Single-cell detection by gradient echo 9.4 T MRI: a parametric study

Therapeutic Applications of Magnetotactic Bacteria and Magnetosomes: A Review Emphasizing on the Cancer Treatment

Magnetotactic bacteria (MTB) are aquatic microorganisms have the ability to biomineralize magnetosomes, which are membrane-enclosed magnetic nanoparticles. Magnetosomes are organized in a chain inside the MTB, allowing them to align with and traverse along the earth’s magnetic field. Magnetosomes have several potential applications for targeted cancer therapy when isolated from the MTB, including magnetic hyperthermia, localized medication delivery, and tumour monitoring. Magnetosomes features and properties for various applications outperform manufactured magnetic nanoparticles in several ways. Similarly, the entire MTB can be regarded as prospective agents for cancer treatment, thanks to their flagella’s ability to self-propel and the magnetosome chain’s ability to guide them. MTBs are conceptualized as nanobiots that can be guided and manipulated by external magnetic fields and are driven to hypoxic areas, such as tumor sites, while retaining the therapeutic and imaging characteristics of isolated magnetosomes. Furthermore, unlike most bacteria now being studied in clinical trials for cancer treatment, MTB are not pathogenic but might be modified to deliver and express certain cytotoxic chemicals. This review will assess the current and prospects of this burgeoning research field and the major obstacles that must be overcome before MTB can be successfully used in clinical treatments.

Contribution of macrophages in the contrast loss in iron oxide-based MRI cancer cell tracking studies

Magnetic resonance imaging (MRI) cell tracking of cancer cells labeled with superparamagnetic iron oxides (SPIO) allows visualizing metastatic cells in preclinical models. However, previous works showed that the signal void induced by SPIO on T₂(*)-weighted images decreased over time. Here, we aim at characterizing the fate of iron oxide nanoparticles used in cell tracking studies and the role of macrophages in SPIO metabolism.

In vivo MRI cell tracking of SPIO positive 4T1 breast cancer cells revealed a quick loss of T₂* contrast after injection. We next took advantage of electron paramagnetic resonance (EPR) spectroscopy and inductively coupled plasma mass spectroscopy (ICP-MS) for characterizing the evolution of superparamagnetic and non-superparamagnetic iron pools in 4T1 breast cancer cells and J774 macrophages after SPIO labeling. These in vitro experiments and histology studies performed on 4T1 tumors highlighted the quick degradation of iron oxides by macrophages in SPIO-based cell tracking experiments.

In conclusion, the release of SPIO by dying cancer cells and the subsequent uptake of iron oxides by tumor macrophages are limiting factors in MRI cell tracking experiments that plead for the use of (MR) reporter-gene based imaging methods for the long-term tracking of metastatic cells.

Antitumoral Effect of Mural Cells Assessed With High-Resolution MRI and Fluorescence Microscopy

OBJECTIVE

The purpose of this study was to detect labeled mural cells in vivo and study their therapeutic effect on tumor growth and on functional changes in the vascular network by use of MRI and fibered confocal fluorescence microscopy (FCFM).

MATERIALS AND METHODS

Twenty-eight mice were allocated to the following three groups 7 days after injection of TC1 tumor cells (C157 black 6): control, no injection (n = 7); sham, injection of phosphate-buffered saline solution (n = 10); and treated, injection of human mural cells (n = 11). Tumor growth was measured with calipers. Labeled mural cells were tracked with high-resolution MRI and FCFM. Microvessel density was assessed with MRI and FCFM, and the findings were compared with the histologic results.

RESULTS

Tumor growth was significantly slowed in the treated group starting on day 10 (p = 0.001). Round signal-intensity voids were observed in the center of six of seven tumors treated with magnetically labeled mural cells. Positive staining for iron was observed in histologic sections of two of five of these tumors. Microvessel density measured with FCFM was greater in the treated mice (p = 0.03). Flow cytometry revealed viable human mural cells only in treated tumors.

CONCLUSION

In this study, imaging techniques such as high-resolution MRI and FCFM showed the therapeutic effect of mural cell injection on tumor growth and microvessel function.

