeled by incubation with Endorem® or Resovist®, were transplanted into Sprague–Dawley rats through the portal vein. Liver MR images of recipient rats were acquired at different time points (3–42 days) after transplantation. Animals were sacrificed during this period and their livers were excised and prepared for histology and electron microscopy. Hypointense spots originating from iron particles were observed in MR images. The number of separate spots was counted. Three days after transplantation one spot for every three or four transplanted islets was observed. Seven days after transplantation, histological sections showed the presence of iron within pancreatic islets. The time course of MR images showed a decrease in the number of spots, at 42 days, amounting to 65 and 22% of the initial value, for Resovist® and Endorem® respectively, while no immunopositive endocrine cells were detected in histological slices. The present work shows that pancreatic islets can be labeled using clinically approved SPIO contrast agents and visualized using in vivo MRI with high sensitivity, consistently with findings in the literature. Differently from reports in the literature, our findings indicate that iron particles could last in the liver for long periods, independently of the presence of intact pancreatic islets. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface functionalization of superparamagnetic nanoparticles for the development of highly efficient magnetic resonance probe for macrophages

In vivo magnetic resonance imaging (MRI) tracking of macrophages plays an important role in monitoring and understanding numerous human diseases with high macrophage activity. In this work, superparamagnetic iron oxide nanoparticles (SPIONs) of ～12 nm were surface‐functionalized with poly(DL ‐lactic acid‐co‐malic acid) copolymer (PLMA) via a nanoprecipitation method. The r₁, r₂ and r₂/r₁ values of the PLMA‐SPIONs obtained at a magnetic field of 3 T were 0.38, 196 and 516 mM ^?1 s^?1, respectively. The high r₂/r₁ ratio can be expected to provide enhanced MR contrast. The PLMA‐SPIONs were readily taken in by macrophages and the high iron uptake was confirmed via Prussian Blue staining and quantified by inductively coupled plasma mass spectrometry (ICP‐MS). No significant cytotoxicity was found even at a high nanoparticle loading of 67.7 pg Fe per cell. A linear relationship between R₂ and R values and the number of PLMA‐SPIONs labeled cells was observed in vitro. As a result of the significantly higher R than R₂ effects, an in vitro detection threshold of about 2820 labeled cells was achieved with short labeling time and low nanoparticle concentration using a clinical 3 T MRI scanner. Thus, the PLMA‐SPIONs can be potentially useful as magnetic resonance probes for targeting and tracking macrophages. Copyright © 2011 John Wiley & Sons, Ltd.     

Dual‐modality in vivo monitoring of subventricular zone stem cell migration and metabolism

Rat subventricular zone (SVZ) stem cells were labeled with superparamagnetic iron oxide particles (SPIO) to follow their fate and migratory potential with magnetic resonance imaging (MRI) and positron emission tomography (PET). Labeled cells were transplanted into either the right rostral migratory stream (RMS) or striatum of normal adult Sprague–Dawley rats and serially followed for 3 months. Minimal migration of the cells implanted into the striatum was observed after 3 weeks whereas SVZ cells implanted into the RMS migrated toward the olfactory bulb at 1 week post‐transplantation. PET studies of glucose metabolism using ¹⁸F‐FDG demonstrated enhanced glucose utilization in the striatum of transplanted animals. PET studies conducted 3 months after transplantation showed elevated accumulation of ¹¹C‐raclopride (dopamine receptor type 2) and ¹¹C‐CFT (dopamine transporter) binding in the striatal grafts. Implanted SVZ cells did not induce significant inflammation as identified by PET using ¹¹C‐PK11195, a ligand detecting activated microglia. Histological analysis identified viable SPIO‐labeled cells (some of which were nestin‐positive) 7 weeks post‐transplantation, suggesting a prolonged presence of undifferentiated neural stem cells within transplants. In addition, double immunostaining for neuronal and astrocytic markers (NeuN and GFAP) indicated that differentiation into neuronal and astrocytic phenotypes also occurred. Thus, combining MRI and PET enables monitoring of cell migration and metabolism non‐invasively in vivo for extended periods of time. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and in vitro evaluation of MR molecular imaging probes using J591 mAb‐conjugated SPIONs for specific detection of prostate cancer

