Development of Timd2 as a reporter gene for MRI

Abstract

PurposeTo assess the potential of an MRI gene reporter based on the ferritin receptor Timd2 (T‐cell immunoglobulin and mucin domain containing protein 2), using T1‐ and T2‐weighted imaging.MethodsPellets of cells that had been modified to express the Timd2 transgene, and incubated with either iron‐loaded or manganese‐loaded ferritin, were imaged using T1‐ and T2‐weighted MRI. Mice were also implanted subcutaneously with Timd2‐expressing cells and the resulting xenograft tissue imaged following intravenous injection of ferritin using T2‐weighted imaging.ResultsTimd2‐expressing cells, but not control cells, showed a large increase in both R2 and R1 in vitro following incubation with iron‐loaded and manganese‐loaded ferritin, respectively. Expression of Timd2 had no effect on cell viability or proliferation; however, manganese‐loaded ferritin, but not iron‐loaded ferritin, was toxic to Timd2‐expressing cells. Timd2‐expressing xenografts in vivo showed much smaller changes in R2 following injection of iron‐loaded ferritin than the same cells incubated in vitro with iron‐loaded ferritin.ConclusionTimd2 has demonstrated potential as an MRI reporter gene, producing large increases in R2 and R1 with ferritin and manganese‐loaded ferritin respectively in vitro, although more modest changes in R2 in vivo. Manganese‐loaded apoferritin was not used in vivo due to the toxicity observed in vitro. Magn Reson Med, 2015. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Magn Reson Med 75:1697–1707, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance.

Non-invasive imaging using reporter genes altering cellular water permeability

“…In contrast to optical techniques, magnetic resonance imaging (MRI) enables the acquisition of in vivo images with excellent depth penetration and high spatial and temporal resolution. Consequently, there is intense interest in the development of genetically encoded reporters for MRI67891011121314151617181920212223242526. Previous efforts to develop such reporters have focused primarily on two classes of proteins.…”

“…Previous efforts to develop such reporters have focused primarily on two classes of proteins. In one class, metalloproteins and metal ion transporters are overexpressed to enrich the paramagnetic content of cells, thereby enhancing nuclear relaxation rates and producing contrast in T 1 - or T 2 -weighted MRI91213141516171819252627. In the second strategy, proteins with large numbers of basic or acidic amino acids are used to generate contrast through chemical exchange saturation transfer (CEST) between protein-bound and aqueous protons68212228.…”

Biomolecular MRI reporters: Evolution of new mechanisms

“…Another early example was beta galactosidase, which cleaves a sugar group from a specially designed Gd 3+ chelate, thereby unblocking water accessibility and increasing T 1 relaxivity [42]. Other reporters have been based on proteins that transport paramagnetic species such as Mn 2+ [11], gadolinium chelates [43], transferrin [44, 45] or ferritin [46] into cells or trap small molecule CEST reporters [47]. Alternatively, proteins have been engineered to display biotin on the cell surface, allowing binding and accumulation of an inorganic imaging agent linked to a biotin-binding protein such as streptavidin or transferrin [48, 49].…”

Molecular Imaging in Synthetic Biology, and Synthetic Biology in Molecular Imaging

“…Pioneering examples include enzymes that alter the relaxivity of gadolinium chelates 39 , human iron storage and transport genes such as ferritin 40, 41 and transferrin 42 , and natural and engineered proteins with large numbers of chemically labile protons for chemical exchange saturation transfer (CEST) imaging 43–48 . Recent developments have also included reporter genes causing accumulation of MRI-detectable compounds 49 , proteins interacting with hyperpolarized molecules 50, 51 , channels that alter the diffusion of water across cell membranes 52, 53 and vasodilators altering hemodynamic signals 54 . Several of these reporter genes are covered in detail in previous review articles 55–57 .…”