Development of selective probes to highlight cellular organelles of human cell and tissue samples in X-ray fluorescence imaging

• Applicant: Axel Steinbrueck, Ph.D.
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation ; Analytical Chemistry ; Biochemistry
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 518777768

In the arena of medicinal research, X-ray fluorescence imaging (XRFI) is emerging as a powerful analytical technique that allows for the simultaneous detection of virtually all elements heavier than aluminium in a wide range of samples including human cells and tissue sections. After a series of technological advances over the past decades, modern XRFI now offers sufficient resolving power to generate 2D and 3D elemental distribution maps from biological samples, providing researchers with the ability to localise and quantify virtually all medicinally relevant metals and non-metals with sub-cellular precision in a single analysis step. Unfortunately, these unprecedented opportunities offered by XRFI are thus far undermined by a severe lack of available probes to highlight relevant biological structures (e.g., mitochondria, lysosomes). Consequently, researchers are currently forced to subject their biological samples to additional deleterious analysis steps that are time consuming and prone to generating undesired artefacts, which ultimately limits the reliability of collected data and slows down research progress.To address these pitfalls and to render XRFI more useful for medicinal research and drug development purposes, I herewith propose the development of a set of urgently required, facile-to-use XRFI probes that will enable researchers to directly interpret generated XRFI data. These novel XRFI probes will be constructed with a fluorescent, XRFI-active, bio-orthogonal transition metal complex featuring an inert iridium-, ruthenium-, or rhenium core. The fluorescent reporter unit will be connected via a robust linker to a recognition-based targeting moiety that directs the probe’s localisation towards a selected cellular organelle.This modular design will enable a versatile mix-and-match synthetic approach to generate an array of probes with different dual-modal reporter units and targeting moieties, respectively, that can be traced by both XRFI and conventional fluorescence live-cell imaging. This strategy will facilitate the validation and optimization of the generated XRFI probes as well as provide end-users with a range of usable probes to suit the respective confines of their individual projects.With my diverse background in supramolecular- and medicinal chemistry, ranging from the development of fluorescent probes and chemosensors to the design, synthesis, and biological evaluation of new, organelle-targeted potential chemotherapeutics, I consider myself the ideal candidate for the development of these urgently required probes. Additionally, the Metzler-Nolte group at the Ruhr-University Bochum is the perfect, complementary host institution to facilitate the successful completion of this impactful research project due to their extensive knowledge base on the synthesis of metal complexes, wealth of available instrumentation, and valuable access to external synchrotron facilities to validate the final XRFI probes.

• DFG Programme: WBP Position