Ferritin has gained significant attention as a potential reporter gene for in vivo imaging by magnetic resonance imaging (MRI). However, due to the ferritin ferrihydrite core, the relaxivity and sensitivity for detection of native ferritin is relatively low. We report here on a novel chimeric magneto-ferritin reporter gene – ferritin-M6A – in which the magnetite binding peptide from the magnetotactic bacteria magnetosome-associated Mms6 protein was fused to the C-terminal of murine h-ferritin. Biophysical experiments showed that purified ferritin-M6A assembled into a stable protein cage with the M6A protruding into the cage core, enabling magnetite biomineralisation. Ferritin-M6A-expressing C6-glioma cells showed enhanced (per iron) r2 relaxivity. MRI in vivo studies of ferritin-M6A-expressing tumour xenografts showed enhanced R2 relaxation rate in the central hypoxic region of the tumours. Such enhanced relaxivity would increase the sensitivity of ferritin as a reporter gene for non-invasive in vivo MRI-monitoring of cell delivery and differentiation in cellular or gene-based therapies.
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The research leading to these results has received funding from the EU Seventh Framework Programme (FP7/2007–2013 under grant agreements ⚬239182), from the Israel Science Foundation and the Israeli Ministry of Science Technology and Space (to R.Z.), and from the European Commission FP7 Integrated Project ENCITE and the ERC Advanced project 232640-IMAGO (to M.N.).
Radoul, Marina; Lewin, Limor; Cohen, Batya; Oren, Roni; Popov, Stanislav; Davidov, Geula; Vandsburger, Moriel H.; Harmelin, Alon; Bitton, Ronit; Greneche, Jean-Marc; Neeman, Michal; and Zarivach, Raz, "Genetic Manipulation of Iron Biomineralization Enhances MR Relaxivity in a Ferritin-M6A Chimeric Complex" (2016). Physiology Faculty Publications. 87.