E. Kay Jordan

Self-assembling nanocomplexes by combining ferumoxytol, heparin and protamine for cell tracking by magnetic resonance imaging

We report on a new straightforward magnetic cell-labeling approach that combines three US Food and Drug Administration (FDA)-approved drugs—ferumoxytol, heparin and protamine—in serum-free medium to form self-assembling nanocomplexes that effectively label cells for in vivo magnetic resonance imaging (MRI). We observed that the ferumoxytol-heparin-protamine (HPF) nanocomplexes were stable in serum-free cell culture medium. HPF nanocomplexes show a threefold increase in T2 relaxivity compared to ferumoxytol. Electron microscopy showed internalized HPF in endosomes, which we confirmed by Prussian blue staining of labeled cells. There was no long-term effect or toxicity on cellular physiology or function of HPF-labeled hematopoietic stem cells, bone marrow stromal cells, neural stem cells or T cells when compared to controls. In vivo MRI detected 1,000 HPF-labeled cells implanted in rat brains. This HPF labeling method should facilitate the monitoring by MRI of infused or implanted cells in clinical trials.

Study of relapsing remitting experimental allergic encephalomyelitis SJL mouse model using MION-46L enhanced in vivo MRI: Early histopathological correlation

MION‐46L, a superparamagnetic iron oxide contrast agent, was investigated for its ability to increase the sensitivity of in vivo 3D MRI in the detection of brain lesions in a chronic experimental allergic encephalomyelitis (crEAE) mouse model. Lesion conspicuity on postcontrast 3D MRI was dramatically enhanced as compared to precontrast images corresponding to areas of inflammatory and demyelinating lesions. MION‐46L could be detected on Prussian blue iron stain in the vascular endothelium, the perivascular space, and in macrophages within perivascular cuffs and areas of inflammation and demyelination. By taking advantage of the MION‐46L induced macroscopic susceptibility effect, acute early lesions measuring only 100 μm in diameter could be detected. MION‐46L enhanced MRI may be used to 1) provide a unique sensitivity in EAE lesion detection and correlate imaging to histopathology; 2) help to understand EAE lesion development and its underlying pathophysiology; and 3) eventually assist in preclinical screening of new experimental therapies directed at patients with multiple sclerosis (MS). J. Neurosci. Res. 52:549–558, 1998. Published 1998 Wiley‐Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.

Ultrashort T2* Relaxometry for Quantitation of Highly Concentrated Superparamagnetic Iron Oxide (SPIO) Nanoparticle Labeled Cells

A new method was developed to measure ultrashort T  2* relaxation in tissues containing a focal area of superparamagnetic iron oxide (SPIO) nanoparticle‐labeled cells in which the T  2* decay is too short to be accurately measured using regular gradient echo T  2* mapping. The proposed method utilizes the relatively long T2 relaxation of SPIO‐labeled cells and acquires a series of spin echo images with the readout echo shifted to sample the T  2* decay curve. MRI experiments in phantoms and rats with SPIO‐labeled tumors demonstrated that it can detect ultrashort T  2* down to 1 ms or less. The measured T  2* values were about 10% higher than those from the ultrashort TE (UTE) technique. The shorter the TE, the less the measurements deviated from the UTE T  2* mapping. Combined with the regular T  2* mapping, this technique is expected to provide quantitation of highly concentrated iron‐labeled cells from direct cell transplantation. Magn Reson Med, 2009.

Differential microstructure and physiology of brain and bone metastases in a rat breast cancer model by diffusion and dynamic contrast enhanced MRI.