Silica nanoparticle-based dual imaging colloidal hybrids: cancer cell imaging and biodistribution

In this study, fluorescent dye-conjugated magnetic resonance (MR) imaging agents were investigated in T mode. Gadolinium-conjugated silica nanoparticles were successfully synthesized for both MR imaging and fluorescence diagnostics. Polyamine and polycarboxyl functional groups were modified chemically on the surface of the silica nanoparticles for efficient conjugation of gadolinium ions. The derived gadolinium-conjugated silica nanoparticles were investigated by zeta potential analysis, transmission electron microscopy, inductively coupled plasma mass spectrometry, and energy dispersive x-ray spectroscopy. MR equipment was used to investigate their use as contrast-enhancing agents in T₁ mode under a 9.4 T magnetic field. In addition, we tracked the distribution of the gadolinium-conjugated nanoparticles in both lung cancer cells and organs in mice.

In vivo visualization and ex vivo quantification of murine breast cancer cells in the mouse brain using MRI cell tracking and electron paramagnetic resonance

Cell tracking could be useful to elucidate fundamental processes of cancer biology such as metastasis. The aim of this study was to visualize, using MRI, and to quantify, using electron paramagnetic resonance (EPR), the entrapment of murine breast cancer cells labeled with superparamagnetic iron oxide particles (SPIOs) in the mouse brain after intracardiac injection. For this purpose, luciferase-expressing murine 4 T1-luc breast cancer cells were labeled with fluorescent Molday ION Rhodamine B SPIOs. Following intracardiac injection, SPIO-labeled 4 T1-luc cells were imaged using multiple gradient-echo sequences. Ex vivo iron oxide quantification in the mouse brain was performed using EPR (9 GHz). The long-term fate of 4 T1-luc cells after injection was characterized using bioluminescence imaging (BLI), brain MRI and immunofluorescence. We observed hypointense spots due to SPIO-labeled cells in the mouse brain 4 h after injection on T2 *-weighted images. Histology studies showed that SPIO-labeled cancer cells were localized within blood vessels shortly after delivery. Ex vivo quantification of SPIOs showed that less than 1% of the injected cells were taken up by the mouse brain after injection. MRI experiments did not reveal the development of macrometastases in the mouse brain several days after injection, but immunofluorescence studies demonstrated that these cells found in the brain established micrometastases. Concerning the metastatic patterns of 4 T1-luc cells, an EPR biodistribution study demonstrated that SPIO-labeled 4 T1-luc cells were also entrapped in the lungs of mice after intracardiac injection. BLI performed 6 days after injection of 4 T1-luc cells showed that this cell line formed macrometastases in the lungs and in the bones. Conclusively, EPR and MRI were found to be complementary for cell tracking applications. MRI cell tracking at 11.7 T allowed sensitive detection of isolated SPIO-labeled cells in the mouse brain, whereas EPR allowed the assessment of the number of SPIO-labeled cells in organs shortly after injection.

Positive contrast of SPIO-labeled cells by off-resonant reconstruction of 3D radial half-echo bSSFP

This article describes a new acquisition and reconstruction concept for positive contrast imaging of cells labeled with superparamagnetic iron oxides (SPIOs). Overcoming the limitations of a negative contrast representation as gained with gradient echo and fully balanced steady state (bSSFP), the proposed method delivers a spatially localized contrast with high cellular sensitivity not accomplished by other positive contrast methods. Employing a 3D radial bSSFP pulse sequence with half-echo sampling, positive cellular contrast is gained by adding artificial global frequency offsets to each half-echo before image reconstruction. The new contrast regime is highlighted with numerical intravoxel simulations including the point-spread function for 3D half-echo acquisitions. Furthermore, the new method is validated on the basis of in vitro cell phantom measurements on a clinical MRI platform, where the measured contrast-to-noise ratio (CNR) of the new approach exceeds even the negative contrast of bSSFP. Finally, an in vivo proof of principle study based on a mouse model with a clear depiction of labeled cells within a subcutaneous cell islet containing a cell density as low as 7 cells/mm(3) is presented. The resultant isotropic images show robustness to motion and a high CNR, in addition to an enhanced specificity due to the positive contrast of SPIO-labeled cells.

Mesenchymal stromal cell labeling by new uncoated superparamagnetic maghemite nanoparticles in comparison with commercial Resovist--an initial in vitro study

OBJECTIVE

Cell therapies have emerged as a promising approach in medicine. The basis of each therapy is the injection of 1-100×10(6) cells with regenerative potential into some part of the body. Mesenchymal stromal cells (MSCs) are the most used cell type in the cell therapy nowadays, but no gold standard for the labeling of the MSCs for magnetic resonance imaging (MRI) is available yet. This work evaluates our newly synthesized uncoated superparamagnetic maghemite nanoparticles (surface-active maghemite nanoparticles - SAMNs) as an MRI contrast intracellular probe usable in a clinical 1.5 T MRI system.

