Ex-vivo cellular MRI with b-SSFP: quantitative benefits of 3 T over 1.5 T

Cellular Magnetic Resonance Imaging for Tracking Metastatic Cancer Cells in the Brain

Cellular magnetic resonance imaging (MRI) enables visualization of cells in vivo. This is accomplished by labeling cells with superparamagnetic iron oxide nanoparticles. Here, we describe the steps for labeling human cancer cells with iron for tracking them after injection into nude mice. We also provide details for validation of cell labeling, ultrasound guided intra-cardiac injection, and MRI.

MRI surveillance of cancer cell fate in a brain metastasis model after early radiotherapy

PURPOSE

Incidence of brain metastasis attributed to breast cancer is increasing and prognosis is poor. It is thought that disseminated dormant cancer cells persist in metastatic organs and may evade treatments, thereby facilitating a mechanism for recurrence. Radiotherapy is used to treat brain metastases clinically, but assessment has been limited to macroscopic tumor volumes detectable by clinical imaging. Here, we use cellular MRI to understand the concurrent responses of metastases and nonproliferative or slowly cycling cancer cells to radiotherapy.

METHODS

MRI cell tracking was used to investigate the impact of early cranial irradiation on the fate of individual iron-labeled cancer cells and outgrowth of breast cancer brain metastases in the human MDA-MB-231-BR-HER2 cell model.

RESULTS

Early whole-brain radiotherapy significantly reduced the outgrowth of metastases from individual disseminated cancer cells in treated animals compared to controls. However, the numbers of nonproliferative iron-retaining cancer cells in the brain were not significantly different.

CONCLUSIONS

Radiotherapy, when given early in cancer progression, is effective in preventing the outgrowth of solitary cancer cells to brain metastases. Future studies of the nonproliferative cancer cells' clonogenic potentials are warranted, given that their persistent presence suggests that they may have evaded treatment. Magn Reson Med 78:1506-1512, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Cellular Imaging With MRI

Cellular magnetic resonance imaging (MRI) is an evolving field of imaging with strong translational and research potential. The ability to detect, track, and quantify cells in vivo and over time allows for studying cellular events related to disease processes and may be used as a biomarker for decisions about treatments and for monitoring responses to treatments. In this review, we discuss methods for labeling cells, various applications for cellular MRI, the existing limitations, strategies to address these shortcomings, and clinical cellular MRI.

MRI and histopathologic study of a novel cholesterol-fed rabbit model of xanthogranuloma

PURPOSE

To develop a rabbit model of xanthogranuloma based on supplementation of dietary cholesterol. The aim of this study was to analyze the xanthogranulomatous lesions using magnetic resonance imaging (MRI) and histological examination.

MATERIALS AND METHODS

Rabbits were fed a low-level cholesterol (CH) diet (n = 10) or normal chow (n = 5) for 24 months. In vivo brain imaging was performed on a 3T MR system using fast imaging employing steady state acquisition, susceptibility-weighted imaging, spoiled gradient recalled, T1 -weighted inversion recovery imaging and T1 relaxometry, PD-weighted and T2 -weighted spin-echo imaging and T2 relaxometry, iterative decomposition of water and fat with echo asymmetry and least-squares estimation, ultrashort TE MRI (UTE-MRI), and T2* relaxometry. MR images were evaluated using a Likert scale for lesion presence and quantitative analysis of lesion size, ventricular volume, and T1 , T2 , and T2* values of lesions was performed. After imaging, brain specimens were examined using histological methods.

RESULTS

In vivo MRI revealed that 6 of 10 CH-fed rabbits developed lesions in the choroid plexus. Region-of-interest analysis showed that for CH-fed rabbits the mean lesion volume was 8.5 ± 2.6 mm(3) and the volume of the lateral ventricle was significantly increased compared to controls (P < 0.01). The lesions showed significantly shorter mean T2 values (35 ± 12 msec, P < 0.001), longer mean T1 values (1581 ± 146 msec, P < 0.05), and shorter T2* values (22 ± 13 msec, P < 0.001) compared to adjacent brain structures. The ultrashort T2* components were visible using UTE-MRI. Histopathologic evaluation of lesions demonstrated features of human xanthogranuloma.

CONCLUSION

Rabbits fed a low-level CH diet develop sizable intraventricular masses that have similar histopathological features as human xanthogranuloma. Multiparametric MRI techniques were able to provide information about the complex composition of these lesions. J. Magn. Reson. Imaging 2016;44:673-682.

Imaging tumor growth non-invasively using expression of MagA or modified ferritin subunits to augment intracellular contrast for repetitive MRI

PURPOSE

The bacterial gene MagA imparts magnetic properties to mammalian cells and provides a basis for cell tracking by magnetic resonance imaging (MRI). In a mouse model of tumor growth from transplanted cells, we used repetitive MRI to demonstrate the in vivo imaging potential of MagA expression relative to a modified ferritin overexpression system, lacking regulation through iron response elements (HF + LF).