Pharmacological approaches to treat breast cancer metastases in the brain have been met with limited success. In part, the impermeability of the blood brain barrier (BBB) has hindered delivery of chemotherapeutic agents to metastatic tumors in the brain. BBB-permeable chemotherapeutic drugs are being developed, and noninvasively assessing the efficacy of these agents will be important in both preclinical and clinical settings. In this regard, dynamic contrast enhanced (DCE) and diffusion weighted imaging (DWI) are magnetic resonance imaging (MRI) techniques to monitor tumor vascular permeability and cellularity, respectively. In a rat model of metastatic breast cancer, we demonstrate that brain and bone metastases develop with distinct physiological characteristics as measured with MRI. Specifically, brain metastases have limited permeability of the BBB as assessed with DCE and an increased apparent diffusion coefficient (ADC) measured with DWI compared to the surrounding brain. Microscopically, brain metastases were highly infiltrative, grew through vessel co-option, and caused extensive edema and injury to the surrounding neurons and their dendrites. By comparison, metastases situated in the leptomenengies or in the bone had high vascular permeability and significantly lower ADC values suggestive of hypercellularity. On histological examination, tumors in the bone and leptomenengies were solid masses with distinct tumor margins. The different characteristics of these tissue sites highlight the influence of the microenvironment on metastatic tumor growth. In light of these results, the suitability of DWI and DCE to evaluate the response of chemotherapeutic and anti-angiogenic agents used to treat co-opted brain metastases, respectively, remains a formidable challenge.

Effective Antigen-Specific Immunotherapy in the Marmoset Model of Multiple Sclerosis

Mature T cells initially respond to Ag by activation and expansion, but high and repeated doses of Ag cause programmed cell death and can suppress T cell-mediated diseases in rodents. We evaluated repeated systemic Ag administration in a marmoset model of experimental allergic encephalomyelitis that closely resembles the human disease multiple sclerosis. We found that treatment with MP4, a chimeric, recombinant polypeptide containing human myelin basic protein and human proteolipid protein epitopes, prevented clinical symptoms and did not exacerbate disease. CNS lesions were also reduced as assessed in vivo by magnetic resonance imaging. Thus, specific Ag-directed therapy can be effective and nontoxic in primates.

Quantification of SPIO nanoparticles in vivo using the finite perturber method

The susceptibility gradients generated by super‐paramagnetic iron oxide (SPIO) nanoparticles make them an ideal contrast agent in magnetic resonance imaging. Traditional quantification methods for SPIO nanoparticle‐based contrast agents rely on either mapping T  2* values within a region or by modeling the magnetic field inhomogeneities generated by the contrast agent. In this study, a new model‐based SPIO quantification method is introduced. The proposed method models magnetic field inhomogeneities by approximating regions containing SPIOs as ensembles of magnetic dipoles, referred to as the finite perturber method. The proposed method was verified using data acquired from a phantom and in vivo mouse models. The phantom consisted of an agar solution with four embedded vials, each vial containing known but different concentrations of SPIO nanoparticles. Gaussian noise was also added to the phantom data to test performance of the proposed method. The in vivo dataset was acquired using five mice, each of which was subcutaneously implanted in the flanks with 1 × 105 labeled and 1 × 106 unlabeled C6 glioma cells. For the phantom data set, the proposed algorithm was generate accurate estimations of the concentration of SPIOs. For the in vivo dataset, the method was able to give estimations of the concentration within SPIO‐labeled tumors that are reasonably close to the known concentration. Magn Reson Med, 2011.

Pharmacokinetics of a High-Generation Dendrimer–Gd-DOTA

Dendrimers are three-dimensional branching polymers that have received much attention as transfection agents (1), drug delivery agents (2), and magnetic resonance (MR) contrast agents (3–5). To be used as MR contrast agents, dendrimers have been conjugated with paramagnetic metal ion complexes. The large number of paramagnetic metal ion complexes that can be covalently attached per dendrimer molecule, which depends on the dendrimer generation, has resulted in a new class of macromolecular MR contrast agents. Unlike other macromolecular-based MR contrast agents such as albumin, dextran, and poly-Llysine, dendrimers are discrete reagents with well-defined sizes and shapes. The paramagnetic metal ion complexes have included gadolinium chelated to the derivatized acyclic ligand of diethylenetriaminepentaacetic acid (DTPA) and the derivatized macrocylic ligands of 1,4,7,10-tetra