METHODS

MSCs from rat and human donors were isolated, and then incubated at different concentrations (10-200 μg/mL) of SAMN maghemite nanoparticles for 48 hours. Viability, proliferation, and nanoparticle uptake efficiency were tested (using fluorescence microscopy, xCELLigence analysis, atomic absorption spectroscopy, and advanced microscopy techniques). Migration capacity, cluster of differentiation markers, effect of nanoparticles on long-term viability, contrast properties in MRI, and cocultivation of labeled cells with myocytes were also studied.

RESULTS

SAMNs do not affect MSC viability if the concentration does not exceed 100 μg ferumoxide/mL, and this concentration does not alter their cell phenotype and long-term proliferation profile. After 48 hours of incubation, MSCs labeled with SAMNs show more than double the amount of iron per cell compared to Resovist-labeled cells, which correlates well with the better contrast properties of the SAMN cell sample in T2-weighted MRI. SAMN-labeled MSCs display strong adherence and excellent elasticity in a beating myocyte culture for a minimum of 7 days.

CONCLUSION

Detailed in vitro tests and phantom tests on ex vivo tissue show that the new SAMNs are efficient MRI contrast agent probes with exclusive intracellular uptake and high biological safety.

[Life cycle of magnetic nanoparticles in the organism]

The use of nanomaterials drastically increases and yet their behavior in living organisms remains poorly examined. At the same time a better comprehension of the interactions between nanoparticles and the biological environment would allow us to limit potential nanoparticle-based toxicity and fully exploit nanoparticles medical applications. In this perspective, it is high time we develop methods to detect, quantify and follow the evolution of nanoparticles in the complex biological environment, spanning all relevant scales from the nanometer up to the tissue level. In this work we follow the life cycle of magnetic nanoparticles in vivo, focusing on their transformations over time from administration to elimination. As opposed to traditional nano-toxicological approaches, we herein take the nanoparticle perspective and try to establish how biological environment might impact the particles properties and their fate (interaction with proteins, cell confinement, degradation...) from their initial state to a series of changes a nanoparticle might undergo on its journey throughout the organism.

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.

Cell labeling with magnetic nanoparticles: opportunity for magnetic cell imaging and cell manipulation

This tutorial describes a method of controlled cell labeling with citrate-coated ultra small superparamagnetic iron oxide nanoparticles. This method may provide basically all kinds of cells with sufficient magnetization to allow cell detection by high-resolution magnetic resonance imaging (MRI) and to enable potential magnetic manipulation. In order to efficiently exploit labeled cells, quantify the magnetic load and deliver or follow-up magnetic cells, we herein describe the main requirements that should be applied during the labeling procedure. Moreover we present some recommendations for cell detection and quantification by MRI and detail magnetic guiding on some real-case studies in vitro and in vivo.

Cell-derived vesicles as a bioplatform for the encapsulation of theranostic nanomaterials

There is a great deal of interest in the development of nanoplatforms gathering versatility and multifunctionality. The strategy reported herein meets these requirements and further integrates a cell-friendly shell in a bio-inspired approach. By taking advantage of a cell mechanism of biomolecule transport using vesicles, we engineered a hybrid biogenic nanoplatform able to encapsulate a set of nanoparticles regardless of their chemistry or shape. As a proof of versatility, different types of hybrid nanovesicles were produced: magnetic, magnetic-metallic and magnetic-fluorescent vesicles, either a single component or multiple components, combining the advantageous properties of each integrant nanoparticle. These nanoparticle-loaded vesicles can be manipulated, monitored by MRI and/or fluorescence imaging methods, while acting as efficient nano-heaters. The resulting assets for targeting, imaging and therapy converge for the outline of a new generation of nanosystems merging versatility and multifunctionality into a bio-camouflaged and bio-inspired approach.

