Dual Magnetic Particle Imaging and Akaluc Bioluminescence Imaging for Tracking Cancer Cell Metastasis

Abstract

Magnetic particle imaging (MPI) provides hotspot tracking and direct quantification of superparamagnetic iron oxide nanoparticle (SPIO)-labelled cells. Bioluminescence imaging (BLI) with the luciferase reporter gene Akaluc can provide complementary information on cell viability. Thus, we explored combining these technologies to provide a more holistic view of cancer cell fate in mice. Akaluc-expressing 4T1Br5 cells were labelled with the SPIO Synomag-D and injected into the mammary fat pads (MFP) of four nude mice. BLI was performed on days 0, 6 and 13, and MPI was performed on days 1, 8 and 14. Ex vivo histology and fluorescence microscopy of MFP and a potential metastatic site was conducted. The BLI signal in the MFP increased significantly from day 0 to day 13 (p < 0.05), mirroring tumor growth. The MPI signal significantly decreased from day 1 to day 14 (p < 0.05) due to SPIO dilution in proliferating cells. Both modalities detected secondary metastases; however, they were visualized in different anatomical regions. Akaluc BLI complemented MPI cell tracking, allowing for longitudinal measures of cell viability and sensitive detection of distant metastases at different locations. We predict this multimodal imaging approach will help to evaluate novel therapeutics and give a better understanding of metastatic mechanisms.

Magnetic Particle Imaging Reveals that Iron-Labeled Extracellular Vesicles Accumulate in Brains of Mice with Metastases

“…Coincubation of 4T1-fLuc2 (4T1L2) or 4T1BR5-fLuc2/GFP (4T1BR5-L2G) cells in culture with SPIO nanoparticles resulted in the cell secretion of iron-labeled EVs (FeEVs) into the culture medium. This method of protamine sulfate/heparin assemblies to aid in Synomag-D internalization into 4T1BR5 cells has been performed previously, with no changes in viability of cells up to 3 days postlabeling . Upon isolation from conditioned medium via differential centrifugation, the SPIOs were found to be associated with the cell-secreted EVs, as confirmed using transmission electron microscopy (TEM) visualizing the EV membranes (stained with uranyl acetate for contrast) and our dextran-coated iron nanoparticles.…”

“…In addition, there is no loss of signal due to mammalian tissues, and thus the depth of particles within the body does not adversely affect quantitative imaging. MPI has been used for cancer detection ,− and has been used to track engineered EVs to primary tumors in animal models. In addition to this, other applications of MPI have included vascular imaging, − inflammation, , therapeutic studies , and cell tracking. − Further, groups are working toward improved nanoparticles tailored for MPI, − improvements in MPI hardware and acquisition , and image analysis. , Other imaging methods such as in vivo bioluminescence imaging (BLI) can be used as a complementary imaging modality in rodent models to associate or correlate MPI signals with other biological processes such as sites of metastatic lesions …”

Magnetic particle imaging reveals that iron-labeled extracellular vesicles accumulate in brains of mice with metastases

“…Co-incubation of 4T1-fLuc2 (4T1L2) or 4T1BR5-fLuc2/GFP (4T1BR5-L2G) cells in culture with SPIO nanoparticles resulted in cell secretion of iron-labeled EVs (FeEVs) into the culture medium. This method of protamine sulfate/heparin assemblies to aid in Synomag-D internalization into 4T1BR5 cells has been performed previously, with no changes in viability of cells up to 3 days post labeling 42 . Upon isolation from conditioned medium via differential centrifugation, the SPIOs were found to be associated with the cell-secreted EVs, as confirmed using transmission electron microscopy (TEM) visualizing the EV membranes (stained with uranyl acetate for contrast) and our dextran-coated iron nanoparticles.…”

“…In addiAon, there is no loss of signal due to mammalian Assues and thus the depth of parAcles within the body does not adversely affect quanAtaAve imaging. MPI has been used for cancer detecAon 36,[39][40][41][42] and has been used to track engineered EVs to primary tumors 32 in animal models. Other imaging methods such as in vivo bioluminescence imaging (BLI) can be used as a complementary imaging modality in rodent models to associate or correlate MPI signals with other biological processes such as sites of metastaAc lesions 43 .…”

“…In addition, there is no loss of signal due to mammalian tissues and thus the depth of particles within the body does not adversely affect quantitative imaging. MPI has been used for cancer detection 39,42–45 and has been used to track engineered EVs to primary tumors 34 in animal models. In addition to this, other applications of MPI have included vascular imaging 46–50 , inflammation 51,52 , therapeutic studies 53,54 and cell tracking 54–60 .…”