Carcinoma of the prostate is the most frequent diagnosed malignant tumor in men and is the second leading cause of cancer‐related death in this group. The cure rate of prostate cancer is highly dependent on the stage of disease at the diagnosis and early detection is key to designing effective treatment strategies. The objective of the present study is to make a specific MR imaging probe for targeted imaging of cancer cells. We take advantage of the fact that many types of prostate cancer cells express high levels of prostate‐specific membrane antigen (PSMA) on their cell surface. The imaging strategy is to use superparamagnetic iron oxide nanoparticles (SPIONs), attached to an antibody (J591) that binds to the extracellular domain of PSMA, to specifically enhance the contrast of PSMA‐expressing prostate cancer cells. Conjugation of mAb J591 to commercial SPIONs was achieved using a heterobifunctional linker, sulfo‐SMCC. Two types of prostate cancer cell lines were chosen for experiments: LNCaP (PSMA+) and DU145 (PSMA?). MRI and cell uptake experiments demonstrated the high potential of the synthesized nanoprobe as a specific MRI contrast agent for detection of PSMA‐expressing prostate cancer cells. Copyright © 2012 John Wiley & Sons, Ltd.     

Gd2O3 nanoparticles: size‐dependent nuclear magnetic resonance

In this communication, we demonstrate that there is an optimum gadolinium oxide (Gd₂O₃) nanoparticle size of 2.3 nm; in the presence of Gd₂O₃ particles smaller and larger than this critical size, the spin‐lattice relaxation rate (T₁ = 1/r₁) of water protons at 7.0 T drastically decreases. Since r₁ is directly related to the quality of magnetic resonance imaging, the results presented here have significant implications for clinical diagnostics. Copyright © 2012 John Wiley & Sons, Ltd.     

携HMME-Gd液态氟碳纳米粒造影剂的制备及体外双模态成像研究

目的 制备携带血卟啉单甲醚-钆(HMME-Gd)的液态氟碳纳米粒(HMME-Gd-PFPNPs),观察体外US/MRI的成像效果。方法 以磷脂、胆固醇、HMME-Gd和全氟戊烷(PFP)为原料,用薄膜水化法和乳化法制备脂质体纳米粒HMME-Gd-PFPNPs。倒置光学显微镜、透射电子显微镜及激光共聚焦显微镜检测其基本表征;粒径分析仪分析粒径及表面电位;紫外分光光度计分析HMME-Gd的包封率;观察HMME-Gd-PFPNPs体外US/MRI成像的效果。结果 成功制备HMME-Gd-PFPNPs,光镜下为形态规则、大小均一的球形,电镜下为黑色的球形结构。HMME-Gd-PFPNPs平均粒径为(250.27 ± 11.9)nm,电位为(-26.17 ± 0.45)mV,HMME-Gd的包封率为(84.7 ± 0.35)%。在低强度聚焦超声辐照下,体外US成像信号显著增强,与LIFU激发强度成正相关。随HMME-Gd-PFPNPs浓度增加,体外MRI成像效果显著增强。结论 成功制备了携带HMME-Gd的液态氟碳纳米粒,可用于体外US/MRI双模态成像。     

Specific targeting and noninvasive magnetic resonance imaging of an asthma biomarker in the lung using polyethylene glycol functionalized magnetic nanocarriers

