Dual-modality gene reporter for in vivo imaging

Abstract

The ability to track cells and their patterns of gene expression in living organisms can increase our understanding of tissue development and disease. Gene reporters for bioluminescence, fluorescence, radionuclide, and magnetic resonance imaging (MRI) have been described but these suffer variously from limited depth penetration, spatial resolution, and sensitivity. We describe here a gene reporter, based on the organic anion transporting protein Oatp1a1, which mediates uptake of a clinically approved, Gd3+-based, hepatotrophic contrast agent (gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid). Cells expressing the reporter showed readily reversible, intense, and positive contrast (up to 7.8-fold signal enhancement) in T1-weighted magnetic resonance images acquired in vivo. The maximum signal enhancement obtained so far is more than double that produced by MRI gene reporters described previously. Exchanging the Gd3+ ion for the radionuclide, 111In, also allowed detection by single-photon emission computed tomography, thus combining the spatial resolution of MRI with the sensitivity of radionuclide imaging.

Use of gadoxetate disodium for functional MRI based on its unique molecular mechanism

“…Known MRI reporter genes such as the chemical exchange saturation transfer reporter, transferrin receptor and ferritin have shown reproducibility from many research groups, but none have been able to overcome the sensitivity issues. 43 Recently, Patrick et al 44 investigated the feasibility of the OATP1A1 MRI reporter gene as a MRI reporter candidate. The authors transfected an OATP1A1-expressing vector into several cell lines including human embryonic kidney cells (HEK 293T), breast adenocarcinoma cells (MCF-7) and human colon adenocarcinoma cells (HCT 116), and confirmed the feasibility of OATP1A1 as an MRI reporter gene.…”

Organic anion‐transporting polypeptide 1B3 as a dual reporter gene for fluorescence and magnetic resonance imaging

“…(16), providing a milestone in MR reporter systems. Although OATP1B1 and -3 both belong to the OATP family, they differ slightly.…”

“…OATP1B1 has been reported as a plasma membrane transporter for d -luciferin, the substrate of luciferase (36). The bioluminescence can be enhanced by overexpressing OATP1B1 for cell tracking (16). Our study showed that OATP1B3 overexpression would facilitate the cellular uptake of d -luciferin, and this phenomenon was repressed by OATP1B3 inhibitor, rifampicin (Supplemental Fig.…”

“…Furthermore, the U.S. Food and Drug Administration (FDA) has approved the use of Gd-EOB-DTPA as a safe MRI contrast medium. The in vivo efficacy of the MR reporter of OATP1B1 has been shown to be a milestone toward discovering the MR reporter (16). Despite its better maximum velocity ( V max ), but weaker K m toward Gd-EOB-DTPA, compared with those of OATP1B1, the feasibility of OATP1B3 as an MR reporter has not been investigated.…”

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].…”