PROCEDURES

Subcutaneous tumor xenografts were monitored weekly from days 2 to 34 post-injection. Small animal MRI employed balanced steady-state free precession. Imaging was correlated with tumor histology using hematoxylin, Prussian Blue, Ki-67, and BS-1 lectin.

RESULTS

Tumor heterogeneity with respect to tissue morphology and magnetic resonance (MR) contrast was apparent within a week of cell transplantation. In MagA- and HF + LF-expressing tumors, MR contrast enhancement was recorded up to day 20 post-injection and 0.073-cm(3) tumor volumes. MagA-expressing tumors showed increases in both quantity and quality of MR contrast as measured by fractional void volume and contrast-to-noise ratio, respectively. MR contrast in both MagA- and HF + LF-expressing tumors was maximal by day 13, doubling fractional void volume 1 week ahead of controls.

CONCLUSIONS

MagA- and HF + LF-expressing tumor xenografts augment MR contrast after 1 week of growth. MagA expression increases MR contrast within days of cell transplantation and provides MR contrast comparable to HF + LF. MagA has utility for monitoring cell growth and differentiation, with potential for in vivo detection of reporter gene expression using MRI.

Tracking and evaluation of dendritic cell migration by cellular magnetic resonance imaging

Cellular magnetic resonance imaging (MRI) is a means by which cells labeled ex vivo with a contrast agent can be detected and tracked over time in vivo. This technology provides a noninvasive method with which to assess cell-based therapies in vivo. Dendritic cell (DC)-based vaccines are a promising cancer immunotherapy, but its success is highly dependent on the injected DC migrating to a secondary lymphoid organ such as a nearby lymph node. There the DC can interact with T cells to elicit a tumor-specific immune response. It is important to verify DC migration in vivo using a noninvasive imaging modality, such as cellular MRI, so that important information regarding the anatomical location and persistence of the injected DC in a targeted lymph node can be provided. An understanding of DC biology is critical in ascertaining how to label DC with sufficient contrast agent to render them detectable by MRI. While iron oxide nanoparticles provide the best sensitivity for detection of DC in vivo, a clinical grade iron oxide agent is not currently available. A clinical grade (19) Fluorine-based perfluorcarbon nanoemulsion is available but is less sensitive, and its utility to detect DC migration in humans remains to be demonstrated using clinical scanners presently available. The ability to quantitatively track DC migration in vivo can provide important information as to whether different DC maturation and activation protocols result in improved DC migration efficiency which will determine the vaccine's immunogenicity and ultimately the tumor immunotherapy's outcome in humans.

Migration of iron-labeled KHYG-1 natural killer cells to subcutaneous tumors in nude mice, as detected by magnetic resonance imaging

BACKGROUND AIMS

A novel cell line of cytotoxic natural killer (NK) cells, KHYG-1, was examined in vivo for immunotherapy against prostate cancer. The feasibility of using magnetic resonance imaging (MRI) tracking to monitor the fate of injected NK cells following intravenous (i.v.), intraperitoneal (i.p.) and subcutaneous (s.c.) administration was assessed.

METHODS

PC-3M human prostate cancer cells were injected s.c. into the flank of nude mice (day 0). KHYG-1 NK cells were labeled with an iron oxide contrast agent and injected s.c., i.v. or i.p. on day 8. Mice were imaged by MRI on days 7, 9 and 12. Tumor sections were examined with fluorescence microscopy and immunohistologic staining for NK cells.

RESULTS

NK cells were detected in the tumors by histology after all three administration routes. NK cells and fluorescence from the iron label were co-localized. Signal loss was seen in the areas around the tumors and between the tumor lobes in the s.c. group.

CONCLUSIONS

We are the first to label this cell line of NK cells with an iron oxide contrast agent. Accumulation of NK cells was visualized by MRI after s.c. injection but not after i.v. and i.p. injection.

In vivo single scan detection of both iron-labeled cells and breast cancer metastases in the mouse brain using balanced steady-state free precession imaging at 1.5 T

PURPOSE

To simultaneously detect iron-labeled cancer cells and brain tumors in vivo in one scan, the balanced steady-state free precession (b-SSFP) imaging sequence was optimized at 1.5 T on mice developing brain metastases subsequent to the injection of micron-sized iron oxide particle-labeled human breast cancer cells.

MATERIALS AND METHODS

b-SSFP sequence parameters (repetition time, flip angle, and receiver bandwidth) were varied and the signal-to-noise ratio, contrast between the brain and tumors, and the number of detected iron-labeled cells were evaluated.

RESULTS

Optimal b-SSFP images were acquired with a 26 msec repetition time, 35° flip angle, and bandwidth of ±21 kHz. b-SSFP images were compared with T(2) -weighted 2D fast spin echo (FSE) and 3D spoiled gradient recalled echo (SPGR) images. The mean tumor-brain contrast-to-noise ratio and the ability to detect iron-labeled cells were the highest in the b-SSFP images.

CONCLUSION

A single b-SSFP scan can be used to visualize both iron-labeled cells and brain metastases.