Simultaneous inhibition of IL4 and IL13 via the common receptor chain IL4Rα to block adequately their biologic effects presents a promising therapeutic approach to give the additional relief required for asthma patients. In this study, superparamagnetic iron oxide nanoparticles were conjugated with anti‐IL4Rα blocking antibodies via polyethylene glycol (PEG) polymers. The delivery of these blocking antibodies to the inflammatory sites in the lung via the developed nanocarriers was assessed using noninvasive free‐breathing pulmonary MRI. Biocompatibility assays confirmed the safety of the developed nanocarriers for pre‐clinical investigations. For all the investigated formulations, nanocarriers were found to be very stable at neutral pH. However, the stability noticeably decreased with the PEG length in acidic environment and thus the loaded antibodies were preferentially released. Immunofluorescence and fluorimetry assays confirmed the binding of the nanocarriers to the IL4Rα asthma biomarker. Pulmonary MRI performed using an ultra‐short echo time sequence allowed simultaneous noninvasive monitoring of inflammatory responses induced by ovalbumin challenge and tracking of the developed nanocarriers, which were found to colocalize with the inflammatory sites in the lung. Targeting of the developed nanocarriers to areas rich in IL4Rα positive inflammatory cells was confirmed using histological and flow cytometry analyses. The anti‐IL4Rα‐conjugated nanocarriers developed here have been confirmed to be efficient in targeting key inflammatory cells during chronic lung inflammation following intrapulmonary administration. Targeting efficiency was monitored using noninvasive MRI, allowing detection of the nanocarriers’ colocalizations with the inflammatory sites in the lung of ovalbumin‐challenged asthmatic mice. Copyright © 2015 John Wiley & Sons, Ltd.     

Variations in labeling protocol influence incorporation,distribution and retention of iron oxide nanoparticles into human umbilical vein endothelial cells

Various studies have shown that various cell types can be labeled with iron oxide particles and visualized by magnetic resonance imaging (MRI). However, reported protocols for cell labeling show a large variation in terms of labeling dose and incubation time. It is therefore not clear how different labeling protocols may influence labeling efficiency. Systematic assessment of the effects of various labeling protocols on labeling efficiency of human umbilical vein endothelial cells (HUVEC) using two different types of iron oxide nanoparticles, i.e. super paramagnetic iron oxide particles (SPIOs) and microparticles of iron oxide (MPIOs), demonstrated that probe concentration, incubation time and particle characteristics all influence the efficiency of label incorporation, label distribution, label retention and cell behavior. For SPIO the optimal labeling protocol consisted of a dose of 12.5 µg iron/2 ml/9.5 cm² and an incubation time of 24 h, resulting in an average iron load of 12.0 pg iron/per cell (uptake efficiency of 9.6%). At 4 h many SPIOs are seen sticking to the outside of the cell instead of being taken up by the cell. For MPIO optimal labeling was obtained with a dose of 50 µg iron/2 ml/9.5 cm². Incubation time was of less importance since most of the particles were already incorporated within 4 h with a 100% labeling efficiency, resulting in an intracellular iron load of 626 pg/cell. MPIO were taken up more efficiently than SPIO and were also better tolerated. HUVEC could be exposed to and contain higher amounts of iron without causing significant cell death, even though MPIO had a much more pronounced effect on cell appearance. Using optimal labeling conditions as found for HUVEC on other cell lines, we observed that different cell types react differently to identical labeling conditions. Consequently, for each cell type separately an optimal protocol has to be established. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessment and comparison of magnetic nanoparticles as MRI contrast agents in a rodent model of human hepatocellular carcinoma

The purpose of this study was to synthesize, characterize and tailor the surface properties of magnetic nanoparticles with biocompatible copolymer coatings and to evaluate the efficiency of the resulting nanoconjugates as magnetic resonance imaging (MRI) contrast agents for liver imaging. Magnetic nanoparticles with core diameters of 10 and 30 nm were synthesized by pyrolysis and were subsequently coated with a copolymer containing either carboxyl (SHP) or methoxy groups as termini. All four formulas, and ferumoxides (Feridex I.V.®), were individually injected intravenously into separate, normal Balb/C mice (at 2.5, 1.0 and 0.56 mg Fe kg^?1), and the animals underwent T₂‐weighted MRI at multiple time points post injection (p.i.) to evaluate the hepatic uptake and clearance. Furthermore, we compared the abilities of the new formulas and Feridex to detect tumors in an orthotropic Huh7 tumor model. Transmission electron microscopy (TEM) revealed a narrow size distribution of both the 10 and 30 nm nanoparticles, in contrast to a wide size distribution of Feridex. MTT, apoptosis and cyclin/DNA flow cytometry assays showed that the polymer coated nanoparticles had no adverse effect on cell growth. Among all the tested formulas, including Feridex, SHP‐30 showed the highest macrophage uptake at the in vitro level. In vivo MRI studies on normal mice confirmed the superiority of SHP‐30 in inducing hypointensities in the liver tissue, especially at clinical dose (0.56 mg Fe kg^?1) and 3 T field. SHP‐30 showed better contrast‐to‐noise ratio than Feridex on the orthotropic Huh7 tumor model. SHP‐30 was found to be an efficient contrast agent for liver MR imaging. The success of this study suggests that, by improving the synthetic approach and by tuning the surface properties of IONPs, one can arrive at better formulas than Feridex for clinical practice. Copyright © 2012 John Wiley & Sons, Ltd.     