High-resolution cellular MRI: gadolinium and iron oxide nanoparticles for in-depth dual-cell imaging of engineered tissue constructs

Recent advances in cell therapy and tissue engineering opened new windows for regenerative medicine, but still necessitate innovative noninvasive imaging technologies. We demonstrate that high-resolution magnetic resonance imaging (MRI) allows combining cellular-scale resolution with the ability to detect two cell types simultaneously at any tissue depth. Two contrast agents, based on iron oxide and gadolinium oxide rigid nanoplatforms, were used to "tattoo" endothelial cells and stem cells, respectively, with no impact on cell functions, including their capacity for differentiation. The labeled cells' contrast properties were optimized for simultaneous MRI detection: endothelial cells and stem cells seeded together in a polysaccharide-based scaffold material for tissue engineering appeared respectively in black and white and could be tracked, at the cellular level, both in vitro and in vivo. In addition, endothelial cells labeled with iron oxide nanoparticles could be remotely manipulated by applying a magnetic field, allowing the creation of vessel substitutes with in-depth detection of individual cellular components.

Real-time high-resolution magnetic resonance tracking of macrophage subpopulations in a murine inflammation model: a pilot study with a commercially available cryogenic probe

Macrophages present different polarization states exhibiting distinct functions in response to environmental stimuli. However, the dynamic of their migration to sites of inflammation is not fully elucidated. Here we propose a real-time in vivo cell tracking approach, using high-resolution (HR)-MRI obtained with a commercially available cryogenic probe (Cryoprobe™), to monitor trafficking of differently polarized macrophages after systemic injection into mice. Murine bone marrow-derived mononuclear cells were differentiated ex vivo into nonpolarized M0, pro-inflammatory M1 and immunomodulator M2 macrophage subsets and labeled with citrate-coated anionic iron oxide nanoparticles (AMNP). These cells were subsequently intravenously injected to mice bearing calf muscle inflammation. Whole body migration dynamics of macrophage subsets was monitored by MRI at 4.7 T with a volume transmission/reception radiofrequency coil and macrophage infiltration to the inflamed paw was monitored with the cryogenic probe, allowing 3D spatial resolution of 50 µm with a scan time of only 10 min. Capture of AMNP was rapid and efficient regardless of macrophage polarization, with the highest uptake in M2 macrophages. Flow cytometry confirmed that macrophages preserved their polarization hallmarks after labeling. Migration kinetics of labeled cells differed from that of free AMNP. A preferential homing of M2-polarized macrophages to inflammation sites was observed. Our in vivo HR-MRI protocol highlights the extent of macrophage infiltration to the inflammation site. Coupled to whole body imaging, HR-MRI provides quantitative information on the time course of migration of ex vivo-polarized intravenously injected macrophages.

MRI contrast variation of thermosensitive magnetoliposomes triggered by focused ultrasound: a tool for image-guided local drug delivery

Improved drug delivery control during chemotherapy has the potential to increase the therapeutic index. MRI contrast agent such as iron oxide nanoparticles can be co-encapsulated with drugs in nanocarrier liposomes allowing their tracking and/or visualization by MRI. Furthermore, the combination of a thermosensitive liposomal formulation with an external source of heat such as high intensity focused ultrasound guided by MR temperature mapping allows the controlled local release of the content of the liposome. MRI-guided high-intensity focused ultrasound (HIFU), in combination represents a noninvasive technique to generate local hyperthermia for drug release. In this study we used ultrasmall superparamagnetic iron oxide nanoparticles (USPIO) encapsulated in thermosensitive liposomes to obtain thermosensitive magnetoliposomes (TSM). The transverse and longitudinal relaxivities of this MRI contrast agent were measured upon TSM membrane phase transition in vitro using a water bath or HIFU. The results showed significant differences for MRI signal enhancement and relaxivities before and after heating, which were absent for nonthermosensitive liposomes and free nanoparticles used as controls. Thus, incorporation of USPIO as MRI contrast agents into thermosensitive liposomes should, besides TSM tumor accumulation monitoring, allow the visualization of TSM membrane phase transition upon temperature elevation. In conclusion, HIFU under MR image guidance in combination with USPIO-loaded thermosensitive liposomes as drug delivery system has the potential for a better control of drug delivery and to increase the drug therapeutic index.

Endowing carbon nanotubes with superparamagnetic properties: applications for cell labeling, MRI cell tracking and magnetic manipulations

Coating of carbon nanotubes (CNTs) with magnetic nanoparticles (NPs) imparts novel magnetic, optical, and thermal properties with potential applications in the biomedical domain. Multi-walled CNTs have been decorated with iron oxide superparamagnetic NPs. Two different approaches have been investigated based on ligand exchange or "click chemistry". The presence of the NPs on the nanotube surface allows conferring magnetic properties to CNTs. We have evaluated the potential of the NP/CNT hybrids as a contrast agent for magnetic resonance imaging (MRI) and their interactions with cells. The capacity of the hybrids to magnetically monitor and manipulate cells has also been investigated. The NP/CNTs can be manipulated by a remote magnetic field with enhanced contrast in MRI. They are internalized into tumor cells without showing cytotoxicity. The labeled cells can be magnetically manipulated as they display magnetic mobility and are detected at a single cell level through high resolution MRI.

