Improving diagnostic imaging and therapy by targeted compound delivery to pathological areas and across biological barriers is of urgent need. A lipopeptide, P‐CrA‐A2, composed of a highly cationic peptide sequence (A2), an N‐terminally attached palmitoyl chain (P) and cryptophane molecule (CrA) for preferred uptake into blood–brain barrier (BBB) capillary endothelial cells, was generated. CrA allows reversible binding of Xe for NMR detection with hyperpolarized nuclei. The lipopeptide forms size‐optimized micelles with a diameter of about 11 nm at low micromolar concentration. Their high local CrA payload has a strong and switchable impact on the bulk magnetization through Hyper‐CEST detection. Covalent fixation of CrA does not impede micelle formation and does not hamper its host functionality but simplifies Xe access to hosts for inducing saturation transfer. Xe Hyper‐CEST magnetic resonance imaging (MRI) allows for distinguishing BBB endothelial cells from control aortic endothelial cells, and the small micelle volume with a sevenfold improved CrA‐loading density compared to liposomal carriers allows preferred cell labelling with a minimally invasive volume (≈16 000‐fold more efficient than 19F cell labelling). Thus, these nanoscopic particles combine selectivity for human brain capillary endothelial cells with great sensitivity of Xe Hyper‐CEST MRI and might be a potential MRI tool in brain diagnostics.
In article number 1900251, Margitta Dathe, Leif Schröder, and co‐workers demonstrate an MRI contrast agent that uses the available magnetization in a highly efficient way to enable selective cell labelling at minimally invasive concentrations. The micelle approach for 129Xe HyperCEST imaging provides highly efficient depolarization points to impact hyperpolarized spin ensembles and yield a switchable image contrast with a highly reduced labelling volume of target cells. Illustration credits: Barth van Rossum, FMP.
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