Ultra‐small gadolinium oxide nanoparticles to image brain cancer cells in vivo with MRI

The majority of contrast agents used in magnetic resonance imaging (MRI) is based on the rare‐earth element gadolinium. Gadolinium‐based nanoparticles could find promising applications in pre‐clinical diagnostic procedures of certain types of cancer, such as glioblastoma multiforme. This is one of the most malignant, lethal and poorly accessible forms of cancer. Recent advances in colloidal nanocrystal synthesis have led to the development of ultra‐small crystals of gadolinium oxide (US‐Gd₂O₃, 2–3 nm diameter). As of today, this is the smallest and the densest of all Gd‐containing nanoparticles. Cancer cells labeled with a sufficient quantity of this compound appear bright in T₁‐weighted MRI images. Here we demonstrate that US‐Gd₂O₃ can be used to label GL‐261 glioblastoma multiforme cells, followed by localization and visualization in vivo using MRI. Very high amounts of Gd are efficiently internalized and retained in cells, as confirmed with TEM and ICP‐MS. Labeled cells were visualized in vivo at 1.5 T using the chicken embryo model. This is one more step toward the development of “positively contrasted” cell tracking procedures with MRI. Copyright © 2010 John Wiley & Sons, Ltd.     

Covalent coupling of gum arabic onto superparamagnetic iron oxide nanoparticles for MRI cell labeling: physicochemical and in vitro characterization

Gum arabic (GA) is a hydrophilic composite polysaccharide derived from exudates of Acacia senegal and Acacia seyal trees. It is biocompatible, possesses emulsifying and stabilizing properties and has been explored as coating agent of nanomaterials for biomedical applications, namely magnetic nanoparticles (MNPs). Previous studies focused on the adsorption of GA onto MNPs produced by co‐precipitation methods. In this work, MNPs produced by a thermal decomposition method, known to produce uniform particles with better crystalline properties, were used for the covalent coupling of GA through its free amine groups, which increases the stability of the coating layer. The MNPs were produced by thermal decomposition of Fe(acac)₃ in organic solvent and, after ligand‐exchange with meso‐2,3‐dimercaptosuccinic acid (DMSA), GA coating was achieved by the establishment of a covalent bond between DMSA and GA moieties. Clusters of several magnetic cores entrapped in a shell of GA were obtained, with good colloidal stability and promising magnetic relaxation properties (r₂/r₁ ratio of 350). HCT116 colorectal carcinoma cell line was used for in vitro cytotoxicity evaluation and cell‐labeling efficiency studies. We show that, upon administration at the respective IC₅₀, GA coating enhances MNP cellular uptake by 19 times compared to particles bearing only DMSA moieties. Accordingly, in vitro MR images of cells incubated with increasing concentrations of GA‐coated MNP present dose‐dependent contrast enhancement. The obtained results suggest that the GA magnetic nanosystem could be used as a MRI contrast agent for cell‐labeling applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Lentiviral transduction and subsequent loading with nanoparticles do not affect cell viability and proliferation in hair‐follicle‐bulge‐derived stem cells in vitro