[Magnetic nanoparticles as tools for cell therapy]

Labelling living cells with magnetic nanoparticles creates opportunities for numerous biomedical applications such as Magnetic Resonance Imaging (MRI) cell tracking, cell manipulation, cell patterning for tissue engineering and magnetically-assisted cell delivery. The unique advantage of magnetic-based methods is to activate or monitor cell behavior by a remote stimulus, the magnetic field. Cell labelling methods using superparamagnetic nanoparticles have been widely developed, showing no adverse effect on cell proliferation and functionalities while conferring magnetic properties to various cell types. This paper first describes how cells can become responsive to magnetic field by safely internalizing magnetic nanoparticles. We next show how magnetic cells can be detected by MRI, giving the opportunity for non-invasive in vivo monitoring of cell migration. We exemplify the fact that MRI cell tracking has become a method of choice to follow the fate of administrated cells in cell therapy assay, whether the cells are grafted locally or administrated in the circulation. Finally we give different examples of magnetic manipulation of cells and their applications to regenerative medicine. Magnetic cell manipulation are forecasted to be more and more developed, in order to improve tissue engineering technique and assist cell-based therapies. Owing to the clinical approval of iron-oxide nanoparticles as MRI contrast agent, there is no major obstacle in the translation to human clinics of the magnetic methods summarized in this paper.

Managing magnetic nanoparticle aggregation and cellular uptake: a precondition for efficient stem-cell differentiation and MRI tracking

The labeling of stem cells with iron oxide nanoparticles is increasingly used to enable MRI cell tracking and magnetic cell manipulation, stimulating the fields of tissue engineering and cell therapy. However, the impact of magnetic labeling on stem-cell differentiation is still controversial. One compromising factor for successful differentiation may arise from early interactions of nanoparticles with cells during the labeling procedure. It is hypothesized that the lack of control over nanoparticle colloidal stability in biological media may lead to undesirable nanoparticle localization, overestimation of cellular uptake, misleading MRI cell tracking, and further impairment of differentiation. Herein a method is described for labeling mesenchymal stem cells (MSC), in which the physical state of citrate-coated nanoparticles (dispersed versus aggregated) can be kinetically tuned through electrostatic and magnetic triggers, as monitored by diffusion light scattering in the extracellular medium and by optical and electronic microscopy in cells. A set of statistical cell-by-cell measurements (flow cytometry, single-cell magnetophoresis, and high-resolution MRI cellular detection) is used to independently quantify the nanoparticle cell uptake and the effects of nanoparticle aggregation. Such aggregation confounds MRI cell detection as well as global iron quantification and has adverse effects on chondrogenetic differentiation. Magnetic labeling conditions with perfectly stable nanoparticles-suitable for obtaining differentiation-capable magnetic stem cells for use in cell therapy-are subsequently identified.

How cellular processing of superparamagnetic nanoparticles affects their magnetic behavior and NMR relaxivity

Cellular processing of nanomaterials may affect their physical properties at the root of various biomedical applications. When nanoparticles interact with living cells, their spatial distribution is progressively modified by cellular activity, which tends to concentrate them into intracellular compartments, changing in turn their responsivity to physical stimuli. In this paper, we investigate the consequences of cellular uptake on the related magnetic properties and NMR relaxivity of iron oxide nanoparticles. The superparamagnetic behavior (field-dependent and temperature-dependent magnetization curves investigated by SQUID (Superconducting Quantum Interference Device) measurements) and nuclear magnetic relaxation dispersion (NMRD) R(1) profiles of citrate-coated maghemite nanoparticles (mean diameter 8 nm) were characterized in colloidal suspension and after being uptaken by several types of cells (tumor cells, stem cells and macrophages). The temperature-dependent magnetization as well as the NMRD profile were changed following cellular uptake depending on the stage of endocytosis process while the field-dependent magnetization at room temperature remained unchanged. Magnetic coupling between nanoparticles confined in cell lysosomes accounts for the modification in magnetic behavior, thereby reflecting the local organization of nanoparticles. NMR longitudinal relaxivity was directly sensitive to the intracellular distribution of nanoparticles, in line with Transmission Electron Microscopy TEM observations. This study is the first attempt to link up magnetic properties and NMR characterization of iron oxide nanoparticles before and after their cell processing.