Optimization of the balanced steady state free precession (bSSFP) pulse sequence for magnetic resonance imaging of the mouse prostate at 3T

INTRODUCTION

MRI can be used to non-invasively monitor tumour growth and response to treatment in mouse models of prostate cancer, particularly for longitudinal studies of orthotopically-implanted models. We have optimized the balanced steady-state free precession (bSSFP) pulse sequence for mouse prostate imaging.

METHODS

Phase cycling, excitations, flip angle and receiver bandwidth parameters were optimized for signal to noise ratio and contrast to noise ratio of the prostate. The optimized bSSFP sequence was compared to T1- and T2-weighted spin echo sequences.

RESULTS

SNR and CNR increased with flip angle. As bandwidth increased, SNR, CNR and artifacts such as chemical shift decreased. The final optimized sequence was 4 PC, 2 NEX, FA 50°, BW ±62.5 kHz and took 14-26 minutes with 200 µm isotropic resolution. The SNR efficiency of the bSSFP images was higher than for T1WSE and T2WSE. CNR was highest for T1WSE, followed closely by bSSFP, with the T2WSE having the lowest CNR. With the bSSFP images the whole body and organs of interest including renal, iliac, inguinal and popliteal lymph nodes were visible.

CONCLUSION

We were able to obtain fast, high-resolution, high CNR images of the healthy mouse prostate with an optimized bSSFP sequence.

Concise review: Nanoparticles and cellular carriers-allies in cancer imaging and cellular gene therapy?

Ineffective treatment and poor patient management continue to plague the arena of clinical oncology. The crucial issues include inadequate treatment efficacy due to ineffective targeting of cancer deposits, systemic toxicities, suboptimal cancer detection and disease monitoring. This has led to the quest for clinically relevant, innovative multifaceted solutions such as development of targeted and traceable therapies. Mesenchymal stem cells (MSCs) have the intrinsic ability to "home" to growing tumors and are hypoimmunogenic. Therefore, these can be used as (a) "Trojan Horses" to deliver gene therapy directly into the tumors and (b) carriers of nanoparticles to allow cell tracking and simultaneous cancer detection. The camouflage of MSC carriers can potentially tackle the issues of safety, vector, and/or transgene immunogenicity as well as nanoparticle clearance and toxicity. The versatility of the nanotechnology platform could allow cellular tracking using single or multimodal imaging modalities. Toward that end, noninvasive magnetic resonance imaging (MRI) is fast becoming a clinical favorite, though there is scope for improvement in its accuracy and sensitivity. In that, use of superparamagnetic iron-oxide nanoparticles (SPION) as MRI contrast enhancers may be the best option for tracking therapeutic MSC. The prospects and consequences of synergistic approaches using MSC carriers, gene therapy, and SPION in developing cancer diagnostics and therapeutics are discussed.

Chapter 4 - Applications of nanotechnology in molecular imaging of the brain

Rapid advances in the field of nanotechnology promise revolutionary improvements in the diagnosis and therapy of neuroinflammatory disorders. An array of iron oxide nano- and microparticle agents have been developed for in vivo molecular magnetic resonance imaging (mMRI) of cerebrovascular endothelial targets, such as vascular cell adhesion molecule-1 (VCAM-1), E-selectin, and the glycoprotein receptor GP IIb/IIIa expressed on activated platelets. Molecular markers of glioma cells, such as matrix metalloproteinase-2 (MMP-2), and markers for brain tumor angiogenesis, such as alpha (v) beta (3) integrin (alpha(v)beta(3)), have also been successfully targeted using nanoparticle imaging probes. This chapter provides an overview of targeted, iron oxide nano- and microparticles that have been applied for in vivo mMRI of the brain in experimental models of multiple sclerosis (MS), brain ischemia, cerebral malaria (CM), brain cancer, and Alzheimer's disease. The potential of targeted nanoparticle agents for application in clinical imaging is also discussed, including multimodal and therapeutic approaches.

In vivo magnetic resonance imaging of spinal cord injury in the mouse

The feasibility of performing high-resolution in vivo magnetic resonance imaging (MRI) to visualize the injured mouse spinal cord using a three-dimensional (3D)-FIESTA (fast imaging employing steady state acquisition) pulse sequence, in a clip compression injury model, is presented. Images were acquired using a 3-Tesla clinical whole-body MR system equipped with a high-performance gradient coil insert. High-resolution mouse cord images were used to detect and monitor the cord lesions for 6 weeks after spinal cord injury (SCI). The epicenter of the injury appeared as a region of mixed signal intensities on day 2 post-SCI. Regions of signal hypointensity appeared at the lesion site by 2 weeks post-SCI and became more apparent with time. In some mice, large cyst-like lesions were detected rostral to the lesion epicenter, as early as 2 weeks post-SCI, and increased in volume with time. In addition, MRI was used to detect and monitor iron-labeled mesenchymal stem cells (MSCs) after their transplantation into the injured cord. MSCs appeared as large, obvious regions of signal loss in the cord, which decreased in size over time.