IMPROVING SPATIAL DISTRIBUTION, SENSITIVITY AND SELECTIVITY IN MSI, USING A NOVEL DESI QQQ AND A HR-MULTI REFLECTING TOF SYSTEMS

Importance of the topic

Mass spectrometry imaging (MSI) enables spatial mapping of small molecules directly in tissue sections. However, tissue complexity and low analyte concentrations at therapeutic levels present challenges in sensitivity, selectivity, and spatial resolution. Enhancing MSI performance is essential for accurate drug distribution studies, biomarker localization, and comprehensive tissue metabolomics in pharmaceutical and clinical research.

Study objectives and overview

The study investigates a novel DESI-QqQ (triple quadrupole) and a high-resolution multi-reflecting TOF (MRT-TOF) system to improve spatial distribution, sensitivity, and selectivity in DESI MSI. It evaluates limits of detection (LODs) for theophylline, ranitidine, and atenolol using untargeted full-scan MSI on MRT-TOF and targeted MRM imaging on TQ-MS. Drug distribution was assessed in rat ileum tissue sections at 4 h and 7 h post intravenous dosing.

Methodology

• Tissue preparation: Spotting drug dilution series (0.1–100 μM) on control porcine liver sections; preparing fresh-frozen rat ileum sections after dosing with 2.5 mg/mL drug solutions, collected at 4 h and 7 h.
• Full-scan MSI: Waters SELECT SERIES™ MRT-TOF, resolution >200,000 FWHM, mass range m/z 50–2400, acquisition at 2 Hz, 50 μm pixel size.
• Targeted MSI: Triple quadrupole DESI TQ-MS with optimized MRM transitions, acquisition at 10 Hz, pixel sizes of 50 μm and 15 μm.
• Data processing: MassLynx™ and High Definition™ Imaging (HDI™) for visualization; MSI Quantify MicroApp for quantitative calibration and mapping.

Instrumentation

• DESI XS ion source with High-Performance Sprayer (HPS).
• Waters SELECT SERIES™ MRT multi-reflecting TOF system.
• Waters tandem quadrupole mass spectrometer.
• Software: MassLynx, HDI v1.7, MSI Quantify MicroApp.

Main results and discussion

• Calibration and LODs: All compounds exhibited linear calibration (R² > 0.99). Targeted MRM on TQ-MS achieved LODs of 0.1 μM for atenolol and ranitidine, and 0.5 μM for theophylline. Untargeted MRT-TOF reached LODs between 0.5 and 1 μM.
• Spatial distribution: Theophylline localized in mucosa, submucosa, and muscularis at both 4 h and 7 h. Atenolol and ranitidine were detected only at 7 h, primarily in the mucosa layer.
• High-resolution imaging at 15 μm pixel size confirmed precise localization of ranitidine in ileum sections.
• Untargeted data allowed concurrent imaging of endogenous lipids with mass accuracy below 500 ppb, broadening molecular insight.

Benefits and practical applications

• Enhanced sensitivity and specificity for targeted drug imaging enable detection at lower concentrations relevant to pharmacokinetic studies.
• High spatial resolution facilitates detailed mapping within tissue microstructures.
• Combined untargeted and targeted workflows provide comprehensive molecular coverage for drug distribution and biomarker research.

Future trends and opportunities

• Integration with ion mobility separation and ultra-high-resolution mass analyzers for improved molecular discrimination.
• Automation and machine learning–driven data analysis to accelerate quantitative imaging workflows.
• Application of DESI MSI in clinical diagnostics, precision medicine, and high-throughput pharmaceutical screening.

Conclusion

The novel DESI-QqQ and HR-MRT-TOF platforms demonstrate superior sensitivity, selectivity, and spatial resolution for small-molecule MSI in tissue sections. The dual approach of targeted MRM and high-resolution untargeted analysis delivers robust quantitative and qualitative insights, advancing pharmaceutical tissue imaging methodologies.

References

• Claude E. et al., Improving spatial distribution, sensitivity and selectivity in MSI using a novel DESI QQQ and HR-MRT systems, Waters Corporation, 2023.
• Jahouh F. et al., Preclinical Sciences & Translational Safety, Janssen R&D, 2023.