A universal scaling law to predict the efficiency of magnetic nanoparticles as MRI T(2)-contrast agents

Magnetic particles are very efficient magnetic resonance imaging (MRI) contrast agents. In recent years, chemists have unleashed their imagination to design multi-functional nanoprobes for biomedical applications including MRI contrast enhancement. This study is focused on the direct relationship between the size and magnetization of the particles and their nuclear magnetic resonance relaxation properties, which condition their efficiency. Experimental relaxation results with maghemite particles exhibiting a wide range of sizes and magnetizations are compared to previously published data and to well-established relaxation theories with a good agreement. This allows deriving the experimental master curve of the transverse relaxivity versus particle size and to predict the MRI contrast efficiency of any type of magnetic nanoparticles. This prediction only requires the knowledge of the size of the particles impermeable to water protons and the saturation magnetization of the corresponding volume. To predict the T(2) relaxation efficiency of magnetic single crystals, the crystal size and magnetization - obtained through a single Langevin fit of a magnetization curve - is the only information needed. For contrast agents made of several magnetic cores assembled into various geometries (dilute fractal aggregates, dense spherical clusters, core-shell micelles, hollow vesicles…), one needs to know a third parameter, namely the intra-aggregate volume fraction occupied by the magnetic materials relatively to the whole (hydrodynamic) sphere. Finally a calculation of the maximum achievable relaxation effect - and the size needed to reach this maximum - is performed for different cases: maghemite single crystals and dense clusters, core-shell particles (oxide layer around a metallic core) and zinc-manganese ferrite crystals.

Labeling stem cells with superparamagnetic iron oxide nanoparticles: analysis of the labeling efficacy by microscopy and magnetic resonance imaging

Stem cell therapy has emerged as a potential therapeutic option for cell death-related heart diseases. Application of non-invasive cell tracking approaches is necessary to determine tissue distribution and lifetime of stem cells following their injection and will likely provide knowledge about poorly understood stem cells mechanisms of tissue repair. Magnetic resonance imaging (MRI) is a potentially excellent tool for high-resolution visualization of the fate of cells after transplantation and for evaluation of therapeutic strategies. The application of MRI for in vivo cell tracking requires contrast agents to achieve efficient cell labeling without causing any toxic cellular effects or eliciting any other side effects. For these reasons clinically approved contrast agents (e.g., ferumoxides) and incorporation facilitators (e.g., protamine) are currently the preferred materials for cell labeling and tracking. Here we describe how to use superparamagnetic iron oxide nanoparticles to label cells and to monitor cell fate in several disease models.

In vivo MR tracking of therapeutic microglia to a human glioma model

A knowledge of the spatial localization of cell vehicles used in gene therapy against glioma is necessary before launching therapy. For this purpose, MRI cell tracking is performed by labeling the cell vehicles with contrast agents. In this context, the goal of this study was to follow noninvasively the chemoattraction of therapeutic microglial cells to a human glioma model before triggering therapy. Silica nanoparticles grafted with gadolinium were used to label microglia. These vehicles, expressing constitutively the thymidine kinase suicide gene fused to the green fluorescent protein gene, were injected intravenously into human glioma-bearing nude mice. MRI was performed at 4.7 T to track noninvasively microglial accumulation in the tumor. This was followed by microscopy on brain slices to assess the presence in the glioma of the contrast agents, microglia and fusion gene through the detection of silica nanoparticles grafted with tetramethyl rhodamine iso-thiocyanate, 3,3'-dioctadecyloxacarbocyanine perchlorate and green fluorescent protein fluorescence, respectively. Finally, gancyclovir was administered systemically to mice. Human microglia were detectable in living mice, with strong negative contrast on T(2) *-weighted MR images, at the periphery of the glioma only 24 h after systemic injection. The location of the dark dots was identical in MR microscopy images of the extracted brains at 9.4 T. Fluorescence microscopy confirmed the presence of the contrast agents, exogenous microglia and suicide gene in the intracranial tumor. In addition, gancyclovir treatment allowed an increase in mice survival time. This study validates the MR tracking of microglia to a glioma after systemic injection and their use in a therapeutic strategy against glioma.

