Combining magnetic particle imaging and magnetic fluid hyperthermia in a theranostic platform

Magnetic nanoparticle hyperthermia potentiates paclitaxel activity in sensitive and resistant breast cancer cells

Introduction

Overcoming resistance to antimitotic drugs, such as paclitaxel (PTX), would represent a major advance in breast cancer treatment. PTX induces mitotic block and sensitive cells exit mitosis dying by mitotic catastrophe. Resistant cells remain in block and continue proliferation after drug decay, denoting one of the PTX resistance mechanisms. Mild hyperthermia (HT) triggers mitotic exit of PTX-pretreated cells, overcoming PTX resistance and suggesting HT-forced mitotic exit as a promising strategy to potentiate PTX.

Methods and results

Superparamagnetic iron oxide nanoparticles (SPIONs) were used to deliver mild HT at 42°C in PTX-pretreated breast adenocarcinoma MCF-7 cells sensitive and resistant to PTX. To evaluate mechanism of cell death, cells were classified based on nuclear morphology into interphase, mitotic, micronucleated, and apoptotic. The combined PTX→SPION treatment resulted in an increase in the percentage of micronucleated cells, an indication of forced mitotic exit. Importantly, in PTX-resistant cells, the combination therapy using SPION HT helps to overcome resistance by reducing the number of cells relative to the control.

Conclusion

SPION HT potentiates PTX by significantly reducing cell survival, suggesting potential of combined treatment for future clinical translation.

Magnetic particle imaging for radiation-free, sensitive and high-contrast vascular imaging and cell tracking

Magnetic particle imaging (MPI) is an emerging ionizing radiation-free biomedical tracer imaging technique that directly images the intense magnetization of superparamagnetic iron oxide nanoparticles (SPIOs). MPI offers ideal image contrast because MPI shows zero signal from background tissues. Moreover, there is zero attenuation of the signal with depth in tissue, allowing for imaging deep inside the body quantitatively at any location. Recent work has demonstrated the potential of MPI for robust, sensitive vascular imaging and cell tracking with high contrast and dose-limited sensitivity comparable to nuclear medicine. To foster future applications in MPI, this new biomedical imaging field is welcoming researchers with expertise in imaging physics, magnetic nanoparticle synthesis and functionalization, nanoscale physics, and small animal imaging applications.

A perspective on a rapid and radiation-free tracer imaging modality, magnetic particle imaging, with promise for clinical translation

Magnetic particle imaging (MPI), introduced at the beginning of the twenty-first century, is emerging as a promising diagnostic tool in addition to the current repertoire of medical imaging modalities. Using superparamagnetic iron oxide nanoparticles (SPIOs), that are available for clinical use, MPI produces high contrast and highly sensitive tomographic images with absolute quantitation, no tissue attenuation at-depth, and there are no view limitations. The MPI signal is governed by the Brownian and Néel relaxation behavior of the particles. The relaxation time constants of these particles can be utilized to map information relating to the local microenvironment, such as viscosity and temperature. Proof-of-concept pre-clinical studies have shown favourable applications of MPI for better understanding the pathophysiology associated with vascular defects, tracking cell-based therapies and nanotheranostics. Functional imaging techniques using MPI will be useful for studying the pathology related to viscosity changes such as in vascular plaques and in determining cell viability of superparamagnetic iron oxide nanoparticle labeled cells. In this review article, an overview of MPI is provided with discussions mainly focusing on MPI tracers, applications of translational capabilities ranging from diagnostics to theranostics and finally outline a promising path towards clinical translation.

In vivo tracking and quantification of inhaled aerosol using magnetic particle imaging towards inhaled therapeutic monitoring

Pulmonary delivery of therapeutics is attractive due to rapid absorption and non-invasiveness but it is challenging to monitor and quantify the delivered aerosol or powder. Currently, single-photon emission computed tomography (SPECT) is used but requires inhalation of radioactive labels that typically have to be synthesized and attached by hot chemistry techniques just prior to every scan. Methods: In this work, we demonstrate that superparamagnetic iron oxide nanoparticles (SPIONs) can be used to label and track aerosols in vivo with high sensitivity using an emerging medical imaging technique known as magnetic particle imaging (MPI). We perform proof-of-concept experiments with SPIONs for various lung applications such as evaluation of efficiency and uniformity of aerosol delivery, tracking of the initial aerosolized therapeutic deposition in vivo, and finally, sensitive visualization of the entire mucociliary clearance pathway from the lung up to the epiglottis and down the gastrointestinal tract to be excreted. Results: Imaging of SPIONs in the lung has previously been limited by difficulty of lung imaging with magnetic resonance imaging (MRI). In our results, MPI enabled SPION lung imaging with high sensitivity, and a key implication is the potential combination with magnetic actuation or hyperthermia for MPI-guided therapy in the lung with SPIONs. Conclusion: This work shows how magnetic particle imaging can be enabling for new imaging and therapeutic applications of SPIONs in the lung.

