Magnetic Particle Imaging - from particle science to imaging technology

The possibility of using magnetic nanoparticles to increase the therapeutic efficiency of Herceptin antibody

INTRODUCTION

Herceptin is an expensive humanized antibody used for the treatment of early-stage breast cancers. This antibody can cause cardiotoxicity in some patients. In this study, we evaluated the possibility of increasing the therapeutic efficacy of Herceptin by combining magnetic nanoparticles and a permanent magnet for more accumulation in the tumor site.

METHODS

Herceptin magnetic nanoparticles (HMNs) were synthesized and some of their characteristics, such as stability, magnetization, particle size by transmission electron microscopy (TEM), and dynamic light scattering (DLS) technique, were measured. The biodistribution study was checked in mice bearing breast tumor with and without a permanent magnet on the position of the tumor. The therapeutic effects of HMNs were considered in this condition.

RESULTS

The size distribution of HMNs determined by the DLS technique was 182±7 nm and the average size by TEM was 100±10 nm. The reductions of 81% and 98% in the mean tumor volume for the group that received HMNs with magnetic field were observed at 42 and 45 days after injection, respectively.

CONCLUSION

The good results in mice indicated that Herceptin-loaded iron oxide nanoparticles with external magnetic field have good potential for use in humans as a targeted drug delivery that needs more investigation.

Quantitative "Hot Spot" Imaging of Transplanted Stem Cells using Superparamagnetic Tracers and Magnetic Particle Imaging (MPI)

Magnetic labeling of stem cells enables their noninvasive detection by magnetic resonance imaging (MRI). In practical terms, most MRI studies have been limited to the visualization of local engraftment because other sources of endogenous hypointense contrast complicate the interpretation of systemic (whole-body) cell distribution. In addition, MRI cell tracking is inherently nonquantitative in nature. We report herein on the potential of magnetic particle imaging (MPI) as a novel tomographic technique for noninvasive “hot-spot” imaging and quantification of stem cells using superparamagnetic iron oxide (SPIO) tracers. Neural and mesenchymal stem cells, representing small and larger cell bodies, were labeled with 3 different SPIO tracer formulations, including 2 preparations (Feridex and Resovist) that have previously been used in clinical MRI cell-tracking studies. Magnetic particle spectroscopy measurements demonstrated a linear correlation between MPI signal and iron content for both free particles in homogeneous solution and for internalized and aggregated particles in labeled cells over a wide range of concentrations. The overall MPI signal ranged from 1 × 10⁻³ to 3 × 10⁻⁴ Am²/g Fe, which was equivalent to 2 × 10⁻¹⁴ to 1 × 10⁻¹⁵ Am² per cell, indicating that cell numbers can be quantified with MPI analogous to the use of radiotracers in nuclear medicine or fluorine tracers in ¹⁹F MRI. When SPIO-labeled cells were transplanted in the mouse brain, they could be readily detected by MPI at a detection threshold of about 5 × 10⁴ cells, with MPI/MRI overlays showing an excellent agreement between the hypointense MRI areas and MPI hot spots. The calculated tissue MPI signal ratio for 100 000 vs 50 000 implanted cells was 2.08. Hence, MPI can potentially be further developed for quantitative and easy-to-interpret, tracer-based noninvasive cell imaging, preferably with MRI as an adjunct anatomical imaging modality.