DESI-Mass Spectrometry Imaging Investigation of Discrete and Cassette Drug Dosed Tissues

Importance of DESI-MSI for Drug Distribution Studies

Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) enables label-free, multiplexed mapping of drug compounds and their metabolites within biological tissues. This approach addresses limitations of traditional autoradiography by distinguishing parent molecules from metabolites and simultaneously profiling endogenous lipids, which enhances understanding of drug distribution and mechanism of action in DMPK studies.

Objectives and Study Overview

This investigation aimed to apply DESI-MSI to mouse liver sections following cassette and discrete dosing regimens. Four drugs (Terfenadine, Olanzapine, Moxifloxacin, Erlotinib) were administered simultaneously or individually, with tissue harvested at 2 and 6 hours post dose alongside vehicle controls. The goal was to visualize spatial distribution of parent drugs, metabolites, and endogenous lipids in a single experiment.

Methodology and Instrumentation

• Animal model: Oral administration of four-drug cassette (25, 10, 10, 25 mg/kg) or discrete Olanzapine (25 mg/kg), plus vehicle control; liver sections collected at 2 h and 6 h.
• MSI acquisition: Prosolia 2D DESI source with Waters sprayer on a Waters Xevo G2-XS QTof Mass Spectrometer; imaging step size of 150 μm; data processed and normalized using Waters HDI v1.4 software.

Main Results and Discussion

• Label-free detection of all four drugs in liver tissue, with consistent signal intensities across dosing regimens and time points.
• Identification and spatial mapping of metabolites such as hydroxyterfenadine (m/z 488.31) and carboxyterfenadine (m/z 502.29) alongside parent Terfenadine (m/z 472.32).
• Concurrent imaging of endogenous phosphatidylcholine lipids revealed distinct anatomical microstructures and baseline tissue features.
• RGB overlays combining drug, metabolite, and lipid ion images provided enhanced visualization of molecular distribution relative to histological landmarks.

Applications and Practical Benefits

• Eliminates need for radiolabeling, reducing synthesis complexity, time, and cost compared to whole-body autoradiography.
• Enables simultaneous profiling of multiple analyte classes from a single tissue section, streamlining DMPK workflows.
• Supports identification of biomarkers and companion diagnostics by correlating drug localization with endogenous molecular changes.

Future Trends and Potential Uses

• Adoption of higher spatial resolution imaging through optimized solvent systems or sequential section analysis for subcellular localization.
• Integration with complementary MSI modalities (SIMS, MALDI) to balance spatial resolution and compound coverage.
• Expansion into mechanistic toxicology, biomarker discovery, and quality control in pharmaceutical development pipelines.

Conclusion

DESI-MSI offers a powerful, label-free approach to visualize drug and metabolite distributions alongside endogenous molecules within tissue sections. Its multiplexed capabilities and compatibility with existing instrumentation provide actionable insights in DMPK research, improving efficiency and depth of analysis.

Used Instrumentation

• Prosolia 2D DESI source with Waters® sprayer
• Waters Xevo® G2-XS QTof Mass Spectrometer
• Waters High Definition Imaging (HDI®) v1.4 software

References

• Swales J.G. et al. Analytical Chemistry, 2014, 86, 8473–8480.
• Swales J.G. et al. Scientific Reports, 2016, DOI:10.1038/srep37648.