Magnetically Labeled Glial Cells as Cellular MR Contrast Agents

Demyelination is a common pathologic finding in human neurologic diseases and frequently persists as a result of failure of endogenous repair. Recent research has suggested that it is possible to promote remyelination in animal models of abnormal myelination or demyelination (1), either by endogenous glial cells or exogenous myelinating cells. The migratory capacity of transplanted cells is of key importance in determining the extent of remyelination and can, at present, only be evaluated using invasive and irreversible procedures. A technique that could monitor the grafted cell migration continuously and noninvasively is crucial to guide further advances in neurotransplantation research. We hypothesized that tagging grafted cells with a magnetic label might allow magnetic resonance (MR) tracking of their migratory capacity. Because oligodendrocyte progenitors have a greater migratory and myelinating capacity than mature glial cells, we decided to use the rat oligodendrocyte progenitor cell line CG-4 (2) as the graft, with the md (myelindeficient) rat as a recipient (3). We show here that CG-4 cells can be made highly magnetic by the addition of magnetic nanoparticles that are targeted to the transferrin receptor (Tfr). After neurotransplantation, the tagged glial cells appeared to fully retain their migratory and myelinating capacity in vivo, and their migratory pattern could be easily detected by MR imaging.

Phase Contrast MRI is an Early Marker of Micrometastatic Breast Cancer Development in the Rat Brain

The early growth of micrometastatic breast cancer in the brain often occurs through vessel co‐option and is independent of angiogenesis. Remodeling of the existing vasculature is an important step in the evolution of co‐opting micrometastases into angiogenesis‐dependent solid tumor masses. The purpose of this study was to determine whether phase contrast MRI, an intrinsic source of contrast exquisitely sensitive to the magnetic susceptibility properties of deoxygenated hemoglobin, could detect vascular changes occurring independent of angiogenesis in a rat model of breast cancer metastases to the brain. Twelve nude rats were administered 106 MDA‐MB‐231BRL ‘brain‐seeking’ breast cancer cells through intracardiac injection. Serial, multiparametric MRI of the brain was performed weekly until metastatic disease was detected. The results demonstrated that images of the signal phase (area under the receiver operating characteristic curve, 0.97) were more sensitive than T2* gradient echo magnitude images (area under the receiver operating characteristic curve, 0.73) to metastatic brain lesions. The difference between the two techniques was probably the result of the confounding effects of edema on the magnitude of the signal. A region of interest analysis revealed that vascular abnormalities detected with phase contrast MRI preceded tumor permeability measured with contrast‐enhanced MRI by 1–2 weeks. Tumor size was correlated with permeability (R2 = 0.23, p < 0.01), but phase contrast was independent of tumor size (R2 = 0.03). Histopathologic analysis demonstrated that capillary endothelial cells co‐opted by tumor cells were significantly enlarged, but less dense, relative to the normal brain vasculature. Although co‐opted vessels were vascular endothelial growth factor‐negative, vessels within larger tumor masses were vascular endothelial growth factor‐positive. In conclusion, phase contrast MRI is believed to be sensitive to vascular remodeling in co‐opting brain tumor metastases independent of sprouting angiogenesis, and may therefore aid in preclinical studies of angiogenic‐independent tumors or in the monitoring of continued tumor growth following anti‐angiogenic therapy. Published 2011. This article is a US Government work and is in the public domain in the USA.

Color Transformation and Fluorescence of Prussian Blue- Positive Cells: Implications for Histologic Verification of Cells Labeled with Superparamagnetic Iron Oxide Nanoparticles

Superparamagnetic iron oxide (SPIO) nanoparticles, either modified or in combination with other macromolecules, are being used for magnetic labeling of stem cells and other cells to monitor cell trafficking by magnetic resonance imaging (MRI) in experimental models. The correlation of histology to MRI depends on the ability to detect SPIO-labeled cells using Prussian blue (PB) stain and fluorescent tags to cell surface markers. Exposure of PB-positive sections to ultraviolet light at a wavelength of 365 nm commonly used fluorescence microscopy can result in color transformation of PB-positive material from blue to brown. Although the PB color transformation is primarily an artifact that may occur during fluorescence microscopy, the transformation can be manipulated using imaging process software for the detection of low levels of iron labeled cells in tissues samples