Journal
FRONTIERS IN MICROBIOLOGY
Volume 5, Issue -, Pages -Publisher
FRONTIERS RESEARCH FOUNDATION
DOI: 10.3389/fmicb.2014.00029
Keywords
magnetic resonance imaging; MagA; modified ferritin subunits; relaxation rates; iron; cancer cells
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Funding
- Ontario Research Fund award (ORF-ICT Project) [02-038]
- Multi-Magnetics Inc.
- Lawson Internal Research Fund Studentship
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We compared overexpression of the magnetotactic bacterial gene MagA with the modified mammalian ferritin genes HF + LF, in which both heavy and light subunits lack iron response elements. Whereas both expression systems have been proposed for use in non-invasive, magnetic resonance (MR) reporter gene expression, limited information available regarding their relative potential for providing gene-based contrast. Measurements of MR relaxation rates in these expression systems are important for optimizing cell detection and specificity, for developing qunatification methods, and for refinement of gene-based iron contrast using magnetosome associated genes. We measure the total transverse relaxation rate (R2*), its irreversible and reversible components (R2 and R2', respectively) and the longitudinal relaxation rate (R1) in MDA-MB-435 tumor cells. Clonal lines overexpressing MagA and HF + LF were cultured in the presence and absence of iron supplementation, and mounted in a spherical phantom for relaxation mapping at 3 Tesla. In coupled plasma mass spectrometry, in ATP by luciferase bioluminescence and in transferrin receptor by Western blot. Only transverse relaxation rates were significiantly higher in iron-supplemented, MagA- and HF + LF-expressing cells compared to non-supplemented cells and the parental control. R2* provided the greatest absolute difference and R2' showed the greatest relative difference, consistent with the notion that R2' may be a more specific indicator of iron-based contrast than R2 as observed in brain tissue. Iron supplementation of MagA- and HF + LF-expressing cells increased the iron/zinc ratio approximately 20-fold, while transferrin receptor expression decreased approximately 10-fold. Level of ATP was similar across all cell types and culture conditions. These results highlight the potential of magnetotactic bacterial gene expression for improving MR contrast.
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