Magnetic Hyperthermia and Radiation Therapy: Radiobiological Principles and Current Practice †

Hyperthermia, though by itself generally non-curative for cancer, can significantly increase the efficacy of radiation therapy, as demonstrated by in vitro, in vivo, and clinical results. Its limited use in the clinic is mainly due to various practical implementation difficulties, the most important being how to adequately heat the tumor, especially deep-seated ones. In this work, we first review the effects of hyperthermia on tissue, the limitations of radiation therapy and the radiobiological rationale for combining the two treatment modalities. Subsequently, we review the theory and evidence for magnetic hyperthermia that is based on magnetic nanoparticles, its advantages compared with other methods of hyperthermia, and how it can be used to overcome the problems associated with traditional techniques of hyperthermia.

Magnetic Particle Imaging-Guided Heating in Vivo Using Gradient Fields for Arbitrary Localization of Magnetic Hyperthermia Therapy

Image-guided treatment of cancer enables physicians to localize and treat tumors with great precision. Here, we present in vivo results showing that an emerging imaging modality, magnetic particle imaging (MPI), can be combined with magnetic hyperthermia into an image-guided theranostic platform. MPI is a noninvasive 3D tomographic imaging method with high sensitivity and contrast, zero ionizing radiation, and is linearly quantitative at any depth with no view limitations. The same superparamagnetic iron oxide nanoparticle (SPIONs) tracers imaged in MPI can also be excited to generate heat for magnetic hyperthermia. In this study, we demonstrate a theranostic platform, with quantitative MPI image guidance for treatment planning and use of the MPI gradients for spatial localization of magnetic hyperthermia to arbitrarily selected regions. This addresses a key challenge of conventional magnetic hyperthermia-SPIONs delivered systemically accumulate in off-target organs ( e.g., liver and spleen), and difficulty in localizing hyperthermia results in collateral heat damage to these organs. Using a MPI magnetic hyperthermia workflow, we demonstrate image-guided spatial localization of hyperthermia to the tumor while minimizing collateral damage to the nearby liver (1-2 cm distance). Localization of thermal damage and therapy was validated with luciferase activity and histological assessment. Apart from localizing thermal therapy, the technique presented here can also be extended to localize actuation of drug release and other biomechanical-based therapies. With high contrast and high sensitivity imaging combined with precise control and localization of the actuated therapy, MPI is a powerful platform for magnetic-based theranostics.

Development of a Trimodal Contrast Agent for Acoustic and Magnetic Particle Imaging of Stem Cells

Stem cell therapy has the potential to improve tissue remodeling and repair. For cardiac stem cell therapy, methods to improve the injection and tracking of stem cells may help to increase patient outcomes. Here we describe a multimodal approach that combines ultrasound imaging, photoacoustic imaging, and magnetic particle imaging (MPI). Ultrasound imaging offers real-time guidance, photoacoustic imaging offers enhanced contrast, and MPI offers high-contrast, deep-tissue imaging. This work was facilitated by a poly(lactic-co-glycolic acid) (PLGA)-based iron oxide nanobubble labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide (DiR) as a trimodal contrast agent. The PLGA coating facilitated the ultrasound signal, the DiR increased the photoacoustic signal, and the iron oxide facilitated the MPI signal. We confirmed that cell metabolism, proliferation, differentiation, and migration were not adversely affected by cell treatment with nanobubbles. The nanobubble-labeled cells were injected intramyocardially into live mice for real-time imaging. Ultrasound imaging showed a 3.8-fold increase in the imaging intensity of labeled cells postinjection compared to the baseline; photoacoustic imaging showed a 10.2-fold increase in the cardiac tissue signal postinjection. The MPI intensity of the nanobubble-treated human mesenchymal stem cells injected into the hearts of mice was approximately 20-fold greater than the negative control.

Iron Oxide Nanoparticles: Innovative Tool in Cancer Diagnosis and Therapy

Although cancer is one of the most dangerous and the second most lethal disease in the world, current therapy including surgery, chemotherapy, radiotherapy, etc., is highly insufficient not in the view of therapy success rate or the amount of side effects. Accordingly, procedures with better outcomes are highly desirable. Iron oxide nanoparticles (IONPs) present an innovative tool-ideal for innovation and implementation into practice. This review is focused on summarizing some well-known facts about pharmacokinetics, toxicity, and the types of IONPs, and furthermore, provides a survey of their use in cancer diagnosis and therapy.