Quantification of punctate iron sources using magnetic resonance phase

Iron-mediated tissue damage is present in cerebrovascular and neurodegenerative diseases and neurotrauma. Brain microbleeds are often present in these maladies and are assuming increasing clinical importance. Because brain microbleeds present a source of pathologic iron to the brain, the noninvasive quantification of this iron pool is potentially valuable. Past efforts to quantify brain iron have focused on content estimation within distributed brain regions. In addition, conventional approaches using "magnitude" images have met significant limitations. In this study, a technique is presented to quantify the iron content of punctate samples using phase images. Samples are modeled as magnetic dipoles and phase shifts due to local dipole field perturbations are mathematically related to sample iron content and radius using easily recognized geometric features in phase images. Phantoms containing samples of a chitosan-ferric oxyhydroxide composite (which serves as a mimic for hemosiderin) were scanned with a susceptibility-weighted imaging sequence at 11.7 T. Plots relating sample iron content and radius to phase image features were compared to theoretical predictions. The primary result is the validation of the technique by the excellent agreement between theory and the iron content plot. This research is a potential first step toward quantification of punctate brain iron sources such as brain microbleeds.

Magnetic labeling, imaging and manipulation of endothelial progenitor cells using iron oxide nanoparticles

Endothelial progenitor cells (EPCs), originating from bone marrow, play a significant role in the repair of ischemic tissue and injured blood vessels. They are also involved in tumor angiogenesis. The therapeutic potential of EPCs for regenerative medicine and cancer treatment calls for new methods for monitoring and controlling cell migration. This review focuses on promising magnetic methods based on the internalization of magnetic nanoparticles by EPCs. We first describe the cellular uptake of iron oxide nanoparticles depending on their surface properties. We thus review the use of MRI for the detection of labeled cells and for noninvasive follow-up of EPCs homing in sites of endothelium regeneration. Finally, we show that remotely applied magnetic forces may enable intracellular manipulation and may optimize cell-delivery strategies for localizing cell therapy to target sites.

The MRI assessment of intraurethrally--delivered muscle precursor cells using anionic magnetic nanoparticles

Autografting of cultured myogenic precursor cells (MPC) is a therapeutic strategy for muscle disorders, including striated urethral sphincter insufficiency. Implantation of myofibers with their satellite cells into the urethra is a recently described method of MPC transfer aimed at generating a new sphincter in incontinent patients. In this study, we magnetically labeled muscle implants with dextran-free anionic iron oxide nanoparticles (AMNP). The aim was to evaluate the biocompatibility of the labeling procedure and its utility for non-invasive MRI follow-up of cell therapy in a female pig model. After adsorption of AMNP to the implant surface, various cell types, including MPC, were magnetically labeled within the implants. Magnetic labeling did not affect cell proliferation or differentiation. Autograft detection in vivo by 0.3-T MRI was possible for up to 1 month. Ex vivo, Perl's, anti-desmin and anti-myosin heavy chain staining confirmed the co-localization of AMNP and regenerated myofibers. AMNP labeling was thus useful for locating myofiber implant autografts in vivo and for ex vivo monitoring of the biology of this cell transfer method.

Cellular magnetic resonance imaging using superparamagnetic anionic iron oxide nanoparticles: applications to in vivo trafficking of lymphocytes and cell-based anticancer therapy

In current cancer research, the application of cytotoxic T lymphocytes with specificity to tumor antigens is regarded as a real therapeutic hope. The objective of imaging is to provide a follow-up of these killer cells in real time, in order to gain a better understanding of the mechanisms and action modes of lymphocytes on the tumor. Magnetic resonance imaging (MRI) has the advantage of the innocuousness of the applied magnetic field. Moreover, it has an exceptional spatial resolution allowing the visualization of anatomical areas without in-depth limitations. These features make MRI particularly adapted for cellular imaging. The use of " (ultrasmall) superparamagnetic iron oxide " particles [(U) SPIO] offers the adequate sensitivity required for cellular imaging. To promote a sufficient capture of these particles in nonphagocytic cells and make the cell of interest " detectable " by MRI after its injection, an important challenge in cellular imaging is to develop improved cell-labeling techniques. Superparamagnetic anionic nanoparticles (iron oxides of 10-nm diameter) are adsorbed in a nonspecific way on the membrane of the majority of cells, allowing their spontaneous internalization in intracellular vesicles. This pathway of cellular labeling confers a particular status to these nanoparticles as MRI contrast agents; the cells labeled in this manner possess magnetic and contrast properties that allow their in vivo detection and follow-up by MRI. This chapter describes the synthesis, the potential use, and the features of cellular labeling with these types of anionic nanoparticles. We also focus on the MRI contrast properties of the labeled cells, as well as on the feasibility of in vivo detection of immunizing circulating cells by MRI, with direct implications in cell-based anticancer therapy using lymphocytes.

