Since the start of the ZincMRI project, significant scientific and technological progress has been made toward building a new molecular MRI platform for monitoring zinc ions (Zn²⁺) and zinc-regulated gene activity in living organisms.
1. Development of Zn²⁺-Responsive 19F-MRI Sensors (Activity-Based Sensing)
One major breakthrough was the design and validation of a synthetic, fluorinated molecular probe that reacts selectively with Zn²⁺. Upon interaction with zinc, the probe undergoes a chemical transformation that shifts its fluorine-19 (¹⁹F) NMR signal by 12 ppm, producing a sharp, background-free contrast in MRI scans. This "turn-on" contrast may enable, upon implementation in vivo, rapid, quantitative detection of transient zinc elevations in cells and tissues, including under conditions that mimic disease-related stress.
2. Implementation of Genetically Encoded MRI Reporters for Zinc-Regulated Gene Expression
To complement chemical sensing, a reporter system was engineered based on human thymidine kinase 1 (hTK1) and a deuterated nucleoside analog (d₃-thymidine). When cells express the hTK1 gene, they phosphorylate and retain the deuterated compound, which can then be detected with deuterium MRI (²H-MRI). This approach offers a fully orthogonal imaging channel, separate from both conventional proton (¹H) MRI, used for anatomical MRI, and ¹⁹F-MRI, used for Zn²⁺ sensing, enabling multiplexed detection of both zinc and gene expression in the same subject without signal interference. This system marks the first demonstration of in vivo gene expression imaging using a clinically relevant, non-mutated human enzyme and an unmodified, naturally derived imaging agent.
3. Integration and Validation of Orthogonal MRI Modalities
The two major components of ZincMRI, the synthetic and genetic components, are now being established and are ready to be integrated into a single, multifaceted MRI platform. Experiments confirmed the feasibility of simultaneous ¹⁹F-, ²H-, and ¹H-MRI imaging, showing the potential of dynamic zinc levels, gene expression, and anatomical context to be visualized together in phantoms and in vivo systems.
4. Extension Toward Ion Discrimination Technologies
A further achievement was the development of a magnetic resonance fingerprinting (MRF) strategy, based on ¹⁹F-paraGEST (paramagnetic guest exchange saturation transfer), that allows identification and quantification of different metal ions in complex mixtures. Although initially designed for lanthanides, this technology establishes the foundation for future extensions of ZincMRI to other biologically relevant metals.