Seeing SPIOs Directly In Vivo with Magnetic Particle Imaging

Magnetic particle imaging (MPI) is a new molecular imaging technique that directly images superparamagnetic tracers with high image contrast and sensitivity approaching nuclear medicine techniques-but without ionizing radiation. Since its inception, the MPI research field has quickly progressed in imaging theory, hardware, tracer design, and biomedical applications. Here, we describe the history and field of MPI, outline pressing challenges to MPI technology and clinical translation, highlight unique applications in MPI, and describe the role of the WMIS MPI Interest Group in collaboratively advancing MPI as a molecular imaging technique. We invite interested investigators to join the MPI Interest Group and contribute new insights and innovations to the MPI field.

Commentary on the clinical and preclinical dosage limits of interstitially administered magnetic fluids for therapeutic hyperthermia based on current practice and efficacy models

We offer a critique of what constitutes a suitable dosage limit, in both clinical and preclinical studies, for interstitially administered magnetic nanoparticles in order to enable therapeutic hyperthermia under the action of an externally applied alternating magnetic field. We approach this first from the perspective of the currently approved clinical dosages of magnetic nanoparticles in the fields of MRI contrast enhancement, sentinel node detection, iron replacement therapy and magnetic thermoablation. We compare this to a simple analytical model of the achievable hyperthermia temperature rise in both humans and animals based on the interstitially administered dose, the heating and dispersion characteristics of the injected fluid, and the strength and frequency of the applied magnetic field. We show that under appropriately chosen conditions a therapeutic temperature rise is achievable in clinically relevant situations. We also show that in such cases it may paradoxically be harder to achieve the same therapeutic temperature rise in a preclinical model. We comment on the implications for the evidence-based translation of hyperthermia based interventions from the laboratory to the clinic.

Establishing the overlap of IONP quantification with echo and echoless MR relaxation mapping

PURPOSE

Iron-oxide nanoparticles (IONPs) have shown tremendous utility for enhancing image contrast and delivering targeted therapies. Quantification of IONPs has been demonstrated at low concentrations with gradient echo (GRE) and spin echo (SE), and at high concentrations with echoless sequences such as swept imaging with Fourier transform (SWIFT). This work examines the overlap of IONP quantification with GRE, SE, and SWIFT.

METHODS

The limit of quantification of GRE, SE, inversion-recovery GRE, and SWIFT sequences was assessed using IONPs at a concentration range of 0.02 to 89.29 mM suspended in 1% agarose. Empirically derived limits of quantification were compared with International Union of Pure and Applied Chemistry definitions. Both commercial and experimental IONPs were used.

RESULTS

All three IONPs assessed demonstrated an overlap of concentration quantification with GRE, SE, and SWIFT sequences. The largest dynamic range observed was 0.004 to 35.7 mM with Feraheme.

CONCLUSIONS

The metrics established allow upper and lower quantitative limitations to be estimated given the relaxivity characteristics of the IONP and the concentration range of the material to be assessed. The methods outlined in this paper are applicable to any pulse sequence, IONP formulation, and field strength. Magn Reson Med 79:1420-1428, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

The Relaxation Wall: Experimental Limits to Improving MPI Spatial Resolution by Increasing Nanoparticle Core size

Magnetic Particle Imaging (MPI) is a promising new tracer modality with zero attenuation in tissue, high contrast and sensitivity, and an excellent safety profile. However, the spatial resolution of MPI is currently around 1 mm in small animal scanners. Especially considering tradeoffs when scaling up MPI scanning systems to human size, this resolution needs to be improved for clinical applications such as angiography and brain perfusion. One method to improve spatial resolution is to increase the magnetic core size of the superparamagnetic nanoparticle tracers. The Langevin model of superparamagnetism predicts a cubic improvement of spatial resolution with magnetic core diameter. However, prior work has shown that the finite temporal response, or magnetic relaxation, of the tracer increases with magnetic core diameter and eventually leads to blurring in the MPI image. Here we perform the first wide ranging study of 5 core sizes between 18-32 nm with experimental quantification of the spatial resolution of each. Our results show that increasing magnetic relaxation with core size eventually opposes the expected Langevin behavior, causing spatial resolution to stop improving after 25 nm. Different MPI excitation strategies were experimentally investigated to mitigate the effect of magnetic relaxation. The results show that magnetic relaxation could not be fully mitigated for the larger core sizes and the cubic resolution improvement predicted by the Langevin was not achieved. This suggests that magnetic relaxation is a significant and unsolved barrier to achieving the high spatial resolutions predicted by the Langevin model for large core size SPIOs.