The application of stem cells in the treatment of various degenerative diseases is highly promising. However, cell‐based therapy could be limited by the problem of low viability of grafted cells and uncertainty about their fate. The combination of molecular imaging and contrast‐enhanced MRI may give more insight into the survival and behavior of grafted stem cells. We explore hair‐follicle‐bulge‐derived stem cells (HFBSCs) as a potential candidate for autologous cell‐based therapy. HFBSCs are transduced with a lentiviral construct with genes coding for bioluminescent (Luc2) and fluorescent (copGFP) reporter proteins, and subsequently loaded with magnetic nanoparticles to enable MRI visualization. Thus, we investigate for the first time if lentiviral transduction and cellular loading with nanoparticles have a cytotoxic effect upon these stem cells. Transduction efficiency, proliferation rate, cell viability and reporter protein co‐expression during long‐term culture of transduced HFBSCs were studied using fluorescence and bioluminescence microscopy. In addition, the effect of TMSR50 nanoparticles on proliferation and viability was investigated using the MTS assay and bioluminescence microscopy. The amount of TMSR50‐loaded HFBSCs needed to reach signal threshold for MRI was assessed using an agarose phantom. Transduction with the Luc2‐copGFP construct did not influence senescence, proliferation, doubling time, and differentiation of the HFBSCs. CopGFP expression was visible immediately after transduction and persisted for at least 15 passages, concomitantly with Luc2 expression. Cellular loading with TMSR50 nanoparticles did not affect cell viability and proliferation. The results imply that combined MRI and bioluminescence imaging may enable in vivo localization and long‐term monitoring of grafted viable HFBSCs. Copyright © 2016 John Wiley & Sons, Ltd.     

脑性瘫痪MRI研究进展

MRI技术是目前明确脑部结构损伤的重要诊断技术,对确定脑瘫的病理类型、病因及损伤时间有重要意义,其改变与脑瘫类型、出生胎龄、病因及损伤时间密切相关。作者就不同类型脑瘫的MRI影像学改变及其与出生胎龄、损伤时间、病因相关性的研究进展做一综述。     

Polyglycerol‐grafted superparamagnetic iron oxide nanoparticles: highly efficient MRI contrast agent for liver and kidney imaging and potential scaffold for cellular and molecular imaging

Polyglycerol as a water‐soluble and biocompatible hyperbranched polymer was covalently grafted on the surface of superparamagnetic iron oxide nanoparticles. With this aim, superparamagnetic magnetite nanoparticles were prepared by coprecipitation in aqueous media, then the surface of nanoparticles was modified to introduce the reactive groups on the surface of nanoparticles. After that, polyglycerol was grafted on the surface of nanoparticles by ring‐opening anionic polymerization of glycidol using n‐bulyllithium as initiator. The magnetometry, relaxometry and phantom MRI experiments of this highly stable ferrofluid showed its high potential as a negative MRI contrast agent. Calculated r₁ and r₂ relaxivities at different magnetic fields were higher than the values reported for commercially available iron oxide contrast agents. The in vivo MRI studies showed that, after intravenous injection into mice, the particles produced a strong negative contrast in liver and kidneys, which persisted for 80 min (in liver) to 110 min (in kidneys). The negative contrast of the liver and kidneys weakened over the time, suggesting that polyglycerol coating renders the nanoparticles stealth and possibly optimal for renal excretion. Copyright © 2012 John Wiley & Sons, Ltd.     

In vivo quantification of SPIO nanoparticles for cell labeling based on MR phase gradient images

Along with the development of modern imaging technologies, contrast agents play increasingly important roles in both clinical applications and scientific research. Super‐paramagnetic iron oxide (SPIO) nanoparticles, a negative contrast agent, have been extensively used in magnetic resonance imaging (MRI), such as in vivo labeling and tracking of cells. However, there still remain many challenges, such as in vivo quantification of SPIO nanoparticles. In this work, an MR phase gradient‐based method was proposed to quantify the SPIO nanoparticles. As a calibration, a phantom experiment using known concentrations (10, 25, 50, 100, 150 and 250 µg/ml) of SPIO was first conducted to verify the proposed quantification method. In a following in vivo experiment, C6 glioma cells labeled with SPIO nanoparticles were implanted into flanks of four mice, which were scanned 1–3 days post‐injection for in vivo quantification of SPIO concentration. The results showed that the concentration of SPIO nanoparticles could be determined in both phantom and in vivo experiments using the developed MR phase gradients approach. Copyright © 2014 John Wiley & Sons, Ltd.