Synthetic Cargo Internalization Receptor System for Nanoparticle Tracking of Individual Cell Populations by Fluorine Magnetic Resonance Imaging

Abstract

Specific detection of target structures or cells lacking particular surface epitopes still poses a serious problem for all imaging modalities. Here, we demonstrate the capability of synthetic "cargo internalization receptors" (CIRs) for tracking of individual cell populations by 1 H/ 19 F magnetic resonance imaging (MRI). To this end, a nanobody for green fluorescent protein (GFP) was used to engineer cell-surface-expressed CIRs which undergo rapid internalization after GFP binding. For 19 F MR visibility, the GFP carrier was equipped with "contrast cargo", in that GFP was coupled to perfluorocarbon nanoemulsions (PFCs). To explore the suitability of different uptake mechanisms for this approach, CIRs were constructed by combination of the GFP nanobody and three different cytoplasmic tails that contained individual internalization motifs for endocytosis of the contrast cargo (CIR1−3). Exposure of CIR + cells to GFP-PFCs resulted in highly specific binding and internalization as confirmed by fluorescence microscopy as well as flow cytometry and enabled visualization by 1 H/ 19 F MRI. In particular, expression of CIR2/3 resulted in substantial incorporation of 19 F cargo and readily enabled in vivo visualization of GFP-PFC recruitment to transplanted CIR + cells by 1 H/ 19 F MRI in mice. Competition experiments with blood immune cells revealed that CIR + cells are predominantly loaded with GFP-PFCs even in the presence of cells with strong phagocytotic capacity. Importantly, binding and internalization of GFP-PFCs did not result in the activation of signaling cascades and therefore does not alter cell physiology. Overall, this approach represents a versatile in vivo imaging platform for tracking of individual cell populations by making use of cell-type-specific CIR + mice.

Combination of bioresponsive chelates and perfluorinated lipid nanoparticles enables in vivo MRI probe quantification

“…Thanks to their biochemical inertness and high density of fluorine nuclei, PFCs have been successfully used for cell labelling and quantitative tracking in vivo. [11][12][13] In attempts to improve the performances of PFC-based CAs, nanosized systems have been designed, combining PFC cores and paramagnetic ions such as Gd(III) and Fe(III). [14][15][16] In such systems, the paramagnetic relaxation enhancement (PRE) effect of the paramagnetic ions does not result in a responsive behaviour for the probe, but usually decreases the relaxation times of the 19 F nuclei, allowing for faster acquisitions.…”

Cell penetrating peptide functionalized perfluorocarbon nanoemulsions for targeted cell labeling and enhanced fluorine‐19 MRI detection

“…Phospholipid surfactants are often chosen to mimic the membranes of live cells and impart biocompatibility. 45,46 Nonetheless, phospholipid-formulated nanoemulsions are prone to instability under storage conditions because of oxidation-mediated changes to the lipid, 47 especially if metal ions are present, and lipid oxidation by-products may lead to cytotoxicity on cell contact. 48 Additionally, the formulation of phospholipid-based nanoemulsions requires a time consuming multi-step chemical process.…”

MRI-based molecular imaging of epicardium-derived stromal cells (EpiSC) by peptide-mediated active targeting

“…This technology has been successfully used for imaging a variety of different inflammatory diseases like myocardial infarction, myocarditis, transplant rejection and pneumonia 21 . To further enhance the specificity of PFCs, and to expand the repertoire of target cells and structures we have recently established a platform to functionalize PFCs with specific ligands 30 , 32 , 44 . Using this platform, we have visualized thrombi with 1 H/ 19 F MRI, employing FXIIIa-specific short peptides for delivery of 19 F-based contrast agents 30 .…”

“…One important aspect of the targeting of EP9 PFCs is the overall biodistribution. In general, unmodified PFCs have a size of 100–200 nm and strongly accumulate in organs of the reticuloendothelial system like the liver and the spleen 44 , 53 , 54 . To a lesser extent, PFCs do also accumulate in the kidneys, the bone marrow and the lymph nodes 19 .…”