Magnetic resonance methods and applications in pharmaceutical research

This review presents an overview of some recent magnetic resonance (MR) techniques for pharmaceutical research. MR is noninvasive, and does not expose subjects to ionizing radiation. Some methods that have been used in pharmaceutical research MR include magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) methods, among them, diffusion-weighted MRI, perfusion-weighted MRI, functional MRI, molecular imaging and contrast-enhance MRI. Some applications of MR in pharmaceutical research include MR in metabonomics, in vivo MRS, studies in cerebral ischemia and infarction, degenerative joint diseases, oncology, cardiovascular disorders, respiratory diseases and skin diseases. Some of these techniques, such as cardiac and joint imaging, or brain fMRI are standard, and are providing relevant data routinely. Skin MR and hyperpolarized gas lung MRI are still experimental. In conclusion, considering the importance of finding and characterizing biomarkers for improved drug evaluation, it can be expected that the use of MR techniques in pharmaceutical research is going to increase in the near future.

Universal cell labelling with anionic magnetic nanoparticles

Magnetic labelling of living cells creates opportunities for numerous biomedical applications, from individual cell manipulation to MRI tracking. Here we describe a non-specific labelling method based on anionic magnetic nanoparticles (AMNPs). These particles first adsorb electrostatically to the outer membrane before being internalized within endosomes. We compared the labelling mechanism, uptake efficiency and biocompatibility with 14 different cell types, including adult cells, progenitor cells, immune cells and tumour cells. A single model was found to describe cell/nanoparticle interactions and to predict uptake efficiency by all the cell types. The potential impact of the AMNP label on cell functions, in vitro and in vivo, is discussed according to cellular specificities. We also show that the same label provides sufficient magnetization for MRI detection and distal manipulation.

Measuring brain tissue oxygenation under oxidative stress by ESR/MR dual imaging system

The in vivo measurement of oxygen in tissues is of great interest because of oxygen's fundamental role in life. Many methods have been developed for such measurement, but all have been limited, especially with regard to repeated measurement, degree of invasiveness, and sensitivity. We describe electron spin resonance (ESR) oximetry with paramagnetic oxygen-sensing probe for in vivo measurement of oxygen in brain tissues by home-made ESR/MR dual imaging spectroscopy. Lithium 5, 9, 14, 18, 23, 27, 32, 36-octa-n-butoxy-2,3-naphthlocyanine (LiNc-BuO) radical was employed as the solid oxygen-sensing probe, and we confirmed its ability to report partial pressure of oxygen (pO(2)) in brain tissues of live animals under normal and pathological conditions for more than a month. pO(2) measurements could also be made repeatedly on the same animal and at the same location. The implantation site of LiNc-BuO in examined rats was verified by 0.5 T magnetic resonance (MR) imaging. Septic-shock rats were used to monitor tissue oxygenation during pathological state. A decline in pO(2) levels from severe hypotension during sepsis was detected, and generation of nitric oxide (NO) in brain tissues was confirmed by NO spin trapping. ESR oximetry using oxygen-sensing probe and NO spin-trapping can be used to monitor pO(2) change and NO production simultaneously and repeatedly at the same site in examined animals.

Magnetic control of vascular network formation with magnetically labeled endothelial progenitor cells

We describe the applications of new cellular magnetic labeling method to endothelial progenitor cells (EPC), which have therapeutic potential for revascularization. Via their negative surface charges, anionic magnetic nanoparticles adsorb non-specifically to the EPC plasma membrane, thereby triggering efficient spontaneous endocytosis. The label is non-toxic and does not affect the cells' proliferative capacity. The expression of major membrane proteins involved in neovascularisation is preserved. Labeled cells continue to differentiate in vitro and to form tubular structures in Matrigel (an in vitro model of neovascularization). This process was followed in situ by using high-resolution MRI. Finally, we show that magnetic forces can be used to move magnetically labeled EPC in vitro and to modify their organization in Matrigel both in vitro an in vivo. Magnetic cell targeting opens up new possibilities for vascular tissue engineering and for delivering localized cell-based therapies.