Characterization of Magneto-Endosymbionts as MRI Cell Labeling and Tracking Agents

Abstract

Purpose Magneto-endosymbionts (MEs) show promise as living magnetic resonance imaging (MRI) contrast agents for in vivo cell tracking. Here we characterize the biomedical imaging properties of ME contrast agents, in vitro and in vivo. Procedures By adapting and engineering magnetotactic bacteria to the intracellular niche, we are creating magneto-endosymbionts (MEs) that offer advantages relative to passive iron-based contrast agents (superparamagnetic iron oxides, SPIOs) for cell tracking. This work presents a biomedical imaging characterization of MEs including: MRI transverse relaxivity (r2) for MEs and ME-labeled cells (compared to a commercially available iron oxide nanoparticle); microscopic validation of labeling efficiency and subcellular locations; and in vivo imaging of a MDA-MB-231BR (231BR) human breast cancer cells in a mouse brain. Results At 7T, r2 relaxivity of bare MEs was higher (250 s−1 mM−1) than that of conventional SPIO (178 s−1 mM−1). Optimized in vitro loading of MEs into 231BR cells yielded 1–4 pg iron/cell (compared to 5–10 pg iron/cell for conventional SPIO). r2 relaxivity dropped by a factor of ~3 upon loading into cells, and was on the same order of magnitude for ME-loaded cells compared to SPIO-loaded cells. In vivo, ME-labeled cells exhibited strong MR contrast, allowing as few as 100 cells to be detected in mice using an optimized 3D SPGR gradient-echo sequence. Conclusions Our results demonstrate the potential of magneto-endosymbionts as living MR contrast agents. They have r2 relaxivity values comparable to traditional iron oxide nanoparticle contrast agents, and provide strong MR contrast when loaded into cells and implanted in tissue.

Novel MRI Contrast Agent from Magnetotactic Bacteria Enables In Vivo Tracking of iPSC-derived Cardiomyocytes

“…AMB-1 coordinates over 100 genes to synthesize membrane enclosed magnetic nanoparticles, (magnetosomes), which are highly effective MRI contrast agents24. In metastatic breast cancer cells, ME-labeled cells show strong contrast with as few at 100 ME-labeled cells, demonstrating high sensitivity for detection25. More importantly, the MEs do not appear to persist long-term in macrophages, eliminating any confounding MRI signal of cell viability.…”

Fabrication of a spherical inclusion phantom for validation of magnetic resonance-based magnetic susceptibility imaging

“…In the literature, r 1 and r 2 of the iron oxide particles (in particular, Molday ION) have been reported at different field strengths. For example, the vendor's website (http://www.biopal.com/pdf-downloads/data-sheets/data-sheet-CL-30Q02-2.pdf, accessed 2019/05/24) provides r 1 = 36 [s -1 mM -1 ] and r 2 = 71 [s -1 mM -1 ] at 0.47 T. Brewer et al [15] reported r 2 = 178 [s -1 mM -1 ] at 7T for particles with comparable magnetic core with different functionalization. Given that r 1 decreases and r 2 increases with the main magnetic fields [16], our results of r 1 = 6.1 [s -1 mM -1 ] and r 2 = 142 [s -1 mM -1 ] at 3T are compatible with the literature values.…”

Stem Cell Tracing Through MR Molecular Imaging

“…Recently, non-toxic forms of iron compounds such as ferumoxytol, magneto-endosymbionts, bicycle[6.1.0]nonyne-modified glycol chitosan nanoparticles (BCN-CNPs) have been tested successfully [26][27][28][29]. Among them, ferumoxytol has been found as an FDA approved agent for clinical applications [30].…”

“…Because, low contrast is the main disadvantage of reporter genes for tracking of stem cells, scientists have tried to improve MRI signals using novel or dual reporter gene imaging. Development of novel reporter genes such as T cell immunoglobulin and mucin domain containing protein 2, adenoviral vector encoding ferritin heavy chain and magneto-endosymbionts are some example that have been produced in recent years [61][62][63]. In a study by Guo et al studied tracing of MSCs in rabbit using two reporter genes including ferritin heavy subunit and transferrin receptor.…”