Artificial nucleoside and DNA functionalization as a platform for ultrasound imaging and magnetic resonance imaging

RWTH Publications (RWTH Aachen)

Abstract

In medicine, targeted molecular imaging presents a key technology for the detection and investigation of pathogenic sites and tissues with spatial resolution. Accordingly, the equipment with targeting moieties enables the enrichment of contrast agents at the desired tissue, whereby aptamers as targeting ligands provide high affinity and specificity. However, there are only limited and special examples of contrast agents equipped with aptamers for magnetic resonance imaging (MRI) and ultrasound (US) imaging. In this thesis, a general strategy was developed to combine aptamers with MRI or US contrast agents by using novel artificial DNA nucleosides.In chapter 2, unsaturated functions were used as precursors for hyperpolarization via hydrogenation for MRI applications. After a screening of precursors on the nucleoside level, promising functionalities were investigated within nucleotide strands. Hereby, a basic concept of ParaHydrogen-Induced Polarization (PHIP) was developed that utilizes unsaturated functional groups attached to the nucleobase or the sugar units. The identified conditions allow the selective hydrogenation without altering the DNA structure and impairing secondary structure formation of the nucleic acids. The induced hyperpolarization showed enhancement factors of up to 52. In chapter 3, the approach of functionalization of nucleic acids by unsaturated functionalities was extended to achieve the unprecedented hyperpolarization of a cancer-targeting, biologically relevant DNA aptamer via a PHIP label. Therefore, two polarity-engineering methods were established for the successful hydrogenation of the unsaturated moieties. In organic solvent, the polarity of DNA was adjusted through complexation with PEG chains to enable the selective reaction with parahydrogen and a commercial catalyst. For aqueous solutions, a new sulfonated water-soluble catalyst enabled the selective hydrogenation of the DNA’s unsaturated groups. Both polarity engineering approaches are based on straightforward synthetic procedures and facilitate reaction selectivity that the DNA structure remains unaffected. This aptamer hyperpolarization approach paves the way for enhanced MRI detection schemes in the future. The next chapter was dedicated to functionalize microbubbles with nucleic acids. In chapter 4, hydrophobic or acrydite modifications were included into the nucleoside for the later tuning of microbubbles for US imaging applications. The hydrophobically modified DNA facilitated the microfluidic generation of monodisperse microbubbles with long-term stability. Furthermore, the 3D master printing approach enabled the production of monodisperse surfactant microbubbles with a precise size control within the medical relevant range of 1 to 10 µm. Polymer shell microbubbles were manufactured using a microfluidic three-phase system to ensure superior stability and the incorporation capability of acrydite DNA. Both microbubble systems, the surfactant-based one and the polymer based one, enable the future use of aptamer equipped microbubbles as contrast agents for targeted imaging and theranostics. The findings of the efficient signal amplification of a hyperpolarized aptamer and the concept to equip microbubbles with DNA show the universal applicability of using modified nucleosides for the generation of aptamer contrast agents for MRI and US.

Authors 1

1. Kai‐Oliver Brenske corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen